In addition to transport due to convection and diffusion, the Transport of Diluted Species interface supports ionic species transport by migration. This is done by selecting the Migration in Electric Field check box under the Transport Mechanisms section for the physics interface. The mass balance then becomes:

The velocity, u, can be a computed fluid velocity field from a Fluid Flow interface or a specified function of the spatial variables x, y, and z. The potential can be provided by an expression or by coupling the system of equations to a current balance, such as the Electrostatics interface. Sometimes it is assumed to be a supporting electrolyte present, which simplifies the transport equations. In that case, the modeled charged species concentration is very low compared to other ions dissolved in the solution. Thus, the species concentration does not influence the solution’s conductivity and the net charge within the fluid.

where R (SI unit: J/(mol·K)) is the molar gas constant and T (SI unit: K) is the temperature.