RU2783366C1 - Installation for determination of thermal conductivity of materials under pressure - Google Patents

Abstract

FIELD: thermophysical research.

SUBSTANCE: invention relates to the field of thermophysical research and can be used to determine thermophysical characteristics, namely: the thermal conductivity of deformable materials (in particular, contact resistances in a multilayer metal package were studied depending on pressure) under high pressure. The installation includes a housing with a heater and a cooler located inside it, which are mounted on the free ends of the upper and lower pistons. The pistons have the same diameter, between which the test sample of the material is located in a special ceramic container. On the side surfaces of the upper and lower pistons, special blind holes (recesses) with a depth of 1-2 mm are made, in which temperature values ​​are monitored using a contact surface control thermocouple. On the upper piston there is a heater in the form of a nichrome wire, on which heat-conducting dielectric rings are dressed. On the free part of the lower piston there is a refrigerator, which is a closed chamber, and the piston has through drillings - hydraulic channels to improve its cooling. Coolant flows continuously through the refrigerator chamber. In the assembled (working) form, the structure has an inner metal screen and an outer insulating casing made of asbestos cement to eliminate radial heat losses and achieve a steady state of the heat flow flowing through the material under study. The assembled installation is based between the traverses of the compressing press to ensure compression of the pistons of the installation in their axial direction and maintain the necessary pressure on the material under study.

EFFECT: increasing the reliability of the results of measurements of the effective thermal conductivity of powder thermal insulation.

4 cl, 3 dwg

Description

The invention relates to the field of thermophysical research and can be used to determine thermophysical characteristics.

A known installation for studying the thermal conductivity of heat-insulating materials at high temperatures (the temperature on the hot side of the sample is from 400 to 1350 ° C) with a thermal conductivity of less than 0.1 W/(mK) [Penkov M.M., Vedernikov M.V., Naumchik I. V., Zhiganov E.B., Shatov S.V. Installation for the study of thermal conductivity of heat-insulating materials. Patent for invention RU 2289126 C1, 10.12.2006. Application No. 2005111442/28 dated April 18, 2005].

A known installation for determining the thermal conductivity of heat-insulating materials in which the proposed design of the body of a material with a negative coefficient of linear thermal expansion, allowing in the process of heating the sample to reduce air gaps on the surface of the sample [Klimova T.I., Marchenko T.P., Ovchinnikova O.N. . Device for determining the thermal conductivity of thermal insulation materials. Utility model patent RU 94712 U1, May 27, 2010. Application No. 2010108209/22 dated March 9, 2010].

A known installation for studying the effective thermal conductivity of powder-vacuum and screen-vacuum thermal insulation, in which the heat source, the means for measuring the temperature on the hot and cold sides of the sample, pumps of various types to achieve the required vacuum [Plotnikov V.V., Grishin R.V. , Voshchilo O.G., Plotnikova S.V., Kuznetsov A.S. Installation for the study of thermal conductivity of powder-vacuum and screen-vacuum thermal insulation. Patent for invention 2750289 C1, 06/25/2021. Application No. 2020110792 dated 03/14/2020]. The study is carried out by determining the temperature difference on the walls of the samples in the mode of stationary heat exchange with the environment at a known heat flow rate.

A device is known for measuring the thermal conductivity of porous bodies fluid-saturated under pressure at temperatures up to 227 ° C, designed to evaluate deep thermal fields in geophysics and membrane separation processes in the chemical industry [Kuznetsov M.A., Grigoriev E.B., Bogdanov A.V. , Lazarev A.S. A device for measuring the thermal conductivity of fluid-saturated porous bodies under pressure. Patent for invention RU 2492455 C1, 09/10/2013. Application No. 2012105859/28 dated February 17, 2012]. However, the design of this device is very complex and has drawbacks, the main of which are structurally incorporated uncontrolled heat losses from the heater and shell. Mainly, it is aimed at achieving results in the study of precisely fluid-saturated porous bodies, which greatly limits the breadth of the spectrum of its application.

Also known are two devices of the same type for determining the thermal conductivity of deformable materials, in which sensors for measuring temperature and heat flow are installed on the end surfaces of the refrigerator and heater in contact with the test sample [Nikitina T.E., Kazakova V.E., Grishnina N.N. Device for determining the thermal conductivity of deformable materials. Utility model patent RU 141298 U1, May 27, 2014. Application No. 2014104673/28 dated February 11, 2014; Aloyan E.L., Kolodiy B.M., Kolodiy N.V., Retyunskaya T.M. Device for determining the thermal conductivity of deformable heat-insulating materials. Utility model patent RU 147966 U1, 11/20/2014. Application No. 2014130145/28 dated 22.07.2014]. They also have a limiter installed on the heater, in the form of a rigid container with the test deformable material placed inside it, installed on the periphery around the test sample.

There is also known an installation for determining the thermal conductivity of substances and materials (coarse, loose, rubber in the form of plates and packages) by the stationary method of a flat layer, which allows you to determine the thermal conductivity of the material in the stationary mode of thermal exposure to it [Rogov I.V., Polunina N.Yu., Rozhkov A.V., Zhukov N.P. Measuring system based on the IT-3 device for studying the thermal conductivity of materials. Factory laboratory. material diagnostics. 2015. V. 81. No. 8. S. 31-34].

A known device for determining and transmitting thermal conductivity values in the range of 100-500 W/(mK) [Cherepanov V.Y. et al. Measuring equipment and a comparator for measuring high values of thermal conductivity // Measurement techniques. 2009 Vol. 52, No. 10. P. 1107–1111] with a measurement error of up to 5% and a temperature of the test samples up to 70 °C. The possible size of the studied samples is 60×34×8 mm and the time of the measurement experiment is no more than 30 min.

An installation for measuring the thermal conductivity of materials, already in the lower range from 0.04 to 2.0 W / (mK), is shown in [Bol’shev K.N., Zarichnyak Y.P., Ivanov V.A. Determination of Thermal Conductivity by the Method of the Initial Stage of Warming up a Sample by a Constant Heat Flux // Journal of Engineering Physics and Thermophysics. 2018 Vol. 91, No. 5. P. 1342-1346.]. Its measurement error is no more than 7%. A significant disadvantage is the limitation in the duration of the experiment varies from 1 to 30 minutes. It depends on the thickness and thermophysical properties of the studied material samples.

The disadvantages of the devices is the impossibility of determining the thermophysical properties of materials under the influence of any pressure. Also, all of them require the physical installation of measuring instruments on the measured object. Thus, the measuring instruments (thermocouples) become fixed in their position (become part of the installation) and subsequently, the error of their operation is no longer taken into account, and their dismantling and replacement requires significant impact.

The objective of the invention is to create a plant for studying, in particular, the effective thermal conductivity of powder thermal insulation under high pressure up to 75 MPa.

The technical result of the claimed invention is to determine and improve the reliability of the measurement results of the effective thermal conductivity of powder thermal insulation.

This technical result is achieved in that a device for determining the thermal conductivity of a deformable material, including a housing with a heater and a cooler located inside it, between which the test material is located, characterized in that the heater and cooler are mounted directly on the free ends of the upper (hot) and lower (cold) ) pistons between which the test sample is placed; control points (blind holes) for measuring temperature to determine the heat flux are made on the side surfaces of the pistons that compress the test sample of the deformable material placed inside the rigid container; at the same time, the cooler is made integral in the form of a closed chamber together with the lower piston, which has hydraulic channels for better cooling.

The proposed device relates to the field of testing technology, namely the creation of installations for the experimental determination of the thermal characteristics of loose or powdered material (mainly heat-insulating), used to create and test thermal protection of the bearing part of the body of a vessel or apparatus operating under high pressure and having internal heating technological (reaction) space.

The figure 1 schematically shows the proposed device with the following designations:

1 - lower piston;

2 - upper piston;

3 - base;

4 - generatrix of the cooler chamber;

5 - upper generatrix of the cooler chamber - support of the inner metal casing;

6 - inner metal casing;

7 - outer heat-insulating casing;

8 - ceramic container;

9 - dividing wall;

10 - remote ring;

11 - fittings for inlet and outlet of coolant;

12 - protective asbestos disk;

13 - asbestos partition;

14 - spiral heating element;

15 - thermocouple input holes for monitoring temperature values;

16 - an element of a mechanical shutter of holes for input of a thermocouple.

The inventive device for determining the thermal conductivity of deformable materials under high pressure includes the upper 1 and lower 2 pistons made of steel 12X18H10T, the base 3 forming the cooler chamber 4 , the inner metal casing 6 , and the support of the inner metal casing 5 . The outer heat-insulating casing of the installation 7 is made in one piece from an asbestos-cement pipe. Between the upper and lower power pistons in the container 8 , which can be made of ceramic or other material with low thermal conductivity, there is a test deformable material under pressure. The dividing wall 9 separates the heater chamber and the functional chamber in which a stationary heat flow is achieved. The distance ring 10 is designed to ensure alignment between the outer heat-insulating casing 7 and the power pistons 1 and 2 . In the lower part of the installation there is a cooler through which cold running water continuously flows through the inlet and outlet fittings 11 during the entire experimental period. A protective asbestos disk 12 closes the chamber with a heater on top, and an asbestos partition 13 is located between the two technological casings.

The upper part of the upper piston has a radial groove for mounting a spiral heating element 14 in it in a heat-conducting dielectric shell, which excludes the possibility of electric current short circuiting on the rods and the unit housing. The lower part of the lower piston has cross-shaped drilling through holes (hydraulic channels), the axes of which are located in the same plane and perpendicular to each other to increase the degree of efficiency of the cooling zone.

The functional chamber, in which a stationary heat flow is achieved, flowing through the pistons and the test material located between them in a ceramic container 8 , is formed by a composite metal casing 6 , which, during installation, is wrapped with a special heat-insulating tape made of fiberglass to completely eliminate radial heat losses and maintain equivalent temperatures pistons and this casing. The metal casing 6 is also separated from the external environment by an outer heat-insulating casing 7 in order to prevent heat loss to the environment.

The inner surface of the composite metal casing 6 , which performs a shielding function in the radial direction, must be at a distance less than or equal to 10 mm from the surface of the corresponding power piston in order to exclude the phenomenon of convective heat transfer (convection) [Mikheev M.A., Mikheeva I.M. Fundamentals of heat transfer. 2nd ed. Moscow: Energy, 1977. 344 p.]. The gasket from the insulator 13 ensures the heat flow between the parts of the casing 6 in the axial direction, similar to the heat flow along the rod.

The device works as follows. The determination of the thermal conductivity of the material under study is implemented by creating and maintaining a stationary heat flow in the cylindrical parts (pistons) of the observation zone, between which the material under study is located in a closed volume.

The control of the thermal field in the functional chamber of the installation is carried out by means of a contact surface measurement of temperature values through special thermocouple input holes made in both casings 6 and 7 (see Fig. 1).

In FIG. 2 and 3 show the basing of the installation on the traverse of a compression press in laboratory conditions. The basic elements are the end surfaces of the power pistons, for which the cold piston 1 is provided for the lower plane of the base 3 , as well as the protrusion of the hot piston 2 beyond the outer side of the protective disk 12 . Also, the end surface of the hot piston 2 has a centering recess, in which a metal spherical stop can be placed, directing the vector of application of the compressive force strictly to the axis of the pistons to ensure the most uniform compression of the test material in the container in the absence of a ball mechanism for changing the position of the upper traverse of the press.

Claims (4)

1. A device for determining the thermal conductivity of a deformable material, including a housing with a heater and a cooler located inside it, characterized in that the heater and cooler are mounted directly on the free ends of the upper hot and lower cold pistons, made with the possibility of placing between them the test sample located inside the rigid container, and its compression, moreover, the temperature measurement control points for determining the heat flow, made in the form of blind holes, are formed on the side surfaces of the pistons, and the cooler is made one-piece in the form of a closed chamber together with the lower piston, which has hydraulic channels for better cooling. 2. The device according to claim 1, characterized in that the upper hot and lower cold pistons are simultaneously power-receiving and transmitting compressive load elements and are driven by the flat surfaces of the press traverses from their free end ends. 3. The device according to claim 1, characterized in that the temperature measurement at the control points of the pistons is carried out by the contact method using a thermocouple of the surface contact point method of measurement manually without any permanent technological connection of the thermocouple with the control object. 4. Apparatus according to claim 1, characterized in that the temperature of the heating element can be accurately controlled in any range using a power supply that controls the AC voltage that is applied to the heating element.

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