Investigation of Dissolved Air Effects on Subcooled Flow Boiling Heat Transfer for Boiling Two-Phase Flow Experiment onboard the ISS
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Boiling is a very efficient mode of heat transfer due to phase change, whereas the gravity effects on the two-phase flow phenomena have not been clarified in detail. To clarify these effects, boiling two-phase flow experiments onboard the Japanese Experiment Module “KIBO” are proposed as an official JAXA project and this project concerns the effects of dissolved air on flow boiling heat transfer, which remain to be clarified when using an inner diameter 4mm tube. This research involved conducting subcooled flow boiling experiments using various different dissolved air concentrations in the Perfluorohexane (PFH) in order to clarify its effects on flow boiling heat transfer through a tube with an inner diameter of 4mm, the following parameters were calculated and discussed: excess temperature, boiling curve and condensing heat transfer. Consequently, the dissolved air was shown to affect boiling characteristics. In particular, dissolved air significantly affected the boiling curve in the low heat flux region, and the boiling curve was continuously decreased with increasing the effective heat flux for both G=100 and G=300 kg/m2s respectively. Also, dissolved air significantly affect the onset of boiling. These effects include decreasing the cluster radius required to form a nucleus. Furthermore, despite the different dissolved air concentrations, none of the difference among the boiling curves in the high heat flux region due to fully developed flow regime, where a boiling curve was calculated by the S.G. Kandlikar proposed correlation effectively matched the experimental results in the fluid-surface parameter Ffl=1.7 usage case.