Experimental study of heat rejection performance of water membrane evaporator in vacuum environment

The water membrane evaporator (WME) is a kind of consumable heat sink proposed for application in spacecraft thermal control systems. It has great potential to be applied as a primary or auxiliary heat sink in the thermal control systems of spacecraft such as the Mars extravehicular spacesuit, the near space vehicle and others. In the space high vacuum pressure atmosphere, the water evaporates to the environment and absorbs the latent heat of vaporization to achieve the purpose of cooling the fluid. The heat rejection of WME is a very complex physical process of heat and mass transfer, and its performance is affected by the coupling of several parameters. How-ever, the influence laws of various operating and structural parameters of the WME on its performance have not been adequately investigated in previous studies. Thus leading to the considerable challenge of optimizing design of WME and its usage strategies. In this paper, five groups of tests were conducted on three WME prototypes with different structures and the effect laws of temperature, backpressure, circulating water flow rate, and hollow fiber (HoFi) tube distance on their heat rejection and water consumption rate were obtained. The WME based on porous HoFi membranes has a very considerable heat rejection capacity. Several WME prototypes tested in this study obtained a maximum heat rejection of 589 W/m2 at the inlet water temperature of 45 degrees C. The structure of HoFi membrane tubes and parameters such as inlet flow rate have a significant effect on its performance. The heat rejection per unit area for Case 1 is about 3.76 times that of Case 4 at the inlet water temperature of about 45 degrees C and the backpressure of about 700 Pa. In addition, the dimensionless analysis was also carried out, and the correlations that can be used to predict the heat rejection performance were obtained. These results are of guiding significance for optimizing the structural design, heat rejection performance and operating strategy of WME.