Electroviscous and thermal effects on non-Newtonian liquid flows through microchannels

Electroviscous and thermal effects on steady, fully developed, combined pressure driven and electroosmotic flow of power-law liquids through a uniform microannulus subject to uniform wall heat flux are studied numerically by solving the Poisson-Boltzmann, momentum and energy equations using a finite difference method. Considering the Poisson-Boltzmann equation in the exact form without using the Debye-Huckel approximation and taking into account phenomena such as viscous dissipation and Joule heating in the energy equation, influences of major parameters, namely, the radius ratio of the annuli, flow behavior index, dimensionless pressure gradient, dimensionless electric force, dimensionless wall zeta potential, Debye-Huckel parameter, Brinkman number, and Joule number on the velocity and temperature distributions as well as the Nusselt number are discussed. The results reveal that higher velocities exist in case of pressure assisted flow compared to the purely electroosmotic and pressure opposed flows. Moreover, in the presence of a favorable pressure gradient, the system experiences the maximum absolute dimensionless temperature. Also, at higher values of the Debye-Huckel parameter, the effect of the non-Newtonian behavior on the thermal characteristics of the flow reduces. As for the Nusselt number, depending on the value of the flow parameters some singularities may occur in the Nusselt profile at the inner wall for the pressure assisted shear-thinning and shear-thickening flows in case of wall cooling. In addition, the effect of Joule heating on the inner Nusselt number diminishes as the value of the dimensionless electric force approaches relatively high positive or negative values, independent of the value of the flow behavior index. (C) 2012 Elsevier B.V. All rights reserved.