Low-temperature heat exchanger

Abstract

The invention discloses a low-temperature heat exchanger, and relates to the technical field of dilution refrigerators, the low-temperature heat exchanger comprises a distillation chamber, the bottom of the distillation chamber is provided with a mixture inlet pipe used for introducing a helium-3 and helium-4 mixture, the top of the distillation chamber is provided with a steam outlet channel used for helium-3 steam circulation, and the inner bottom of the distillation chamber is provided with a bottom heater; the pre-cooling device is arranged in the distillation chamber, one end of the pre-cooling device is externally connected with an inlet pipe, the other end of the pre-cooling device is externally connected with an outlet pipe, and helium-3 steam is introduced into the inlet pipe; the superflow suppression assembly is arranged in the distillation chamber, the superflow suppression assembly comprises a copper baffle, and the copper baffle comprises a side baffle and a top baffle and can suppress the superflow state of helium-4. According to the low-temperature heat exchanger provided by the invention, the superflow of helium-4 can be inhibited, and the helium-4 is prevented from climbing out of the low-temperature heat exchanger in a superflow state to cause extra heat leakage.

Description

Technical Field

[0001] The invention relates to the technical field of dilution refrigerators, and in particular to a low-temperature 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 a dilution refrigerator, 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 different saturated vapor pressures of helium-3 and helium-4 at the same temperature, the main vapor evaporated is helium-3 vapor, thereby achieving the separation of helium-3 and helium-4.

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

[0004] The object of the present invention is to provide a low-temperature heat exchanger to solve the problems existing in the above-mentioned prior art, which can suppress the superflow of helium-4 and prevent helium-4 from climbing out of the low-temperature heat exchanger in the superflow state and causing additional heat leakage.

[0005] To achieve the above object, the present invention provides the following solutions: The present invention provides a low-temperature heat exchanger, comprising: A distillation chamber, wherein a mixture inlet pipe for introducing a mixture of helium-3 and helium-4 is provided at the bottom of the distillation chamber, a steam outlet channel for circulating helium-3 steam is provided at the top, and a bottom heater is provided at the inner bottom of the distillation chamber; A precooling device is arranged in the distillation chamber, and one end of the precooling device is connected to an inlet pipe, and the other end of the precooling device is connected to an outlet pipe, and the inlet pipe is used to pass helium-3 vapor; A superflow suppression component is arranged in the distillation chamber, the distillation chamber includes a bottom plate, a side plate is fixedly and sealedly provided on the bottom plate, a top plate is provided on the top of the side plate, the mixture inlet pipe is connected to the bottom plate, and the bottom heater is fixedly provided on the bottom plate between the side plate and the mixture inlet pipe, and the steam outlet channel is penetrated through the top plate; the superflow suppression component includes a copper baffle, the copper baffle includes a side baffle and a top baffle, the side baffle is fixedly provided on the bottom plate, and the side baffle is located between the bottom heater and the side plate, the top baffle is located on the top of the side baffle and extends horizontally away from one end of 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, and the copper baffle can suppress the superflow state of helium-4.

[0006] Preferably, two copper baffles are provided in the distillation chamber, and the two copper baffles are respectively a first copper baffle and a second copper baffle, the side baffles of the first copper baffle are arranged in parallel with the side baffles 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.

[0007] Preferably, the overflow suppression assembly further comprises a polishing plate, wherein the polishing plate is fixedly arranged on the inner bottom of the top plate, and the polishing plate is arranged in a ring on the outer side of the steam outlet channel.

[0008] Preferably, the superflow suppression component also includes a first thin-walled tube and a second thin-walled tube which are coaxially arranged with the steam outlet channel and annularly arranged on 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, and the first thin-walled tube is located between the second thin-walled tube and the steam outlet channel; an arc-shaped knife edge is provided at the bottom of the first thin-walled tube extending to the inside of the distillation chamber.

[0009] Preferably, the superflow suppression component further comprises a porous plug, and the porous plug is fixedly disposed in the steam outlet channel.

[0010] Preferably, the superflow suppression component further comprises a film heater, and the film heater is located outside the top flange of the steam outlet channel, and the steam outlet channel and the top flange of the steam outlet channel are both made of copper.

[0011] Preferably, the precooling device includes a precooling coil, which is fixed in the distillation chamber through a precooling coil support frame, one end of the precooling coil is connected to an inlet pipe, and the other end is connected to an outlet pipe, the inlet pipe is passed through the top plate, and the outlet pipe is passed through the bottom plate.

[0012] Compared with the prior art, the present invention has achieved the following technical effects: The present invention provides a superflow suppression component in the distillation chamber. When a mixture of helium-4 and helium-3 is introduced into the distillation chamber and heated, the superflow of helium-4 can be suppressed on the premise that helium-3 can be evaporated by heat, thereby preventing helium-4 from climbing out of the distillation chamber due to superflow, and reducing the heat leakage problem caused by helium-4 leakage. The precooling device is arranged in the distillation chamber and immersed in the mixture of helium-4 and helium-3, so as to achieve the effect of precooling the helium-3 vapor introduced into the precooling device. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 It is a cross-sectional schematic diagram of one embodiment of the low-temperature heat exchanger of the present invention; In the figure: 1-film heater, 2-steam outlet channel, 3-first thin-walled tube, 4-second thin-walled tube, 5-porous plug, 6-polishing plate, 7-knife edge, 8-precooling coil, 9-precooling 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

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The object of the present invention is to provide a low-temperature heat exchanger to solve the problems existing in the above-mentioned prior art, which can suppress the superflow of helium-4 and prevent helium-4 from climbing out of the low-temperature heat exchanger in the superflow state and causing additional heat leakage.

[0017] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] 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 tens of millikelvin. The dilution refrigerator is used to heat the liquid mixture of helium-3 and helium-4. Based on the physical characteristics of different saturated vapor pressures of helium-3 and helium-4 at the same temperature, the main vapor in the distillation chamber is helium-3 vapor, thereby achieving the separation of helium-3 and helium-4. The liquid phase transition temperature of helium-3 superfluid is 2.6 millikelvin, which is much lower than the superfluid transition temperature of helium-4. At one atmosphere, when the temperature of helium-4 is reduced to 2.17K, helium-4 suddenly changes from the original normal fluid to a "superfluid" with a series of extremely unusual properties. This "superfluid" has almost no viscosity and has a very high thermal conductivity, which can be up to 800 times that of copper at room temperature. Therefore, the helium-4 superfluid liquid will crawl upward along the side walls of the distillation chamber with almost no viscous loss. The helium-4 superfluid crawls out of the low-temperature heat exchanger, which is likely to cause additional heat leakage.

[0019] In order to avoid the above problems, the present invention provides a low temperature heat exchanger, such as Figure 1 As shown, the distillation chamber includes a bottom plate 14, a side plate 12 is fixedly and sealed on the bottom plate 14, a top plate 11 is arranged on the top of the side plate 12, and 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 copper with high thermal conductivity; the bottom plate 14 of the distillation chamber is provided with a mixture inlet pipe 15 for passing a mixture of helium-3 and helium-4, and the mixture inlet pipe 15 is made of stainless steel. In this embodiment, the top plate 11 is provided with a steam outlet channel 2 for the circulation of helium-3 steam, and the bottom plate 14 of the distillation chamber is provided with a bottom heater 13 for heating the mixed liquid of helium-3 and helium-4 to evaporate the helium-3; a precooling device is arranged in the distillation chamber , and one end of it is externally connected to an inlet pipe, and the other end is externally connected to an outlet pipe, the inlet pipe is used to pass helium-3 steam, the present invention heats the helium-3 and helium-3 liquid mixture in the distillation chamber through the bottom heater 13, so that the helium-3 in the mixture evaporates, and at the same time the precooling device is immersed in the mixture, so that the helium-3 steam passed into the precooling device can exchange heat with the mixture to achieve precooling; the superflow suppression component is arranged in the distillation chamber, and is used to suppress the superflow state of helium-4 in the distillation chamber to prevent the helium-4 superflow from climbing out of the distillation chamber.

[0020] When liquid helium-4 forms a superfluid at an extremely low temperature (such as below 2.17 K), it can form a superfluid film on the wall. The helium-4 superfluid film will climb along the wall. Therefore, it is only necessary to destroy the superfluid film to suppress the helium-4 superfluid state. Based on this, one of the structures of the superfluid suppression component of this embodiment is a copper baffle 10. The copper baffle 10 includes a side baffle and a top baffle. The side baffle is fixed 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 on 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 will not hinder the circulation of helium-3 steam. Figure 1 As shown, in this embodiment, two copper baffles 10 are provided in the distillation chamber, 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 on the inner side of 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 helium-4 superfluidizes, helium-4 will be hindered 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 plates 12 and the top plate 11 of the distillation chamber, thereby suppressing the helium-4 superfluid phenomenon.

[0021] Although the copper baffle 10 can suppress the helium-4 superfluid phenomenon, based on the above technical solution, in order to further suppress the superfluid problem, the present embodiment adds a structure of a superfluid suppression component. An annular polishing plate 6 is welded on the bottom of the top plate 11. The polishing plate 6 is arranged on the outside of the steam outlet channel 2. The outer surface of the polishing plate 6 is finely processed to achieve an extremely low surface roughness, and the creeping of the helium-4 superfluid film is suppressed by the smooth surface. At the same time, a first thin-walled tube 3 and a second thin-walled tube 4 are coaxially arranged on the outside of the steam outlet channel 2. One end of the second thin-walled tube 4 is inserted on 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 blade 7 extending to the inside of 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 a blade 7 with an arc-shaped structure with an outward warped edge. The helium-4 superfluid film is broken by the sharp tip of the blade 7, so that the helium-4 superfluid film drips back into the mixed liquid below. The second thin-walled tube 4 is usually made of stainless steel and is used to support the connection between the steam outlet channel 2 and the top plate 11. The second thin-walled tube 4 is made of stainless steel with low thermal conductivity and is processed into a thin wall to reduce heat conduction and heat 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 flow of the helium-4 superfluid film is suppressed by the porous material of the porous plug 5.

[0022] Furthermore, the superfluid state of helium-4 can also be destroyed by changing the temperature of the helium-4 by heating. Based on this, in this embodiment, the steam outlet channel 2 and the top flange of the steam outlet channel 2 are both made of copper material, and 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 and heating of the steam outlet channel 2, so as to achieve the effect of heating and breaking the helium-4 superfluid film. The bottom heater 13 and the film heater 1 are both known structures, and for example, electric heating wire heating or electromagnetic heating can be used, so they are not described in detail.

[0023] The precooling device of this embodiment includes a precooling coil 8, which is used to precool and liquefy the reflux circulating helium-3 vapor. The precooling coil 8 is usually made of copper-nickel material. The precooling coil 8 is fixed in the distillation chamber through a precooling coil support frame 9 and immersed in the helium-3 and helium-4 mixed liquid. One end of the precooling coil 8 is externally connected to an inlet pipe, and the other end is externally connected to an outlet pipe. The inlet pipe is penetrated on the top plate 11, and the outlet pipe is penetrated on the bottom plate 14.

[0024] When the present invention is working, the helium-3 vapor passes through the inlet pipe of the top plate 11 into the precooling coil 8, is precooled and liquefied in the mixed liquid, and finally flows out from the outlet pipe of the bottom plate 14. The mixed liquid of helium-3 and helium-4 coming out of the mixing chamber flows into the cavity of the distillation chamber from the mixture inlet pipe 15, is heated by the bottom heater 13 in the distillation chamber, so that the helium-3 evaporates, and the helium-3 vapor evaporates and leaves from the steam outlet channel 2. When helium-4 superfluid occurs, the helium-4 superfluid film will first climb along the copper baffle 10, and after being suppressed by two layers of copper baffles 10, it will continue to climb along the wall of the side plate 12 of the distillation chamber, and then flow through the polishing plate 6 to be further suppressed. Part of the helium-4 superfluid film will drip back into the mixed liquid on the polishing plate 6, and then part of the helium-4 superfluid film will continue to climb to the tip of the knife edge 7 of the first thin-walled tube 3 through the second thin-walled tube 4. The damaged part of the superfluid film will drip back into the mixed liquid, and part of the helium-4 superfluid film will continue to climb over the knife edge 7 to the steam outlet channel 2, and evaporate after being heated by the film heater 1. Finally, the porous plug 5 arranged at the bottom of the steam outlet channel 2 further suppresses the crawling of the helium-4 superfluid film, thereby greatly limiting the outflow of the helium-4 superfluid film from the low-temperature heat exchanger.

[0025] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A low temperature heat exchanger, characterized in that: include: A distillation chamber, wherein a mixture inlet pipe for introducing a mixture of helium-3 and helium-4 is provided at the bottom of the distillation chamber, a steam outlet channel for circulating helium-3 steam is provided at the top, and a bottom heater is provided at the inner bottom of the distillation chamber; A precooling device is arranged in the distillation chamber, and one end of the precooling device is connected to an inlet pipe, and the other end of the precooling device is connected to an outlet pipe, and the inlet pipe is used to pass helium-3 vapor; A superflow suppression component is arranged in the distillation chamber, the distillation chamber includes a bottom plate, a side plate is fixedly and sealedly provided on the bottom plate, a top plate is provided on the top of the side plate, the mixture inlet pipe is connected to the bottom plate, and the bottom heater is fixedly provided on the bottom plate between the side plate and the mixture inlet pipe, and the steam outlet channel is penetrated through the top plate; the superflow suppression component includes a copper baffle, the copper baffle includes a side baffle and a top baffle, the side baffle is fixedly provided on the bottom plate, and the side baffle is located between the bottom heater and the side plate, the top baffle is located on the top of the side baffle and extends horizontally away from one end of 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, and the copper baffle can suppress the superflow state of helium-4.

2. The low-temperature heat exchanger according to claim 1, characterized in that: Two copper baffles are arranged in the distillation chamber, and the two copper baffles are respectively a first copper baffle and a second copper baffle. The side baffles of the first copper baffle are arranged in parallel with the side baffles 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, characterized in that: The overflow suppression component also includes a polishing plate, which is fixed to the inner bottom of the top plate and is annularly arranged on the outer side of the steam outlet channel.

4. The low-temperature heat exchanger according to claim 1, characterized in that: The superflow suppression component also includes a first thin-walled tube and a second thin-walled tube which are coaxially arranged with the steam outlet channel and are annularly arranged on 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, and the first thin-walled tube is located between the second thin-walled tube and the steam outlet channel; an arc-shaped knife edge is provided at the bottom of the first thin-walled tube, extending to the interior of the distillation chamber.

5. The low temperature heat exchanger according to claim 1, characterized in that: The superflow suppression component further includes a porous plug, which is fixed in the steam outlet channel.

6. The low-temperature heat exchanger according to claim 1, characterized in that: The superflow suppression component further includes a film heater, which is located outside the top flange of the steam outlet channel. The steam outlet channel and the top flange of the steam outlet channel are both 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 fixed in the distillation chamber through a precooling coil support frame. One end of the precooling coil is connected to an inlet pipe, and the other end is connected to an outlet pipe. The inlet pipe is passed through the top plate, and the outlet pipe is passed through the bottom plate.

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