Abstract

Boiling heat transfer is used in industrial processes, such as heat exchangers, nuclear reactors, and high-powered electronics. There is a need to generate effective heat dissipation techniques to increase the operation limits of these technologies. To enhance heat dissipation with boiling flows, it is important to study boiling phenomena from a fundamental perspective to identify the relation between the fluid and heat transfer behavior near the interface during bubble growth. Boiling simulations have been used as a tool to visualize and quantify the heat transfer mechanisms near the interface. However, challenges exist in modeling bubble growth with a sharp interface and with a saturation condition. In addition, 3D modeling of bubble growth leads to simulations with millions of computational cells and requires expensive computer resources with multicore capabilities. The present work proposes methods to perform high-fidelity and time-saving 3D simulations of nucleate boiling. These methods account for 3D sharp interface and thermal conditions of saturation temperature while considering adaptive mesh refinement. The adaptive mesh refinement creates small cells only at critical regions near the interface and coarse cells at regions far from the bubble edge. User defined functions (UDFs) were developed to customize the software Ansys-Fluent to preserve the interface sharpness, maintain saturation temperature conditions, and perform effective adaptive mesh refinement in 3D. UDFs preserve the interface sharpness by declaring mass transfer only at interface-cells located next to vapor-cells. To impose a condition of saturation temperature, a UDF interpolates the temperature of the interface-cell based on the saturation temperature and the interface curvature. Adaptive mesh refinement is accomplished by a UDF that identifies the cells near the contact line and liquid-vapor interface and applies the adaptive mesh refinement algorithms only at the identified cells. Additionally, an external microlayer model was implemented to account for submicron evaporation at the contact line. Validating the approach considered spherical bubble growth in superheated liquid, and the observed agreement between theoretical and simulation bubble growth rates within 10%. Simulations results of bubble growth over a heated surface revealed an influence region of 3 times the bubble departure diameter. The simulation captured temperature distribution near the contact line showing a meniscus with high temperature gradients. Moreover, results revealed a reduction of 75 hours of computational time with adaptive mesh compared with the uniform computational mesh. The present work demonstrates the use of customized Ansys-Fluent in performing 3D numerical simulations of nucleate boiling. The developed simulation approach is a reliable and effective tool to investigate 3D boiling phenomena by accurately capturing the thermal and fluid dynamic interfacial vapor-liquid interaction and reducing the computational time.

Library of Congress Subject Headings

Ebullition--Mathematical models; Heat--Transmission--Mathematical models; Nucleate boiling--Mathematical models; Multiphase flow--Mathematical models; Bubbles--Mathematical models

Publication Date

8-7-2023

Document Type

Thesis

Student Type

Graduate

Degree Name

Mechanical Engineering (MS)

Department, Program, or Center

Mechanical Engineering (KGCOE)

Advisor

Isaac Perez-Raya

Advisor/Committee Member

Michael Schertzer

Advisor/Committee Member

Howard Tu

Campus

RIT – Main Campus

Plan Codes

MECE-MS

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