SU765712A1 - Device for measuring thermal conductivity coefficient of electroconductive materials - Google Patents

Description

I

The invention relates to thermophysical instrumentation and is intended primarily for use in materials science in the study of the properties of electrically conductive materials.

Experimental installations are known, designed to measure the thermal conductivity by the Kolrausz method, consisting of a heater with a sample placed in it, through which an electric current l is passed.

A known installation by G.E. Ivanchikhina, designed to measure the thermal conductivity coefficient of electrically conductive materials 2. The device implements the Kohlrausch method, which means that the sample used is heated by passing through it with an electric current in an environment whose temperature is set by the heater. The temperature field of the medium (heater) can be either uniform or parabolic, but the temperature of the medium and the sample do not coincide, and the lateral heat transfer is taken into account in the calculated form by the Eger and Disselhorst corrections system. The design formula for the coefficient of thermal conductivity is

lUt

(one)

TV |

8S9

where is 7

- thermal conductivity of the rod,

"

- force passed through the current bar,

U

- voltage drop in the working section of the rod between two extreme thermocouples,

e

- the length of the working section of the rod,

S

- rod cross section area,

b

-temperature difference on the rod between its middle and extreme sections, which could have been formed under the conditions of the adiabatic isoderm of the rod. the temperature difference on the sample, which could have been formed under conditions of adiabatic isolation, is associated with the temperature difference on the sample under the conditions of experience by the following dependence: © -A-LN,. ,, where t is the temperature difference on the sample between its the mean extreme cross sections under the conditions of the experiment, 6.N is the introduced designation comp -4n e -liin -b

where si is the effect of the heat transfer coefficient in the gap between the core and the heater; G is the radius of the rod.

(four)

N -tc-4 A,

where tc, is the ambient temperature (heater),

to - the temperature of the rod in its middle section.

Magnitude. is determined from experience, which is more appropriate, by measuring the stationary distribution of the temperature on the sample with the current on.

Thus, the calculation of corrections requires the investigation of the temperature field along the sample, complicates the measurement process and reduces its accuracy.

The aim of the invention is to improve the accuracy and simplify the process of measuring the coefficient of thermal conductivity of conductive materials.

This is achieved by the fact that in the device for measuring the thermal conductivity of electrically conductive materials, having a heater with a rod-shaped sample placed in it and with three thermocouples fixed on average and extreme sections of the working section of the rod, the power control is set a heater with a thermocouple attached to its inner tube, made of high thermally conductive material, such as copper, and on the rod, in sections, located at a distance of 1/5 dtsh our working area from the middle. regardless of direction, set to the temperature difference between

where the medium and the rod in its middle section.

Subject to conditions (5), the correction for lateral heat transfer in the first approximation is zero, and the calculation formula for the coefficient of thermal conductivity is:

1U2

6)

Aazl

FIG. Figure 1 shows the qualitative distribution of temperatures along the length of the sample (curve a) and its environment (curve b). The choice of X.d2 cross section for securing the fourth thermocouple is determined by the intersection point of curves a and b, for which equality holds:

 f

(7)

8x. 6

by

density of passage

where is the current bar

resistivity of rods n,

X is the current coordinate, measured from the average cross section of the rod.

FIG. 2 shows schematically the proposed device for measuring the thermal conductivity of electrically conductive materials.

It includes sample 1, made in the form of a rod with shafts and ends 2, placed in the inner tube 3 of the security heater 4 made of extruded heat-conducting material, such as copper, the main heater 5, 124 of the full-length thermocouple, and the thermocouple of the security heater and the additional sample thermocouple included differentially, and introduced an automatic control system that controls the operation of the security heater ;. by maintaining a zero temperature difference between the corresponding points of the security heater and the rod. Maintaining a zero temperature difference between the security heater and the rod g in cross section, at an distance of 1/5 the length of its working area from the middle, ensures that the condition is met.

heat shield wrap 6, thermocouples 7 and 8, fixed in the extreme sections of the working section of the rod, thermocouple 9, fixed in its middle section, automatic control system 10 and differentially included thermocouples 11 and 12, one of which is fixed on the inner pipe 3 of the security heater 4 , and the second - on the rod, in the section, located at a distance of

1/5 of the length of its working area from the middle.

The temperature level of experience is set by the main heater 5.

The central zone of the rod under the action of the passing electric current turns out to be overheated relative to the ends 2, which play the role of refrigerators due to the large cross-section and developed outer surface. Temperature

the dip on the rod is determined by thermocouple readings 7-9.

The automatic control system 10 controls the operation of the security heater 4 and ensures that the condition (5) disappears, maintaining a zero temperature difference between the inner tube of the security heater and the rod in cross section that is 1/5 the length of its working section from the center of the rod.

The voltage drop at the ends of the working section of the rod and the current passing through it are also measured.

The use of new elements of a security heater, two differentially connected thermocouples and an automatic control system favorably distinguishes the proposed device for measuring the heat conduction coefficient of electrically conductive materials, since the measurement process is simplified, the need for determination is eliminated

values, and N

which increases the accuracy of the SM measurement.

The proposed device can be used in the study of the initial chemical composition, structure and mode of heat treatment on the properties of materials, as well as in the creation of industrial samples of thermophysical devices.

Claims (2)

1.Osipova V.A. Experimental study of heat transfer processes. M., Energie, 1969, p. 195-2O5. 2. Pepetsky V.E. and others. High-temperature studies of the thermal and electrical conductivity of solids. - M., Energie, 1971, p. 66-67. t Vz 4s 0 g