Elmer includes a Poisson-Boltzmann solver for solving the charge density of electric double layers (EDL). This solver is needed only when the thickness of EDL is comparable to the other dimensions of the system. Due to the charge density an external electric field may be used to create a net force acting on the fluid. This force then induces an electrokinetic flow.

The current example shows how an varying external field may be used as a pump in a junction. It is assumed that there is a marker fluid coming from the up and it is then further convected with the flow. A small diffusivity is also assumed since otherwise the equation for the marker would be purely convective.

Still pictures refer to a moment when the electric field is set along the longer tube only.

• jpg, Potential of the electric double layer (EDL)
• jpg, Charge density of the electric double layer (EDL)
• jpg, External potential field.
• jpg, Induced velocity field.
• jpg, Induced velocity field, a close up at the junction.
• jpg, Resulting concentration field after three cycles.

• mpg, Resulting concentration field in the third cycle.
• mpg, Concentration field with a sharp interface.

• pbe-flow.sif, command file
• junction.grd, mesh file
• Cycle.f90, user defined subroutine