Desenvolvimento de métodos experimentais para a determinação da difusividade térmica e condutividade térmica de materiais não metálicos usando somente uma superfície de acesso

Abstract

This work describes three experimental techniques for determining simultaneously the properties, thermal diffusivity and thermal conductivity of non-metallic materials. All techniques use experimental data from one of the same sample surfaces. It means that the imposing heat flux and the temperature response are measured at the same surface of the sample. The first technique determines the properties by using sequential unconstrained optimization methods, which minimizes a least square error function. In the second, two different objective functions are used. In this case, the thermal diffusivity is estimated from a correlation function while the thermal conductivity is estimated from the square error function. Both correlation and error function are defined from experimental temperature and calculated temperature using a theoretical model. These first two techniques have presented low sensitivity in the thermal diffusivity estimation. To avoid this problem, a third method is proposed. This method works in the frequency domain for the estimation of thermal diffusivity. In this case, an objective function representing the eigenvalue phase angle is used to determine the thermal diffusivity while the square error function is used for the thermal conductivity estimation. A comparison with the flash method and the guarded hot plate method gives a deviation of 2,97 % and 0,63 % for thermal diffusivity and thermal conductivity, respectively, for a Polychloroethylene (PVC) sample. At the end of this work an uncertainty analysis and an investigation for conductive materials application are also presented.