Heat transfer in open cell polyurethane foam insulation |
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Authors: | J-W Wu H-S Chu |
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Institution: | (1) Department Mechanical Engineering National Chiao Tung University Hsinchu, Taiwan, Republic of China, TW |
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Abstract: | This paper study systematic investigates the combined conductive and non-gray radiative heat transfer of open cell polyurethane
(PU) foam in the pressure range between 760 and 0.02 Torr. Direct transmission measurements are also taken using Fourier transform
infrared (FTIR) spectrometer. In doing so, experimental results are obtained for the spectral extinction coefficient from
2.5 to 25 μm. In addition, the P-3 approximation method along with the box model is employed to calculate the non-gray radiative
heat flux. The diffusion approximation method is also applied to calculated the radiative conductivity. Also tested herein
are three samples with different cell sizes ranging from 330 to 147 μm. According to those results, the spectral extinction
coefficient increases with a decrease of cell size, leading to a decrease of thermal conductivity. Moreover, evacuating the
gases in the foam cells can reduce the thermal conductivity of the PU foam by as much as 75%. Furthermore, radiative heat
transfer accounts for about 4% of total heat transfer at 760 Torr and increases to 20% at 0.02 Torr.
Received on 20 April 1998 |
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