SU445892A1 - Apparatus for determining the thermal conductivity of solids - Google Patents

Description

The invention relates to devices for thermophysical measurements.

Devices are known for determining the coefficient of thermal conductivity of solids containing a linear source of heat of constant power — a cylindrical probe. An thermocouple heated by an alternating current is used as such a probe. . ,

However, the use of these devices is limited due to hard-to-findable heat loss from the middle to the ends of the probe, especially when examining samples of finite length.

The purpose of the invention is to improve the measurement accuracy,

In this, two additional thermoelectrodes are connected to thermoelectrodes of the probe opposite to them at the points of their exit from the sample and are connected with the ends of the probe so that two pairs of thermoelectrodes of the same name are feedback links forming signals that are in the middle of the center. and at the ends of the probe.

The drawing shows a schematic diagram of the proposed device.

The device contains a system

0 automatic compensation of heat losses at the ends of Zrnd I, consisting of two channels, each of which, independently of the other, heats the exit point of the Zoyd from the sample to the probe temperature, two differential thermocouples serve as feedback links, formed by connecting additional thermoelectrodes 2 sec.

0 by a thermocouple probe, the compound is made at the point where the probe exits sample 3 in such a way that each additional thermocouple | type is joined to the opposite

five

In relation to it, there is a thermal electrode of the probe, and the control signals are thermo-emf. dj (| potential thermocouples are coupled with homogeneous Tej) electrical electrode,

Each channel of the automatic heat loss compensation system consists of an EC-Filter 4, a phase-sensitive amplifier 5, a reversible Electra motor 6, which regulates the current for heating the probe ends from the power source 7 by moving the collector contacts of the rheostat 8,

Thermocouple probe heating is produced from an alternating current source 9 with a frequency of 10-30 kHz using a property meter 10 and split capacitors II and 12, which, like capacitors 13-16, serve to exclude shunting of thermocouples by the output power supply stages.

To record the temperature of the probe is an electromix potentiometer 17, and the input of which has — with a noise immunity meter ;-( iltr 18.

A sample with end caps 19 and 20, a probe with additional thermowells and 2G tires and 22 leads to a probe. Power Hocji: the heater is placed in the thermostat 23,. for 1 h; equal: and T1:; temperature to the sample before starting the test.

ycTpof GTBO | works as follows

.; a hedgehog near the plates from the substance under study is placed in a thermocouple probe T, the Zystiny IUIOTHO clamp is clamped and the valve is inserted into a 2o thermostat. After some time, the sample takes the temperature. the thermostat, the time of occurrence of the legs, is determined by the indications of the electronic (ktron potentiometer 17. this turns on the heating current, as well as the automatic compensation of heat losses, and the temperature change of the probe in v.1x1 is recorded. As the temperature in the center of the probe changes, Emf differential thermocouples, which are fed to the junction of phase-sensitive amplifiers 5 and are tested by reversible motor 6, (the output of the motors of the motors moving the rheostat engines 8, regulating the heating currents through each The end of the zone and the adjacent 1SH4 to it are an additional thermal electrode, thus reducing the signals of the disposable thermocouple to zero.

The device makes it possible to exclude the systematic error in measuring the thermal conductivity of the patient due to the loss of heat at the ends of the probe, and, consequently, to increase the measurement accuracy.

PRGDM51G IZOBRETN1VD

The device, the definition of the heat coefficient of heat conduction of solids, containing the probe-thermopair linear, the compensation system. Loss of the probe and the system of temperature registration, that is, with / for the sake of accuracy of measurement, two additional thermal electrodes are connected to the same temperature as the thermoelectrodes of the probe at their exit points from the sample and are connected with the end of the probe into the system of heat loss companion

probe in such a way that two pairs of identical thermoelectrodes are feedback links, (which form signals proportional to the frequency of the meshes in the middle and on K0 iij, ax of the probe.