RU126837U1 - DEVICE FOR DETERMINING THE HEAT CONDUCTIVITY OF DEFORMABLE MATERIALS - Google Patents

Abstract

A device for determining the thermal conductivity of deformable materials, including a housing with a heater located inside it, a refrigerator, between which the test sample is located, temperature and heat flux sensors installed on the end surfaces of the refrigerator and heater in contact with the test sample, as well as a limiter mounted on the heater perpendicular to its end surface, characterized in that the limiter is made in the form of a cylindrical hollow ring, vn whose morning diameter is equal to the outer diameter of the test sample.

Description

The utility model relates to the field of thermophysical research and can be used to determine the thermal conductivity of insulating materials.

A device is known for determining the thermal conductivity of materials, including a test sample, a heater for heating the sample, and temperature meters (see V. A. Osipova. Experimental study of heat transfer processes, Moscow, ed. Energia, 1969, p. 194). The disadvantage of this device is the difficulty in determining the desired characteristic (thermal conductivity) due to the non-stationary method.

The closest in technical essence to the claimed utility model is a device for determining the thermal conductivity of deformable materials, comprising a housing, with a heater, a refrigerator located inside it, between which the test sample is located, temperature and heat flux sensors installed on the end surfaces of the refrigerator and heater, contacting with the test sample, as well as a limiter mounted on the heater perpendicular to its end surface (see atent Russian Federation for useful model №116641, IPC G01N 25/18, 2012). The disadvantage of this device is the low accuracy of determining the thermal conductivity of deformable materials due to heat leakage through the side surface of the sample.

The fact is that the real heat distribution in the sample is not one-dimensional, as is taken into account when calculating the coefficient of thermal conductivity, but two-dimensional. Part of the heat from the heater in the form of losses goes through the side surface of the sample. To do this, they try to make the ratio of the diameter of the sample to its thickness as large as possible. However, in any case, heat losses will occur. The greater these losses, the greater the error in determining the thermal conductivity.

The aim of the proposed technical solution is to increase the accuracy of determining the thermal conductivity of wrought materials.

This goal is achieved by the fact that in the known device for determining the thermal conductivity of deformable materials, including a housing with a heater located inside it, a refrigerator, between which the test sample is located, temperature and heat flow sensors installed on the end surfaces of the refrigerator and heater in contact with the test sample, as well as a limiter mounted on the heater perpendicular to its end surface, in it the limiter is made in the form of cyl an Indian hollow ring, the inner diameter of which is equal to the outer diameter of the test sample. In the proposed device, the limiter not only eliminates excessive deformation of the test sample, but also significantly reduces heat leakage through the side surface of the sample, since the limiter has a certain thermal resistance. The lower the coefficient of thermal conductivity of the material of the limiter, the less these leaks will be. In addition, given that the internal diameter of the limiter is equal to the external diameter of the test sample, the latter will not change its dimensions in the radial direction when loaded, that is, the structure of the sample will not change, which is very important for understanding: for what material we determined the thermal conductivity.

The figure shows the inventive device with the following notation:

1 - housing;

2 - electric heater;

3 - refrigerator;

4 - test sample;

5 - temperature and heat flux sensors;

6 - cargo;

7 - nozzles for supplying coolant;

8 - limiter.

The inventive device for determining the thermal conductivity of deformable materials includes a housing 1 made of heat-insulating material. A heater 2 and a refrigerator 3 are located inside the housing 1. A flat test sample 4 is placed between them. Sensors for measuring temperature and heat flux 5 are mounted on the end surfaces of the heater 2 and the refrigerator 3. Weights 6 are placed on the refrigerator, which provide the force of pressing the refrigerator 3 against the sample 4 The supply of coolant to the refrigerator 3 is carried out through pipes 7. On the heater 2, a limiter 8, made in the form of a cylindrical hollow ring, is fixed perpendicular to its end surface whose inner diameter is equal to the outer diameter of the test sample. The height of the limiter 8 is less than the thickness of the test sample 4 by Δ.

The device operates as follows. An electric heater 2 with a limiter 8, a test sample 4 and a refrigerator 3 are installed in the device’s case. Temperature and heat flux sensors 5 are already included in the heater 2 and the refrigerator 3. Then, loads 6 are applied to the refrigerator 3 until the refrigerator 3 rests against the limiter 8. Given that the height of the limiter 8 is slightly less than the thickness of the test sample 4, the latter is slightly deformed and thereby eliminates air gaps between the test sample 4 and the refrigerator 3, as well as the heater 2. In this case, the material structure of the test sample does not change due to the insignificant gap Δ and the impossibility of deformation in the radial direction. Then, voltage U is supplied to the heater 2 to create a predetermined temperature, and coolant is supplied through the nozzles 7 to the refrigerator 3. During the test, the temperature is measured on the surface of the heater 2 Tn and on the surface of the refrigerator 3 Tx, as well as the heat flux q passing from the heater to the refrigerator. The value of thermal conductivity itself after the establishment of a stationary heating mode is determined by the formula:

Where: λ is the thermal conductivity of the test sample; δ is the thickness of the test sample; q is the heat flux from the heater; (Tn-Tx) - temperature difference across the thickness of the test sample.

Introduction to the design of the device of the limiter in the form of a cylindrical hollow ring by reducing heat leakage through the side surface of the test sample can significantly improve the accuracy of determining the thermal conductivity of deformable materials: rubbers, foams, fibrous heat insulators and some others. Due to the equality of the outer diameter of the sample and the inner diameter of the limiter, the structure of the studied material does not change and the obtained value of thermal conductivity refers specifically to the starting material. The limiter to perform its function, on the one hand, must be made of a sufficiently hard material, and on the other hand, this material must have high thermal resistance. Such materials include, for example, thermosetting plastics.

The authors conducted an experimental verification of the claimed technical solution, which showed good results. The result is an increase in the accuracy of determining the thermal conductivity of heat-insulating materials by 6-8%.

Claims (1)

A device for determining the thermal conductivity of deformable materials, including a housing with a heater located inside it, a refrigerator, between which the test sample is located, temperature and heat flux sensors installed on the end surfaces of the refrigerator and heater in contact with the test sample, as well as a limiter mounted on the heater perpendicular to its end surface, characterized in that the limiter is made in the form of a cylindrical hollow ring, vn whose morning diameter is equal to the outer diameter of the test sample.

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