Abstract
An unguarded, unidirectional heat flow technique is described for measuring the apparent thermal conductivity (λ a) of insulating materials in the range 300 to 330°K. Vertical heat flow is generated by a 0.9 m by 1.5 m electrically heated nichrome screen that is instrumented and sandwiched between two test speci mens. The test specimens are bounded by two temperature-controlled copper plates. The system has been used to measure λ a of fiberglass batts and obtain data that show the effects of density, temperature, temperature difference, thickness, plate emittance, and heat flow direction on λ a. A determinate error analysis indicates a λ a measurement uncertainty of ±1.7%. The system repeat ability and reproducibility were found to be ±0.2%. The measured performance of the tester agrees with that predicted by a thermal model. Analysis of the transient characteristics of the screen when it is subjected to a step change in power suggests that the apparatus can be used to determine apparent thermal diffusivity.
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