Characterization of laminar and turbulent supercritical carbon dioxide slot jet impingement heat transfer

Abstract

Supercritical carbon dioxide (sCO2) has recently been proposed as a promising alternative to conventional fluids for thermal management because of its unique thermophysical properties near the critical point. Jet impingement is also recognized as one of the most effective configurations for high intensity heat transfer. Therefore, leveraging the favorable thermophysical properties of sCO2 in microscale jet impingement may lead to high performance thermal management solutions. However, the effects of thermophysical property variations in the pseudo-critical temperature range on the flow and heat transfer behavior in such configurations is not well understood. The present investigation seeks to address this need through computational simulations of laminar and turbulent slot sCO2 jet impingement. Large eddy simulations (LES) are validated and employed for turbulent cases. The studied range of conditions span reduced pressures of Pr=1.03−1.10, Reynolds numbers Re=225−11,000, dimensionless jet lengths H/W=2−4, jet inlet temperatures Tin=294−330K, and impingement plate temperatures Tplate=270−370K. The turbulent simulations reveal varying spatial distributions of heat transfer coefficient with different jet and plate temperatures, which can be explained in terms of the temperature-dependent properties of sCO2. Heat transfer deterioration (HTD) is observed for both laminar and turbulent flows. HTD is found to be most significant in the stagnation zone, and its relative magnitude decreases downstream more sharply for turbulent flows than laminar. Heat transfer enhancement (HTE) is observed when both the jet inlet and impingement plate temperatures are at opposite ends of the pseudo-critical temperature range. For cooling applications, HTD and HTE effects can be explained in terms of opposing temperature-dependent variations in boundary layer thermal conductivity and overall thermal boundary layer thickness with Prandtl number. Considering the dependence of thermophysical properties on Pr, a thermal management system control strategy is proposed in which Pr is adjusted depending on Tplate to achieve optimal performance over varying operating conditions.