Numerical analysis of flow and conjugate heat transfer for supercritical CO2 and liquid sodium in square microchannels

Abstract

A numerical analysis of the developing laminar flow and conjugate heat transfer in a rectangular micro-channel was performed for supercritical CO2 and liquid sodium as working fluids for better understanding of the flow and heat transfer mechanisms. Three-dimensional Navier-Stokes, energy, and Laplace equations describing simultaneously developing flow and conjugate heat transfer in multiple micro-channels were solved numerically using Fluent code for the parallel- and counter-flow arrangements. The physical and transport properties of CO2 at supercritical conditions and their influence on fluid flow and heat transfer are presented and discussed. Liquid sodium and supercritical CO2 (sCO2) were used as the heat transfer and hot and cold working fluids, respectively. The values of friction coefficient and Nusselt number predicted by the numerical analysis were compared to the analytical solutions from the literature. Numerical results show that large variations in sCO2 properties in the critical and pseudo-critical regions affect the flow and heat transfer. This effect diminishes for operating conditions (pressure and temperature) further away from the Critical Point. Also, in the fully-developed region the local values of wall shear stress and heat transfer coefficient are not constant, but are strong functions of the local heat flux at the solid-fluid interface which varies due to large variation in sCO2 properties.