Apparatus and method for measuring apparent thermal conductivity of powder at low temperature

Abstract

The application provides a device and method for measuring apparent thermal conductivity of powder at low temperature, and the device for measuring apparent thermal conductivity of powder at low temperature provided by the application adopts a G-M refrigerator to provide a cold boundary temperature, compared with a traditional method of providing a cold boundary temperature by using a low-temperature liquid, the application can save a large amount of low-temperature liquid, greatly shorten the experimental time, and achieve a lower cold boundary temperature, and the cold boundary temperature can be as low as 4.2 K, so that measurement at a lower temperature can be realized. Moreover, a heater is arranged for a secondary cold head, and the secondary cold head is heated when needed, so that the cold boundary temperature can be adjusted, and thus the measurement of apparent thermal conductivity of powder at a wide temperature range (4.2 K-400 K) can be realized. The device can realize measurement at a liquid hydrogen temperature range and a wide temperature range, is accurate and fast in measurement, and can save cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of powder thermal property measurement, and particularly relates to a device and method for measuring apparent thermal conductivity of powder at low temperature. BACKGROUND

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

[0003] The method for measuring the thermal conductivity of materials is generally divided into transient method and steady-state method. Chinese patent CN104215654B discloses a new method for measuring the thermal conductivity of trace powder samples under variable temperature and pressure conditions, which measures the thermal conductivity of particulate matter based on the transient method and uses a thermal conductivity instrument. The test results of this method are the solid thermal conductivity of the particulate matter itself, and are not the apparent thermal conductivity considering the thermal conductivity of dilute gas and radiation heat transfer, which is not suitable for measuring the apparent thermal conductivity of powder material at low temperature for low-temperature liquid storage. For the measurement of the apparent thermal conductivity of powder material at low temperature in vacuum, the steady-state method is more in line with the actual heat transfer process. The steady-state method is a method for measuring the apparent thermal conductivity of a sample by calculating the heat leakage and heat transfer path after the heat transfer reaches a steady state. The usual method is to use a low-temperature liquid (such as liquid nitrogen) to create a low-temperature boundary temperature, which is not easy to achieve measurement in a lower temperature range (such as the liquid hydrogen temperature range). For example, the scheme disclosed in Chinese patent application CN111537555A can only complete the measurement in the normal temperature and above temperature range, and the schemes disclosed in Chinese patent application CN106525899A and Chinese patent CN115266814B cannot adjust the cold boundary temperature, and cannot achieve the measurement of the apparent thermal conductivity in a wide temperature range. Moreover, the test method using a low-temperature liquid to create a low-temperature boundary temperature takes a long time, which easily causes waste of low-temperature liquid and is not easy to control the boundary temperature. SUMMARY

[0004] In order to solve the problems of the prior art, the application provides a device and method for measuring the apparent thermal conductivity of powder at low temperature, which can achieve measurement in the liquid hydrogen temperature range and a wide temperature range, is accurate and fast, and saves cost.

[0005] The application is implemented by the following technical solutions:

[0006] The application provides a device for measuring apparent thermal conductivity of powder at low temperature, comprising a helium compressor, a G-M 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.

[0007] The helium compressor is connected with the G-M refrigerator; the G-M refrigerator is connected with the open end of the vacuum cover, and the G-M refrigerator comprises a first cold head and a second cold head, and the first cold head, the second cold head and the powder sample bin are located inside the vacuum cover; the vacuum pump is connected with the vacuum cover through a vacuum pipe.

[0008] One end of the powder sample bin is tightly connected with the second cold head; the heater is used for heating the second cold head, and the temperature controller is used for detecting and controlling the temperature of the second cold head.

[0009] A heating rod and a thermal boundary thermometer in contact with the heating rod are arranged in the powder sample bin; the heating rod is electrically connected with the constant current source located outside the vacuum cover; and the thermal boundary thermometer is electrically connected with the data acquisition device located outside the vacuum cover.

[0010] Preferably, the powder sample bin comprises a powder sample bin body and a cover plate connected with the powder sample bin body; one end of the powder sample bin body away from the cover plate is tightly connected with the second cold head; and the heating rod and the thermal boundary thermometer are arranged in the powder sample bin body.

[0011] Further, the material of the powder sample bin body and the cover plate is copper.

[0012] Further, an inner thread is formed on the inner wall of the cover plate, and an outer thread is formed on one end of the powder sample bin body; the powder sample bin body and the cover plate are connected through the threads.

[0013] Further, a filter screen is arranged in the central part of the cover plate.

[0014] Further, a detachable support is sealingly connected to the side wall of the powder sample bin body, and the support is a hollow structure; a sealing joint is arranged on the side wall of the vacuum cover; the lead of the heating rod passes through the support and the sealing joint in sequence and is electrically connected with the constant current source located outside the vacuum cover; and the lead of the thermal boundary thermometer passes through the support and the sealing joint in sequence and is electrically connected with the data acquisition device located outside the vacuum cover.

[0015] Further, the sealing joint is an aviation joint.

[0016] 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.

[0017] The application provides a method for measuring apparent thermal conductivity of powder material at low temperature, based on the device for measuring apparent thermal conductivity of powder material at low temperature, comprising the following steps:

[0018] The powder material is filled in the powder sample bin, the heating rod and the thermal boundary thermometer are arranged in the middle of the powder sample bin, the powder sample bin is connected and fixed with the secondary cold head, and is placed in the vacuum cover;

[0019] The vacuum pump is started to vacuumize the vacuum cover to a preset vacuum degree, the G-M refrigerator, the heater and the temperature controller are started until the cold boundary temperature at the secondary cold head reaches the preset cold boundary temperature, the constant current source is started and adjusted to output current until the thermal boundary temperature at the thermal boundary thermometer reaches the preset thermal boundary temperature and the temperature change is less than 0.5 K / h, the output current of the constant current source, the thermal boundary temperature and the cold boundary temperature at this time are recorded, and the apparent thermal conductivity is calculated according to the output current, the thermal boundary temperature and the cold boundary temperature.

[0020] Preferably, the axis of the heating rod is perpendicular to the axis of the powder sample bin, and the calculation formula for calculating the apparent thermal conductivity is as follows:

[0021]

[0022] Wherein, 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 diameter of the heating rod, h is the height of the powder sample bin, T 热边界 is the thermal boundary temperature, T 冷边界 is the cold boundary temperature.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] Compared with the traditional method of providing the cold boundary temperature by using low-temperature liquid, the device can save a large amount of low-temperature 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 lower temperature measurement can be realized. Moreover, the device also provides a heater for the secondary cold head, because after the G-M refrigerator is started, the temperature can always decrease as long as the refrigeration capacity is greater than the heat leakage capacity, but the specific decrease is unknown and uncontrollable, so the heater and the temperature controller are arranged to be controllable. When needed, the secondary cold head is heated, the cold boundary temperature can be adjusted, so that the apparent thermal conductivity of the powder in a wide temperature range (4.2 K-400 K) can be measured. The device can also change the output current of the constant current source to control the hot boundary temperature, and change the working time of the vacuum pump to change the vacuum degree of the test environment, so that the apparent thermal conductivity of the powder in the full pressure range (0.01 Pa-101325 Pa) can be measured. The device has the advantages of simple structure, simple principle, accurate and rapid measurement, cost saving and the like, and can complete the rapid measurement of the thermal insulation performance of the powder thermal insulation material in the low-temperature liquid storage working condition.

[0025] Further, the powder sample bin of the present application only includes a powder sample bin body and a cover plate connected with the powder sample bin body, and the powder sample bin body is an integral whole, which can reduce the leakage of the powder sample.

[0026] Further, the material of the powder sample bin body and the cover plate is copper, and the thermal conductivity of copper is large, so that the cold energy of the secondary cold head can be quickly transmitted to the whole powder sample bin, accelerating the test process, and at the same time, the overall temperature of the powder sample bin is relatively uniform, and there is no obvious temperature difference in each part, so that the accuracy of the test result can be improved.

[0027] Further, the hollow support and the sealing joint are provided, which can ensure that the lead wire is led out of the vacuum cover without causing powder leakage and affecting the vacuum in the vacuum cover.

[0028] Further, two hot boundary thermometers are provided, and the hot boundary temperature is obtained by the average value, which can reduce the test error and improve the reliability of the result.

[0029] The method for measuring the apparent thermal conductivity of powder at low temperature of the present application is based on the steady-state method, and considers the influence of the thin gas heat conduction and the radiation heat exchange on the powder thermal conductivity, and can realize the apparent thermal conductivity measurement of the powder in the liquid hydrogen temperature range, the wide temperature range and the full pressure range. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0031] Figure 1 Figure 1 is a schematic diagram of a hollow glass microsphere low-temperature apparent thermal conductivity measurement device;

[0032] Figure 2 Figure 2 is a two-dimensional sectional view of a powder sample chamber;

[0033] Figure 3 Figure 3 is a three-dimensional sectional view of a powder sample chamber.

[0034] 1-helium compressor; 2-G-M refrigerator; 3-radiation screen; 4-first cold head; 5-second 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 screen. DETAILED DESCRIPTION

[0035] The present application is described herein with reference to specific embodiments thereof, which are illustrative of the principles of the present application. Other advantages and efficiencies of the present application will be apparent to those skilled in the art from the disclosure of the present application. The present application can be implemented or applied in other different specific embodiments, and the details in the present specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0036] It should be noted that the process equipment or device not specifically mentioned in the following examples all uses the conventional equipment or device in the art.

[0037] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units 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 a limitation on the arrangement order of each method step or a limitation on the scope of the present application, and changes or adjustments of the relative relationship, without substantial changes in the technical content, are also considered as the scope of the present application.

[0038] In addition, it should be noted that the terms "first", "second" and the like in the present application are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than that illustrated or described herein. The terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used to facilitate the description of the application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the application; in addition, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected; it can be directly connected, or indirectly connected through an intermediate medium; it can be internal communication of two elements.

[0039] As shown in Figure 1 The device for measuring the apparent thermal conductivity of powder at low temperature according to the present application comprises a helium compressor 1, a G-M 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.

[0040] The helium compressor 1 is connected with the G-M refrigerator 2. The G-M refrigerator 2 is connected with the open end of the vacuum cover 7, and the G-M 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 cover 7 is used to create a closed space.

[0041] The vacuum pump 12 is connected with the vacuum cover 7 through a vacuum pipe, and the environment inside the vacuum cover 7 is vacuumized as a whole. The vacuum degree is monitored by using a vacuum gauge 11 arranged on the vacuum pipe.

[0042] As shown in Figure 2 and Figure 3 The powder sample chamber 6 mainly comprises two parts, i.e. a powder sample chamber body 13 and a cover plate 18 connected with the powder sample chamber body 13. Both the powder sample chamber body 13 and the cover plate 18 are made of copper, preferably red copper. The end of the powder sample chamber body 13 away from the cover plate 18 is tightly connected with the secondary cold head 5.

[0043] The heating rod 15 is electrically connected with the constant current source 10 outside the vacuum cover 7, and the thermal boundary temperature meter is electrically connected with the data acquisition device 9 outside the vacuum cover 7. As a preferred solution, the thermal boundary temperature meter comprises a first temperature meter 14 and a second temperature meter 17, which are respectively located on the opposite sides of the heating rod 15, and are used for obtaining the average temperature, so that the obtained thermal boundary temperature is more accurate.

[0044] The heater is used for heating the secondary cold head 5, and the temperature controller is electrically connected with the heater and is used for controlling the temperature of the secondary cold head 5 at the preset cold boundary temperature. Because the refrigeration temperature of the G-M refrigerator 2 is not easy to control, the heater and the temperature controller are additionally arranged, so that the measurement of the wide range of cold boundary temperature can be realized.

[0045] In an embodiment of the present application, an inner thread is formed on the inner wall of the cover plate 18, and an outer thread is formed on one end of the powder sample chamber body 13, and the two are connected through the threads.

[0046] In an embodiment of the present application, a filter screen 19 is arranged in the central part of the cover plate 18, which can be used to block the powder material and allow the gas to pass through, so as to prevent the powder material from being sucked out when the vacuum pump 12 is pumping.

[0047] In an embodiment of the present application, a detachable support 16 is connected to the side wall of the powder sample chamber body 13, which is made of polytetrafluoroethylene, has an outer thread formed on the surface and is hollow inside to allow the fine wires to pass through. The wires of the heating rod 15 pass through the support 16 and are electrically connected with the constant current source 10 outside the vacuum cover 7; the wires of the first temperature meter 14 and the second temperature meter 17 pass through the support 16 and are electrically connected with the data acquisition device 9 outside the vacuum cover 7. Further, a sealing joint 8 is arranged 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 enables the wires of the heating rod and the temperature meter to pass through the vacuum cover 7 and be connected with the data acquisition device 9 and the constant current source 10.

[0048] As a preferred solution, the heating rod 15 is arranged in the center of the powder sample chamber 6, and the first temperature meter 14 and the second temperature meter 17 are respectively arranged on the two sides of the heating rod 15, and the three are fixed in position by the support 16 and the powder material filled in the powder sample chamber 6, and the wires of the three are connected to the aviation joint 8 through the support 16.

[0049] As a preferred solution, a plurality of through holes are arranged on the end of the powder sample chamber body 13 connected with the secondary cold head 5, and the same number of through holes are arranged on the secondary cold head 5, and the positions of the through holes correspond to each other, so that the powder sample chamber body 13 and the secondary cold head 5 are connected through bolts and nuts.

[0050] The G-M refrigerator 2 adopted in the application is provided with a radiation screen 3, which is installed around the cold head to weaken the radiation heat leakage.

[0051] The experimental principle of the application is that the vacuum pump 12 and the secondary cold head 5 of the G-M refrigerator 2 can respectively create a vacuum low-temperature environment at the powder position, and the secondary cold head 5 of the G-M refrigerator 2 can reach as low as 4.2 K. Since the powder sample bin body 6 is made of red copper material and has a large thermal conductivity coefficient, it can be considered that the four sides of the powder sample bin 6 are consistent with the temperature 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 using the temperature controller. T 冷边界 In the experiment, the G-M refrigerator 2 is started to provide an extremely low cold boundary temperature, then the constant current source 10 is started to heat the heating rod 15, and it is assumed that all the electric quantity is used for heating, at this time the heating quantity is I 2 R Since the powder material has excellent heat insulation performance under vacuum, the heat generated by the heating rod 15 will not be transmitted to the cold boundary. By adjusting the output current of the constant current source 10 I the temperature at the hot boundary temperature meter is maintained near the preset hot 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 , and the reading of the hot boundary temperature meter is T 热边界 .

[0052] The apparent thermal conductivity calculation method: using the thermal shape factor method, the axis of the heating rod is perpendicular to the axis of the powder sample bin, the length of the heating rod l is much larger than the diameter of the heating rod d , and the height (i.e. the distance between the two ends) of the powder sample bin h is greater than 3 times the diameter of the heating rod d , at this time the problem is equivalent to a horizontal isothermal cylinder buried in a semi-infinite medium. The calculation formula is: , Lambda is the apparent thermal conductivity of the measured sample under the set working condition, R is the resistance of the heating rod 15.

[0053] When the hot boundary temperature meter includes the first temperature meter 14 and the second temperature meter 17, the reading is T 热边界 The average value of the reading of the first temperature meter 14 T 1 and the reading of the second temperature meter 17 T 2, at this time the calculation formula is:

[0054] .

[0055] Example 1

[0056] As shown in Figure 1 The device for measuring apparent thermal conductivity of powder at low temperature in the embodiment comprises a helium compressor 1, a G-M refrigerator 2, a heater, a temperature controller, a powder sample chamber 6, a vacuum chamber 7, a data acquisition device 9, a constant current source 10 and a vacuum pump 12.

[0057] The helium compressor 1 is connected with the G-M refrigerator 2. The G-M refrigerator 2 is connected with the opening end of the vacuum chamber 7. The G-M refrigerator 2 comprises a primary cold head 4, a secondary cold head 5 and a radiation screen 3. The radiation screen 3 is installed around the cold head to weaken the 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 chamber 7.

[0058] The vacuum pump 12 is connected with the vacuum chamber 7 through a vacuum pipe. The vacuum pump 12 is used to vacuumize the whole environment in the vacuum chamber 7. The vacuum degree is monitored by a vacuum gauge 11 arranged on the vacuum pipe.

[0059] As shown in Figure 2 and Figure 3 The powder sample chamber 6 comprises two parts, i.e. a powder sample chamber body 13 and a cover plate 18 connected with the powder sample chamber body 13. The material of the two parts is red copper. An inner thread is formed on the inner wall of the cover plate 18. An outer thread is formed on one end of the powder sample chamber body 13. The cover plate 18 and the powder sample chamber body 13 are connected through the threads. A filter screen 19 is arranged in the center of the cover plate 18. The filter screen 19 is used to block the powder material and allow the gas to pass through, so as to prevent the powder material from being sucked out by the vacuum pump 12 during the vacuumization.

[0060] The end of the powder sample chamber body 13 far from the cover plate 18 is tightly connected with the secondary cold head 5. A plurality of through holes are arranged on the end of the powder sample chamber body 13 connected with the secondary cold head 5. The same number of through holes are arranged on the secondary cold head 5. The positions of the through holes are corresponding. The powder sample chamber body 13 and the secondary cold head 5 are connected through bolts and nuts. The heater is used to heat the secondary cold head 5. The temperature controller is used to control the temperature of the secondary cold head 5.

[0061] A heating rod 15, a first thermometer 14 and a second thermometer 17 are arranged in the powder sample chamber body 13. The heating rod 15 is arranged in the center of the powder sample chamber 6. The first thermometer 14 and the second thermometer 17 are arranged on the opposite sides of the heating rod 15 respectively. A detachable support 16 is connected with the side wall of the powder sample chamber body 13. The material of the support 16 is polytetrafluoroethylene. An outer thread is formed on the surface of the support 16. The inside of the support 16 is hollow to allow the fine wires to pass through. An aviation joint is arranged on the side wall of the vacuum chamber 7. The wires of the heating rod 15 pass through the support 16 and the aviation joint and are electrically connected with the constant current source 10 located outside the vacuum chamber 7. The wires of the first thermometer 14 and the second thermometer 17 pass through the support 16 and the aviation joint and are electrically connected with the data acquisition device 9 located outside the vacuum chamber 7.

[0062] Preparation before experiment: twist the cover plate 18 of the powder sample bin 6, fill the measured powder sample (for example hollow glass microspheres) into the powder sample bin 6 uniformly and vibrate, arrange the heating rod 15, the first thermometer 14 and the second thermometer 17 during the filling of the powder sample, and then seal the hole in the support 16 with a small amount of vacuum sealant to prevent the powder sample from leaking out. After the filling is completed, the powder sample bin 6 and the secondary cold head 5 are connected and fixed by using a bolt. The wires inside and outside the vacuum cover 7 are welded and connected with aviation joints. The wires of the heating rod 5 are connected with the constant current source 10 through the aviation joints. The wires of the first thermometer 14 and the second thermometer 17 are connected with the data acquisition device 9 through the aviation joints.

[0063] Experimental process: start the vacuum pump 12 to pump the whole vacuum cover 7, and start the G-M refrigerator 2 through the vacuum gauge 11 when the vacuum degree reaches the set requirement, until the temperature detected by the temperature controller reaches the experimental requirement, at this time, the output current of the constant current source 10 is turned on and adjusted, and when the reading of the first thermometer 14 T 1and the reading of the second thermometer 17 T 2reach about 300 K, keep for a period of time, until the readings of the first thermometer 14 and the second thermometer 17 change less than 0.5 K / h, record the data at this time I 、 T 1、 T 2、 T 冷边界 , the vacuum degree, and calculate the apparent thermal conductivity by using the calculation method in the experimental principle.

[0064] The G-M refrigerator 2 used in the application selects KDE425SA produced by China Shipbuilding Heavy Industry Pengli, and the refrigeration temperature of the refrigerator is 4.2 K. When the apparent thermal conductivity at other temperatures needs to be tested, the secondary cold head 5 is heated by the heater, and the temperature controller controls the temperature, for example, heated to 20 K or 100 K. The temperature controller can select Lakeshore 336.

[0065] The first thermometer and the second thermometer can select PT100.

[0066] The application can also change the temperature at the heating rod 15 by adjusting the output current of the constant current source 10, so as to realize the measurement of a wide range of thermal boundary temperature.

[0067] The application can also change the working time of the vacuum pump 12 to realize the measurement under different vacuum degrees.

[0068] The application can also replace different powder sample models to realize the measurement of the apparent thermal conductivities of more kinds of powder samples.

[0069] Therefore, the device for measuring apparent thermal conductivity of powder at low temperature can realize measurement of apparent thermal conductivities of powder samples at different temperatures, different pressures and different powder samples.

[0070] The above merely illustrates the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application.

Claims

1. A device for measuring the apparent thermal conductivity of a powder at low temperature, characterized in that, It comprises: a helium compressor (1), a G-M 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); the helium compressor (1) is connected with the G-M refrigerator (2); the G-M refrigerator (2) is connected with the opening end of the vacuum cover (7), and the G-M refrigerator (2) comprises a first cold head (4) and a second cold head (5); the first cold head (4), the second cold head (5) and the powder sample chamber (6) are all located inside the vacuum cover (7); the vacuum pump (12) is connected with the vacuum cover (7) through a vacuumizing pipe; one end of the powder sample chamber (6) is tightly connected with the second cold head (5); the heater is used for heating the second cold head (5), and the temperature controller is used for detecting and controlling the temperature of the second 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 with the constant current source (10) located outside the vacuum cover (7); and the thermal boundary thermometer is electrically connected with the data acquisition device (9) located outside the vacuum cover (7); the powder sample chamber (6) comprises a powder sample chamber body (13) and a cover plate (18) connected with the powder sample chamber body (13); one end of the powder sample chamber body (13) far from the cover plate (18) is tightly connected with the second cold head (5); the heating rod (15) and the thermal boundary thermometer are arranged in the powder sample chamber body (13); and the axis of the heating rod is perpendicular to the axis of the powder sample chamber.

2. The apparatus for measuring the apparent thermal conductivity of a powder at low temperature according to claim 1, wherein The material of the powder sample chamber body (13) and the cover plate (18) is copper.

3. The apparatus for measuring the apparent thermal conductivity of a powder at low temperature according to claim 1, wherein An inner thread is formed on the inner wall of the cover plate (18), an outer thread is formed on one end of the powder sample chamber body (13), and the powder sample chamber body (13) and the cover plate (18) are connected through the threads.

4. The apparatus for measuring the apparent thermal conductivity of a powder at low temperature according to claim 1, wherein A filter screen (19) is arranged in the central part of the cover plate (18).

5. The apparatus for measuring the apparent thermal conductivity of a powder at cryogenic temperatures of claim 1, wherein, A detachable support (16) is sealingly connected to the side wall of the powder sample chamber body (13), and the support (16) has a hollow structure; a sealing joint (8) is arranged on the side wall of the vacuum cover (7); the lead wire of the heating rod (15) passes through the support (16) and the sealing joint (8) in sequence and is electrically connected with the constant current source (10) located outside the vacuum cover (7); and the lead wire of the thermal boundary thermometer passes through the support (16) and the sealing joint (8) in sequence and is electrically connected with the data acquisition device (9) located outside the vacuum cover (7).

6. The apparatus for measuring the apparent thermal conductivity of a powder at low temperature according to claim 5, wherein The sealing joint (8) is an aviation joint.

7. The apparatus for measuring the apparent thermal conductivity of a powder at cryogenic temperatures of claim 1, wherein, The thermal boundary thermometer comprises a first thermometer (14) and a second thermometer (17), and the first thermometer (14) and the second thermometer (17) are arranged on opposite sides of the heating rod (15).

8. A method for measuring the apparent thermal conductivity of a powder material at low temperature, characterized in that, The device for measuring the apparent thermal conductivity of powder at low temperature according to any one of claims 1-7 comprises: filling a powder material in the powder sample chamber (6), arranging the heating rod (15) and the thermal boundary thermometer in the middle of the powder sample chamber (6), connecting and fixing the powder sample chamber (6) with the second cold head (5) and placing the powder sample chamber (6) in the vacuum cover (7); Start the vacuum pump (12) to vacuumize the vacuum cover (7) to a preset vacuum degree, start the G-M 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, open and adjust the output current of the constant current source (10), until the hot boundary temperature at the hot boundary temperature meter reaches the preset hot boundary temperature, and the temperature change is less than 0.5 K / h, record the output current of the constant current source, the hot boundary temperature, the cold boundary temperature at this time, and calculate the apparent thermal conductivity according to the output current, the hot boundary temperature and the cold boundary temperature.

9. The method of measuring the apparent thermal conductivity of a powder at cryogenic temperatures according to claim 8, wherein, The calculation formula for calculating the apparent thermal conductivity is: wherein, 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 diameter of the heating rod, h is the height of the powder sample compartment (6), T 热边界 is the hot boundary temperature, T 冷边界 is the cold boundary temperature.

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