Highly Porous Metal Foams: Effective Thermal Conductivity Measurement Using a Photothermal Technique

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Use of a pseudo-random heating excitation to investigate the thermal properties of thermally fragile materials

International audienceIn this numerical study, a photothermal method with random excitation is implemented in order to measure the thermal diffusivity of thermally fragile materials. The principle of this technique is based on rebuilding the sample impulse response through input-output cross-correlatoin. A D-optimality criterion is used to determine the optimal duration of the experiment. The thermophysical properties are identified through the rebuilt impulse response using an iterative method which minimizes the gap between simulated measurements and theoretical temperature calculated using the thermal quadripoles method. The obtained results show a good agreement with literature values

Optimal design and measurement of the effective thermal conductivity of a powder using a crenel heating excitation

International audienceThis paper presents an experimental optimal design of a photothermal radiometry method using a crenel heating excitation. This method is used for the determination of the effective thermal conductivity of a powder in imperfect contact with a coating, and in presence of convective heat losses. The parameter identification is performed by the minimization of the ordinary least squares objective function comparing the measured temperatures to the response of a direct model function of thermophysical parameters. The used iterative algorithm is based on the Gauss–Newton method

Thermal characterization of poorly conducting solids by the flash method

International audienceEstimation of the thermal diffusivity of a poorly conducting solid placed between two metallic layers by the flash method is described. The method consists of applying a brief heat pulse to the front face of the three-layer composite and measuring the temperature rise versus time of the rear face. The thermal contact resistance between the layers and the heat transfer coefficient are obtained simultaneously with the thermal diffusivity of the poorly conducting solid. These parameters are identified by minimisation of the least-squares function comparing the measured and the calculated temperatures. Three models are developed using the thermal quadrupole method. An optimal design of the experiment is also presented and the choice of thermal model for parameter estimation is discussed. The experimental results are in good agreement with the theoretical analysis

High Temperatures ^ High Pressures, 2003/2007, volume 35/36, pages 633 ^ 647 DOI:10.1068/htjr140 Thermal characterization of poorly conducting solids by the flash method

Abstract. Estimation of the thermal diffusivity of a poorly conducting solid placed between two metallic layers by the flash method is described. The method consists of applying a brief heat pulse to the front face of the three-layer composite and measuring the temperature rise versus time of the rear face. The thermal contact resistance between the layers and the heat transfer coefficient are obtained simultaneously with the thermal diffusivity of the poorly conducting solid. These parameters are identified by minimisation of the least-squares function comparing the measured and the calculated temperatures. Three models are developed using the thermal quadrupole method. An optimal design of the experiment is also presented and the choice of thermal model for parameter estimation is discussed. The experimental results are in good agreement with the theoretical analysis. Nomenclature ai thermal diffusivity (m 2 s �1) Greek symbols Cp heat capacity (J kg �1 K �1) r density (kg m �3) ei layer thickness (m) y1 Laplace temperature on the front h heat transfer coefficient (W m �2 K �1) face of the first layer (K s