SU290211A1 - DEVICE FOR DETERMINATION OF HEATING WIRE - Google Patents

Description

The invention relates to the field of thermophysical measurements.

Devices are known for measuring the thermal conductivity of homogeneous solids by the absolute method of stationary heat transfer.

The known devices for determining the thermal conductivity contain an oOraze heater, a heat source, a heat pipe from the heat source to the cold-coolant, temperature-sensitive elements for measuring the temperature difference between the ends of the sample, the radiation screen ;; II thermostating screen with heater located.

In all existing devices, the temperatures and the temperature distribution over the padding screens are significantly (1-10 ° K or more) different from the temperatures and temperature distributions over the sample and heaters.

In this case, the main contribution to heat1,1o is the loss of heat exchange by radiation. Heat losses due to radiation in existing ycTpoii factions can reach significant values; and, as a rule, are not taken into account.

The aim of the present invention is to reduce the error in determining the heat conductivity coefficient of homogeneous solids by the absolute method of stationary longitudinal heat flux in the temperature range 4.2-450 ° K.

This is achieved by the fact that in the proposed device a radiation shield made of high-conductive material, such as copper or silver, made in the form of two coaxial cylinders, is equipped with a heater installed concentrically with the sample heater, and the hepatitis line is made in the form of a thin layer of low heat conductive material, for example, stainless steel, filled with gas, gas, 0: Example i, with nepeMCHHiiiM adjustable pressure.

FIG. I depicts the described device; in fig. 2 - heat design water.

The device is made of figurative /, clamped with the help of threads 2 (for example, from capr. Of nylon) and adjusting BiniTOB between the heater 3 of the sample and the thermal receiver. Sample 7 is surrounded by radiation; 1nn screen G 1 5. 6 with its own heater 7, which have d, /, equal to the length pb.kkgtsa / o c are made of high-temperature, thin-nymosteramide material (eg copper, silver). The inner and outer surfaces of the radiation shields 5, 6, heaters 7, and the upper surfaces of the receiver 4 and heater 3 of the sample are nosirondants and polished for less than 1 and heat exchange by radiation (if

The pattern is polished, preferably polished).

The screens are located as close as possible to the surface of the sample / and have the same geometric shape of the section as the sample. The heater 3 is surrounded on all sides except the side contacting with sample 1, the heater 7 of the radiation shields, the temperature of which is maintained equal to the temperature of the heater 3 and is controlled by using two or multi-differential differential seals.

In the heater 7 of the radiation shields 5, 6 and in the heat receiver 4, exemplary (or laboratory) resistance thermometers 9 of the TSG or TSPN type are located. The thermostating screen 10 (the silver screen surfaces of the TC and are polished), having its own heater 11, is in thermal contact with the heat sink 4.

Between the heat sink 4 and the flange of the vacuum chamber 12 there is a heat pipe 13, which is a cylinder-shaped device with a sheath 14 of low heat-conducting material, for example stainless steel (see Fig. 2). The internal cavity of the heat conductor consists of two blocks of thin-walled cylinders 15 of a material with high thermal conductivity, nard: Imer of copper, placed with a minimum gap between each other and fixed alternately on the lower 16 and upper 17 flanges of the heat pipe. The heat pipe is filled with a tenlo exchange gas, such as helium, under pressure within 5. 10-760 tor / 5, through a capillary 18. The entire device is attached to the inner surface of the vacuum chamber 12, which is placed in a Dewar vessel filled with refrigerant For example, with liquid helium, hydrogen, aeotome, etc.

A device placed in a vacuum chamber 12 of a cryostat accepts a temperature close to the coolant temperature. The pressure in the vacuum chamber is maintained at up to 5 10 Torr.

With the help of heaters 3, 7, the device is brought to the desired temperature range. The temperature of the heater 7 is controlled by adjusting the current. The heater resistance is maintained equal to the heater temperature "3 samples, control is carried out using a differential thermocouple 8. The temperature of the heater 7 and the receiver 10 is measured by reference thermometers 9 resistance thermometers. The radiation screens 5, 6 and the sample have the same length, are placed at the same levels and have exactly the same temperature of the ends, which results (taking into account the thermal conductivity of the screen material to neglect the heat losses from the screen to the outside compared to the heat flux from the screen 7 to the heat sink 4) to the spontaneous establishment of the same temperature gradients on them in a stationary mode. This provides a significant reduction in heat transfer between the screen and the sample.

An inner screen 5 for further reducing heat exchange by radiation between it and sample 1 is located as close as possible to the sample. The outer screen o serves to minimize heat exchange between the inner screen 5 and the surrounding space, i.e., to ensure: 1 and strictly identical temperature gradients but a pattern on the inner screen along their entire length. The thermostating screen 10 with a self-contained heater 11 is designed to reduce heat exchange by radiation between the measuring part ycTpoiiCTBa and the surface of the vacuum chamber 12, which has a refrigerant temperature, and allows you to provide opps; you can measure different measurements over the entire temperature range by reducing the power level allocated heaters x 3, 7, reduction of possible temperature gradients but heaters m 3, 7, etc.

The heat pipe 13 is designed to set the temperature of the heat sink 4 and to make measurements possible both at M minimal temperatures (close to the refrigerant temperature) and npin maximum (i.e., up to 450 ° K).

The inner space of the heat pipe 13 for performing measurements at minimum temperatures is filled with heat-exchange gas, for example gel, at the required pressure (up to 760 Torr), which provides a sufficiently high thermal conductivity of the heat pipe, i.e. the minimum temperature difference of the heat sink and refrigerant. At maximum temperatures, the heat exchange gas from the heat pipe is pumped out to the torr pressure, which leads to a substantial reduction in the heat conduction of the heat pipe (practically only the heat conductivity of the thin-walled shell 14 of low heat conductive material remains) while maintaining optimal temperature gradient patterned.

At intermediate temperatures, the pressure in the heat pipe is set in such a way as to perform the optimum modes of experiments.

The calculation of thermal conductivity is made by the known formula

1 -1 ts

where Q is the heat flux passing in the unit

time through the sample; 1o is the length of the sample;

5 is the cross-sectional area of the sample;

47 — established at 1 times the temperature over the entire length of the sample. The characteristics of the sample / o and 5 are known before the experiment.

the receiver, the heater of radiation screens, the sample heater, the thermostating screen, the heat conductor are selected taking into account the tenconductivity of the sample being measured, its length and diameter.

Subject invention

A device for determining the thermal conductivity of solids, containing temperature-sensitive elements, a sample heater, a concentric with a sample, a radiation screen surrounded by a thermostating screen located in a thermal

contact with a heat receiver connected to the flange of the vacuum chamber by a heat conductor, characterized in that, in order to increase accuracy, the radiation shield of a highly heat-conducting material, such as copper or silver, made in the form of two coaxial cylinders is equipped with a heater installed concentrically with the sample heater, the heat pipe is made in the form of a cylindrical shell of a low heat-conducting material, for example, "stainless steel welded with heat-exchanging gas, for example helium, with variable adjustable pressure iem.

- (Ladagent

Fig /

to x adag.entu Heat-expelled gas

five

 A heat sink

Phi .2