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    Thermal Properties of Selected Materials from Steady-State and Transient Tests

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    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.


    thermal conductivity, thermal diffusivity, specific heat, thin-heater apparatus, gypsum containing wax, wood products, calcium silicate, plastic foams, extruded polystyrene, polyisocyanurate

    Author Information:

    Graves, RS
    Oak Ridge National Laboratory, Oak Ridge, TN

    Yarbrough, DW
    Oak Ridge National Laboratory, Oak Ridge, TN

    McElroy, DL
    Oak Ridge National Laboratory, Oak Ridge, TN

    Fine, HA
    Oak Ridge National Laboratory, Oak Ridge, TN

    Committee/Subcommittee: C16.30

    DOI: 10.1520/STP16370S