Use of numerical heat-transfer techniques to analyze thermal-comparator conductivity measurements
The thermal conductivity of solid samples with conductivities in the range approx. = .2 to 50 W/m-K, is frequently measured by the comparative or cut-bar method. In this technique, the specimen under test is sandwiched between two similarly sized reference materials of known conductivity which act as heat flux gages. An axial heat flow is established by means of heaters at the top and bottom of the reference-sample-reference stack. The thermal conductivity of the sample is then calculated from the measured temperature gradients across the references and the sample, with the implicit assumption that the axial heat flux is uniform throughout the stack. We have made a detailed numerical heat transfer analysis of the commercially available Dynatech TCFM 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. Several situations of experimental interest have been analyzed in detail in order to facilitate the determination of accurate conductivity information from raw experimental data. Correction factors are given for correcting the measured conductivities of samples with true conductivities in the range approx. = 0.05 to 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.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5777883
- Report Number(s):
- SAND-83-2109C; CONF-8310163-3; ON: DE84000945
- Resource Relation:
- Conference: 18. international thermal conductivity conference, Rapid City, SD, USA, 3 Oct 1983
- Country of Publication:
- United States
- Language:
- English
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