Thermal design improvement of a double-layered microchannel heat sink by using multi-walled carbon nanotube (MWCNT) nanofluids with non-Newtonian viscosity

Abstract

In the present study, numerical optimization of a double layer micro channel heat sink is addressed. Carbon based nanofluids with a non-Newtonian viscosity is assumed as the coolant. A conjugate numerical model based on finite volume method and two-phase mixture model is used to simulate the heat and fluid flow through the two three-dimensional domains; the solid walls and the coolant. A direct search method is applied to find the optimal design of the micro channel heat sinks such that the thermal resistance of the heat sink is minimized under the constraint of fixed pumping powers. The numerical model is validated against experimental data. A comprehensive sensitivity analysis is undertaken to properly bracket the optimum design point of the heat sink and the optimum point is directly searched for several pumping powers. It is shown that using carbon based nanofluid results in the reduction of overall thermal resistance of the double layer microchannel heat sink in comparison with oxide-metallic nanofluid (with Newtonian rheological behavior). The superior thermal performance of MWCNT/water nanofluids is attributed to the high conductivity of the carbon nano particles and the shear thinning behavior of the nanofluid. Up to 14% enhancement in the thermal performance of the micro channel heat sink is reached by the use of non-Newtonian carbon base nanofluids.