Study On The Test Of Thermal Conductivity And Thermal Diffusivity For Thermal Insulation Materials For Building Application With Hot-wire Method

Abstract:Many new types of thermal insulation materials for building application are developed because of improvement of energy saving technology and the requirement of building energy conservation, An effective testing device was designed based on hot wire surface-parallel method, which is effective for us to obtain the thermal conductivities and thermal diffusivities of thermal insulation amterial for application. The techonology is useful to promote the developing, producing and applying of the thermal insulation materials for building application too. The main research and conclusions are as follows:(1)The hot wire surface-parallel method was proposed to measure the thermal conductivities and thermal diffusivities of thermal insulation amterial for application, and the computational formulas were deduced.(2) An effective test equipment for the test of thermal conductivity and thermal diffusivity was designed, which includes the heating system, testing system and data acquisition system. The length of the hot wire is determined as300mm and the radius of the hot wire is less than0.2mm. The sample length is300mm, and the thickness (W) and width are greater than80mm and160mm respectively. A detachable structure of the hot wire and an insulation mantle were designed.(3) The influences of the hot wire radius and the corresponding relative distance between the thermocouple and hot wire (R) on the testing error were analyzed with the Matlab and Fluent software. The theoretical calculating results show that the hot wire radius has weak influence on the testing error of the thermal conductivity when the radius varies from0.1to0.6mm. The hot wire surface-parallel method has a high testing accuracy for thermal conductivity and thermal diffusivity testing. When W≥80mm and0.1≤R/W≤0.5, the location of the measuring point has weak influence on the testing error of the thermal conductivity and thermal diffusivity, and the natural convection is almost negligible. R/W is determined as0.1～0.2, at this time, R is15mm.(4) For the organic foam insulation materials, the thermal conductivity and thermal diffusivity measured by hot wire surface-parallel method was stable, while it showed lage fluctuation for that of the foam glasses. The hot wire is determined as the nichrome wire with radius of0.095mm. The corresponding minimum effective testing time(τmim) is140s, and the maximum effective testing time (τmax)is the moment when the temperature increases by0.1℃compared with the initial temperature at the top surface. The appropriate range of the linear heat flux for the organic foam insulation materials, the aerated concrete block and the foam glasses are0.7-3.7W/m,5～11W/m, and2-9W/m respectively. A visual data acquisition and processing software was designed based on the Visual Studio.NET2008platform.(5) The thermal conductivities and thermal diffusivities of the organic foam insulation materials, the aerated concrete block and the foam glasses were measured with the hot wire surface-parallel method. A new simplified method for the test of thermal conductivity was proposed. It shows that the testing accuracy of the thermal conductivity is high with the hot wire surface method, and the error of the thermal conductivity is within3.4%for EPS plate. The testing error of thermal diffusivity is large with the hot wire surface method, which is resulted from the location difference of the temperature measuring point. The thermal diffusivities measured are in general accord with the literature value. The new simplified method for the test of thermal conductivity can be used to measure the thermal conductivity rapidly and reliably for the thermal insulation materials, though its accuracy is a little lower than that of the hot wire surface-parallel method.