Non-isothermal effects in the slippage condition and absolute viscosity for an electroosmotic flow

In this work, we have developed a novel asymptotic analysis using perturbation techniques for an electroosmotic flow in a rectangular microchannel, considering that the absolute viscosity η is a function of temperature; a situation that affects also the slip condition at the walls of the microchannel, u =−sη∂ u/∂ n . The physical importance of this temperature dependence is based on the presence of the applied external electric field on the electrolyte solution, which originates the Joule heating effect that disturbances the isothermal hydrodynamic behavior. The above leads to a significant increase of the volumetric flow rate for this non-isothermal condition in comparison to the purely isothermal electroosmotic flow. This result is simultaneously controlled by the heat losses to the ambient and

the slip effect: the lower the presence of the heat dissipation mechanism on the outer walls of the microchannel and the higher the sliding condition, the higher the values of the volumetric flow rate. The above trend differs substantially from the isothermal case and finds its justification in the recognition of the presence of the Joule heating effect that induces significant longitudinal and transverse temperature gradients along the microchannel. Considering the proper limitations of the asymptotic analysis, we compare the present asymptotic results with a full numerical solution of the governing equations, which are composed of the continuity, momentum, and energy equations for the electrolyte flow, together with the Poisson–Boltzmann.