Research On Thermophysical Property Of Polyimide Foams

The polyimide foams have characteristics such as low density, low temperature resistance, no harmful gas release etc. And began to apply in aerospace, aviation, navigation as well as electronic equipment. But thermalphysical property parameters is deficient, especially at low temperature and pressure. The thermal conductivity of polyimide form at NPT has been measured by WSW. However it can't meet the demand of aerospace exploration. The relationship between thermal conductivity and temperature, pressure and density was studied from two experimental and theoretical method.In order to study the relationship between temperature and thermal conductivity of polyimide foams, an experiment platform is built based on the theory of transient hot-wire method. Compared the experimental results to WSW results at NPT, the maximum relative error is less than 3%. The thermal conductivity of five different density hard polyimide foam is measured from room temperature to-160?, and results showed that the thermal conductivity decrease as the temperature decrease. The bases for how to select right material has been provided through these experiments.In order to study the relationship between pressure and thermal conductivity of polyimide foams, the thermal conductivity of two different soft foams has been measured from normal pressure to 5 k Pa. The experimental results shows that the thermal conductivity decrease as the pressure decrease and the lower density it has, the lower thermal conductivity it gets. After returning to normal pressure, the thermal conductivity became lower than before the pressure drops. The data for application of aerospace has been provided through these experiments.The randomly heterogeneous model is used to calculate the thermal conductivity of the polyimide foams. The pore structure of material is observed through microscope, and the randomly heterogeneous model is established. The two dimension and three dimension steady heat conduction model have been calculated, and the relationship between thermal conductivity and density(i.e. porosity) has been analyzed. The results shows that the thermal conductivity increase as the density increase and porosity decrease.