Subcooled Boiling Heat Transfer Using a Semi-mechanistic Wall Boiling Model

Modern cooling system design is challenging because of increasingly stringent requirements, such as high compactness, reduced cost, and limited space envelopes. Providing a subcooled boiling flow in thermally highly loaded regions became popular compared to pure single-phase convection as it significantly enhances the heat transfer rate. Though nucleate boiling increases the cooling effect, the subsequent film boiling decreases the heat transfer drastically. Therefore, it is essential to understand the boiling characteristics of a given cooling system. Experimental investigations for boiling are highly challenging, and numerical simulations provide a comparably more straightforward and fast solution. In the present work, a semi-mechanistic wall boiling model implemented in Ansys Fluent software captures the complex phenomena associated with the two-phase flow heat transfer. Heat transfer augmentation at the wall is modeled by empirical correlations proposed by Chen et al. The semi-mechanistic boiling model is implemented within the single momentum mixture multiphase model. The wall heat flux is partitioned according to Kutateladze following an asymptotic power law. Nucleate boiling heat flux contribution is modeled following Foster and Zuber. The new implementation is validated using data from experiments of water flowing over a heated plate in a channel. A sensitivity study is conducted for the different controlling parameters for the semi-mechanistic boiling model, such as superposition constant, evaporation frequency, and optimum settings captured. A mesh sensitivity study is also conducted. The numerical results show a reasonable match with the experimental with a maximum error of about 10% for a few data points at high temperatures.