Heat transfer in open cell polyurethane foam insulation

This paper study systematic investigates the combined conductive and non-gr ay radiative heat transfer of open cell polyurethane (PU) foam in the press ure range between 760 and 0.02 Torr. Direct transmission measurements are a lso taken using Fourier transform infrared (FTIR) spectrometer. In doing so , experimental results are obtained for the spectral extinction coefficient from 2.5 to 25 mu m. In addition, the P-3 approximation method along with the box model is employed to calculate the non-gray radiative heat flux. Th e diffusion approximation method is also applied to calculated the radiativ e conductivity. Also tested herein are three samples with different cell si zes ranging from 330 to 147 mu m. 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 fo am cells can reduce the thermal conductivity of the PU foam by as much as 7 5%. Furthermore, radiative heat transfer accounts for about 4% of total hea t transfer at 760 Torr and increases to 20% at 0.02 Torr.