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Document Type

Thesis - University Access Only

Award Date

2015

Degree Name

Master of Science (MS)

Department / School

Mechanical Engineering

First Advisor

Gregory Michna

Abstract

Microelectronic devices require relatively low and uniform temperatures for maximum reliability, and oscillating heat pipes (OHPs) may prove to be extremely well suited to this application. A 20-turn OHP was constructed from copper tubing with inner and outer diameters of 1.65 mm and 3.58 mm, respectively, which further divided into evaporator, adiabatic and condenser each of equal length (85 mm). An electric resistance heater was fitted to the evaporator section, and the condenser section was immersed in a temperature controlled water bath. Insulation surrounded all of the OHP outside of condenser bath so as to minimize ambient heat loss. The effect of various OHP operating parameters on the heat transfer performance and oscillating characters, such as working fluid (deionized water, methanol and acetone), inclination angle (vertical, 45 and horizontal), fill ratio (50%, 60%, 70%, and 80%), and heat load (10 W, 20 W, and 30 W) were investigated. All working fluids performed best at 30 W. Water, in most cases, did not have any overshoot and oscillated well only in vertical at 80% fill ratio. However, methanol and acetone performed best (lowest thermal resistance) at 50% fill ratio irrespective of inclination angle (except at 80% in horizontal). Low power input (10 W) was not sufficient to initiate fluid oscillations when fill ratio was high, and start-up temperature overshoot occurred for both methanol and acetone at different conditions. Methanol, in general, withstood overshoot either at low power and low fill ratio or xiii high power and high fill ratio and did not have any overshoot at 50% or 60% fill ratio when power was at 30 W. Acetone had overshoot only at high heat load irrespective of fill ratio. Overshoot did not occur with acetone for 50%, 60% and 70% fill ratios, especially in vertical when power 10 W and 20 W was given. Start-up behavior was somewhat unpredictable, with repeated test runs showing different results despite identical operating parameters. Water was found to be the best choice for extremely high heat load application over methanol and acetone. With the progress achieved so far, choice of working fluid, its fill ratio and the application of heat can allow for a significant improvement in both start up and overall thermal performance of a given OHP, although some nuances of the device operation still remain unexplored and this information could be used by a designer to optimize an OHP system to reduce the risk of start-up temperature overshoot before the system begins cooling.

Library of Congress Subject Headings

Heat pipes
Heat--Transmission
Oscillations

Description

Includes bibliographical references (pages 66-69)

Format

application/pdf

Number of Pages

82

Publisher

South Dakota State University

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Rights Statement

In Copyright