Document Type

Thesis - Open Access

Award Date

1974

Degree Name

Master of Science (MS)

Department

Electrical Engineering

Abstract

A transient heat-flow, cylindrical-probe method for measuring thermal resistivity of &oils in situ is investigated. The theory of conduction of heat in a medium containing a cylindrical heat source is studied in detail. Effects of finite probe radius, length, and thermal conductivity are investigated and minimized. The effect of thermal contact-resistance at the probe surface is also studied. Errors in measurements of samples of finite dimensions are considered. An electronic system which uses the cylindrical-probe method to measure thermal resistivity of soils is described. Results are given for the use of the system in the measurement of thermal resistivity of a fine white sand. Thermal resistivity was found to vary significantly with moisture content. The objective of this thesis is to propose a practical method to measure thermal resistivity of soils. To allow field measurements, the measuring system must be portable. That is, it must be easily moveable and must have its own (portable) power supply. The system should also require a minimum of technical knowledge from its operator. The system should measure thermal resistivity directly, rather than supplying data which must be interpreted by the use of charts, tables, graphs, etc. Application of the measurements to determination of soil moisture may, however, require charts, tables, or graphs to account for such variables as mineral content and density of soils. The system should be available at a cost that is not prohibitive. The system is obviously of no use if the potential user cannot afford it. Above all, the system must operate reliably over a large range of climatic conditions. Temperature variations from below freezing to over 100° F will affect the thermal conductivity of the soil but should not appreciably affect the operation of the measuring system.

Library of Congress Subject Headings

Heat -- Conduction

Thermistors

Thermal analysis

Soils -- Thermal properties

Format

application/pdf

Number of Pages

98

Publisher

South Dakota State University

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