Storage tank type cryostat

Abstract

The utility model discloses a storage tank type cryostat. The storage tank type cryostat comprises a cold conduction assembly, a liquid nitrogen storage tank and a gas-liquid pipe, the gas-liquid pipe is positioned at the top of the liquid nitrogen storage tank and is communicated with the liquid nitrogen storage tank; the cold conduction assembly is located at the bottom of the liquid nitrogen storage tank and makes contact with liquid nitrogen in the liquid nitrogen storage tank; and the gas-liquid pipe is used for injecting liquid nitrogen into the liquid nitrogen storage tank and discharging gasified nitrogen. The device is convenient to align with an object, automatic in connection, short in operation time and high in efficiency. Nitrogen is discharged after liquid nitrogen exchanges heat and is completely gasified, the refrigerant phase change process is controllable, and the utilization rate of the liquid nitrogen cooling capacity can be increased.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the technical field of ultralow temperature refrigeration, specifically relates to a storage tank type cryostat. BACKGROUND

[0002] As high-precision microscopic observation equipment, the scanning electron microscope includes a vacuum cavity and a sample table located in the vacuum cavity, and the sample table needs to maintain an extremely low temperature environment to guarantee observation accuracy and stability, which puts special technical requirements on the cryostat. The prior art mainly realizes low-temperature control in two ways: one is to use a liquid helium / liquid nitrogen continuous flow system to cool through latent heat and sensible heat; and the other is to use a compressor refrigeration unit to realize expansion refrigeration.

[0003] However, the continuously flowing liquid nitrogen of the existing cryostat is discharged from the system in an incomplete gasification state, resulting in a cold energy utilization rate of less than 30%, and problems such as uncontrollable refrigerant phase change process and low heat exchange efficiency, which significantly increase experimental costs. UTILITY MODEL CONTENTS

[0004] Therefore, the utility model provides a storage tank type cryostat, so that the liquid nitrogen is discharged after heat exchange and complete gasification, the refrigerant phase change process is controllable, and the utilization rate of the liquid nitrogen cold energy can be improved.

[0005] The utility model is realized through the following technical solutions:

[0006] A storage tank type cryostat comprises a cold conducting assembly, a liquid nitrogen storage tank and a gas-liquid pipe.

[0007] The gas-liquid pipe is located at the top of the liquid nitrogen storage tank and communicates with the liquid nitrogen storage tank.

[0008] The cold conducting assembly is located at the bottom of the liquid nitrogen storage tank and contacts the liquid nitrogen in the liquid nitrogen storage tank.

[0009] The gas-liquid pipe is used to inject liquid nitrogen into the liquid nitrogen storage tank and discharge gasified nitrogen.

[0010] Further, the cryostat further comprises a temperature control rod assembly, a temperature control plug and a temperature control pipe.

[0011] The temperature control pipe is located at the bottom of the liquid nitrogen storage tank, the top end of the temperature control pipe communicates with the liquid nitrogen storage tank, and the bottom end is connected with the cold conducting assembly; one end of the temperature control rod assembly is located outside the liquid nitrogen storage tank, and the other end is arranged to extend into the liquid nitrogen storage tank, and the temperature control plug is connected to the end of the temperature control rod assembly located in the liquid nitrogen storage tank.

[0012] When the temperature control rod assembly is moved outward, the temperature control plug is separated from the temperature control pipe, the liquid nitrogen enters the temperature control pipe and contacts the cold conducting assembly, and heat exchange of the cryostat is realized.

[0013] When the temperature control rod assembly is moved inward, the temperature control plug enters the temperature control tube, discharges part or all of the liquid nitrogen in the temperature control tube, and adjusts the amount of liquid nitrogen in the temperature control tube.

[0014] Further, the temperature control rod assembly further comprises a temperature control rod and a nut;

[0015] The outer wall of the liquid nitrogen storage tank is provided with a sleeve in communication with the liquid nitrogen storage tank, the end of the sleeve is provided with external threads, one end of the temperature control rod extends into the liquid nitrogen storage tank along the sleeve, and the temperature control plug is connected to the end of the temperature control rod extending into the liquid nitrogen storage tank; the other end of the temperature control rod is coaxially connected with the nut, and the temperature control rod can rotate relative to the nut; the nut is threadedly connected with the sleeve, and the length of the temperature control rod extending into the liquid nitrogen storage tank can be adjusted by rotating the nut.

[0016] Further, the sleeve comprises a first segment I, a second segment I and a third segment I connected in sequence, the first segment I and the third segment I are made of stainless steel pipes, and the second segment I is made of a glass steel pipe I, the two ends of the glass steel pipe I are respectively bonded to the first segment I and the third segment I by glue.

[0017] Further, the tank type low-temperature thermostat further comprises a vacuum cover I; the vacuum cover I is sleeved outside the liquid nitrogen storage tank, and a vacuum cavity is formed between the vacuum cover I and the liquid nitrogen storage tank; the glass steel pipe I is located in the cavity.

[0018] Further, the gas-liquid pipe comprises a first segment II, a second segment II and a third segment II connected in sequence, the first segment II and the third segment II are made of stainless steel pipes, and the second segment II is made of a glass steel pipe II, the two ends of the glass steel pipe II are respectively bonded to the first segment II and the third segment II by glue.

[0019] Further, the tank type low-temperature thermostat further comprises a vacuum cover I; the vacuum cover I is sleeved outside the liquid nitrogen storage tank, and a vacuum cavity is formed between the vacuum cover I and the liquid nitrogen storage tank; the glass steel pipe II is located in the cavity.

[0020] Further, a cold guide head is arranged in the cold guide assembly, a circular groove is arranged at the top of the cold guide head, and the circular groove is coaxially arranged with and in contact with the bottom end of the temperature control tube.

[0021] Further, the temperature control tube is divergent from the middle part to the top part, the temperature control plug comprises a converging segment and an equal-diameter segment, the converging segment is converging from top to bottom, and the equal-diameter segment is integrally formed at the bottom of the converging segment.

[0022] Further, the tank type low-temperature thermostat further comprises a vacuum cover I, a flange and a cold shield;

[0023] The vacuum cover I is sleeved outside the liquid nitrogen storage tank, and a cavity is formed between the vacuum cover I and the liquid nitrogen storage tank;

[0024] The top end of the vacuum cover I is in sealing connection with the bottom surface of the flange, and the top of the flange is provided with a vacuum sleeve I and a vacuum sleeve II; the sleeve is in connection with the top of the liquid nitrogen storage tank through the vacuum sleeve I and the cavity in sequence; and the top end of the vacuum sleeve I is in closed connection with the outer wall of the sleeve;

[0025] The gas-liquid pipe is in connection with the top of the liquid nitrogen storage tank through the vacuum sleeve II and the cavity in sequence, and the top end of the vacuum sleeve II is in closed connection with the outer wall of the gas-liquid pipe;

[0026] The cold shield is arranged outside the cold conducting assembly, the top end of the cold shield is in communication with the bottom end of the vacuum cover I, and the other end of the cold shield is in sealing connection with the outer wall of the vacuum cavity.

[0027] Advantages:

[0028] (1) The low-temperature thermostat of the storage tank type provided by the utility model is provided with a liquid nitrogen storage tank, can make liquid nitrogen exchange heat and completely gasify before discharging nitrogen, reduces the consumption of liquid nitrogen fluid, can more fully utilize the cold quantity of liquid nitrogen, and thus reduces the use cost.

[0029] (2) The utility model also includes temperature control rod assembly, temperature control plug and temperature control pipe, can adjust the amount of liquid nitrogen in the temperature control pipe by controlling the plugging of the temperature control rod assembly, realizes the temperature control of the low-temperature thermostat.

[0030] (3) The temperature control rod assembly of the utility model further includes a nut, the length of the temperature control rod inserted into the liquid nitrogen storage tank can be adjusted by screwing the nut, so that the amount of liquid nitrogen in the temperature control pipe is adjusted, and thus accurate and stable temperature control is realized.

[0031] (4) The middle part of the sleeve of the utility model is a glass steel pipe I, and is bonded with the stainless steel pipes at both ends, the connection mode exhibits strong sealing property and excellent heat insulation performance in a low-temperature environment, can effectively prevent the leakage of cold quantity along the sleeve, and thus reduces the boiling phenomenon of liquid nitrogen, and reduces the vibration from the source.

[0032] (5) The liquid nitrogen storage tank of the utility model is located in the vacuum cavity, and the glass steel pipe I is located in the cavity. While preventing the leakage of cold quantity along the sleeve, the liquid nitrogen in the liquid nitrogen storage tank is also prevented from exchanging heat through air, and the leakage of cold quantity is further reduced.

[0033] (6) The middle part of the gas-liquid pipe of the utility model is a glass steel pipe II, and is bonded with the stainless steel pipes at both ends, the connection mode exhibits strong sealing property and excellent heat insulation performance in a low-temperature environment, can effectively prevent the leakage of cold quantity along the gas-liquid pipe, and thus reduces the boiling phenomenon of liquid nitrogen, and reduces the vibration from the source.

[0034] (7) The liquid nitrogen storage tank of the utility model is located in the vacuum cavity, and the glass steel pipe II is located in the cavity, which prevents the leakage of cold energy along the gas-liquid pipe and prevents the liquid nitrogen in the liquid nitrogen storage tank from being exchanged by air, further reducing the leakage of cold energy.

[0035] (8) The top circular groove of the cold guide head is coaxial with and in contact with the bottom end of the temperature control pipe, which can increase the contact area of the liquid nitrogen and the cold guide head, so that the liquid nitrogen and the cold guide head are in full contact, and the heat exchange efficiency is improved.

[0036] (9) The shape of the temperature control pipe and the temperature control plug is convenient for positioning and plugging of the temperature control plug.

[0037] (10) The vacuum cavity, the cold screen and the cavity are in communication and are all in vacuum, effectively preventing air exchange of the low-temperature thermostat and reducing heat leakage. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a structure diagram of the utility model one kind storage tank type low-temperature thermostat;

[0039] Figure 2 is Figure 1 the enlarged view of partial A;

[0040] Wherein, 1-electric connection assembly, 2-temperature control rod assembly, 3-gas-liquid pipe, 4-flange, 5-vacuum cover I, 6-liquid nitrogen storage tank, 7-coupling, 8-temperature control plug, 9-temperature control pipe, 10-cold guide head, 11-cold screen, 12-cold transmission rod, 13-soft connection line, 14-sample table, 15-aviation plug fixed terminal, 16-signal line guide pipe, 17-nut, 18-radial sealing rod, 19-sleeve, 20-vacuum sleeve I, 21-temperature control rod, 22-liquid injection port, 23-vacuum sleeve II, 24-glass steel pipe I, 25-glass steel pipe II. DETAILED DESCRIPTION

[0041] The utility model will be described in detail in combination with the drawings and examples.

[0042] The embodiment provides a kind of storage tank type low-temperature thermostat, referring to attached Figure 1 , comprising: cold guide assembly, liquid nitrogen storage tank 6 and gas-liquid pipe 3;

[0043] Gas-liquid pipe 3 is located at the top of liquid nitrogen storage tank 6, and is communicated with liquid nitrogen storage tank 6;

[0044] Cold guide assembly is located at the bottom of liquid nitrogen storage tank 6, and contacts with the liquid nitrogen in liquid nitrogen storage tank 6;

[0045] Gas-liquid pipe 3 is used to inject liquid nitrogen and discharge gasified nitrogen into liquid nitrogen storage tank 6.

[0046] The storage tank type cryogenic thermostat provided in this embodiment enables liquid nitrogen to exchange heat and be completely vaporized before nitrogen gas is discharged, reducing the consumption of liquid nitrogen fluid and making fuller use of the cooling capacity of liquid nitrogen, thereby reducing the operating cost.

[0047] The storage tank type low temperature thermostat also includes a temperature control rod assembly 2, a temperature control plug 8, and a temperature control tube 9;

[0048] The temperature control tube 9 is located at the bottom of the liquid nitrogen storage tank 6. The top of the temperature control tube 9 is connected to the liquid nitrogen storage tank 6, and the bottom is connected to the cooling component. One end of the temperature control rod assembly 2 is located outside the liquid nitrogen storage tank 6, and the other end extends into the liquid nitrogen storage tank 6. The temperature control plug 8 is connected to the end of the temperature control rod assembly 2 located inside the liquid nitrogen storage tank 6.

[0049] When the temperature control rod assembly 2 is moved outward, the temperature control plug 8 is separated from the temperature control tube 9, and liquid nitrogen enters the temperature control tube 9 and comes into contact with the cooling component to achieve heat exchange in the low-temperature thermostat.

[0050] When the temperature control rod assembly 2 is moved inward, the temperature control plug 8 enters the temperature control tube 9, discharging part or all of the liquid nitrogen in the temperature control tube 9, adjusting the amount of liquid nitrogen in the temperature control tube 9, thereby achieving temperature control.

[0051] Temperature control of the low-temperature thermostat is achieved by controlling the insertion and removal of the temperature control plug 8 by the temperature control rod assembly 2.

[0052] In one embodiment, see Appendix Figure 2 The temperature control rod assembly 2 also includes a temperature control rod 21 and a nut 17;

[0053] A sleeve 19 communicating with the liquid nitrogen storage tank 6 is provided on the outer wall of the liquid nitrogen storage tank 6. The end of the sleeve 19 is provided with an external thread. One end of the temperature control rod 21 extends into the liquid nitrogen storage tank 6 along the sleeve 19. The temperature control plug 8 is connected to the end of the temperature control rod 21 that extends into the liquid nitrogen storage tank 6. The other end of the temperature control rod 21 is coaxially engaged with the nut 17, and the temperature control rod 21 can rotate relative to the nut 17. The nut 17 is threadedly connected to the sleeve 19. By rotating the nut 17, the length of the temperature control rod 21 extending into the liquid nitrogen storage tank 6 can be adjusted, thereby adjusting the amount of liquid nitrogen in the temperature control tube 9, thereby achieving temperature control.

[0054] By setting nut 17, the amount of liquid nitrogen in the temperature control tube 9 can be adjusted by turning nut 17, which facilitates precise and stable temperature control.

[0055] Specifically, the sleeve 19 is set on the top of the liquid nitrogen storage tank 6, the top of the temperature control rod 21 is provided with an annular edge, the nut 17 is provided with a coaxial through hole, and a stepped surface is provided in the through hole. The annular edge of the temperature control rod 21 is located on the stepped surface and abuts against the stepped surface under the action of gravity. The height of the stepped surface can be adjusted by turning the nut 17, thereby adjusting the insertion and removal of the temperature control rod 21.

[0056] In one embodiment, the sleeve 19 includes a first section I, a second section I, and a third section I connected sequentially. The first section I and the third section I are made of stainless steel pipes, and the second section I is made of fiberglass pipe I24. The two ends of the fiberglass pipe I24 are respectively bonded to the first section I and the third section I with adhesive. This connection method exhibits strong sealing performance and excellent thermal insulation performance in low-temperature environments, effectively preventing cold energy from leaking along the sleeve 19, thereby reducing the boiling phenomenon of liquid nitrogen and reducing vibration at the source.

[0057] In one embodiment, the gas-liquid pipe 3 includes a first section II, a second section II, and a third section II connected sequentially. The first section II and the third section II are made of stainless steel pipes, while the second section II is made of fiberglass pipe II25. The two ends of the fiberglass pipe II25 are respectively bonded to the first section II and the third section II with adhesive. This connection method exhibits strong sealing performance and excellent thermal insulation performance in low-temperature environments, effectively preventing the leakage of cold energy along the gas-liquid pipe 3, thereby reducing the boiling phenomenon of liquid nitrogen and reducing vibration at the source.

[0058] In one embodiment, the temperature control tube 9 diffuses from the middle to the top, and the temperature control plug 8 includes a contraction section and an equal diameter section. The contraction section contracts from top to bottom, and the equal diameter section is integrally formed at the bottom of the contraction section. The shape of the temperature control tube 9 and the temperature control plug 8 facilitates the positioning and insertion / removal of the temperature control plug 8.

[0059] In one embodiment, see Appendix Figure 1 and 2 The cooling component is equipped with a temperature control tube 10. The top of the temperature control tube 10 is provided with a circular groove. The circular groove is coaxial with the bottom end of the temperature control tube 9 and is in contact with it. The circular groove can increase the contact area between liquid nitrogen and temperature control tube 10, so that liquid nitrogen can fully contact temperature control tube 10 and improve heat exchange efficiency.

[0060] In one embodiment, the cooling assembly further includes a cooling rod 12 and a flexible connecting wire 13; one end of the cooling rod 12 is connected to the temperature control tube 10, and the other end is connected to one end of the flexible connecting wire 13, the other end of which is connected to the sample stage 14 of the peripheral device. Connecting the cooling rod 12 and the sample stage 14 via the flexible connecting wire 13 prevents vibrations from being transmitted to the sample stage 14 during the vaporization process of liquid nitrogen, thereby ensuring the imaging effect of the electron microscope.

[0061] Specifically, the cooling rod 12 is threaded to the temperature control tube 10, and thermally conductive adhesive is applied to the contact surface between the cooling rod 12 and the temperature control tube 10 to conduct heat and reduce thermal resistance. The cooling rod 12 and the flexible connecting wire 13 are connected by welding, screwing, or snapping, and the flexible connecting wire 13 and the sample stage 14 are connected by welding or screwing.

[0062] In one embodiment, the flexible connector 13 is made by welding multiple strands of oxygen-free copper wire or by pressing and welding multiple layers of oxygen-free copper sheets, and the outer surface of the flexible connector 13 is treated with a mirror coating to enhance its resistance to heat radiation.

[0063] In one embodiment, the storage tank type cryogenic thermostat also includes a vacuum hood I5, a flange 4, and a cold shield 11;

[0064] Vacuum shield I5 is fitted outside liquid nitrogen storage tank 6, and a cavity is formed between vacuum shield I5 and liquid nitrogen storage tank 6;

[0065] The top of vacuum shroud I5 is sealed to the bottom of flange 4. Vacuum sleeve I20 and vacuum sleeve II23 are installed on the top of flange 4. Sleeve 19 passes through vacuum sleeve I20 and the cavity in sequence and is connected to the top of liquid nitrogen storage tank 6. The top of vacuum sleeve I20 is sealed to the outer wall of sleeve 19 (e.g., by welding). Gas-liquid pipe 3 passes through vacuum sleeve II23 and the cavity in sequence and is connected to the top of liquid nitrogen storage tank 6. The top of vacuum sleeve II23 is sealed to the outer wall of gas-liquid pipe 3 (e.g., by welding).

[0066] One end of the cooling rod 12 connected to the flexible connecting wire 13 extends into the vacuum chamber; the cooling screen 11 is sleeved on the outer periphery of the temperature control tube 10 and the cooling rod 12, the top end of the cooling screen 11 is connected to the bottom end of the vacuum cover I5, and the other end of the cooling screen 11 is sealed to the outer wall of the vacuum chamber. The vacuum chamber, the cooling screen 11, and the cavity are connected and all are in a vacuum, which effectively isolates the air heat exchange of the low temperature thermostat and reduces heat leakage.

[0067] Furthermore, both fiberglass tube I24 and fiberglass tube II25 are located inside the cavity.

[0068] In one embodiment, the flange 4 is also provided with an electrical connection assembly 1, including a signal line conduit 16 and a flight plug fixing terminal 15, for the installation and fixing of the electrical connector. The function of the electrical connector is to connect the temperature sensor and heater components used for temperature measurement and control of the cold head.

[0069] In one embodiment, a radial sealing rod 18 is provided between the temperature control rod 21 and the sleeve 19 to prevent liquid nitrogen leakage.

[0070] In one embodiment, the temperature control rod 21 is connected to the temperature control plug 8 via a coupling 7. Specifically, the coupling 7 is threadedly connected to both the temperature control rod 21 and the temperature control plug 8.

[0071] In one embodiment, both the liquid nitrogen storage tank 6 and the vacuum hood are cylindrical, and the liquid nitrogen storage tank 6 and the vacuum hood are arranged concentrically.

[0072] In one embodiment, the temperature control tube 10 and the temperature control tube 9 are welded together, and the temperature control tube 9 and the liquid nitrogen storage tank 6 are welded together.

[0073] Working principle:

[0074] When the thermostat is working, the liquid nitrogen storage tank 6 has an open structure. It is filled with liquid nitrogen through the liquid injection port 22 of the gas-liquid pipe 3. After the liquid nitrogen exchanges heat with the bottom temperature control pipe 10, it cools the sample stage 14 through the connected cooling rod 12 and the flexible connection. The evaporated nitrogen gas is discharged into the atmosphere through the liquid injection port 22.

[0075] In summary, the above are merely preferred embodiments of this utility model and are not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A cryostat of the Dewar type, characterized in that, The application relates to a tank type low-temperature thermostat. The cold conducting assembly, the liquid nitrogen storage tank and the gas-liquid pipe are included. The gas-liquid pipe is located at the top of the liquid nitrogen storage tank and communicates with the liquid nitrogen storage tank. The cold conducting assembly is located at the bottom of the liquid nitrogen storage tank and contacts with the liquid nitrogen in the liquid nitrogen storage tank. The gas-liquid pipe is used for injecting liquid nitrogen into the liquid nitrogen storage tank and discharging the gasified nitrogen.

2. The dewar cryostat of claim 1, wherein, The thermostat further comprises a temperature control rod assembly, a temperature control plug and a temperature control pipe. The temperature control pipe is located at the bottom of the liquid nitrogen storage tank, the top end of the temperature control pipe communicates with the liquid nitrogen storage tank, and the bottom end is connected with the cold conducting assembly. One end of the temperature control rod assembly is located outside the liquid nitrogen storage tank, and the other end is arranged in the liquid nitrogen storage tank. When the temperature control rod assembly is moved outward, the temperature control plug is separated from the temperature control pipe, the liquid nitrogen enters the temperature control pipe and contacts with the cold conducting assembly, and heat exchange of the low-temperature thermostat is realized.

3. The dewar cryostat of claim 2, wherein, When the temperature control rod assembly is moved inward, the temperature control plug enters the temperature control pipe, and part or all of the liquid nitrogen in the temperature control pipe is discharged, so that the amount of the liquid nitrogen in the temperature control pipe is adjusted. The temperature control rod assembly further comprises a temperature control rod and a nut.

4. The dewar cryostat of claim 3, wherein, An outer wall of the liquid nitrogen storage tank is provided with a sleeve communicating with the liquid nitrogen storage tank, the end of the sleeve is provided with an external thread, one end of the temperature control rod is inserted into the liquid nitrogen storage tank along the sleeve, the temperature control plug is connected to the end of the temperature control rod inserted into the liquid nitrogen storage tank, the other end of the temperature control rod is coaxially connected with the nut, and the temperature control rod can rotate relative to the nut; the nut is threadedly connected with the sleeve, and the length of the temperature control rod inserted into the liquid nitrogen storage tank can be adjusted by rotating the nut.

5. The dewar cryostat of claim 4, wherein, The sleeve comprises a first section I, a second section I and a third section I connected in sequence, the first section I and the third section I are made of stainless steel pipes, and the second section I is made of a glass steel pipe I, and the two ends of the glass steel pipe I are respectively bonded with the first section I and the third section I by glue.

6. A cryostat according to any one of claims 1 to 5, wherein The tank type low-temperature thermostat further comprises a vacuum cover I; the vacuum cover I is sleeved outside the liquid nitrogen storage tank, a vacuum cavity is formed between the vacuum cover I and the liquid nitrogen storage tank, and the glass steel pipe I is located in the cavity.

7. The dewar cryostat of claim 6, wherein, The gas-liquid pipe comprises a first section II, a second section II and a third section II connected in sequence, the first section II and the third section II are made of stainless steel pipes, and the second section II is made of a glass steel pipe II, and the two ends of the glass steel pipe II are respectively bonded with the first section II and the third section II by glue.

8. A cryostat according to any one of claims 2 to 5, wherein, The glass steel pipe II is located in the cavity.

9. A cryostat according to any one of claims 2 to 5, wherein, The cold conducting assembly is provided with a cold conducting head, the top of the cold conducting head is provided with a circular groove, and the circular groove is coaxially arranged with and in contact with the bottom end of the temperature control pipe.

10. A cryostat of the Dewar type according to claim 3 or 4, characterised in that, The temperature control pipe is diffused from the middle part to the top part, the temperature control plug comprises a contraction section and an equal-diameter section, the contraction section is contracted from top to bottom, and the equal-diameter section is integrally formed at the bottom of the contraction section. The tank type low-temperature thermostat further comprises a vacuum cover I, a flange and a cold shield. The vacuum cover I is sleeved outside the liquid nitrogen storage tank, and a cavity is formed between the vacuum cover I and the liquid nitrogen storage tank. The top end of the vacuum cover I is sealingly connected with the bottom surface of the flange, the top of the flange is provided with a vacuum sleeve I and a vacuum sleeve II; the sleeve is connected with the top of the liquid nitrogen storage tank in sequence through the vacuum sleeve I and the cavity; and the top end of the vacuum sleeve I is sealingly connected with the outer wall of the sleeve. The gas-liquid pipe is connected with the top of the liquid nitrogen storage tank in sequence through the vacuum sleeve II and the cavity, and the top end of the vacuum sleeve II is sealingly connected with the outer wall of the gas-liquid pipe. The cold shield is sleeved outside the cold conducting assembly, the top end of the cold shield communicates with the bottom end of the vacuum cover I, and the other end of the cold shield is sealingly connected with the outer wall of the vacuum cavity.

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