On the effect of substrate thermal conductivity and nano-region on subcooled nucleate boiling in zero-gravity conditions

Prediction of heat transfer in configurations of nucleate boiling is a topic that still require new studies for a better understanding of the overall process, which involves multiscale interactions between different physical phenomena. In particular, for space applications, that imply microgravity conditions, experimental data are limited, and numerical simulations offer an efficient alternative to investigate nucleate boiling in such conditions. In the present work, the impact of the nano-region heat flux at the contact line on the equivalent bubble radius is thoroughly studied by means of numerical simulations. A parametric study is carried out by varying several physical variables. From these numerical data, the strong impact of the nano-region heat flux on the overall bubble growth is highlighted, as well as the strong coupling between the nano-region and the thermal conductivity ratio between the liquid and the solid substrate. Finally, a correlation on the bubble size at equilibrium state is drawn, and the heat transfer coefficient is characterized. This enables to show the heat transfer enhancement related to the nano-region. • Direct Numerical Simulations of nucleate boiling in subcooled conditions in microgravity are carried out. • The impact of the nano-region at the contact line over the bubble equilibrium is analyzed. • The ratio between the substrate and the fluid thermal conductivities is shown to have a major impact on the nano-region and on the bubble growth. • A parametric study is carried out and a model for the bubble equilibrium accounting for the substrate conductivity is proposed.