SEDL / STP / STP1030-EB / STP23298S

Thermal Resistance of Fine Powders at Atmospheric Pressure and under Vacuum

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

Weaver, FJ
Oak Ridge National Laboratory, Oak Ridge, TN

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

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

Pages: 14    Published: Jan 1990

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Abstract

Heat transport measurements are reported on candidate insulation systems with relatively high thermal resistances for use in appliances. The thermal resistances of small diameter silica powders at atmospheric pressure and under vacuum were measured from 295 to 340 K using unguarded radial heat flow techniques. The thermal resistances of rectangular panels containing perlite or silica powder at reduced pressure were determined using an unguarded linear heat flow technique.

Values of 1.2 m² ∙ K/W for 0.0254 m (R-7 per inch) were obtained at atmospheric pressure for powders of pure, fumed, amorphous (0.01 μm diameter) silica particles compacted to about 10% of theoretical density. Values of 0.7 m² ∙ K/W for 0.0254 m (R-4 per inch) were obtained at atmospheric pressure for powders of impure, amorphous (0.3 μm diameter) silica particles. Under vacuum these particle systems yielded thermal resistances as high as 6 m² ∙ K/W for 0.0254 m (R-34 per inch), and mixtures with the pure silica particles yielded over 9 m² ∙ K/W for 0.0254 m (R-50 per inch). Evacuated panels of pure silica particles yielded thermal resistance values over 3 m² ∙ K/W for 0.0254 m (R-17 per inch) and decreased about 5% in resistance in 39 months. Evac-uated panels of a perlite powder yielded similar values.