Analysis of electroviscous effect and heat transfer for flow of non-Newtonian fluids in a microchannel with surface charge-dependent slip at high zeta potentials

Abstract

In hydrophobic surfaces, pressure-driven flows induce electrokinetic flow retardation, where the slip length decreases due to the surface charge. In the current work, we investigate the thermal transport and fluid flow behavior of a pressure-driven flow of shear-thinning fluid with an electroviscous effect, accounting for the influence of surface charge on the slip. The electrical potential field induced in the electrical double layer (EDL), velocity, streaming potential, and temperature is obtained after solving the Poisson–Boltzmann equation, mass, momentum, and energy conservation equations without invoking the Debye–Hückel linearization. Results are presented for a broad range of dimensionless parameters, such as surface charge-independent slip length, Debye–Hückel parameter, zeta potential, heat flux, and flow consistency index ( n). The flow velocity decreases after considering the effect of surface charge on slip, and such decrement is more for lower value of n, higher magnitude of zeta potential, and thicker EDL. Moreover, for lower value of n (1/3), the alteration of the Nusselt number with the surface charge is non-monotonic, whereas it increases with the surface charge magnitude for higher value of n (1/2). Further, for lower value of n, the Nusselt number enhances by the surface charge effect on the slip, whereas, for higher value of n, the trend is the opposite. Also, there is a strong interplay of the rheology of the fluid and EDL thickness in dictating the variation of the Nusselt number.