INFLUENCE OF UNSTEADY CONDITIONS ON HEAT EXCHANGE DURING A SHARPY TRANSITION TO FILM BOILING

Abstract

Boiling is one of the main physical processes, which that take place in heat exchange equipment designed for various purposes. The problem of removing large thermal loads from the heated surface is important for nuclear energy, chemical industry, metallurgy, electronics and other areas where intense heat is released. Boiling processes in process equipment perform important protective functions and can control its effectiveness. According to the boiling curve, with increasing temperature power, the flow passes through five regions, starting from the single-phase region of free convection and ending with the region of developed film boiling. The purpose of this article is an analytical study of heat transfer at spontaneous transition to the film boiling (explosive type of boiling), taking into account the unsteady nature of this process. In order to achieve the aim of this research, two analytical approaches were used, namely, the symmetry method and the Laplace method. As a result of mathematical transformations, expressions for the nonstationary temperature distribution and the Nusselt number are obtained. The obtained expressions make it possible to analyze the dynamics of non-stationary heat exchange processes. The results of analytical and numerical modeling were also compared. It was found that the results of the self-similar solution have a better comparison with numerical data compared to the results according to the Laplace method.