CFD study on film boiling features of cryogenic fluid influenced by heat structures and gravity levels

Abstract

Understanding bubble behaviors and thermal characteristics under various working conditions is of great significance to the efficient utilization of cryogenic propellants. In the present study, simulation models of pool film boiling at horizontal plate and cylinder surface are proposed with Volume of Fluid (VOF) method combined with Lee’s phase change model. Based on the physical and thermal performance, the gravity levels, physical properties, and heater structure dimensions are investigated respectively, which could satisfy the common application conditions of cryogenic propellants. The results show that the movement of bubbles at gas–liquid interface is critical to the pool film boiling heat transfer, and also the heat transfer mechanism affects the bubble motion behaviors. The critical wavelength and the most dangerous wavelength are significant length scales for the bubble behaviors in pool film boiling. When the cylindrical heater size is larger than the most dangerous wavelength, the bubble behaviors as well as the heat flux appear the similar characteristics with that at the plate heater surface. Moreover, the critical wavelength is approximately two times of the bubble departure diameter in the present cryogenic liquid boiling events, and the parameters, including liquid–vapor density difference, surface tension, and gas thermal conductivity, could affect the boiling heat flux significantly. In addition, under 0.03g condition, the bubble departure diameter could reach 27 mm and the boiling heat flux decreases to 800 W/m2, which are significantly different from that in normal gravity. In general, the present CFD model could execute a film boiling study accurately, and a series of detailed results on the bubble behaviors as well as the heat flux could be revealed.