Initiating Homogeneous Bubbles in Pure Liquid
- Barkhudarov and C.W. Hirt
Flow Science, Inc.
The combined Temperature-Dependent-Cavitation and Homogenous Bubble models work together as a way to simulate the formation and growth of vapor bubbles by locally heating a liquid. The Homogeneous Bubble model is only activated when a bubble has a size that encompasses at least one complete grid cell, i.e., can be resolved as a “bubble” or void region.
The Cavitation model contains a mechanism for the initiation of bubbles, which works in the follow way. At the end of each time cycle of a transient computation every grid cell containing liquid is tested to see if its pressure is less than the saturation pressure corresponding to the temperature in the cell. The saturation pressure is computed from the pressure-temperature saturation relation specified by the user (e.g., usually a Clapeyron relation). If the cell pressure is less than its saturation pressure it is assumed that boiling can begin. The essential assumption is that there exist sufficient impurities or nucleation sites for this to happen. A very simple model nucleation has been incorporated into FLOW-3D®.
Once a cell has been identified for possible boiling it is given a time delay before vaporization begins. For vaporization to occur it is necessary to have at least 1% void fraction in the cell. This small void can be thought of as the nucleation process. The time delay is input as variable CAVRT (denoted as Ccav in the following).