Numerical simulation of the effect of micro-layer slopes on bubble growth and heat transfer during nucleate pool boiling

Abstract

In conducted water nucleate pool boiling experiments, the initial micro-layer slopes exhibited fluctuations ranging from 0.04 to 0.05. Considering that the mechanisms by which the micro-layer slopes affect bubble growth have not been well elucidated, numerical simulations of the bubble growth process under different initial micro-layer slopes were performed in this study. The interface dynamics were accurately captured by the coupled LS and VOF methods (CLSVOF). The phase-change model, coupled with smear methods, was developed to simulate bubble growth. Furthermore, the models of initial micro-layer thickness and thermal resistance were developed to investigate the heat-transfer mechanisms within the micro-layer. The coupling methods and proposed models were then validated against measurements from pool boiling experiments. The results demonstrate that the micro-layer slopes (C_slope) increase in a linear relationship with the time after nucleation since the extension of the dry-spot. In addition, the thermal conductivity resistance and the evaporation resistance are found to be of the same order of magnitude, but show opposite trends with respect to the radius. As C_slope increases from 3.79e-3 to 5.13e-3, the bubble equivalent radius and height increase by 7.8 % and 5.3 % with bubble departure, respectively. When the initial C_slope is 4.46e-3, the micro-layer contributes 21.6 % to the bubble growth, and its evaporation time fraction in the bubble growth time increases from 0.56 to 0.68 with C_slope increasing from 3.79e-3 to 5.13e-3. This study contributes to a deeper understanding of the role of the micro-layer in bubble growth dynamics.