SU1599740A2 - Method of measuring heat conduction of substances - Google Patents

Abstract

The invention relates to thermal tests, namely the determination of the thermal conductivity of substances. The purpose of the invention is to increase accuracy and sensitivity. The goal is achieved by narrowing the measurement range, in which the thermal conductivity is determined, by introducing between the thermally conductive element and the samples, both test and reference, additional elements with thermal resistance R @ and R @, which are chosen depending on the required measurement range. 1 il.

Description

(ABOUT

with:

The invention relates to thermophysical measurements and can be used. This is used to measure the thermal conductivity of a wide range of substances.

The aim of the invention is to improve accuracy and sensitivity by narrowing the measurement range.

The drawing shows a schematic diagram of a device that implements the proposed method.

The device consists of an electric heater 1 placed on the heat-conducting element 2 with the possibility of movement along its axis. The sample 4 and the reference sample 5, identical in geometric dimensions, are applied to the heat sinks 3. The heat-leveling layer of the 6 flues are located between the samples and the heat-conducting element, with differential differentials mounted in them. thermo, pairs 7 and elements 8 and 9 with calculated thermal resistances, respectively Rg, and Rg. The equation for plate temperature is controlled by a null indicator 10.

The method is implemented as follows.

P1 examined 4 and reference 5 samples, heat leveling plates 6 and elements 8 and 9 are pressed to heat conducting element 2 by means of QTOKOB heat 3. The electric heater 1 is connected to the network. After the readings of the zero indicator 10 are set. The electric heater 1 is moved along the heat conductor of the element 2 so that in the stationary thermal mode the signal of the differential thermocouple 7 is equal to zero, and according to the position of the heater 1 relative to the reference and investigated range

(R

:about

m

(the samples determine the thermal conductivity of the material under study but the formula

about. B 1

S,

1 + k, lj:

GT1G

nineteen,

(one)

H; C

tolvsin respectively studied and reference samples;

Ig; Ig is the thickness of elements 8 and 9;

ten

15

1 20

5 - the area of cross sections of the standard and the sample;

 thermal conductivity of the studied and reference samples;

the distance from the heater to the test and reference samples, respectively, at the time of the equilibrium condition of the bridge circuit; coefficients that establish the relationship between the thermal conductivity of 25 L 9,, L 3t elements 8 and 9, and L of the heat conducting element 2 (K,

 Le, K,).

The thermal resistances of the elements and 9 K 3 and Rg are calculated preliminarily depending on the required measuring range according to the formulas

 Ko 30

(2)

(3)

de Rg - thermal resistance

an element that comes into contact with a heat conduction device: an element from the side of the sample under study; Rg - thermal resistance

the element in contact with the heat conductor: m element from the side of the reference sample; thermal resistance

heat conductive element;

NJ; Nj is the lower and upper limit of the intended measurement range, N ,, COOT-55. veteran;

R. jj / R- is the ratio of the thermal resistances of the sample and the standard.

0

five

0

five

Example. It is necessary to measure the deviation of the coefficient of thermal conductivity in samples of the same material and the same geometric dimensions. It is assumed that it varies by ± 10%, i.e. Ry / R 0.9; 1.1. In order to increase the sensitivity of the installation that implements the proposed method, we calculate the thermal resistances of the additional elements, taking into account that the heat conductor, the element, is made of low carbon steel (A 54 W / (m K)) and has a diameter of 15 mm and a length of 70 mm:

R 7.34.0.9 (1, H1) 4 (K (W) - 4, 1.1-0.9 LV, 4 (. K (.5Т,

 M-5 G -69.7 (C / c.).

. h. , l

The thermal resistance of a heat-conducting element made of carbon steel is equal to

70PO-3 34 (K / W).

H

,, 7-15-п-с 54. -7 10

Elements 8 and 9 were made of

-. f

organic glass with 7 0.194 W /. m K, diameter 15 mm. The thickness was calculated from the formula: R -.

P

69.4

19, -MO

-3

0.194. ten

 0 -.-.-.

0.194

152

 ten

b

From here 1з, 2.4 mm; 1d 2,4 mm.

Measurements were measured: the changes in thermal conductivity along the length of a semiconductor ingot with a diameter of 10 mm, from which samples of the same thickness were made — 2 mm. The measurements showed a non-monotonic change in the thermal conductivity of a semiconductor material and the length of the ingot within 1.38-1.56 W / m · K. The data obtained is in good agreement with the passport data.

The proposed method makes it possible to increase the accuracy of measuring the heat conductivity of substances by choosing the required measurement range and increasing the sensitivity.

51

Claims (1)

The invention The method of measuring the thermal conductivity of substances according to ed. St. No. 1376021, characterized in that, in order to increase measurement accuracy and sensitivity, the contact between the heat-conducting element and the samples, both the test and the reference, is made through additional elements with thermal resistances, which are chosen depending on the required formula measurement range  RT-N, (N + 1). Nj - N,  RT (Ni 1) - N, - N, R g - thermal resistance J M -f N the element in contact with the heat conductor; - an element from the side of the sample under study; Rg is the thermal resistance of the element in contact with the heat-conducting element from the side of the reference sample; thermal resistance of heat-conducting element4 , 2. lower and upper limits of the estimated measurement range Rx / R 9, respectively; Rj, thermal resistance of the sample and the reference, respectively. I