Forced Convection Heat Transfer in Parallel Channel Array Microchannel Heat Exchanger

Abstract

Abstract An experimental study is underway to investigate heat transfer and pressure drop in a microchannel heat exchanger. Devices with geometry consisting of an array of 54 parallel microchannels with rectangular cross-section, 1.0 mm deep and 0.27 mm wide (aspect ratio approximately 4, with hydraulic diameter 425 mm) have been tested using Refrigerant 124 as the working fluid. Conditions tested include a range of Reynolds numbers between 100 and 570 (where Red is defined using the hydraulic diameter of the channels), uniform heat flux up to approximately 40 W/cm2, and wall surface superheats ranging from approximately 0 to 65 K, in both single-phase and two-phase flow. The average liquid-side heat transfer coefficient showed a significant increase over the expected value in macroscopic flow at the same Reynolds numbers. In the single-phase tests, the Nusselt number values ranged from about 5 to 12 for the conditions tested and varied with Reynolds number, showing increasing Nu with increasing Red. In the two-phase tests, the Nusselt number appeared to be approximately constant with Red, at a value of approximately 20. Exit qualities achieved in the two-phase testing ranged from approximately 4% up to nearly 60%, as determined from an energy balance on the system. These results indicate that substantial improvements in thermal hydraulic performance can be realized in microscale heat exchangers with no significant penalty in the pressure drop.