Modelling the effects of particle migration and viscous dissipation on a nanofluid-cooled microchannel heat sink using porous medium approach

Abstract

This study investigates the combined effect of particle migration, specifically Brownian diffusion and thermophoresis, and viscous dissipation on fluid flow and heat transfer of titania-oxide nanofluids in an asymmetrically heated microchannel heat sink as the transport of nanofluids alters its momentum diffusion and the heat advection. The heat sink is modelled using the porous medium approach and the solid and fluid temperatures are solved numerically using MATLAB’s BVP4C solver. The presence of solid fins causes a more uniform fluid velocity and temperature profile, with heat transfer dominated by solid conduction due to the solid fins’ high thermal conductivity. Particle migration enhances heat advection near the heated wall and improves heat diffusion in the core, resulting in an increase of up to 5.11 % in Nusselt number (Nu) when the porosity of the porous medium is 0.9. However, viscous dissipation dilutes the Nu enhancement due to particle migration, leading to a deterioration of up to 4.76 % as the Brinkman number (Br) increases from 0 to 5. Titania-oxide water nanofluid lowers the thermal resistance for fluid conduction near the heated wall and increases the heat transfer coefficient by up to 12.78 %. The more dominant effect of the increased viscosity over the increased thermal conductivity in the nanofluid, however, leads to a Performance Evaluation Criteria (PEC) $<1$ trend for Brownian Diffusivity to Thermophoretic Diffusivity Ratio (N_BT) in the range of 1 and 5 and Br in the range of 0 and 5. This numerical study incorporates particle migration in the porous medium approach to model a microchannel heat sink, offering insights on the local heat transfer effects due to the use of nanofluids.