On the flow field and heat transfer characteristics of a supercritical CO2-cooled microchannel heat sink under high heat flux conditions

Abstract

Supercritical CO2 (sCO2) is a suitable choice as a coolant due to its favorable thermodynamic characteristics (lower density and viscosity, and higher specific heat) compared to water. In the current investigation, sCO2 is considered a coolant in a micro heat sink under high heat fluxes 75, 100, 125, and 150 W/cm2 and the operating pressure 8 MPa. The effects of the operating conditions, including the change in coolant mass flux (1250–3125 kg/s-m2), the change in the inlet temperature (305-308 K) under the mentioned heat fluxes on the heat transfer coefficient, thermal resistance, pressure drop, pumping power, and performance evaluation criteria (PEC) are investigated numerically using the finite volume method. Results indicated that thermohydraulic performance of the sCO2-cooled heat sink depends on the inlet coolant temperature and the applied heat flux due to the dramatic variation of the local thermophysical properties. It was found that increase in the heat flux from 75 to 150 W/cm2 results in increase of the pumping power by 48%, diminishing the PEC from 2.35 to 0.5. Overall, sCO2-cooled heat sink performs better than water-cooled heat sink if the mass flow rate is high and the inlet temperature is below the pseudocritical temperature. Otherwise, using sCO2 is not beneficial, especially under higher heat flux conditions.