The Impact of Installation Angles on Flow Boiling Heat Transfer of Refrigerants in Elliptical Microchannels with Micro Fins

Abstract

The microchannel heat exchangers are characterized by their high thermal efficiency and compact volume. This study investigates the boiling heat transfer characteristics of R454B, R134a, and R410A refrigerant in elliptical microchannel heat exchangers with micro fins. The effects of varying heat flux and installation angles on the heat transfer, mass transfer, and pressure drop in microchannels are explored. Furthermore, the gas-liquid two-phase flow patterns within microchannel heat exchangers are clarified. A novel numerical model for phase change heat and mass transfer is introduced, which includes adaptive correction of mass transfer intensity based on the vapor volume fraction of refrigerant in channels. An analysis is conducted to understand the intricate relationship between bubble dynamics and superheating during phase change. The examination and subsequent comparison of each wall's heat transfer coefficient are meticulously examined. In comparison to R134a under similar conditions, R454B achieves a higher heat transfer coefficient of up to 1.36 times greater, while its pressure drop constitutes only 62.51% of that of R134a. Moreover, the impact of installation angle and wall position on the heat transfer coefficient exceeds 14.45%. Overall, both operating conditions and performance metrics demonstrate that R454B can serve as a viable alternative refrigerant parallel to R410A.

Keywords: Elliptical microchannel, Heat and mass transfer, Flow boiling, Two phase flow, Micro Fins