Rectangular Heat Source on a Semi-infinite Solid—An Analysis for a Thin Film Heat Flux Gage Calibration

Abstract

For a thin film heat flux gage designed to provide both rapid response and long use time, initial calibrations using standard techniques indicated differences between the literature and the estimated properties. In order to estimate thermophysical properties and subsequently the gage sensitivity, an analytical model of the response to a step change in heating current was developed. Starting from a Green’s function description, the model is reduced to three algebraic expressions, which correspond to the early, middle, and late time regimes. These expressions provide a framework for least-squares estimates of gage parameters. This provides an in-situ, nondestructive measurement of the thermal impedance of the substrate. There is very good agreement between the model and the experimental data. The estimated parameter values demonstrated good to excellent repeatability and good agreement with both new literature data and results from destructive property measurements.

Experimental Performance of a Heat Flux Microsensor

“…If the thermal properties of the substrate are known, a change in the surface heat flux will create a predictable temperature response in the substrate. Conversely, measurements of the timetemperature history of the thin metal film coupled with the appropriate analytical model allows calculation of the surface heat flux history (Jones, 1977;Doorly and Oldfield, 1987;Keltner et al, 1984). The actual signal manipulation can be done with either analogue circuits or by digital signal processing.…”