A Flat Insulation Tester that Uses an Unguarded Nichrome Screen Wire Heater

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.