Mixed Pressure and AC Electroosmotically Driven Flow With Asymmetric Wall Zeta Potential and Hydrophobic Surfaces

Abstract

The present study examines Alternating Current (AC) electroosmotic flows in a parallel plate microchannel subject to constant wall temperature. Numerical method consists of a central finite difference scheme for spatial terms and a forward difference scheme for the temporal term. Asymmetric boundary conditions are assumed for Poison-Boltzmann equation for determining the electric double layer (EDL) potential distribution. The potential distribution is then used to evaluate the velocity distribution. The velocity distribution is obtained by applying slip boundary conditions on the walls which accounts for probable hydrophobicity of surfaces. After determining the velocity distribution numerically, the energy equation is solved by taking into account the effects of viscous dissipation and non-uniform Joule heating. The results reveal that the effect of increasing Knudsen number is a slight increase in the dimensionless temperature profile. Furthermore, the effect of increasing dimensionless time is an increase in dimensionless oscillatory temperature which leads to a steady oscillatory condition. Also, the effect of increasing dimensionless Debye-Huckel parameter is a decrease in mean oscillation value and an increase in the required time for reaching steady oscillatory condition. In addition, increasing forward or backward pressure leads to increased viscous heating near the walls. Furthermore, the effect of increasing zeta potential is an increase in the dimensionless mean velocity oscillation amplitude.