Analysis of thermal properties and heat transfer mechanisms for polyurethane foams blown with water

Rigid polyurethane foam (PUF) is one of the outstanding insulation materials and has been widely used in freezers and cryogenic facilities. Among the various blowing agents used in the manufacturing PUF, water-blown PUF is attracting much attention as environmentally friendly PUF as prominent replacements for the environmentally hazardous CFCs and HCFCs due to their significant ozone depletion potential. We investigated the effective thermal conductivity of PUF blown with different amounts of water, on the basis of the heat transfer mechanisms in terms of thermal conduction of solids and gases and the thermal conductivity of radiation in the cells. A predictive model for the effective thermal conductivity of PUFs with different densities is presented. The predictive model was validated by comparing the predicted values with the experimentally measured ones. The result showed that the effective thermal conductivity increased from 0.023 to 0.027 W m(-1) K-1 as the PUF density increased from 48 to 120 kg m(-3): increased by 158% from 0.0034 to 0.0089 W m(-1) K-1 for the thermal conductivity of solid PUF and decreased by 50% from 0.0037 to 0.0018 for the thermal conductivity of radiation.