Date of Award

2011

Degree Type

Report

Degree Name

Master of Science (MS)

Department

Mechanical and Aerospace Engineering

First Advisor

Dr. Stephen A. Whitmore

Abstract

Bearings are commonly used in mechanical systems when there are rotating parts in the system. For bearings that run at speeds above about 1000 revolutions per minute, such as those used in aircraft turbines, machining tools, and automotive engines, it is important to take into account the heat transfer through the bearing system due to friction. Heat transfer is generally not considered for applications where the bearing is rotating at low speeds, such as clocks and bicycles. However, for certain aerospace applications, such as precision instruments or wind turbines, the heat transfer through the bearing becomes relevant. The case where the bearing is rotating rapidly has been extensively studied in the literature; however, bearings rotating at low speeds are not often studied due to the small amount of heat flowing through the bearing. This report extends the current body of knowledge by analytically determining the thermal resistance of bearings that rotate at low angular velocities and comparing the analytic values to experimental values. Using this information will help in system design where an accurate knowledge of bearing heat transfer is needed.

Thermal resistance is a measure of temperature drop due to the resistance of an object to heat flow. A literature review led to the conclusion that for increasing rotational speeds the thermal resistance of the bearing should decrease due to increased convection heat transfer on the inside surfaces of the bearing. Using correlations from the literature a bearing heat transfer model was developed to provide a quick engineering tool to determine the thermal resistance of a bearing given the bearing dimensions, rotational speed, and input heat flow.

A rough examination of the heat transfer model was made using an experimental apparatus developed to sense the temperature drop across a representative bearing system. This apparatus allowed the thermal resistance to be calculated and compared against predicted model values. This test was repeated for several different shaft rotational rates.

Comments

Publication made available electronically February 3, 2012.

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