SU817563A1 - Method of complex determining of thermal characteristics of materials - Google Patents

Description

where L is the heat conduction coefficient;

with

-mass heat capacity;

-coefficient of temperature;

I

-density;

- sample thickness;

- heat flux densities on sample surfaces;

t is the temperature difference; and - the rate of temperature change.

In addition, the temperature difference on the sample is kept constant by changing the temperature of both its surfaces at the same speed, equal to (0.3 - 0.6) uta / h.

The measurements are carried out as follows.

A flat sample is placed between the surfaces of the source and heat receiver equipped with temperature and heat flux density sensors. In the first embodiment of the method, the source emits a constant power flow towards the sample, and the temperature of the receiver is changed at a constant rate. In the second variant, the temperature difference between the source and the heat receiver is kept constant and their temperatures are changed at the same constant speed. In both ways, the rate of temperature change is set so that the heat flux passes through the sample, and the ratio of the heat flux densities at the entrance to the sample and the output from it was within 1.35-1.85, at which the highest accuracy of measurements is achieved.

At that moment, when the heat flux densities through both surfaces of the sample stabilize with time, the quasistationary thermal regime is established. In this case, by measuring for any time simultaneously the heat flux density through both surfaces of the sample and the temperature at the same points, it is possible to calculate the values of the thermophysical characteristics of the sample.

The substantiation of the possibility of determining TFH from the results of such measurements was obtained from the solution of the problem for two-sided heating of an unbounded plate from a source with a constant heat flux density. Consider in the plate only a thin flat layer located on one side of the axial plane of the plate parallel to its surfaces. If the density of the heat flux passing through the surface of this layer is constant over time, then the regularity of the quasistationary mode e, the rates of temperature change for each point with constant TFC are constant and constant, and the temperature distribution in the layer is described by the parabolic law. This means that the fields of heat flux densities and temperatures are described by well-known equations, from which we obtain the following formulas for determining TFH

-p

(ty ttyzn

/ j and

2u.t, su)

 (. (, -%;

All values of TFH obtained by these formulas correspond to the average integral temperature of the layer t, defined by the following formula

 a.bl () 1 TIv

where t. and 2 surface temperatures of the layer,

In this fool, the second term determines the deviation of the value of the average integral temperature of the layer from the arithmetic mean temperature. When the ratio of the density of the heat flux q./q If45 this deviation can be ignored.

The proposed method allows the measurement of temperature and density. Only on the surfaces of the sample, examine the thermal characteristics of thin layers of liquid and solid materials. The time of experience is reduced by reducing the initial (non-working stage of the regime).

The proposed method is expediently used to quickly and accurately study the temperature dependences of the complex TPC of solid and liquid materials;

Claims (2)

1. The method of complex determination of thermophysical. characteristics of materials in a flat layer in a quasi-stationary mode by measuring temperatures and heat flux densities on the surface of the specimen, in order to improve the accuracy of measurements, the heat flux is passed through the sample, affecting one of its surfaces by a heat flux of constant density and the temperature of the second surface changes at a constant speed equal to (0, .25-0.45), and the thermophysical characteristics are determined for any moment from the measurement results using the following formulas ( P-TTF 2l  and (W1-sug) 2ut ((VHVi) e. - coefficient of thermal conductivity; c is the mass heat capacity; a is the temperature transmittance coefficient; p- - density; h is the sample thickness; and q - heat flux density on sample surfaces; ut is the temperature difference; U is the rate of change of temperature. 2. The way pop.Ch, differing by the fact that they support the temperature difference by C o racie, change the temperature of both its surfaces with the same speed, equal to (0.3 - 0.6) Ata / h. Sources of information taken into account in the examination 1. Chudnovsky A.F. Thermophysical characteristics of dispersed materials. M., GIFML, 1962, p. 173-190. o 2. Half Sintsev D.N., Dudorov I.G. - Factory Laboratory, 1965, V. 31, No. 11, p. 1410-1412 (prototype).