Desenvolvimento e uso de uma técnica experimental para medição de propriedades térmicas "in situ"

Abstract

This work presents an experimental technique to obtain the thermal diffusivity and thermal conductivity in solid and isotropic materials, using only a single access surface. Initially, the proposed technique was numerically evaluated using COMSOL multiphysics. The experimental estimation of the parameters was carried out from two different experimental configurations, for the thermal diffusivity measurement a thermal blower to generate the heat flux and two thermocouples for the temperature measurement were used. For the estimation of the thermal conductivity, an electric resistance, a heat flow transducer and a thermocouple were used. In both experiments the sample was partially heated in a specific region of the surface. For the determination of diffusivity, the temperature measurements of the unheated region were used. To obtain k, was used one point of temperature located below and in the center of the resistance. The technique relies on the minimization of two different objective functions using the quadratic error function. The functions were defined from the measurements of temperatures on the surface of the sample, but using different thermal problems. The first objective function is characterized by the use of the gain ratio between two surface temperatures for the determination of the thermal diffusivity. The second objective function was defined between the experimental and theoretical values of the temperature to estimate the thermal conductivity. In the numerical analysis, not metallic, polyvinyl chloride (PVC) and metalic materials such as AISI 304, titanium, aluminum and copper were evaluated, with errors less than 1 %. In the experimental analysis, the thermal diffusivity was estimated for samples of PVC, AISI 304, AISI 1045, aluminum and bovine femur, and the results are in agreement with the literature. The experimental thermal conductivity was estimated with greater efficiency in the PVC, already in the AISI 304 obtained an error in the estimation around 10 %.