Experimental Investigation of the Effect of Gravity on Heat Transfer and Instability in Parallel Mini-channel Heat Exchanger

Abstract

Mini-channel heat exchangers draw significant attention due to their capability of dissipating high flux heat in a relatively controllable way. The properties of heat transfer and instability of the parallel minichannel heat exchangers were investigated on orbit. The heat exchangers were installed as the evaporators of a two-phaseflow loop in the first Chinese cargo ship (TZ1). R134a was selected as working fluid of the loop. The heat exchangers were designed to be gravitydominated, with the channels’ cross section of 1 × 3 mm2, or larger. Small temperature fluctuation was found on the surface of one heat exchanger. It may be caused by the flow-rate fluctuation among the channels; and it could be more likely occur in microgravity. The necking at each entrance of the channels could suppress the fluid fluctuation inside the heat exchanger. For gravity-dominated channels, gravity plays a decisive role in the vapor-liquid distribution in the channels, which in turn affects the heat transfer coefficient of the heat exchanger.