Subcooled pool film boiling heat transfer from sphere: experiment and modelling

Abstract

Abstract Experiments were conducted to study heat and mass transfer at film boiling on a metal sphere immersed into subcooled liquid. A model was elaborated to calculate the thickness of the vapor film and the speed of vapor flow in the film. The model also includes a detachment model for vapor bubbles lifting off the surface of the film. The model shows agreement with the results of the pool film boiling experiments with various liquids as well as for Leidenfrost drops. Quite reasonable agreement is also observed for the frequency of bubble detachment in saturated liquid. While processing the experimental data the calculations showed that the heat transfer into the bulk of liquid from vapor-liquid boundary is much more intense than expected. The effect is not determined solely by natural convection within the liquid as the heat flows determined by natural convection are two orders of magnitude less than those obtained. An attempt was made to determine the consequent heat transfer coefficient based upon experimental data for the frequency of bubble detachment from off the vapor film around the sphere. The abnormally high heat transfer detected could be important in practical applications.