Award Date

12-1-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Committee Member

William Culbreth

Second Committee Member

Hui Zhao

Third Committee Member

Yi-Tung Chen

Fourth Committee Member

Brendan O'Toole

Fifth Committee Member

David James

Number of Pages

298

Abstract

Heat pipes are used to transfer heat through phase change in a liquid/vapor contained in a metal tube. They are passive devices that require no pumps to circulate the fluid and can transfer heat far more efficiently than a solid copper rod of the same diameter. They are commonly used in laptop computers where copper heat pipes filled with water take heat away from the CPU and transfer the heat to air through a heat exchanger. Heat pipes were also used in the Kilopower nuclear reactor where higher temperatures required sodium as the working fluid with stainless steel tubes. Computer models of heat pipes are complicated due to the two-phase flow within the pipe and one- or two-dimensional flow is typically modeled. One possible failure mode within a nuclear reactor that uses heat pipes to remove heat produced by fission involves possible failure of a single heat pipe. This could result in high temperatures within the reactor fuel at the location of the failure and induce failure in adjacent heat pipes, resulting in catastrophic overheating of the reactor. This "cascade failure" must be computationally modeled if heat pipes are to be used in future nuclear reactor designs and requires a full three-dimensional code to capture the transient two-phase flow and heat transfer within a heat pipe. The code must also be capable of coupling to existing reactor heat generation and neutronics codes, such as Abaqus and MCNP. For this work, a new computer code, Blinky, was developed to analyze heat pipes. The results from Blinky were validated through comparison with the SAFE-30 sodium heat pipe experiment conducted at the Los Alamos National Laboratory. Additional results were obtained from Blinky to model asymmetric heating of a heat pipe because this is expected during cascade failure within a reactor. The effect of asymmetric heating affects the temperature distribution near the evaporator section of a heat pipe, but the asymmetry dissipates as the fluid within the vapor core reaches the condenser end of the pipe. Blinky serves as the first 3D transient computer model of a heat pipe for two-phase flow and can be coupled to other reactor codes to model reactor performance and accident scenarios.

Keywords

cascade failure; fluid mechanics; heat pipe; heat transfer; MacCormack's Method; nuclear reactor

Disciplines

Aerodynamics and Fluid Mechanics | Mechanical Engineering | Thermodynamics

File Format

pdf

File Size

4900 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

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