Session: 7.7.1 - Numerical Methods for Multiphase Flows I

Paper Number: 158691

158691 - Modeling of Bubble Merging With Localized Adaptive Mesh Refinement in Customized Ansys-Fluent 

Abstract: 

In boiling heat transfer, understanding the behavior of bubble dynamics is essential for improving thermal systems. Generating effective heat dissipation techniques to increase the operation limits of heat emitting thermal systems like heat exchangers, boilers and electronic technologies is essential for improving capability for heat dissipation in industry. To enhance heat dissipation with boiling flows, it is important to study boiling phenomena from a fundamental perspective as a means of identifying the relation between the fluid and heat transfer behavior near the interface during bubble growth. This involves analyzing merging dynamics of bubbles on a heated surface. A key aspect of this is calculation the heat transfer coefficient (HTC) and influence region, which significantly influences bubble effectiveness to dissipate heat. This study aims to analyze and compare the impact bubble growth, merging and departing a heated surface. A model for 3D multiphase boiling flows using the VOF interface tracking method in Ansys-Fluent is developed in the current study. The simulation focuses on the heat transfer and fluid transport mechanisms during bubble merging. The developed approach is able to observe 3D bubble growth and merging on a heated surface under super-heated conditions and is able to visualize and quantify the heat transfer mechanisms near the interface. Total computational time and required computer resources to achieve bubble departure of is quantified and compared against the results of one, two and three bubble nucleation cases. The departure times of each of the bubble merger cases was analyzed against cases of single bubble merger results. The simulation identified a 10.8 mm the influence region for the three bubble merger case in terms of the local variation of the wall shear stress. This significant influence on the liquid surrounding the bubble helps better fluid mixing and suppresses the thermal boundary layer. The fluid mixing improves the heat transfer as colder fluid moves towards the heated surface. An average heat transfer coefficient of 13,150  near bubble departure was observed for the three bubble merger. The findings suggest that the simulation provides accurate representation of boiling heat transfer and bubble dynamics in the single, two and three bubble merging cases. This analysis provides insight into the modeling of boiling heat transfer, emphasizing the importance of accurate modeling of the thermal conditions of the bubble. The results could guide future improvements in the design and optimization of boiling heat transfer equipment, where accurate HTC predictions are critical for enhancing efficiency and performance.

Presenting Author: Winston James Rochester Institute of Technology

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