Date of Award

2017

Document Type

Open Access Dissertation

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Chen Li

Abstract

Heat pipes with broad applications in thermal systems have the ability to provide effective heat transport with minimal losses in over reasonable distances due to their passive nature. Their exceptional flexibility, simple fabrication, and easy control, not to mention, all without any external pumping power make them especially attractive in electronics cooling. Heat pipe development is motivated to overcome the need to presumably manage thermal dissipation in progressively compressed and higher-density microelectronic components, while preserving the components temperatures to specification.

Computation of flow and heat transfer in a heat pipe is complicated by the strong coupling among the velocity, pressure and temperature fields with phase change at the interface between the vapor and wick. Not to mention, the small size and high aspect ratio of heat pipes brings their own challenges to the table. In this dissertation, a robust numerical scheme is employed and developed to investigate transient and steady-state operation of cylindrical heat pipes with hybrid wick structure for high heat fluxes based on an incompressible flow model. Despite many existing works, this is accomplished assuming as few assumptions as possible. The fundamental formulation of heat pipe is developed in such a way to properly take into account the change in the system pressure based on mass depletion\addition in the vapor core. The numerical sensitivity of the solution procedure on phase change at the liquid-vapor interface are recognized and effectively handled by reformulating the mathematical equations governing the phase change. Hybrid wick structure of the heat pipe is modeled accurately to further investigate thermal and vicious novel wick structures.

A fully implicit, axisymmetric sequential finite volume method is devised in conjunction with the SIMPLE algorithm to solve the governing equations. ANSYS Fluent software with the power of User Defined Functions and User Defined Scalars is used to apply the numerical procedure in coupled system and standard levels. This two-dimensional simulation can solve for symmetrical cylindrical and flat heat pipes, as well as three-dimensional flat and non-symmetrical cylindrical heat pipes.

Using this powerful and reliable solver, a comprehensive parameter study is carried out to study the importance and effects of thermal properties, viscous properties, charging ratio, design parameter and the assumptions.

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