Express method for determining thermal properties of materials using a two-layer “sample – standard” system

The article considers the determination of thermal properties of a sample of various materials based on the results of measuring the temperature of a reference body (standard). The existing method for determining the thermal properties of a sample in a system of three contacting bodies "standard – sample – standard" (in a three-layer system) includes complex calculation formulas and labor-intensive experimental techniques. Therefore, this method must be simplified. An express method for determining the thermal properties (thermal and thermal diffusivity) of materials using a two-layer "sample – standard" system is theoretically substantiated. For large Fourier numbers, the standard temperature depends on one input parameter, which is determined by the ratio of the dimensionless thermal conductivity to the dimensionless thermal diffusivity. If the above parameter is taken as an independent variable, the time dependence of the standard temperature at a selected point contains a straight-line section, which allows one to quickly find a good approximation for the coefficients included in the mathematical model of the thermal energy transfer process in a two-layer system. For this system, an exact solution of the heat exchange problem during heating by a constant heat flow is obtained and an algorithm for solving the inverse problem is constructed: determining the thermal and thermal diffusivity of the sample under study based on the results of measuring the temperature of the standard. The efficiency of the algorithm is shown using a specific example. The results of calculations with the found coefficients are consistent with experimental data in the entire range of variation of the Fourier number. The proposed method can be implemented in thermophysical instrumentation.