RU1790759C - Method of measuring thermal conductivity of electroconductive specimen - Google Patents

Abstract

The invention relates to rapid methods for measuring the thermal conductivity of electrically conductive materials, in particular low-resistance semiconductor materials for thermoelectric converters. In the process, a sample 5 is mounted on the heat-equalizing plate 3. By means of thermocouples 9 and 10, the temperature differences between the external medium and the heat-contact and free faces are measured. Next, an alternating current is passed through sample 5, while the temperature of the hepal leveling plate 3 is maintained at the same level. Measure the current through the sample and the voltage across it, the second ratio of the temperature difference between the external medium and the heat-contact and free faces using thermocouples 9 and 10. Using the measured values, the thermal conductivity of the sample is calculated. 1 ill. ate with

Description

The invention relates to rapid methods for measuring the thermal conductivity of electrically conductive materials, in particular low-resistance semiconductor materials for thermoelectric converters.

There is a known Kohlrausch method for measuring the thermal conductivity coefficient, which consists in passing an electric current through a sample, eliminating the influence of heat exchange with the environment through screen heaters, taking into account or calculating the thermal conductivity coefficient of heat release in the sample, geometric dimensions, values of electrical signals taken from thermocouples.

A disadvantage of the known method is the considerable complexity due to the need to provide ideal lateral insulation by means of screen heaters and the installation of thermocouples at equipotential points of the sample.

The closest to the invention in technical essence and the achieved result is a method of measuring the thermal conductivity of a sample by passing a heat flux through a heat-contact face, exchanging heat with the external environment, measuring the geometric dimensions of the sample and the ratio of electrical signals that determine the temperature difference between the external environment and heat-contact and free faces, taking these parameters into account when calculating the coefficient of thermal conductivity.

 The disadvantage of this method lies in the experimental complexity, which consists in the need to simultaneously carry out a complex of measurements of both the parameters determining the heat transfer coefficient and the temperature difference between the side surface and the free face of the sample and the external environment.

The purpose of the invention is to simplify the method of measuring the thermal conductivity of an electrically conductive sample by eliminating measurements of the heat transfer coefficient.

The goal is achieved by passing the heat flux through the heat-contacting face and exchanging heat with the external environment, measuring the geometric dimensions of the sample and the ratio of electrical signals that determine the temperature difference between the external medium and the heat-contact and free faces, then additionally passing through the sample is alternating current and, ensuring that the values of the temperature of the heat-contacting face and the intensity of heat exchanges are the same as before passing the current through the sample, the heat ovydeleni in the sample and the second value is the ratio of the electrical signals, and for calculating the coefficient of thermal conductivity into account both the value of the ratio.

The drawing shows a device for implementing the proposed method.

The device includes a thermopile 1, one spas mounted on a heat exchanger 2, and other spas connected to a heat-equalizing plate 3, on which samples 5 made of an electrically conductive material, such as low-volume semiconductor samples for a thermopile of a thermoelectric cooler, are installed through an insulating film 4 .

By means of patch bars 6 soldered to the heat-contact beads of samples 5 and wires 7 soldered to the free beads of samples 5, the latter are electrically connected in series with each other.

In the space surrounding the sample, a plate 8 is placed on which side junctions of thermocouples 9 and 10 are installed, while the main junction of thermocouple 9 is installed

on one of the busbars 6 (it is assumed that the device is provided with a high degree of isothermal ™ bus 6 of all samples installed on the isothermal plate 3), and the main junctions of thermocouples

10 are mounted on the free faces of samples 5. The free ends of the thermocouples are connected to a switch (not shown in the drawing), the output of which is connected to the input of the measuring unit (for example, a microvoltmeter

B7-28).

The method is carried out as follows.

The thermopile 1 is connected to a power source (not shown in the drawing) and the achievement and subsequent stabilization of the temperature of the plate 3 at a certain level T0 different from the ambient temperature Tc.

Pre-measurement

geometric dimensions of the samples: length I, cross-sectional area S, perimeter R.

Due to heat exchange with the external environment with temperature Tc determined by the heat transfer coefficient a, temperature differences are established on samples 5, namely: the temperature of the heat-contacting face will be equal to T0, and the temperature of the free face will be equal to TgCh

Further, to determine the coefficient of thermal conductivity, two cycles of measurements are carried out sequentially,

The 1st cycle includes measuring the ratio p0 of electrical signals that determine the temperature difference between the external environment (Tc) and the heat-contact (T0) and free (Tir ° 0 faces of samples 5, i.e.

The heat release in the samples is measured, for example, by measuring the current through the sample and the voltage drop across it, i.e. .

When calculating the thermal conductivity coefficient I of the samples in accordance with the formula

ioi y ° gtc

Ti, °) -Tc

0)

From the theory of the method for determining the coefficient of thermal conductivity it follows that

o chw + Ј- | jshu),

(2)

where (about I

Equation (2) establishes the transcendental dependence between the thermal conductivity of sample R, its geometrical dimensions, and heat transfer coefficient a.

Here, Ј is a parameter determining the increase in heat transfer intensity on the free surface in connection with the use of thermocouples 10.

After the 1st measurement cycle, the 2nd cycle is carried out by passing alternating current through samples 5. In this case, the temperature of the heat-leveling plate 3 is maintained at the same level T0 by means of the thermopile 1, and the heat exchange intensity is not changed.

On the free facets of samples 5, new temperatures Tii are set which, in turn, determine new values.

 about

That-ts

(3)

Claims (1)

SUMMARY OF THE INVENTION A method for measuring the thermal conductivity of an electrically conductive sample by passing a heat flux through a heat-contacting face, exchanging heat with the external environment, measuring the geometric dimensions of the sample and the ratio of electrical signals that determine the temperature differences between the external medium and the heat-contacting face, as well as between the external environment and free a sample face, characterized in that  . f (floi) S (T0 - Tc) poi P (4) where f Ooi) (), taking into account both the ratio (measured at I 0 and the ratio (pv, measured by passing current through the samples). Moreover, the dependence f (oi) included in formula (4) can be preliminarily constructed for the selected values of I, s and p with a very high degree of accuracy using equation (2). Thus, in the proposed method for determining the thermal conductivity coefficient of electrically conductive samples, there is no need to shield the side surface or to determine the heat transfer coefficient between the surface of the sample and the external environment: the method reduces to measuring the amount of electric power released in the sample, as well as the value ratios of electrical signals that determine the temperature difference between the external environment and the heat-contact and free faces before and after passing alternating current. The proposed method can be applied for the rapid determination of thermal conductivity coefficients directly in the branches of thermal batteries that are not switched by one of the junctions, in their manufacturing process. which, in order to simplify by eliminating measurements of the heat transfer coefficient, is additionally passed through the sample alternating current and maintain the value of the temperature of the heat-contact face and the heat transfer rate are the same as before passing the current through the sample, while the heat release in the sample is measured and the ratio of electrical signals, and when calculating the coefficient of thermal conductivity, both values of the ratios are taken into account.