SU1627948A1 - Device for thermal physics measurements - Google Patents

Abstract

The invention relates to thermal testing. The purpose of the invention is to expand the range of measurements to low temperatures and increase the accuracy of measurements. The device implements the mode of dynamic heating of the sample placed between the heat source and the heat meter. It is equipped with a horizontally detachable shell for pouring cryogenic liquid. The upper part of the shell has an opening for the spill of cryogenic liquid in the lower part, and the lower part is equipped with two drainage tubes dispensing the volume of cryogenic liquid. The expansion of the measurement range to the low temperature region is achieved by limiting the heat influx to the sample at the initial stage of testing, and the increase in accuracy is due to the possibility of limiting the rate of heating the sample. Yo

Description

The invention relates to thermal tests, namely to measurements of the thermophysical properties of substances.

The purpose of the invention is to expand the range of measurements to low temperatures and increase the accuracy of measurements.

The drawing shows a schematic representation of the device.

The device consists of a detachable body 1, a heat insulating sheath 2, and a heat metering cell consisting of plates 3 and 4 in contact with the surfaces of sample 5 in the form of a disk. Plate 3 is provided with a heater — a source of heat, and plate 4 is a heat sink. The contact plates are surrounded by a system of adiabatic shells 6–9, equipped with heaters and thermal receivers. Between the cell and the heat insulating casing, there is a dismountable horizontal casing for pouring a cryogenic liquid. The upper part of this shell 10 is made in the form of a cap with a double side wall, is open at the top, and the lower part is in the form of a cup 11 separating the heat measuring cell. thermal insulation shell 2. A drain tube 12, the upper level of which coincides with the upper edge of glass 11, limits the level of cryogenic liquid in the glass, and tube 13 determines the amount of cryogenic liquid in glass 11 before the start of the experiment. The rod 14 serves to transfer the pressure to the upper plate 4, the funnel 15 is used to pour the cryogenic liquid into the cooling device.

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cells The device is equipped with automatic control systems (SAR) 16-21, which determine the heating mode of the device and maintain the equality of temperatures between the individual parts of the cell (the adjustable parameters are described in more detail later).

The device works as follows.

The test sample 5 is placed on the lower contact plate 3 and pressed against the contact plate 4. Then, through a funnel 15, a cryogenic liquid, such as liquid nitrogen, is poured into the device. The fluid washes in successively all the details of the cell, spilling through holes in the upper part of the shell 10 and in the bottoms of adiabatic shells 6–9. through which a large number of wires from heat sinks and heaters are taken out and through which the cryogenic liquid after filling the volume of the double wall of shell 10, washing the part with a heat meter cell and the sample, accumulates in glass 11. Cooling the parts of the measuring cell is due to evaporation of the cryogenic liquid at all parts. When the temperature of the upper part of the shell 10 reaches the boiling point of the liquid, the shell 10 and the cup 11 are filled to the upper level of the drain tube 12. When all parts have reached the boiling point t0 of cryogenic liquid, the valve of the tube 13 is opened and the calculated amount of cryogenic liquid remains in the vessel.

The control systems are turned on and the working stage of the experiment begins. ATS 17 sets the required heating rate bo of the contact plate 4, ATS 18 maintains an optimal beaver temperature drop on the sample. Automatic control systems 16, 19-21 maintain the temperature equality between the individual parts of the cell. In the process of heating, a measurement is made of the power released in the contact plate 3, the temperature drop across the sample in Obr, the heating rate of the upper contact plate 4. The thermal conductivity is calculated by the formula

W W ((C + 0.5Co6p)

Я50обр (j

where W is the power released in the plate 3, W;

S is the sample section area, m2; h is the sample thickness, m;

Cn is the heat capacity of the contact plate 3, J / K;

The specimen heat capacity of the sample, j / k.

The placement between the heat meter cell and the heat insulating sheath of an additional detachable sheath filled with a cryogenic liquid allows the working range of measurements to be extended to low temperatures and to increase the measurement accuracy. In the presence of a shell with

at a temperature equal to the boiling point of a cryogenic liquid, the heat inflows to the heat meter cell from the environment are reduced. At the same time, the rate of natural heat of the heat meter

The cells will be less than or equal to the nominal heating rate selected, which allows measurements to be made from lower temperatures.

In the initial stage of the experiment in glass 11

A certain amount of cryogenic liquid is retained due to the protruding part of the nozzle 13, which is capable of vertical movement.

Level h of the upper edge of the tube 13

relative to the bottom of the glass is determined by the formula

) + MHi-o

where to. tcp, tr — according to the boiling point of a cryogenic liquid at normal pressure, the ambient temperature, the limiting temperature of the measuring cell, at which the rate of natural heating of the measuring cell becomes equal to the given speed;

p, g — density and heat of evaporation of a cryogenic liquid, kg / m, J / kg;

B o the given heating rate of the measuring cell;

L - thermal conductivity between the measuring cell, on the one hand, the shell 10 and the glass 11 on the other, W / K;

/ V — thermal conductivity between the measuring cell and the medium, (W / K); 5d - the area of the bottom of the glass 11, m Formula (2) is obtained from the condition that the rate of natural warming of the heat meter cell does not exceed the specified one, and

heat tolerated by insulating

shell, goes to the evaporation of the remaining cryogenic liquid.

The first measurement of thermal conductivity can be performed almost as high as the boiling point of a cryogenic liquid by about half the temperature difference across the sample. The initial test temperature can be estimated by the formula

Tnach to + 0,5 $ arr b DO

where the beaver temperature difference on the sample, K;

Fop is the value of the Fourier criterion at which regulation of the temperature field in the sample occurs;

a - thermal diffusivity of the sample, m2 / s

A decrease in bo, as can be seen from (3), lowers the initial test temperature. At the same time, this makes it possible to increase the measurement accuracy by reducing, in accordance with (1), the final result of the error in determining the total heat capacity Cn of the plate 3 and the test sample Coll. Usually, the 1st Sobriz “is only tentatively with T 10–30%. Sci; kenio bo allows umenpamt relative role of the second term in the numerator of formula (1), and accordingly, the non-excluded part of the error. In addition, it allows to increase the sample fineness, which is important in the study of composite heterogeneous materials. At the level of correction for the heat capacity of the sample 5%, which is easily achieved at a heating rate of 0.025 K / s, the error of the task of Colr 20% does not exclude a part of the error in measuring A of 1% or less. At a rate of bo boil 0.1 K / s, this error increases to 4%. In the study of materials with low thermal diffusivity, for example, organic glass with a 0.1 m2 / s, 2h 4 mm thick with a temperature difference on a sample of 20 K, the initial test temperature when using liquid nitrogen in accordance with (3) is 185 ° C.

In the absence of a shell for placing a cryogenic liquid, the natural heating rate is 0.3-0.15 K / s and measurements can be carried out only from (-80H-100) ° C.

Testing of the layout of the proposed device confirmed its effectiveness. The model was created to measure the thermal conductivity of materials with, 1-10 W / (m K) in the temperature range -170-400 ° C. The diameter of the cup 11 and the shell 10 was chosen to be 65 mm, the floor of the shell 10 had double walls at a distance of 8 mm, and the height of the heat cell was about 120 mm. The cell was cooled with liquid nitrogen, consumption

nitrogen does not exceed 1 liter per o; .hj will test; - - The tube is 13 high, no HEH tggl, - | t. 11 was 20 mm. The npii temperature — 170 ° С, the rate of natural g-tsg -ccc so5 was 0.025 K / s. Test about samples from organic glass,;, zarya, glass, TF-1 glass; The market has exceeded 5%.

10Thus, in comparison with the prototype model, the invention of sbcep / - expansion, - range; with low temperatures. It also provides accurate enhancement. and 1.mer. yi

15 C due to decreasing the primary - ig.lop ittoko to a drinking cell in the initial stage ist due to treatment of the patient more optimally than the pattern of heating the sample.

The device in accordance with image 120 f. oxer is used in physical studies and in npt thermal imaging.

cG) formula of the invention. Device for heating. Izgrecheny, containing a housing in a horizontal plane detachable, located inside it is a toppozo sheath dismountable in the same plane, r-co-operating heat thermometer, cr. About 30 of the two PTSTN, contact1 surfaces of the sample, one of which is provided with a heater — a source of heat, and the second is a heat source. adiabatic ooochochek around the plates,

35 characterized in that, in order to expand the measurement range of the low temperature region and increase the measurement accuracy, it is equipped with: - a% in the horizontal plane with a shell for

40 is a cryogenic liquid, with its upper part made in the form of a double side wall, open at the top, and placed between the heat meter cell and the upper part of the heat removal shell, and the lower part of the shell is made in the form of a cup, and the heat insulator is located between the heat meter cell and the lower part. This shell is provided with two drain pipes, the upper

50, the level of the first tube coincides with the upper bead of the glass, and the second. I tube of the tube with the possibility of rectification, with its upper level located above the bottom of the glass.

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Claims (1)

Claim Device for thermophysical ·. measurements, containing a body that is detachable in the horizontal plane, a heat-insulating shell located inside of it that is detachable in the same plane, which surrounds the heat-measuring cell, which consists of two plates in contact with the surfaces of the sample, one of which is equipped with a heater - a heat source, and the second is a heat receiver, and adiabatic shells around the plates, characterized in that, in order to expand the measurement range b low temperature region and improve measurement accuracy, it is equipped with a detachable the horizontal plane of the casing for cryogenic liquid, the upper part of which is made in the form of a kelpack with a double side wall open on top and placed between the heat measuring cell and the upper part of the heat-insulating shell, and the lower part of the shell is made in the form of a glass, placed between the heat measuring cell and the lower part insulating sheath and provided with two overflow tube, the upper level of the first tube coincides with the upper edge of the cup, and the second tube you ^claim opnecha for vertical n remescheniya. and its upper level is located above the bottom of the glass.