The Use of Numerical Heat Transfer Techniques to Analyze Thermal Comparator Conductivity Measurements
In the comparative conductivity measurement technique, a uniform axial heat flow is assumed to exist in a stack composed of two reference disks with a sample disk sandwiched between them. The sample conductivity is found from measured temperature drops across and thicknesses of the stack elements. In practice, the heat flow in the stack is non-uniform and corrections must be made for this effect. We have made a detailed numerical heat transfer analysis of the commercially available Dynatech TCFCM comparator with the aid of a finite difference numerical heat transfer code (SINDA). The goal of this study has been to determine the effect of non-uniform axial heat flux on the measured conductivity and to define the magnitude of the errors likely to be observed in various experimental situations. Correction factors are given for correcting the measured conductivities of samples with true conductivities in the range ≈0.05–1 W/m-K when measured against Pyrex or Pyroceram. Estimated errors are given for measurements with various combinations of Pyrex and Pyroceram references and samples. Results are also given to show the utility of numerical calculations in situations where the sample diameter is significantly less than the reference diameter. Various approximate methods of correcting for nonuniform heat flow are compared to the numerical predictions for selected cases.
KeywordsNumerical Heat Transfer Uniform Heat Flux Auxiliary Heater Insulation Region Centerline Temperature
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