Figure 5 A schematic of the water model of reactor URO 200.

Physical and Numerical Modeling of the Impeller Construction Impact on the Aluminum Degassing Process

알루미늄 탈기 공정에 미치는 임펠러 구성의 물리적 및 수치적 모델링

Kamil Kuglin,1 Michał Szucki,2 Jacek Pieprzyca,3 Simon Genthe,2 Tomasz Merder,3 and Dorota Kalisz1,*

Mikael Ersson, Academic Editor

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Data Availability Statement

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Abstract

This paper presents the results of tests on the suitability of designed heads (impellers) for aluminum refining. The research was carried out on a physical model of the URO-200, followed by numerical simulations in the FLOW 3D program. Four design variants of impellers were used in the study. The degree of dispersion of the gas phase in the model liquid was used as a criterion for evaluating the performance of each solution using different process parameters, i.e., gas flow rate and impeller speed. Afterward, numerical simulations in Flow 3D software were conducted for the best solution. These simulations confirmed the results obtained with the water model and verified them.

Keywords: aluminum, impeller construction, degassing process, numerical modeling, physical modeling

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1. Introduction

Constantly increasing requirements concerning metallurgical purity in terms of hydrogen content and nonmetallic inclusions make casting manufacturers use effective refining techniques. The answer to this demand is the implementation of the aluminum refining technique making use of a rotor with an original design guaranteeing efficient refining [1,2,3,4]. The main task of the impeller (rotor) is to reduce the contamination of liquid metal (primary and recycled aluminum) with hydrogen and nonmetallic inclusions. An inert gas, mainly argon or a mixture of gases, is introduced through the rotor into the liquid metal to bring both hydrogen and nonmetallic inclusions to the metal surface through the flotation process. Appropriately and uniformly distributed gas bubbles in the liquid metal guarantee achieving the assumed level of contaminant removal economically. A very important factor in deciding about the obtained degassing effect is the optimal rotor design [5,6,7,8]. Thanks to the appropriate geometry of the rotor, gas bubbles introduced into the liquid metal are split into smaller ones, and the spinning movement of the rotor distributes them throughout the volume of the liquid metal bath. In this solution impurities in the liquid metal are removed both in the volume and from the upper surface of the metal. With a well-designed impeller, the costs of refining aluminum and its alloys can be lowered thanks to the reduced inert gas and energy consumption (optimal selection of rotor rotational speed). Shorter processing time and a high degree of dehydrogenation decrease the formation of dross on the metal surface (waste). A bigger produced dross leads to bigger process losses. Consequently, this means that the choice of rotor geometry has an indirect impact on the degree to which the generated waste is reduced [9,10].

Another equally important factor is the selection of process parameters such as gas flow rate and rotor speed [11,12]. A well-designed gas injection system for liquid metal meets two key requirements; it causes rapid mixing of the liquid metal to maintain a uniform temperature throughout the volume and during the entire process, to produce a chemically homogeneous metal composition. This solution ensures effective degassing of the metal bath. Therefore, the shape of the rotor, the arrangement of the nozzles, and their number are significant design parameters that guarantee the optimum course of the refining process. It is equally important to complete the mixing of the metal bath in a relatively short time, as this considerably shortens the refining process and, consequently, reduces the process costs. Another important criterion conditioning the implementation of the developed rotor is the generation of fine diffused gas bubbles which are distributed throughout the metal volume, and whose residence time will be sufficient for the bubbles to collide and adsorb the contaminants. The process of bubble formation by the spinning rotors differs from that in the nozzles or porous molders. In the case of a spinning rotor, the shear force generated by the rotor motion splits the bubbles into smaller ones. Here, the rotational speed, mixing force, surface tension, and fluid density have a key effect on the bubble size. The velocity of the bubbles, which depends mainly on their size and shape, determines their residence time in the reactor and is, therefore, very important for the refining process, especially since gas bubbles in liquid aluminum may remain steady only below a certain size [13,14,15].

The impeller designs presented in the article were developed to improve the efficiency of the process and reduce its costs. The impellers used so far have a complicated structure and are very pricey. The success of the conducted research will allow small companies to become independent of external supplies through the possibility of making simple and effective impellers on their own. The developed structures were tested on the water model. The results of this study can be considered as pilot.

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2. Materials and Methods

Rotors were realized with the SolidWorks computer design technique and a 3D printer. The developed designs were tested on a water model. Afterward, the solution with the most advantageous refining parameters was selected and subjected to calculations with the Flow3D package. As a result, an impeller was designed for aluminum refining. Its principal lies in an even distribution of gas bubbles in the entire volume of liquid metal, with the largest possible participation of the bubble surface, without disturbing the metal surface. This procedure guarantees the removal of gaseous, as well as metallic and nonmetallic, impurities.

2.1. Rotor Designs

The developed impeller constructions, shown in Figure 1Figure 2Figure 3 and Figure 4, were printed on a 3D printer using the PLA (polylactide) material. The impeller design models differ in their shape and the number of holes through which the inert gas flows. Figure 1Figure 2 and Figure 3 show the same impeller model but with a different number of gas outlets. The arrangement of four, eight, and 12 outlet holes was adopted in the developed design. A triangle-shaped structure equipped with three gas outlet holes is presented in Figure 4.

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Figure 1

A 3D model—impeller with four holes—variant B4.

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Figure 2

A 3D model—impeller with eight holes—variant B8.

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Figure 3

A 3D model—impeller with twelve holes—variant B12.

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Figure 4

A 3D model—‘red triangle’ impeller with three holes—variant RT3.

2.2. Physical Models

Investigations were carried out on a water model of the URO 200 reactor of the barbotage refining process (see Figure 5).

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Figure 5

A schematic of the water model of reactor URO 200.

The URO 200 reactor can be classified as a cyclic reactor. The main element of the device is a rotor, which ends the impeller. The whole system is attached to a shaft via which the refining gas is supplied. Then, the shaft with the rotor is immersed in the liquid metal in the melting pot or the furnace chamber. In URO 200 reactors, the refining process lasts 600 s (10 min), the gas flow rate that can be obtained ranges from 5 to 20 dm3·min−1, and the speed at which the rotor can move is 0 to 400 rpm. The permissible quantity of liquid metal for barbotage refining is 300 kg or 700 kg [8,16,17]. The URO 200 has several design solutions which improve operation and can be adapted to the existing equipment in the foundry. These solutions include the following [8,16]:

  • URO-200XR—used for small crucible furnaces, the capacity of which does not exceed 250 kg, with no control system and no control of the refining process.
  • URO-200SA—used to service several crucible furnaces of capacity from 250 kg to 700 kg, fully automated and equipped with a mechanical rotor lift.
  • URO-200KA—used for refining processes in crucible furnaces and allows refining in a ladle. The process is fully automated, with a hydraulic rotor lift.
  • URO-200KX—a combination of the XR and KA models, designed for the ladle refining process. Additionally, refining in heated crucibles is possible. The unit is equipped with a manual hydraulic rotor lift.
  • URO-200PA—designed to cooperate with induction or crucible furnaces or intermediate chambers, the capacity of which does not exceed one ton. This unit is an integral part of the furnace. The rotor lift is equipped with a screw drive.

Studies making use of a physical model can be associated with the observation of the flow and circulation of gas bubbles. They require meeting several criteria regarding the similarity of the process and the object characteristics. The similarity conditions mainly include geometric, mechanical, chemical, thermal, and kinetic parameters. During simulation of aluminum refining with inert gas, it is necessary to maintain the geometric similarity between the model and the real object, as well as the similarity related to the flow of liquid metal and gas (hydrodynamic similarity). These quantities are characterized by the Reynolds, Weber, and Froude numbers. The Froude number is the most important parameter characterizing the process, its magnitude is the same for the physical model and the real object. Water was used as the medium in the physical modeling. The factors influencing the choice of water are its availability, relatively low cost, and kinematic viscosity at room temperature, which is very close to that of liquid aluminum.

The physical model studies focused on the flow of inert gas in the form of gas bubbles with varying degrees of dispersion, particularly with respect to some flow patterns such as flow in columns and geysers, as well as disturbance of the metal surface. The most important refining parameters are gas flow rate and rotor speed. The barbotage refining studies for the developed impeller (variants B4, B8, B12, and RT3) designs were conducted for the following process parameters:

  • Rotor speed: 200, 300, 400, and 500 rpm,
  • Ideal gas flow: 10, 20, and 30 dm3·min−1,
  • Temperature: 293 K (20 °C).

These studies were aimed at determining the most favorable variants of impellers, which were then verified using the numerical modeling methods in the Flow-3D program.

2.3. Numerical Simulations with Flow-3D Program

Testing different rotor impellers using a physical model allows for observing the phenomena taking place while refining. This is a very important step when testing new design solutions without using expensive industrial trials. Another solution is modeling by means of commercial simulation programs such as ANSYS Fluent or Flow-3D [18,19]. Unlike studies on a physical model, in a computer program, the parameters of the refining process and the object itself, including the impeller design, can be easily modified. The simulations were performed with the Flow-3D program version 12.03.02. A three-dimensional system with the same dimensions as in the physical modeling was used in the calculations. The isothermal flow of liquid–gas bubbles was analyzed. As in the physical model, three speeds were adopted in the numerical tests: 200, 300, and 500 rpm. During the initial phase of the simulations, the velocity field around the rotor generated an appropriate direction of motion for the newly produced bubbles. When the required speed was reached, the generation of randomly distributed bubbles around the rotor was started at a rate of 2000 per second. Table 1 lists the most important simulation parameters.

Table 1

Values of parameters used in the calculations.

ParameterValueUnit
Maximum number of gas particles1,000,000
Rate of particle generation20001·s−1
Specific gas constant287.058J·kg−1·K−1
Atmospheric pressure1.013 × 105Pa
Water density1000kg·m−3
Water viscosity0.001kg·m−1·s−1
Boundary condition on the wallsNo-slip
Size of computational cell0.0034m

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In the case of the CFD analysis, the numerical solutions require great care when generating the computational mesh. Therefore, computational mesh tests were performed prior to the CFD calculations. The effect of mesh density was evaluated by taking into account the velocity of water in the tested object on the measurement line A (height of 0.065 m from the bottom) in a characteristic cross-section passing through the object axis (see Figure 6). The mesh contained 3,207,600, 6,311,981, 7,889,512, 11,569,230, and 14,115,049 cells.

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Figure 6

The velocity of the water depending on the size of the computational grid.

The quality of the generated computational meshes was checked using the criterion skewness angle QEAS [18]. This criterion is described by the following relationship:

QEAS=max{βmax−βeq180−βeq,βeq−βminβeq},

(1)

where βmaxβmin are the maximal and minimal angles (in degrees) between the edges of the cell, and βeq is the angle corresponding to an ideal cell, which for cubic cells is 90°.

Normalized in the interval [0;1], the value of QEAS should not exceed 0.75, which identifies the permissible skewness angle of the generated mesh. For the computed meshes, this value was equal to 0.55–0.65.

Moreover, when generating the computational grids in the studied facility, they were compacted in the areas of the highest gradients of the calculated values, where higher turbulence is to be expected (near the impeller). The obtained results of water velocity in the studied object at constant gas flow rate are shown in Figure 6.

The analysis of the obtained water velocity distributions (see Figure 6) along the line inside the object revealed that, with the density of the grid of nodal points, the velocity changed and its changes for the test cases of 7,889,512, 11,569,230, and 14,115,049 were insignificant. Therefore, it was assumed that a grid containing not less than 7,900,000 (7,889,512) cells would not affect the result of CFD calculations.

A single-block mesh of regular cells with a size of 0.0034 m was used in the numerical calculations. The total number of cells was approximately 7,900,000 (7,889,512). This grid resolution (see Figure 7) allowed the geometry of the system to be properly represented, maintaining acceptable computation time (about 3 days on a workstation with 2× CPU and 12 computing cores).

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Figure 7

Structured equidistant mesh used in numerical calculations: (a) mesh with smoothed, surface cells (the so-called FAVOR method) used in Flow-3D; (b) visualization of the applied mesh resolution.

The calculations were conducted with an explicit scheme. The timestep was selected by the program automatically and controlled by stability and convergence. From the moment of the initial velocity field generation (start of particle generation), it was 0.0001 s.

When modeling the degassing process, three fluids are present in the system: water, gas supplied through the rotor head (impeller), and the surrounding air. Modeling such a multiphase flow is a numerically very complex issue. The necessity to overcome the liquid backpressure by the gas flowing out from the impeller leads to the formation of numerical instabilities in the volume of fluid (VOF)-based approach used by Flow-3D software. Therefore, a mixed description of the analyzed flow was used here. In this case, water was treated as a continuous medium, while, in the case of gas bubbles, the discrete phase model (DPM) model was applied. The way in which the air surrounding the system was taken into account is later described in detail.

The following additional assumptions were made in the modeling:

  • —The liquid phase was considered as an incompressible Newtonian fluid.
  • —The effect of chemical reactions during the refining process was neglected.
  • —The composition of each phase (gas and liquid) was considered homogeneous; therefore, the viscosity and surface tension were set as constants.
  • —Only full turbulence existed in the liquid, and the effect of molecular viscosity was neglected.
  • —The gas bubbles were shaped as perfect spheres.
  • —The mutual interaction between gas bubbles (particles) was neglected.

2.3.1. Modeling of Liquid Flow 

The motion of the real fluid (continuous medium) is described by the Navier–Stokes Equation [20].

dudt=−1ρ∇p+ν∇2u+13ν∇(∇⋅ u)+F,

(2)

where du/dt is the time derivative, u is the velocity vector, t is the time, and F is the term accounting for external forces including gravity (unit components denoted by XYZ).

In the simulations, the fluid flow was assumed to be incompressible, in which case the following equation is applicable:

∂u∂t+(u⋅∇)u=−1ρ∇p+ν∇2u+F.

(3)

Due to the large range of liquid velocities during flows, the turbulence formation process was included in the modeling. For this purpose, the k–ε model turbulence kinetic energy k and turbulence dissipation ε were the target parameters, as expressed by the following equations [21]:

∂(ρk)∂t+∂(ρkvi)∂xi=∂∂xj[(μ+μtσk)⋅∂k∂xi]+Gk+Gb−ρε−Ym+Sk,

(4)

∂(ρε)∂t+∂(ρεui)∂xi=∂∂xj[(μ+μtσε)⋅∂k∂xi]+C1εεk(Gk+G3εGb)+C2ερε2k+Sε,

(5)

where ρ is the gas density, σκ and σε are the Prandtl turbulence numbers, k and ε are constants of 1.0 and 1.3, and Gk and Gb are the kinetic energy of turbulence generated by the average velocity and buoyancy, respectively.

As mentioned earlier, there are two gas phases in the considered problem. In addition to the gas bubbles, which are treated here as particles, there is also air, which surrounds the system. The boundary of phase separation is in this case the free surface of the water. The shape of the free surface can change as a result of the forming velocity field in the liquid. Therefore, it is necessary to use an appropriate approach to free surface tracking. The most commonly used concept in liquid–gas flow modeling is the volume of fluid (VOF) method [22,23], and Flow-3D uses a modified version of this method called TrueVOF. It introduces the concept of the volume fraction of the liquid phase fl. This parameter can be used for classifying the cells of a discrete grid into areas filled with liquid phase (fl = 1), gaseous phase, or empty cells (fl = 0) and those through which the phase separation boundary (fl ∈ (0, 1)) passes (free surface). To determine the local variations of the liquid phase fraction, it is necessary to solve the following continuity equation:

dfldt=0.

(6)

Then, the fluid parameters in the region of coexistence of the two phases (the so-called interface) depend on the volume fraction of each phase.

ρ=flρl+(1−fl)ρg,

(7)

ν=flνl+(1−fl)νg,

(8)

where indices l and g refer to the liquid and gaseous phases, respectively.

The parameter of fluid velocity in cells containing both phases is also determined in the same way.

u=flul+(1−fl)ug.

(9)

Since the processes taking place in the surrounding air can be omitted, to speed up the calculations, a single-phase, free-surface model was used. This means that no calculations were performed in the gas cells (they were treated as empty cells). The liquid could fill them freely, and the air surrounding the system was considered by the atmospheric pressure exerted on the free surface. This approach is often used in modeling foundry and metallurgical processes [24].

2.3.2. Modeling of Gas Bubble Flow 

As stated, a particle model was used to model bubble flow. Spherical particles (gas bubbles) of a given size were randomly generated in the area marked with green in Figure 7b. In the simulations, the gas bubbles were assumed to have diameters of 0.016 and 0.02 m corresponding to the gas flow rates of 10 and 30 dm3·min−1, respectively.

Experimental studies have shown that, as a result of turbulent fluid motion, some of the bubbles may burst, leading to the formation of smaller bubbles, although merging of bubbles into larger groupings may also occur. Therefore, to be able to observe the behavior of bubbles of different sizes (diameter), the calculations generated two additional particle types with diameters twice smaller and twice larger, respectively. The proportion of each species in the system was set to 33.33% (Table 2).

Table 2

Data assumed for calculations.

NoRotor Speed (Rotational Speed)
rpm
Bubbles Diameter
m
Corresponding Gas Flow Rate
dm3·min−1
NoRotor Speed (Rotational Speed)
rpm
Bubbles Diameter
m
Corresponding Gas Flow Rate
dm3·min−1
A2000.01610D2000.0230
0.0080.01
0.0320.04
B3000.01610E3000.0230
0.0080.01
0.0320.04
C5000.01610F5000.0230
0.0080.01
0.0320.04

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The velocity of the particle results from the generated velocity field (calculated from Equation (3) in the liquid ul around it and its velocity resulting from the buoyancy force ub. The effect of particle radius r on the terminal velocity associated with buoyancy force can be determined according to Stokes’ law.

ub=29 (ρg−ρl)μlgr2,

(10)

where g is the acceleration (9.81).

The DPM model was used for modeling the two-phase (water–air) flow. In this model, the fluid (water) is treated as a continuous phase and described by the Navier–Stokes equation, while gas bubbles are particles flowing in the model fluid (discrete phase). The trajectories of each bubble in the DPM system are calculated at each timestep taking into account the mass forces acting on it. Table 3 characterizes the DPM model used in our own research [18].

Table 3

Characteristic of the DPM model.

MethodEquations
Euler–LagrangeBalance equation:
dugdt=FD(u−ug)+g(ϱg−ϱ)ϱg+F.
FD (u − up) denotes the drag forces per mass unit of a bubble, and the expression for the drag coefficient FD is of the form
FD=18μCDReϱ⋅gd2g24.
The relative Reynolds number has the form
Re≡ρdg|ug−u|μ.
On the other hand, the force resulting from the additional acceleration of the model fluid has the form
F=12dρdtρg(u−ug),
where ug is the gas bubble velocity, u is the liquid velocity, dg is the bubble diameter, and CD is the drag coefficient.

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3. Results and Discussion

3.1. Calculations of Power and Mixing Time by the Flowing Gas Bubbles

One of the most important parameters of refining with a rotor is the mixing power induced by the spinning rotor and the outflowing gas bubbles (via impeller). The mixing power of liquid metal in a ladle of height (h) by gas injection can be determined from the following relation [15]:

pgVm=ρ⋅g⋅uB,

(11)

where pg is the mixing power, Vm is the volume of liquid metal in the reactor, ρ is the density of liquid aluminum, and uB is the average speed of bubbles, given below.

uB=n⋅R⋅TAc⋅Pm⋅t,

(12)

where n is the number of gas moles, R is the gas constant (8.314), Ac is the cross-sectional area of the reactor vessel, T is the temperature of liquid aluminum in the reactor, and Pm is the pressure at the middle tank level. The pressure at the middle level of the tank is calculated by a function of the mean logarithmic difference.

Pm=(Pa+ρ⋅g⋅h)−Paln(Pa+ρ⋅g⋅h)Pa,

(13)

where Pa is the atmospheric pressure, and h is the the height of metal in the reactor.

Themelis and Goyal [25] developed a model for calculating mixing power delivered by gas injection.

pg=2Q⋅R⋅T⋅ln(1+m⋅ρ⋅g⋅hP),

(14)

where Q is the gas flow, and m is the mass of liquid metal.

Zhang [26] proposed a model taking into account the temperature difference between gas and alloy (metal).

pg=QRTgVm[ln(1+ρ⋅g⋅hPa)+(1−TTg)],

(15)

where Tg is the gas temperature at the entry point.

Data for calculating the mixing power resulting from inert gas injection into liquid aluminum are given below in Table 4. The design parameters were adopted for the model, the parameters of which are shown in Figure 5.

Table 4

Data for calculating mixing power introduced by an inert gas.

ParameterValueUnit
Height of metal column0.7m
Density of aluminum2375kg·m−3
Process duration20s
Gas temperature at the injection site940K
Cross-sectional area of ladle0.448m2
Mass of liquid aluminum546.25kg
Volume of ladle0.23M3
Temperature of liquid aluminum941.15K

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Table 5 presents the results of mixing power calculations according to the models of Themelis and Goyal and of Zhang for inert gas flows of 10, 20, and 30 dm3·min−1. The obtained calculation results significantly differed from each other. The difference was an order of magnitude, which indicates that the model is highly inaccurate without considering the temperature of the injected gas. Moreover, the calculations apply to the case when the mixing was performed only by the flowing gas bubbles, without using a rotor, which is a great simplification of the phenomenon.

Table 5

Mixing power calculated from mathematical models.

Mathematical ModelMixing Power (W·t−1)
for a Given Inert Gas Flow (dm3·min−1)
102030
Themelis and Goyal11.4923.3335.03
Zhang0.821.662.49

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The mixing time is defined as the time required to achieve 95% complete mixing of liquid metal in the ladle [27,28,29,30]. Table 6 groups together equations for the mixing time according to the models.

Table 6

Models for calculating mixing time.

AuthorsModelRemarks
Szekely [31]τ=800ε−0.4ε—W·t−1
Chiti and Paglianti [27]τ=CVQlV—volume of reactor, m3
Ql—flow intensity, m3·s−1
Iguchi and Nakamura [32]τ=1200⋅Q−0.4D1.97h−1.0υ0.47υ—kinematic viscosity, m2·s−1
D—diameter of ladle, m
h—height of metal column, m
Q—liquid flow intensity, m3·s−1

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Figure 8 and Figure 9 show the mixing time as a function of gas flow rate for various heights of the liquid column in the ladle and mixing power values.

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Figure 8

Mixing time as a function of gas flow rate for various heights of the metal column (Iguchi and Nakamura model).

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Figure 9

Mixing time as a function of mixing power (Szekly model).

3.2. Determining the Bubble Size

The mechanisms controlling bubble size and mass transfer in an alloy undergoing refining are complex. Strong mixing conditions in the reactor promote impurity mass transfer. In the case of a spinning rotor, the shear force generated by the rotor motion separates the bubbles into smaller bubbles. Rotational speed, mixing force, surface tension, and liquid density have a strong influence on the bubble size. To characterize the kinetic state of the refining process, parameters k and A were introduced. Parameters kA, and uB can be calculated using the below equations [33].

k=2D⋅uBdB⋅π−−−−−−√,

(16)

A=6Q⋅hdB⋅uB,

(17)

uB=1.02g⋅dB,−−−−−√

(18)

where D is the diffusion coefficient, and dB is the bubble diameter.

After substituting appropriate values, we get

dB=3.03×104(πD)−2/5g−1/5h4/5Q0.344N−1.48.

(19)

According to the last equation, the size of the gas bubble decreases with the increasing rotational speed (see Figure 10).

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Figure 10

Effect of rotational speed on the bubble diameter.

In a flow of given turbulence intensity, the diameter of the bubble does not exceed the maximum size dmax, which is inversely proportional to the rate of kinetic energy dissipation in a viscous flow ε. The size of the gas bubble diameter as a function of the mixing energy, also considering the Weber number and the mixing energy in the negative power, can be determined from the following equations [31,34]:

  • —Sevik and Park:

dBmax=We0.6kr⋅(σ⋅103ρ⋅10−3)0.6⋅(10⋅ε)−0.4⋅10−2.

(20)

  • —Evans:

dBmax=⎡⎣Wekr⋅σ⋅1032⋅(ρ⋅10−3)13⎤⎦35 ⋅(10⋅ε)−25⋅10−2.

(21)

The results of calculating the maximum diameter of the bubble dBmax determined from Equation (21) are given in Table 7.

Table 7

The results of calculating the maximum diameter of the bubble using Equation (21).

ModelMixing Energy
ĺ (m2·s−3)
Weber Number (Wekr)
0.591.01.2
Zhang and Taniguchi
dmax
0.10.01670.02300.026
0.50.00880.01210.013
1.00.00670.00910.010
1.50.00570.00780.009
Sevik and Park
dBmax
0.10.2650.360.41
0.50.1390.190.21
1.00.1060.140.16
1.50.0900.120.14
Evans
dBmax
0.10.2470.3400.38
0.50.1300.1780.20
1.00.0980.1350.15
1.50.0840.1150.13

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3.3. Physical Modeling

The first stage of experiments (using the URO-200 water model) included conducting experiments with impellers equipped with four, eight, and 12 gas outlets (variants B4, B8, B12). The tests were carried out for different process parameters. Selected results for these experiments are presented in Figure 11Figure 12Figure 13 and Figure 14.

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Figure 11

Impeller variant B4—gas bubbles dispersion registered for a gas flow rate of 10 dm3·min−1 and rotor speed of (a) 200, (b) 300, (c) 400, and (d) 500 rpm.

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Figure 12

Impeller variant B8—gas bubbles dispersion registered for a gas flow rate of 10 dm3·min−1 and rotor speed of (a) 200, (b) 300, (c) 400, and (d) 500 rpm.

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Figure 13

Gas bubble dispersion registered for different processing parameters (impeller variant B12).

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Figure 14

Gas bubble dispersion registered for different processing parameters (impeller variant RT3).

The analysis of the refining variants presented in Figure 11Figure 12Figure 13 and Figure 14 reveals that the proposed impellers design model is not useful for the aluminum refining process. The number of gas outlet orifices, rotational speed, and flow did not affect the refining efficiency. In all the variants shown in the figures, very poor dispersion of gas bubbles was observed in the object. The gas bubble flow had a columnar character, and so-called dead zones, i.e., areas where no inert gas bubbles are present, were visible in the analyzed object. Such dead zones were located in the bottom and side zones of the ladle, while the flow of bubbles occurred near the turning rotor. Another negative phenomenon observed was a significant agitation of the water surface due to excessive (rotational) rotor speed and gas flow (see Figure 13, cases 20; 400, 30; 300, 30; 400, and 30; 500).

Research results for a ‘red triangle’ impeller equipped with three gas supply orifices (variant RT3) are presented in Figure 14.

In this impeller design, a uniform degree of bubble dispersion in the entire volume of the modeling fluid was achieved for most cases presented (see Figure 14). In all tested variants, single bubbles were observed in the area of the water surface in the vessel. For variants 20; 200, 30; 200, and 20; 300 shown in Figure 14, the bubble dispersion results were the worst as the so-called dead zones were identified in the area near the bottom and sidewalls of the vessel, which disqualifies these work parameters for further applications. Interestingly, areas where swirls and gas bubble chains formed were identified only for the inert gas flows of 20 and 30 dm3·min−1 and 200 rpm in the analyzed model. This means that the presented model had the best performance in terms of dispersion of gas bubbles in the model liquid. Its design with sharp edges also differed from previously analyzed models, which is beneficial for gas bubble dispersion, but may interfere with its suitability in industrial conditions due to possible premature wear.

3.4. Qualitative Comparison of Research Results (CFD and Physical Model)

The analysis (physical modeling) revealed that the best mixing efficiency results were obtained with the RT3 impeller variant. Therefore, numerical calculations were carried out for the impeller model with three outlet orifices (variant RT3). The CFD results are presented in Figure 15 and Figure 16.

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Object name is materials-15-05273-g015.jpg

Figure 15

Simulation results of the impeller RT3, for given flows and rotational speeds after a time of 1 s: simulation variants (a) A, (b) B, (c) C, (d) D, (e) E, and (f) F.

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Figure 16

Simulation results of the impeller RT3, for given flows and rotational speeds after a time of 5.4 s.: simulation variants (a) A, (b) B, (c) C, (d) D, (e) E, and (f) F.

CFD results are presented for all analyzed variants (impeller RT3) at two selected calculation timesteps of 1 and 5.40 s. They show the velocity field of the medium (water) and the dispersion of gas bubbles.

Figure 15 shows the initial refining phase after 1 s of the process. In this case, the gas bubble formation and flow were observed in an area close to contact with the rotor. Figure 16 shows the phase when the dispersion and flow of gas bubbles were advanced in the reactor area of the URO-200 model.

The quantitative evaluation of the obtained results of physical and numerical model tests was based on the comparison of the degree of gas dispersion in the model liquid. The degree of gas bubble dispersion in the volume of the model liquid and the areas of strong turbulent zones formation were evaluated during the analysis of the results of visualization and numerical simulations. These two effects sufficiently characterize the required course of the process from the physical point of view. The known scheme of the below description was adopted as a basic criterion for the evaluation of the degree of dispersion of gas bubbles in the model liquid.

  • Minimal dispersion—single bubbles ascending in the region of their formation along the ladle axis; lack of mixing in the whole bath volume.
  • Accurate dispersion—single and well-mixed bubbles ascending toward the bath mirror in the region of the ladle axis; no dispersion near the walls and in the lower part of the ladle.
  • Uniform dispersion—most desirable; very good mixing of fine bubbles with model liquid.
  • Excessive dispersion—bubbles join together to form chains; large turbulence zones; uneven flow of gas.

The numerical simulation results give a good agreement with the experiments performed with the physical model. For all studied variants (used process parameters), the single bubbles were observed in the area of water surface in the vessel. For variants presented in Figure 13 (200 rpm, gas flow 20 and dm3·min−1) and relevant examples in numerical simulation Figure 16, the worst bubble dispersion results were obtained because the dead zones were identified in the area near the bottom and sidewalls of the vessel, which disqualifies these work parameters for further use. The areas where swirls and gas bubble chains formed were identified only for the inert gas flows of 20 and 30 dm3·min−1 and 200 rpm in the analyzed model (physical model). This means that the presented impeller model had the best performance in terms of dispersion of gas bubbles in the model liquid. The worst bubble dispersion results were obtained because the dead zones were identified in the area near the bottom and side walls of the vessel, which disqualifies these work parameters for further use.

Figure 17 presents exemplary results of model tests (CFD and physical model) with marked gas bubble dispersion zones. All variants of tests were analogously compared, and this comparison allowed validating the numerical model.

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Object name is materials-15-05273-g017.jpg

Figure 17

Compilations of model research results (CFD and physical): A—single gas bubbles formed on the surface of the modeling liquid, B—excessive formation of gas chains and swirls, C—uniform distribution of gas bubbles in the entire volume of the tank, and D—dead zones without gas bubbles, no dispersion. (a) Variant B; (b) variant F.

It should be mentioned here that, in numerical simulations, it is necessary to make certain assumptions and simplifications. The calculations assumed three particle size classes (Table 2), which represent the different gas bubbles that form due to different gas flow rates. The maximum number of particles/bubbles (Table 1) generated was assumed in advance and related to the computational capabilities of the computer. Too many particles can also make it difficult to visualize and analyze the results. The size of the particles, of course, affects their behavior during simulation, while, in the figures provided in the article, the bubbles are represented by spheres (visualization of the results) of the same size. Please note that, due to the adopted Lagrangian–Eulerian approach, the simulation did not take into account phenomena such as bubble collapse or fusion. However, the obtained results allow a comprehensive analysis of the behavior of gas bubbles in the system under consideration.

The comparative analysis of the visualization (quantitative) results obtained with the water model and CFD simulations (see Figure 17) generated a sufficient agreement from the point of view of the trends. A precise quantitative evaluation is difficult to perform because of the lack of a refraction compensating system in the water model. Furthermore, in numerical simulations, it is not possible to determine the geometry of the forming gas bubbles and their interaction with each other as opposed to the visualization in the water model. The use of both research methods is complementary. Thus, a direct comparison of images obtained by the two methods requires appropriate interpretation. However, such an assessment gives the possibility to qualitatively determine the types of the present gas bubble dispersion, thus ultimately validating the CFD results with the water model.

A summary of the visualization results for impellers RT3, i.e., analysis of the occurring gas bubble dispersion types, is presented in Table 8.

Table 8

Summary of visualization results (impeller RT3)—different types of gas bubble dispersion.

No Exp.ABCDEF
Gas flow rate, dm3·min−11030
Impeller speed, rpm200300500200300500
Type of dispersionAccurateUniformUniform/excessiveMinimalExcessiveExcessive

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Tests carried out for impeller RT3 confirmed the high efficiency of gas bubble distribution in the volume of the tested object at a low inert gas flow rate of 10 dm3·min−1. The most optimal variant was variant B (300 rpm, 10 dm3·min−1). However, the other variants A and C (gas flow rate 10 dm3·min−1) seemed to be favorable for this type of impeller and are recommended for further testing. The above process parameters will be analyzed in detail in a quantitative analysis to be performed on the basis of the obtained efficiency curves of the degassing process (oxygen removal). This analysis will give an unambiguous answer as to which process parameters are the most optimal for this type of impeller; the results are planned for publication in the next article.

It should also be noted here that the high agreement between the results of numerical calculations and physical modelling prompts a conclusion that the proposed approach to the simulation of a degassing process which consists of a single-phase flow model with a free surface and a particle flow model is appropriate. The simulation results enable us to understand how the velocity field in the fluid is formed and to analyze the distribution of gas bubbles in the system. The simulations in Flow-3D software can, therefore, be useful for both the design of the impeller geometry and the selection of process parameters.

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4. Conclusions

The results of experiments carried out on the physical model of the device for the simulation of barbotage refining of aluminum revealed that the worst results in terms of distribution and dispersion of gas bubbles in the studied object were obtained for the black impellers variants B4, B8, and B12 (multi-orifice impellers—four, eight, and 12 outlet holes, respectively).

In this case, the control of flow, speed, and number of gas exit orifices did not improve the process efficiency, and the developed design did not meet the criteria for industrial tests. In the case of the ‘red triangle’ impeller (variant RT3), uniform gas bubble dispersion was achieved throughout the volume of the modeling fluid for most of the tested variants. The worst bubble dispersion results due to the occurrence of the so-called dead zones in the area near the bottom and sidewalls of the vessel were obtained for the flow variants of 20 dm3·min−1 and 200 rpm and 30 dm3·min−1 and 200 rpm. For the analyzed model, areas where swirls and gas bubble chains were formed were found only for the inert gas flow of 20 and 30 dm3·min−1 and 200 rpm. The model impeller (variant RT3) had the best performance compared to the previously presented impellers in terms of dispersion of gas bubbles in the model liquid. Moreover, its design differed from previously presented models because of its sharp edges. This can be advantageous for gas bubble dispersion, but may negatively affect its suitability in industrial conditions due to premature wearing.

The CFD simulation results confirmed the results obtained from the experiments performed on the physical model. The numerical simulation of the operation of the ‘red triangle’ impeller model (using Flow-3D software) gave good agreement with the experiments performed on the physical model. This means that the presented model impeller, as compared to other (analyzed) designs, had the best performance in terms of gas bubble dispersion in the model liquid.

In further work, the developed numerical model is planned to be used for CFD simulations of the gas bubble distribution process taking into account physicochemical parameters of liquid aluminum based on industrial tests. Consequently, the obtained results may be implemented in production practice.

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Funding Statement

This paper was created with the financial support grants from the AGH-UST, Faculty of Foundry Engineering, Poland (16.16.170.654 and 11/990/BK_22/0083) for the Faculty of Materials Engineering, Silesian University of Technology, Poland.

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Author Contributions

Conceptualization, K.K. and D.K.; methodology, J.P. and T.M.; validation, M.S. and S.G.; formal analysis, D.K. and T.M.; investigation, J.P., K.K. and S.G.; resources, M.S., J.P. and K.K.; writing—original draft preparation, D.K. and T.M.; writing—review and editing, D.K. and T.M.; visualization, J.P., K.K. and S.G.; supervision, D.K.; funding acquisition, D.K. and T.M. All authors have read and agreed to the published version of the manuscript.

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Institutional Review Board Statement

Not applicable.

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Informed Consent Statement

Not applicable.

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Data Availability Statement

Data are contained within the article.

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Conflicts of Interest

The authors declare no conflict of interest.

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Footnotes

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Fig. 1. (a) Dimensions of the casting with runners (unit: mm), (b) a melt flow simulation using Flow-3D software together with Reilly's model[44], predicted that a large amount of bifilms (denoted by the black particles) would be contained in the final casting. (c) A solidification simulation using Pro-cast software showed that no shrinkage defect was contained in the final casting.

AZ91 합금 주물 내 연행 결함에 대한 캐리어 가스의 영향

TianLiabJ.M.T.DaviesaXiangzhenZhuc
aUniversity of Birmingham, Birmingham B15 2TT, United Kingdom
bGrainger and Worrall Ltd, Bridgnorth WV15 5HP, United Kingdom
cBrunel Centre for Advanced Solidification Technology, Brunel University London, Kingston Ln, London, Uxbridge UB8 3PH, United Kingdom

Abstract

An entrainment defect (also known as a double oxide film defect or bifilm) acts a void containing an entrapped gas when submerged into a light-alloy melt, thus reducing the quality and reproducibility of the final castings. Previous publications, carried out with Al-alloy castings, reported that this trapped gas could be subsequently consumed by the reaction with the surrounding melt, thus reducing the void volume and negative effect of entrainment defects. Compared with Al-alloys, the entrapped gas within Mg-alloy might be more efficiently consumed due to the relatively high reactivity of magnesium. However, research into the entrainment defects within Mg alloys has been significantly limited. In the present work, AZ91 alloy castings were produced under different carrier gas atmospheres (i.e., SF6/CO2, SF6/air). The evolution processes of the entrainment defects contained in AZ91 alloy were suggested according to the microstructure inspections and thermodynamic calculations. The defects formed in the different atmospheres have a similar sandwich-like structure, but their oxide films contained different combinations of compounds. The use of carrier gases, which were associated with different entrained-gas consumption rates, affected the reproducibility of AZ91 castings.

연행 결함(이중 산화막 결함 또는 이중막이라고도 함)은 경합금 용융물에 잠길 때 갇힌 가스를 포함하는 공극으로 작용하여 최종 주물의 품질과 재현성을 저하시킵니다. Al-합금 주물을 사용하여 수행된 이전 간행물에서는 이 갇힌 가스가 주변 용융물과의 반응에 의해 후속적으로 소모되어 공극 부피와 연행 결함의 부정적인 영향을 줄일 수 있다고 보고했습니다. Al-합금에 비해 마그네슘의 상대적으로 높은 반응성으로 인해 Mg-합금 내에 포집된 가스가 더 효율적으로 소모될 수 있습니다. 그러나 Mg 합금 내 연행 결함에 대한 연구는 상당히 제한적이었습니다. 현재 작업에서 AZ91 합금 주물은 다양한 캐리어 가스 분위기(즉, SF6/CO2, SF6/공기)에서 생산되었습니다. AZ91 합금에 포함된 연행 결함의 진화 과정은 미세 조직 검사 및 열역학 계산에 따라 제안되었습니다. 서로 다른 분위기에서 형성된 결함은 유사한 샌드위치 구조를 갖지만 산화막에는 서로 다른 화합물 조합이 포함되어 있습니다. 다른 동반 가스 소비율과 관련된 운반 가스의 사용은 AZ91 주물의 재현성에 영향을 미쳤습니다.

Keywords

Magnesium alloy, Casting, Oxide film, Bifilm, Entrainment defect, Reproducibility

1. Introduction

As the lightest structural metal available on Earth, magnesium became one of the most attractive light metals over the last few decades. The magnesium industry has consequently experienced a rapid development in the last 20 years [1,2], indicating a large growth in demand for Mg alloys all over the world. Nowadays, the use of Mg alloys can be found in the fields of automobiles, aerospace, electronics and etc.[3,4]. It has been predicted that the global consumption of Mg metals will further increase in the future, especially in the automotive industry, as the energy efficiency requirement of both traditional and electric vehicles further push manufactures lightweight their design [3,5,6].

The sustained growth in demand for Mg alloys motivated a wide interest in the improvement of the quality and mechanical properties of Mg-alloy castings. During a Mg-alloy casting process, surface turbulence of the melt can lead to the entrapment of a doubled-over surface film containing a small quantity of the surrounding atmosphere, thus forming an entrainment defect (also known as a double oxide film defect or bifilm) [7][8][9][10]. The random size, quantity, orientation, and placement of entrainment defects are widely accepted to be significant factors linked to the variation of casting properties [7]. In addition, Peng et al. [11] found that entrained oxides films in AZ91 alloy melt acted as filters to Al8Mn5 particles, trapping them as they settle. Mackie et al. [12] further suggested that entrained oxide films can act to trawl the intermetallic particles, causing them to cluster and form extremely large defects. The clustering of intermetallic compounds made the entrainment defects more detrimental for the casting properties.

Most of the previous studies regarding entrainment defects were carried out on Al-alloys [7,[13][14][15][16][17][18], and a few potential methods have been suggested for diminishing their negative effect on the quality of Al-alloy castings. Nyahumwa et al.,[16] shows that the void volume within entrainment defects could be reduced by a hot isostatic pressing (HIP) process. Campbell [7] suggested the entrained gas within the defects could be consumed due to reaction with the surrounding melt, which was further verified by Raiszedeh and Griffiths [19].The effect of the entrained gas consumption on the mechanical properties of Al-alloy castings has been investigated by [8,9], suggesting that the consumption of the entrained gas promoted the improvement of the casting reproducibility.

Compared with the investigation concerning the defects within Al-alloys, research into the entrainment defects within Mg-alloys has been significantly limited. The existence of entrainment defects has been demonstrated in Mg-alloy castings [20,21], but their behaviour, evolution, as well as entrained gas consumption are still not clear.

In a Mg-alloy casting process, the melt is usually protected by a cover gas to avoid magnesium ignition. The cavities of sand or investment moulds are accordingly required to be flushed with the cover gas prior to the melt pouring [22]. Therefore, the entrained gas within Mg-alloy castings should contain the cover gas used in the casting process, rather than air only, which may complicate the structure and evolution of the corresponding entrainment defects.

SF6 is a typical cover gas widely used for Mg-alloy casting processes [23][24][25]. Although this cover gas has been restricted to use in European Mg-alloy foundries, a commercial report has pointed out that this cover is still popular in global Mg-alloy industry, especially in the countries which dominated the global Mg-alloy production, such as China, Brazil, India, etc. [26]. In addition, a survey in academic publications also showed that this cover gas was widely used in recent Mg-alloy studies [27]. The protective mechanism of SF6 cover gas (i.e., the reaction between liquid Mg-alloy and SF6 cover gas) has been investigated by several previous researchers, but the formation process of the surface oxide film is still not clearly understood, and even some published results are conflicting with each other. In early 1970s, Fruehling [28] found that the surface film formed under SF6 was MgO mainly with traces of fluorides, and suggested that SF6 was absorbed in the Mg-alloy surface film. Couling [29] further noticed that the absorbed SF6 reacted with the Mg-alloy melt to form MgF2. In last 20 years, different structures of the Mg-alloy surface films have been reported, as detailed below.(1)

Single-layered film. Cashion [30,31] used X-ray Photoelectron Spectroscopy (XPS) and Auger Spectroscopy (AES) to identify the surface film as MgO and MgF2. He also found that composition of the film was constant throughout the thickness and the whole experimental holding time. The film observed by Cashion had a single-layered structure created from a holding time from 10 min to 100 min.(2)

Double-layered film. Aarstad et. al [32] reported a doubled-layered surface oxide film in 2003. They observed several well-distributed MgF2 particles attached to the preliminary MgO film and grew until they covered 25–50% of the total surface area. The inward diffusion of F through the outer MgO film was the driving force for the evolution process. This double-layered structure was also supported by Xiong’s group [25,33] and Shih et al. [34].(3)

Triple-layered film. The triple-layered film and its evolution process were reported in 2002 by Pettersen [35]. Pettersen found that the initial surface film was a MgO phase and then gradually evolved to the stable MgF2 phase by the inward diffusion of F. In the final stage, the film has a triple-layered structure with a thin O-rich interlayer between the thick top and bottom MgF2 layers.(4)

Oxide film consisted of discrete particles. Wang et al [36] stirred the Mg-alloy surface film into the melt under a SF6 cover gas, and then inspect the entrained surface film after the solidification. They found that the entrained surface films were not continues as the protective surface films reported by other researchers but composed of discrete particles. The young oxide film was composed of MgO nano-sized oxide particles, while the old oxide films consist of coarse particles (about 1  µm in average size) on one side that contained fluorides and nitrides.

The oxide films of a Mg-alloy melt surface or an entrained gas are both formed due to the reaction between liquid Mg-alloy and the cover gas, thus the above-mentioned research regarding the Mg-alloy surface film gives valuable insights into the evolution of entrainment defects. The protective mechanism of SF6 cover gas (i.e., formation of a Mg-alloy surface film) therefore indicated a potential complicated evolution process of the corresponding entrainment defects.

However, it should be noted that the formation of a surface film on a Mg-alloy melt is in a different situation to the consumption of an entrained gas that is submerged into the melt. For example, a sufficient amount of cover gas was supported during the surface film formation in the studies previously mentioned, which suppressed the depletion of the cover gas. In contrast, the amount of entrained gas within a Mg-alloy melt is finite, and the entrained gas may become fully depleted. Mirak [37] introduced 3.5%SF6/air bubbles into a pure Mg-alloy melt solidifying in a specially designed permanent mould. It was found that the gas bubbles were entirely consumed, and the corresponding oxide film was a mixture of MgO and MgF2. However, the nucleation sites (such as the MgF2 spots observed by Aarstad [32] and Xiong [25,33]) were not observed. Mirak also speculated that the MgF2 formed prior to MgO in the oxide film based on the composition analysis, which was opposite to the surface film formation process reported in previous literatures (i.e., MgO formed prior to MgF2). Mirak’s work indicated that the oxide-film formation of an entrained gas may be quite different from that of surface films, but he did not reveal the structure and evolution of the oxide films.

In addition, the use of carrier gas in the cover gases also influenced the reaction between the cover gas and the liquid Mg-alloy. SF6/air required a higher content of SF6 than did a SF6/CO2 carrier gas [38], to avoid the ignition of molten magnesium, revealing different gas-consumption rates. Liang et.al [39] suggested that carbon was formed in the surface film when CO2 was used as a carrier gas, which was different from the films formed in SF6/air. An investigation into Mg combustion [40] reported a detection of Mg2C3 in the Mg-alloy sample after burning in CO2, which not only supported Liang’s results, but also indicated a potential formation of Mg carbides in double oxide film defects.

The work reported here is an investigation into the behaviour and evolution of entrainment defects formed in AZ91 Mg-alloy castings, protected by different cover gases (i.e., SF6/air and SF6/CO2). These carrier gases have different protectability for liquid Mg alloy, which may be therefore associated with different consumption rates and evolution processes of the corresponding entrained gases. The effect of the entrained-gas consumption on the reproducibility of AZ91 castings was also studied.

2. Experiment

2.1. Melting and casting

Three kilograms AZ91 alloy was melted in a mild steel crucible at 700 ± 5 °C. The composition of the AZ91 alloy has been shown in Table 1. Prior to heating, all oxide scale on the ingot surface was removed by machining. The cover gases used were 0.5%SF6/air or 0.5%SF6/CO2 (vol.%) at a flow rate of 6 L/min for different castings. The melt was degassed by argon with a flow rate of 0.3 L/min for 15 min [41,42], and then poured into sand moulds. Prior to pouring, the sand mould cavity was flushed with the cover gas for 20 min [22]. The residual melt (around 1 kg) was solidified in the crucible.

Table 1. Composition (wt.%) of the AZ91 alloy used in this study.

AlZnMnSiFeNiMg
9.40.610.150.020.0050.0017Residual

Fig. 1(a) shows the dimensions of the casting with runners. A top-filling system was deliberately used to generate entrainment defects in the final castings. Green and Campbell [7,43] suggested that a top-filling system caused more entrainment events (i.e., bifilms) during a casting process, compared with a bottom-filling system. A melt flow simulation (Flow-3D software) of this mould, using Reilly’s model [44] regarding the entrainment events, also predicted that a large amount of bifilms would be contained in the final casting (denoted by the black particles in Fig. 1b).

Fig. 1. (a) Dimensions of the casting with runners (unit: mm), (b) a melt flow simulation using Flow-3D software together with Reilly's model[44], predicted that a large amount of bifilms (denoted by the black particles) would be contained in the final casting. (c) A solidification simulation using Pro-cast software showed that no shrinkage defect was contained in the final casting.

Shrinkage defects also affect the mechanical properties and reproducibility of castings. Since this study focused on the effect of bifilms on the casting quality, the mould has been deliberately designed to avoid generating shrinkage defects. A solidification simulation using ProCAST software showed that no shrinkage defect would be contained in the final casting, as shown in Fig. 1c. The casting soundness has also been confirmed using a real time X-ray prior to the test bar machining.

The sand moulds were made from resin-bonded silica sand, containing 1wt. % PEPSET 5230 resin and 1wt. % PEPSET 5112 catalyst. The sand also contained 2 wt.% Na2SiF6 to act as an inhibitor [45]. The pouring temperature was 700 ± 5 °C. After the solidification, a section of the runner bars was sent to the Sci-Lab Analytical Ltd for a H-content analysis (LECO analysis), and all the H-content measurements were carried out on the 5th day after the casting process. Each of the castings was machined into 40 test bars for a tensile strength test, using a Zwick 1484 tensile test machine with a clip extensometer. The fracture surfaces of the broken test bars were examined using Scanning Electron Microscope (SEM, Philips JEOL7000) with an accelerating voltage of 5–15 kV. The fractured test bars, residual Mg-alloy solidified in the crucible, and the casting runners were then sectioned, polished and also inspected using the same SEM. The cross-section of the oxide film found on the test-bar fracture surface was exposed by the Focused Ion Beam milling technique (FIB), using a CFEI Quanta 3D FEG FIB-SEM. The oxide film required to be analysed was coated with a platinum layer. Then, a gallium ion beam, accelerated to 30 kV, milled the material substrate surrounding the platinum coated area to expose the cross section of the oxide film. EDS analysis of the oxide film’s cross section was carried out using the FIB equipment at accelerating voltage of 30 kV.

2.2. Oxidation cell

As previously mentioned, several past researchers investigated the protective film formed on a Mg-alloy melt surface [38,39,[46][47][48][49][50][51][52]. During these experiments, the amount of cover gas used was sufficient, thus suppressing the depletion of fluorides in the cover gas. The experiment described in this section used a sealed oxidation cell, which limited the supply of cover gas, to study the evolution of the oxide films of entrainment defects. The cover gas contained in the oxidation cell was regarded as large-size “entrained bubble”.

As shown in Fig. 2, the main body of the oxidation cell was a closed-end mild steel tube which had an inner length of 400 mm, and an inner diameter of 32 mm. A water-cooled copper tube was wrapped around the upper section of the cell. When the tube was heated, the cooling system created a temperature difference between the upper and lower sections, causing the interior gas to convect within the tube. The temperature was monitored by a type-K thermocouple located at the top of the crucible. Nie et al. [53] suggested that the SF6 cover gas would react with the steel wall of the holding furnace when they investigated the surface film of a Mg-alloy melt. To avoid this reaction, the interior surface of the steel oxidation cell (shown in Fig. 2) and the upper half section of the thermocouple were coated with boron nitride (the Mg-alloy was not in contact with boron nitride).

Fig. 2. Schematic of the oxidation cell used to study the evolution of the oxide films of the entrainment defects (unit mm).

During the experiment, a block of solid AZ91 alloy was placed in a magnesia crucible located at the bottom of the oxidation cell. The cell was heated to 100 °C in an electric resistance furnace under a gas flow rate of 1 L/min. The cell was held at this temperature for 20 min, to replace the original trapped atmosphere (i.e. air). Then, the oxidation cell was further heated to 700 °C, melting the AZ91 sample. The gas inlet and exit valves were then closed, creating a sealed environment for oxidation under a limited supply of cover gas. The oxidation cell was then held at 700 ± 10 °C for periods of time from 5 min to 30 min in 5-min intervals. At the end of each holding time, the cell was quenched in water. After cooling to room temperature, the oxidised sample was sectioned, polished, and subsequently examined by SEM.

3. Results

3.1. Structure and composition of the entrainment defects formed in SF6/air

The structure and composition of the entrainment defect formed in the AZ91 castings under a cover gas of 0.5%SF6/air was observed by SEM and EDS. The results indicate that there exist two types of entrainment defects which are sketched in Fig. 3: (1) Type A defect whose oxide film has a traditional single-layered structure and (2) Type B defect, whose oxide film has two layers. The details of these defects were introduced in the following. Here it should be noticed that, as the entrainment defects are also known as biofilms or double oxide film, the oxide films of Type B defect were referred to as “multi-layered oxide film” or “multi-layered structure” in the present work to avoid a confusing description such as “the double-layered oxide film of a double oxide film defect”.

Fig. 3. Schematic of the different types of entrainment defects found in AZ91 castings. (a) Type A defect with a single-layered oxide film and (b) Type B defect with two-layered oxide film.

Fig. 4(a-b) shows a Type A defect having a compact single-layered oxide film with about 0.4 µm thickness. Oxygen, fluorine, magnesium and aluminium were detected in this film (Fig. 4c). It is speculated that oxide film is the mixture of fluoride and oxide of magnesium and aluminium. The detection of fluorine revealed that an entrained cover gas was contained in the formation of this defect. That is to say that the pores shown in Fig. 4(a) were not shrinkage defects or hydrogen porosity, but entrainment defects. The detection of aluminium was different with Xiong and Wang’s previous study [47,48], which showed that no aluminium was contained in their surface film of an AZ91 melt protected by a SF6 cover gas. Sulphur could not be clearly recognized in the element map, but there was a S-peak in the corresponding ESD spectrum.

Fig. 4. (a) A Type A entrainment defect formed in SF6/air and having a single-layered oxide film, (b) the oxide film of this defect, (c) SEM-EDS element maps (using Philips JEOL7000) corresponding to the area highlighted in (b).

Fig. 5(a-b) shows a Type B entrainment defect having a multi-layered oxide film. The compact outer layers of the oxide films were enriched with fluorine and oxygen (Fig. 5c), while their relatively porous inner layers were only enriched with oxygen (i.e., poor in fluorine) and partly grew together, thus forming a sandwich-like structure. Therefore, it is speculated that the outer layer is the mixture of fluoride and oxide, while the inner layer is mainly oxide. Sulphur could only be recognized in the EDX spectrum and could not be clearly identified in the element map, which might be due to the small S-content in the cover gas (i.e., 0.5% volume content of SF6 in the cover gas). In this oxide film, aluminium was contained in the outer layer of this oxide film but could not be clearly detected in the inner layer. Moreover, the distribution of Al seems to be uneven. It can be found that, in the right side of the defect, aluminium exists in the film but its concentration can not be identified to be higher than the matrix. However, there is a small area with much higher aluminium concentration in the left side of the defect. Such an uneven distribution of aluminium was also observed in other defects (shown in the following), and it is the result of the formation of some oxide particles in or under the film.

Fig. 5. (a) A Type B entrainment defect formed in SF6/air and having a multi-layered oxide film, (b) the oxide films of this defect have grown together, (c) SEM-EDS element maps (using Philips JEOL7000) corresponding to the area shown in (b).

Figs. 4 and 5 show cross sectional observations of the entrainment defects formed in the AZ91 alloy sample cast under a cover gas of SF6/air. It is not sufficient to characterize the entrainment defects only by the figures observed from the two-dimensional section. To have a further understanding, the surface of the entrainment defects (i.e. the oxide film) was further studied by observing the fracture surface of the test bars.

Fig. 6(a) shows fracture surfaces of an AZ91 alloy tensile test bar produced in SF6/air. Symmetrical dark regions can be seen on both sides of the fracture surfaces. Fig. 6(b) shows boundaries between the dark and bright regions. The bright region consisted of jagged and broken features, while the surface of the dark region was relatively smooth and flat. In addition, the EDS results (Fig. 6c-d and Table 2) show that fluorine, oxygen, sulphur, and nitrogen were only detected in the dark regions, indicating that the dark regions were surface protective films entrained into the melt. Therefore, it could be suggested that the dark regions were an entrainment defect with consideration of their symmetrical nature. Similar defects on fracture surfaces of Al-alloy castings have been previously reported [7]Nitrides were only found in the oxide films on the test-bar fracture surfaces but never detected in the cross-sectional samples shown in Figs. 4 and 5. An underlying reason is that the nitrides contained in these samples may have hydrolysed during the sample polishing process [54].

Fig. 6. (a) A pair of the fracture surfaces of a AZ91 alloy tensile test bar produced under a cover gas of SF6/air. The dimension of the fracture surface is 5 mm × 6 mm, (b) a section of the boundary between the dark and bright regions shown in (a), (c-d) EDS spectrum of the (c) bright regions and (d) dark regions, (e) schematic of an entrainment defect contained in a test bar.

Table 2. EDS results (wt.%) corresponding to the regions shown in Fig. 6 (cover gas: SF6/air).

Empty CellCOMgFAlZnSN
Dark region in Fig. 6(b)3.481.3279.130.4713.630.570.080.73
Bright region in Fig. 6(b)3.5884.4811.250.68

In conjunction with the cross-sectional observation of the defects shown in Figs. 4 and 5, the structure of an entrainment defect contained in a tensile test bar was sketched as shown in Fig. 6(e). The defect contained an entrained gas enclosed by its oxide film, creating a void section inside the test bar. When the tensile force applied on the defect during the fracture process, the crack was initiated at the void section and propagated along the entrainment defect, since cracks would be propagated along the weakest path [55]. Therefore, when the test bar was finally fractured, the oxide films of entrainment defect appeared on both fracture surfaces of the test bar, as shown in Fig. 6(a).

3.2. Structure and composition of the entrainment defects formed in SF6/CO2

Similar to the entrainment defect formed in SF6/air, the defects formed under a cover gas of 0.5%SF6/CO2 also had two types of oxide films (i.e., single-layered and multi-layered types). Fig. 7(a) shows an example of the entrainment defects containing a multi-layered oxide film. A magnified observation to the defect (Fig. 7b) shows that the inner layers of the oxide films had grown together, presenting a sandwich-like structure, which was similar to the defects formed in an atmosphere of SF6/air (Fig. 5b). An EDS spectrum (Fig. 7c) revealed that the joint area (inner layer) of this sandwich-like structure mainly contained magnesium oxides. Peaks of fluorine, sulphur, and aluminium were recognized in this EDS spectrum, but their amount was relatively small. In contrast, the outer layers of the oxide films were compact and composed of a mixture of fluorides and oxides (Fig. 7d-e).

Fig. 7. (a) An example of entrainment defects formed in SF6/CO2 and having a multi-layered oxide film, (b) magnified observation of the defect, showing the inner layer of the oxide films has grown together, (c) EDS spectrum of the point denoted in (b), (d) outer layer of the oxide film, (e) SEM-EDS element maps (using Philips JEOL7000) corresponding to the area shown in (d).

Fig. 8(a) shows an entrainment defect on the fracture surfaces of an AZ91 alloy tensile test bar, which was produced in an atmosphere of 0.5%SF6/CO2. The corresponding EDS results (Table 3) showed that oxide film contained fluorides and oxides. Sulphur and nitrogen were not detected. Besides, a magnified observation (Fig. 8b) indicated spots on the oxide film surface. The diameter of the spots ranged from hundreds of nanometres to a few micron meters.

Fig. 8. (a) A pair of the fracture surfaces of a AZ91 alloy tensile test bar, produced in an atmosphere of SF6/CO2. The dimension of the fracture surface is 5 mm × 6 mm, (b) surface appearance of the oxide films on the fracture surfaces, showing spots on the film surface.

To further reveal the structure and composition of the oxide film clearly, the cross-section of the oxide film on a test-bar fracture surface was onsite exposed using the FIB technique (Fig. 9). As shown in Fig. 9a, a continuous oxide film was found between the platinum coating layer and the Mg-Al alloy substrate. Fig. 9 (b-c) shows a magnified observation to oxide films, indicating a multi-layered structure (denoted by the red box in Fig. 9c). The bottom layer was enriched with fluorine and oxygen and should be the mixture of fluoride and oxide, which was similar to the “outer layer” shown in Figs. 5 and 7, while the only-oxygen-enriched top layer was similar to the “inner layer” shown in Figs. 5 and 7.

Fig. 9. (a) A cross-sectional observation of the oxide film on the fracture surface of the AZ91 casting produced in SF6/CO2, exposed by FIB, (b) a magnified observation of area highlighted in (a), and (c) SEM-EDS elements map of the area shown in (b), obtained by CFEI Quanta 3D FEG FIB-SEM.

Except the continuous film, some individual particles were also observed in or below the continuous film, as shown in Fig. 9. An Al-enriched particle was detected in the left side of the oxide film shown in Fig. 9b and might be speculated to be spinel Mg2AlO4 because it also contains abundant magnesium and oxygen elements. The existing of such Mg2AlO4 particles is responsible for the high concentration of aluminium in small areas of the observed film and the uneven distribution of aluminium, as shown in Fig. 5(c). Here it should be emphasized that, although the other part of the bottom layer of the continuous oxide film contains less aluminium than this Al-enriched particle, the Fig. 9c indicated that the amount of aluminium in this bottom layer was still non-negligible, especially when comparing with the outer layer of the film. Below the right side of the oxide film shown in Fig. 9b, a particle was detected and speculated to be MgO because it is rich in Mg and O. According to Wang’s result [56], lots of discrete MgO particles can be formed on the surface of the Mg melt by the oxidation of Mg melt and Mg vapor. The MgO particles observed in our present work may be formed due to the same reasons. While, due to the differences in experimental conditions, less Mg melt can be vapored or react with O2, thus only a few of MgO particles formed in our work. An enrichment of carbon was also found in the film, revealing that CO2 was able to react with the melt, thus forming carbon or carbides. This carbon concentration was consistent with the relatively high carbon content of the oxide film shown in Table 3 (i.e., the dark region). In the area next to the oxide film.

Table 3. EDS results (wt.%) corresponding to the regions shown in Fig. 8 (cover gas: SF6/ CO2).

Empty CellCOMgFAlZnSN
Dark region in Fig. 8(a)7.253.6469.823.827.030.86
Bright region in Fig. 8(a)2.100.4482.8313.261.36

This cross-sectional observation of the oxide film on a test bar fracture surface (Fig. 9) further verified the schematic of the entrainment defect shown in Fig. 6(e). The entrainment defects formed in different atmospheres of SF6/CO2 and SF6/air had similar structures, but their compositions were different.

3.3. Evolution of the oxide films in the oxidation cell

The results in Section 3.1 and 3.2 have shown the structures and compositions of entrainment defects formed in AZ91 castings under cover gases of SF6/air and SF6/CO2. Different stages of the oxidation reaction may lead to the different structures and compositions of entrainment defects. Although Campbell has conjectured that an entrained gas may react with the surrounding melt, it is rarely reported that the reaction occurring between the Mg-alloy melt and entrapped cover gas. Previous researchers normally focus on the reaction between a Mg-alloy melt and the cover gas in an open environment [38,39,[46][47][48][49][50][51][52], which was different from the situation of a cover gas trapped into the melt. To further understand the formation of the entrainment defect in an AZ91 alloy, the evolution process of oxide films of the entrainment defect was further studied using an oxidation cell.

Fig. 10 (a and d) shows a surface film held for 5 min in the oxidation cell, protected by 0.5%SF6/air. There was only one single layer consisting of fluoride and oxide (MgF2 and MgO). In this surface film. Sulphur was detected in the EDS spectrum, but its amount was too small to be recognized in the element map. The structure and composition of this oxide film was similar to the single-layered films of entrainment defects shown in Fig. 4.

Fig. 10. Oxide films formed in the oxidation cell under a cover gas of 0.5%SF6/air and held at 700 °C for (a) 5 min; (b) 10 min; (c) 30 min, and (d-f) the SEM-EDS element maps (using Philips JEOL7000) corresponding to the oxide film shown in (a-c) respectively, (d) 5 min; (e) 10 min; (f) 30 min. The red points in (c and f) are the location references, denoting the boundary of the F-enriched layer in different element maps.

After a holding time of 10 min, a thin (O, S)-enriched top layer (around 700 nm) appeared upon the preliminary F-enriched film, forming a multi-layered structure, as shown in Fig. 10(b and e). The thickness of the (O, S)-enriched top layer increased with increased holding time. As shown in Fig. 10(c and f), the oxide film held for 30 min also had a multi-layered structure, but the thickness of its (O, S)-enriched top layer (around 2.5 µm) was higher than the that of the 10-min oxide film. The multi-layered oxide films shown in Fig. 10(b-c) presented a similar appearance to the films of the sandwich-like defect shown in Fig. 5.

The different structures of the oxide films shown in Fig. 10 indicated that fluorides in the cover gas would be preferentially consumed due to the reaction with the AZ91 alloy melt. After the depletion of fluorides, the residual cover gas reacted further with the liquid AZ91 alloy, forming the top (O, S)-enriched layer in the oxide film. Therefore, the different structures and compositions of entrainment defects shown in Figs. 4 and 5 may be due to an ongoing oxidation reaction between melt and entrapped cover gas.

This multi-layered structure has not been reported in previous publications concerning the protective surface film formed on a Mg-alloy melt [38,[46][47][48][49][50][51]. This may be due to the fact that previous researchers carried out their experiments with an un-limited amount of cover gas, creating a situation where the fluorides in the cover gas were not able to become depleted. Therefore, the oxide film of an entrainment defect had behaviour traits similar to the oxide films shown in Fig. 10, but different from the oxide films formed on the Mg-alloy melt surface reported in [38,[46][47][48][49][50][51].

Similar with the oxide films held in SF6/air, the oxide films formed in SF6/CO2 also had different structures with different holding times in the oxidation cell. Fig. 11(a) shows an oxide film, held on an AZ91 melt surface under a cover gas of 0.5%SF6/CO2 for 5 min. This film had a single-layered structure consisting of MgF2. The existence of MgO could not be confirmed in this film. After the holding time of 30 min, the film had a multi-layered structure; the inner layer was of a compact and uniform appearance and composed of MgF2, while the outer layer is the mixture of MgF2 and MgO. Sulphur was not detected in this film, which was different from the surface film formed in 0.5%SF6/air. Therefore, fluorides in the cover gas of 0.5%SF6/CO2 were also preferentially consumed at an early stage of the film growth process. Compared with the film formed in SF6/air, the MgO in film formed in SF6/CO2 appeared later and sulphide did not appear within 30 min. It may mean that the formation and evolution of film in SF6/air is faster than SF6/CO2. CO2 may have subsequently reacted with the melt to form MgO, while sulphur-containing compounds accumulated in the cover gas and reacted to form sulphide in very late stage (may after 30 min in oxidation cell).

Fig. 11. Oxide films formed in the oxidation cell under a cover gas of 0.5%SF6/CO2, and their SEM-EDS element maps (using Philips JEOL7000). They were held at 700 °C for (a) 5 min; (b) 30 min. The red points in (b) are the location references, denoting the boundary between the top and bottom layers in the oxide film.

4. Discussion

4.1. Evolution of entrainment defects formed in SF6/air

HSC software from Outokumpu HSC Chemistry for Windows (http://www.hsc-chemistry.net/) was used to carry out thermodynamic calculations needed to explore the reactions which might occur between the trapped gases and liquid AZ91 alloy. The solutions to the calculations suggest which products are most likely to form in the reaction process between a small amount of cover gas (i.e., the amount within a trapped bubble) and the AZ91-alloy melt.

In the trials, the pressure was set to 1 atm, and the temperature set to 700 °C. The amount of the cover gas was assumed to be 7 × 10−7 kg, with a volume of approximately 0.57 cm3 (3.14 × 10−8 kmol) for 0.5%SF6/air, and 0.35 cm3 (3.12 × 10−8 kmol) for 0.5%SF6/CO2. The amount of the AZ91 alloy melt in contact with the trapped gas was assumed to be sufficient to complete all reactions. The decomposition products of SF6 were SF5, SF4, SF3, SF2, F2, S(g), S2(g) and F(g) [57][58][59][60].

Fig. 12 shows the equilibrium diagram of the thermodynamic calculation of the reaction between the AZ91 alloy and 0.5%SF6/air. In the diagram, the reactants and products with less than 10−15 kmol have not been shown, as this was 5 orders of magnitude less than the amount of SF6 present (≈ 1.57 × 10−10 kmol) and therefore would not affect the observed process in a practical way.

Fig. 12. An equilibrium diagram for the reaction between 7e-7 kg 0.5%SF6/air and a sufficient amount of AZ91 alloy. The X axis is the amount of AZ91 alloy melt having reacted with the entrained gas, and the vertical Y-axis is the amount of the reactants and products.

This reaction process could be divided into 3 stages.

Stage 1: The formation of fluorides. the AZ91 melt preferentially reacted with SF6 and its decomposition products, producing MgF2, AlF3, and ZnF2. However, the amount of ZnF2 may have been too small to be detected practically (1.25 × 10−12 kmol of ZnF2 compared with 3 × 10−10 kmol of MgF2), which may be the reason why Zn was not detected in any the oxide films shown in Sections 3.13.3. Meanwhile, sulphur accumulated in the residual gas as SO2.

Stage 2: The formation of oxides. After the liquid AZ91 alloy had depleted all the available fluorides in the entrapped gas, the amount of AlF3 and ZnF2 quickly reduced due to a reaction with Mg. O2(g) and SO2 reacted with the AZ91 melt, forming MgO, Al2O3, MgAl2O4, ZnO, ZnSO4 and MgSO4. However, the amount of ZnO and ZnSO4 would have been too small to be found practically by EDS (e.g. 9.5 × 10−12 kmol of ZnO,1.38 × 10−14 kmol of ZnSO4, in contrast to 4.68 × 10−10 kmol of MgF2, when the amount of AZ91 on the X-axis is 2.5 × 10−9 kmol). In the experimental cases, the concentration of F in the cover gas is very low, whole the concentration f O is much higher. Therefore, the stage 1 and 2, i.e, the formation of fluoride and oxide may happen simultaneously at the beginning of the reaction, resulting in the formation of a singer-layered mixture of fluoride and oxide, as shown in Figs. 4 and 10(a). While an inner layer consisted of oxides but fluorides could form after the complete depletion of F element in the cover gas.

Stages 1- 2 theoretically verified the formation process of the multi-layered structure shown in Fig. 10.

The amount of MgAl2O4 and Al2O3 in the oxide film was of a sufficient amount to be detected, which was consistent with the oxide films shown in Fig. 4. However, the existence of aluminium could not be recognized in the oxide films grown in the oxidation cell, as shown in Fig. 10. This absence of Al may be due to the following reactions between the surface film and AZ91 alloy melt:(1)

Al2O3 + 3Mg + = 3MgO + 2Al, △G(700 °C) = -119.82 kJ/mol(2)

Mg + MgAl2O4 = MgO + Al, △G(700 °C) =-106.34 kJ/molwhich could not be simulated by the HSC software since the thermodynamic calculation was carried out under an assumption that the reactants were in full contact with each other. However, in a practical process, the AZ91 melt and the cover gas would not be able to be in contact with each other completely, due to the existence of the protective surface film.

Stage 3: The formation of Sulphide and nitride. After a holding time of 30 min, the gas-phase fluorides and oxides in the oxidation cell had become depleted, allowing the melt reaction with the residual gas, forming an additional sulphur-enriched layer upon the initial F-enriched or (F, O)-enriched surface film, thus resulting in the observed multi-layered structure shown in Fig. 10 (b and c). Besides, nitrogen reacted with the AZ91 melt until all reactions were completed. The oxide film shown in Fig. 6 may correspond to this reaction stage due to its nitride content. However, the results shows that the nitrides were not detected in the polished samples shown in Figs. 4 and 5, but only found on the test bar fracture surfaces. The nitrides may have hydrolysed during the sample preparation process, as follows [54]:(3)

Mg3N2 + 6H2O =3Mg(OH)2 + 2NH3↑(4)

AlN+ 3H2O =Al(OH)3 + NH3

In addition, Schmidt et al. [61] found that Mg3N2 and AlN could react to form ternary nitrides (Mg3AlnNn+2, n= 1, 2, 3…). HSC software did not contain the database of ternary nitrides, and it could not be added into the calculation. The oxide films in this stage may also contain ternary nitrides.

4.2. Evolution of entrainment defects formed in SF6/CO2

Fig. 13 shows the results of the thermodynamic calculation between AZ91 alloy and 0.5%SF6/CO2. This reaction processes can also be divided into three stages.

Fig. 13. An equilibrium diagram for the reaction between 7e-7 kg 0.5%SF6/CO2 and a sufficient amount of AZ91 alloy. The X axis denotes the amount of Mg alloy melt having reacted with the entrained gas, and the vertical Y-axis denotes the amounts of the reactants and products.

Stage 1: The formation of fluorides. SF6 and its decomposition products were consumed by the AZ91 melt, forming MgF2, AlF3, and ZnF2. As in the reaction of AZ91 in 0.5%SF6/air, the amount of ZnF2 was too small to be detected practically (1.51 × 10−13 kmol of ZnF2 compared with 2.67 × 10−10 kmol of MgF2). Sulphur accumulated in the residual trapped gas as S2(g) and a portion of the S2(g) reacted with CO2, to form SO2 and CO. The products in this reaction stage were consistent with the film shown in Fig. 11(a), which had a single layer structure that contained fluorides only.

Stage 2: The formation of oxides. AlF3 and ZnF2 reacted with the Mg in the AZ91 melt, forming MgF2, Al and Zn. The SO2 began to be consumed, producing oxides in the surface film and S2(g) in the cover gas. Meanwhile, the CO2 directly reacted with the AZ91 melt, forming CO, MgO, ZnO, and Al2O3. The oxide films shown in Figs. 9 and 11(b) may correspond to this reaction stage due to their oxygen-enriched layer and multi-layered structure.

The CO in the cover gas could further react with the AZ91 melt, producing C. This carbon may further react with Mg to form Mg carbides, when the temperature reduced (during solidification period) [62]. This may be the reason for the high carbon content in the oxide film shown in Figs. 89. Liang et al. [39] also reported carbon-detection in an AZ91 alloy surface film protected by SO2/CO2. The produced Al2O3 may be further combined with MgO, forming MgAl2O4 [63]. As discussed in Section 4.1, the alumina and spinel can react with Mg, causing an absence of aluminium in the surface films, as shown in Fig. 11.

Stage 3: The formation of Sulphide. the AZ91 melt began to consume S2(g) in the residual entrapped gas, forming ZnS and MgS. These reactions did not occur until the last stage of the reaction process, which could be the reason why the S-content in the defect shown Fig. 7(c) was small.

In summary, thermodynamic calculations indicate that the AZ91 melt will react with the cover gas to form fluorides firstly, then oxides and sulphides in the last. The oxide film in the different reaction stages would have different structures and compositions.

4.3. Effect of the carrier gases on consumption of the entrained gas and the reproducibility of AZ91 castings

The evolution processes of entrainment defects, formed in SF6/air and SF6/CO2, have been suggested in Sections 4.1 and 4.2. The theoretical calculations were verified with respect to the corresponding oxide films found in practical samples. The atmosphere within an entrainment defect could be efficiently consumed due to the reaction with liquid Mg-alloy, in a scenario dissimilar to the Al-alloy system (i.e., nitrogen in an entrained air bubble would not efficiently react with Al-alloy melt [64,65], however, nitrogen would be more readily consumed in liquid Mg alloys, commonly referred to as “nitrogen burning” [66]).

The reaction between the entrained gas and the surrounding liquid Mg-alloy converted the entrained gas into solid compounds (e.g. MgO) within the oxide film, thus reducing the void volume of the entrainment defect and hence probably causing a collapse of the defect (e.g., if an entrained gas of air was depleted by the surrounding liquid Mg-alloy, under an assumption that the melt temperature is 700 °C and the depth of liquid Mg-alloy is 10 cm, the total volume of the final solid products would be 0.044% of the initial volume taken by the entrapped air).

The relationship between the void volume reduction of entrainment defects and the corresponding casting properties has been widely studied in Al-alloy castings. Nyahumwa and Campbell [16] reported that the Hot Isostatic Pressing (HIP) process caused the entrainment defects in Al-alloy castings to collapse and their oxide surfaces forced into contact. The fatigue lives of their castings were improved after HIP. Nyahumwa and Campbell [16] also suggested a potential bonding of the double oxide films that were in contact with each other, but there was no direct evidence to support this. This binding phenomenon was further investigated by Aryafar et.al.[8], who re-melted two Al-alloy bars with oxide skins in a steel tube and then carried out a tensile strength test on the solidified sample. They found that the oxide skins of the Al-alloy bars strongly bonded with each other and became even stronger with an extension of the melt holding time, indicating a potential “healing” phenomenon due to the consumption of the entrained gas within the double oxide film structure. In addition, Raidszadeh and Griffiths [9,19] successfully reduced the negative effect of entrainment defects on the reproducibility of Al-alloy castings, by extending the melt holding time before solidification, which allowed the entrained gas to have a longer time to react with the surrounding melt.

With consideration of the previous work mentioned, the consumption of the entrained gas in Mg-alloy castings may diminish the negative effect of entrainment defects in the following two ways.

(1) Bonding phenomenon of the double oxide films. The sandwich-like structure shown in Fig. 5 and 7 indicated a potential bonding of the double oxide film structure. However, more evidence is required to quantify the increase in strength due to the bonding of the oxide films.

(2) Void volume reduction of entrainment defects. The positive effect of void-volume reduction on the quality of castings has been widely demonstrated by the HIP process [67]. As the evolution processes discussed in Section 4.14.2, the oxide films of entrainment defects can grow together due to an ongoing reaction between the entrained gas and surrounding AZ91 alloy melt. The volume of the final solid products was significant small compared with the entrained gas (i.e., 0.044% as previously mentioned).

Therefore, the consumption rate of the entrained gas (i.e., the growth rate of oxide films) may be a critical parameter for improving the quality of AZ91 alloy castings. The oxide film growth rate in the oxidization cell was accordingly further investigated.

Fig. 14 shows a comparison of the surface film growth rates in different cover gases (i.e., 0.5%SF6/air and 0.5%SF6/CO2). 15 random points on each sample were selected for film thickness measurements. The 95% confidence interval (95%CI) was computed under an assumption that the variation of the film thickness followed a Gaussian distribution. It can be seen that all the surface films formed in 0.5%SF6/air grew faster than those formed in 0.5%SF6/CO2. The different growth rates suggested that the entrained-gas consumption rate of 0.5%SF6/air was higher than that of 0.5%SF6/CO2, which was more beneficial for the consumption of the entrained gas.

Fig. 14. A comparison of the AZ91 alloy oxide film growth rates in 0.5%SF6/air and 0.5%SF6/CO2

It should be noted that, in the oxidation cell, the contact area of liquid AZ91 alloy and cover gas (i.e. the size of the crucible) was relatively small with consideration of the large volume of melt and gas. Consequently, the holding time for the oxide film growth within the oxidation cell was comparatively long (i.e., 5–30 min). However, the entrainment defects contained in a real casting are comparatively very small (i.e., a few microns size as shown in Figs. 36, and [7]), and the entrained gas is fully enclosed by the surrounding melt, creating a relatively large contact area. Hence the reaction time for cover gas and the AZ91 alloy melt may be comparatively short. In addition, the solidification time of real Mg-alloy sand castings can be a few minutes (e.g. Guo [68] reported that a Mg-alloy sand casting with 60 mm diameter required 4 min to be solidified). Therefore, it can be expected that an entrained gas trapped during an Mg-alloy melt pouring process will be readily consumed by the surrounding melt, especially for sand castings and large-size castings, where solidification times are long.

Therefore, the different cover gases (0.5%SF6/air and 0.5%SF6/CO2) associated with different consumption rates of the entrained gases may affect the reproducibility of the final castings. To verify this assumption, the AZ91 castings produced in 0.5%SF6/air and 0.5%SF6/CO2 were machined into test bars for mechanical evaluation. A Weibull analysis was carried out using both linear least square (LLS) method and non-linear least square (non-LLS) method [69].

Fig. 15(a-b) shows a traditional 2-p linearized Weibull plot of the UTS and elongation of the AZ91 alloy castings, obtained by the LLS method. The estimator used is P= (i-0.5)/N, which was suggested to cause the lowest bias among all the popular estimators [69,70]. The casting produced in SF6/air has an UTS Weibull moduli of 16.9, and an elongation Weibull moduli of 5.0. In contrast, the UTS and elongation Weibull modulus of the casting produced in SF6/CO2 are 7.7 and 2.7 respectively, suggesting that the reproducibility of the casting protected by SF6/CO2 were much lower than that produced in SF6/air.

Fig. 15. The Weibull modulus of AZ91 castings produced in different atmospheres, estimated by (a-b) the linear least square method, (c-d) the non-linear least square method, where SSR is the sum of residual squares.

In addition, the author’s previous publication [69] demonstrated a shortcoming of the linearized Weibull plots, which may cause a higher bias and incorrect R2 interruption of the Weibull estimation. A Non-LLS Weibull estimation was therefore carried out, as shown in Fig. 15 (c-d). The UTS Weibull modulus of the SF6/air casting was 20.8, while the casting produced under SF6/CO2 had a lower UTS Weibull modulus of 11.4, showing a clear difference in their reproducibility. In addition, the SF6/air elongation (El%) dataset also had a Weibull modulus (shape = 5.8) higher than the elongation dataset of SF6/CO2 (shape = 3.1). Therefore, both the LLS and Non-LLS estimations suggested that the SF6/air casting has a higher reproducibility than the SF6/CO2 casting. It supports the method that the use of air instead of CO2 contributes to a quicker consumption of the entrained gas, which may reduce the void volume within the defects. Therefore, the use of 0.5%SF6/air instead of 0.5%SF6/CO2 (which increased the consumption rate of the entrained gas) improved the reproducibility of the AZ91 castings.

However, it should be noted that not all the Mg-alloy foundries followed the casting process used in present work. The Mg-alloy melt in present work was degassed, thus reducing the effect of hydrogen on the consumption of the entrained gas (i.e., hydrogen could diffuse into the entrained gas, potentially suppressing the depletion of the entrained gas [7,71,72]). In contrast, in Mg-alloy foundries, the Mg-alloy melt is not normally degassed, since it was widely believed that there is not a ‘gas problem’ when casting magnesium and hence no significant change in tensile properties [73]. Although studies have shown the negative effect of hydrogen on the mechanical properties of Mg-alloy castings [41,42,73], a degassing process is still not very popular in Mg-alloy foundries.

Moreover, in present work, the sand mould cavity was flushed with the SF6 cover gas prior to pouring [22]. However, not all the Mg-alloy foundries flushed the mould cavity in this way. For example, the Stone Foundry Ltd (UK) used sulphur powder instead of the cover-gas flushing. The entrained gas within their castings may be SO2/air, rather than the protective gas.

Therefore, although the results in present work have shown that using air instead of CO2 improved the reproducibility of the final casting, it still requires further investigations to confirm the effect of carrier gases with respect to different industrial Mg-alloy casting processes.

7. Conclusion

Entrainment defects formed in an AZ91 alloy were observed. Their oxide films had two types of structure: single-layered and multi-layered. The multi-layered oxide film can grow together forming a sandwich-like structure in the final casting.2.

Both the experimental results and the theoretical thermodynamic calculations demonstrated that fluorides in the trapped gas were depleted prior to the consumption of sulphur. A three-stage evolution process of the double oxide film defects has been suggested. The oxide films contained different combinations of compounds, depending on the evolution stage. The defects formed in SF6/air had a similar structure to those formed in SF6/CO2, but the compositions of their oxide films were different. The oxide-film formation and evolution process of the entrainment defects were different from that of the Mg-alloy surface films previous reported (i.e., MgO formed prior to MgF2).3.

The growth rate of the oxide film was demonstrated to be greater under SF6/air than SF6/CO2, contributing to a quicker consumption of the damaging entrapped gas. The reproducibility of an AZ91 alloy casting improved when using SF6/air instead of SF6/CO2.

Acknowledgements

The authors acknowledge funding from the EPSRC LiME grant EP/H026177/1, and the help from Dr W.D. Griffiths and Mr. Adrian Carden (University of Birmingham). The casting work was carried out in University of Birmingham.

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T. Li, W.D. Griffiths, J. Chen

Metall. Mater. Trans. A-Phys. Metall. Mater. Sci., 48A (2017), pp. 5516-5528 View PDF

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M. Tiryakioglu, D. Hudak

J. Mater. Sci., 42 (2007), pp. 10173-10179 View PDF

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Y. Yue, W.D. Griffiths, J.L. Fife, N.R. Green

Proceedings of the 1st International Conference on 3d Materials Science (2012), pp. 131-136 View PDF

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Z.C. Hu, E.L. Zhang, S.Y. Zeng

Mater. Sci. Technol., 24 (2008), pp. 1304-1308 View PDF

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Fig. 3. Experimental angled top-view setup for laser welding of zinc-coated steel with a laser illumination.

Effect of zinc vapor forces on spattering in partial penetration laser welding of zinc-coated steels

Yu Hao a, Nannan Chen a,b, Hui-Ping Wang c,*, Blair E. Carlson c, Fenggui Lu a,*
a Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai,
200240, PR China b Department of Industrial and Manufacturing Eng

ABSTRACT

A three-dimensional thermal-fluid numerical model considering zinc vapor interaction with the molten pool was developed to study the occurrence of zinc vapor-induced spatter in partial penetration laser overlap welding of zinc-coated steels. The zinc vapor effect was represented by two forces: a jet pressure force acting on the keyhole rear wall as the vapor bursts into the keyhole and a drag force on the upper keyhole wall as the vapor escapes upwards. The numerical model was calibrated by comparing the predicted keyhole shape with the keyhole shape observed by high-speed X-ray imaging and applied for various weld schedules. The study showed that large jet pressure forces induced violent fluctuations of the keyhole rear wall, resulting in an unstable keyhole and turbulent melt flow. A large drag force pushed the melt adjacent to the keyhole surface upward and accelerated the movement of the melt whose velocities reached 1 m/s or even higher, potentially inducing spatter. Increased heat input facilitated the occurrence of large droplets of spatter, which agreed with experimental observations captured by high-speed camera.

아연도금강의 부분용입 레이저 겹침용접에서 아연증기유도 스패터의 발생을 연구하기 위하여 용융풀과의 아연증기 상호작용을 고려한 3차원 열유체 수치모델을 개발하였습니다.

아연 증기 효과는 증기가 열쇠 구멍으로 폭발할 때 키홀 뒤쪽 벽에 작용하는 제트 압력력과 증기가 위쪽으로 빠져나갈 때 위쪽 키홀 벽에 작용하는 항력의 두 가지 힘으로 표시됩니다.

수치 모델은 예측된 열쇠 구멍 모양과 고속 X선 영상으로 관찰된 키홀 모양을 비교하여 보정하고 다양한 용접 일정에 적용했습니다.

이 연구는 큰 제트 압력이 키홀 뒷벽의 격렬한 변동을 유발하여 불안정한 열쇠 구멍과 난류 용융 흐름을 초래한다는 것을 보여주었습니다. 큰 항력은 키홀 표면에 인접한 용융물을 위로 밀어올리고 속도가 1m/s 이상에 도달한 용융물의 이동을 가속화하여 잠재적으로 스패터를 유발할 수 있습니다.

증가된 열 입력은 고속 카메라로 포착한 실험적 관찰과 일치하는 큰 방울의 스패터 발생을 촉진했습니다.

Fig. 1. Schematic of zero-gap laser welding of zinc-coated steel.
Fig. 1. Schematic of zero-gap laser welding of zinc-coated steel.
Fig. 2. Experimental setup for capturing a side view of the laser welding of zinc-coated steel enabled by use of high-temperature glass.
Fig. 2. Experimental setup for capturing a side view of the laser welding of zinc-coated steel enabled by use of high-temperature glass.
Fig. 3. Experimental angled top-view setup for laser welding of zinc-coated steel with a laser illumination.
Fig. 3. Experimental angled top-view setup for laser welding of zinc-coated steel with a laser illumination.
Fig. 4. Schematic of the rotating Gaussian body heat source.
Fig. 4. Schematic of the rotating Gaussian body heat source.
Fig. 5. Schematic of jet pressure force caused by zinc vapor: (a) locating the outlet of zinc vapor (point A), (b) schematic of assigning the jet pressure force.
Fig. 5. Schematic of jet pressure force caused by zinc vapor: (a) locating the outlet of zinc vapor (point A), (b) schematic of assigning the jet pressure force.
Fig. 6. Schematic of drag force caused by zinc vapor.
Fig. 6. Schematic of drag force caused by zinc vapor.
Fig. 7. Procedure for calculating the outgassing velocity of zinc vapor.
Fig. 7. Procedure for calculating the outgassing velocity of zinc vapor.
Fig. 8. Schematic related to calculating the zone of vaporized zinc.
Fig. 8. Schematic related to calculating the zone of vaporized zinc.
Fig. 9. The meshed domains for the thermal-fluid simulation of laser welding.
Fig. 9. The meshed domains for the thermal-fluid simulation of laser welding.
Fig. 10. The calculated temperature field and validation: (a) 3-D temperature field; (b)-(f) Comparison of experimental and simulated weld cross section: (b) P = 2000 W, v = 50 mm/s; (c) P = 2500 W, v = 50 mm/s; (d) P = 3000 W, v = 50 mm/s; (e) P = 3000 W, v = 60 mm/s; (f) P = 3000 W, v = 70 mm/s.
Fig. 10. The calculated temperature field and validation: (a) 3-D temperature field; (b)-(f) Comparison of experimental and simulated weld cross section: (b) P = 2000 W, v = 50 mm/s; (c) P = 2500 W, v = 50 mm/s; (d) P = 3000 W, v = 50 mm/s; (e) P = 3000 W, v = 60 mm/s; (f) P = 3000 W, v = 70 mm/s.
Fig. 11. Comparison of X-Ray images of in-process keyhole profiles and the numerical predictions: (a) Single sheet penetration (P = 480 W, v = 150 mm/s); (b) Two sheet penetration (P = 532 W, v = 150 mm/s).
Fig. 11. Comparison of X-Ray images of in-process keyhole profiles and the numerical predictions: (a) Single sheet penetration (P = 480 W, v = 150 mm/s); (b) Two sheet penetration (P = 532 W, v = 150 mm/s).
Fig. 12. High-speed images of dynamic keyhole in laser welding of steels: (a) without zinc coating (b) with zinc coating.
Fig. 12. High-speed images of dynamic keyhole in laser welding of steels: (a) without zinc coating (b) with zinc coating.
Fig. 13. Mass loss and molten pool observation under different laser power and welding velocity for 1.2 mm + 1.2 mm HDG 420LA stack-up
Fig. 13. Mass loss and molten pool observation under different laser power and welding velocity for 1.2 mm + 1.2 mm HDG 420LA stack-up
Fig. 14. Numerical results of keyhole and flow field in molten pool: (a) without zinc vapor forces, (b) with zinc vapor forces.
Fig. 14. Numerical results of keyhole and flow field in molten pool: (a) without zinc vapor forces, (b) with zinc vapor forces.
Fig. 18. Calculated velocity fields for different welding parameters: (a) P = 2 kW, v = 50 mm/s, (b) P = 2.5 kW, v = 50 mm/s, (c) P = 3 kW, v = 50 mm/s, (d) P = 3 kW, v = 60 mm/s, (e) P = 3 kW, v = 70 mm/s.
Fig. 18. Calculated velocity fields for different welding parameters: (a) P = 2 kW, v = 50 mm/s, (b) P = 2.5 kW, v = 50 mm/s, (c) P = 3 kW, v = 50 mm/s, (d) P = 3 kW, v = 60 mm/s, (e) P = 3 kW, v = 70 mm/s.
Fig. 19. Schematic of the generation of spatter in different sizes: (a) small size, (b) large size.
Fig. 19. Schematic of the generation of spatter in different sizes: (a) small size, (b) large size.

References

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Detecting Porosity with the Core Gas Model

Detecting Porosity with the Core Gas Model

Producing High Quality Castings

 

Results options such as core gas flux, binder weight fraction and out-gassing rate can be analyzed using the core gas model

주조공장의 첫 번째 시험에서 주조 품질을 보장하기 위해 많은 선행 엔지니어링을 수행해야 합니다. 최근에는 금속 흐름, 응고, 미세 구조 진화 및 잔류 응력을 모델링하기 위한 수치 도구가 보편화되었습니다. 그러나 아직 완전히 다루어지지 않은 주조 결함 중 하나는 일반적인 코어 가스 불량 결함입니다. 이 문제의 물리학은 금속, 코어 및 바인더 사이의 복잡한 상호 작용을 포함합니다. 이를 해결하지 않으면 고철 수준이 높아질 수 있습니다. 대부분의 문제는 고온의 주입 온도를 사용하고 영향을 받는 영역에 벽체를 추가하여 문제를 관리하지만 완전히 해결할 수는 없습니다.

Designing the Optimum Break-Down

과거에는 재료 및 주조 엔지니어가 코어 가스 버블로 인해 다공성 결함 문제를 발견했을 경우 바인더 함량을 줄이거나 코어 환기량을 늘리거나 코어 환기 시간을 늘리거나 코어를 미리 굽거나 하는 등 일련의 표준 문제를 해결할 수 있었습니다. 가스가 따라가는 경로를 보는 것은 불가능했기 때문에 이것은 한 부분을 완성하는 데 수주가 걸리는 긴 인출 과정이었습니다. 그리고 다른 부분에 문제가 있을 때마다 반복해야 했습니다.

이 가공 일정을 단축해야 하는 시장 중심의 필요성 때문에 주조 시뮬레이션 소프트웨어가 개발되었습니다. 설계 및 제조에 모두 유용한 컴퓨터 기반 모델링을 통해 엔지니어는 실제 비용을 낭비 없이 다양한 접근 방식을 테스트 할 수 있습니다. 주조 공장이 환기 설계에 시뮬레이션을 적용 할 수 있도록 Flow Science는 주조 해석 기능에 핵심 가스 모델을 추가했습니다.

GM engine block water jacket, showing binder weight fraction

Applying CFD Methods to Core Gas Flow

수지 기반 바인더의 화학적 복잡성으로 인해 샌드 코어 열 차단 후 가스가 어디서 어떻게 흐르는 지 이해하는 것은 복잡합니다. 그러나 Flow Science는 여러 그룹과 협력하여 실험 데이터를 얻고 이를 수치 모델의 결과와 비교합니다. 이 회사는 General Motors, Graham-White Manufacturing 및 AlchemCast의 핵심 가스 유량 정보를 수집하여 알루미늄, 철 및 강철과 함께 사용되는 모래 수지 코어에 대한 실제 데이터를 얻었습니다.

GM Powertrain의 캐스팅 분석 엔지니어 인 David Goettsch 박사는 금속 주조물의 충진 및 응고 분석을 위해 15 년 동안 FLOW-3D를 사용했습니다. 새로운 코어 가스 모델은 설계 단계에서 자켓 코어 배출을 최적화하는 데 매우 유용합니다. 모든 요구 사항이 핵심 인화물에 있는 코어 박스에 vent tracks를 구현하기는 매우 어렵습니다.  “핵심 가스 배출에 대한 선행 분석 작업을 통해 시동 시 높은 스크랩률로 부터 벗어날 수 있습니다.”라고 그는 설명합니다. “아마도 프로세스 변경으로 문제가 해결 될 수 있습니다. 그러나 그 시점에 도달하려면 오랜 테스트 기간이 필요할 수 있습니다. “

현재 FLOW-3D에서 사용할 수 있는 코어 가스 모델을 통해 Goettsch는 다양한 삽입 및 배출 위치를 시도하고 글로벌 진단을 받을 수 있습니다. 가스가 얼마나 많이 발생하는지, 어디로 가는지, 금속 프런트가 따라 잡기 전에 얼마만큼 빠져 나오는지 확인하십시오.

Multi-Core Challenges

Core prints for casting with internal geometries

GM Powertrain jacket slab assembly

또 다른 노련한 주조공장 엔지니어인 Graham-White Manufacturing Co.의 Elizabeth Ryder는 가스 다공성은 항상 조사하기가 어려웠다고 주장했다. 그녀는 “특히 다중 코어의 경우, 어떤 코어가 문제의 원인인지 정확하게 찾아 내기가 어려웠으며 전체적인 시스템을 처리 하려고 했습니다. “

1700개의 부품으로 구성된 지속적인 생산으로, 그 중 일부는 연간 10,000개의 부품으로 구성되었으며, Graham-White는 시뮬레이션을 통해 제조 공정을 개선하는 데 매우 익숙했습니다.

Graham-White는 레이저 스캐닝으로 제작한 회주철 부품(약 3 x 4in)의 3D 모델로 작업하면서 평가를 위해 현재 vent 디자인을 제공했습니다. 이 탕구 디자인은 수평으로 분할된 금형에서 패턴 플레이트당 4개의 인상이 포함되었으며, 각 인상은 각 코어에 대한 vent가 있습니다. 중앙 sprue는 2 초 이내에 각각의 몰드를 충진할 수 있게 해주었습니다.

FLOW-3D를 이용한 시뮬레이션은 주입률을 확인시켜 주었지만, 또한 한 코어의 배출량이 충분하지 않다는 것을 보여주었다. Graham-White는 기존 분출구를 통해 가스를 더 많이 공급할 수 있도록 코어에 깊은 구멍을 뚫기 시작했습니다. 새로운 vent 디자인으로 전환한 이후, 회사는 코어 블로우 스크랩을 약 30% 감소 시켰습니다.

Ryder는 FLOW-3D 결과가 디자인 초점을 결정하는데 도움을 주었고, 어떤 코어 (멀티 코어 디자인)가 문제였는지, 코어의 어느 부분이 문제의 근원인지에 대해 파악할 수 있었습니다.

Learn more about the versatility and power of modeling metal casting processes with FLOW-3D Cast>

Sand Core Making / 모래 코어 제작

Sand Core Making / 모래 코어 제작

This article on sand core making was contributed by Dr. Matthias Todte and Frieder Semler, Flow Science Deutschland GmbH.

주조 품질에 대한 수요가 증가하고 고성능 구성 요소에 대한 박막형 구조로의 추세로 인해 품질에 대한 요구가 강화되었으며 동시에 모래 코어의 기하학적 복잡성도 증가했습니다. 시뮬레이션은 코어 박스의 설계를 최적화하는 데 도움이 되며, 저온 및 고온 코어 박스를 위한 유기 및 무기 바인더 시스템의 촬영, 가스 처리 및 경화를 위한 강력한 공정 조건을 확립합니다.

기체 주입, 건조 및 템퍼링의 기본 프로세스에 대한 논의는 실험적 검증을 거쳐야 합니다. 그런 다음 주물 결함을 방지하기 위해 코어 사격 공정 시뮬레이션이 필수적이었는지를 보여 줍니다. 마지막으로 코어 박스의 마모와 수명을 예측하는 수치모델을 개발한 연구 프로젝트를 소개합니다.

Water jacket core

Simulation of sand core making processes

Shooting

Shooting Simulation에서 모래로 채워진 타격 헤드가 공기를 통해 가압되고, 이로 인해 공기/모래/실린더/바인더 혼합물로 구성된 “유체”가 생성됩니다. 이 유체는 분사 노즐을 통해 코어 박스로 흐르고 배출 노즐을 통해 상자 밖으로 공기가 배출됩니다. Shooting Simulation의 목적은 코어 박스에 있는 모래의 밀도분포를 높히고 균일하게 하는 것입니다.

촬영 과정에서 모래로 채워진 블로 헤드가 공기를 통해 가압되어 공기/모래/바인더 혼합물로 구성된 “유체”가 생성됩니다. 이 유체는 블로우 헤드에서 분사 노즐을 통해 코어 박스로 흘러 나와 공기를 환기 노즐을 통해 박스 밖으로 밀어냅니다. Shooting 의 목표는 가능한 한 높고 균일하게 코어 박스에 있는 모래의 밀도 분포를 달성하는 것입니다. 변경할 수 있는 프로세스 매개 변수는 분사 압력과 발사 및 배기 노즐의 수와 위치입니다. 시간과 비용을 절약하기 위해 코어의 품질을 저하시키지 않고 가능한 한 노즐을 적게 사용하는 것이 바람직합니다.

Sand density distribution

Sand density distribution after the shooting

시뮬레이션을 사용하여 다양한 사격 및 환기 노즐 구성과 그 구성이 결과 모래 밀도 분포에 미치는 영향을 분석할 수 있습니다. 엔지니어는 속도와 전단 응력을 예측하여 코어 상자의 마모 및 이에 따른 수명에 대한 결론을 도출할 수 있습니다.

Gassing

유기 바인더 시스템에서는 모래가 유기 수지로 코팅됩니다. 이 수지의 경화는 보통 아민이라는 기체에 의해 이루어지는데, 이것은 일반적으로 분사에 사용된 노즐을 통해 주입됩니다. 이 가스는 코어가 모든 부분에서 경화되도록 하기위해 모든부분에 도달할 만큼 길어야 한다. 반면에, 유독 가스를 줄이기 위해서는 가스 배출이 필요이상으로 길어서는 안됩니다.

유기 바인더 시스템에서는 모래가 유기 레진으로 코팅되어 있습니다. 이 레진의 경화는 보통 아민 가스 작용제에 의해 이루어지는데, 아민은 주로 인젝션에 사용되는 노즐을 통해 분사됩니다. 이 가스 주입은 가스가 코어의 모든 부분에 도달할 수 있도록 충분히 길어야 합니다. 코어가 모든 곳에서 경화되도록 하기 위해서입니다. 반면, 가스 배출은 독성 가스를 절약하기 위해 필요 이상으로 길지 않아야 합니다.

Amine concentration core

Amine concentration in a core

시뮬레이션은 시간 경과에 따른 코어의 아민 농도 분포를 예측하며, 이는 코어의 경도와 동일하다. 이를 통해 엔지니어들은 가스 생성 공정에 대한 합리적인 시간 규모를 결정할 수 있습니다.

Drying

주조물의 수가 증가하는 경우, 독성이 있는 유기적 시스템 대신 무기, 수성-기반 바인더 시스템이 사용됩니다. 배기 가스 배출이 없는 코어 생산 공정의 이점 외에도 이 시스템은 주조 공정 중 코어 가스 생산량을 줄여 주조 품질을 향상시킵니다.

모래 코어의 경화를 위해서는 일반적으로 뜨거운 공기가 주입되어 이루어지는 코어에서 물을 제거해야 합니다. 이러한 바인더 시스템의 경우, 코어의 잔류 수분은 경도에 대한 측정 값입니다. 시뮬레이션은 코어를 통과하는 공기의 흐름뿐만 아니라 물이나 증기의 증발과 응축, 뜨거운 공기와 함께 증기의 이동을 모델링 해야 합니다.

아래 이미지는 예측된 잔류 수분과 실제 코어의 강도(또는 손상)의 상관 관계를 보여 줍니다.

Correlation of predicted residual moisture and the damage of a real core

Tempering of core boxes                                                                    

핫 박스 및 크로닝과 같은 특정 코어 제조 공정에서는 가열된 코어 박스에 있는 바인더의 열 반응을 통해 코어의 경화가 이루어집니다. 상자의 가열은 가열 채널과 전기 가열 요소를 사용하여 수행됩니다. 좋은 코어 품질을 위해서는 코어 상자의 균일한 온도 분포가 바람직합니다. 시뮬레이션은 특정 가열 소자 구성에 대한 온도 분포를 시간 경과에 따른 예측하고 발열의 균일성과 원하는 온도에 도달하는 데 필요한 시간을 표시합니다.

Heated core box

Temperature distribution in a heated core box

Validation of the core blowing model

Experiments and simulations for a water jacket core

핵심 shooting 실험은 TU 뮌헨의 파운드리 연구소에서 실시되었습니다. shooting  시간과 압력, 흡입구와 환기구의 수 등의 공정 매개 변수들이 다양하였으며 이들 매개 변수들이 분석된 코어 품질에 미치는 영향이 다양하였다. 실제 코어에서 발생한 결점은 시뮬레이션에서 모래 밀도가 낮은 영역과 상관 관계가 있습니다(아래 그림 참조).

Core blowing validation

Core defects compared to simulated density distribution

Application of the core blowing model : 리어 액슬 하우징의 주조 품질 개선

품질 보증에서 리어 액슬 하우징의 주물 결함을 감지했습니다(아래 그림 참조). 그 결함들은 중심부의 표면 결함의 결과인 것처럼 보였다. 이 가설을 뒷받침하고 코어 표면 품질을 개선하기 위한 조치를 권고하기 위해 시뮬레이션이 수행되었다. 마지막으로, 코어 박스 환기구의 다른 구성(숫자 및 위치)을 통해 주조 품질을 개선할 수 있었습니다.

Casting defects of a rear axle housing

Casting defects of a rear axle housing

Validation surface defects

Correlation of surface defects and simulated density distribution

Research project: Prediction of the lifetime of core boxes

코어 박스는 대부분 폴리우레탄 수지 코팅의 알루미늄으로 제작된다. 사격 과정에서 모래에 의한 코어 박스 표면의 침식은 코어 박스의 수명을 제한하는 요인이다. 프로젝트 목표는 표면 처리가 수명에 미치는 영향을 이해하고 단일 시뮬레이션에서 다수의 샷에 의해 발생하는 침식을 예측할 수 있는 연산 모델을 개발하는 침식 프로세스를 분석하는 것이었다.

일반적인 코어 상자(아래 참조)는 다른 모양의 삽입물로 제작되었습니다.

Core box with different inserts

Core box with different inserts

수치 모델은 코어 박스 벽의 압력과 전단력의 공간적, 시간적 통합에 기초하여 부식에 대한 양을 도출한다. 모형에 의해 예측된 침식은 실험 값과 일치했습니다(아래 그림 참조).

Measured and simulated erosion

Comparison of measured and simulated erosion

General Applications Bibliography

다음은 일반 응용 분야의 기술 문서 모음입니다.
이 모든 논문은 FLOW-3D  결과를 포함하고 있습니다. 복잡한 다중 물리와 관련된 문제를 성공적으로 시뮬레이션하기 위해 FLOW-3D를 사용 하는 방법에 대해 자세히 알아보십시오.

Below is a collection of technical papers in our General Applications Bibliography. All of these papers feature FLOW-3D results. Learn more about how FLOW-3D can be used to successfully simulate problems that involve complex multiphysics.

2024년 2월 19일 Upate

204-23   Togo Shinonaga, Hibiki Tajima, Yasuhiro Okamoto, Akira Okada, Application of large-area electron beam irradiation to micro-edge filleting, Journal of Manufacturing Processes, 107; pp. 65-73, 2023. doi.org/10.1016/j.jmapro.2023.10.039

167-23   Xiaoyong Cheng, Zhixian Cao, Ji Li, Alistair Borthwick, A numerical study of the settling of non-spherical particles in quiescent water, Physics of Fluids, 35.9; 2023. doi.org/10.1063/5.0165555

109-23 Dileep Karnam, Yu-Lung Lo, Chia-Hua Yang, Simulation study and parameter optimization of laser TSV using artificial neural networks, Journal of Materials Research and Technology, 25; pp. 3712-3727, 2023. doi.org/10.1016/j.jmrt.2023.06.199

66-23   Erik Holmen Olofsson, Michael Roland, Jon Spangenberg, Ninna Halberg Jokil, Jesper Henri Hattel, A CFD model with free surface tracking: predicting fill level and residence time in a starve-fed single-screw extruder, The International Journal of Advanced Manufacturing Technology, 126; pp. 3579-3591, 2023. doi.org/10.1007/s00170-023-11329-w

20-23   Giampiero Sciortino, Valentina Lombardi, Pietro Prestininzi, Modelling of cantilever-based flow energy harvesters featuring C-shaped vibration inducers: The role of the fluid/beam interaction, Applied Sciences, 13.1; 416, 2023. doi.org/10.3390/app13010416

134-22   Guozheng Ma, Shuying Chen, Haidou Wang, Impact spread behavior of flying droplets and properties of splats, Micro Process and Quality Control of Plasma Spraying, pp. 87-202, 2022. doi.org/10.1007/978-981-19-2742-3_3

111-22   Chia-Lin Chiu, Chia-Ming Fan, Chia-Ren Chu, Numerical analysis of two spheres falling side by side, Physics of Fluids, 34; 072112, 2022. doi.org/10.1063/5.0096534

58-21   Ruizhe Liu, Haidong Zhao, Experimental study and numerical simulation of infiltration of AlSi12 alloys into Si porous preforms with micro-computed tomography inspection characteristics, Journal of the Ceramic Society of Japan, 129.6; pp. 315-322, 2021. doi.org/10.2109/jcersj2.21018

56-20   Nils Steinau, CFD modeling of ascending Strombolian gas slugs through a constricted volcanic conduit considering a non-linear rheology, Thesis, Universität Hamburg, Hamburg, Germany, 2020.

30-20   Bita Bayatsarmadi, Mike Horne, Theo Rodopoulos and Dayalan Gunasegaram, Intensifying diffusion-limited reactions by using static mixer electrodes in a novel electrochemical flow cell, Journal of The Electrochemical Society, 167.6, 2020. doi.org/10.1149/1945-7111/ab7e8f

75-19   Raphaël Comminal, Marcin Piotr Serdeczny, Navid Ranjbar, Mehdi Mehrali, David Bue Pedersen, Henrik Stang, Jon Spangenberg, Modelling of material deposition in big area additive manufacturing and 3D concrete printing, Proceedings, Advancing Precision in Additive Manufacturing, Nantes, France, September 16-18, 2019.

35-19     Sung-Won Ha, Tae-Won Kim, Joo-Hwan Choi, and Young-Jin Park, Study for flow phenomenon in the circulation water pump chamber using the Flow-3D model, Journal of the Korea Academia-Industrial Cooperation Society, Vol. 20, No. 4, pp. 580-589, 2019. doi: 10.5762/KAIS.2019.20.4.580

27-19     Rolands Cepuritis, Elisabeth L. Skare, Evgeny Ramenskiy, Ernst Mørtsell, Sverre Smeplass, Shizhao Li, Stefan Jacobsen, and Jon Spangeberg, Analysing limitations of the FlowCyl as a one-point viscometer test for cement paste, Construction and Building Materials, Vol. 218, pp. 333-340, 2019. doi: 10.1016.j.conbuildmat.2019.05.127

26-19     Shanshan Hu, Lunliang Duan, Qianbing Wan, and Jian Wang, Evaluation of needle movement effect on root canal irrigation using a computational fluid dynamics model, BioMedical Engineering OnLine, Vol. 18, No. 52, 2019. doi: 10.1186/s12938-019-0679-5

83-18   Elisabeth Leite Skare, Stefan Jacobsen, Rolands Cepuritis, Sverre Smeplass and Jon Spangenberg, Decreasing the magnitude of shear rates in the FlowCyl, Proceedings of the 12th fib International PhD Symposium in Civil Engineering, Prague, Czech Republic, August 29-31, 2018.

71-18   Marc Bascompta, Jordi Vives, Lluís Sanmiqeul and José Juan de Felipe, CFD friction factors verification in an underground mine, Proceedings of the 4th World Congress on Mechanical, Chemical, and Material Engineering, August 16 – 18, 2018, Madrid, Spain, Paper No. MMME 105, 2018. doi.org/10.11159/mmme18.105

56-18   J. Spangenberg, A. Uzala, M.W. Nielsen and J.H. Hattel, A robustness analysis of the bonding process of joints in wind turbine blades, International Journal of Adhesion and Adhesives, vol. 85, pp. 281-285, 2018. doi.org/10.1016/j.ijadhadh.2018.06.009

21-18   Zhang Weikang and Gong Hongwei, Numerical Simulation Study on Characteristics of Airtight Water Film with Flow Deflectors, IOP Conference Series: Earth and Environmental Science vol. 153, no. 3, pp. 032025, 2018. doi.org/10.1088/1755-1315/153/3/032025

59-17  Han Eol Park and In Cheol Bang, Design study on mixing performance of rotational vanes in subchannel with fuel rod bundles, Transactions of the Korean Nuclear Society Autumn Meeting, Gyeongju, Korea, October 26-27, 2017.

58-17  Jian Zhou, Claudia Cenedese, Tim Williams and Megan Ball, On the propagation of gravity currents over and through a submerged array of circular cylinders, Journal of Fluid Mechanics, Vol. 831, pp. 394-417, 2017. doi.org/10.1017/jfm.2017.604

24-17   Zhiyuan Ge, Wojciech Nemec, Rob L. Gawthorpe, Atle Rotevatn and Ernst W.M. Hansen, Response of unconfined turbidity current to relay-ramp topography: insights from process-based numerical modelling, doi: 10.1111/bre.12255 This article is protected by copyright. All rights reserved.

06-17   Masoud Hosseinpoor, Kamal H. Khayat, Ammar Yahia, Numerical simulation of self-consolidating concrete flow as a heterogeneous material in L-Box set-up: coupled effect of reinforcing bars and aggregate content on flow characteristics, A. Mater Struct (2017) 50: 163. doi:10.1617/s11527-017-1032-8

94-16   Mehran Seyed Ahmadi, Markus Bussmann and Stavros A. Argyropoulos, Mass transfer correlations for dissolution of cylindrical additions in liquid metals with gas agitation, International Journal of Heat and Mass Transfer, Volume 97, June 2016, Pages 767-778

83-16   Masoud Hosseinpoor, Numerical simulation of fresh SCC flow in wall and beam elements using flow dynamics models, Ph.D. Thesis: University of Sherbrooke, September 2016.

51-16   Aditi Verma, Application of computational transport analysis – Oil spill dynamics, Master Thesis: State University of New York at Buffalo, 2016, 56 pages; 1012775

37-16   Hannah Dietterich, Einat Lev, and Jiangzhi Chen, Benchmarking computational fluid dynamics models for lava flow simulation, Geophysical Research Abstracts, Vol. 18, EGU2016-2202, 2016, EGU General Assembly 2016, © Author(s) 2016. CC Attribution 3.0 License.

 19-16   A.J. Vellinga, M.J.B. Cartigny, E.W.M. Hansen, P.J. Tallinga, M.A. Clare, E.J. Sumner and J.T. Eggenhuisen, Process-based Modelling of Turbidity Currents – From Computational Fluid-dynamics to Depositional Signature, Second Conference on Forward Modelling of Sedimentary Systems, 25 April 2016, DOI: 10.3997/2214-4609.201600374

106-15    Hidetaka Oguma, Koji Tsukimoto, Saneyuki Goya, Yoshifumi Okajima, Kouichi Ishizaka, and Eisaku Ito, Development of Advanced Materials and Manufacturing Technologies for High-efficiency Gas Turbines, Mitsubishi Heavy Industries Technical Review Vol. 52 No. 4, December 2015

93-15   James M. Brethour, Modelling of Cavitation within Highly Transient Flows with the Volume of Fluid Method, 1st Pan-American Congress on Computational Mechanics, April 27-29, 2015

90-15   Troy Shinbrot, Matthew Rutala, Andrea Montessori, Pietro Prestininzi and Sauro Succi, Paradoxical ratcheting in cornstarch, Phys. Fluids 27, 103101 (2015); http://dx.doi.org/10.1063/1.4934709

84-15   Nicolas Roussel, Annika Gram, Massimiliano Cremonesi, Liberato Ferrara, Knut Krenzer, Viktor Mechtcherine, Sergiy Shyshko, Jan Skocec, Jon Spangenberg, Oldrich Svec, Lars Nyholm Thrane and Ksenija Vasilic, Numerical simulations of concrete flow: A benchmark comparison, Cem. Concr. Res. (2015), http://dx.doi.org/10.1016/j.cemconres.2015.09.022

02-15   David Souders, FLOW-3D Version 11 Enhances CFD Simulation, Desktop Engineering, January 2015

125-14   Herbert Obame Mve, Romuald Rullière, Rémi Goulet and Phillippe Haberschill, Numerical Analysis of Heat Transfer of a Flow Confined by Wire Screen in Lithium Bromide Absorption Process, Defect and Diffusion Forum, ISSN: 1662-9507, Vol. 348, pp 40-50, doi:10.4028/www.scientific.net/DDF.348.40, © 2014 Trans Tech Publications, Switzerland

55-14   Agni Arumugam Selvi, Effect of Linear Direction Oscillation on Grain Refinement, Master’s Thesis: The Ohio State University, Graduate Program in Mechanical Engineering, Copyright by Agni Arumugam Selvi, 2014

99-13   R. C. Givler and M. J. Martinez, Computational Model of Miniature Pulsating Heat Pipes, SANDIA REPORT, SAND2012-4750, Unlimited Release, Printed January 2013.

82-13    Shizhao Li, Jon Spangenberg, Jesper Hattel, A CFD Approach for Prediction of Unintended Porosities in Aluminum Syntactic Foam A Preliminary Study, 8th International Conference on Porous Metals and Metallic Foams (METFOAM 2013), Raleigh, NC, June 2013

81-13   S. Li, J. Spangenberg, J. H. Hattel, A CFD Model for Prediction of Unintended Porosities in Metal Matrix Composites A Preliminary Study, 19th International Conference on Composite Materials (ICCM 2013), Montreal, Canada, July 2013

78-13   Haitham A. Hussein, Rozi Abdullah, Sobri, Harun and Mohammed Abdulkhaleq, Numerical Model of Baffle Location Effect on Flow Pattern in Oil and Water Gravity Separator Tanks, World Applied Sciences Journal 26 (10): 1351-1356, 2013, ISSN 1818-4952, DOI: 10.5829/idosi.wasj.2013.26.10.1239, © IDOSI Publications, 2013

74-13  Laetitia Martinie, Jean-Francois Lataste, and Nicolas Roussel, Fiber orientation during casting of UHPFRC: electrical resistivity measurements, image analysis and numerical simulations, Materials and Structures, DOI 10.1617/s11527-013-0205-3, November 2013. Available for purchase online at SpringerLink.

67-13 Stefan Jacobsen, Rolands Cepuritis, Ya Peng, Mette R. Geiker, and Jon Spangenberg, Visualizing and simulating flow conditions in concrete form filling using Pigments, Construction and Building Materials 49 (2013) 328–342, © 2013 Elsevier Ltd. All rights reserved. Available for purchase at ScienceDirect.

60-13 Huey-Jiuan Lin, Fu-Yuan Hsu, Chun-Yu Chiu, Chien-Kuo Liu, Ruey-Yi Lee, Simulation of Glass Molding Process for Planar Type SOFC Sealing Devices, Key Engineering Materials, 573, 131, September 2013. Available for purchase at Scientific.net.

32-13 M A Rashid, I Abustan and M O Hamzah, Numerical simulation of a 3-D flow within a storage area hexagonal modular pavement systems, 4th International Conference on Energy and Environment 2013 (ICEE 2013), IOP Conf. Series: Earth and Environmental Science 16 (2013) 012056 doi:10.1088/1755-1315/16/1/012056. Full paper available at IOP.

105-12 Jon Spangenberg, Numerisk modellering af formfyldning ved støbning i selvkompakterende beton, Ph.D. Thesis: Technical University of Denmark, ID: 0eeede98-fb07-4800-86e2-0a6baeb1e7a3, 2012.

100-12 Nurul Hasan, Validation of CFD models using FLOW-3D for a Submerged Liquid Jet, Ninth International Conference on CFD in the Minerals and Process Industries, CSIRO, Melbourne, Australia, 10-12 December 2012.

87-12  Abustan, Ismail, Hamzah, Meor Othman and Rashid, Mohd Aminur, A 3-Dimensional Numerical Study of a Flow within a Permeable Pavement, OIDA International Journal of Sustainable Development, Vol. 04, No. 02, pp. 37-44, April 2012.

86-12 Abustan, Ismail, Hamzah, Meor Othman and Rashid, Mohd Aminur, Review of Permeable Pavement Systems in Malaysia Conditions, OIDA International Journal of Sustainable Development, Vol. 04, No. 02, pp. 27-36, April 2012.

85-12  Mohd Aminur Rashid, Ismail Abustan, Meor Othman Hamzah, Infiltration Characteristic Modeling Using FLOW-3D within a Modular Pavement, Procedia Engineering, Volume 50, 2012, Pages 658-667, ISSN 1877-7058, 10.1016/j.proeng.2012.10.072.

73-12  Mohd Aminur Rashid, Ismail Abustan, Meor Othman Hamzah, Infiltration Characteristic Modeling Using FLOW-3D within a Modular Pavement, Procedia Engineering, Volume 50, 2012, Pages 658-667, ISSN 1877-7058, 10.1016/j.proeng.2012.10.072.

65-12  X.H. Yang, T.J. Lu, T. Kim, Influence of non-conducting pore inclusions on phase change behavior of porous media with constant heat flux boundaryInternational Journal of Thermal Sciences, Available online 10 October 2012. Available online at SciVerse.

56-12  Giancarlo Alfonsi, Agostino Lauria, Leonardo Primavera, Flow structures around large-diameter circular cylinder, Journal of Flow Visualization and Image Processing, DOI: 10.1615/JFlowVisImageProc.2012005088, 2012. Available for purchase online at Begell Digital Library.

49-12  M. Janocko, M.B.J. Cartigny, W. Nemec, E.W.M. Hansen, Turbidity current hydraulics and sediment deposition in erodible sinuous channels: laboratory experiments and numerical simulations, Marine and Petroleum Geology, Available online 17 September 2012. Available for purchase online at SciVerse.

32-12  Fatih Karadagli, Bruce E. Rittmann, Drew C. McAvoy, and John E. Richardson, Effect of Turbulence on the Disintegration Rate of Flushable Consumer Products, Water Environment Research, Volume 84, Number 5, May 2012

31-12    D. Valero Huerta and R. García-Bartual, Optimization of Air Conditioning Diffusers Location in Large Agricultural Warehouses Using CFD Techniques, International Conference of Agricultural Engineering (CIGR-AgEng2012) Valencia, Spain, July 8-12, 2012

16-12 Yi Fan Fu, Wei Dong, Ying Li, Yi Tan, Ming Hui Yi, Akira Kawasaki, Simulation of the Effects of the Physical Properties on Particle Formation of Pulsated Orifice Ejection Method (POEM), 2012, Advanced Materials Research, 509, 161. Available for purchase online at Scientific.Net.

92-11  Giancarlo Alfonsi, Agostino Lauria, Leonardo Primavera, The lower vertical structure past the Ahmed car model, International Conference on Computational Science, ICCS 2011. Available for purchase online at Begell Digital Library.

80-11  Ismail Abustan, Meor Othman Hamzah, Mohd Aminur Rashid, A 3-Dimensional Numerical Study of a Flow within a Permeable Pavement, OIDA International Conference on Sustainable Development, ISSN 1923-6670, Putrajaya, Malaysia, 5-7th December 2011

66-11   H. Kondo, T. Furukawa, Y. Hirakawa, K. Nakamura, M. Ida, K.Watanabe, T. Kanemura, E. Wakai, H. Horiike, N. Yamaoka, H. Sugiura, T. Terai, A. Suzuki, J. Yagi, S. Fukada, H. Nakamura, I. Matsushita, F. Groeschel, K. Fujishiro, P. Garin and H. Kimura, IFMIF-EVEDA lithium test loop design and fabrication technology of target assembly as a key componentNuclear Fusion Volume 51 Number 12, doi:10.1088/0029-5515/51/12/123008

49-11     N.I. Vatin, A.A. Girgidov, K.I. Strelets, Numerical modelling the three-dimensional velocity field in the cyclone, Inzhenerno-Stroitel’nyi Zhurnal, No. 4, 2011. In Russian.

41-11    Maiko Hosoda, Taichi Hirano, and Keiji Sakai, Low-Viscosity Measurement by Capillary Electromagnetically Spinning Technique, © 2011 The Japan Society of Applied Physics, Japanese Journal of Applied Physics, July 20, 2011.

18-11  Ortloff, C.R., Vogel, M., Spray cooling heat transfer — Test and CFD analysis, Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM), 2011 27th Annual IEEE, 20-24 March 2011, pp 245 – 252, San Jose, CA, 10.1109/STHERM.2011.5767208.

82-10   Dr. John Abbott, Two problems on the flow of viscous sheets of molten glass, 26th Annual Workshop on Mathematical Problems in Industry, Rensselear Polytechnic Institute, June 14-18, 2010

57-10  Chouet, B. A., Dawson, P. B., James, M. R. and Lane, S. J., Seismic source mechanism of degassing bursts at Kilauea Volcano, Hawaii: Results from waveform inversion in the 10–50 s band, J. Geophys. Res., 115, B09311, doi:10.1029/2009JB006661, September 2010. Available online at JOURNAL OF GEOPHYSICAL RESEARCH.

55-10 Pamela Waterman, FEA and CFD: Getting Better All the Time, Desktop Engineering, December 2010.

53-10  Nicolas Fries, Capillary transport processes in porous materials – experiment and model, Cuvillier Verlag Göttingen; 2010; ISBN 978-3-86955-507-2. Available at www.cuvillier.de  and www.amazon.de.

45-10  Meiring Beyers, Thomas Harms, and Johan Stander, Mitigating snowdrift at the elevated SANAE IV research station in Antarctica CFD simulation and field application, The Fifth International Symposium on Computational Wind Engineering (CWE2010), Chapel Hill, North Carolina, USA, May 23-27, 2010.

31-10 J. Spangenberg, N. Roussel, J.H. Hattel, J. Thorborg, M.R. Geiker, H. Stang and J. Skocek, Prediction of the Impact of Flow-Induced Inhomogeneities in Self-Compacting Concrete (SCC), Ch. 25 of “Design, Production and Placement of Self-Consolidating Concrete,” RILEM Bookseries, 2010, Volume 1, Part 5, 209-215, DOI: 10.1007/978-90-481-9664-7_18. Available online at Springer Link.

28-10 Sirisha Burra, Daniel P. Nicolella, W. Loren Francis, Christopher J. Freitas, Nicholas J. Mueschke, Kristin Poole, and Jean X. Jiang, Dendritic processes of osteocytes are mechanotransducers that induce the opening of hemichannels, Proc Natl Acad Sci U S A. 2010 Jul 19. [Epub ahead of print], Available for purchase at PNAS.

19-10 Michael T. Tolley, Michael Kalontarov, Jonas Neubert, David Erickson and Hod Lipson, Stochastic Modular Robotic Systems A Study of Fluidic Assembly Strategies, IEEE Transactions on Robotics, Vol. 26, NO. 3, June 2010

59-17   Han Eol Park and In Cheol Bang, Design study on mixing performance of rotational vanes in subchannel with fuel rod bundles, Transactions of the Korean Nuclear Society Autumn Meeting, Gyeongju, Korea, October 26-27, 2017.

44-09 Micah Fuller, Fabian Bombardelli, Deb Niemeier, Particulate Matter Modeling in Near-Road Vegetation Environments, Contract AQ-04-01: Developing Effective and Quantifiable Air Quality Mitigation Measures, UC Davis, Caltrans, September 2009

28-09 D. C. Lo, Dong-Taur Su and Jan-Ming Chen (2009), Application of Computational Fluid Dynamics Simulations to the Analysis of Bank Effects in Restricted Waters, Journal of Navigation, 62, pp 477-491, doi:10.1017/S037346330900527X; Purchase the article online (clicking on this link will take you to the Cambridge Journals website).

24-09 Richard C. Givler and Mario J. Martinez, Modeling of Pulsating Heat Pipes, Sandia Report, SAND2009-4520, Sandia National Laboratories, August 2009.

45-08  J. Saeki, Seikei Kakou, Three-Dimensional Flow Analysis of a Thermosetting Compound in a Motor Stator, 20, 750-754 (2008) [in Japanese] (Zipped file contains paper and appendices)

38-08 Yoshifumi Kuriyama, Ken’ichi Yano and Masafumi Hamaguchi, Trajectory Planning for Meal Assist Robot Considering Spilling Avoidance, 17th IEEE International Conference on Control Applications, Part of 2008 1EEE Multi-conference on Systems and Control, San Antonio, Texas, September 3-5, 2008

29-08 Ernst W.M. Hansen, Wojciech Nemec and Snorre Heimsund, Numerical CFD simulations — a new tool for the modelling of turbidity currents and sand dispersal in deep-water basins, Production Geoscience 2008 in Stavanger, Norway, © 2008

17-08 James, M. R., Lane, S. J. & Corder, S. B., Modelling the rapid near-surface expansion of gas slugs in low-viscosity magmas, In Lane S. J., Gilbert J. S. (eds) Fluid Motion in Volcanic Conduits: A Source of Seismic and Acoustic Signals. Geol. Soc., London, Spec. Pub., 307, 147-167, doi: 10.1144/SP307.9. 2008

16-08 Stefano Malavasi, Nicola Trabucchi, Numerical Investigation of the Flow Around a Rectangular Cylinder Near a Solid Wall, BBAA VI International Colloquium on: Bluff Bodies Aerodynamics & Applications, Milano, Italy, July 2008

41-07 Nicolas Roussel, Mette R. Geiker, Frederic Dufour, Lars N. Thrane and Peter Szabo, Computational modeling of concrete flow General Overview, Cement and Concrete Research 37 (2007) 1298-1307, © 2007 Elsevier Ltd.

40-07 Nemec, W., Heimsund, S., Xu, J. & Hansen, E.W.M., Numerical CFD simulation of turbidity currents, British Sedimentological Research Group (BSRG) Annual Meeting, Birmingham, 17-18 December 2007

39-07 Heimsund, S, Xu, J. & Nemec, W., Numerical Simulation of Recent Turbidity Currents in the Monterey Canyon System, Offshore California, American Geophysical Union Fall Meeting, 10-14 December 2007

32-07 James, M. R., Lane, S. J. & Corder, S. B., Modeling the near-surface expansion of gas slugs in basaltic magmaEos Trans. A.G.U., 88(52), Fall Meet. Suppl.. Abs. V12B-03. 2007

31-07 James, M. R., Lane, S. J. and Corder, S. B., Degassing low-viscosity magma: Quantifying the transition between passive bubble-burst and explosive activityE.G.U. Geophys. Res. Abstr., 905336, SRef-ID: 1607-7962/gra/EGU2007-A-05336. 2007

35-06  S. Green and C. Manepally, Software Validation Report for FLOW-3D Version 9.0, Center for Nuclear Waste Regulatory Analyses, August 2006

33-06 N. Roussel, Correlation between yield stress and slump: Comparison between numerical simulations and concrete rheometers results, © RILEM 2006, Materials and Structures (2006) 39:501-509, Purchase online at Springer Link.

32-06 Heimsund, S., Möller, N. and Guargena, C., FLOW-3D simulation of the Ormen Lange field, mid-Norway, In: Hoyanagi, K., Takano, O. and Kano, K. (Ed.), Abstracts, International Association of Sedimentologists 17th International Sedimentological Congress, Fukuoka, Vol. B, p. 107, 2006

10-06 Gengsheng Wei, An Implicit Method to Solve Problems of Rigid Body Motion Coupled with Fluid Flow, Flow Science Technical Note #76, FSI-05-TN76.

8-06 Gengsheng Wei, Three-Dimensional Collision Modeling for Rigid Bodies and its Coupling with Fluid Flow Computation, Flow Science Technical Note #75, FSI-06-TN75.

34-05  Young Bae Kim, Kyung Do Kim, Sang Eui Hong, Jong Goo Kim, Man Ho Park, and Ju Hyun Kim, and Jae Keun Kweon, 3D Simulation of PU Foaming Flow in a Refrigerator Cabinet, Appliance Magazine.com, January 2005.

33-05 N. Roussel, Fifty-cent rheo-meter for yield stress measurements From slump to spreading flow, @2005 by The Society of Rheolgoy, Inc., J. Rheol. 49(3), 705-718 May/June (2005)

32-05 Heimsund, S., Möller, N., Guargena, C. and Thompson, L., Field-scale modeling of turbidity currents by FLOW-3D simulations, In: Workshop Abstracts, Modeling of Turbidity Currents and Related Gravity Currents, University of California, Santa Barbara, 2 p., (2005)

15-05 Gengsheng Wei, A Fixed-Mesh Method for General Moving Objects, Flow Science Technical Note #73, FSI-05-TN73

14-05 James M. Brethour, Incremental Thermoelastic Stress Model, Flow Science Technical Note #72, FSI-05-TN72

9-05 Gengsheng Wei, A Fixed-Mesh Method for General Moving Objects in Fluid Flow, Modern Physics Letters B, Vol. 19, Nos. 28-29 (2005) 1719-1722

1-05 C.W. Hirt, Electro-Hydrodynamics of Semi-Conductive Fluids: With Application to Electro-Spraying Flow Science Technical Note #70, FSI-05-TN70

35-04  J. Saeki, T. Kono and T. Teramae, Seikei Kakou, Formulation of Mathematical Models for Estimating Residual Stress and Strain Components Correlated with 3-D Flow of Thermosetting Compounds, 16, 5, 309-316 (2004) [in Japanese]. (Zipped file contains paper and appendices)

31-04 Heimsund, S., Möller, N., Guargena, C. and Thompson, L., The control of seafloor topography on turbidite sand dispersal in the Ormen Lange field: a large-scale application of FLOW-3D simulations, In: Martinsen, O.J. (Ed.), Abstracts and Proceedings of the Geological Society of Norway (NGF), Deep Water Sedimentary Systems of Arctic and North Atlantic Margins, Stavanger, 3, p. 25, (2004)

26-04 Beyers, J.H.M., Harms, T.M. and Sundsbø, P.A., 2004, Numerical simulation of three dimensional, transient snow drifting around a cube, Journal of wind engineering and industrial aerodynamics, vol. 92, pp. 725-747, ISSN 0167-6105

25-04 Beyers, J.H.M, Harms, T.M. and Sundsbø, P.A., 2004, Numerical simulation of snow drifting around an elevated obstacle, Proceedings of the 5th conference on snow engineering, Davos, Switzerland, pp.185-191

17-04 Michael Barkhudarov, Multi-Block Gridding Technique for FLOW-3D (Revised), Flow Science Technical Note #59-R2, FSI-00-TN59-R2

36-03 Heimsund, S., Hansen, E.W.M. and Nemec, W., Numerical CFD simulation of turbidity currents and comparison with laboratory data, In: Hodgetts, D., Hodgson, D. and Smith, R. (Ed.), Slope Modelling Workshop Abstracts, Experimental, Reservoir and Forward Modelling of Turbidity Currents and Deep-Water Sedimentary Systems, Liverpool Univ., p. 13., (2003b)

35-03 Heimsund, S., Hansen, E.W.M. and Nemec, W. Computational 3-D fluid-dynamics model for sediment transport, erosion and deposition by turbidity currents, In: Nakrem, H.A. (Ed.), Abstracts and Proceedings of the Geological Society of Norway (NGF), Den 18. Vinterkonferansen, Oslo, 1, p. 39., (2003a)

33-03 Beyers, J.H.M., Sundsbø, P.A. and Harms, T.M., 2003, Numerical simulation and verification of drifting snow around a cube, Proceedings of the 11th international conference on wind engineering, Texas Tech University, Lubbock, Texas, USA, pp. 1886-1893

27-03 Jun Zeng, Daniel Sobek and Tom Korsmeyer, Electro-Hydrodynamic Modeling of Electrospray Ionization CAD for a µFluidic Device-Mass Spectrometer Interface, Agilent Technologies Inc, paper presented at Transducers 2003, June 03 Boston (note: Reference #10 is to FLOW-3D)

25-03 J. M Brethour, Moving Boundaries an Eularian Approach, Moving Boundaries VII, Computational Modelling of Free and Moving Boundary Problems, A. A. Mammoli & C.A. Brebbia, WIT Press

19-03 James Brethour, Incremental Elastic Stress Model, Flow Science Technical Note (FSI-03-TN64)

18-03 Michael Barkhudarov, Semi-Lagrangian VOF Advection Method for FLOW-3D, Flow Science Technical Note (FSI-03-TN63)

11-02 Junichi Saeki and Tsutomu Kono, Three-Dimensional Flow Analysis of a Thermosetting Compound during Mold Filling, Polymer Processing Society 18th Annual Meeting, June 2002, Guimares, Portugal.

46-01 Yasunori Iwai, Takumi Hayashi, Toshihiko Yamanishi, Kazuhiro Kobayashi and Masataka Nishi, Simulation of Tritium Behavior after Intended Tritium Release in Ventilated Room, Journal of Nuclear Science and Technology, Vol. 38, No. 1, p. 63-75, January 2001

23-01 Borre Bang, Dag Lukkassen, Application of Homogenization Theory Related to Stokes Flow in Porous Media, Applications of Mathematics, Narvik, Norway, No 4, pp. 309-319.

15-01 Ernst Hansen, SINTEF Energy Research, Trondheim, Norway, Computer Simulation Helps Increase Flow Rate in Three-Phase Separator, Drilling Marketplace, Vol 55, No 10, May 15, 2001, pp.14

10-01 Ernst Hansen, SINTEF Energy Research, Phenomeological Modeling and Simulation of Fluid Flow and Separation Behaviour in Offshore Gravity Separators, PVP-Col 431, Emerging Technologies for Fluids, Structures and Fluids, Structures and Fluid Structure Interaction — 2001, ASME 2001, pp. 23-29

7-01 C. Bohm, D. A. Weiss, and C. Tropea, Multi-droplet Impact onto Solid Walls Droplet-droplet Interaction and Collision of Kinemeatic Discontinuities, DaimlerChrysler Research and Technology, ILASS-Europe 2000, September 11-13, 2000

6-01 Ernst Hansen, Simulation Raises Separator Flow RateEngineering Talk, March 21, 2001

3-01 M. Sick, H. Keck, G. Vullioud, and E. Parkinson, New Challenges in Pelton Research

1-01 Y. Darsht, K. Kuvanov, A. Puzanov, I. Kholkin, FLOW-3D in Designing Hydraulic Systems for Heavy Machinery  (in Russian), SAPR I Grafika (CAD and Graphics), August 2000, pp. 50-55.

22-00 A. K. Temu, O. K. Sønju and E. W. M. Hansen, Criteria for Minimum Particle Deposition onto a Cylinder in Crossflow, International Symposium on Multiphase Flow and Transport Phenomena, November 2000, Tekirova, Antalya, Turkey

21-00 Claus Maier, Stefan aus der Wiesche and Eberhard P. Hofer, Impact of Microdrops on Solid Surfaces for DNA-Synthesis, Department of Measurement, Control and Microtechnology, University of Ulm, Technical Proceedings of the 2000 International Conference on Modeling and Simulation of Microsystems, pp. 586-589

11-00 Thomas K. Thiis, A Comparison of Numerical Simulations and Full-scale Measurements of Snowdrifts around Buildings, Wind and Structures – ISSN: 1226-6116,Vol. 3, nr. 2 (2000), pp. 73-81

10-00 P.A. Sundsbo and B. Bang, Snow drift control in residential areas-Field measurements and numerical simulations, Fourth International Conference on Snow Engineering, pp. 377-382

9-00 Thomas K. Thiis and Christian Jaedicke, The Snowdrift Pattern Around Two Cubical Obstacles with Varying Distance—Measurement and Numerical Simulations, Snow Engineering, edited by Hjorth-Hansen, et al, Balkema, Rotterdam, 2000, pp.369-375.

8-00 Thomas K. Thiis and Christian Jaedicke, Changes in the Snowdrift Pattern Caused by a Building Extension—Investigations Through Scale Modeling and Numerical Simulations, Snow Engineering, edited by Hjorth-Hansen, et al, Balkema, Rotterdam, 2000, pp. 363-368

7-00 Bruce Letellier, Louis Restrepo, and Clinton Shaffer, Near-Field Dispersion of Fission Products in Complex Terrain Using a 3-D Turbulent Fluid-Flow Model, CCPS International Conference, San Francisco, CA, September 28-October 1, 1999

6-00 Bruce Letellier, Patrick McClure, and Louis Restrepo, Source-Term and Building-Wake Consequence Modeling for the GODIVA IV Reactor at Los Alamos National Laboratory, 1999 Safety Analysis Workshop, Portland, Oregon, June 13-18, 1999

11-99 Thomas K. Thiis and Yngvar Gjessing, Large-scale Measurements of Snowdrifts Around Flat-roofed and Single-pitch-roofed Buildings, Cold Regions Science and Technology 30, Narvik, Norway, May 17, 1999, pp. 175-181

3-99 A. A. Gubaidullin, Jr., T. N. Dinh, and B. R. Sehgal, Analysis of Natural Convection Heat Transfer and Flows in Internally Heated Stratified Liquid, accepted for publication 33rd Natl. Heat Transfer Conf. CD proceedings, Albuquerque, NM, August 15-17, 1999

20-98 Mark W. Silva, A Computational Study of Highly Viscous Impinging Jets, published by the Amarillo National Resource Center for Plutonium, ANRCP-1998-18, November 1998

17-98 P. A. Sundsbo and B. Bang, 1998, Calculation of Snowdrift Around Roadside Safety Barriers, Proc of the International Snow Science Workshop, Sept. 1998, Sunriver, Oregon, USA 279-283

11-98 P-A Sundsbo, Numerical simulations of wind deflection fins to control snow accumulation in building steps, Journal of Wind Engineering and Industrial Aerodynamics 74-76 (1998) 543-552

23-97  P.E. O’Donoghue, M.F. Kanninen, C.P. Leung, G. Demofonti, and S. Venzi, The development and validation of a dynamic propagation model for gas transmission pipelines, Intl J. Pres. Ves. & Piping 70 (1997) 11-25, P11 : S0308 – 0161 (96) 00012 – 9.

22-97  Christopher J. Matice, Simulation of High Speed Filling, Presented at High Speed Processing & Filling of Plastic Containers, SME, Chicago, Illinois, November 11, 1997.

12-97 B. Entezam and W. K. Van Moorhem, University of Utah, Salt Lake City, UT and J. Majdalani, Marquette University, Milwaukee, WI, Modeling of a Rijke-Tube Pulse Combustor Using Computational Fluid Dynamics, presented at 33rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, Seattle, WA, July 6-9, 1997.

11-97 B. Entezam, Computational and Experimental Investigation of Unsteady Flowfield Inside the Rijke Tube, doctoral thesis submitted to University of Utah, Dept. Mechanical Engineering, Salt Lake City, UT, June 1997

2-97 K. Fujisaki, T. Ueyama, and K. Okazawa, Magnetohydrodynamic Calculation of In-Mold Electromagnetic Stirring, Nippon Steel Corp., IEEE Transactions on Magnetics, Vol. 33, No. 2, March 1997

1-97 P. A. Sundsbo, Four Layer Modelling and Numerical Simulations of Snow Drift, to be submitted to the Journal of Glaciology, 1997

23-96 Andy K Palmer, Computational Fluid Dynamic Software Comparison and Electrostatic Precipitator Modeling, Presented to the Faculty of California State University, Summer 1996

21-96 P. A. Sundsbo, Computer Simulation of Snow-Drift around Structures, Proceedings of the 4th Symposium on Building Physics in the Nordic Countries, Vol. 2, 533-539, Finland, 9-10 Sep. 1996

20-96 P. A. Sundsbo and E.W.M. Hansen, Modelling and Numerical Simulation of Snow-Drift around Snow Fences, Proceedings of the 3rd International Conference on Snow Engineering, Sendai, Japan, 26-31 May 1996

19-96 P. A. Sundsbo, Numerical Modelling and Simulation of Snow Accumulations around Porous FencesProceedings of the International Snow Science Workshop, Banff, Alberta, Canada, 6-10 Oct. 1996

18-96 T. Iverson, Editor, Applied Modelling and Simulation, Proceedings of the 38th SIMS Simulation Conference, Norwegian University of Science and Technology, Trondheim, Norway, June 11-13, 1996

17-96 C. L. Parish, Modeling Compressible Flow Through an Orifice Stack Using Numerical Methods, thesis submitted for M.S. Mech. Engineering, NM State University, Las Cruces, NM, December 1996

15-96 T. Wiik and R. K. Calay, A Study of Balcony on Flow-Field and Wind Loads for Low-Rise Buildings, Fourth Symposium on Building Physics in the Nordic Countries, Dipoli, Espoo, Finland, September 1996

14-96 T. Wiik, E.W.M. Hansen, The Assessment of Wind Loads on Roof Overhang of Low-Rise Buildings, Second International Symposium Wind Engineering, Fort Collins, CO, September 1996

13-96 T. Wiik, R. K. Calay, and A. Holdo, A Study of Effects of Eaves on Flow-Field and Wind Loads for Low-Rise Houses, Third International Colloquium on Bluff Body Aerodynamics and Applications, Blacksburg, Virginia, August 1996

11-96 Y. Miyamoto and M. Harada, A Flow Analysis accompanied by Formation of the Liquid Droplets shown with an Animation Display Technique, SEA Corporation, presented at Visualization Information Conference, Tokyo, Japan, July 17, 1996

8-96 J. Bakken, E. Naess, T. Engebretsen, and E. W. M. Hansen, Fluid Flow in Porous Media, proceedings of the 38th SIMS Simulations Conference, Norwegian Univ. of Science & Technology, Trondheim, Norway, June 11-13, 1996

7-96E. W. M. Hansen, Performance of Oil/Water Gravity Separators Imposed to Motion, proceedings of the 38th SIMS Simulations Conference, Norwegian Univ. of Science & Technology, Trondheim, Norway, June 11-13, 1996

8-95 J. J. Francis, Computational Hydrodynamic Study of Flow through a Vertical Slurry Heat Exchanger, NSF Summer Research Program, Dept. Mech. Engineering, Univ. of Nevada Las Vegas, August 9, 1995

4-94 J. L. Ditter and C. W. Hirt, A Scalable Model for Mixing Vessels, Flow Science report, FSI-94-00-1, presented at the 1994 ASME Fluids Engineering Summer Meeting, Incline Village, NV, June 1994

3-94 A. Nielsen, B. Bang, P. A. Sundsbo and T. Wiik, Computer Simulation of Windspeed, Windpressure and Snow Accumulation around Buildings (SNOW-SIM), 1st International Conference on HVAC in Cold Climate, Rovaniemi, Finland, from Narvik Institute of Technology, Narvik, Norway, March 1994

2-94 J. M. Sicilian, Addition of an Extended Bubble Model to FLOW-3D, Flow Science report, FSI-94-58-1, March 1994

1-94 T. Hong, C. Zhu, P. Cal and L-S Fan, Numerical Modeling of Basic Modes of Formation and Interactions of Bubbles in Liquids, Dept. Chem. Engineering, Ohio State University, Columbus, OH 43210, March 1994

14-93 J. L. Ditter and C. W. Hirt, A Scalable Model for Stir Tanks, Flow Science Technical Note #38, December 1993 (FSI-93-TN38)

13-93 J. Partinen, N. Saluja and J. K. Kirtley, Jr., Experimental and Computational Investigation of Rotary Electromagnetic Stirring in a Woods Metal System, Dept. of Math, Science and Engr. and Dept. of Electrical Engr. and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139-4307

12-93 J. Partinen, N. Saluja and J. K. Kirtley, Jr., Modeling of Surface Deformation in an Electromagnetically Stirred Metallic Melt, Dept. of Math, Science, and Engr. and Dept. of Electrical Engr. and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139-4307

10-93 C. Philippe, Summary Report on Test Calculations with FLOW-3D/CAST93, (coupled-rigid-body dynamics model), ESTEC, Noordwijk, The Netherlands, September 17, 1993

5-93 J. M. Sicilian, J. L. Ditter and C. L. Bronisz, FLOW-3D Analyses of CFD Triathlon Benchmark, Flow Science report, presented at the ASME Fluids Engineering Conference, Washington DC, June 20-24, 1993

4-93 T. Wiik, Ventilation of the Attic due to Wind Loads on Low-Rise Buildings, paper for 3rd Symposium of Building Physics in Nordic Countries, Narvik Institute of Technology, Narvik, Norway, summer 1993

3-93 E. W. M. Hansen, Modelling and Simulation of Separation Effects and Fluid Flow Behaviour in Process-Units, SIMS’93 – 35th Simulation Conference, Kongsberg, Norway, June 9-11, 1993

2-93 M. A. Briones, R. S. Brodsky and J. J. Chalmers, Computer Simulation of the Rupture of a Gas Bubble at a Gas-Liquid Interface and its Implications in Animal Cell Damage, Dept. Chemical Engineering, Ohio State University, Manuscript No. RB68, April 1993

11-92 G. Trapaga, E. F. Matthys, J. J. Valencia and J. Szekely, Fluid Flow, Heat Transfer, and Solidification of Molten Metal Droplets Impinging on Substrates: Comparison of Numerical and Experimental Results, Metallurgical Transactions B, Vol. 23B, pp. 701-718, December 1992

10-92 J. B. Dalin, J. M. Le Guilly, P. Le Roy and E. Maas, Numerical Simulations Applied to the Production of Automotive Foundry Components, Numerical Methods in Industrial Forming Processes, Wood & Zienkiewicz (eds), Balkema, Rotterdam, 1992

5-92 C. W. Hirt, Volume-Fraction Techniques: Powerful Tools for Flow Modeling, Flow Science report (FSI-92-00-02), presented at the Computational Wind Engineering Conference, University of Tokyo, August 1992

3-92 C. L. Bronisz and C.W. Hirt, Lubricant Flow in a Rotary Lip Seal, Flow Science Technical Note #33, February 1992 (FSI-92-TN33)

16-91 A. Nielsen, SNOW-SIM – Computer Model for Simulation of Wind and Snow Loads on Buildings and Structures, Building Science, Narvik Institute of Technology, Narvik, Norway, (not dated)

15-91 E. W. M. Hansen, H. Heitmann, B. Laska, A. Ellingsen, O. Ostby, T. B. Morrow and F. T. Dodge, Fluid Flow Modelling of Gravity Separators, SINTEF, Norway and Southwest Research Institute, Texas, Elsevier Science Publishers, 1991

14-91 E. W. M. Hansen, H. Heitmann, B. Laska and M. Loes, Numerical Simulation of Fluid Flow Behaviour Inside, and Redesign of a Field Separator, SINTEF, Norway and STATOIL, Norway (not dated)

13-91 G. Trapaga and J. Szekely, Mathematical Modeling of the Isothermal Impingement of Liquid Droplets in Spraying Processes, Metallurgical Transactions, Vol. 22B, pp. 901-914, December 1991

11-91 N. Saluja and J. Szekely, Velocity Fields and Free Surface Phenomena in an Inductively Stirred Mercury Pool, European Journal of Mechanics, B/Fluids, Vol. 10, No. 5, pp. 563-572, Oct. 1991

4-90 J. M. Sicilian, A Note on Implementing Specified Velocities and Momentum Sources, Flow Science report, September 1990 (FSI-90-00-5)

13-90 P. Jonsson, N. Saluja, O. J. Ilegbusi, and J. Szekely, Fluid Flow Phenomena in the Filling of Cylindrical Molds Using Newtonian (Turbulent) and Non-Newtonian (Power Law) Fluids, submitted to Trans. of the American Foundrymen’s Soc., June 1990

12-90 N. Saluja, O. J. Ilegbusi, and J. Szekely, On the Computation of the Velocity Fields and the Dynamic Free Surface Generated in a Liquid Metal Column by a Rotating Magnetic Field, submitted to J. Fluid Mech., July 1990

7-90 C. L. Bronisz and C. W. Hirt, Modeling Unsaturated Flow in Porous Media: A FLOW-3D Extension, Flow Science report, July 1990 (FSI-90-48-2)

5-90 C. L. Bronisz and C. W. Hirt, Hydrodynamic Ram Simulations Using FLOW-3D, Flow Science report, May 1990 (FSI-90-49-1)

3-90 C. W. Hirt, Turbojet Plume Flow Analysis, Flow Science report, February 1990 (FSI-90-45-1)

5-89 K. S. Eckhoff and E. W. M. Hansen, Mathematical Modelling and Numerical Investigation of Separation in Two-Phase Rotating Flow, SINTEF-Foundation for Scientific and Industrial Research at the Norwegian Institute of Technology, Trondheim, Norway, Report No. OR 22 1907.00.01.89, 29 April 1989

2-89 J. M. Sicilian and J. R. Tegart, Comparisons of FLOW-3D Calculations with Very Large Amplitude Slosh Data, presented at the Symposium on Computational Experiments, PVP ASME Conference, Honolulu, HI, July 22-27, 1989

2-88 J. M. Sicilian and C. W. Hirt, AFT Field Joint: CFD Analysis Using the FLOW-3D Program, in Redesigned Solid Rocket Motor Circumferential Flow Technical Interchange Meeting Final Report, NASA-TWR-17788, February 1988

14-87 C. J. Freitas, S. T. Green, and T. B. Morrow, Fluid Dynamics Associated with Ductile Pipeline Fracture, Southwest Research Institute report presented at ASME Winter Annual Meeting, Boston, MA, December 1987

13-87 J. Sicilian, The FLOW-3D Model for Thermal Conduction in Solids, Flow Science report, Dec. 1987 (FSI-87-00-4)

7-87 C.W. Hirt, Vectored Nozzle Flow with Turbulence Modeling, Flow Science report, Sept. 1987 (FSI-87-29-1)

4-87 J.M. Sicilian, C.W. Hirt, and R. P. Harper, FLOW-3D: Computational Modeling Power for Scientists and Engineers, Flow Science report, 1987 (FSI-87-00-1)

3-86 J. M. Sicilian, Natural-Convection Heat-Transfer Analysis, Flow Science Technical Note #4, June 1986 (FSI-86-00-TN4)

2-86 J. Navickas and C. R. Cross, Air Circulation Characteristics and Convective Losses in a 5-MW Molten Salt Cavity Solar Receiver, ASME 8th Annual Conference on Solar Engineering, Anaheim, California, April 13-16, 1986

5-85 C. W. Hirt and R. P. Harper, Calculations of Vent Clearing in a Chemical Process Tank, Flow Science report, December 1985 (FSI-85-28-1)

2-84 Applications of SOLA-3D/FSI to Fluid Slosh, Flow Science report, May 1984