Combined electroosmotic and pressure driven flow in a microchannel at high zeta potential and overlapping electrical double layer

• For high wall potential and thick double layer, centerline potential is significant.
• Channel velocity decreases for thick double layer.
• Channel velocity decreases with wall potential.
• Nusselt number decreases with wall potential.
• Nusselt number increases with thin double layer.

A mathematical model for combined electroosmotic and pressure driven flow in a rectangular microchannel at high zeta potential and overlapping electrical double-layer is presented. The potential distribution is solved numerically without Debye–Hückel approximation using site dissociation model. The corresponding hydrodynamic analysis along with the associated heat transfer problem was performed. For wall potential of 120 mv, the centerline potential could be 95% of wall potential at non-dimensional channel height κa = 0.3 and it was 90% for κa = 1.0, where κ−1 is Debye length and a is half height of the channel. Centerline potential was 84% of wall potential at pH 5.5 and beyond pH 6.5, centerline potential was close to zero, even at lower value of κa (=0.3). Centerline velocity decreases by 16% as κa decreases from 1 to 0.5, when both pressure driven flow and electroosmotic flow are equally dominant, for non-dimensional zeta potential α = 3 (77 mV). For ratio of Joule heating to surface cooling beyond 5, the non-dimensional temperature in the channel is always positive. In absence of Joule heating (G = 0), Nusselt number decreases by 28% as κa decreases from 1 to 0.5. Nusselt number also decreases by 34% with increase in non-dimensional wall zeta potential from 3 to 5.

Nusselt number increases with the dominant electroosmotic flow compared to that of pressure driven flow. At constant heat flux at the wall, Nusselt number increases as the surface heat flux transitions from heating to cooling.Figure optionsDownload as PowerPoint slide