Development of numerical models for conjugate heat transfer, phase change, and non-condensable gas effects: Validation against single bubble growth in microgravity

Nucleate boiling and the underlying growth of single bubbles have been subjects of research for many years. Despite this, the process remains to be completely understood. Numerical simulations of this process aim to contribute to further understanding. However, numerical simulations of the relevant energy and fluid transport processes, including all relevant features such as multiregion, multiphase, and phase change capabilities, are very complex and sensitive to parameters. In this work, we present crucial models for the numerical simulation of single bubble growth in microgravity. These models concern the heat and mass transfer in the vicinity of the three-phase contact line and thus have a general applicability to bubbles and droplets in contact with a solid wall. We validate these models and the full numerical solver against a high-quality experiment on the International Space Station, the Multiscale Boiling Experiment (RUBI). The validation process reveals the presence of non-condensable gases in the experiment. We demonstrate that even small concentrations of non-condensable gases dissolved in the liquid significantly impact single bubble growth, particularly in the subcooled boiling regime with concurrent evaporation and condensation at the vapor bubble. We introduce a successful workaround for the effect of non-condensable gases on the local saturation temperature. For the first time, a relatively extensive parameter range from the RUBI experiment is numerically simulated. Satisfactory agreement with all cases is achieved, and the heat transfer paths from the heated solid to the liquid, through the process of single bubble growth, are evaluated.