Method of Nondestructive Determination of Thermophysical Properties of Solid Materials

Mainikova

Рогов

et al. 2014

J Eng Phys Thermophy

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We have considered the results of the analysis and estimation of systematic errors involved in the multimodel method for determining the thermophysical properties of solid materials. We have analytically obtained the condition that determines the upper limit of the reliably determinable thermal conductivity of the materials under study.Introduction. The multimodel method of nondestructive determination of the thermophysical properties (TPP) of materials relates to indirect measurement methods because not the very thermophysical quantity is measured directly in the course of an experiment, but rather thermograms (time dependences of temperature) are recorded [1][2][3]. The method is based on analytical solutions of the mathematical models of heat transfer processes occurring in a body under study exposed to the action of a constant strength round heat source (with the use of data for various portions of a thermogram [4,5]).Multimodel Method for Nondestructive Determining the Thermophysical Properties of Materials. The method is based on the following assumptions: 1) on a thermogram there are portions for which a highly accurate coincidence with the results of computational experiments by analytical models is ensured. Moreover, corresponding to these portions (Fig. 1, portions II and IV) there are the thermal regimes of the experiments that came up to the regularization stage (in what follows these portions will be called working);2) for the working portions there exist expedient computational relations allowing one to unambiguously determine the values of thermophysical properties depending on the parameters of the analytical function that describes the thermogram within the given interval.According to the method of [1, 2, 5], portion II of the thermogram (Fig. 1) is described by the equation of the form

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confidence: 99%

Estimation of Systematic Errors of the Multimodel Method for Nondestructive Determination of the Thermophysical Properties of Solid Materials

Mainikova

Рогов

et al. 2014

J Eng Phys Thermophy

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“…In the present work, we consider a method of nondestructive determination of the thermophysical properties (TPP) of solid materials, a bounded portion of whose surface is subjected to thermal action from a circular plane heat source of constant power [1][2][3][4].An analysis of the well-known methods of measuring the thermophysical properties of solid materials and of the errors they incur shows that within the time interval of measurement of a thermal system the latter undergoes profound changes not allowing one to describe the entire process of heat transfer by a single analytical model with invariable restrictions and conditions. Neglect of this fact leads to a marked increase of errors in determining the thermophysical properties of a solid material.…”

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confidence: 99%

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confidence: 99%

Multimodel method of nondestructive determination of the thermophysical properties of solid materials

Mainikova

Рогов

et al. 2012

J Eng Phys Thermophy

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A multidimensional method of nondestructive determination of the thermophysical properties of solid materials subjected to thermal action from a circular plane heat source of constant power is considered.Introduction. In the present work, we consider a method of nondestructive determination of the thermophysical properties (TPP) of solid materials, a bounded portion of whose surface is subjected to thermal action from a circular plane heat source of constant power [1][2][3][4].An analysis of the well-known methods of measuring the thermophysical properties of solid materials and of the errors they incur shows that within the time interval of measurement of a thermal system the latter undergoes profound changes not allowing one to describe the entire process of heat transfer by a single analytical model with invariable restrictions and conditions. Neglect of this fact leads to a marked increase of errors in determining the thermophysical properties of a solid material.The methods of determining the thermophysical properties of solid materials based on the assumption of the existence of a regular thermal regime allow one to most accurately take into account systematic and random errors of such determination. It was proved by Academician A. V. Luikov that regular thermal regimes of the first and second kind have a common property characterized by the fact that the ratio of the heat flux at any point of a body to the heat flux on the body surface is independent of time. In the given case, most often the thermogram is described by a mathematical model linear with respect to parameters or easily linearized [5]. Many of the indicated methods are intended for investigation of bodies of finite dimensions (plates, cylinders, spheres); however, a major portion is based on models of half-spaces (flat, cylindrical, spherical).In relation to such models, one should refer not to a regular thermal regime for the entire body (since it is considered infinite), but rather to regularization of the thermal process only for a definite region. Consequently, if the thermophysical properties of a solid material are determined only from the thermogram portions corresponding to the thermal regime regularization in the region of heaters and thermal detectors, then, first, the computational relations will be simpler and in many cases linear with respect to parameters and, second, systematic error components will be either much smaller than random ones or constant, i.e., independent of time. In such a case, the major part of such characteristic portions can be found and described analytically, and more possibilities will be afforded by an informationmeasurement system that implements the method of exercising self-control, i.e., it becomes possible to determine the complex of thermophysical properties of a studied object in one experiment using various mathematical models that adequately reflect actual heat transfer processes at certain time intervals.Experimental Implementation of the Method. The measuring and thermal schemes of the multimode...

“…These methods also call for simple facilities for their technical realization and a short experimental time [3][4][5][6]. However, the indicated methods should be further improved since, in them, the thermophysical parameters of a material are determined on the basis of the data of indirect experiments with the use of definite mathematical models.…”

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confidence: 99%

“…At large τ, this expression becomes simpler and has the form [4] T (r, τ) = q _ 0 R 2λ Rewriting (26) in terms of the power per unit heater length (q 0 = q _ 0 πR, see Fig. 9I), we obtain expression (13).…”

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confidence: 99%

Simulation of the Heat Transfer from a Linear Pulsed-Heat Source in Thermophysical Measurements

2005

J Eng Phys Thermophys

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The process of heat transfer from a linear pulsed-heat source in a semibounded body has been investigated. A nondestructive method of determining the thermophysical parameters of a material by the working portion of its thermogram, which allows one to substantially decrease the measurement error, has been developed. Since the model developed is linear by the parameters used, it allows one to estimate, using classical statistical methods, the random error in measuring the thermophysical parameters of materials.