Development of Boiling and Two-Phase Flow Experiments on Board ISS: Void Fraction Characteristics in the Observation Section just at the Downstream of the Heating Section

Abstract

An observation section has been developed for the detail observation of gas-liquid interfacial structure in boiling and two-phase flow experiments onboard International Space Station. A stereoscopic photography method was applied for 3D measurement using one high frame-rate camera, and the accuracy in measurement of liquid film thickness was evaluated. It was confirmed in the preliminary experiment that liquid film thickness could be measured from images within plus or minus 5 % accuracy. Moreover, to evaluate the development of the flow structure from the exit of the heating section, flow observation and cross-sectional average void fraction measurement was performed at four locations at the downstream of the heating section. As the result, under the condition where slug flow was observed in the developed region, the fluctuation band of void fraction was small just at downstream of the exit of the heating section due to many small bubbles in liquid slugs. Under the conditions where annular flow was observed in the developed region, annular flow had been already formed at the exit, and then liquid film thickness became thicker.