Document Type

Thesis - Open Access

Award Date

1961

Degree Name

Master of Science (MS)

Department

Agricultural Engineering

Abstract

Thermoelectricity is the direct conversion of heat energy to electrical energy, or vice versa. Conventional electrical generating systems convert heat energy by one or more intermediate processes to mechanical energy, which in turn is used to drive a generator. Each intermediate process has an associated energy loss or inefficiency which accumulates until the over-all conversion efficiency may range from less than 1 per cent to about 40 per cent depending on the system used and the amount of energy produced (9)*. It is reasonable to assume that elimination of the intermediate processes by use of thermoelectricity could reduce the heat energy required per unit of electrical energy developed. Until recently, however, the efficiency of conversion by thermoelectric means using metals was so low (less than one per cent) that little serious thought was given to such uses. As a result, the primary use of thermoelectricity has been for temperature measurement and control with thermocouples, where the low efficiency was of little importance. In recent years the development of improved semiconductor materials has led to renewed interest in the possibility of thermoelectric power generation competing economically with mechanical systems of power generation. These new materials have already improved the conversion efficiency tenfold (2) and promise much more in the future. Since the efficiency of a thermoelectric generator is essentially unaffected by its size or power output, the first take-over by thermoelectric generators is expected to be in the low power-producing region where conventional mechanical systems are least efficient. Figure 1 graphically represents the present and future expected areas of competition. One area in which thermoelectricity could first become economically competitive is where otherwise waste heat could be utilized to produce electrical energy, and first cost rather than efficiency could be the controlling factor. There are many power generating systems in use today which emit considerable amounts of heat as waste. One of these is the internal combustion engine, which expels from the exhaust system about one-third of its total heat generated (1). If this heat could be utilized by a thermoelectric generator to recharge the engine’s battery or as an auxiliary power source for portable electrically operated equipment, the output of that engine could be increased at very little or no additional operating cost. It is acknowledged that the thermoelectric materials for such a generator are not economically competitive at the present time. Based upon future expectations of highly efficient and low-cost materials, however, a preliminary investigation of requirements and limitations of such a system appeared justified. The purpose of this project was to (a) make a preliminary investigation of some of the design principles involved in developing an exhaust-gas thermoelectric generator, (b) construct a low-power generator utilizing the design principles established, and (c) test the generator under actual operating conditions to verify or disprove the design and the expected performance. It is also highly desirable that the generator be adaptable to new thermoelectric materials as they are developed. In that way a compatible generator design could be available for the new materials when they become available for use in commercial thermoelectric devices.

Library of Congress Subject Headings

Electrical generators -- Design and construction
Thermoelectricity
Electric generators -- Testing

Description

Includes bibliographical references

Format

application/pdf

Number of Pages

78

Publisher

South Dakota State University

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