67 The Layered Insulation Model and Mean Apparent Thermal Conductivity of an Environmental Friendly Polyurethane Foam at Low Temperatures Available to Purchase

A new environmental friendly polyurethane(PU) foam with blowing agent of HFC-245fa was developed in order to substitute for traditional foam with blowing agent of CFCs, which has been phased out according to Montreal protocol and subsequent treaties. But the coefficient of thermal conductivity of the new foam is not available at present when it is used for cryogenic storage tanks and pipes. In this paper, the mechanism of heat transfer in the foams was analyzed and a layered insulation model used at low temperatures was described accordingly. The mean apparent thermal conductivity under low temperature of the new PU foam, which has zero ODP, was investigated. The relationship between density and the thermal conductivity was experimentally studied. The results proved that the newly developed material had a better performance in thermal insulating system and provided a reference data when use the material under low temperatures.