Date of Award:

2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Mechanical and Aerospace Engineering

Advisor/Chair:

Heng Ban

Co-Advisor/Chair:

Nicholas Roberts

Third Advisor:

Thomas Fronk

Abstract

Many materials are made up of small crystals, or grains. Grain boundaries are the interfaces between two grains and affect the flow of heat through the material. These interfaces serve to interfere with the energy carriers by scattering or disrupting them. Because of the negative effect these interfaces have on these energy carriers, they inhibit heat flow and act as thermal resistors. The thermal boundary resistance between two grains of the same material is sometimes referred to as the Kapitza resistance, although this term is also used to describe the thermal resistance between solid/solid interfaces of different materials or solid/liquid interfaces. A better understanding of the heat transport process on a micro-scale is especially relevant to nuclear energy applications. Nuclear fuels are polycrystalline materials that experience large heat differences over small distances. An improved understanding of these grain boundaries and the role they play in transferring heat can help better predict nuclear fuel performance and improve nuclear reactor efficiency and safety.

The study of the thermal resistance across crystal interfaces and their potential influence on nuclear fuels is a topic that has received relatively little attention. While the thermal resistance across a single grain boundary is rather small, the total resistance generated from many grain boundaries can have a big impact on the material. Smaller grains mean there are more interfaces, which will result in a lower overall thermal conductivity.

For this study, Kapitza resistance across individual grain boundaries was measured using a laser-based measurement technique. The sample material was Cerium Oxide. It was used because of its similar properties to Uranium Oxide, which is a popular material used in nuclear fuel. The average interfacial thermal resistance measured at room temperature in this thesis study was 9.88∙10-9 𝑚2𝐾/𝑊. The average measured value fit in an accepted range from other results found in similar studies.

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