Numerical simulation on the heat transfer characteristics during the bubble growth considering microlayer evaporation in nucleate boiling

Abstract

In the previous studies, it was confirmed that there is a microlayer that forms between a growing bubble and the heat transfer surface in nucleate pooling boiling. The initial microlayer thickness was found to increase linearly with distance from the bubble inception site. Although a large amount of heat transport results from the evaporation of microlayer during the growth process of bubble, the quantitative degree of contribution of microlayer evaporation was not elucidated. In this study, numerical simulation was carried out on the two phase vapor-liquid flow induced by the growth of a single bubble in nucleate boiling by using the VOF (Volume of Fluid) method. The objective of this study is to clarify the heat transfer characteristics, especially the effect of evaporation of microlayer in nucleate pool boiling. A special model for simulating the microlayer evaporation was proposed, in which the microlayer was not considered in the calculation of flow field while its amount of evaporation was considered by applying the source term of the basic equations as an existence of virtual microlayer. Similar tendencies were shown between the calculation and experimental results on the variations of microlayer radius and bubble volume. The proportion of the amount of evaporation from microlayer to the volume of bubble is generally agreed with the previous results, which showed the ratio of microlayer evaporation to the total vapor volume change was approximately 40 percent.