Transient electro-osmotic pumping in rectangular microchannels

Two-dimensional Poisson-Boltzmann and momentum equations are solved simultaneously to study the transient characteristics of electro-osmotic pumping in a rectangular microchannel. A finite difference scheme with variable grid spacing is used to calculate electric potential distribution. Time variations of velocity profiles are obtained by using a combined ADI-TDMA technique. Numerical solutions show significant influences of the channel hydraulic diameter, the aspect ratio, and the applied voltage on the transient and steady state velocity fields and the resulting volumetric flow rates. As the channel hydraulic diameter is increased, it takes a longer period for the flow to reach steady state condition. On the other hand, as the channel aspect ratio deviates from the square, a steady-state flow field is reached in a shorter period, and a slightly larger flow can be obtained. The numerical results also show that the steady state channel throughput is linearly increasing with the applied voltage along the channel length.