Abstract
Film boiling is characterized by the existence of a continuous vapor layer between a heated solid surface and a liquid layer. The evolution of the vapor-liquid interface during film boiling on a horizontal surface is determined by Rayleigh-Taylor instability. To predict the heat transfer rates in film boiling, many studies have been reported in literature. Early attempts to model this phenomenon had used semi-empirical correlations. Recent work on simulation of the evolution of vapor-liquid interface without assuming any empirical vapor-liquid interface shape and by assuming the solid surface temperature to be constant has shown that the convective heat transfer coefficients, associated with the interface, vary both spatially and temporally. Consequently, the assumption of constant solid surface temperature in film boiling is not strictly valid.
In this work, saturated film boiling on a horizontal surface is simulated numerically. Finite difference method is used to simultaneously solve the equations governing conservation of mass, momentum and energy in the vapor and liquid layers. The equations for the two fluid phases are coupled through matching of normal and tangential stresses and continuity of mass and energy at the liquid vapor interface. Second order projection method is used along with numerical grid generation to construct a grid system which is aligned with the vapor-liquid interface. The heat conduction equation is solved separately in the solid, to obtain the wall temperature.
The results show that for most surfaces little coupling takes place between thermal response of the solid substrate and hydrodynamics of evolution of the interface. However, for thin plate heaters of relatively low thermal conductivity materials, the thermal response of the solid can significantly affect the hydrodynamics of the interface and in turn the local heat transfer.
