CN116344150A

CN116344150A - Cooling system, superconducting magnet system and cooling method

Info

Publication number: CN116344150A
Application number: CN202310343349.4A
Authority: CN
Inventors: 吕秉坤; 王维; 信纪军; 梁磐仪; 方志春; 王春栋; 赵婉吟; 李来风
Original assignee: Songshan Lake Materials Laboratory
Current assignee: Songshan Lake Materials Laboratory
Priority date: 2023-04-03
Filing date: 2023-04-03
Publication date: 2023-06-27

Abstract

The invention belongs to the technical field of superconducting magnets, and particularly discloses a cooling system, a superconducting magnet system and a cooling method. The cooling system comprises a vacuum cover, a refrigerator, a thermal switch and a temperature control device, wherein the refrigerator is provided with a first-stage cold head and a second-stage cold head, the cooled load, the first-stage cold head and the second-stage cold head are all positioned in the vacuum cover, the thermal switch comprises a first low-temperature pulsating heat pipe, a condensation section of the first low-temperature pulsating heat pipe is thermally connected with the first-stage cold head, an evaporation section of the first low-temperature pulsating heat pipe is connected with the cooled load, a heat conduction piece is connected between the second-stage cold head and the cooled load, the final refrigeration temperature of the first-stage cold head is lower than the three-phase temperature of a working medium in the first low-temperature pulsating heat, and the temperature control device is used for controlling the preset working temperatures of the first-stage cold head and the second-stage cold head. The invention can improve the cooling efficiency of the cooled load, reduce the harm caused by the overhigh temperature rise in the working process of the cooled load, and improve the operation safety and reliability of the cooling system and the superconducting magnet system.

Description

Cooling system, superconducting magnet system and cooling method

Technical Field

The invention relates to the technical field of superconducting magnets, in particular to a cooling system, a superconducting magnet system and a cooling method.

Background

The wide application of superconductivity is always indistinguishable from low temperature density, the superconductivity can be realized only by cooling a magnet below the superconductivity transition temperature, and once the superconductivity transition temperature is exceeded, huge joule heat generated by quench can burn out a superconducting wire and even cause explosion accidents. The most widely used superconducting magnet at present is a low-temperature superconducting magnet, the superconducting transition temperature of which is very low, for example, nbTi has a superconducting transition temperature of 9.6K, nb ₃ The superconducting transition temperature of Sn is 18.1K, and even a liquid nitrogen temperature zone superconducting magnet called a high temperature superconducting magnet needs to have a superconducting transition temperature of approximately 77K. Therefore, ensuring that superconducting magnets operate stably in a low temperature environment is critical to the application of superconducting technology.

With the development of the technology of a small refrigerator, the application of a superconducting magnet system directly cooled by the refrigerator is more and more extensive, and compared with the traditional low-temperature liquid soaking method, the superconducting magnet system has the advantages of no liquid helium consumption, low cost, small volume, compact structure, easiness in use and maintenance and the like. The typical chiller cooling system includes a chilled load, a radiation protection cold screen, a chiller, a vacuum vessel and other accessories, the radiation protection cold screen is connected to a primary chiller of the chiller, and the chilled load is connected to a secondary chiller. When the cooling system is running, the secondary cold head of the refrigerator reaches the lowest temperature of the closed circulation refrigerator.

Because the primary cold head has a much higher cooling power than the secondary cold head, the temperature of the primary cold head will soon approach the final temperature, and when the heat capacity of the load being cooled is large, the secondary cold head may take a longer time to cool the load to the lowest temperature. In order to shorten the time for cooling the cooled load to the lowest temperature, a low-temperature heat switch can be arranged between a first-stage cold head of the refrigerator and the cooled load, and in the on state, the low-temperature heat switch is used as a high-efficiency heat conduction piece, a large amount of cold energy of the first-stage cold head is used for precooling the cooled load, and after the lowest temperature of the first-stage cold head is reached, the low-temperature heat switch is required to be interrupted, and the second-stage cold head can continue to cool the cooled load to a lower temperature.

Low temperature thermal switches typically include mechanical contact thermal switches, superconducting thermal switches, air gap thermal switches, magnetoresistive thermal switches, and the like. The mechanical contact type thermal switch realizes the switching of the state of the thermal switch by utilizing the contact or disconnection of the movable surface, has the advantages of unrestricted working temperature area and complete disconnection, but has the advantages that the thermal conduction is difficult to be higher due to pressure limitation, and an additional driving structure is required to be arranged to drive the thermal switch to move, so that the design difficulty is higher and the occupied space is larger; the principle of the superconducting thermal switch is that the thermal switch is switched by utilizing the difference of the thermal conductivity of superconducting materials in a normal state and a superconducting state, the thermal conductivity coefficient is higher when the thermal switch is conducted, but the thermal switch is only suitable for a temperature region below 0.5K, a magnetic field acting on the superconducting thermal switch needs to be additionally applied, so that the complexity of a system and the cost of the system are increased, meanwhile, the magneto-thermal effect when the magnetic field is applied to the thermal switch also generates heat, and heat leakage exists when the thermal switch is disconnected; the working principle of the air gap type thermal switch is that an adsorbent is placed on one side with lower temperature, when the temperature of the side is lower, the adsorbent adsorbs gas, so that the air pressure of a blade gap is lower, the thermal switch is in an off state, as the temperature of the side is increased, the adsorbent is desorbed, the gas enters the gap, and the thermal switch is in an on state, so that the thermal switch can be driven passively, but the requirement on the preset working temperature range is higher, precise manufacturing is needed, and the cost is higher; the reluctance type thermal switch principle is that the reluctance effect of certain metals is utilized, when a magnetic field is applied, the action of Lorentz force is applied, the movement of heat-carrying electrons is restrained, the heat conductivity of the material can be reduced to the level of heat conduction only by phonons, so that the switch is larger, but the reluctance type thermal switch is only limited to extremely low-temperature application, a large magnetic field and a corresponding electromagnet are needed, the cost is higher, the occupied space is larger, meanwhile, the reluctance material is too fragile and easy to damage, and the processing and maintenance cost is increased.

Disclosure of Invention

An object of the present invention is to provide a cooling system capable of improving the cooling efficiency of a load to be cooled, reducing the occupied space and the installation cost of a thermal switch while increasing the on-off ratio and the thermal conductivity at the time of conduction, and improving the structural compactness, the operation safety and the operation stability of the cooling system.

Another object of the present invention is to provide a superconducting magnet system capable of improving the structural compactness of the superconducting magnet system and improving the operation efficiency, operation safety and operation reliability of the superconducting magnet system.

It is still another object of the present invention to provide a cooling method capable of improving the cooling efficiency of a cooled load, reducing the cooling time, and improving the operation safety and the operation efficiency of the cooled load.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

the utility model provides a cooling system for cool off by the cooling load, cooling system includes vacuum hood, refrigerator, thermal switch and temperature control device, the refrigerator has one-level cold head and second grade cold head, by the cooling load one-level cold head and second grade cold head all are located in the vacuum hood, the thermal switch includes first low temperature pulsation heat pipe, the condensation segment of first low temperature pulsation heat pipe with one-level cold head is connected thermally, the evaporation segment of first low temperature pulsation heat pipe with by the cooling load connection, second grade cold head with be connected with the heat conduction spare between the cooling load, the final refrigeration temperature of one-level cold head is less than the interior worker's of first low temperature pulsation heat pipe triple temperature, temperature control device is used for controlling the one-level cold head with the refrigeration temperature of second grade cold head.

As an alternative technical scheme of a cooling system, the thermal switch comprises an evaporating plate and a condensing plate, wherein the condensing section of the first low-temperature pulsating heat pipe is fixed on the condensing plate, the evaporating plate and the condensing plate are made of heat conducting metal, the evaporating section of the first low-temperature pulsating heat pipe is fixed on the evaporating plate, the condensing plate is connected with the primary cold head, and the evaporating plate is connected with a cooled load.

As an alternative technical scheme of the cooling system, the thermal switch comprises at least two first low-temperature pulsating heat pipes, and the evaporating plate and the condensing plate are arranged in one-to-one correspondence with the first low-temperature pulsating heat pipes;

all the condensation plates are arranged in a laminated mode and fixedly connected, and one condensation plate positioned on the outer side is connected with the primary cold head;

all the evaporation plates are divided into at least two groups which are arranged separately, each group of evaporation plates comprises at least one evaporation plate or a plurality of evaporation plates which are stacked and fixedly arranged, and one evaporation plate positioned at the outer side of each group of evaporation plates is connected with the cooled load.

As an alternative technical scheme of the cooling system, the cooling system further comprises a primary radiation protection screen, the primary radiation protection screen is suspended in the vacuum cover, the cooled load is suspended in the primary radiation protection screen, and the primary cold head is thermally connected with the primary radiation protection screen.

As an alternative technical scheme of the cooling system, the cooling system further comprises a secondary radiation protection screen, the secondary radiation protection screen is suspended in the primary radiation protection screen, the cooled load is suspended in the secondary radiation protection screen, and the secondary cold head is in thermal connection with the secondary radiation protection screen.

As an alternative technical scheme of the cooling system, the heat conduction piece comprises a second low-temperature pulsating heat pipe, an evaporation section of the second low-temperature pulsating heat pipe is connected with the cooled load, a condensation section of the second low-temperature pulsating heat pipe is thermally connected with the second-stage cold head, and the final refrigeration temperature of the second-stage cold head is between the three-phase point temperature and the critical point temperature of the working medium in the second low-temperature pulsating heat pipe.

As an alternative technical scheme of the cooling system, the working medium in the first low-temperature pulsating heat pipe is argon, nitrogen, oxygen or methane;

and working media in the second low-temperature pulsating heat pipe are helium, hydrogen or neon.

As an alternative technical scheme of the cooling system, the refrigerator is provided with at least two heat switches and heat conduction pieces, and the heat switches and the heat conduction pieces are arranged in one-to-one correspondence with the refrigerator.

As an alternative solution of a cooling system, the outer surfaces of the primary cold head, the secondary cold head, the thermal switch, the cooled load and/or the heat conducting member are coated with a plurality of layers of insulating materials;

And/or the thermal switch is provided with a first connecting surface and a second connecting surface, the first connecting surface is in thermal connection with the primary cold head, the second connecting surface is in thermal connection with the cooled load, and the first connecting surface and/or the second connecting surface are/is provided with a heat conducting coating and/or a heat conducting sheet.

A superconducting magnet system comprising a superconducting magnet, and further comprising a cooling system as described above, the superconducting magnet being the cooled load.

A cooling method applied to the above cooling system, the cooling method comprising:

vacuumizing the inside of the vacuum cover until the vacuum value is smaller than a preset vacuum value;

starting the refrigerator;

when the temperature of the primary cold head reaches the gas-liquid two-phase flow temperature zone of the first low-temperature pulsating heat pipe, controlling the temperature of the primary cold head to be kept to the gas-liquid two-phase flow temperature zone so as to enable the thermal switch to be in a conducting state;

and when the temperature of the cooled load is lower than the three-phase temperature of the thermal switch, stopping controlling the temperature of the primary cold head so as to enable the temperature of the primary cold head to be reduced to the three-phase temperature of the working medium in the first low-temperature pulsating heat pipe, and enabling the thermal switch to be disconnected.

As an alternative to the cooling method, the cooling method further includes:

and in the running process of the cooled load, when the temperature of the cooled load is increased to the gas-liquid two-phase flow temperature zone of the first low-temperature pulsating heat pipe, regulating and controlling the temperature of the primary cold head to the gas-liquid two-phase flow temperature zone so as to enable the thermal switch to be converted from an off state to an on state.

The invention has the beneficial effects that:

according to the cooling system provided by the invention, the thermal switch comprises the first low-temperature pulsating heat pipe, so that the cooling capacity of the primary cold head of the refrigerator can be effectively utilized, the cooled load is accelerated to be cooled to the preset working temperature, the efficiency of the cooling system is improved, the time for recovering the cooled load from the temperature rise state to the normal working state can be shortened, and the running safety and reliability of the cooling system are improved; meanwhile, when the first low-temperature pulsating heat pipe is conducted, the heat conductivity coefficient is higher than that of heat conducting metal by several orders of magnitude, the heat transfer efficiency is high, the cooling efficiency of a cooled load and the recovery efficiency of the cooled load can be effectively improved, meanwhile, the switch is relatively large, the heat insulation performance of the heat switch when the heat switch is disconnected can be effectively ensured, and the use reliability of a cooling system is ensured; moreover, as the thermal switch can be automatically disconnected and connected according to temperature change, mechanical and electromagnetic driving is not needed, the control difficulty is reduced, the control precision is improved, the use reliability of the thermal switch is ensured, the structural complexity and the space occupation rate of the thermal switch are reduced, and the cost of a cooling system is reduced; furthermore, the first low-temperature pulsating heat pipe is small in size, light in weight and long in heat transfer distance, and can be arranged in a bending mode, so that the first low-temperature pulsating heat pipe can be easily integrated into a structure with strict quality and space limitation, and the structural compactness of a cooling system is improved.

According to the superconducting magnet system provided by the invention, by adopting the cooling system, the time for precooling the superconducting magnet to the preset working temperature can be reduced, the running efficiency of the superconducting magnet system is improved, the time for returning to the superconducting state when the superconducting magnet is in a failure overtime state is shortened, and the running safety and reliability of the superconducting magnet system are improved; meanwhile, as the thermal switch occupies smaller space, the arrangement is flexible, and the structural compactness of the superconducting magnet system can be effectively improved.

The cooling method provided by the invention can improve the cooling efficiency of the cooled load, thereby improving the working efficiency of the cooled load and improving the operation safety and reliability of the cooled load.

Drawings

Fig. 1 is a schematic view of a superconducting magnet system according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a pulsating heat pipe according to a first embodiment of the present invention;

FIG. 3 is a schematic illustration of a fluid-filled system according to a second embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a thermal switch according to a third embodiment of the present invention;

FIG. 5 is a top view of the structure of FIG. 4;

FIG. 6 is a side view of the structure of FIG. 4;

FIG. 7 is a schematic diagram of a thermal switch according to a fourth embodiment of the present invention;

Fig. 8 is a schematic structural view of a superconducting magnet system provided in a fifth embodiment of the present invention;

fig. 9 is a schematic structural view of a superconducting magnet system provided in a sixth embodiment of the present invention;

fig. 10 is a schematic structural view of a superconducting magnet provided in a seventh embodiment of the present invention.

The figures are labeled as follows:

1. a vacuum cover; 11. an outer cylinder; 12. a flange plate; 2. a primary radiation shield; 3. a refrigerating machine; 31. a primary cold head; 32. a second-stage cold head; 4. a thermal switch; 41. a first low temperature pulsating heat pipe; 411. a parallel tube portion; 412. a bending part; 413. a joint pipe section; 42. a condensing plate; 421. a first positioning groove; 43. an evaporation plate; 431. a second positioning groove; 44. a liquid injection joint; 5. a heat conductive member; 6. a power supply assembly; 61. a superconducting wire; 62. high temperature superconductive current lead; 63. an internal current wiring assembly; 64. an external current wiring assembly; 65. a superconducting excitation power supply; 7. a first support structure; 8. a second support structure; 9. a secondary radiation shield; 10. a cooled load; 101. a room temperature hole; 20. a liquid charging system; 201. a buffer tank; 202. a gas cylinder; 203. a molecular pump unit; 204. a first stop valve; 205. a second shut-off valve; 206. a third stop valve; 207. a first pressure sensor; 208. a second pressure sensor; 209. a filling pipe;

100a, an evaporation section; 100b, a condensation section; 100c, an insulation section; 100d, air plug; 100e, liquid plug.

Detailed Description

The invention is described in further detail below with reference to the drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting thereof. It should be further noted that, for convenience of description, only some, but not all of the structures related to the present invention are shown in the drawings.

In the description of the present invention, unless explicitly stated and limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly under and obliquely below the second feature, or simply means that the first feature is less level than the second feature.

In the description of the present embodiment, the terms "upper", "lower", "right", etc. orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are merely for convenience of description and simplicity of operation, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the invention. Furthermore, the terms "first," "second," and the like, are used merely for distinguishing between descriptions and not for distinguishing between them.

Example 1

As shown in fig. 1, the present embodiment provides a cooling system that can cool a cooled load 10 to a preset operating temperature, so that the cooled load 10 is kept operating in a low-temperature environment, ensuring the operational safety and reliability of the cooled load 10. Wherein the load 10 to be cooled may be a superconducting magnet or other device having a relatively high specific heat capacity and requiring operation in a cryogenic environment.

Specifically, the cooling system comprises a vacuum cover 1, a refrigerator 3, a thermal switch 4 and a temperature control device. The refrigerator 3 is provided with a first-stage cold head 31 and a second-stage cold head 32, the cooled load 10, the first-stage cold head 31 and the second-stage cold head 32 are all positioned in the vacuum cover 1, the thermal switch 4 comprises a first low-temperature pulsating heat pipe 41, a condensation section of the first low-temperature pulsating heat pipe 41 is thermally connected with the first-stage cold head 31, an evaporation section of the first low-temperature pulsating heat pipe 41 is connected with the cooled load 10, a heat conduction piece 5 is connected between the second-stage cold head 32 and the cooled load 10, the three-phase temperature of a working medium (hereinafter referred to as a first working medium) in the first low-temperature pulsating heat pipe 41 is higher than the final refrigeration temperature of the first-stage cold head 31, and the temperature control device is used for controlling the refrigeration temperature of the first-stage cold head 31 and the second-stage cold head 32. The final cooling temperature is a temperature that the primary cooling head 31 can reach when the temperature of the secondary cooling head 32 drops to the target cooling temperature.

In the cooling system provided in this embodiment, when the refrigerator 3 does not work, the working medium in the first low-temperature pulsating heat pipe 41 is in a gaseous state, and at this time, the thermal resistance of the thermal switch 4 is larger, and the thermal switch 4 is in an off state; in the cooling process of the cooling system, the temperature of the primary cold head 31 is firstly reduced to be lower than the critical temperature of the first low-temperature pulsating heat pipe 41, the working medium of the condensing section of the first low-temperature pulsating heat pipe 41 is condensed into a liquid state, the first low-temperature pulsating heat pipe 41 is in a partial gas-liquid two-phase flow state, the effective heat conductivity coefficient is higher, the thermal switch 4 is in a conducting state, the cold quantity of the primary cold head 31 is transmitted to the cooled load 10, the cooled load 10 is accelerated to cool down, the time required by the cooled load 10 to be cooled to the preset working temperature is shortened, and the running efficiency of the cooling system is improved; after the cooled load 10 is cooled to be lower than the three-phase temperature, the temperature of the condensation section of the first low-temperature pulsating heat pipe 41 is reduced to be lower than the three-phase temperature along with the first-stage cold head 31, the working medium in the first low-temperature pulsating heat pipe 41 is condensed into a solid state, the flow is stopped, the thermal resistance is increased, the thermal switch 4 is in an off state, the cooled load 10 is mainly in heat conduction with the second-stage cold head 32 through the heat conduction piece 5, the temperature of the cooled load 10 is reduced along with the reduction of the temperature of the second-stage cold head 32, and finally the cooled load 10 is cooled to a preset working temperature.

Meanwhile, in the operation process of the cooled load 10, if the temperature of the cooled load 10 rises to be higher than the three-phase temperature of the first low-temperature pulsating heat pipe 41, the working medium in the evaporation section of the first low-temperature pulsating heat pipe 41 is converted from a solid state to a gas-liquid two-phase flow state, the temperature of the first-stage cold head 31 is controlled, so that the first working medium in the condensation section of the first low-temperature pulsating heat pipe 41 is also in the gas-liquid two-phase flow state, namely the heat switch 4 is conducted, the heat of the cooled load 10 is quickly transferred to the first-stage cold head 31 through the heat switch 4, the heat conduction between the heat switch 4 and the heat conduction piece 5 is realized, the heat transfer efficiency is improved, the temperature rise of the cooled load 10 is avoided to be larger, the return of the cooled load 10 from the temperature rise state to the normal working state is effectively promoted, and the return time of the cooled load 10 to the normal working state is shortened.

Namely, by enabling the thermal switch 4 to comprise the first low-temperature pulsating heat pipe 41, the cooling capacity of the first-stage cold head 31 of the refrigerator 3 can be effectively utilized, the cooled load 10 is quickened to be cooled to the preset working temperature, the efficiency of the cooling system is improved, the time for the cooled load 10 to return to the normal working state from the temperature rise state can be shortened, and the running safety and reliability of the cooling system are improved; meanwhile, when the first low-temperature pulsating heat pipe 41 is conducted, the heat conductivity coefficient is higher than that of heat conducting metal by several orders of magnitude, the heat transfer efficiency is high, the cooling efficiency of the cooled load 10 can be effectively improved, meanwhile, the switch is relatively large (can reach more than 2500), the heat insulation performance of the heat switch 4 when the heat switch is disconnected can be effectively ensured, and the use reliability of a cooling system is ensured; moreover, as the thermal switch 4 can be automatically disconnected and connected according to temperature change, mechanical and electromagnetic driving is not needed, the control difficulty is reduced, the control precision is improved, the use reliability of the thermal switch 4 is ensured, meanwhile, the structural complexity and the space occupation rate of the thermal switch 4 are reduced, and the cost of a cooling system is reduced; furthermore, the first low-temperature pulsating heat pipe 41 is small in size, light in weight and long in heat transfer distance, and can be arranged in a bending manner, so that the first low-temperature pulsating heat pipe 41 can be easily integrated into a structure with strict quality and space limitation, and the structural compactness of the cooling system is improved.

As shown in FIG. 2, it is worth noting that the pulsating heat pipe is a passive heat transfer device, which is a serpentine tubular structure formed by repeatedly bending a metal capillary tube with a smaller inner diameter, typically 0.5-3 mm, between a hot end and a cold end, and the tube is filled with two-phase fluid. Because the pipe diameter is small enough, capillary action is dominant, and surface tension enables working medium to form air plugs 100d and liquid plugs 100e which are distributed in random and alternating mode in the capillary.

Pulsating heat pipes generally include a condensing section 100b, an evaporating section 100a, and an insulating section 100c between condensing section 100b and evaporating section 100 a. In the running process of the pulsating heat pipe, a heat load is applied to the evaporation section 100a, working medium positioned in the evaporation section 100a absorbs heat, and evaporates in the liquid or on the surface of the liquid film to generate new bubbles or increase the volume of the original bubbles, so that the length of the air lock 100d is increased, and the pressure in the evaporation section 100a is increased; meanwhile, a cold load is applied to the condensation section 100b, and the gaseous working medium in the condensation section 100b is liquefied and released into a liquid working medium, so that bubbles in the condensation section 100b are reduced or disappear, and the pressure in the condensation section 100b is reduced. That is, the pressure difference between the evaporation section 100a and the condensation section 100b of the pulsating heat pipe, which is generated by the temperature difference, pushes the working medium from the evaporation section 100a to the condensation section 100b, and the growth and the rupture of bubbles cause the pressure difference between the evaporation section 100a and the condensation section 100b and the pressure imbalance between the adjacent pipes, so that the working medium is pushed to perform pulsating movement or guide the circulating flow in the pipes, and the sensible heat transfer heat is generated when the working medium flows through the latent heat of the gas-liquid phase change and the liquid plug 100e. That is, the oscillating fluid flow and heat transfer in the pulsating heat pipe are driven entirely by transient pressure differences caused by local evaporation and condensation, mechanical power output is not needed, and moving parts are not needed, so that the pulsating heat pipe has higher reliability. Meanwhile, compared with other heat pipes, the pulsating heat pipe has the advantages that the gas phase and the liquid phase of the pulsating heat pipe flow in the same direction generally, the problem that the gas hinders the liquid backflow does not exist, the forced convection heat transfer between the working medium and the pipe wall is very obvious besides the phase change heat transfer, and the pulsating heat pipe has stronger heat transfer capability.

The working medium in the pulsating heat pipe is a working medium with high heat conductivity, and the low-temperature pulsating heat pipe is a pulsating heat pipe with lower critical temperature of the working medium in the pipe. In this embodiment, the first working medium is preferably nitrogen, which has low cost, and the gas-liquid saturation temperature under normal pressure is about 77K, so that the temperature of the primary cold head 31 can be easily controlled to the saturation temperature of liquid nitrogen in the cooling process. In other embodiments, the first working medium may be selected as an argon, oxygen, methane or other low-temperature pulsating heat pipe working medium according to the preset operating temperature of the load to be cooled 10 and the final cooling temperature that the primary cold head 31 can reach.

In this embodiment, the condensation section may be directly connected to the primary cold head 31, and/or the evaporation section may be directly connected to the cooled load 10, or the condensation section and/or the evaporation section may be fixed on a metal plate with high heat conductivity, and then the metal plate is connected to the corresponding primary cold head 31 or the cooled load 10.

It is to be understood that, in the present embodiment, the heat insulation section, the evaporation section and/or the condensation section of the first low temperature pulsating heat pipe 41 may be vertically arranged or bent, so as to be suitable for the connection of the first low temperature pulsating heat pipe 41 to the primary cold head 31 and the cooled load 10, which is not particularly limited in the present invention.

The thermal switch 4 has a first connection surface thermally connected to the primary cold head 31 and a second connection surface thermally connected to the cooled load 10, and the first connection surface and/or the second connection surface are provided with a heat conductive structure including a heat conductive coating and/or a heat conductive sheet to increase the thermal conductivity at the connection and reduce the contact thermal resistance for improving the heat conduction efficiency. Preferably, the heat conducting layer is an apizon N high heat conducting grease layer, and the heat conducting sheet is an indium sheet.

As shown in fig. 1, refrigerator 3 is preferably a GM refrigerator or a pulse tube refrigerator, and exemplary, primary cold head 31 provides about 35W of cold at 50K and secondary cold head 32 typically provides about 1.5W of cold at 4.2K. It will be appreciated that the final refrigeration temperature that can be reached by the primary cold head 31 and the target refrigeration temperature that can be reached by the secondary cold head 32 of the refrigerator 3 can be specifically determined according to the preset operating temperature required by the load 10 to be cooled. The refrigerator 3 is an existing mature product, and the specific structure of the refrigerator 3 will not be described in detail in this embodiment.

In this embodiment, the vacuum cover 1 includes an outer cylinder 11 with two open ends and flanges 12 mounted on the upper and lower ends of the outer cylinder 11, and the flanges 12 are detachably connected with the outer cylinder 11 and block corresponding ports of the outer cylinder 11. The structure of this kind of vacuum cover 1 sets up, is favorable to the dismouting of vacuum cover 1 inner structure, improves cooling system's dismouting and maintenance convenience. In other embodiments, the outer cylinder 11 may be open at the upper end, i.e. the flange 12 is provided at the upper end of the outer cylinder 11.

The vacuum housing 1 is preferably made of a non-magnetic stainless steel material to avoid rust and to improve the support stability of its internal structure. The outer cylinder 11 may be, but not limited to, a cylinder, and the shape of the flange 12 is adapted to the shape of the outer cylinder 11.

The cooling system further comprises a vacuumizing device, wherein the vacuumizing device is used for vacuumizing the inner space of the vacuum cover 1. An aviation socket and a vacuum extraction opening are formed in a flange plate 12 at the upper end of the vacuum cover 1, the vacuumizing device is located outside the vacuum cover 1, and vacuumizing is carried out inside the vacuum cover 1 through the vacuum extraction opening, so that gas heat conduction is reduced.

In order to further improve the cooling efficiency of the cooled load 10, the cooling system further comprises a primary radiation protection screen 2, wherein the primary radiation protection screen 2 is suspended in the vacuum cover 1, and the cooled load 10 is suspended in the primary radiation protection screen 2. The primary radiation shield 2 is used for reducing heat radiation from the outside of the vacuum enclosure 1 to the cooled load 10 and reducing interference of the external environment to the cooled load 10.

The primary radiation shield 2 is preferably suspended within the vacuum enclosure 1 using a first support structure 7 and the cooled load 10 is suspended within the primary radiation shield 2 by a second support structure 8. The first support structure 7 and the second support structure 8 may be made of a high-strength low-thermal-conductivity material, such as G10 glass fiber reinforced plastic, according to the prior art, and the present invention is not limited thereto. The primary radiation shield 2 is preferably made of oxygen free high purity copper.

The primary radiation shield 2 is preferably thermally coupled to the primary cold head 31 such that the temperature of the primary radiation shield 2 approaches the temperature of the primary cold head 31, reducing the radiant heat leak from the vacuum enclosure 1 and the external environment to the load 10 being cooled.

In this embodiment, the heat conducting member 5 is a metal member, and the metal member is preferably made of pure copper or other metal material with high thermal conductivity. That is, in an embodiment, the heat conductive member 5 may be a conventional copper braid structure.

To reduce radiation leakage, the outside of the primary radiation shield 2, the outer surface of the thermal switch 4, the primary cold head 31, the secondary cold head 32, the cooled load 10 and/or the outer surface of the heat conductor 5 are covered with a heat insulating Layer, preferably made of a high vacuum Multi-Layer Insulation (MLI).

Further, the cooling system further includes a charging system for charging the first low-temperature pulsating heat pipe 41 with a working fluid. The structure of the liquid charging system and the liquid charging method of the first low-temperature pulsating heat pipe 41 may refer to the prior art, and this embodiment is not limited thereto.

The present embodiment also provides a superconducting magnet system, which includes a superconducting magnet and the cooling system described above, and the superconducting magnet is the cooled load 10. According to the superconducting magnet system provided by the embodiment, by adopting the cooling system, the time for precooling the superconducting magnet to the preset working temperature can be reduced, the operation efficiency of the superconducting magnet system is improved, the time for returning to the superconducting state when the superconducting magnet is in a failure overtime state is shortened, and the operation safety and reliability of the superconducting magnet system are improved; meanwhile, the thermal switch 4 occupies a small space, so that the arrangement is flexible, and the structural compactness of the superconducting magnet system can be effectively improved. It is understood that the preset operating temperature of the superconducting magnet is lower than the superconducting transition temperature.

Further, the superconducting magnet includes a superconducting magnet coil and a support frame for mounting the superconducting magnet coil. The superconducting magnet is fixed in the primary radiation shield 2 by a second support structure 8, the second support structure 8 may comprise a pull rod or a pull ring, and the second support structure 8 is preferably made of a material with low thermal conductivity, high insulation and high strength, such as G10 glass fiber reinforced plastic, etc. The support skeleton is a cylindrical structure, and the inner hole forms a room temperature hole 101 for placing a sample. When the superconducting magnet is operated, a uniform magnetic field is present in the room temperature bore 101.

In order to obtain high magnetic field strength, the superconducting magnet coil may be composed of a plurality of coils, and the coil material may be NbTi, nb ₃ Sn, or magnesium diboride, yttrium barium copper oxide, or the like. The supporting framework can be made of 6063-T1 aluminum alloy and other materials.

The central axis of the room temperature hole 101 may be disposed in a vertical direction or a horizontal direction, or may be disposed in other directions, that is, the central axis of the room temperature hole 101 may be specifically disposed according to a specific type of superconducting magnet system and an application scenario.

In this embodiment, the evaporation section of the thermal switch 4 and the heat conducting member 5 are both connected to the supporting frame, so as to improve the convenience of connection between the thermal switch 4 and the heat conducting member 5 and the superconducting magnet.

The superconducting magnet system further includes a diode assembly for quench protection of the superconducting magnet. The superconducting magnet system further includes a power supply assembly 6, the power supply assembly 6 including a superconducting field power supply 65 and a wire connected between the superconducting field power supply 65 and the superconducting magnet coils. The superconducting excitation power supply 65 is located outside the vacuum enclosure 1.

To better achieve the connection between the superconducting magnet and the superconducting excitation power supply 65, the superconducting magnet system further includes an internal current connection assembly 63 and an external current connection assembly 64, the internal current connection assembly 63 is mounted on the primary radiation shield 2 to butt-joint the wires inside and outside the primary radiation shield 2, and the external current connection assembly 64 is mounted on the vacuum enclosure 1 to butt-joint the wires located on both sides inside and outside the vacuum enclosure 1. The inner current connection assembly 63 is provided to be insulated from the primary radiation shield 2, and the outer current connection assembly 64 is provided to be insulated from the vacuum envelope 1. The specific structure of the internal current connection assembly 63 and the external current connection assembly 64 may refer to the prior art, and the present invention is not repeated and limited thereto.

Further, the power supply assembly 6 further includes a high temperature superconductive current lead 62 located inside the primary radiation shield 2, the high temperature superconductive current lead 62 is thermally connected and insulated with the secondary cold head 32 of the refrigerator 3, a superconductive wire 61 is connected between the high temperature superconductive current lead 62 and the superconductive magnet, and a wire is connected between the high temperature superconductive current lead 62 and the internal current wiring assembly 63.

The superconducting magnet system provided by the embodiment can be applied to the aspects of information technology, biomedicine, environmental technology, military industry, industrial processing, sea, transportation, major science engineering and superconducting power, such as medical nuclear magnetic resonance imaging equipment MRI, nuclear magnetic resonance spectrometer MNR, superconducting magnetic separation system, superconducting energy storage system, superconducting motor, superconducting cable, superconducting transformer, superconducting current limiter, superconducting induction heating, superconducting particle accelerator, superconducting magnetic suspension train and the like.

Example two

The present embodiment provides a cooling system and a superconducting magnet system, and the cooling system and the superconducting magnet system provided in the present embodiment are based on further improvements of the structure in the first embodiment, and the description of the same structure as that in the first embodiment is omitted.

As shown in fig. 3, in the present embodiment, the cooling system further includes a charging system 20, and the charging system 20 is configured to charge the first working medium into the first low-temperature pulsating heat pipe 41 of the thermal switch 4. The charging system 20 is located primarily outside the vacuum enclosure 1.

Specifically, the liquid filling system 20 includes a buffer tank 201, a gas storage bottle 202, a molecular pump unit 203 and a filling pipe 209, wherein the buffer tank 201 is connected with an air inlet end of the filling pipe 209 through a first pipeline, the molecular pump unit 203 is connected with an air inlet end of the filling pipe 209 through a second pipeline, an air outlet end of the filling pipe 209 is connected with the thermal switch 4, and the gas storage bottle 202 is connected with the air inlet end of the filling pipe 209 through a third pipeline. Wherein, be provided with first stop valve 204 on the filling pipe 209, be provided with second stop valve 205 on the second pipeline, be provided with third stop valve 206 on the third pipeline.

The charging system 20 further includes a first pressure sensor 207 disposed on the charging tube 209 for detecting pressure fluctuations in the condensing section of the first cryopulsation heat pipe 41. A second pressure sensor 208 is provided at the buffer tank 201 for detecting the pressure of the buffer tank 201 and calculating the filling rate.

The gas cylinder 202 stores a first working medium with high purity (purity is 99.999%) and in a gaseous state, and the liquid filling process of the first low-temperature pulsating heat pipe 41 specifically comprises the following operation steps:

(1) Temperature and pressure data are collected and recorded.

(2) The high purity first working fluid and a set of molecular pump units 203 are used to purge and purify the gas from the first low temperature pulsating heat pipe 41, buffer tank 201, and the conduits within the charging system 20 to prevent residual air or other impurities in the conduits from affecting the experiment.

The specific process is as follows:

first, the first stop valve 204 and the second stop valve 205 are opened, the third stop valve 206 is closed, and the molecular pump unit 203 is used to pump the first low-temperature pulsating heat pipe 41 and the charging system 20 to a high vacuum (vacuum value < 1×10) ^-3 Pa)；

Then the second stop valve 205 is closed, the first stop valve 204 and the third stop valve 206 are opened, and 99.999 percent of Gao Chundi working medium is filled into the first low-temperature pulsating heat pipe 41 and the buffer tank 201 from the gas storage bottle 202;

The same process is repeated more than 5 times to thoroughly remove the impurity gases from the pulsating heat pipe and the fluid-filled system 20 and after completion, a high vacuum is drawn.

(3) After the purification process is completed, the third stop valve 206 is opened, the first stop valve 204 and the second stop valve 205 are closed, the gas cylinder 202 is opened, the buffer tank 201 is filled with the high-purity first working medium, then the first stop valve 204 is closed, and the initial pressure P of the buffer tank 201 at the moment is recorded ₀ 。

(4) The first stop valve 204 is opened, the second stop valve 205 and the third stop valve 206, gao Chundi are closed, and working medium enters the first low-temperature pulsating heat pipe 41 from the buffer tank 201.

(5) Vacuumizing the vacuum cover 1 by using another group of molecular pump units 203 until the vacuum degree in the vacuum cover 1 is less than 1×10 ^-3 After Pa, the refrigerator 3 is started to the first low levelThe thermal pulsation heat pipe 41 performs cooling.

(6) As the temperature of the condensing section of the first low-temperature pulsating heat pipe 41 decreases, the pressure also decreases, and when the temperature drops to the vapor-liquid two-phase flow temperature zone of the first working medium, the liquid first working medium starts to be generated, the pressure rapidly decreases, and the liquid first working medium moves from the condensing section to the evaporating section under the action of gravity, so that the evaporating section is accelerated to be cooled to the vapor-liquid two-phase flow temperature zone. When the pressure of the buffer tank 201 is reduced to the pressure P corresponding to the target filling rate ₁ When the first stop valve 204 is closed, the first low temperature pulsating heat pipe 41 is isolated from the charging system 20. At this time, the inside of the first low-temperature pulsating heat pipe 41 is in an initial state in which air plugs and liquid plugs are alternately distributed, and the liquid filling process is ended.

The mass of the first working medium filled in the first low-temperature pulsating heat pipe 41 is represented by the liquid filling rate, which is defined as the ratio of the liquid nitrogen volume to the pulsating heat pipe volume at 77.34K when the first working medium is nitrogen, for comparison with the existing research data.

When the liquid filling rate is calculated, the first low-temperature pulsating heat pipe 41 and the first working substance in the liquid filling system 20 are regarded as ideal gas, and the mass m of the first working substance is filled according to the law of conservation of mass and the ideal gas state equation _t Can be calculated by the following formula:

wherein: p (P) ₀ And P ₁ The initial pressure and the final pressure of the buffer vessel 201 at the beginning and end of the filling process, respectively, are given in Pa; v (V) _FT And V _BT The volumes of the liquid charging pipe (the part from the first stop valve 204 to the first low-temperature pulsating heat pipe 41) and the buffer tank 201 are respectively m ³ ；T _FT And T _BT Average temperature of the liquid charging pipeline and the buffer tank 201 is K; r is R _g The gas constant of the first working medium; m is m _t The unit is kg for filling the working medium of the pulsating heat pipe.

The mass of the liquid working medium charged into the first low-temperature pulsating heat pipe 41 is the sum of the saturated gas mass and the saturated liquid mass of the first working medium. Taking the first working medium as nitrogen as an example, the mass of the liquid nitrogen charged into the first low-temperature pulsating heat pipe 41 is the sum of the mass of the saturated nitrogen and the mass of the saturated liquid nitrogen. Since the densities of the saturated nitrogen gas and the saturated liquid nitrogen and the mass of the nitrogen charged into the first cryogenic pulsating heat pipe 41 are known, the volume of the saturated liquid nitrogen can be found by:

m _t ＝ρ _l V _l +ρ _v (V _PHP -V _l ) (formula 2);

wherein V is _PHP And V _l The unit is m, which is the volume of the first low-temperature pulsating heat pipe 41 and the volume of liquid nitrogen in the pipe respectively ³ ；ρ _v And ρ _l The densities of saturated nitrogen and saturated liquid nitrogen at 77.34K are kg/m ³ 。

Therefore, the filling ratio is:

the liquid filling rate of the first low-temperature pulsating heat pipe 41 can be determined based on the initial pressure and the final pressure of the buffer tank 201 in the combined type 1 to 3. The charge rate calculation takes into account the effect of the charge tube volume while the volume of the remaining portion of the tubing of the charging system 20 is considered to be a fraction of the volume of the buffer tank 201.

It should be noted that the liquid filling method is also applicable to other low-temperature working media.

The liquid filling rate of the first low-temperature pulsating heat pipe 41 is recommended to be between 20% and 80%, the liquid filling rate is too low to be burnt out, the flow resistance is large, and the operation is difficult to start.

In addition to controlling the liquid filling rate before the operation of the first low temperature pulsating heat pipe 41, the buffer tank 201 can automatically adjust the liquid filling rate and pressure during the operation of the first low temperature pulsating heat pipe 41 to prevent dry out. The first stop valve 204 is only required to be opened, so that the buffer tank 201 is connected with the first low-temperature pulsating heat pipe 41 to operate.

Example III

The present embodiment provides a cooling system and a low-temperature superconducting magnetic system, and the cooling system provided in the present embodiment is a further improvement of the cooling system in the first embodiment, and the details of the cooling system in the first embodiment are not described in detail.

As shown in fig. 4 to 6, in the present embodiment, the thermal switch 4 further includes a condensation plate 42, an evaporation plate 43, and a liquid injection joint 44. The first low-temperature pulsating heat pipe 41 is formed in a serpentine structure by bending a capillary tube, and includes a plurality of parallel pipe portions 411 arranged in parallel and at intervals in a first direction and a bending portion 412 connected between two adjacent parallel pipe portions 411. The parallel pipe portion 411 has a condensing section, an insulating section, and an evaporating section connected in order.

The condensing plate 42 is provided with a plurality of first positioning grooves 421, the surface of the evaporating plate 43 is provided with a plurality of second positioning grooves 431, the first positioning grooves 421 and the second positioning grooves 431 are arranged in one-to-one correspondence with the parallel pipe portions 411, the condensing section of the parallel pipe portions 411 is positioned in the first positioning grooves 421, the evaporating section of the parallel pipe portions 411 is positioned in the second positioning grooves 431, and soldering tin is filled in the first positioning grooves 421 and the second positioning grooves 431 so as to fix the first low-temperature pulsating heat pipes 41 and the corresponding condensing plate 42 and evaporating plate 43, heat resistance is reduced, and good thermal contact between the first low-temperature pulsating heat pipes 41 and the condensing plate 42 and the evaporating plate 43 is ensured. The bending part 412 connected to the condensation section is located at one side of the condensation plate 42 away from the evaporation plate 43, and the bending part 412 connected to the evaporation section evaporates one side of the condensation plate 42 away from the evaporation plate 43.

The groove widths of the first positioning groove 421 and the second positioning groove 431 are preferably larger than the outer diameter of the first low-temperature pulsating heat pipe 41, so that the first low-temperature pulsating heat pipe 41 is accommodated in the first positioning groove 421 and the second positioning groove 431, and space is provided for filling soldering tin. The evaporating plate 43 and the condensing plate 42 are preferably made of pure copper, so that the heat conduction efficiency is high. The first cryopulse heat pipe 41 is preferably made of stainless steel or pure copper.

The thermal switch 4 is preferably a multi-layer structure, that is, the parallel tube portion 411 extends along the second direction, the thermal switch 4 preferably includes multiple layers of first low-temperature pulsating heat pipes 41 arranged side by side along the third direction, the evaporating plate 43 and the condensing plate 42 are respectively arranged in one-to-one correspondence with the first low-temperature pulsating heat pipes 41, and the first direction, the second direction and the third direction are mutually perpendicular. The thermal switch 4 having the multilayer first low-temperature pulsating heat pipe 41 can increase the thermal conductivity, save the space occupied by the thermal switch 4, and improve the structural compactness of the thermal switch 4.

In the present embodiment, all the evaporation plates 43 are stacked and fastened together in the third direction, and all the condensation plates 42 are stacked and fastened together in the third direction.

A liquid filling channel is arranged in the liquid filling joint 44, and a filling pipe of the liquid filling system is communicated with the first low-temperature pulsating heat pipe 41 through the liquid filling channel. In this embodiment, all the first low-temperature pulsating heat pipes 41 are arranged in parallel, the two ends of each first low-temperature pulsating heat pipe 41 are formed with joint pipe portions 413, the liquid injection channels are arranged in one-to-one correspondence with the first low-temperature pulsating heat pipes 41, and the two joint pipe portions 413 of each first low-temperature pulsating heat pipe 41 are inserted into the liquid injection channels and are communicated with the liquid injection channels in a sealing manner. This arrangement can simplify the processing of the thermal switch 4 and improve the convenience of assembling and disassembling the thermal switch 4.

In other embodiments, all the first low-temperature pulsating heat pipes 41 are arranged in series, i.e. the corresponding ends of two adjacent first low-temperature pulsating heat pipes 41 are connected, all the first low-temperature pulsating heat pipes 41 have only two joint pipe portions 413, the liquid injection joint 44 is provided with one liquid injection channel, and the two joint pipe portions 413 are inserted into the liquid injection channel and are in sealing communication with the liquid injection channel.

Illustratively, the first low-temperature pulsating heat pipe 41 is provided with four layers, each layer of the first low-temperature pulsating heat pipe 41 having 12 parallel pipe sections 411. In other embodiments, the number of layers of the first low-temperature pulsating heat pipe 41 and the number of parallel pipe sections 411 included in the first low-temperature pulsating heat pipe 41 may be set according to requirements, for example, three, five or more layers may be provided, and each layer includes 6 to 18 parallel pipe sections 411.

Further, during the process of the thermal switch 4, the evaporating plate 43 between two adjacent layers and the condensing plate 42 between two adjacent layers are welded with tin, so that the gap is filled with tin as much as possible; all evaporation plates 43 and all condensation plates 42 are fastened by bolts or screws.

In other embodiments, the thermal switch 4 may also include a plurality of first low-temperature pulsating heat pipes 41 disposed side by side in the first direction, where each first low-temperature pulsating heat pipe 41 is separately provided with a priming joint 44 and a priming system, i.e. each first low-temperature pulsating heat pipe 41 may be separately controlled to be primed. In still another embodiment, the thermal switch 4 may include a plurality of first low-temperature pulsating heat pipes 41 arranged side by side in the first direction, and both ends of each of the first low-temperature pulsating heat pipes 41 are connected into a communication pipe, which communicates with the charging system.

The thermal switch 4 has a first connection surface thermally connected to the primary cold head 31 and a second connection surface thermally connected to the load 10 to be cooled. In the present embodiment, the evaporating plate 43 of the outermost layer has a second connection surface on a side away from the adjacent evaporating plate 43, and the condensing plate 42 of the outermost layer has a first connection surface on a side away from the adjacent condensing plate 42.

In order to improve the heat conduction efficiency, the first connecting surface and/or the second connecting surface are/is provided with a heat conduction structure, and the heat conduction structure comprises a heat conduction coating and/or a heat conduction sheet so as to increase the heat conduction rate of the connecting part and reduce the contact thermal resistance. Preferably, the heat conducting layer is an apizon N high heat conducting grease layer, and the heat conducting sheet is an indium sheet.

Example IV

As shown in fig. 7, the present embodiment provides a cooling system and a superconducting magnet system, which are substantially the same as those of the third embodiment, and only have differences in partial arrangement, so that the present embodiment will not be repeated for the same structure as that of the third embodiment.

In the present embodiment, the plurality of evaporation plates 43 are divided into at least two groups separately provided, each group of evaporation plates 43 includes one evaporation plate 43 or at least two evaporation plates 43 provided in a stacked manner, and adjacent two groups of evaporation plates 43 are provided at intervals in the first direction. Each group of evaporation plates 43 has a second connection surface therein which is in contact with the cooled load 10.

By providing at least two sets of evaporation plates 43, the contact position of the thermal switch 4 with the load 10 to be cooled can be increased, thereby improving the cooling uniformity across the load 10 to be cooled, and further improving the cooling efficiency.

Preferably, the evaporation plates 43 are provided in two groups, and the two groups of evaporation plates 43 are connected to both ends of the cooled load 10, respectively, to effectively improve the cooling uniformity of the cooled load 10 while reducing the number of evaporation plates 43.

Example five

As shown in fig. 8, the present embodiment provides a cooling system and a superconducting magnet system, and the basic structure of the cooling system provided in the present embodiment is the same as that of the first embodiment, only the arrangement of the heat conduction members 5 is different, and the present embodiment will not be repeated for the same structure as that of the first embodiment.

In this embodiment, the heat conduction member 5 includes a second low-temperature pulsating heat pipe, in which a second working medium is filled, and the critical temperature of the second working medium is lower than that of the first working medium, and the final cooling temperature of the second-stage cold head 32 is between the triple point temperature and the critical point temperature of the second working medium. When the secondary coldhead 32 is at a final refrigeration temperature (i.e., a target refrigeration temperature), the second working fluid within the second cryogenic pulsating heat pipe is in a two-phase flow state. The evaporation section of the second low-temperature pulsating heat pipe is thermally connected to the cooled load 10, and the condensation section of the second low-temperature pulsating heat pipe is thermally connected to the secondary cold head 32.

By making the heat conductive member 5 include a second low-temperature pulsating heat pipe, that is, transmitting the cold of the secondary cold head 32 to the cooled load 10 by using the second low-temperature pulsating heat pipe, it is possible to improve the heat conductivity of the heat conductive member 5, improve the heat conductive efficiency, thereby reducing the time required for the cooled load 10 to cool to a preset operating temperature, and improving the efficiency of the cooling system; meanwhile, as the heat conductivity of the second low-temperature pulsating heat pipe is higher, the temperature drop of the cooled load 10 can be rapidly realized, the temperature rise probability of the cooled load 10 is reduced, and the operation safety and reliability of a cooling system are improved; meanwhile, the first low-temperature pulsating heat pipe 41 and the second low-temperature pulsating heat pipe are flexibly connected with other structures, are flexible to install, are not limited by directions and structures, not only lighten weight, but also can play a role in isolating the vibration of the refrigerator 3, and are particularly suitable for being applied to remote-conduction superconducting magnets which are sensitive to the vibration, such as nuclear magnetic resonance imaging.

The second working medium filled in the second low-temperature pulsating heat pipe is preferably helium, and the critical temperature is lower. It is understood that the working medium of the second low-temperature pulsating heat pipe may be hydrogen, neon, or the like. The working medium of the first low-temperature pulsating heat pipe 41 may be nitrogen, argon, krypton, oxygen, ammonia, methane, etc., and the first working medium in the first low-temperature pulsating heat pipe 41 and the second working medium in the second low-temperature pulsating heat pipe may be specifically selected according to the preset working temperature required by the cooled load 10.

The structure of the heat conduction member 5 can be set with reference to the structure of the thermal switch 4 in the first, third or fourth embodiments, and the description of this embodiment is omitted. The structure of the thermal switch 4 in this embodiment may also be the structure of the thermal switch in the third embodiment and the fourth embodiment, and will not be described here again.

In this embodiment, the liquid filling system and the liquid filling method corresponding to the second low-temperature pulsating heat pipe may refer to the arrangement in the second embodiment, and this embodiment will not be described in detail.

In the superconducting magnet system provided in this embodiment, when the superconducting magnet is cooled to the liquid helium working temperature region, the superconducting excitation power supply 65 works to start excitation, and a magnetic field is generated, and during excitation, heat generated by ac loss is efficiently transferred to the secondary cooling head 32 of the refrigerator 3 by the second low-temperature pulsating heat pipe, so that the temperature of the superconducting magnet is prevented from exceeding the critical temperature and being quenched. Meanwhile, because of the extremely high effective heat conductivity coefficient (the effective heat conductivity coefficient exceeds copper by several orders of magnitude) of the second low-temperature pulsating heat pipe, even if the superconducting magnet is quenched during excitation, the second low-temperature pulsating heat pipe can quickly transfer heat to the secondary cold head 32 of the refrigerator 3, so that the temperature of the superconducting magnet can be quickly restored to an operating temperature region. In addition, the second low-temperature pulsating heat pipe has the advantage of small temperature difference, even if the heat transfer distance is far, the temperature difference between the superconducting magnet and the secondary cold head 32 of the refrigerator 3 is still small, so that the refrigerator 3 can be far away from the superconducting magnet, and the refrigerator 3 is not influenced by a magnetic field when in operation, and the refrigeration performance is ensured. In addition, the connection between the second low-temperature pulsating heat pipe and the first low-temperature pulsating heat pipe 41 and the refrigerator 3 as well as the superconducting magnet is flexible connection, the installation is flexible, the direction and structure limitations are avoided, the weight is reduced, the effect of isolating the refrigerator 3 from vibration is achieved, and the low-temperature pulsating heat pipe is particularly suitable for the application of the remote conductive superconducting magnet which is sensitive to vibration, such as nuclear magnetic resonance imaging.

It should be noted that, a heat insulating layer is wrapped outside the superconducting magnet, outside the primary radiation shield 2, outside the first low-temperature pulsating heat pipe 41, outside the second low-temperature pulsating heat pipe, outside the primary cold head 31 and/or the secondary cold head 32, and the heat insulating layer is preferably made of MLI material, so as to improve heat insulating effect and reduce radiation heat leakage. The heat insulating layer preferably has at least 20 layers to enhance the heat insulating effect.

Example six

The present embodiment provides a cooling system and a superconducting magnet system, where the cooling system of the superconducting magnet system provided in the present embodiment is a further improvement of the cooling system in any one of the foregoing embodiments, and the structure of the present embodiment that is the same as that of the foregoing embodiment is not repeated.

In this embodiment, the primary radiation shield 2 has a secondary radiation shield 9 suspended therein, and the cooled load 10 is located inside the secondary radiation shield 9. That is, by providing the secondary radiation shield 9 inside the primary radiation shield 2, the load to be cooled 10 is provided inside the secondary radiation shield 9, further reducing radiation heat leakage.

Preferably, in the present embodiment, the primary coldhead 31 is connected to the primary radiation shield 2 to absorb heat radiation from the environment to the primary radiation shield 2; the secondary coldhead 32 is connected to the secondary radiation shield 9 to absorb heat radiation from the primary radiation shield 2 to the secondary radiation shield 9 and to maintain the secondary radiation shield 9 at a temperature similar to that of the load 10 being cooled, facilitating better maintenance of the operating environment temperature of the load 10 being cooled.

In this embodiment, the secondary cooling head 32 is connected to the secondary radiation shield 9 and the heat conduction member 5, respectively, so that the cooling capacity of the secondary cooling head 32 is directly transferred to the second low-temperature pulsating heat pipe. In other embodiments, the secondary cooling head 32 may be connected to the secondary radiation protection screen 9, and the condensation section of the second low-temperature pulsating heat pipe is connected to the secondary radiation protection screen 9, so as to realize the thermal connection between the condensation section and the secondary cooling head 32, thereby simplifying the connection structure between the secondary cooling head 32 and the secondary radiation protection screen 9 and the second low-temperature pulsating heat pipe, and reducing the assembly difficulty.

Preferably, the outer parts of the primary radiation protection screen 2 and the secondary radiation protection screen 9 are coated with heat insulation layers, and the heat insulation layers are preferably made of high-vacuum multi-layer heat insulation materials so as to further reduce heat radiation.

Further, the primary cold head 31, the secondary cold head 32, the first low-temperature pulsating heat pipe 4 and the second low-temperature pulsating heat pipe are all wrapped with heat insulation layers, and the heat insulation layers are preferably made of high-vacuum multilayer heat insulation materials.

Example seven

As shown in fig. 10, the present embodiment provides a cooling system and a superconducting magnet system, and the cooling system and the superconducting magnet system provided in the present embodiment are based on further improvements of the superconducting magnet system provided in the fifth embodiment, and the present embodiment does not provide a redundant description of the same structure as in the fifth embodiment.

By employing at least two refrigerators 3, the present embodiment can separate the operation time between each redundant refrigerator 3, and reduce the duty ratio of the refrigerator 3, thereby extending the service life of the refrigerator 3. The plurality of refrigerators 3 may also be operated in parallel to improve the cooling efficiency of the cooled load 10 and ensure the operational safety and reliability of the cooled load.

In this embodiment, at least two refrigerators 3 are provided, each refrigerator 3 has a primary cold head 31 and a secondary cold head 32, each primary cold head 31 is connected to the cooled load 10 through a thermal switch 4, each secondary cold head 32 is connected to the cooled load 10 through a thermal conduction member 5, the thermal switch 4 includes at least one first low-temperature pulsating heat pipe 41, the thermal conduction member 5 includes at least one second low-temperature pulsating heat pipe, and the critical temperature of the first working substance in the first low-temperature pulsating heat pipe 41 is higher than the critical temperature of the second working substance in the second low-temperature pulsating heat pipe.

In the cooling system provided in this embodiment, when one of the refrigerators fails or stops operating, the temperatures of the condensation sections of the first low-temperature pulsating heat pipe 41 and the second low-temperature pulsating heat pipe connected to the refrigerator 3 exceed the critical temperature, and stop operating, the first low-temperature pulsating heat pipe 41 and the second low-temperature pulsating heat pipe are disconnected, so that the heat load is prevented from being transferred from the refrigerator 3 returning to normal temperature to the cooled load 10, and at the same time, the remaining refrigerator 3 works normally, so that the normal operation of the cooling system is not affected.

In this embodiment, a charging system is preferably disposed corresponding to each thermal switch 4, so as to implement separate charging control for the first low-temperature pulsating heat pipe 41 in each thermal switch 4. In other embodiments, all of the thermal switches 4 may share the same charging system, i.e., the same charging system charges the first cryopump heat pipe 41 in all of the thermal switches 4 simultaneously.

Further, a liquid filling system is correspondingly arranged on each heat conduction piece 5, so that independent liquid filling control of the second low-temperature pulsating heat pipe in each heat conduction piece 5 is realized. In other embodiments, all of the heat transfer elements 5 may share the same charging system, i.e., the same charging system charges the second cryopump heat pipes in all of the heat transfer elements 5 simultaneously.

Example eight

The present embodiment provides a cooling method applied to the cooling system and the superconducting magnet system provided in any one of the first to seventh embodiments. The structures of the cooling system and the superconducting magnet system will not be described in detail in this embodiment.

Specifically, the cooling method provided in this embodiment includes:

s1, vacuumizing the inside of a vacuum cover 1 until the vacuum value is smaller than a preset vacuum value;

wherein the vacuum degree corresponding to the preset vacuum value is less than 1 multiplied by 10 ^-3 Pa。

S2, starting the refrigerator 3;

s3, when the temperature of the primary cold head 31 reaches the gas-liquid two-phase flow temperature zone of the first low-temperature pulsating heat pipe 41, controlling the temperature of the primary cold head 31 to be kept to the gas-liquid two-phase flow temperature zone so as to enable the thermal switch 4 to be in a conducting state;

s4, when the temperature of the cooled load 10 is lower than the three-phase temperature of the thermal switch 4, stopping controlling the temperature of the first-stage cold head 31 so as to enable the temperature of the first-stage cold head 31 to be reduced to be lower than the three-phase temperature of the first working medium in the first low-temperature pulsating heat pipe, and enabling the thermal switch 4 to be disconnected;

s5, when the cooled load 10 is reduced to the preset working temperature along with the temperature of the secondary cold head 32, the cooled load 10 starts to operate.

The cooling method provided in this embodiment can improve the cooling efficiency of the cooled load 10, thereby improving the working efficiency of the cooled load 10 and improving the operation safety and reliability of the cooled load 10.

Further, the cooling method further includes: during the operation of the cooled load, when the temperature of the cooled load increases to the gas-liquid two-phase flow temperature region of the first low-temperature pulsating heat pipe 41, the temperature of the primary cold head 31 is regulated to the gas-liquid two-phase flow temperature region, so that the thermal switch 4 is converted from the off state to the on state.

By the arrangement, the efficiency of returning to the preset working temperature when the cooled load 10 rises in the operation process can be improved, and the operation safety and reliability of the cooled load 10 can be improved.

Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.

Claims

1. The utility model provides a cooling system for cool off by cooling load (10), its characterized in that, cooling system includes vacuum cap (1), refrigerator (3), hot switch (4) and temperature control device, refrigerator (3) have one-level cold head (31) and second grade cold head (32), by cooling load (10) one-level cold head (31) and second grade cold head (32) all are located in vacuum cap (1), hot switch (4) include first low temperature pulsation heat pipe (41), the condensation segment of first low temperature pulsation heat pipe (41) with one-level cold head (31) heat connection, the evaporation zone of first low temperature pulsation heat pipe (41) with by cooling load (10) connection, second grade cold head (32) with be connected with heat conduction piece (5) between by cooling load (10), the final refrigeration temperature of one-level cold head (31) is less than three-phase point temperature in first low temperature pulsation heat pipe (41), the device is used for controlling one-level cold head (31) and second grade cold head (32) temperature control device.

2. The cooling system according to claim 1, characterized in that the thermal switch (4) further comprises an evaporation plate (43) and a condensation plate (42), both the evaporation plate (43) and the condensation plate (42) being made of a heat conducting metal, the condensation section of the first pulsating heat pipe (41) being fixed to the condensation plate (42), the evaporation section of the first pulsating heat pipe (41) being fixed to the evaporation plate (43), the condensation plate (42) being connected to the primary cold head (31), the evaporation plate (43) being connected to the cooled load (10).

3. The cooling system according to claim 2, wherein the thermal switch (4) comprises at least two first low-temperature pulsating heat pipes (41), and the evaporating plate (43) and the condensing plate (42) are arranged in one-to-one correspondence with the first low-temperature pulsating heat pipes (41);

all the condensation plates (42) are arranged in a stacked mode and fixedly connected, and one condensation plate (42) positioned on the outer side is connected with the primary cold head (31);

all the evaporation plates (43) are divided into at least two groups which are arranged separately, each group of the evaporation plates (43) comprises at least one evaporation plate (43) or a plurality of evaporation plates (43) which are stacked and fixedly arranged, and one evaporation plate (43) positioned at the outer side in each group of the evaporation plates (43) is connected with the cooled load (10).

4. The cooling system according to claim 1, further comprising a primary radiation shield (2), the primary radiation shield (2) being suspended within the vacuum enclosure (1), the cooled load (10) being suspended within the primary radiation shield (2), the primary coldhead (31) being thermally coupled to the primary radiation shield (2).

5. The cooling system according to claim 4, further comprising a secondary radiation shield (9), the secondary radiation shield (9) being suspended inside the primary radiation shield (2), the cooled load (10) being suspended inside the secondary radiation shield (9), the secondary coldhead (32) being thermally connected to the secondary radiation shield (9).

6. A cooling system according to any one of claims 1-5, characterized in that the heat transfer element (5) comprises a second cryogenic pulsating heat pipe, the evaporator section of which is connected to the load (10) to be cooled, the condenser section of which is thermally connected to the secondary cold head (32), the final refrigeration temperature of which is between the triple point temperature and the critical point temperature of the working medium in the second cryogenic pulsating heat pipe.

7. The cooling system according to claim 6, characterized in that the working medium in the first cryogenic pulsating heat pipe (41) is argon, nitrogen, oxygen or methane;

8. The cooling system according to claim 6, characterized in that the refrigerator (3) is provided with at least two, the thermal switch (4) and the heat conductor (5) being arranged in a one-to-one correspondence with the refrigerator (3).

9. The cooling system according to any one of claims 1-5, characterized in that the outer surfaces of the primary cold head (31), the secondary cold head (32), the thermal switch (4), the cooled load (10) and/or the heat conductor (5) are clad with a multilayer insulation material;

and/or the thermal switch (4) is provided with a first connecting surface and a second connecting surface, the first connecting surface is thermally connected with the primary cold head (31), the second connecting surface is thermally connected with the cooled load (10), and the first connecting surface and/or the second connecting surface is/are provided with a heat conducting coating and/or a heat conducting sheet.

10. A superconducting magnet system comprising a superconducting magnet, further comprising a cooling system according to any of claims 1-9, the superconducting magnet being the cooled load (10).

11. A cooling method, applied to the cooling system according to any one of claims 1 to 9, comprising:

vacuumizing the inside of the vacuum cover (1) until the vacuum value is smaller than a preset vacuum value;

-starting the refrigerator (3);

when the temperature of the primary cold head (31) reaches the gas-liquid two-phase flow temperature zone of the first low-temperature pulsating heat pipe (41), controlling the temperature of the primary cold head (31) to be kept to the gas-liquid two-phase flow temperature zone so as to enable the thermal switch (4) to be in a conducting state;

when the temperature of the cooled load (10) is lower than the three-phase point temperature of the thermal switch (4), stopping controlling the temperature of the primary cold head (31) so as to enable the temperature of the primary cold head (31) to be reduced to be lower than the three-phase point temperature of the working medium in the first low-temperature pulsating heat pipe (31) and enable the thermal switch (4) to be disconnected;

when the cooled load (10) is reduced to a preset working temperature along with the temperature of the secondary cold head (32), the cooled load (10) starts to operate.

12. The cooling method according to claim 11, characterized in that the cooling method further comprises:

during the operation of the cooled load (10), when the temperature of the cooled load (10) is increased to the gas-liquid two-phase flow temperature zone of the first low-temperature pulsating heat pipe (41), the temperature of the primary cold head (31) is regulated and controlled to the gas-liquid two-phase flow temperature zone, so that the thermal switch (4) is converted from an off state to an on state.