Progress towards prediction of subcooled boiling phenomena: Insight on isolated-bubble evaporation and condensation from numerical simulations

Boiling is a highly effective heat transfer mode found in industrial scenarios. At present, no comprehensive, complete understanding of the phenomenon has emerged. Advances in interface resolving modelling techniques for two-phase flows provide an opportunity to investigate the fundamental processes in boiling phenomena by capturing vapour bubble behaviour at the microscopic scale. A methodology for the modelling of phase change phenomena in two-phase flow, based on interface capturing simulation and the mechanistic modelling of phase change at the vapour-liquid interface, is verified against a set of evaporation and condensation problems, demonstrating good agreement with the analytical solutions in each case. The model is evaluated against two experimental test cases of isolated vapour bubbles under zero-gravity conditions. Modelling of the growth of a vapour bubble in superheated ethanol is presented, as well as a novel case of the condensation of a spherical vapour bubble surrounded by subcooled water. Good agreement with experimental results is observed in both cases, demonstrating the applicability of the approach to the modelling of evaporation and condensation phenomena under conditions of high rates of phase change and large density ratios, such as those found in real fluids of industrial interest. The current methodology is also in broad agreement with reference numerical solutions and experimental data for vapour bubble condensation under gravity. The successful validation of the simulation methodology against the experimental test cases strengthens confidence in its applicability to the modelling of subcooled flow boiling in future work. The primary interest in this work is the assessment of a mechanistic and computationally efficient modelling approach to investigate single bubble behaviour under subcooled flow boiling conditions relevant to improving the predictive modelling capabilities for Pressurised Water Reactor (PWR) applications.