A low-temperature heat exchanger

Abstract

The present invention discloses a cryogenic heat exchanger, which relates to the technical field of dilution refrigerators. It includes a distillation chamber. A mixture inlet pipe for introducing a mixture of helium-3 and helium-4 is provided at the bottom of the distillation chamber, and a steam outlet channel for the circulation of helium-3 steam is provided at the top. And a bottom heater is provided at the inner bottom of the distillation chamber; A pre-cooling device is arranged in the distillation chamber, and one end of it is externally connected with an inlet pipe, and the other end is externally connected with an outlet pipe. Helium-3 steam is used to be introduced into the inlet pipe; A superfluidity suppression component is arranged in the distillation chamber. The superfluidity suppression component includes a copper baffle. The copper baffle includes a side baffle and a top baffle, which can suppress the superfluid state of helium-4. The cryogenic heat exchanger provided by the present invention can suppress the superfluidity of helium-4, avoiding the leakage of helium-4 out of the cryogenic heat exchanger in the superfluid state, bringing additional heat leakage.

Description

Technical Field

[0001] The present invention relates to the technical field of dilution refrigerators, and particularly to a cryogenic heat exchanger. Background Art

[0002] A dilution refrigerator is a refrigeration device that can reach extremely low temperatures (usually below 10 mK). The cryogenic heat exchanger is one of the key components in the dilution refrigerator, which is used to achieve efficient energy exchange and ensure the smooth progress of the refrigeration process. A mixture of liquid helium-3 and liquid helium-4 is introduced into the cryogenic heat exchanger. Based on the characteristics of different saturated vapor pressures of helium-3 and helium-4 at the same temperature, mainly helium-3 vapor evaporates inside it, thereby realizing the separation of helium-3 and helium-4.

[0003] Under normal atmospheric pressure, when the temperature drops below 2.17K, helium-4 will exhibit superfluidity. The superfluid liquid of helium-4 will crawl upward along the side wall of the cryogenic heat exchanger. If this superfluid flow is not properly handled, it will bring huge heat leakage and heat conduction losses. At the same time, a large amount of helium-4 is entrained in the helium-3 vapor, which will affect the normal operation of the dilution refrigerator. To avoid this problem, a technical solution that can suppress the superfluidity of helium-4 needs to be designed. Summary of the Invention

[0004] The purpose of the present invention is to provide a cryogenic heat exchanger to solve the problems existing in the above-mentioned prior art, which can suppress the superfluidity of helium-4 and avoid the extra heat leakage caused by helium-4 climbing out of the cryogenic heat exchanger in the superfluid state.

[0005] To achieve the above purpose, the present invention provides the following solutions:

[0006] The present invention provides a cryogenic heat exchanger, comprising:

[0007] A distillation chamber, at the bottom of which there is a mixture inlet pipe for introducing a mixture of helium-3 and helium-4, at the top of which there is a steam outlet channel for the circulation of helium-3 vapor, and a bottom heater is provided at the inner bottom of the distillation chamber;

[0008] A precooling device, which is arranged in the distillation chamber, and one end of which is externally connected with an inlet pipe, and the other end is externally connected with an outlet pipe. The inlet pipe is used for introducing helium-3 vapor;

[0009] The superfluidity suppression component is arranged in the distillation chamber. The distillation chamber includes a bottom plate, on which a side plate is fixedly sealed. The top of the side plate is provided with a top plate. The mixture inlet pipe communicates with the bottom plate, and the bottom heater is fixedly arranged on the bottom plate between the side plate and the mixture inlet pipe. The steam outlet channel penetrates through the top plate. The superfluidity suppression component includes a copper baffle, which includes a side baffle and a top baffle. The side baffle is fixedly arranged on the bottom plate and is located between the bottom heater and the side plate. The top baffle is located at the top of the side baffle and horizontally extends towards the end away from the side plate. There is a gap between the top baffle and the top plate, and the vertical projection of the top baffle is located between the vertical projections of the side plate and the steam outlet channel. The copper baffle can suppress the superfluid state of helium-4.

[0010] Preferably, two copper baffles are arranged in the distillation chamber, which are respectively a first copper baffle and a second copper baffle. The side baffles of the first copper baffle and the second copper baffle are arranged in parallel, and the top baffle of the first copper baffle is located above the top baffle of the second copper baffle.

[0011] Preferably, the superfluidity suppression component further includes a polishing plate, which is fixedly arranged on the inner bottom of the top plate and is arranged in a ring around the outside of the steam outlet channel.

[0012] Preferably, the superfluidity suppression component further includes a first thin-walled tube and a second thin-walled tube that are coaxially arranged with the steam outlet channel and are arranged in a ring around the outside of the steam outlet channel. One end of the second thin-walled tube is inserted into the top plate, and the other end is connected to the top flange of the steam outlet channel. The first thin-walled tube is located between the second thin-walled tube and the steam outlet channel. An arc-shaped cutting edge extending to the inside of the distillation chamber is provided at the bottom of the first thin-walled tube.

[0013] Preferably, the superfluidity suppression component further includes a porous plug, which is fixedly arranged in the steam outlet channel.

[0014] Preferably, the superfluidity suppression component further includes a film heater, which is located outside the top flange of the steam outlet channel. Both the steam outlet channel and the top flange of the steam outlet channel are made of copper.

[0015] Preferably, the pre-cooling device includes a pre-cooling coil, which is fixedly arranged in the distillation chamber through a pre-cooling coil support frame. One end of the pre-cooling coil is externally connected with an inlet pipe, and the other end is externally connected with an outlet pipe. The inlet pipe penetrates through the top plate, and the outlet pipe penetrates through the bottom plate.

[0016] The present invention has achieved the following technical effects compared with the prior art:

[0017] The present invention is provided with a superfluidity suppression component in the distillation chamber. When a mixture of helium-4 and helium-3 is introduced into the distillation chamber and heated, on the premise of ensuring that helium-3 can be evaporated by heating, the superfluidity of helium-4 can be suppressed, thereby avoiding the climbing out of the distillation chamber by helium-4 due to superfluidity and reducing the heat leakage problem caused by the leakage of helium-4; the pre-cooling device is arranged in the distillation chamber and immersed in the mixture of helium-4 and helium-3, realizing the pre-cooling effect on the helium-3 vapor introduced into the pre-cooling device. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0019] Figure 1 It is a schematic cross-sectional view of one embodiment of the cryogenic heat exchanger of the present invention;

[0020] In the figure: 1 - film heater, 2 - steam outlet channel, 3 - first thin-walled tube, 4 - second thin-walled tube, 5 - porous plug, 6 - polished plate, 7 - knife edge, 8 - pre-cooling coil, 9 - pre-cooling coil support frame, 10 - copper baffle, 11 - top plate, 12 - side plate, 13 - bottom heater, 14 - bottom plate, 15 - mixture inlet pipe, 16 - gas-liquid interface. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0022] The object of the present invention is to provide a cryogenic heat exchanger to solve the problems existing in the above-mentioned prior art, which can suppress the superfluidity of helium-4 and avoid the climbing out of the cryogenic heat exchanger by helium-4 in the superfluid state, bringing additional heat leakage.

[0023] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0024] Helium-3 and helium-4 are isotopes. Using a mixture of helium-3 and helium-4 in a dilution refrigerator can provide a refrigeration temperature of dozens of millikelvins. The distillation chamber in the dilution refrigerator is used to heat the liquid mixture of helium-3 and helium-4. Based on the physical properties of different saturated vapor pressures of helium-3 and helium-4 at the same temperature, the main evaporated substance in the distillation chamber is helium-3 vapor, thereby realizing the separation of helium-3 and helium-4; the superfluid liquid phase transition temperature of helium-3 is 2.6 millikelvins, which is much lower than the superfluid transition temperature of helium-4. At one atmosphere, when the temperature of helium-4 is lowered to 2.17 K, helium-4 suddenly changes from the original normal fluid to a "superfluid" with a series of extremely unusual properties. This "superfluid" hardly exhibits any viscosity and has a very high thermal conductivity, and its thermal conductivity can reach 800 times that of copper at room temperature. Therefore, the superfluid helium-4 will climb upward along the side wall of the distillation chamber with almost no viscous consumption, and the superfluid helium-4 climbs out of the low-temperature heat exchanger, which is likely to bring additional heat leakage.

[0025] To avoid the above problems, the present invention provides a low-temperature heat exchanger, as Figure 1 shown, which includes a distillation chamber. The distillation chamber includes a bottom plate 14. A side plate 12 is fixedly sealed on the bottom plate 14. A top plate 11 is provided at the top of the side plate 12. The top plate 11, the side plate 12 and the bottom plate 14 are connected by welding or flange sealing. The materials of the top plate 11 and the side plate 12 can be stainless steel or copper, and the material of the bottom plate 14 is usually highly thermally conductive copper; a mixture inlet pipe 15 for introducing a mixture of helium-3 and helium-4 is provided on the bottom plate 14 of the distillation chamber. The mixture inlet pipe 15 is made of stainless steel material. In this embodiment, a steam outlet channel 2 for the flow of helium-3 vapor is provided on the top plate 11, and a bottom heater 13 is provided on the bottom plate 14 of the distillation chamber for heating the mixture of helium-3 and helium-4 so that helium-3 evaporates; a precooling device is arranged in the distillation chamber, and one end of it is externally connected with an inlet pipe, and the other end is externally connected with an outlet pipe. The inlet pipe is used to introduce helium-3 vapor. In the present invention, the bottom heater 13 heats the liquid mixture of helium-3 and helium-3 in the distillation chamber, so that helium-3 in the mixture evaporates. At the same time, the precooling device is immersed in the mixture, so that the helium-3 vapor introduced into the precooling device can exchange heat with the mixture to achieve precooling; a superfluid suppression component is arranged in the distillation chamber to suppress the superfluid state of helium-4 in the distillation chamber and prevent the superfluid helium-4 from climbing out of the distillation chamber.

[0026] When liquid helium-4 forms a superfluid at extremely low temperatures (below 2.17 K), it can form a superfluid film on the wall surface. The helium-4 superfluid film will climb along the wall surface. Therefore, only by destroying this superfluid film can the suppression of the superfluid state of helium-4 be achieved. Based on this, one of the structures of the superfluid suppression component in this embodiment is the copper baffle 10. The copper baffle 10 includes a side baffle and a top baffle. The side baffle is fixedly arranged on the bottom plate 14, and the side baffle is located between the bottom heater 13 and the side plate 12. The top baffle is located at the top of the side baffle and extends horizontally away from the side plate 12; there is a gap between the top baffle and the top plate 11, and the vertical projection of the top baffle is located between the vertical projection of the side plate 12 and the vertical projection of the steam outlet channel 2, so that the copper baffle 10 does not hinder the flow of helium-3 steam. As Figure 1 shown, two copper baffles 10 are provided in the distillation chamber in this embodiment. The side baffles of the two copper baffles 10 are arranged in parallel, and the top baffle of the first copper baffle is located above the top baffle of the second copper baffle. The liquid mixture of helium-3 and helium-4 is located inside the second copper baffle, and the gas-liquid interface 16 of the liquid mixture of helium-3 and helium-4 is located below the top baffle. When the superfluid phenomenon of helium-4 occurs, helium-4 will be blocked by the two copper baffles 10, increasing the crawling distance of the helium-4 superfluid film, so that it cannot directly crawl out along the side plate 12 and the top plate 11 of the distillation chamber, thereby suppressing the superfluid phenomenon of helium-4.

[0027] Although the above copper baffle 10 can suppress the superfluid phenomenon of helium-4, on the basis of the above technical solution, in order to further suppress the superfluid problem, the structure of the superfluid suppression component is increased in this embodiment. A circular polished plate 6 is welded to the inner bottom of the top plate 11. The polished plate 6 is arranged around the outside of the steam outlet channel 2. The outer surface of the polished plate 6 is finely processed to achieve extremely low surface roughness, and the crawling of the helium-4 superfluid film is suppressed through the smooth surface. At the same time, a first thin-walled tube 3 and a second thin-walled tube 4 are coaxially arranged outside the steam outlet channel 2. One end of the second thin-walled tube 4 is inserted into the top plate 11, and the other end is connected to the top flange of the steam outlet channel 2. The first thin-walled tube 3 is located between the second thin-walled tube 4 and the steam outlet channel 2; an arc-shaped knife edge 7 extending into the distillation chamber is provided at the bottom of the first thin-walled tube 3. The first thin-walled tube 3 is usually made of stainless steel, and the bottom is processed into an arc-shaped structure with an outwardly turned edge of the knife edge 7. The sharp tip of the knife edge 7 breaks the helium-4 superfluid film, so that the helium-4 superfluid film drips back into the lower mixed liquid again. The second thin-walled tube 4 is usually made of stainless steel and is used to support and connect the steam outlet channel 2 and the top plate 11. The material of the second thin-walled tube 4 is stainless steel with a low thermal conductivity, and at the same time it is processed into a thin wall to reduce the heat conduction leakage from the steam outlet channel 2 to the top plate 11. A porous plug 5 is provided in the steam outlet channel 2, and the porous material of the porous plug 5 suppresses the flow of the helium-4 superfluid film.

[0028] Furthermore, changing the temperature of helium-4 by heating can also destroy its superfluid state. Based on this, in this embodiment, both the steam outlet channel 2 and the top flange of the steam outlet channel 2 are made of copper. A film heater 1 is arranged outside the top flange of the steam outlet channel 2. The film heater 1 is controlled by a controllable precision power supply to achieve precise temperature control heating of the steam outlet channel 2, so as to achieve the effect of heating to break the superfluid film of helium-4. The bottom heater 13 and the film heater 1 are both known structures. For example, electric wire heating can be used, or electromagnetic heating and other methods can also be used. Therefore, they will not be elaborated.

[0029] The pre-cooling device of this embodiment includes a pre-cooling coil 8. The pre-cooling coil 8 is used to pre-cool and liquefy the helium-3 steam in the reflux cycle. The pre-cooling coil 8 is usually made of copper-nickel material. The pre-cooling coil 8 is fixedly arranged in the distillation chamber through a pre-cooling coil support frame 9 and is immersed in the helium-3 and helium-4 mixture. One end of the pre-cooling coil 8 is externally connected with an inlet pipe, and the other end is externally connected with an outlet pipe. The inlet pipe penetrates through the top plate 11, and the outlet pipe penetrates through the bottom plate 14.

[0030] When the present invention works, helium-3 steam enters the pre-cooling coil 8 from the inlet pipe of the top plate 11, is pre-cooled and liquefied in the mixture, and finally flows out from the outlet pipe of the bottom plate 14. The helium-3 and helium-4 mixture coming out of the mixing chamber flows into the cavity of the distillation chamber from the mixture inlet pipe 15, and is heated by the bottom heater 13 in the distillation chamber, so that helium-3 evaporates, and the helium-3 steam evaporates and leaves from the steam outlet channel 2. When helium-4 undergoes superfluidity, the helium-4 superfluid film will first climb along the copper baffle 10, continue to climb along the wall surface of the side plate 12 of the distillation chamber after being inhibited by two layers of copper baffles 10, and then flow through the polished plate 6 to be further inhibited. Part of the helium-4 superfluid film will drip back into the mixture on the polished plate 6. After that, part of the helium-4 superfluid film continues to climb to the tip of the blade 7 of the first thin-walled tube 3 through the second thin-walled tube 4. The damaged part of the superfluid film drips back into the mixture, and part of the helium-4 superfluid film crosses the blade 7 and continues to climb to the steam outlet channel 2, and evaporates after being heated by the film heater 1. Finally, the porous plug 5 arranged at the bottom in the steam outlet channel 2 further inhibits the crawling of the helium-4 superfluid film, thus greatly restricting the outflow of the helium-4 superfluid film from the cryogenic heat exchanger.

[0031] Specific examples are applied in the present invention to elaborate the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. To sum up, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A low-temperature heat exchanger, characterized in that: Comprising: A distillation chamber, at the bottom of which there is a mixture inlet pipe for introducing a mixture of helium-3 and helium-4, at the top of which there is a steam outlet channel for the circulation of helium-3 steam, and at the inner bottom of the distillation chamber there is a bottom heater; A precooling device, which is arranged inside the distillation chamber, and one end of which is externally connected with an inlet pipe and the other end is externally connected with an outlet pipe, and the inlet pipe is used for introducing helium-3 steam; A superfluidity suppression assembly, which is arranged inside the distillation chamber. The distillation chamber includes a bottom plate, on which a side plate is fixedly sealed, and at the top of the side plate there is a top plate. The mixture inlet pipe communicates with the bottom plate, and the bottom heater is fixedly arranged on the bottom plate between the side plate and the mixture inlet pipe. The steam outlet channel penetrates through the top plate; the superfluidity suppression assembly includes a copper baffle, and the copper baffle includes a side baffle and a top baffle. The side baffle is fixedly arranged on the bottom plate, and the side baffle is located between the bottom heater and the side plate. The top baffle is located at the top of the side baffle and horizontally extends towards the end away from the side plate; there is a gap between the top baffle and the top plate, and the vertical projection of the top baffle is located between the vertical projection of the side plate and the vertical projection of the steam outlet channel. The copper baffle can suppress the superfluid state of helium-4.

2. The low-temperature heat exchanger according to claim 1, wherein: There are two copper baffles arranged inside the distillation chamber, and the two copper baffles are respectively a first copper baffle and a second copper baffle. The side baffle of the first copper baffle is arranged in parallel with the side baffle of the second copper baffle, and the top baffle of the first copper baffle is located above the top baffle of the second copper baffle.

3. The low-temperature heat exchanger according to claim 1, wherein: The superfluidity suppression assembly further includes a polishing plate, which is fixedly arranged on the inner bottom of the top plate and is arranged in a ring shape outside the steam outlet channel.

4. The low-temperature heat exchanger according to claim 1, characterized in that: The superfluidity suppression assembly further includes a first thin-walled tube and a second thin-walled tube, which are coaxially arranged with the steam outlet channel and are arranged in a ring shape outside the steam outlet channel. One end of the second thin-walled tube is inserted into the top plate, and the other end is connected to the top flange of the steam outlet channel. The first thin-walled tube is located between the second thin-walled tube and the steam outlet channel; an arc-shaped blade extending to the inside of the distillation chamber is arranged at the bottom of the first thin-walled tube.

5. The low-temperature heat exchanger according to claim 1, wherein: The superfluidity suppression assembly further includes a porous plug, which is fixedly arranged inside the steam outlet channel.

6. The cryogenic heat exchanger according to claim 1, wherein: The superfluidity suppression assembly further includes a film heater, which is located outside the top flange of the steam outlet channel. Both the steam outlet channel and the top flange of the steam outlet channel are made of copper.

7. The low-temperature heat exchanger according to claim 1, characterized in that: The precooling device includes a precooling coil, which is fixedly arranged inside the distillation chamber through a precooling coil support frame. One end of the precooling coil is externally connected with an inlet pipe and the other end is externally connected with an outlet pipe. The inlet pipe penetrates through the top plate, and the outlet pipe penetrates through the bottom plate.

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