Development of Boiling and Two-phase Flow Experiments on Board ISS: Dissolved Air Effects on Subcooled Flow Boiling Characteristics

Abstract

Boiling is a very efficient mode of heat transfer because of the phase change involved and is a promising method for certain thermal management systems. However, the effects of gravity on two-phase flow phenomena in such systems have not been clarified in detail. To clarify these effects, boiling two-phase flow experiments onboard the Japanese Experiment Module “KIBO” have been proposed as an official Japanese Aerospace Exploration Agency project; this project concerns the effects of dissolved air on flow boiling heat transfer, which remains to be clarified in the case of a tube with an inner diameter of 4 mm. The abovementioned study involved conducting subcooled flow boiling experiments using various concentrations of dissolved air in perfluorohexane to clarify its effects on flow boiling heat transfer through a tube with an inner diameter of 4 mm. The excess temperature, boiling curve, and condensing heat transfer were determined and discussed. Consequently, dissolved air was demonstrated to affect boiling characteristics. In particular, dissolved air significantly affected the boiling curve in the low-heat-flux region: the boiling curve continuously decreased with increasing effective heat flux for mass fluxes of both G = 100 and G = 300 kg/m2s. Moreover, dissolved air substantially affected the onset of boiling. These effects include decreasing the cluster radius required to form a nucleus. Furthermore, irrespective of the dissolved air concentration, no difference was observed among the boiling curves in the high-heat-flux region because of the fully developed flow regime, where a boiling curve determined according to the correlation proposed by Kandlikar effectively matched the experimental results in the case of a fluid-surface parameter F(sub fl) of 1.7. This paper includes the contents of the proceedings of the 44th International Conference on Environmental Systems.