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 [1–4]. 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 multimodel method of nondestructive determination of the thermophysical properties of solid materials are presented in Figs. 1 and 2. The body under study experiences a thermal effect from a heater made in the form of a thin disk of radius R pl built into the substrate of a measuring probe. The temperature distribution over the body surface is controlled by several (no
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Jan 1, 2021
S V Mishchenko + 1
