MODELING OF BOILING HEAT TRANSFER PROCESS

Abstract

Boiling has been studied extensively during the last half of the 2Cih century. The impetus for these studies comes not only from the fact that boiling allows accommodation of very high heat fluxes at relatively low wall superheats but also the process very complex and its understanding imposes significant challenges. Many correlations and semi mechanistic models have been developed for various modes of boiling. However, due to the complexity involved in modeling continuously evolving vapor-liquid interfaces, unrealistic assumptions are often made in developing various models. With the advances of recent years in the area of computational science and engineering, it is now possible to solve, completely the conservation equation of mass, momentum, and energy for the liquid and vapor phases simultaneously. Nucleate boiling is a very efficient mode of heat transfer. Some of the applications of boiling heat transfer include Electronic cooling, materials processing, heating and refrigeration process, water-cooled nuclear reactors and power generation. In this thesis, steady state mathematical models have been developed for pool boiling: heat transfer process. The effect of different parameters bubble growth, departure, various forces acting during the growth of a bubble, temperature profiles of macro layer at high heat fluxes has been discussed. These models comprise the set of partial differential equations and also non linear algebraic equations. The set of non linear algebraic equations are solved by Runge-Kutta Method, and the set of partial differential equations are solved by using Laplace transformation technique. From the analytical model results, it is concluded that evaporation of micro layers contributed significantly to the growth of bubbles. The results show that the present bubble growth model is in good agreement with the experimental data of Cole et al, Forster & Zuber, and Scriven etc. The predictions of the analysis bear ± (15 — 25%) to the results of various experimental models with various fluids.