مطالعه اثر عوامل پف زاي مختلف روي ريزساختار و ضريب انتقال حرارت فوم سخت پلي يورتان

Study on the Effect of Alternative Blowing Agents on Microstructure and Heat Transfer Coefficient of Rigid Polyurethane Foam

Rigid polyurethane (RPU) foam is widely used as insulating materials in refrigerator industries. Using of alternative blowing agent makes rigid polyurethane foam with different properties. Usually chlorqfluorocarbons (CFCs),for example CFC-11, are used as blowing agent in rigid polyurethane foam in Iran. CFC-11 is an ozone depletion substance, and hence many researches have been done to replace it with alternative blowing agents. One of these alternatives is HCFC-I4Ib with lower ozone depletion potential (ODP) respect to CFC-11, but with higher thermal conductivity than CFC-11. Thermal conductivity of alternative blowing agent is an important parameter and it could be decreased with controlling of some important parameters in RPU foam. Thermal conductivity coefficient of rigid polyurethane foam depends on some parameters such as cell structure, type and quantity of blowing agent, time, and temperature. This coefficient decreases with cell size decrement. Cell structures of rigid polyurethane foam are different in rise and transverse directions; so the thermal properties of RPU foam will strongly depend on the tests directions. Furthermore, the thermal conductivity coefficient of foam has a direct relationship with thermal conductivity coefficient of blowing agent, time and temperature. It increases monotonically with time and reaches to a constant value at a time scale.