Transient Hot-wire Method Measuring Thermal Conductivity At Low Temperature

Thermal conductivity changes greatly with structure, composition, temperature and humidity, it can’t be found in the table of the basic physical properties that provided from some literatures. So quickly and effectively measuring the thermal conductivity of the insulating material has a great significance for aeronautics, astronautics, cryogenic storage and transport as well as the development of the cryogenic technology.This project is a part of “advanced research of new type of liquefied natural gas(LNG) ship cargo containment system” which is a Ministry of Industry and Information Technology of PRC high technology ship science program. Purpose is to obtain the relationship between the thermal conductivity of polyimide and temperature at liquid nitrogen temperature zone, and to provide the basis for a new LNG cargo tank palisade structure insulation material selection.This paper discussed the parallel hot-wire method measurement of thermal conductivity under low temperature. The transient mathematical model is built according to the parallel hot-wire method form theory. Numerical simulation is conducted. The experiment roof is also built on the basis of theory. It analyzed the error that using platinum resistance instead of thermocouple to measure the temperature, comparing with the actual measurements. The cause of error is analyzed. Using numerical simulation to analysis the error which caused by the thin air, and taken measure to reduce it. On the basis of theory, the thermal conductivity of the polyimide(soft and hard) at a temperature of-160℃~25℃is measured by building experiment roof. The thermal conductivity of the tested materials data which changes with temperature is got.Thermal conductivity at room temperature measured by the platform, including polyurethane and polyimide(soft and hard), is compared with appraisal value by WSW, and the maximum relative error does not exceed 5%. The correctness of thermal conductivity measuring method and mathematical is proved. Therefore the thermal conductivity at low temperature can be used in reality.