Viscous dissipation effect on forced convective transport of nanofluids in an asymmetrically heated parallel-plate microchannel

Abstract

This study intends to investigate the effects of viscous dissipation on the Alumina-water nanofluids transport in an asymmetrically heated microchannel, accounting for Brownian motion and thermophoresis mechanism. An iterative algorithm deploying Runge-Kutta fourth order method was set up to solve the governing equations numerically. Viscous dissipation shifts the highest concentration and lowest fluid temperature away from the adiabatic wall and redistributes the spatial variation of thermal conductivity and viscosity, retarding the Nu as its effect strengthens. It is noteworthy that the trends of Nusselt number variation with an increasing nanoparticle bulk concentration, and Brownian and Themophoretic diffusivity ratio, N BT , highlight the competition between the enhanced thermal diffusion effect and the hindered heat convection by a larger flow resistance. A Brinkman number, Br larger than 0.02 alters the Nu pattern of variation with N BT . Viscous dissipation leads to more pronounced effects of particle migration on the concentration and temperature distribution in particular. Assuming negligible viscous dissipation, Nusselt number deteriorates beyond an Alumina concentration of 3.65 vol %. while Titania-water nanofluids showed an opposite trend. The total entropy generation, caused by fluid flow irreversibility predominantly, amplifies with an increasing nanoparticle concentration, more significantly when the concentration is below 6.5 vol %., for Br = 0.1. Conversely, an increase in Brownian to Thermophoretic diffusivity ratio, N BT , lessens the entropy generation.