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Title: Through The Wall Temperature Measurement Effects In Simple Systems
Author: Thomas O. Maginnis
Source: 2008 Measurement Science Conference
Year Published: 2008
Abstract: A situation that frequently occurs in temperature measurement applications is the need to infer the temperature of one material medium using a temperature sensor attached to an adjacent material medium. For example, one may try to measure the temperature of a corrosive hot fluid using a temperature sensor attached to the outside of the fluid container wall. In a more fundamental sense, one may regard the temperature sensor itself as one material medium, and the sample system whose temperature is to be measured as the second medium. Two physical effects come into play in such situations: the difference in resolution for temperature changes in the two media arising from the heat capacity ratio of the materials and the settling time required for a uniform temperature to be established across both media when they start out at different temperatures. Fortunately, for stationary media, this heat exchange problem can be completely solved for simple geometries in terms of the thermal properties of the two material media and their geometrical dimensions. The solutions enable both the settling time constants and the temperature leverage ratios to be calculated and predicted. Solutions and example illustrations will be provided for simple two-layer systems in planar, cylindrical, and spherical geometries, for the simplest case where the outer surfaces of the two-layer system are thermally insulated, but the internal bounding surfaces are in good thermal contact. These solutions are useful for understanding how closely the measured temperature of the outer layer represents the true temperature of the inner layer in such situations, and for estimating the uncertainty of through the wall temperature measurements.

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