Device and method for measuring apparent heat conductivity coefficient of powder at low temperature

Abstract

According to the device and method for measuring the apparent heat conductivity coefficient of the powder at the low temperature, the G-M refrigerating machine is adopted for providing the cold boundary temperature, and compared with a traditional method for providing the cold boundary temperature through low-temperature liquid, the device and method for measuring the apparent heat conductivity coefficient of the powder at the low temperature have the advantage that measurement accuracy is improved. According to the invention, a large amount of low-temperature liquid can be saved, the experiment time can be greatly shortened, a lower cold boundary temperature can be reached, and the cold boundary temperature can be as low as 4.2 K, so that the measurement of a lower temperature can be realized. Moreover, a heater is arranged for the second-stage cold head, the second-stage cold head is heated when needed, the cold boundary temperature can be adjusted, and therefore powder apparent heat conductivity coefficient measurement under the wide temperature zone (4.2-400 K) can be achieved. The device can realize the measurement of a liquid hydrogen temperature zone and a wide temperature zone, the measurement is accurate and rapid, and the cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of powder thermal property measurement, and in particular relates to a device and method for measuring the apparent thermal conductivity of powder at low temperature. Background Art

[0002] Powder insulation material is an important insulation material. It achieves insulation effect by filling small granular solid powder with low thermal conductivity between hot and cold surfaces. There are many types of powder insulation materials, common ones include hollow glass microspheres, pearl sand, aerogel, etc. However, there are many types of powder insulation materials, and the insulation effects when applied to different cryogenic liquid storage are different, and the insulation performance is difficult to predict when the vacuum degree and the temperature of the hot and cold boundaries change. Therefore, how to accurately measure the apparent thermal conductivity of powder insulation materials at vacuum and low temperature is the research focus in this field, which has important engineering significance for guiding the selection of powder insulation materials and predicting the evaporation rate of cryogenic liquids.

[0003] Methods for measuring thermal conductivity of materials are usually divided into transient methods and steady-state methods. Chinese patent CN104215654B discloses a new method for measuring thermal conductivity of trace powder samples under variable temperature and pressure conditions. The thermal conductivity of the particles is measured based on the transient method and using a thermal conductivity meter. The test result of this method is the solid thermal conductivity of the particles themselves, not the apparent thermal conductivity that takes into account the thermal conductivity of rarefied gases and radiation heat transfer. It is not suitable for measuring the apparent thermal conductivity of powder materials for low-temperature liquid storage at low temperatures. For the measurement of the apparent thermal conductivity of powder materials under vacuum and low temperature, the steady-state method is more in line with the actual heat transfer process. Steady-state measurement refers to a method in which a stable temperature distribution is established inside the sample being tested after the heat transfer reaches a steady state, and the apparent thermal conductivity of the sample is calculated by the amount of heat leakage and the heat transfer path. The usual method is to use cryogenic liquid (such as liquid nitrogen) to create a low-temperature boundary temperature. This method is not easy to achieve measurement in a lower temperature zone (such as liquid hydrogen temperature zone). For example, the solution disclosed in the Chinese patent application with publication number CN111537555A can only complete the measurement of room temperature and above. The solution disclosed in the Chinese patent application with publication number CN106525899A and the Chinese patent CN115266814B cannot adjust the cold boundary temperature and cannot achieve the measurement of the apparent thermal conductivity in a wide temperature range. In addition, the test method using cryogenic liquid to create a low-temperature boundary temperature takes a long time to test, which easily causes waste of cryogenic liquid, and it is not easy to control the boundary temperature. Summary of the invention

[0004] In order to solve the above problems of the prior art, the present invention provides a device and method for measuring the apparent thermal conductivity of powder at low temperature. The device can realize measurement in liquid hydrogen temperature range and wide temperature range, and the measurement is accurate, fast and cost-saving.

[0005] The present invention is achieved through the following technical solutions: The present invention provides a device for measuring the apparent thermal conductivity of powder at low temperature, comprising: a helium compressor, a GM refrigerator, a heater, a temperature controller, a powder sample bin, a vacuum cover, a data acquisition device, a constant current source and a vacuum pump; The helium compressor is connected to the GM refrigerator; the GM refrigerator is connected to the open end of the vacuum cover, the GM refrigerator includes a primary cold head and a secondary cold head, the primary cold head, the secondary cold head and the powder sample chamber are all located inside the vacuum cover; the vacuum pump is connected to the vacuum cover through a vacuum pipe; One end of the powder sample bin is in close contact with and connected to the secondary cold head; the heater is used to heat the secondary cold head, and the temperature controller is used to detect and control the temperature of the secondary cold head; A heating rod and a thermal boundary thermometer in contact with the heating rod are arranged in the powder sample chamber. The heating rod is electrically connected to a constant current source outside the vacuum cover, and the thermal boundary thermometer is electrically connected to a data acquisition device outside the vacuum cover.

[0006] Preferably, the powder sample bin comprises a powder sample bin body and a cover plate connected to the powder sample bin body, and one end of the powder sample bin body away from the cover plate is tightly attached to and connected to the secondary cold head; the heating rod and the thermal boundary thermometer are arranged in the powder sample bin body.

[0007] Furthermore, the powder sample bin body and the cover plate are both made of copper.

[0008] Furthermore, an inner wall of the cover plate is provided with an internal thread, and one end of the powder sample bin body is provided with an external thread, and the powder sample bin body is connected to the cover plate through threads.

[0009] Furthermore, a filter screen is provided in the central portion of the cover plate.

[0010] Furthermore, a detachable support is sealed and connected to the side wall of the powder sample bin body, and the interior of the support is a hollow structure; a sealing joint is provided on the side wall of the vacuum cover; the wires of the heating rod pass through the support and the sealing joint in sequence and are electrically connected to a constant current source located outside the vacuum cover; the wires of the thermal boundary thermometer pass through the support and the sealing joint in sequence and are electrically connected to a data acquisition device located outside the vacuum cover.

[0011] Furthermore, the sealing joint is an aviation joint.

[0012] Preferably, the thermal boundary thermometer comprises a first thermometer and a second thermometer, and the first thermometer and the second thermometer are arranged on opposite sides of the heating rod.

[0013] The present invention provides a method for measuring the apparent thermal conductivity of powder materials at low temperatures, based on the device for measuring the apparent thermal conductivity of powders at low temperatures as described above, comprising: Fill the powder material into the powder sample bin, arrange the heating rod and the thermal boundary thermometer in the middle of the powder sample bin; connect and fix the powder sample bin to the secondary cold head, and place them in a vacuum cover; Start the vacuum pump to evacuate the vacuum cover to the preset vacuum degree, start the GM refrigerator, heater and temperature controller until the cold boundary temperature at the secondary cold head reaches the preset cold boundary temperature, turn on and adjust the output current of the constant current source until the hot boundary temperature at the hot boundary thermometer reaches the preset hot boundary temperature, and the temperature change is less than 0.5 K / h, record the output current, hot boundary temperature and cold boundary temperature of the constant current source at this time, and calculate the apparent thermal conductivity based on the output current, hot boundary temperature and cold boundary temperature.

[0014] Preferably, the axis of the heating rod is perpendicular to the axis of the powder sample chamber, and the calculation formula used to calculate the apparent thermal conductivity is:

[0015] in, I is the output current of the constant current source, R is the resistance of the heating rod, l is the length of the heating rod, d is the heating rod diameter, h is the height of the powder sample chamber, T 热边界 is the thermal boundary temperature, T 冷边界 is the cold boundary temperature.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The device for measuring the apparent thermal conductivity of powder at low temperature of the present invention adopts a GM refrigerator to provide a cold boundary temperature. Compared with the traditional method of using a cryogenic liquid to provide a cold boundary temperature, the present invention can save a large amount of cryogenic liquid and greatly shorten the experimental time, and can achieve a lower cold boundary temperature, which can be as low as 4.2 K, so that a lower temperature measurement can be achieved. In addition, the present invention also provides a heater for the secondary cold head, because after the GM refrigerator is started, as long as the cooling capacity is greater than the heat leakage, the temperature can continue to drop, but the specific drop is unknown and uncontrollable, so the heater and the temperature controller are arranged to make it controllable. When necessary, the secondary cold head is heated, and the cold boundary temperature can be adjusted, so that the apparent thermal conductivity of the powder under a wide temperature range (4.2 K-400 K) can be measured. The present invention can also change the output current of the constant current source to control the thermal boundary temperature, change the working time of the vacuum pump to change the vacuum degree of the test environment, and can achieve the measurement of the apparent thermal conductivity of the powder under the full pressure range (0.01Pa-101325Pa). The device has the advantages of simple structure, clear principle, accurate and fast measurement, and cost saving. It can quickly measure the insulation performance of powder insulation materials in low-temperature liquid storage conditions.

[0017] Furthermore, the powder sample bin of the present invention only includes a powder sample bin body and a cover plate connected to the powder sample bin body. The powder sample bin body is an integral whole, which can reduce leakage of powder samples.

[0018] Furthermore, the powder sample bin body and cover plate of the present invention are made of copper, which has a large thermal conductivity. Therefore, the coldness of the secondary cold head can be quickly transferred to the entire powder sample bin, accelerating the testing process. At the same time, it makes the overall temperature of the powder sample bin more uniform, and there is no obvious temperature difference between the various parts, thereby improving the accuracy of the test results.

[0019] Furthermore, the present invention is provided with a hollow support and a sealing joint, which can ensure that the wire is led out of the vacuum cover without causing powder leakage and affecting the vacuum in the vacuum cover.

[0020] Furthermore, the present invention provides two thermal boundary thermometers, and obtains the thermal boundary temperature through the average value, which can reduce the test error and improve the reliability of the result.

[0021] The method for measuring the apparent thermal conductivity of powder at low temperature of the present invention is based on the steady-state method, and takes into account the influence of rarefied gas heat conduction and radiation heat transfer on the thermal conductivity of powder. It can realize the measurement of the apparent thermal conductivity of powder in liquid hydrogen temperature range, wide temperature range and full pressure range. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 Schematic diagram of the device for measuring the apparent thermal conductivity of hollow glass microspheres at low temperatures; Figure 2 is a two-dimensional cross-sectional view of the powder sample chamber; Figure 3 This is a three-dimensional cross-sectional view of the powder sample chamber.

[0024] 1-helium compressor; 2-GM refrigerator; 3-radiation screen; 4-first-stage cold head; 5-second-stage cold head; 6-powder sample chamber; 7-vacuum cover; 8-sealing joint; 9-data acquisition device; 10-constant current source; 11-vacuum gauge; 12-vacuum pump; 13-powder sample chamber body; 14-first thermometer; 15-heating rod; 16-support; 17-second thermometer; 18-cover plate; 19-filter. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0026] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0027] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0028] In addition, it should be noted that the terms "first", "second", etc. of the present invention are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. The orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements.

[0029] like Figure 1 As shown, the device for measuring the apparent thermal conductivity of powder at low temperature of the present invention comprises: a helium compressor 1, a GM refrigerator 2, a heater, a temperature controller, a powder sample chamber 6, a vacuum cover 7, a data acquisition device 9, a constant current source 10 and a vacuum pump 12.

[0030] The helium compressor 1 is connected to the GM refrigerator 2. The GM refrigerator 2 is connected to the open end of the vacuum cover 7. The GM refrigerator 2 includes a primary cold head 4 and a secondary cold head 5. The primary cold head 4, the secondary cold head 5 and the powder sample chamber 6 are all located inside the vacuum cover 7. The vacuum cover 7 is used to create a closed space.

[0031] The vacuum pump 12 is connected to the vacuum cover 7 through a vacuum pumping pipe to evacuate the entire environment inside the vacuum cover 7, and the vacuum degree is monitored by a vacuum gauge 11 arranged on the vacuum pumping pipe.

[0032] like Figure 2 and Figure 3 As shown, the powder sample bin 6 mainly includes two parts, namely a powder sample bin body 13 and a cover plate 18 connected to the powder sample bin body 13, both of which are made of copper, preferably red copper. The end of the powder sample bin body 13 away from the cover plate 18 is closely attached to and connected to the secondary cold head 5.

[0033] A heating rod 15 and a thermal boundary thermometer are arranged in the powder sample chamber body 13. The heating rod 15 is electrically connected to the constant current source 10 located outside the vacuum cover 7, and the thermal boundary thermometer is electrically connected to the data acquisition device 9 located outside the vacuum cover 7. As a preferred solution, the thermal boundary thermometer includes a first thermometer 14 and a second thermometer 17, which are respectively located on opposite sides of the heating rod 15, and are used to obtain the average temperature so that the obtained thermal boundary temperature is more accurate.

[0034] The heater is used to heat the secondary cold head 5; the temperature controller is electrically connected to the heater and is used to control the temperature of the secondary cold head 5 to a preset cold boundary temperature. Because the refrigeration temperature of the GM refrigerator 2 is not easy to control, the present invention further provides a heater and a temperature controller, so that a wide range of cold boundary temperatures can be measured.

[0035] In one embodiment of the present invention, an inner wall of the cover plate 18 is provided with an internal thread, and one end of the powder sample bin body 13 is provided with an external thread, and the two are connected by threads.

[0036] In one embodiment of the present invention, a filter screen 19 is disposed at the center of the cover plate 18. The filter screen 19 can be used to block the powder material and allow gas to pass through, thereby preventing the vacuum pump 12 from extracting the powder material when evacuating the vacuum.

[0037] In one embodiment of the present invention, a detachable support 16 is connected to the side wall of the powder sample bin body 13, and the support 16 is made of polytetrafluoroethylene, has an external thread on the surface, and is hollow inside to allow thin wires to pass through. The wires of the heating rod 15 pass through the support 16 and are electrically connected to the constant current source 10 located outside the vacuum cover 7; the wires of the first thermometer 14 and the second thermometer 17 pass through the support 16 and are electrically connected to the data acquisition device 9 located outside the vacuum cover 7. Furthermore, a sealing joint 8 is provided on the side wall of the vacuum cover 7, and the wires all pass through the sealing joint and extend out of the vacuum cover 7. The sealing joint 8 is preferably an aviation joint. The aviation joint allows the wires of the heating rod and the thermometer to pass through the vacuum cover 7 and be connected to the data acquisition device 9 and the constant current source 10.

[0038] As a preferred solution, the heating rod 15 is arranged in the center of the powder sample bin 6, and the first thermometer 14 and the second thermometer 17 are arranged on both sides of the heating rod 15 respectively. The positions of the three are fixed by the support 16 and the powder material filled in the powder sample bin 6, and the wires of the three are connected to the aviation connector 8 through the support 16.

[0039] As a preferred solution, a plurality of through holes are provided on one end of the powder sample bin body 13 connected to the secondary cold head 5, and the same number of through holes are provided on the secondary cold head 5, and the positions of the through holes correspond, so that the powder sample bin body 13 and the secondary cold head 5 are connected by bolts and nuts.

[0040] The GM refrigerator 2 used in the present invention is provided with a radiation screen 3, which is installed around the cold head to reduce radiation heat leakage.

[0041] The experimental principle of the present invention is: the vacuum pump 12 and the secondary cold head 5 of the GM refrigerator 2 can respectively create a vacuum low temperature environment for the powder, and the secondary cold head 5 of the GM refrigerator 2 can reach a minimum of 4.2 K. Since the powder sample chamber body 6 is made of copper and has a large thermal conductivity, it can be considered that the temperature around the powder sample chamber 6 is consistent with that of the secondary cold head 5, and the temperature of the secondary cold head 5 (which is also the cold boundary temperature) is monitored by a temperature controller. T 冷边界 In the experiment, the GM refrigerator 2 is started to provide an extremely low cold boundary temperature, and then the constant current source 10 is started to heat the heating rod 15. Assuming that all the electricity is used for heating, the heat generated at this time is I 2 R Since the powder material has excellent thermal insulation properties under vacuum, the heat generated by the heating rod 15 will not be transferred to the cold boundary. I The temperature at the thermal boundary thermometer is maintained near the preset thermal boundary temperature and remains unchanged for a long time so that the heat transfer reaches a steady state. At this time, the output current of the constant current source 10 is recorded. I , the reading of the thermal boundary thermometer T 热边界 .

[0042] Apparent thermal conductivity calculation method: Using the thermal conductivity shape factor method, the axis of the heating rod is perpendicular to the axis of the powder sample chamber, and the length of the heating rod l Much larger than the heating rod diameter d , powder sample chamber height (i.e. the distance between the two ends) h More than 3 times the diameter of the heating rod d , the problem at this time is equivalent to a horizontal isothermal cylinder buried in a semi-infinite medium. The calculation formula is: , λ is the apparent thermal conductivity of the sample under the set working conditions, R is the resistance of the heating rod 15.

[0043] When the thermal boundary thermometer includes the first thermometer 14 and the second thermometer 17, the reading T 热边界 Take the first thermometer 14 reading T 1st and 2nd thermometer 17 readings T 2, the calculation formula is: .

[0044] Example 1 like Figure 1 As shown, the device for measuring the apparent thermal conductivity of powder at low temperature described in this embodiment includes: a helium compressor 1, a GM refrigerator 2, a heater, a temperature controller, a powder sample chamber 6, a vacuum cover 7, a data acquisition device 9, a constant current source 10 and a vacuum pump 12.

[0045] The helium compressor 1 is connected to the GM refrigerator 2. The GM refrigerator 2 is connected to the open end of the vacuum cover 7. The GM refrigerator 2 includes a primary cold head 4, a secondary cold head 5 and a radiation shield 3. The radiation shield 3 is installed around the cold head to reduce radiation heat leakage. The primary cold head 4, the secondary cold head 5 and the powder sample chamber 6 are all located inside the vacuum cover 7.

[0046] The vacuum pump 12 is connected to the vacuum cover 7 through a vacuum pumping pipe to evacuate the entire environment inside the vacuum cover 7, and the vacuum degree is monitored by a vacuum gauge 11 arranged on the vacuum pumping pipe.

[0047] like Figure 2 and Figure 3 As shown, the powder sample bin 6 includes two parts, namely, a powder sample bin body 13 and a cover plate 18 connected to the powder sample bin body 13, both of which are made of copper. An internal thread is provided on the inner wall of the cover plate 18, and an external thread is provided at one end of the powder sample bin body 13, and the two are connected by threads. A filter screen 19 is provided at the center of the cover plate 18, and the filter screen 19 is used to block the powder material and allow gas to pass through, so as to prevent the powder material from being drawn out when the vacuum pump 12 is evacuated.

[0048] The end of the powder sample bin body 13 away from the cover plate 18 is closely attached to and connected with the secondary cold head 5. A plurality of through holes are provided on the end of the powder sample bin body 13 connected with the secondary cold head 5, and the secondary cold head 5 is provided with the same number of through holes, and the positions of the through holes correspond. The powder sample bin body 13 is connected with the secondary cold head 5 by bolts and nuts. The heater is used to heat the secondary cold head 5, and the temperature controller is used to control the temperature of the secondary cold head 5.

[0049] A heating rod 15, a first thermometer 14 and a second thermometer 17 are arranged in the powder sample bin body 13. The heating rod 15 is arranged in the center of the powder sample bin 6, and the first thermometer 14 and the second thermometer 17 are arranged on opposite sides of the heating rod 15. A detachable support 16 is connected to the side wall of the powder sample bin body 13. The support 16 is made of polytetrafluoroethylene, has an external thread on the surface, and is hollow inside to allow thin wires to pass through. An aviation connector is arranged on the side wall of the vacuum cover 7. The wires of the heating rod 15 pass through the support 16 and the aviation connector to be electrically connected to the constant current source 10 outside the vacuum cover 7; the wires of the first thermometer 14 and the second thermometer 17 pass through the support 16 and the aviation connector to be electrically connected to the data acquisition device 9 outside the vacuum cover 7.

[0050] Preparation before the experiment: Unscrew the cover 18 of the powder sample bin 6, fill the powder sample to be tested (such as hollow glass microspheres) evenly into the powder sample bin 6 and vibrate it. During the filling process, arrange the heating rod 15, the first thermometer 14 and the second thermometer 17. After the arrangement, use a small amount of vacuum sealant to seal the hole in the support 16 to prevent the powder sample from leaking out. After the filling is completed, use bolts to connect and fix the powder sample bin 6 and the secondary cold head 5. The inner and outer wires of the vacuum cover 7 are welded to the aviation joint, the wire of the heating rod 5 is connected to the constant current source 10 after passing through the aviation joint, and the wires of the first thermometer 14 and the second thermometer 17 are connected to the data acquisition device 9 after passing through the aviation joint.

[0051] Experimental process: Start the vacuum pump 12 to evacuate the entire vacuum cover 7, observe the vacuum gauge 11-after the vacuum degree reaches the set requirement, start the GM refrigerator 2, until the temperature detected by the temperature controller reaches the experimental requirement, then start and adjust the output current of the constant current source 10, when the reading of the first thermometer 14 T 1 and the reading of the second thermometer 17 T 2 After reaching about 300 K, keep it for a while until the readings of the first thermometer 14 and the second thermometer 17 change less than 0.5 K / h, and record the data at this time ( I , T 1. T 2. T 冷边界 , vacuum degree), and use the calculation method in the experimental principle to calculate the apparent thermal conductivity.

[0052] The GM refrigerator 2 used in the present invention is KDE425SA produced by CSIC Pengli, and the cooling temperature of the refrigerator is 4.2 K. When it is necessary to test the apparent thermal conductivity at other temperatures, the secondary cold head 5 is heated by a heater, and the temperature is controlled by a temperature controller, for example, to 20 K or 100 K. The temperature controller can be Lakeshore336.

[0053] The first thermometer and the second thermometer can be PT100.

[0054] The present invention can also change the temperature at the heating rod 15 by adjusting the output current of the constant current source 10, thereby achieving measurement of a wide range of thermal boundary temperatures.

[0055] The present invention can also change the working time of the vacuum pump 12 to achieve measurements under different vacuum degrees.

[0056] The present invention can also replace different powder sample models to achieve the measurement of the apparent thermal conductivity of more types of powder samples.

[0057] Therefore, the device for measuring the apparent thermal conductivity of powder at low temperature of the present invention can realize the measurement of the apparent thermal conductivity of different powder samples at different temperatures, different pressures, and different powder samples.

[0058] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A device for measuring the apparent thermal conductivity of powder at low temperature, characterized in that: include: Helium compressor (1), GM refrigerator (2), heater, temperature controller, powder sample chamber (6), vacuum cover (7), data acquisition device (9), constant current source (10) and vacuum pump (12); The helium compressor (1) is connected to the GM refrigerator (2); the GM refrigerator (2) is connected to the open end of the vacuum cover (7); the GM refrigerator (2) comprises a primary cold head (4) and a secondary cold head (5); the primary cold head (4), the secondary cold head (5) and the powder sample chamber (6) are all located inside the vacuum cover (7); the vacuum pump (12) is connected to the vacuum cover (7) via a vacuum pump; One end of the powder sample bin (6) is in close contact with and connected to the secondary cold head (5); the heater is used to heat the secondary cold head (5), and the temperature controller is used to detect and control the temperature of the secondary cold head (5); A heating rod (15) and a thermal boundary thermometer in contact with the heating rod (15) are arranged in the powder sample chamber (6); the heating rod (15) is electrically connected to a constant current source (10) located outside the vacuum cover (7); and the thermal boundary thermometer is electrically connected to a data acquisition device (9) located outside the vacuum cover (7).

2. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 1, characterized in that: The powder sample bin (6) comprises a powder sample bin body (13) and a cover plate (18) connected to the powder sample bin body (13); an end of the powder sample bin body (13) away from the cover plate (18) is in close contact with and connected to the secondary cold head (5); and the heating rod (15) and the thermal boundary thermometer are arranged in the powder sample bin body (13).

3. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 2, characterized in that: The powder sample chamber body (13) and the cover plate (18) are both made of copper.

4. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 2, characterized in that: An internal thread is provided on the inner wall of the cover plate (18), an external thread is provided on one end of the powder sample bin body (13), and the powder sample bin body (13) and the cover plate (18) are connected via threads.

5. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 2, characterized in that: A filter screen (19) is provided at the central portion of the cover plate (18).

6. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 2, characterized in that: A detachable support (16) is sealed and connected to the side wall of the powder sample chamber body (13), and the interior of the support (16) is a hollow structure; a sealing joint (8) is provided on the side wall of the vacuum cover (7); the wire of the heating rod (15) passes through the support (16) and the sealing joint (8) in sequence to be electrically connected to a constant current source (10) located outside the vacuum cover (7); and the wire of the thermal boundary thermometer passes through the support (16) and the sealing joint (8) in sequence to be electrically connected to a data acquisition device (9) located outside the vacuum cover (7).

7. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 6, characterized in that: The sealing joint (8) is an aviation joint.

8. The device for measuring the apparent thermal conductivity of powder at low temperature according to claim 1, characterized in that: The thermal boundary thermometer comprises a first thermometer (14) and a second thermometer (17), wherein the first thermometer (14) and the second thermometer (17) are arranged on opposite sides of the heating rod (15).

9. A method for measuring the apparent thermal conductivity of powder materials at low temperatures, characterized in that: The device for measuring the apparent thermal conductivity of powder at low temperature according to any one of claims 1 to 8 comprises: Filling a powder material into a powder sample bin (6), arranging a heating rod (15) and a thermal boundary thermometer in the middle of the powder sample bin (6); connecting and fixing the powder sample bin (6) to a secondary cold head (5), and placing the powder sample bin (6) in a vacuum cover (7); Start the vacuum pump (12) to evacuate the vacuum cover (7) to a preset vacuum degree, start the GM refrigerator (2), the heater and the temperature controller until the cold boundary temperature at the secondary cold head (5) reaches the preset cold boundary temperature, start and adjust the output current of the constant current source (10) until the hot boundary temperature at the hot boundary thermometer reaches the preset hot boundary temperature and the temperature change is less than 0.5 K / h, record the output current, hot boundary temperature and cold boundary temperature of the constant current source at this time, and calculate the apparent thermal conductivity based on the output current, hot boundary temperature and cold boundary temperature.

10. The method for measuring the apparent thermal conductivity of powder at low temperature according to claim 9, characterized in that: The axis of the heating rod is perpendicular to the axis of the powder sample chamber, and the calculation formula used to calculate the apparent thermal conductivity is: in, I is the output current of the constant current source, R is the resistance of the heating rod (15), l is the length of the heating rod, d is the heating rod diameter, h is the height of the powder sample chamber (6), T 热边界 is the thermal boundary temperature, T 冷边界 is the cold boundary temperature.

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