Numerical investigation of nucleate boiling heat transfer on thin substrates

Abstract

The objective of this paper is to define the guidelines for the design of new boiling test sections with a large number of artificial nucleation sites during nucleate boiling for thin substrates horizontally immersed in a saturated liquid with artificial cavities located on the upper surface. The findings of numerical simulations of pool boiling heat transfer for a single bubble and for a large number of nucleation sites based on the analysis of experimental cases were analysed. Dedicated test sections were used in experiments for the study of boiling mechanisms and interactions between active sites so that the numerical models representing the physics of the problem could be improved. The hybrid nature of the code used in this study, combining the complete solution of the three-dimensional time-dependent energy equation in the solid substrate with semi-empirical models representing the physical phenomena occurring in the liquid side, in a simplified way, allows a large number of simulations in a reasonable computational time. The present paper focuses in the first part on the capability of the model to reproduce the experimental results for various conditions, while in the second part, the results for a large number of nucleation sites are analysed. Regarding the single bubble growth, two series of simulations will be presented in this paper: the first one analyses the mechanisms of nucleate boiling on a silicon substrate immersed in the dielectric fluid FC-72. The second series studies the behaviour of bubbles on metallic substrates, platinum and titanium, in saturated water. In the last section, the effect of the position of a site during simulations of a large population of sites (of the order of 100) on the waiting time, growth time, type and occurrence of coalescence and the thermal characteristics is presented. © 2014 Elsevier Ltd. All rights reserved.