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Thermal Properties of Selected Materials from Steady-State and Transient Tests Pages: 21 Published: Jan 1991
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View License Agreement The Unguarded Thin-Heater Apparatus (UTHA, ASTM C 1114) was used to determine the thermal conductivity (k), specific heat (C), and thermal diffusivity (α) of selected building materials from 24 to 50°C. Steady-state and transient measurements yielded data on four types of material: gypsum wall board containing 0, 15, and 30 wt% wax; calcium silicate insulations with densities (ρ) of 307, 444, and 605 kg/m3; three wood products: southern yellow pine flooring (575 kg/m3), Douglas fir plywood (501 kg/m3), and white spruce flooring (452 kg/m3); and two cellular plastic foams: extruded polystyrene (30 kg/m3) blown with HCFC-142b and polyisocyanurate rigid board (30.2 kg/m3) blown with CFC-11. The extruded polystyrene was measured several times after production (25 days, 45 days, 74 days, 131 days, and 227 days). The UTHA is an absolute technique that yields k with an uncertainty of less than ±2% as determined by modeling, by determinate error analyses, and by use of Standard Reference Materials SRM-1450b and SRM-1451. In the transient mode of operation, a step-change in heat flux was applied to specimens that were initially isothermal or that had a steady, imposed temperature gradient. Analysis of the temperature response of the thin heater for short times predicts a temperature rise that is a linear function of the square-root of time. This behavior was observed for materials with densities above 300 kg/m3 and the slope of this relation provided experimental values for the product k∙ρ∙C. The overall error in determining the product k∙ρ∙C is less than 1%. Values of C were calculated from experimental values of k, ρ, and the product of k∙ρ∙C. However, for the 30 kg/m3 foams, the thermal mass of the thin heater delayed the onset of the linear temperature rise with the square-root of time. This effect negated the use of the short-time transient analysis for low density materials. A finite difference program that described this observation provided an alternate method to obtain values for the product k∙ρ∙C from the experimental data. | ||
