Combined Radiation-Evaporation Model of a Liquid Droplet Layer in Space

Abstract

Assuming that the droplet layer is a uniform medium, an evaporation intensity analogous to radiation intensity was defined based on an analysis of vapor molecule transfer characteristics in the droplet layer. An evaporation transfer equation was then established, from which a one-dimensional evaporative mass flux expression was obtained and combined with the radiation heat transfer model. The combined radiation-evaporation model was used to analyze the influence of the exit temperature and the optical thickness of the droplet layer on temperature distribution, evaporation loss rate, and system lifetime. In the case of a certain droplet diameter and a small optical thickness (κD≤1), the numerical results show that temperature decreases approximately linearly with layer length. The evaporation loss rate increases as the exit temperature and optical thickness increase, and the main contribution to the evaporation loss rate comes from the high temperature portion of the liquid layer near the exit of the liquid generator, i.e., the evaporation loss rate increases rapidly in a short length of the liquid droplet layer and approaches a stable value as the length reaches a certain value. With the same working fluid mass overloading proportion of the droplet layer, the system lifetime is mainly determined by the exit temperature of the liquid droplet layer. For example, if the exit temperature decreases from 320 to 310 K, the system lifetime increases by approximately three times. However, system lifetime has a weak relationship with optical thickness.