Air gap heat switch, preparation method thereof and low-temperature refrigerating system

Abstract

The invention relates to the technical field of low-temperature engineering, and provides an air gap heat switch and a preparation method thereof and a low-temperature refrigerating system.The air gap heat switch comprises a supporting shell, a hot end component, a cold end component and a gas adsorption component, the hot end component and the cold end component are both arranged in the supporting shell in a sealed mode, and the gas adsorption component is connected with an air gap; a first functional coating is arranged on the surface, facing the air gap, of the hot end component and / or the cold end component, and the first functional coating is used for providing thermal insulation between the hot end component and the cold end component. The air gap heat switch has the functions of gap control and heat insulation, heat insulation is provided when the air gap heat switch is in an off state, heat conductivity is provided when the air gap heat switch is in an on state, the on-off ratio of the air gap heat switch is increased, and it is ensured that the reliability and the vibration resistance of the air gap heat switch in long-term work are enhanced.

Description

Technical Field

[0001] This invention relates to the field of cryogenic engineering technology, and in particular to an air gap thermal switch and its preparation method, and a cryogenic refrigeration system. Background Technology

[0002] Thermal switches are key devices in cryogenic engineering used to control the connection and disconnection of the heat flow channel between the target object to be cooled and the cold source. They are widely used in cutting-edge cryogenic refrigeration systems such as helium vacuum evaporation refrigeration, adiabatic demagnetization refrigeration, and dilution refrigerators.

[0003] Currently, thermal switches mainly include mechanical thermal switches, superconducting thermal switches, and air-gap thermal switches. Among them, air-gap thermal switches, due to their advantages of having no moving parts, simple structure, and high reliability, have not only been widely used in ground-based cryogenic systems but have also become an ideal choice for space cryogenic applications.

[0004] In existing technologies, traditional finned air-gap thermal switches typically construct an air-gap space for gas filling by fabricating a finned structure between the cold and hot components. The entry or exit of the heat exchange gas (such as helium) in the air gap is controlled by adjusting the temperature of the adsorption pump, thereby opening or closing the thermal channel. Differential expansion air-gap thermal switches utilize the difference in thermal expansion coefficients of different materials (such as stainless steel and copper) at low temperatures. During cooling, the differential contraction of the materials naturally forms a micron-sized gap, thus achieving its switching function.

[0005] However, during research and practice, it was found that the aforementioned air gap thermal switches face the following technical bottlenecks that urgently need to be addressed when facing increasingly stringent application requirements: Traditional finned air-gap thermal switches typically have a height of 50-90 mm. While this meets the needs of some compact cryogenic systems, it is difficult to adapt to multi-stage, large-scale cryogenic systems such as dilution refrigerators, which usually require air-gap thermal switches with a height exceeding 200 mm. Simply scaling up the existing finned structure proportionally while maintaining a micron-level air gap size to ensure conductivity would increase processing difficulty and manufacturing costs. More importantly, as the air gap size decreases, the switch faces the risk of accidental contact at low temperatures, easily leading to unreliable disconnection (i.e., excessive thermal conductivity in the off-state). For air-gap thermal switches designed based on the differential expansion principle, their structural characteristics limit the effective heat exchange area at both the cold and hot ends, directly restricting the potential for improving thermal conductivity in the on-state and making it difficult to meet the application requirements of efficient and rapid heat transfer. Summary of the Invention

[0006] This invention provides an air gap thermal switch and its preparation method, as well as a cryogenic refrigeration system, to solve at least one of the above-mentioned defects in the prior art. It has both gap control and insulation functions, thereby enhancing the reliability and vibration resistance of the air gap thermal switch during long-term operation.

[0007] This invention provides an air gap thermal switch, comprising: Support shell; The hot-end component is sealed within the supporting housing. The cold end component is sealed inside the supporting housing, and a preset air gap is formed between the cold end component and the hot end component; A gas adsorption component, connected to the air gap, is used to control the gas pressure in the air gap to open or close the heat conduction channel. A first functional coating is provided on the surface of the hot end component and / or the cold end component facing the air gap, the first functional coating being used to provide thermal insulation between the hot end component and the cold end component.

[0008] According to the air gap thermal switch provided by the present invention, the first functional coating is a dielectric or ceramic material having low thermal conductivity at low temperatures and good thermal conductivity at high temperatures.

[0009] In the air gap thermal switch provided by the present invention, the first functional coating is an aluminum oxide thin film.

[0010] According to the air gap thermal switch provided by the present invention, the hot end component is an inner copper pillar, and the cold end component is an outer copper ring sleeved outside the inner copper pillar, wherein the inner copper pillar and the outer copper ring are coaxially arranged. The first functional plating layer is provided on the surfaces of both the inner copper pillar and the outer copper ring facing the air gap.

[0011] According to the air gap thermal switch provided by the present invention, the inner copper column is provided with a first step, a second step and a third step at intervals along the axial direction; A first copper pillar segment is formed between the first step and the second step, a second copper pillar segment is formed between the second step and the third step, and a third copper pillar segment is formed between the third step and the end face of the inner copper pillar; the diameters of the first copper pillar segment, the second copper pillar segment, and the third copper pillar segment decrease sequentially. The outer copper ring has an internal receiving hole that matches the shape of the inner copper column. A first annular gap is formed between the first copper column segment and the supporting shell. A second annular gap is formed between the second copper column segment and the wall of the receiving hole. A third annular gap is formed between the third copper column segment and the wall of the receiving hole. The first gap, the second gap, and the third gap are interconnected to form the air gap. The first functional plating layer is provided on both the second copper column segment and the third copper column segment, and the first functional plating layer is provided at the position where the receiving hole mates with the second copper column segment and the third copper column segment.

[0012] According to the air gap thermal switch provided by the present invention, an annular fourth gap is formed between the outer surface of the outer copper ring and the supporting shell, and the fourth gap is in communication with the first gap and the second gap respectively.

[0013] According to the air gap thermal switch provided by the present invention, the outer surface of the outer copper ring is provided with a second functional plating layer, the second functional plating layer being made of the same material as the first functional plating layer, and the second functional plating layer being used to isolate the supporting shell and the outer copper ring during the welding process.

[0014] According to the air gap thermal switch provided by the present invention, the supporting housing is made of stainless steel and is connected to the cold end component by welding. The hot end component has an internal air supply channel with an opening on the end face of the hot end component. The air supply channel extends axially along the hot end component and extends radially through the hot end component, communicating with the air gap.

[0015] The present invention also provides a cryogenic refrigeration system, including the air gap thermal switch described in any one of the above-mentioned methods.

[0016] The present invention also provides a method for preparing the air gap thermal switch according to any one of the above claims, comprising the following steps: A first functional coating is deposited on the surface of the hot end component and / or the cold end component used to form an air gap by means of a coating process. A second functional coating is deposited on the outer peripheral surface of the cold-end component; The hot end component covered with the first functional coating is assembled with the cold end component to precisely form a preset air gap using the thickness of the first functional coating. The support housing is welded to the cold end component, and the second functional coating is used to prevent the support housing from making unintended contact with the cold end component during welding.

[0017] The air gap thermal switch provided by the present invention has a first functional coating on the surface of at least one of the hot end component and the cold end component facing the air gap, which has both gap control and heat insulation functions. When the air gap thermal switch is in the off state, it provides thermal barrier and when the air gap thermal switch is in the on state, it provides thermal conductivity, thereby improving the on / off ratio of the air gap thermal switch and ensuring that the reliability and vibration resistance of the air gap thermal switch are enhanced during long-term operation.

[0018] First, by shifting the micron-level precision requirement from macroscopic machining to microscopic thin film deposition, the machining tolerance requirements for large-sized components such as copper pillars and copper rings are greatly relaxed, thereby simplifying the process, shortening the production cycle, and reducing manufacturing costs. The advantages are even more obvious for large-sized, long-stroke thermal switches.

[0019] Secondly, the first functional coating, when disconnected, acts as a thermal circuit breaker, pre-setting a thermal insulation barrier at points where physical contact might occur. This ensures that even in the event of accidental contact, the massive heat flow is effectively blocked, thus guaranteeing the reliable disconnection of the thermal switch. In other words, the coating itself combines gap control and thermal insulation functions, eliminating the need for complex internal fin structures or auxiliary components such as springs used to prevent accidental contact in traditional designs.

[0020] Furthermore, for applications operating at extremely low temperatures (such as the superfluid helium temperature range), porous ceramic films such as alumina can effectively adsorb and prevent the creeping of superfluid helium, thus avoiding the additional heat leakage problem caused by the extremely high thermal conductivity of superfluid helium.

[0021] In order to improve the thermal conductivity of traditional air gap thermal switches, the air gap spacing needs to be minimized as much as possible; however, an excessively small spacing requires extremely high machining precision, and at low temperatures, due to inconsistent material shrinkage or vibration, accidental metal contact can easily occur, making it difficult for the thermal switch to turn off and deteriorating the switching performance.

[0022] This invention departs from the traditional approach of improving processing precision, instead taking a different route. It transforms the precise control of micron-level air gaps from the mechanical processing (cutting, shaving, grinding) of metal parts to the controllable deposition (plating) of thin film thickness. Thin film deposition technology can easily achieve thickness control at the micron or even nanometer level. This allows for the precise and cost-effective acquisition of the desired micron-sized air gaps by filling a film of a specific thickness within a relatively loose initial mechanical clearance (e.g., 1 mm). The synergistic integration of gap control and thermal insulation into a single first functional coating simplifies the structure.

[0023] The cryogenic refrigeration system provided by the present invention, because it includes the above-mentioned air gap thermal switch, possesses all the advantages of the above-mentioned air gap thermal switch.

[0024] The method for preparing the air gap thermal switch provided by this invention simplifies the process, shortens the production cycle, and reduces manufacturing costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is one of the structural schematic diagrams of the air gap thermal switch provided in the embodiments of the present invention.

[0027] Figure 2 This is the second schematic diagram of the air gap thermal switch provided in the embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the air gap thermal switch provided in an embodiment of the present invention.

[0029] Figure label: 10. Support shell; 20. Hot end component; 21. First step; 22. Second step; 23. Third step; 24. First copper column segment; 25. Second copper column segment; 26. Third copper column segment; 27. First gap; 28. Second gap; 29. ​​Third gap; 210. Gas supply channel; 30. Cold end component; 31. Receiving hole; 32. Fourth gap; 40. Gas adsorption component. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application based on the specific circumstances.

[0032] In the embodiments of this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0033] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0034] Figure 1 This is one of the structural schematic diagrams of the air gap thermal switch provided in the embodiments of the present invention. Figure 2 This is the second schematic diagram of the air gap thermal switch provided in the embodiment of the present invention. Figure 3 This is a schematic diagram of the air gap thermal switch provided in an embodiment of the present invention.

[0035] See Figures 1 to 3 The purpose of the air gap thermal switch provided in this embodiment of the invention is to achieve efficient connection (conduction) and reliable isolation (disconnection) of the heat channel between two objects in a low-temperature environment. The air gap thermal switch includes a supporting shell 10, a hot end component 20, a cold end component 30, and a gas adsorption component 40.

[0036] The support housing 10 provides mechanical support for the internal components and forms a sealed vacuum environment to prevent outside air from entering and causing convective heat transfer, which would affect the disconnection performance of the thermal switch. The support housing 10 is preferably made of a material with low thermal conductivity, such as a thin-walled stainless steel tube, which can effectively reduce parasitic heat leakage from ambient temperature to the low-temperature components through the support housing 10 itself.

[0037] Both the hot-end component 20 and the cold-end component 30 are welded and sealed to the supporting housing 10 and are located inside the supporting housing 10. The hot-end component 20 is used to connect to the target object that needs to be cooled, while the cold-end component 30 is connected to a cold source, such as the cold head of a refrigerator. To achieve efficient heat transfer, both the hot-end component 20 and the cold-end component 30 are preferably made of a material with high thermal conductivity, such as oxygen-free high-conductivity copper.

[0038] In a preferred embodiment, the hot-end component 20 is an inner copper pillar, and the cold-end component 30 is an outer copper ring disposed outside the inner copper pillar, with the two arranged concentrically. This coaxial structure is simple, compact, and easy to manufacture. The annular space formed between the inner copper pillar and the outer copper ring is the preset air gap, and the radial spacing of this air gap is a key dimension for realizing the thermal switching function. Alternatively, the hot-end component 20 and the cold-end component 30 can also be arranged side by side, and their arrangement can be adapted to the actual situation.

[0039] The gas adsorption component 40 is connected to the air gap and is used to control the gas pressure within the air gap to open or close the heat conduction channel. That is, the gas adsorption component 40 is the actuator of a thermal switch, used to control the pressure of the heat exchange gas within the air gap. The gas adsorption component 40 is typically a small container containing a high specific surface area adsorbent (such as activated carbon or zeolite molecular sieve), which is connected to the air gap space via a thin tube. A miniature heater is also installed outside the container.

[0040] Specifically, a first functional coating is provided on the surface of at least one of the hot-end component 20 and the cold-end component 30 facing the air gap. That is, the first functional coating is provided on the surface of the hot-end component 20 and / or the cold-end component 30 facing the air gap. In other words, whether the coating is provided on either surface alone or on both surfaces constituting the air gap, it can play a role in controlling the gap and providing thermal insulation.

[0041] In the preferred embodiment of the concentric cylinders described above, a first functional coating is plated on the outer surface of the inner copper cylinder and / or the inner surface of the outer copper ring. The first functional coating is used to control the spacing of the air gap and to provide thermal barrier when the air gap thermal switch is in the off state and to provide thermal conductivity when the air gap thermal switch is in the on state.

[0042] Therefore, the design and material selection of the first functional coating are innovations of this invention. Preferably, the material of the first functional coating exhibits extremely low thermal conductivity (i.e., it is a thermal insulator) at low temperatures (such as the liquid helium temperature range of 4.2K), while having relatively good thermal conductivity at higher temperatures (such as room temperature or the heating temperature of an adsorption pump). A typical material is alumina.

[0043] The thickness of the first functional coating is typically on the order of micrometers and can be precisely controlled by thin film preparation techniques such as plasma spraying, atomic layer deposition, or physical vapor deposition.

[0044] The working process of the air gap thermal switch of the present invention is divided into two states: on and off, which are switched by controlling the temperature of the gas adsorption component 40.

[0045] On (Open) State: The gas adsorption component 40 is heated (e.g., to 40K-60K) by a micro heater. The adsorbent releases the previously adsorbed heat exchange gas (e.g., helium) due to the increased temperature. The heat exchange gas rapidly fills the air gap between the hot-end component 20 and the cold-end component 30. Gas molecules undergo intense, random thermal motion between the hot and cold-end surfaces, efficiently transferring heat through gas conduction and convection. At this time, the air gap thermal switch is activated, and the cold energy from the cold end is rapidly conducted to the hot end, cooling the target object. In this state, although the first functional coating exhibits some thermal resistance, its effect is negligible compared to the efficient gas heat conduction.

[0046] Disconnected (Off) State: Heating of the gas adsorption component 40 ceases, allowing it to cool naturally or actively to a low temperature via a dedicated thermal link. The adsorbent temperature decreases, and its adsorption capacity increases dramatically, recapturing and fixing the heat-exchange gas molecules in the air gap. A high vacuum is formed within the air gap, cutting off the gas heat conduction path. At this point, heat can only be transferred through conduction via the solid support structure and radiation between the hot and cold end surfaces. The first functional coating plays a crucial role in this state: due to its excellent thermal insulation at low temperatures, even if the hot and cold end components 20 come into microscopic contact due to vibration or thermal stress, the coating effectively blocks the direct heat conduction path between the metals, providing a significant thermal barrier and suppressing parasitic heat leakage.

[0047] Because the first functional coating forms a shielding layer similar to a multi-layered insulating material, it effectively reduces radiative heat leakage between the hot and cold ends. Ultimately, the air gap thermal switch closes, and the hot and cold ends are thermally highly isolated. This prevents contact between the hot and cold end components due to factors such as surface roughness, flatness, and concentricity deviations, ensuring thermal isolation when the air gap thermal switch is in the open state.

[0048] It is understood that the air gap thermal switch provided in the embodiments of the present invention provides a first functional coating on the surface of at least one of the hot end component 20 and the cold end component 30 facing the air gap. The first functional coating has both gap control and heat insulation functions, so that the air gap thermal switch provides thermal barrier when it is in the off state and provides thermal conductivity when it is in the on state, thereby improving the switching ratio of the air gap thermal switch and ensuring that the reliability and vibration resistance of the air gap thermal switch are enhanced during long-term operation, thus solving the inherent contradiction that has long existed in the design of existing air gap thermal switches.

[0049] First, by shifting the micron-level precision requirement from macroscopic machining to microscopic thin film deposition, the machining tolerance requirements for large-sized components such as copper pillars and copper rings are relaxed. This avoids contact between the copper pillars and copper rings due to factors such as surface roughness, flatness, and concentricity deviation, thereby simplifying the process, shortening the production cycle, and reducing manufacturing costs. The advantages are particularly evident for large-sized, long-stroke thermal switches.

[0050] Secondly, the first functional coating, when disconnected, acts as a thermal circuit breaker, pre-setting a thermal insulation barrier at points where physical contact might occur. This ensures that even in the event of accidental contact, the massive heat flow is effectively blocked, thus guaranteeing the reliable disconnection of the thermal switch. In other words, the coating itself combines gap control and thermal insulation functions, eliminating the need for complex internal fin structures or auxiliary components such as springs used to prevent accidental contact in traditional designs. This enhances the long-term operational reliability and vibration resistance of the air gap thermal switch.

[0051] Furthermore, for applications operating at extremely low temperatures (such as the superfluid helium temperature range), porous ceramic films such as alumina can effectively adsorb and prevent the creeping of superfluid helium, thus avoiding the additional heat leakage problem caused by the extremely high thermal conductivity of superfluid helium.

[0052] In order to improve the thermal conductivity of traditional air gap thermal switches, the air gap spacing needs to be minimized as much as possible; however, an excessively small spacing requires extremely high machining precision, and at low temperatures, due to inconsistent material shrinkage or vibration, accidental metal contact can easily occur, making it difficult for the thermal switch to turn off and deteriorating the switching performance.

[0053] This invention departs from the traditional approach of improving processing precision, instead taking a different route. It transforms the precise control of micron-level air gaps from the mechanical processing (cutting, shaving, grinding) of metal parts to the controllable deposition (plating) of thin film thickness. Thin film deposition technology can easily achieve thickness control at the micron or even nanometer level. This allows for the precise and cost-effective acquisition of the desired micron-sized air gaps by filling a film of a specific thickness within a relatively loose initial mechanical clearance (e.g., 1 mm). The synergistic integration of gap control and thermal insulation into a single first functional coating simplifies the structure.

[0054] In some embodiments of the present invention, the first functional coating is a dielectric or ceramic material having low thermal conductivity at low temperatures and good thermal conductivity at high temperatures, preferably an alumina film.

[0055] It is understood that the core technical concept of this invention is not simply to add a coating to the surface of the air gap thermal switch components, but to introduce a functional material layer with specific physical properties in order to fundamentally solve the long-standing and irreconcilable technical contradictions in the prior art.

[0056] To achieve high on-state thermal conductivity, existing air-gap thermal switches require minimizing the air gap distance between the cold and hot end components 20. However, excessively small distances not only place extremely high demands on machining precision, but more importantly, they are prone to accidental physical contact under low-temperature vibration environments or the thermal expansion and contraction effects of materials, resulting in huge parasitic heat leakage in the off-state and severe degradation of switching performance.

[0057] The first functional coating in this embodiment of the invention needs to have the physical properties of having low thermal conductivity at low temperatures and good thermal conductivity at high temperatures, so as to act as an ultimate thermal fuse in the disconnected state; and not to become a bottleneck for heat transfer under specific conditions.

[0058] When the air gap thermal switch is in the off state and the air gap is a vacuum, this first functional coating is crucial to prevent accidental contact that could lead to a thermal short circuit. Because the first functional coating is an excellent thermal insulator at low temperatures, even if point contact occurs between the hot and cold ends of the metal substrate, the film provides significant thermal resistance, effectively blocking heat flow and ensuring reliable disconnection of the thermal switch.

[0059] The excellent thermal conductivity at high temperatures eliminates potential negative effects. For example, during the initial cooling process of the entire cryogenic system from room temperature, or during the stage of heating the gas adsorption component 40 to activate the thermal switch, localized areas of the system may be at higher temperatures. In these situations, the relatively good thermal conductivity of the first functional coating ensures that it will not become an obstacle to cold transfer or heat dissipation, thus guaranteeing the overall thermal management efficiency of the system.

[0060] Among them, alumina thin film is an ideal carrier for realizing the above dual functional properties. It has the physical properties of reduced phonon activity and sharp decrease in thermal conductivity at low temperature. At the same time, it has a stable structure and high hardness, making it suitable as a wear-resistant surface coating.

[0061] In addition to the core functions mentioned above, alumina films offer additional, unexpected benefits: Firstly, as a shielding layer between the high-emissivity copper surface and the surface, they act as a radiation shield similar to multilayer insulation materials, suppressing radiative heat leakage. Secondly, the porous microstructure of alumina films effectively adsorbs and prevents surface creep of superfluid helium, solving a thorny additional heat leakage problem in cryogenic applications.

[0062] In the air gap thermal switch provided in this embodiment of the invention, the hot end component 20 is an inner copper pillar, and the cold end component 30 is an outer copper ring sleeved outside the inner copper pillar. The outer copper ring is a hollow copper cylinder or ring, and the inner copper pillar and the outer copper ring are coaxially arranged. A first functional plating layer is provided on the surfaces of the inner copper pillar and the outer copper ring facing the air gap.

[0063] Compared to traditional, complex finned structures, the manufacturing processes for cylinders and tubes are very mature, tolerances are easy to control, and manufacturing costs are reduced. For the same axial length, this structure provides a maximized relative heat exchange area, which is beneficial for achieving rapid and sufficient heat exchange in the conductive state.

[0064] In a preferred embodiment, a first functional coating is provided on the surfaces of both the inner copper pillar and the outer copper ring facing the air gap. That is, a first functional film is coated on the outer circumferential surface of the inner copper pillar, and a first functional film is also coated on the inner circumferential surface of the outer copper ring.

[0065] Therefore, when the two are coaxially assembled, both sides of the air gap are covered by the first functional thin film, forming a double-layer coating: copper, thin film, air gap, thin film, and copper. This configuration has the following effects: When the thermal switch is open, if the hot and cold end components 20 come into physical contact due to vibration or thermal stress, the contact point will be blocked by two layers of functional films. This is equivalent to setting up double thermal protection, with a thermal resistance much greater than that of a single film, thereby more thoroughly suppressing parasitic heat leakage caused by point contact and making the open state of the thermal switch more reliable.

[0066] In low-temperature and high-vacuum environments, radiation is the primary mode of heat loss besides solid-state heat conduction. When both copper surfaces on either side of the air gap are covered with ceramic thin films such as alumina, these two opposing thin film surfaces form a radiation shielding cavity similar to multilayered vacuum insulation.

[0067] Alumina has a lower infrared emissivity at low temperatures compared to a high-gloss copper surface. When two low-emissivity surfaces face each other, the radiative heat transfer between them decreases, reducing radiative heat leakage during the off state, thus significantly improving the thermal insulation performance of the thermal switch from another dimension.

[0068] In other words, the prototype of the air gap thermal switch in this application is as follows: Figure 1 As shown. To maximize the thermal conductivity in the conductive state, both the cold and hot ends of the copper blocks are made of high-purity oxygen-free copper and arranged in a concentric circle structure, forming a gap of 1 mm as initially designed, resulting in an effective heat exchange area of ​​5.306 cm². 2 However, due to multiple factors such as surface roughness and flatness during processing and concentricity deviation during assembly, the actual local gap may be less than 1 mm. There is a risk of local contact between the cold and hot copper blocks.

[0069] In traditional air-gap thermal switch manufacturing, springs or other supporting components are often installed on the outside of the bottom of the hot-end copper block to prevent contact between the stainless steel casing and the cold and hot-end copper blocks during welding. Although the springs and other components have low thermal conductivity, they still introduce additional heat leakage when the switch is off, leading to an increase in the disconnect thermal conductivity. To solve this problem, a micron-sized aluminum oxide coating is applied to both the inner surface of the cold-end copper block and the outer surface of the hot-end copper block, thus eliminating the need for the installation of springs and other supporting components.

[0070] Because alumina has extremely low thermal conductivity at low temperatures, even if localized point contact occurs between coating layers due to processing errors, heat leakage is negligible. Simultaneously, alumina retains high thermal conductivity at high temperatures, ensuring effective heat transfer during conduction. Furthermore, this design allows for different air gap sizes to be achieved based on specific application requirements. It is worth noting that the thickness of the alumina coating was measured using a micrometer and a coating thickness gauge, with a thickness deviation of approximately 30µm, and a surface roughness of 4-10µm.

[0071] The outer support shell 10 is made of low thermal conductivity stainless steel with a wall thickness of 0.25 mm and a length of 166 mm. This thickness ensures structural rigidity, allowing it to be directly integrated into the cryogenic system as a support rod, while also ensuring good thermal insulation performance of the air gap thermal switch when it is off.

[0072] Continue reading Figure 1 In some embodiments of the present invention, the inner copper pillar is provided with a first step 21, a second step 22 and a third step 23 at intervals along the axial direction; a first copper pillar segment 24 is formed between the first step 21 and the second step 22, a second copper pillar segment 25 is formed between the second step 22 and the third step 23, and a third copper pillar segment 26 is formed between the third step 23 and the end face of the inner copper pillar; the diameters of the first copper pillar segment 24, the second copper pillar segment 25 and the third copper pillar segment 26 decrease sequentially.

[0073] The outer copper ring has a receiving hole 31 that conforms to the shape of the inner copper column. A first annular gap 27 is formed between the first copper column segment 24 and the supporting shell 10. A second annular gap 28 is formed between the second copper column segment 25 and the wall of the receiving hole 31. A third annular gap 29 is formed between the third copper column segment 26 and the wall of the receiving hole 31. The first gap 27, the second gap 28 and the third gap 29 are interconnected to form an air gap. The second copper column segment 25 and the third copper column segment 26 are both provided with a first functional plating layer. The receiving hole 31 is provided with a first functional plating layer at the position where it mates with the second copper column segment 25 and the third copper column segment 26.

[0074] Furthermore, an annular fourth gap 32 is formed between the outer surface of the outer copper ring and the supporting shell 10, and the fourth gap 32 is connected to the first gap 27 and the second gap 28 respectively.

[0075] It is understood that the inner copper pillar provided in this embodiment of the invention is not a simple cylinder, but a complex structure with multiple steps along the axial direction. Specifically, it has a first step 21, a second step 22, and a third step 23 arranged sequentially along the axial direction. These steps naturally divide the inner copper pillar into three sections with progressively decreasing diameters: a first copper pillar section 24, a second copper pillar section 25, and a third copper pillar section 26. The outer copper ring has a receiving hole 31 inside that matches the shape of the stepped inner copper pillar.

[0076] When the two are coaxially assembled, they form a complex but functionally defined multi-gap system: the first gap 27 is an annular gap formed between the first copper pillar segment 24 and the supporting shell 10. It is important to note that this gap is not between the hot and cold ends, but rather between a portion of the hot-end component 20 and the outermost vacuum shell. The second gap 28 and the third gap 29 are formed between the second copper pillar segment 25, the third copper pillar segment 26, and the wall of the outer copper ring receiving hole 31; these two gaps are the core functional areas for achieving heat conduction and disconnection. The fourth gap 32 is an annular gap formed between the outer surface of the outer copper ring and the supporting shell 10. All four gaps are interconnected, collectively forming a unified air gap space inside the thermal switch, managed by the gas adsorption component 40.

[0077] The plating layer can be applied only to the surfaces of the second copper column segment 25 and the third copper column segment 26, while the surface of the first copper column segment 24, which has the largest diameter, may not have a plating layer. Furthermore, the plating layer can be applied not only to the surfaces of the second and third copper column segments 25 and 26 of the inner copper column, but also to the corresponding position on the wall of the outer copper ring receiving hole 31.

[0078] The first copper column segment 24, with the largest diameter, primarily provides strong mechanical support and structural rigidity. The first gap 27 it forms with the supporting housing 10 serves as a channel for gas flow, ensuring structural stability. Because this area has the largest diameter and strongest structure, and can typically be designed with a large gap, the risk of accidental contact is extremely low, eliminating the need for a functional plating layer and simplifying the process.

[0079] The smaller diameter second copper column segment 25 and third copper column segment 26 are the core operating areas of the air gap thermal switch. To achieve optimal switching performance, the size of the air gap needs to be minimized. To address the high risk of contact caused by the small gap, this invention provides functional coatings on both the inner and outer opposing surfaces of this area as a double layer of protection, ensuring effective thermal insulation even in the event of contact.

[0080] By setting a large-diameter support area (first copper column segment 24), the overall rigidity and vibration resistance of the thermal switch are improved. In particular, when manufacturing large-size, long-stroke thermal switches, it effectively solves the problem of easy deformation and failure of traditional slender structures.

[0081] Since the mechanical support is provided by the support area, the switching area (second copper column segment 25 and third copper column segment 26) can be set with a smaller air gap size. Combined with the double protection provided by the double-sided coating, the thermal switch achieves a high level in both the thermal conductivity in the on-state and the thermal resistance in the off-state.

[0082] The presence of the fourth gap 32 allows the entire core switching assembly (outer copper ring) to be insulated from the supporting housing 10 by a vacuum, further reducing parasitic heat leakage from the external environment to the cold end and improving the overall thermal efficiency.

[0083] In some embodiments of the present invention, the outer surface of the outer copper ring is provided with a second functional plating layer, the second functional plating layer being made of the same material as the first functional plating layer, and the second functional plating layer being used to isolate the supporting shell 10 from the outer copper ring during the welding process.

[0084] To ensure the overall structural robustness, the stainless steel outer shell and the copper blocks at the hot and cold ends are welded using vacuum brazing. Because the outer shell is thin-walled and the distance between it and the copper block at the cold end is only 1 mm, softening may occur during welding, leading to unintended lateral point contact between the two. Therefore, in this embodiment of the invention, a second functional coating formed by an alumina plating is applied to the outer surface of the copper block at the cold end to avoid contact heat leakage problems caused by material softening.

[0085] Traditional processes typically employ mechanical isolation methods, such as temporarily or permanently inserting auxiliary components like springs, ceramic gaskets, or fiberglass rings between the stainless steel casing and the outer copper ring. However, this method has significant drawbacks: it increases the number of parts and assembly complexity. If the components are permanent, they introduce additional solid-state heat conduction paths, which also degrades the thermal switch's off-state performance.

[0086] This invention abandons the approach of adding additional physical insulating components. Before welding, a high-temperature resistant, thermally insulating ceramic film (such as alumina) is coated on the outer surface of the outer copper ring. During the welding process, even if the thin-walled stainless steel shell softens and deforms due to high temperatures and comes into contact with the sidewall of the outer copper ring, it does not come into contact with the conductive and thermally conductive copper substrate, but rather with this pre-designed insulating film. Due to the presence of this film, physical contact does not lead to an electrical short circuit or a significant thermal short circuit. After welding, even if the stainless steel shell remains in contact with this coating, its impact on the overall thermal conductivity is negligible.

[0087] Since no additional mechanical isolators are required, these are prevented from becoming sources of parasitic heat leakage in the final product. This allows the thermal switch to achieve a lower theoretical limit in its off-state thermal conductivity, further improving the on / off ratio and overall performance. Eliminating auxiliary isolators that could loosen or fail due to vibration or thermal cycling makes the entire thermal switch structure simpler and more robust, thereby enhancing its long-term reliability in harsh environments, such as vibrations in space applications.

[0088] In some embodiments of the present invention, the support shell 10 is made of stainless steel. In the field of cryogenic engineering, austenitic stainless steel, such as 304 or 316L stainless steel, is preferred. The support shell 10 is connected to the outer copper ring by welding. That is, between the end of the support shell 10 and the end of the outer copper ring (i.e., the cold end component 30), a permanent, high-vacuum sealed dissimilar metal connection is formed by welding processes such as vacuum brazing, laser welding, or tungsten inert gas welding.

[0089] The hot end component 20 has an internal air supply channel 210. The opening of the air supply channel 210 is located on the end face of the hot end component 20. The air supply channel 210 extends along the axial direction of the hot end component 20 and passes through the radial direction of the hot end component 20, communicating with the air gap.

[0090] The hot-end component 20 (inner copper column) is connected to the target cooling object via a flange. This opening is located on the end face of the flange and is used to connect the gas supply line from the gas adsorption component 40. In practice, an axial blind hole can be drilled at the center or eccentric position of the inner copper column, extending from the end face opening to the height of the air gap. Then, one or more radial small holes are drilled from the side wall of the inner copper column, connecting to the bottom of the axial blind hole. This forms an integrated "L" or "T" shaped channel inside the solid inner copper column. It is evident that directly machining the channel inside the robust inner copper column eliminates the need for a fragile, independent pipeline spanning the vacuum, greatly improving the mechanical strength and vibration resistance of the entire device and reducing the risk of pipeline breakage due to vibration or thermal stress.

[0091] To further improve the disconnection efficiency of the air gap thermal switch, the gas adsorption component 40 provided in this embodiment of the invention employs an adsorption pump (2.23 cm³) with a larger volume than previous designs. 3The internal structure is filled with 1.4 g of activated carbon. This mass was selected empirically to ensure that the adsorption pump has sufficient adsorption capacity to fully adsorb helium in the gas gap. To reduce the thermal time constant, the adsorption pump is connected to the outer copper block via a stainless steel pumping pipeline with an inner diameter of 3 mm, an outer diameter of 5 mm, and a length of 25 mm. Due to the short pipeline and large cross-sectional area, the thermal switch achieved rapid dynamic switching in subsequent on / off time tests. In addition, the adsorption pump installation method was changed from the traditional side-outlet type to an axial direct connection type, improving the overall structural compactness.

[0092] This invention also provides a cryogenic refrigeration system, including the gas gap thermal switch of any of the above embodiments. Cryogenic refrigeration systems, such as helium vacuum evaporation refrigeration systems, adiabatic demagnetizing refrigerators, or dilution refrigerators, typically include a cold source (such as a refrigerator cold head or liquid helium pool), multi-stage cold shields, a vacuum jacket, an experimental / sample mounting platform, and complex control electronics.

[0093] The cold end component 30 of the air gap thermal switch (e.g., the outer copper ring) is thermally connected to a low-temperature stage of the refrigeration system (e.g., the second-stage cold head of a refrigerator) via bolts or crimping. The hot end component 20 of the thermal switch (e.g., the inner copper pillar) is thermally connected to the target object requiring temperature control (e.g., scientific experimental samples, high-sensitivity detectors). The supporting housing 10 of the air gap thermal switch is typically fixed to the vacuum enclosure of the refrigeration system or a relatively temperature-stable cold shield. The heater lead of the gas adsorption component 40 (adsorption pump) of the air gap thermal switch is led out from the refrigeration system and connected to an external power supply and temperature control system, thereby enabling remote control of the thermal switch's "on" and "off" states.

[0094] This invention also provides a method for fabricating the air gap thermal switch provided in any of the above embodiments, comprising the following steps: Step 1: A first functional coating is deposited on the surface of the hot end component 20 and / or the cold end component 30 used to form an air gap by means of a coating process.

[0095] For example, in a concentric cylindrical structure, this step corresponds to coating the outer surface of the inner copper pillar and / or the inner surface of the outer copper ring. Possible coating processes include, but are not limited to, plasma spraying, atomic layer deposition, and magnetron sputtering. The deposited material is preferably alumina or other ceramic materials that exhibit thermal insulation at low temperatures and relatively good thermal conductivity at high temperatures. The thickness of this coating is precisely controlled on the micrometer scale. The core purpose of this step is to define the performance of the final product during operation. This coating is used both to precisely control the final air gap size and to provide reliable thermal barrier when the thermal switch is off.

[0096] Step 2: Deposit a second functional coating on the outer peripheral surface of the cold end component 30.

[0097] For example, a thin film of the same material as the first functional plating layer (e.g., also aluminum oxide) is coated on the outer circumferential wall of the outer copper ring, particularly in the region near the end where it will be welded to the supporting housing 10. The core purpose of this step is not for the performance of the product, but to solve a process problem that will be encountered in subsequent manufacturing steps, namely, the problem of accidental short circuits during welding.

[0098] Step 3: Assemble the hot end component 20 and the cold end component 30 coated with the first functional coating to precisely form a preset air gap using the thickness of the first functional coating.

[0099] For example, the coated inner copper pillar is inserted into the receiving hole 31 of the coated outer copper ring. The final gap size between them is precisely determined by subtracting the thickness of the thin films on both sides from the initial machining gap. This transforms the difficult machining of large-size metal parts into controllable deposition of thin film thickness through precise control of the micron-level air gap.

[0100] Step 4: Weld the support housing 10 to the cold end component 30 to form a permanent vacuum seal, and use the second functional coating to prevent the support housing 10 from making unintended contact with the cold end component 30 during welding.

[0101] For example, vacuum brazing is used to weld the end of the thin-walled stainless steel support housing 10 to the end of the outer copper ring. By utilizing the second functional coating as an in-situ, high-temperature resistant insulating firewall, unintended physical contact between the support housing 10 and the cold-end component 30 during welding is effectively prevented.

[0102] By introducing a second functional plating layer as a solder barrier, a soldering process that relied on highly skilled operators has been transformed into a robust, fault-tolerant, standardized procedure. This eliminates the risk of scrapping entire expensive components due to solder short circuits and improves production yield.

[0103] Because the manufacturing process has become reliable, product designers can optimize the design. For example, a thinner support shell 10 can be used to achieve better thermal insulation, or the welding positions can be designed to be more compact without having to leave a safety margin to avoid welding risks.

[0104] By employing in-situ insulation, auxiliary components such as springs and ceramic gaskets used for isolation in traditional processes are eliminated. This not only reduces material costs and inventory management but, more importantly, simplifies the assembly process and reduces reliance on complex tooling and fixtures.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An air gap thermal switch, characterized in that, include: Support shell; The hot-end component is sealed within the supporting housing. The cold end component is sealed inside the supporting housing, and a preset air gap is formed between the cold end component and the hot end component; A gas adsorption component, connected to the air gap, is used to control the gas pressure in the air gap to open or close the heat conduction channel. A first functional coating is provided on the surface of the hot end component and / or the cold end component facing the air gap, the first functional coating being used to provide thermal insulation between the hot end component and the cold end component.

2. The air gap thermal switch according to claim 1, characterized in that, The first functional coating is a dielectric or ceramic material that has low thermal conductivity at low temperatures and good thermal conductivity at high temperatures.

3. The air gap thermal switch according to claim 2, characterized in that, The first functional coating is an aluminum oxide thin film.

4. The air gap thermal switch according to any one of claims 1 to 3, characterized in that, The hot end component is an inner copper pillar, and the cold end component is an outer copper ring sleeved on the outside of the inner copper pillar. The inner copper pillar and the outer copper ring are coaxially arranged. The first functional plating layer is provided on the surfaces of both the inner copper pillar and the outer copper ring facing the air gap.

5. The air gap thermal switch according to claim 4, characterized in that, The inner copper pillar is provided with a first step, a second step and a third step at intervals along the axial direction; A first copper pillar segment is formed between the first step and the second step, a second copper pillar segment is formed between the second step and the third step, and a third copper pillar segment is formed between the third step and the end face of the inner copper pillar; the diameters of the first copper pillar segment, the second copper pillar segment, and the third copper pillar segment decrease sequentially. The outer copper ring has an internal receiving hole that matches the shape of the inner copper column. A first annular gap is formed between the first copper column segment and the supporting shell. A second annular gap is formed between the second copper column segment and the wall of the receiving hole. A third annular gap is formed between the third copper column segment and the wall of the receiving hole. The first gap, the second gap, and the third gap are interconnected to form the air gap. The first functional plating layer is provided on both the second copper column segment and the third copper column segment, and the first functional plating layer is provided at the position where the receiving hole mates with the second copper column segment and the third copper column segment.

6. The air gap thermal switch according to claim 5, characterized in that, An annular fourth gap is formed between the outer surface of the outer copper ring and the supporting shell, and the fourth gap is connected to the first gap and the second gap respectively.

7. The air gap thermal switch according to claim 4, characterized in that, The outer surface of the outer copper ring is provided with a second functional plating layer. The second functional plating layer is made of the same material as the first functional plating layer. The second functional plating layer is used to isolate the supporting shell from the outer copper ring during the welding process.

8. The air gap thermal switch according to any one of claims 1 to 3, characterized in that, The supporting shell is made of stainless steel and is connected to the cold end component by welding. The hot end component has an internal air supply channel with an opening on the end face of the hot end component. The air supply channel extends axially along the hot end component and extends radially through the hot end component, communicating with the air gap.

9. A cryogenic refrigeration system, characterized in that, Includes the air gap thermal switch as described in any one of claims 1 to 8.

10. A method for preparing an air-gap thermal switch according to any one of claims 1 to 8, characterized in that, Includes the following steps: A first functional coating is deposited on the surface of the hot end component and / or the cold end component used to form an air gap by means of a coating process. A second functional coating is deposited on the outer peripheral surface of the cold-end component; The hot end component covered with the first functional coating is assembled with the cold end component to precisely form a preset air gap using the thickness of the first functional coating. The support housing is welded to the cold end component, and the second functional coating is used to prevent the support housing from making unintended contact with the cold end component during welding.

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