화학공학소재연구정보센터
International Journal of Heat and Mass Transfer, Vol.81, 750-759, 2015
On heat transfer and evaporation characteristics in the growth process of a bubble with microlayer structure during nucleate boiling
We have previously observed and experimentally measured a microlayer formed beneath a growing bubble during nucleate pool boiling. The initial microlayer thickness was of micrometer order and increased linearly with distance from the bubble inception site. The quantitative degree of contribution of the microlayer evaporation to bubble growth was still not elucidated, although a large number of experimental studies have been conducted on the distribution and evaporation characteristics of the microlayer. To clarify the heat transfer characteristics, especially the contribution of microlayer evaporation in nucleate pool boiling, numerical simulations are performed here for two phase vapor-liquid flow induced by the growth of a single bubble using the volume of fluid method. Furthermore, a special model is proposed to combine the microlayer and bulk liquid regions, the scales of which are extremely different in the simulations. The microlayer was neglected in the volume fraction calculation, while the evaporation from the microlayer was included by applying the source terms of the basic equations for the presence of a virtual microlayer. Similar tendencies were observed between the calculated and experimental results on the variations in the microlayer radius and bubble volume. The proportion of microlayer evaporation to total bubble volume was generally in agreement with the previous results, and the ratio of microlayer evaporation to the change in the total bubble volume was approximately 40 percent. (C) 2014 Elsevier Ltd. All rights reserved.