Single bubble dynamics under microgravity conditions in the presence of dissolved gas in the liquid

Single bubble dynamics during nucleate pool boiling was experimentally investigated as part of the Nucleate Pool Boiling Experiment (NPBX) on the International Space Station (ISS) where the gravity level was of the order of 10(-7) g(e). The effects of variations in pressures, liquid and surface temperatures, and dissolved gas content on bubble dynamics were studied. Two dimensional axisymmetric numerical computations that account for time-varying system pressures and wall temperatures as well as the presence of dissolved gas in the liquid were carried out to simulate the experimental conditions. Simulated growth and wall heat transfer rates are in good agreement with the experimental results. The simulations show that the noncondensable gas accumulates at the top of the bubble as it grows, thus reducing the effect of subcooling. Although the non-uniform accumulation of gas also induces capillary flow around the bubble due to the varying surface tension force along the liquid-vapor interface, it is shown that this variation is very small and the resulting capillary flow has only a second order effect on the flow field. Numerical simulations predict single bubble departure diameters larger than what the boiling chamber would allow for. The results of the experiments confirmed that single bubbles did not depart and remained in contact with the surface independent of system parameters. (C) 2014 Elsevier Ltd. All rights reserved.