Steady and Unsteady Complex Heat Transfer in Optically Thick Medium During Film Boiling

Abstract

The paper presents the results of a study of radiative-convective heat transfer at film boiling of a liquid on a vertical heated plate. Both a steady-state problem of heat transfer and a transient problem were considered. The latter describes the instantaneous (flash) boiling up of a liquid on a heated surface. The novelty of the present study is the use of the optically thick medium approximation in a mathematical model when studying the process of radiation-convective heat transfer in the film boiling regime. For the first time, radiation heat transfer was considered for an optically thick medium. An analytical solution of the steady-state problems is obtained for boundary conditions involving a constant wall temperature and a constant wall heat flux. The effect of radiation and the temperature difference between the wall and liquid on the temperature profiles in the vapor phase is shown. The effect of radiation becomes more pronounced with an increase in the temperature difference between the wall and the liquid. As a result of solving the transient problem, the variation in time of the temperature profile and the heat transfer coefficient in the vapor film were obtained. The effect of radiation (Stark number) on the heat transfer coefficients is elucidated. An increase in the radiative heat flux leads to an increase in the Nusselt number, as well as the time it takes for the heat transfer process to reach a steady-state regime.