High-precision liquid helium temperature zone material thermal conductivity measuring device and method

Abstract

The invention relates to the technical field of thermophysical property measurement, in particular to a high-precision liquid helium temperature zone material thermal conductivity measurement device and method. A low-temperature refrigeration module is used for generating an ultralow-temperature measurement condition in a set temperature range; the vacuum heat insulation module comprises an anti-radiation secondary cold shield, a multi-layer heat insulation primary cold shield and a vacuum cavity which are sequentially arranged in the outer side space of the sample; the pressure-bearing sample table module comprises an oxygen-free copper clamp used for fixing a sample, a thermal damping fin is arranged in the oxygen-free copper clamp and abuts against a cold head temperature adjusting heater, the cold head temperature adjusting heater is located on the upper surface of a pressure-bearing cold disc, and the lower bottom face of the pressure-bearing cold disc is connected with a solid polytetrafluoroethylene supporting rod through a solid epoxy resin supporting rod. The lower bottom face of the solid polytetrafluoroethylene supporting rod is connected to the stainless steel supporting rod. The thickness measurement and control module controls and measures the thickness between sample interfaces by utilizing a servo linear motor and a transmission rod; the temperature measurement and control module is used for acquiring and controlling the temperature at the axis of the heat flow meter.

Description

Technical Field

[0001] The invention relates to the technical field of thermal property measurement, and in particular to a high-precision device and method for measuring thermal conductivity of materials in a liquid helium temperature zone. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In the research and application of cutting-edge fields such as quantum computing, superconducting materials, and deep space exploration, ultra-low temperature environments (especially liquid helium temperature zones) have become a key condition for achieving technological breakthroughs. These technologies are widely used in fields such as quantum bit manipulation, superconducting sensor manufacturing, and low-temperature thermal management system development. However, in these low-temperature scenarios, the thermal conductivity of materials shows a completely different trend from room temperature, which plays a vital role in thermal performance optimization and system design. However, below the liquid helium temperature zone (4.2K), existing technologies still have many difficulties in accurately measuring the thermal conductivity of materials:

[0004] Influence of temperature fluctuation: During the measurement, the temperature fluctuation caused by the cryogenic refrigeration system is difficult to control, and its temperature amplitude (>100mK) is equivalent to the temperature difference between the two ends of the material to be measured, which seriously affects the accuracy and stability of the thermal conductivity measurement of the material;

[0005] Mechanical vibration interference: During the measurement, the vibration of the refrigeration system (amplitude> 20um) is transmitted to the sample through the structure, affecting the stability of the material sample thickness (~10um) and the measurement;

[0006] Heat leakage control: Adding displacement transmission and support structure will affect the heat leakage of the equipment and the minimum temperature limit of the test area;

[0007] Insufficient accuracy in measuring sample size: Sample thickness is a key parameter for measuring the thermal conductivity of materials. For example, during the thermal conductivity test of thermal interface materials, the material thickness needs to be adjusted in real time at liquid helium temperature. Existing devices cannot accurately measure and control the filling thickness of the material between the upper and lower heat flow meters in the liquid helium temperature zone.

[0008] Insufficient sample pressure control accuracy: In experiments in the liquid helium temperature range, the pressure applied to the sample needs to be precisely controllable to ensure the stability of the interface contact state or sample thickness. However, the control accuracy of the pressure loading device in the prior art is limited, which leads to a significant increase in the uncertainty of the experimental results. Summary of the invention

[0009] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a high-precision thermal conductivity measurement device and method for thermal materials in the liquid helium temperature zone. Through a specific structure, the heat leakage of the system is effectively reduced, the stability and accuracy of temperature and pressure measurement are improved, and the problems in the prior art are solved.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] The first aspect of the present invention provides a high-precision device for measuring thermal conductivity of materials in a liquid helium temperature zone, comprising:

[0012] Low temperature refrigeration module, used to generate ultra-low temperature measurement environment within the set temperature range;

[0013] The vacuum insulation module includes a radiation-proof secondary cold shield, a multi-layer insulation primary cold shield and a vacuum cavity which are sequentially arranged in the outer space of the sample and the heat flow meter. The ultra-low temperature generated by the low-temperature refrigeration module is transferred to the sample and the cold end of the heat flow meter by heat conduction through a copper braided heat bridge;

[0014] A pressure-bearing sample stage module is used to carry and fix the heat flux meter and the sample, including an oxygen-free copper fixture for fixing the lower heat flux meter, a thermal damping sheet is arranged in the oxygen-free copper fixture, the thermal damping sheet is in contact with the cold head temperature regulating heater, the cold head temperature regulating heater is located on the upper surface of the pressure-bearing cold plate and is accommodated by the radiation-proof secondary cold shield, the lower bottom surface of the pressure-bearing cold plate is connected to the solid polytetrafluoroethylene support rod through a solid epoxy resin support rod, and the lower bottom surface of the solid polytetrafluoroethylene support rod is connected to the stainless steel support rod;

[0015] The thickness measurement and control module uses a servo linear motor and a transmission rod to control and measure the thickness between sample interfaces;

[0016] The temperature measurement and control module is used to obtain the temperature of the heat flow meter, including a temperature measuring probe inserted into the heat flow meter, and the temperature measuring probe is connected to the temperature sensor.

[0017] Furthermore, the low-temperature refrigeration module includes a water chiller, a compressor and a refrigerator. The water chiller and the compressor are connected through a cooling water circuit, the compressor and the refrigerator are connected through a high-pressure helium circuit, and the refrigerator is connected to the refrigerator bracket through a bellows to form a shock-absorbing flexible connection.

[0018] Furthermore, the vacuum cavity is supported by a vacuum cavity bracket, the vacuum cavity is a metal cavity of set thickness, the multi-layer insulation primary cold screen in the vacuum cavity is made of multi-layer aluminum foil wrapped on an oxygen-free copper sheet and has a set thickness, and the radiation protection secondary cold screen is made of an oxygen-free copper sheet with a set thickness.

[0019] Furthermore, the solid epoxy resin support rods are located in the space between the radiation protection secondary cold shield and the multi-layer insulation primary cold shield, and the solid polytetrafluoroethylene support rods and the stainless steel support rods are located in the space between the multi-layer insulation primary cold shield and the vacuum cavity.

[0020] Furthermore, the lower bottom surface of the pressure cold plate is connected to a solid epoxy resin support rod, a solid polytetrafluoroethylene support rod and a stainless steel support rod in sequence; wherein the top end of the solid polytetrafluoroethylene support rod is in contact with the multi-layer insulation primary cold screen, and the stainless steel support rod is fixed to the bottom surface of the inner wall of the vacuum chamber.

[0021] Furthermore, the thickness measurement and control module includes a linear servo press, which drives the displacement transmission rod to vertically reciprocate to achieve pressure and displacement control, and uses a pressure sensor fixed at the bottom end of the displacement transmission rod and a contact displacement sensor fixed at the top end of the displacement transmission rod to achieve pressure and displacement measurement.

[0022] Furthermore, the displacement transmission rod is threadedly connected to the sealed end of the bellows on the outside of the vacuum chamber, the hollow stainless steel tube pull rod is fixed on the inside of the sealed end of the bellows, and the linear servo press drives the displacement transmission rod to move in the vertical direction. The displacement transmission rod is connected to the bellows to transmit the displacement into the vacuum chamber, and the displacement is sequentially transmitted to the end of the heat flux meter contacting the sample through the solid polytetrafluoroethylene pull rod, the solid epoxy resin pull rod and the hot end heater.

[0023] Furthermore, a limiting plate is provided on the outer side of the circumference of the solid polytetrafluoroethylene pull rod, and the limiting plate is fixed by using multiple sets of limiting screws.

[0024] Furthermore, the temperature measurement and control module also has a hot end heater, and the hot end heater is connected to the sample and the top of the heat flow meter through threads.

[0025] Furthermore, the oxygen-free copper fixture is connected to the cold head of the refrigerator through a copper flexible braided rope to form a cold end. The oxygen-free copper fixture clamps the heat flux meter at the cold end, and the hot end heater and the oxygen-free copper fixture generate axial heat flow and temperature gradient on the heat flux meter.

[0026] A second aspect of the present invention provides a working method of a high-precision liquid helium temperature zone material thermal conductivity measuring device, comprising the following steps:

[0027] Zero and fill the sample to obtain the initial sample thickness;

[0028] The low-temperature refrigeration module is used to provide ultra-low temperature cooling for the beginning of the lower heat flow meter. After the temperature is stable, the hot end heater is turned on to heat the beginning of the upper heat flow meter. Under the action of the axial high and low temperature difference, the heat is conducted axially in the heat flow meter and the sample, forming a stable temperature field and axial heat flow.

[0029] Obtain the temperature gradient of the upper and lower heat flow meters, calculate the temperature difference between the sample and the contact interface between the upper and lower heat flow meters, and the axial heat flux;

[0030] By repeatedly measuring samples of different thicknesses, the current sample thickness and the corresponding temperature difference between the upper and lower heat flow meter contact interfaces and the axial heat flow are obtained;

[0031] According to Fourier's law of heat conduction, the thermal conductivity of the material to be tested is calculated.

[0032] Compared with the prior art, one or more of the above technical solutions have the following beneficial effects:

[0033] 1. Low mechanical vibration: There is mechanical vibration with an amplitude of about ±20um during the working process of the refrigerator, while the thickness of the thermal interface material in the field of low-temperature heat transfer is at the level of 10um. The method proposed in this device is that the refrigerator and the sample stage are arranged vertically, the refrigerator and the vacuum chamber are softly connected through a bellows, and the refrigerator cold head and the sample stage are softly connected through a copper braided mesh / belt. This can minimize the impact of the mechanical vibration of the refrigerator on the accuracy of the thermal interface material thickness measurement.

[0034] 2. Low temperature fluctuation: There are temperature oscillations with an amplitude of >100mK during the working process of the refrigerator, and the temperature difference between the upper and lower interfaces of the material to be measured is about 10mK. The device uses a method of stacking multiple metal / polymer wave plates and forming thermal damping between the low-temperature sample stage and the lower heat flux meter, which can reduce the temperature oscillation of the cold head to less than 5mK, thereby minimizing the impact of the refrigerator temperature oscillation on the temperature measurement stability and accuracy.

[0035] 3. Displacement transmission with low heat leakage: Due to the large temperature difference between the sample stage and the external environment, direct connection will produce large heat leakage, affecting the lower limit of the measurable temperature zone. This device adopts graded transmission, sample-bearing pull rod and support rod design. According to the working temperature zone of the component, pull rods and support rods with different thermal conductivities and cross-sectional diameters are used to maximize the heat conduction resistance and reduce the heat leakage while ensuring the mechanical strength of the equipment.

[0036] 4. High-precision temperature measurement: The designed temperature measuring probe can be directly inserted into the axis of the heat flow meter through the semi-through hole reserved on the surface of the heat flow meter, thereby measuring the temperature at the axis of the heat flow meter and avoiding temperature measurement errors caused by temperature measurement position deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0038] Figure 1 It is a schematic diagram of the structure of a device for measuring thermal conductivity of liquid helium temperature zone materials provided by one or more embodiments of the present invention.

[0039] In the figure: 1.1 chiller, 1.2 compressor, 1.3 refrigerator, 1.4 refrigerator bracket, 2.1 vacuum chamber bracket, 2.2 bellows, 2.3 vacuum chamber, 2.4 multi-layer insulation first-level cold screen, 2.5 radiation-proof second-level cold screen, 2.6 copper braided thermal bridge, 3.1 oxygen-free copper fixture, 3.2 thermal damping sheet, 3.3 cold head temperature regulating heater, 3.4 pressure-bearing cold plate, 3.5 solid epoxy resin support rod, 3.6 solid polytetrafluoroethylene ethylene support rod, 3.7 stainless steel support rod, 4.1 linear servo press, 4.2 displacement transmission rod, 4.3 pressure sensor, 4.4 contact displacement sensor, 4.5 hollow stainless steel tube tie rod, 4.6 solid polytetrafluoroethylene tie rod, 4.7 solid epoxy resin tie rod, 4.8 limit plate, 4.9 limit screw, 5.1 hot end heater, 5.2 temperature probe, 5.3 temperature sensor, 5.4 upper heat flux meter, 5.5 lower heat flux meter. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0042] It should be noted that the terms herein are only intended to describe specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0043] The liquid helium temperature zone refers to the temperature range formed by the liquefaction of helium. The boiling point of liquid helium is -268.785℃ (or 4.2K) at normal pressure (1 atmosphere), so the liquid helium temperature zone is generally considered to be below -268.785℃ (or 4.2K).

[0044] As introduced in the background technology, due to the rapid change of material thermal conductivity and the complexity of the contact surface state, the existing technology still has problems such as temperature fluctuation influence, mechanical vibration interference, heat leakage control and insufficient measurement accuracy in accurately measuring material thermal conductivity.

[0045] Therefore, the following embodiments provide a high-precision device and method for measuring the thermal conductivity of materials in the liquid helium temperature zone, which effectively reduces system heat leakage, improves the stability and accuracy of temperature measurement, and solves the above-mentioned problems in the prior art through a specific structure.

[0046] Embodiment 1:

[0047] A high-precision liquid helium temperature zone material thermal conductivity measuring device, comprising:

[0048] Low temperature refrigeration module: uses a refrigerator to provide an ultra-low temperature experimental environment within a certain temperature range (e.g., 4.2K-20K). It mainly includes a chiller 1.1, a compressor 1.2, a refrigerator 1.3, and a refrigerator support 1.4.

[0049] Vacuum insulation module: Reduce heat leakage from the device to the environment by taking measures such as vacuuming and setting up multi-layer cold shields. Mainly includes vacuum chamber bracket 2.1, bellows 2.2, vacuum chamber 2.3, multi-layer insulation first-level cold shield 2.4, radiation-proof second-level cold shield 2.5 and copper braided thermal bridge 2.6.

[0050] Pressure sample stage module: used to carry and fix samples and heat flow meters. Mainly includes oxygen-free copper fixture 3.1, thermal damping sheet 3.2, cold head temperature regulating heater 3.3, pressure cold plate 3.4, solid epoxy resin support rod 3.5, solid polytetrafluoroethylene support rod 3.6 and stainless steel support rod 3.7.

[0051] Thickness measurement and control module: equipped with contact displacement sensor, using the combination of servo linear motor and transmission rod to control and measure the thickness of the filling material between solid interfaces. Mainly includes linear servo press 4.1, transmission rod 4.2, pressure sensor 4.3, contact displacement sensor 4.4, hollow stainless steel tube transmission rod 4.5, solid polytetrafluoroethylene transmission rod 4.6, solid epoxy resin transmission rod 4.7, limit plate 4.8 and limit screw 4.9.

[0052] Temperature measurement and control module: By inserting a high-precision temperature probe inside the heat flow meter, the heat leakage error of the traditional method is eliminated, the temperature difference caused by the temperature measurement position deviation is reduced, and the measurement accuracy is ensured. It mainly includes a hot end heater 5.1, a temperature measurement probe 5.2, a temperature sensor 5.3, an upper heat flow meter 5.4 and a lower heat flow meter 5.5.

[0053] In this embodiment, the sample is a thermal interface material or other deep low temperature solid heat medium filled between the upper heat flow meter 5.4 and the lower heat flow meter 5.5.

[0054] like Figure 1 As shown, in the measuring device, the refrigerator 1.3 provides the low temperature of the liquid helium temperature zone for the measuring device, the chiller 1.1 is connected to the compressor 1.2 through a cooling water circuit, the compressor 1.2 is connected to the refrigerator 1.3 through a high-pressure helium circuit, and the refrigerator 1.3 is fastened to the refrigerator bracket 1.4 through threads.

[0055] The device is placed as a whole in a vacuum chamber 2.3 supported by a vacuum chamber bracket 2.1. The vacuum chamber 2.3 is made of stainless steel with a thickness of 20 mm. In order to reduce radiation heat leakage, a multi-layer insulating primary cold screen 2.4 made of multi-layer aluminum foil with a total thickness of about 20 mm and a radiation-proof secondary cold screen 2.5 made of oxygen-free copper sheet with a thickness of about 2 mm are arranged in the vacuum chamber 2.3.

[0056] In order to reduce the adverse effects of mechanical vibration, the vibrating refrigerator 1.3 is connected to the vacuum cavity 2.3, the multi-layer insulation primary cold shield 2.4, and the radiation protection secondary cold shield 2.5 through a bellows 2.2 and a copper braided thermal bridge 2.6 made of high-purity oxygen-free copper.

[0057] The sample and the heat flux meter are fixed in the groove of the oxygen-free copper fixture 3.1 by means of fine-tuning bolts. A thermal damping sheet 3.2 made of 10 stacked stainless steel sheets with a thickness of about 1 mm is placed underneath and fastened to a pressure-bearing cold plate 3.4 made of oxygen-free copper by means of bolts. A cold head temperature regulating heater 3.3 is connected to the pressure-bearing cold plate 3.4 by means of threads.

[0058] A solid epoxy resin support rod 3.5, a solid polytetrafluoroethylene support rod 3.6 and a stainless steel support rod 3.7 are connected in sequence through threads below the pressure cold plate 3.4, wherein the upper end of the solid polytetrafluoroethylene support rod 3.6 is in direct contact with the multi-layer insulation primary cold shield 2.4, and the stainless steel support rod 3.7 is directly fixed to the bottom surface of the inner wall of the vacuum chamber 2.3 through threads.

[0059] The linear servo press 4.1 drives the displacement transmission rod 4.2 to reciprocate vertically to realize the control of pressure and displacement, and the pressure sensor 4.3 fixed at the lower end of the displacement transmission rod 4.2 and the contact displacement sensor 4.4 fixed at the upper end of the displacement transmission rod 4.2 are used to realize accurate measurement of pressure and displacement.

[0060] The displacement transmission rod 4.2 is threadedly connected to the sealed end of the bellows on the outside of the vacuum chamber 2.3, the hollow stainless steel tube pull rod 4.5 is fixed on the inside of the sealed end of the bellows 2.2, the linear servo press 4.1 drives the displacement transmission rod 4.2 to move vertically up and down, and the displacement transmission rod 4.2 is connected to the bellows 2.2 to transmit displacement into the vacuum chamber 2.3.

[0061] The hollow stainless steel tube tie rod 4.5 with an outer diameter of 30 mm and a wall thickness of 5 mm is used to ensure the mechanical strength of the tie rod while reducing heat conduction and heat leakage. The displacement is applied to the contact interface of the cylindrical sample through the solid polytetrafluoroethylene tie rod 4.6, the solid epoxy resin tie rod 4.7, and the hot end heater 5.1 in sequence.

[0062] At the same time, a limit plate 4.8 with a through hole having the same diameter as the solid polytetrafluoroethylene pull rod 4.6 is arranged around the solid polytetrafluoroethylene pull rod 4.6, and six stainless steel limit screws 4.9 with a diameter of 4 mm fix the limit plate 4.8.

[0063] The upper heat flux meter 5.4 is fastened to the hot end heater 5.1 through threads, the lower heat flux meter 5.5 is in contact with and fixed to the oxygen-free copper fixture 3.1, and the sample to be tested is coated in the area between the upper heat flux meter 5.4 and the lower heat flux meter 5.5.

[0064] The high-temperature hot-end heater 5.1 and the low-temperature oxygen-free copper fixture 3.1 generate axial heat flow and temperature gradient on the sample.

[0065] The two sets of heat flow meters are provided with temperature measuring holes with a diameter of 2 mm, and the hole depth is the radius of the bottom surface of the heat flow meter. The temperature measuring probe 5.2 made of high-purity oxygen-free copper is inserted into the temperature measuring hole and fixed with varnish, etc. The temperature sensor 5.3 is fastened to the end of the temperature measuring probe 5.2 by threading to complete the temperature measurement.

[0066] 1. Temperature stability design: In order to reduce the influence of temperature fluctuation on temperature measurement accuracy, a thermal damping sheet 3.2 is added between the pressure cold plate 3.4 and the lower heat flux meter 5.5. The thermal damping sheet 3.2 is made of multiple stainless steel / polytetrafluoroethylene sheets stacked together. Low-temperature thermal interface materials (indium sheets, Apiezon N grease) are added between the sheets to reduce the contact thermal resistance, which can reduce the temperature fluctuation amplitude from >100mK (temperature amplitude of the cold head of the refrigerator) to <10mK.

[0067] 2. Low mechanical vibration design: In order to prevent the mechanical vibration of the refrigerator from being transmitted to the measurement area, the refrigerator 1.3 in the low-temperature refrigeration module 1 is placed horizontally and supported by an independent bracket. The refrigerator 1.3 in the low-temperature refrigeration module 1 is connected to the vacuum chamber 2.2 by a bellows 2.2 soft connection method, and the refrigerator 1.3 is connected to the multi-layer insulation primary cold screen 2.4 and the pressure cold plate 3.4 by a copper braided thermal bridge 2.6 soft connection method to prevent the mechanical vibration generated by the refrigerator from being transmitted to the sample. The displacement control module 2 is placed vertically and supported by the same independent bracket as the vacuum chamber.

[0068] In this embodiment, the refrigerator 1.3 in the low-temperature refrigeration module 1 is horizontally placed and supported by an independent bracket. In addition, the cold head of the refrigerator can also be placed vertically upward or downward, and the specific structural type is not limited.

[0069] 3. Low heat leakage design of transmission and support structure: Since the transmission and support rods connect the 4K sample stage and the 300K vacuum chamber, although the conventional 304 stainless steel parts can provide sufficient mechanical strength, their thermal conductivity is relatively high (14-15.4W m - 1 K -1), if conventional stainless steel parts are directly used, it will lead to large heat leakage, which will directly affect the lower temperature limit of the device. Therefore, in order to minimize the heat leakage from the 300K vacuum chamber to the 4K sample stage and to ensure the stability of the transmission and support structure, this embodiment adopts graded transmission, the pull rod and the support rod that carry the sample together with the heat flux meter according to the working temperature zone and temperature gradient of the transmission and support rods.

[0070] The first displacement transmission part from top to bottom is the 4.5 hollow pull rod, which has an operating temperature range of 50-300K. It is made of 304 stainless steel with high mechanical strength, with an outer diameter of 30mm and an inner diameter of 20mm. The hollow design of the pull rod not only ensures the uniformity of transmission, but also reduces the cross-sectional area of ​​the pull rod through the hollow design, thereby increasing thermal resistance and reducing heat leakage; the operating temperature range of the transmission rod 4.6 is about 4-50K, and its material is polytetrafluoroethylene with low thermal conductivity, and its diameter is 50mm; the operating temperature range of the 4.7 transmission rod is about 4-20K, and its material is epoxy resin with low thermal conductivity and better low temperature resistance, and its diameter is 30mm. The transmission rods are connected by threads, and the displacement provided by the servo press is transmitted to the sample interface step by step through the pull rod of the graded transmission to adjust the thickness between the interfaces.

[0071] A support rod is arranged under the sample stage. The working temperature range of the support rod 3.5 is 4-50K, and its material has a thermal conductivity of 0.07-0.25W m -1 K -1 The low temperature resistant epoxy resin has a diameter of 30mm; the working temperature range of the support rod 3.6 is 50-300K, and its material is low thermal conductivity (0.25Wm -1 K -1 ) of polytetrafluoroethylene, the diameter of which is 50 mm; the operating temperature range of the support rod 3.7 is 250-300 K, and the material thereof has a thermal conductivity of 14-15.4 W m -1 K -1 The above method can effectively reduce the heat leakage through the support rod and avoid deformation caused by ultra-low temperature and excessive temperature gradient.

[0072] 4. Material thickness measurement method: Since the existing distance measuring device cannot directly measure the thickness of the thermal interface material in the 4K liquid helium temperature zone, this embodiment proposes an indirect thermal interface material thickness measurement method. Fix the contact distance meter to the upper end of the transmission rod, and the contact measuring end of the contact distance meter is in contact with the fixed vacuum chamber. Adjust the transmission rod up and down, and the distance meter will also move axially, and the distance measuring end will stretch and retract accordingly. When there is no pressure at the contact interface between the two heat flux meters, this is the zero point of the contact distance meter. When a certain thickness of thermal interface material is filled between the two heat flux meters, the transmission rod moves axially upward, and the contact distance meter is also stretched. The axial stretching length of the distance meter is the thickness of the thermal interface material.

[0073] 5. Heat flux meter installation and temperature measurement design: The pressure cold plate 3.4, the thermal damping plate 3.2 and the clamp 3.1 are all fastened by bolts and transfer cold. The clamp 3.1 contacts the bottom end of the lower heat flux meter 5.5 and serves as the cold end; the hot end heater 5.1 is a solid oxygen-free copper column wrapped with a heating wire, which is threadedly connected to the top of the upper heat flux meter 5.4. The temperature controller is connected to the temperature sensor fixed on the heating wire to control the temperature of the hot end of the sample, forming an axial heat flow and temperature gradient inside the sample;

[0074] The oxygen-free copper fixture 3.1 is provided with a groove in the center part, the diameter of the groove is larger than the diameter of the lower heat flux meter 5.5, and four mutually perpendicular fine-tuning bolts are provided around the groove to adjust the coaxiality of the upper heat flux meter 5.4 and the lower heat flux meter 5.5.

[0075] In order to improve low-temperature refrigeration and improve the accuracy of temperature measurement, a plurality of integral rod-shaped, flat-ended temperature measuring probes 5.2 are made of high thermal conductivity oxygen-free copper and are equidistantly inserted into the axis of the sample. The temperature gradient of the sample with known thermal conductivity in the axial direction is measured by a temperature sensor 5.3 crimped to the end of the temperature measuring probe 5.2, and the axial heat flow of the sample is calculated based on this temperature gradient.

[0076] The advantages of the above device are as follows:

[0077] Lowering the measurable temperature range: Using a refrigerator to provide a low-temperature test environment, the lowest measurable temperature of the material thermal conductivity measurement device is lowered to the 4K liquid helium temperature range.

[0078] Displacement transmission with low heat leakage: Due to the large temperature difference between the sample stage and the external environment, direct connection will produce large heat leakage, affecting the lower limit of the measurable temperature zone. This embodiment adopts a graded transmission, a pull rod and a support rod design for carrying the sample, and uses pull rods and support rods with different thermal conductivities and cross-sectional diameters according to the working temperature zone of the components. On the basis of ensuring the mechanical strength of the equipment, the thermal resistance of heat conduction is maximized and the heat leakage is reduced.

[0079] High-precision temperature measurement: The Cernox high-precision temperature sensor used in the liquid helium temperature zone usually needs to be fixed on the surface of the object to be measured using an M3 threaded hole. The temperature measuring rod designed in this embodiment can be directly inserted into the axis of the heat flow meter through the semi-through hole reserved on the surface of the heat flow meter, thereby measuring the temperature at the axis of the heat flow meter and avoiding temperature measurement errors caused by temperature measurement position deviations.

[0080] Low mechanical vibration: There is mechanical vibration with an amplitude of about ±20um during the working process of the refrigerator, and the thickness of the thermal interface material is at the level of 10um. The method proposed in this embodiment that the refrigerator and the sample stage are arranged vertically, the refrigerator and the vacuum chamber are softly connected by a bellows, and the cold head of the refrigerator and the sample stage are softly connected by a copper braided mesh / belt can minimize the impact of the mechanical vibration of the refrigerator on the accuracy of the thermal interface material thickness measurement.

[0081] Low temperature fluctuation: There are temperature oscillations with an amplitude of >100mK during the working process of the refrigerator, while the temperature difference between the upper and lower interfaces of the solid heat medium material may be only about 10mK. The method adopted in this embodiment is to superimpose multiple metal / polymer wave plates and form thermal damping between the low-temperature sample stage and the lower heat flux meter to reduce the amplitude of the temperature oscillation of the refrigerator cold head to less than 5mK, which can minimize the impact of the refrigerator temperature oscillation on the temperature measurement stability and accuracy.

[0082] Embodiment 2:

[0083] A working method of a high-precision liquid helium temperature zone material thermal conductivity measuring device comprises the following steps:

[0084] Zero and fill the sample to obtain the initial sample thickness;

[0085] Heat flow generation: Use a refrigerator to provide stable cooling capacity. After the temperature of the heat flow meter is stable, turn on the hot end heater to heat the sample. Under the action of the axial high and low temperature difference, the heat is conducted along the axial direction to form a stable temperature field and axial heat flow.

[0086] Temperature measurement: obtain the temperature gradient of the upper and lower heat flow meters, and calculate the temperature difference between the sample and the contact interface between the upper and lower heat flow meters and the axial heat flow according to Fourier's law of heat conduction;

[0087] Measure samples of different thicknesses to obtain the current sample thickness and the corresponding temperature difference between the upper and lower heat flow meter contact interfaces as well as the axial heat flow;

[0088] According to Fourier's law of heat conduction, the thermal conductivity of the material is calculated.

[0089] The working principle of this embodiment is based on Fourier's law of heat conduction, and the main steps are as follows:

[0090] 1. Zero adjustment: Use the servo press to adjust the position of the upper heat flow meter so that the upper and lower heat flow meter surfaces are in contact with each other and the pressure is zero. At this time, the distance between the upper and lower heat flow meter surfaces is considered to be zero, which is the zero point of the distance meter.

[0091] 2. Filling the sample: Use the servo press to raise the upper heat flow meter, fill the sample to be tested between the upper and lower heat flow meters, and then lower the upper heat flow meter until the distance meter reading is δ1, which is recorded as the sample thickness 1.

[0092] 3. Heat flow generation: Use a refrigerator to provide stable cooling for the sample. After the temperature of the heat flow meter stabilizes, turn on the hot end heater to heat the sample. Under the action of the axial high and low temperature difference, the heat is conducted axially in the sample to form a stable temperature field and axial heat flow q1.

[0093] 4. Temperature measurement: The upper and lower heat flow meters are made of oxygen-free copper with known thermal conductivity. The temperature probe equipped with a high-precision temperature sensor is pre-inserted into the pre-designed temperature measurement hole in the upper and lower heat flow meters. The temperature reading is read by a temperature controller to obtain the temperature gradient of the upper and lower heat flow meters. According to Fourier's heat conduction law, the temperature difference (ΔT1) between the sample and the contact interface of the upper and lower heat flow meters, as well as the axial heat flux q1, can be calculated.

[0094] 5. Measure samples of different thicknesses: lower the upper heat flow meter until the rangefinder reading is δ2, stop, record it as sample thickness 2, repeat step 4, obtain the temperature gradient when the sample thickness is δ2, the temperature difference (ΔT2) at the contact interface of the upper and lower heat flow meters, and the axial heat flux q2.

[0095] 6. Calculation of thermal conductivity: According to Fourier's law of heat conduction, the thermal conductivity λ of the material is calculated by the following formula:

[0096]

[0097] Among them, δ is the sample thickness, ΔT is the temperature difference between the upper and lower heat flow meter contact interfaces, and q is the axial heat flux.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-precision device for measuring thermal conductivity of materials in liquid helium temperature zone, characterized in that: include: Low temperature refrigeration module, used to generate ultra-low temperature measurement environment within the set temperature range; The vacuum insulation module includes a radiation-proof secondary cold shield, a multi-layer insulation primary cold shield and a vacuum cavity which are sequentially arranged in the outer space of the sample and the heat flow meter. The ultra-low temperature generated by the low-temperature refrigeration module is transferred to the sample and the cold end of the heat flow meter by heat conduction through a copper braided heat bridge; A pressure-bearing sample stage module is used to carry and fix the heat flux meter and the sample, including an oxygen-free copper fixture for fixing the lower heat flux meter, a thermal damping sheet is arranged in the oxygen-free copper fixture, the thermal damping sheet is in contact with the cold head temperature regulating heater, the cold head temperature regulating heater is located on the upper surface of the pressure-bearing cold plate and is accommodated by the radiation-proof secondary cold shield, the lower bottom surface of the pressure-bearing cold plate is connected to the solid polytetrafluoroethylene support rod through a solid epoxy resin support rod, and the lower bottom surface of the solid polytetrafluoroethylene support rod is connected to the stainless steel support rod; The thickness measurement and control module uses a servo linear motor and a transmission rod to control and measure the thickness between sample interfaces; The temperature measurement and control module is used to obtain the temperature of the heat flow meter, including a temperature measuring probe inserted into the heat flow meter, and the temperature measuring probe is connected to the temperature sensor.

2. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The low-temperature refrigeration module includes a water chiller, a compressor and a refrigerator. The water chiller is connected to the compressor through a cooling water circuit, the compressor is connected to the refrigerator through a high-pressure helium circuit, and the refrigerator is connected to the refrigerator bracket through a bellows to form a shock-absorbing flexible connection.

3. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The vacuum cavity is supported by a vacuum cavity support, and the vacuum cavity is a metal cavity of set thickness. The multi-layer insulation primary cold screen in the vacuum cavity is made of multi-layer aluminum foil wrapped on an oxygen-free copper sheet and has a set thickness, and the radiation protection secondary cold screen is made of an oxygen-free copper sheet with a set thickness.

4. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The solid epoxy resin support rod is located in the space between the radiation protection secondary cold screen and the multi-layer insulation primary cold screen, and the solid polytetrafluoroethylene support rod and the stainless steel support rod are located in the space between the multi-layer insulation primary cold screen and the vacuum cavity.

5. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The lower bottom surface of the pressure cold plate is connected to a solid epoxy resin support rod, a solid polytetrafluoroethylene support rod and a stainless steel support rod in sequence; wherein the top end of the solid polytetrafluoroethylene support rod is in contact with the multi-layer insulation primary cold screen, and the stainless steel support rod is fixed to the bottom surface of the inner wall of the vacuum chamber.

6. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The thickness measurement and control module includes a linear servo press, which drives the displacement transmission rod to vertically reciprocate to achieve pressure and displacement control, and uses a pressure sensor fixed at the bottom end of the displacement transmission rod and a contact displacement sensor fixed at the top end of the displacement transmission rod to achieve pressure and displacement measurement.

7. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 6, characterized in that: The displacement transmission rod is threadedly connected to the sealed end of the bellows outside the vacuum chamber, the hollow stainless steel tube pull rod is fixed on the inner side of the sealed end of the bellows, the linear servo press drives the displacement transmission rod to move in the vertical direction, the displacement transmission rod is connected to the bellows to transmit the displacement into the vacuum chamber, and the displacement is sequentially transmitted to the end of the heat flux meter contacting the sample through the solid polytetrafluoroethylene pull rod, the solid epoxy resin pull rod and the hot end heater.

8. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 7, characterized in that: A limiting plate is arranged on the outer side of the circumference of the solid polytetrafluoroethylene pull rod, and the limiting plate is fixed by using a plurality of groups of limiting screws.

9. A high-precision liquid helium temperature zone material thermal conductivity measuring device as claimed in claim 1, characterized in that: The oxygen-free copper fixture is connected to the cold head of the refrigerator through a copper flexible braided rope to form a cold end. The oxygen-free copper fixture clamps the heat flow meter of the cold end. The hot end heater and the oxygen-free copper fixture generate axial heat flow and temperature gradient on the heat flow meter.

10. A working method based on the high-precision thermal conductivity measuring device for liquid helium temperature zone materials according to any one of claims 1 to 9, characterized in that: The following steps are involved: Zero and fill the sample to obtain the initial sample thickness; The low-temperature refrigeration module is used to provide ultra-low temperature cooling for the beginning of the lower heat flow meter. After the temperature stabilizes, the hot end heater is turned on to heat the beginning of the upper heat flow meter. Under the action of the axial high and low temperature difference, the heat is conducted axially in the heat flow meter and the sample, forming a stable temperature field and axial heat flow. Obtain the temperature gradient of the upper and lower heat flow meters, calculate the temperature difference between the sample and the contact interface between the upper and lower heat flow meters, and the axial heat flux; By repeatedly measuring samples of different thicknesses, the current sample thickness and the corresponding temperature difference between the upper and lower heat flow meter contact interfaces and the axial heat flux are obtained; According to Fourier's law of heat conduction, the thermal conductivity of the material is calculated.

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