A model for electroosmosis has been developed and released in version 8.2 of FLOW-3Dr. It is a general model in which the zeta potential distribution is solved through the electric double layer (EDL). When the EDL thickness (¸D) is very small, such as ¸D < 0:1¹m or in nanoscale, it is very computationally expensive to resolve the physics inside the EDL. In this note, we describe a simple model that has been developed to simulate electroosmosis without resolving the EDL.

That is, the zeta potential distribution is not solved, instead, a zeta potential on the obstacle surface is used as a boundary condition to calculate a slip velocity. This velocity is imposed on the obstacle surface if a zeta potential exists around that obstacle. It is de¯ned by ³²Ex ¹ and called the Helmholtz-Smoluchowski velocity with ³, Ex, ¹ representing zeta potential, electric ¯eld intensity in x-direction, ² permittivity, and liquid viscosity respectively.

However, if the EDL thickness is large compared to the problem geometry such as channel width, the simpli¯ed model is not accurate, and the original model is recommended. The new model has been validated against the corresponding analytical solution in a channel °ow and its application to complex microchannel °ow is demonstrated. The new simpli¯ed model will be incorporated in a future version of FLOW-3D