Nucleate Pool Boiling in Microgravity

Abstract

Nucleate pool boiling is a daily phenomenon transferring effectively high heat flux. It is, however, a very complex and illusive process because of the interrelation of numerous factors and effects as the nucleate process, the growth of the bubbles, the interaction between the heater’s surface with liquid and vapor, the evaporation process at the liquidvapor interface, and the transport process of vapour and hot liquid away from the heater’s surface. Among many sub-processes in boiling phenomenon, gravity can be involved and play much important roles, even enshroud the real mechanism underlying the phenomenon. Our present knowledge on nucleate pool boiling phenomenon has been built with the aid of numerous meticulous experiments in normal gravity environment on the ground where gravity is a dominant factor. Gravity strongly affects boiling phenomenon by creating forces in the systems that drive motions, shape boundaries, and compress fluids. Furthermore, the presence of gravity can mask effects that ever present but comparatively small. Advances in the understanding of boiling phenomenon have been greatly hindered by masking effect of gravity. Microgravity experiments offer a unique opportunity to study the complex interactions without external forces, such as buoyancy, which can affect the bubble dynamics and the related heat transfer. Furthermore, they can also provide a means to study the actual influence of gravity on the boiling. On the other hand, since many potential applications exist in space and in planetary neighbours due to its high efficiency in heat transfer, pool boiling in microgravity has become an increasing significant subject for investigation. Therefore, the microgravity researches will be conductive to revealing of the mechanism underlying the phenomenon, and then developing of more mechanistic models for the related applications both on Earth and in space. Research on boiling heat transfer in microgravity has a history of more than 50 years with a short pause in the 1970s and has been advanced with the development of various microgravity facilities and with increased experimental opportunities, especially in the last two decades. On the progress in this field, many comprehensive reviews and monographs are available now. Among many others, Straub (2001), Di Marco (2003), Kim (2003), and Ohta (2003a, b) summarized the experimental and theoretical works all over the world, which provided the status of this field at the beginning of our research. In the past decade, two research projects on nucleate pool boiling in microgravity have been conducted aboard the Chinese recoverable satellites by our group in the National