Thermalhydraulic comparison of supercritical fluids in minichannel heat sink to assess the suitability of macroscopic scaling rules

Abstract

Suitability of supercritical fluids as heat transport media in mini-/microscale has not been explored much, despite showing enormous potential in macrochannels. One major hindrance thereof is the absence of scaling rules devised specifically for such scales. Present numerical study explores the thermalhydraulic characteristics of five different supercritical fluids, identified based on the diversity in their respective critical-point parameters, for a particular minichannel employing a conventional set of scaling relations. Supercritical fluids exhibit consistently-superior heat transfer coefficient compared to single-phase, and even boiling, channels. Substantial level of similarity has been observed in the visual nature of the dimensionless momentum and thermal fields and local recirculation patterns across the fluids, as a consequence of the imposed scaling. Noticeable difference, however, exists in characterizing dimensionless groups, such as local Reynolds number and local and area-averaged Nusselt number, pointing toward the deficiency of the scaling model. R134a can be earmarked as the optimum fluid among the considered ones, both in terms of Nusselt number and dimensionless pressure drop, though it experiences the largest entropy generation as well. It is suggested to consider the profiles of Prandtl number and dimensionless thermal conductivity with dimensionless enthalpy for improving the used scaling rules.