Interplay of high zeta potential and steric factor on the slip thermofluidics of power law fluids through narrow confinements

Abstract

Thermal transport in a non-Newtonian fluid flow through a parallel plate microchannel is investigated with an emphasis on the effects of high zeta potential and steric factor. The fluid viscosity is modelled using the power law and the flow is driven by a combination of electric field and pressure gradient in the form of a dimensionless flow actuation coefficient. The effects of joule heating, viscous dissipation and slip length at the wall are considered. A semi-analytical formulation for the temperature profile is developed which is solved numerically using the Galerkin Finite Element method. We find that the Nusselt number increases as the flow behaviour index is increased. Velocity slip is also found to have a positive impact on convective heat transfer. However, as the zeta potential and steric factor increase, the Nusselt number begins to decline as there is an increase in viscous dissipation. We highlight the importance of considering variable electrical conductivity in evaluating the effect of joule heating at high zeta potential and moderate steric factor. In this regime, joule heating dominates advective transport and heat flow is reversed which may be detrimental or even damaging to microfluidic devices. A comprehensive thermal map is developed for a wide range of zeta potentials and steric factors.