Three-Dimensional Numerical Investigation of Bubbles Growing and Merging in Superheated Nucleate Boiling

Abstract

To enhance heat dissipation with boiling flows, simulations of bubble merging need to be examined from a fundamental perspective with a focus on the mechanisms near the interface. The current study develops a model for 3D multiphase boiling flows using the volume-of-fluid (VOF) interface tracking method by customizing ansys-fluent. The software is customized to incorporate sharp interface modeling and localized adaptive mesh refinement (AMR) for improved interface tracking. The simulation focuses on the heat transfer and fluid transport mechanisms during bubble merging in water at atmospheric conditions. The developed approach can capture 3D bubble growth and merging dynamics for both two and three bubbles cases at 5 K wall superheat. Detailed visualization and quantification of the heat transfer mechanisms near the interface are explored for the three bubble merger case. The influence region, quantified by the wall shear stress, is 3.1 times the bubble diameter at departure. Peaks in the local heat transfer coefficient (HTC) due to trapped liquid when bubbles are merging were detected. An average heat transfer coefficient of 13,150 W/m2 K was observed near departure. Total computational time required to achieve bubble departure is quantified; the simulation with adaptive mesh refinement of two bubbles required 86 h, and three bubbles required 103 h on a 64-core machine.