SEDL / STP / STP1116-EB / STP16365S

Automated Low-Temperature Guarded Hot Plate for Measuring Apparent Conductivity

Smith, DR
National Institute of Standards and Technology (NIST) Boulder, Colorado

Dube', WP
National Institute of Standards and Technology (NIST) Boulder, Colorado

Filla, BJ
National Institute of Standards and Technology (NIST) Boulder, Colorado

Pages: 22    Published: Jan 1991

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Abstract

A guarded-hot-plate apparatus has been developed for measuring the apparent thermal conductivity of flat-slab thermal insulation materials at low temperatures. Relevant ranges of physical variables which can be accommodated (under different conditions) are: diameter, 203 mm (fixed); thickness, 5 to 30 mm; mean specimen temperatures, 100 to 400 K; temperature differences, 3 to 150 K; temperature gradients, 0.1 to 10 K/mm; and thermal resistance, 0.02 to 1.5 K·m²/W. Conductivity can be measured in dry air, gaseous nitrogen, helium, argon, or neon, or in vacuum. Apparent conductivity of an insulation material can be studied as a function of temperature, fill-gas pressure, or species, giving insight into the heat-transfer processes present in the material. Control of the main heater may be stabilized either at constant heater power or constant heater temperature. This apparatus will be useful in development of low-temperature Standard Reference Materials, and is being used to study heat transfer in closed-cell foam insulation containing HCFC blowing agents.