Mechanical Engineering ETDs

Karl Wally

Publication Date

1-4-1977

Abstract

Beaded thermocouples mounted on the surface of a solid for the purpose of measuring surface temperature are liable to introduce measurement errors as a result of heat transfer between the surface and the bead, and also because of the thermal inertia of the bead. For the prediction or correction of such errors, an accurate model of the thermocouple response is required. This paper uses a solution technique known as Quasi-Coupling to solve for the heat transfer in idealized beaded thermocouples mounted on idealized solids. The parameters controlling the thermocouple response are identified and the sensitivity of the response to these parameters is investigated. It is determined that the thermophysical properties of the surface whose temperature is being measured, of the thermocouple bead, and of the thermocouple lead wires are important in determining the response, as is the geometry and size of the thermocouple bead and lead wires. An interesting result is that in cases where the bead is glued to the surface by means of an adhesive, the thermal capacitance of the adhesive layer has negligible effect on the thermocouple response, while the thermal resistance of the adhesive layer dominates the response. The quasi-coupled solutions are used with numerical convolution to estimate the measurement errors for some typical thermocouple/substrate combinations. When these results are compared to results predicted by exponential response models, considerable disagreement is observed. However, the quasi-coupled solutions agree well with one-dimensional finite-difference solutions, so that it appears that the exponential response models are inadequate for modeling the response of beaded thermocouples mounted on solid substrates. Finally, the results of the sensitivity analysis are used to generate design charts which can be used to design beaded thermocouple installations which will tend to minimize measurement errors.

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Larry Wayne Bickle

Second Committee Member

Ned R. Keltner

Third Committee Member

Karl Thomas Feldman Jr.

Sponsors

Sandia-University Research Program

Document Type

Thesis

Language

English

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