SU797331A1 - Device for measuring radiation capacity of heat insulating materials - Google Patents

Description

The invention relates to the field of thermophysics, in particular to devices for determining the emissivity of heat-insulating materials and coatings.

A device for studying the emissivity of a surface and coating on it is known, containing a vacuum container in which a sample is heated by electric current [1].

The disadvantage of this device is that it is possible to study the emissivity of only electrically conductive materials.

Closest to the invention is a device for determining the emissivity of heat-insulating materials, containing a vacuum chamber, a flat radiation heater with a hole, a thermal insulation unit, a rotation unit of the object under study and a sensor [1].

A disadvantage of the known device is the low accuracy of determining the emissivity of the sample, since it is almost impossible to ensure equal temperatures of the studied sample and the blackbody model. In addition, the wedge-shaped gap used in the device is an imperfect model of the black body.

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

The goal is achieved by the fact that in the device for determining the emissivity of heat-insulating materials containing a vacuum chamber, a flat radiation heater with an aperture, a heat insulation unit, a rotation mechanism of the test object and a radiation sensor, a flat disk with a hole is installed between the heater and the test object, made of heat-conducting material, while both surfaces of the disk and the working surface of the heater have a coating 15 with known emissivity.

In FIG. 1 schematically shows a device; in FIG. Figure 2 shows the dependences of the emissivity of the KO-818 coating on metal (9) and on heat-insulating material (10).

It contains a vacuum chamber 1, a flat radiation heater 2 located in it with temperature sensors 3 mounted on it, a rotation mechanism for the test object 4, a radiant flux sensor 5 and a flat metal disk 7 prepared by temperature sensors 6. The surfaces of the heater and the disk are coated with a known emissivity30. The object under study is mounted on a rotation unit parallel to the disk and the heater.

The device operates as follows.

In the process of testing (heating the sample) after reaching the stationary thermal mode of the heater and the disk, the sample is rotated and the density of the radiant flux from the sample is measured with a sensor. In addition, the temperature of the heater and the disk are measured. The emissivity of the test sample is determined by the formula:

_g _ ^ sensors + ^ε ηρ ' ^σ (^ 2 _____ ^ - ^ (7 ^ -7 ^) -1) and Л ^^ sensor / ®. ⁰ ] ⁷⁴ .

where ε _Π ρ is the reduced degree of blackness of the heater - disk system, equal to _e ______ ^£ 2 ^£ 7_____

-Pr '- ^ε 2 T ^ε 7 - ^ε 2 ^ε 7 σ - Stefan – Boltzmann constant;

T ₂ , T? ', Ta - temperature of the heater, disk and sample, respectively;

e ₂ ; 87; 8c - degrees of blackness of the heater, disk and sample, respectively.

In the case when the sample rotates at a sufficiently high speed, which can be determined by calculation or experimentally, the radiant flux sensor measures the density of the intrinsic radiation of the studied surface of the sample.

Disk 7 in the proposed device performs a dual function. First, taking into account the known degree of blackness of the surfaces of the disk and the heater and the simplicity of measuring their temperatures, the emissivity and temperature of the studied surface of the sample are determined quite accurately. Secondly, by appropriate selection of the material and the thickness of the disk, it is possible to achieve isothermality of the disk and, most importantly, the studied surface of the sample, which also improves the accuracy of determining the emissivity.

From FIG. Figure 2 shows that the accuracy of measuring the emissivity lies within the limits characteristic of measuring the emissivity of coatings on metals. i.e., determined with an accuracy of 5%; while the known devices for determining the emissivity of non-metals have errors of at least 10%, since the errors in measuring the surface temperature of non-metals are considered satisfactory if they are 2–3%, the error in measuring the emissivity will be 8–12%. Thus, this device allows to increase the measurement accuracy compared with the prototype by about 2 times.

Claims (2)

8 is mounted on the rotation assembly in parallel with the disk and the heater. The device works as follows. During the tests (heating the sample) after the heater reaches the steady-state thermal conditions, the sample is rotated and the density of the radiant flux from the sample is measured using a sensor. In addition, the temperatures of the heater and the disk are measured. The emissivity of the test sample is determined by the formula: Dan. .r ° () T, () a ZZ, where epr is the degree of blackness of the heater – disk system, is -2 T –7 7 O — Stefan – Boltzmann constant; 2, Tf, TS are the temperatures of the heater, the disk and the sample, respectively; 2, ate, 88 — degrees of blackness of the heater, disk, and sample, respectively. In the case when the sample rotates at a sufficiently high speed, which can be determined by calculation or experimentally, the radiant flux sensor measures the intrinsic density of the sample surface under investigation. The disk 7 in the proposed device performs a dual function. First, taking into account the degree of blackness of the disk surfaces and the heater, and the simplicity of measuring their temperatures, the emissivity and temperature of the sample surface under study are determined quite accurately. Secondly, by appropriate selection of the material and the thickness of the disk, the isothermality of the disk and, most importantly, the sample surface under investigation can be achieved, 4tO also allows to increase the accuracy of emissivity determination. From FIG. 2 that the accuracy of measuring the emissivity lies within the limits characteristic of measuring the emissivity of coatings on metals, i.e. determined with an accuracy of 5%; While the known devices for determining the emissivity of nonmetals have an error of at least 10%, since the measurement errors of the surface temperature of nonmetals are considered satisfactory if they are 2-3%, the measurement error of the emissivity will be 8-12%. Thus, this device allows to increase the measurement accuracy in comparison with the prototype by about 2 times. Apparatus of the Invention A device for determining the emissivity of thermal insulating materials, comprising a vacuum chamber in which a flat radiation heater with an opening is located, a thermal insulation unit, a rotation mechanism of an object under study, and an emission sensor, characterized in that, in order to improve measurement accuracy, between a heater and The object under study has a flat disk with a hole made of heat-conducting material, with both surfaces of the disk and, the working surface of the heater having a coating with a known emissivity. Sources of information taken into account in the examination 1. The radiative properties of solid materials. Edited by A. K. Sheydlin, M., Energie, 1974, p. 151. 2. Radiating properties of solid materials. Edited by A. K. Sheydlin, M., Energie, 1974, p. 139-140 (prototype). 5 j xxx- J ooo - fS