Rectangular heat source on a semi-infinite solid: an analysis for a thin film heat flux gage calibration

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-square 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.