CN115620986B

CN115620986B - Superconductive heat switch

Info

Publication number: CN115620986B
Application number: CN202211270485.7A
Authority: CN
Inventors: 邱志勇; 刘涛; 常朔
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2022-10-18
Filing date: 2022-10-18
Publication date: 2023-08-01
Anticipated expiration: 2042-10-18
Also published as: CN115620986A

Abstract

A superconducting thermal switch comprising: the cold end polar plate (1), the hot end polar plate (2), the heat insulation supporting shell (3), the superconducting material core (4), the superconducting winding (5) and the magnetic core (6). The cold end polar plate (1) and the hot end polar plate (2) are positioned at two ends of the superconducting thermal switch, and the superconducting material core (4) is positioned at the center of the superconducting thermal switch and is simultaneously kept in contact with the cold end polar plate (1) and the hot end polar plate (2). The superconducting thermal switch provided by the invention has the advantages of simple structure, high efficiency of a thermal circuit and small driving current.

Description

Superconductive heat switch

Technical Field

The invention relates to the field of extremely low temperature refrigeration, in particular to a superconductive heat switch.

Background

The superconducting thermal switch is used for controlling the switching between the superconducting state and the normal state of the superconducting material, and the on-off of a thermal path is realized by utilizing the difference of the thermal conductance of the two states so as to control the heat transmission.

At a temperature point below the superconducting transition temperature, the thermal conductance of the superconducting material in the superconducting state is much less than the thermal conductance in the normal state. Below the superconducting transition temperature, the superconducting material enters a superconducting state, and its thermal conductivity is significantly reduced, causing the thermal path through the superconducting material to become open. When the strength of the externally applied magnetic field exceeds the critical magnetic field strength of the superconducting material, the material can be converted from a superconducting state to a normal state, so that the thermal conductivity is remarkably increased, and a heat path through the material becomes a passage. Thus, the state of the superconducting material can be controlled by using the externally applied magnetic field, and the switching function of controlling the on-off of the heat circuit is achieved.

Shiron et al have proposed a structure of a superconducting thermal switch in 2014. The superconducting thermal switch adopts a group of L-shaped terminals to connect with a superconducting material core, and uses a group of Helmholtz coils to provide a magnetic field for destroying the superconducting state of the superconducting material. The superconducting thermal switch is complex in structure, and an L-shaped contact terminal structure is adopted, so that a thermal path is long, and efficient heat transmission is not facilitated; meanwhile, the use of the Helmholtz coil to provide the driving magnetic field requires a relatively large current to effectively drive the magnetic field, thus accompanying serious parasitic heat problems.

Disclosure of Invention

The invention designs a novel superconducting thermal switch aiming at the problems of the prior switch by utilizing the principle of superconducting and normal metal state thermal conduction switching. Compared with the existing superconducting heat switch, the superconducting heat switch provided by the invention has the advantages of simple structure, high efficiency of a heat circuit and small driving current.

The invention aims to provide a superconducting thermal switch working in an ultralow temperature environment, which controls the on-off of a thermal circuit by controlling the switching between the superconducting state and the normal state of a superconducting material.

In order to achieve the above object, the technical solution of the present invention is as follows:

the superconducting thermal switch comprises a hot end polar plate, a cold end polar plate, a heat insulation supporting shell, a superconducting material core, a superconducting winding and a magnetic core.

The cold end polar plate and the hot end polar plate are made of materials with high low-temperature heat conductivity, and can realize high-efficiency heat conduction when a passage is opened and closed.

The hot end polar plate and the cold end polar plate are connected and fixed into a whole by the heat insulation supporting shell.

The heat insulation supporting shell is of a hollow cylindrical structure and is made of a material with extremely low heat conductivity, so that heat conduction between the two polar plates can be effectively isolated while supporting is provided for the hot end polar plate and the cold end polar plate.

The superconducting material core is arranged between the hot end polar plate and the cold end polar plate, and the two ends of the superconducting material core are respectively kept in good thermal contact with the connecting terminals in the middle of the two polar plates. The superconducting material core, the hot end polar plate and the cold end polar plate together form a heat conduction path when the thermal switch is conducted.

The superconducting winding is arranged between the heat insulation supporting shell and the superconducting material core and provides a control magnetic field for the thermal switch. The superconducting winding is composed of superconducting wires, and a supporting frame of the superconducting winding is connected with the hot end polar plate so as to maintain the required low temperature. The superconducting winding is thermally isolated from the cold end polar plates, so that the two polar plates are prevented from conducting heat through the superconducting winding.

The magnetic core is of split type design, is divided into an upper part and a lower part, is respectively arranged between the connecting terminals of the hot end polar plate and the cold end polar plate and the superconducting winding, and is thermally isolated from the superconducting winding and the support thereof. The magnetic core is matched with the superconducting winding, and the magnetic field intensity of the critical magnetic field is larger than that of the central superconducting material core under the condition of minimum input current, so that the control of switching between the superconducting state and the normal state of the superconducting material at the working temperature is realized.

Drawings

Fig. 1 is a schematic structural diagram of a superconducting thermal switch according to an embodiment of the present invention.

Fig. 2 is a schematic perspective view of the other parts of the superconductive heat switch except the heat insulation supporting case according to the embodiment of the present invention.

Fig. 3 is a schematic diagram of a design scheme of a support shell according to an embodiment of the invention.

Wherein: 1-a cold end polar plate; 2-a hot-end polar plate; 3-an insulating support shell; 4-a core of superconducting material; 5-superconducting windings; 6-a magnetic core; 7-winding support frame.

Detailed Description

The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent. Those skilled in the art will recognize that the present invention is not limited to the drawings and the following examples.

In the description of the present invention, it should be noted that, for the azimuth words such as "length", "width", "upper", "lower", "far", "near", etc., the azimuth or positional relationship is based on the azimuth or positional relationship shown in the drawings, only for convenience of describing the present invention and simplifying the description, and does not indicate or imply that the apparatus or element to be referred to must have a specific azimuth, be constructed and operated in a specific azimuth, and should not be construed as limiting the specific protection scope of the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not intended to be limiting, but rather are not to be construed as indicating or implying a relative importance or implying any particular order of such features.

An embodiment of the present invention provides a superconducting thermal switch having a structure as shown in fig. 1.

The superconducting thermal switch provided by the embodiment of the invention comprises a cold end polar plate 1, a hot end polar plate 2, a heat insulation supporting shell 3, a superconducting material core 4, a superconducting winding 5, a magnetic core 6 and a winding supporting frame 7.

The cold end polar plate 1 and the hot end polar plate 2 are both made of high-heat-conductivity materials. In one embodiment of the present application, the cold-end polar plate 1 and the hot-end polar plate 2 are made of high-purity copper with gold-plated surfaces, the purity of the high-purity copper is greater than 99.99%, one end of the high-purity copper is a flat heat conduction plane for realizing efficient heat conduction with the outside, and the other end of the high-purity copper is a terminal for contacting with a superconducting material block. In order to ensure high heat conductance of the cold end polar plate 1 and the hot end polar plate 2 along the direction of a switch heat path, the length of the whole heat path of the switch is required to be reduced as much as possible, and meanwhile, the cross section area of the heat path is enabled to be large enough in a limited space. In one embodiment of the application, the heat conduction planes of the cold end polar plate 1 and the hot end polar plate 2 are cylinders with the diameter of 30mm and the thickness of 3mm, and the contact terminals are cylinders with the diameter of 10mm and the length of 9 mm.

The heat insulation support shell 3 connects and fixes the cold end polar plate 1 and the hot end polar plate 2 into a whole, provides structural support for the whole superconducting thermal switch, and simultaneously ensures the heat insulation between the two polar plates.

The heat insulation supporting shell 3 is made of a material with low heat conductivity, and is aided with a special hollowed-out shape design to further reduce the cross-sectional area along the direction of a heat path and reduce the heat conductivity along the direction of the heat path, so that heat conduction is effectively insulated. In one embodiment of the present application, the insulating support shell is made of nylon resin with a wall thickness of 1.5mm and a reduced minimum cross-sectional area by a hollowed out design (see fig. 3) to further reduce its heat conduction. In addition to the nylon resin material used in the above-described examples, a processable rigid material having a low thermal conductivity at low temperatures (around 0.5K) can be used as a material for manufacturing the insulating support shell. For example: the thin shell structure with the thickness of less than 0.2mm is made of materials such as titanium alloy and stainless steel with low thermal conductivity in a sub-Kelvin temperature area.

The superconducting material core 4 is arranged between the cold end polar plate 1 and the hot end polar plate 2. The core 4 of superconducting material is in good thermal contact with the connection terminals of the two pole plates. For example, the core 4 of superconducting material may be brought into good thermal contact with the connection terminals of the two pole plates in such a way that: the surfaces of the superconducting material core 4 and the connection terminals of the two electrode plates are mirror polished, and are directly connected and pressed by applying mechanical force by means of direct bolts. The superconducting material core 4, the cold end polar plate 1 and the hot end polar plate 2 together form a heat conduction path when the thermal switch is conducted.

In one embodiment of the present application, the superconducting material core 4 is made of high-purity metallic tin, and the superconducting state and normal state of the superconducting material core can be controlled to be switched by a magnetic field with the intensity of about 70mT at 0.1K.

The superconducting winding 5 is made of superconducting alloy wire and is arranged inside the heat-insulating support shell. The support structure of the superconducting winding 5 realizes thermal connection by direct surface contact of the winding support frame 7 and the hot end polar plate 2 fixed by screws _。 At operating temperatures of less than 0.5K it is possible to ensure that the superconducting wire of the superconducting winding 5 is below the critical transition temperature of superconduction, to ensure that it is in the superconducting state. A gap of more than 2mm is kept between the superconducting winding 5 and the cold end polar plate 1, and thermal isolation is realized in a working vacuum environment so as to prevent the two end polar plates from conducting heat through the superconducting winding 5. The vacuum degree of the vacuum environment may be, for example, 10 or less ^-5 Pa。

The magnetic core 6 is of a split type design and is divided into an upper part and a lower part, and is symmetrically arranged by taking the superconducting material core 4 as a center, so that the superconducting material core 4 is positioned on a center connecting line of the two magnetic cores. The two magnetic cores are thermally isolated, so that the cold end polar plate 1 and the hot end polar plate 2 are prevented from conducting heat through the magnetic core 6 in the disconnection state of the thermal switch.

In one embodiment of the present application, the superconducting winding 5 and the magnetic core 6 may generate a magnetic field with a strength greater than 75mT at the superconducting material core 4, and may control the superconducting material core 4 to realize switching between a superconducting state and a normal state below a superconducting transition temperature, so as to control on-off of the superconducting thermal switch.

In the above embodiment, the superconducting winding 5 is an NbTi superconducting wire winding with a wire diameter of 0.2mm, and a magnetic field with a strength of 75mT can be generated at the superconducting material core 4 when the current density of the superconducting winding 5 is 6A/m. The superconducting switch works in a low-temperature vacuum environment with the temperature less than 0.5K, and at the temperature, the superconducting winding and the support frame thereof are well connected with the hot end polar plate, so that the winding is ensured to be in a superconducting state.

In the illustrated embodiment, the diameter of the superconducting core material 4 of the superconducting thermal switch is 10mm and the operating temperature is 0.5K. First, in the case where no current is supplied to the superconducting winding 5, the magnetic field at the core 4 of the superconducting material is 0, which is in a superconducting state, consisting ofThe thermal circuit formed by the hot end polar plate 2, the superconducting material core 4 and the cold end polar plate 1 is in an open circuit state, and at the moment, the overall heat conduction of the switch comprising the heat insulation supporting shell 3 is about 1.02mW/K, and the heat conduction between the two polar plates is closed. When a current density of 6A/m is supplied to the windings of the superconducting winding 5, a magnetic field of about 75mT is generated at the superconducting material core 4 under the combined action of the windings and the core, exceeding the critical magnetic field that disrupts the superconducting state of the superconducting material core 4, thereby causing it to transition to the normal metallic state. At this time, the heat path formed by the hot end polar plate 2, the superconducting material core 4 and the cold end polar plate 1 is in a conducting state, and the heat conduction between the two polar plates can reach about 1W/K. The on-off ratio of the superconducting thermal switch reaches 10 ³ Magnitude. Wherein the thermal conductivity during on and off can be adjusted by the diameter of the superconducting material core 4 to adapt to different working condition requirements.

Compared with the traditional superconductive thermal switch structure, the superconductive thermal switch structure has the following remarkable differences: (1) The linear type heat circuit design enables the superconducting switch with the same overall dimension to have larger conduction heat conductivity, and improves the heat transport efficiency under the condition of switch conduction; (2) The superconducting coil and the split magnetic core are designed, so that the driving current density of the superconducting winding of the superconducting switch can be reduced to 6A/m, and meanwhile, the volume of the coil winding is greatly reduced to less than 10% of the volume of a Helmholtz coil generating a magnetic field with the same level intensity, thereby effectively reducing the parasitic heat influence of the switch. (3) The selection of the low thermal conductivity shell material and the hollow structural design can maximally reduce the heat leakage between the cold polar plates and the hot polar plates when the switch is closed (in the embodiment, a nylon resin shell structure is adopted, and the effective heat conduction area is reduced to 55mm under the condition of ensuring the supporting strength through the hollow design) ² (mean cross-sectional area of the support housing in the direction of heat flow, i.e. in the vertical direction in FIG. 1; this area is equal to the cross-sectional area of the support housing ring minus the area of the hollowed-out portion), the leakage power at about 0.5K at operating temperature<10 mu W/K) can effectively improve the on-off ratio of the superconducting thermal switch.

The foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited thereto, but it is to be understood that modifications and equivalents of some of the technical features described in the foregoing embodiments may be made by those skilled in the art, although the present invention has been described in detail with reference to the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A superconducting thermal switch, the superconducting thermal switch comprising: the device comprises a cold end polar plate (1), a hot end polar plate (2), a heat insulation supporting shell (3), a superconducting material core (4), a superconducting winding (5) and a magnetic core (6);

the cold end polar plate (1) and the hot end polar plate (2) are positioned at two ends of the superconducting thermal switch, and the superconducting material core (4) is positioned at the center of the superconducting thermal switch and is simultaneously kept in contact with the cold end polar plate (1) and the hot end polar plate (2);

the heat insulation supporting shell (3) is cylindrical, and a hollowed-out structure is arranged on the wall of the cylinder;

the superconducting material core (4) is arranged between the cold end polar plate (1) and the hot end polar plate (2), and the superconducting material core (4) keeps good thermal contact with contact terminals of the cold end polar plate (1) and the hot end polar plate (2); the superconducting material core (4), the cold end polar plate (1) and the hot end polar plate (2) together form a heat conduction path when the thermal switch is conducted;

the superconducting winding (5) is made of superconducting alloy wires and is arranged inside the heat-insulating supporting shell (3); the support structure winding support frame (7) of the superconducting winding (5) is in thermal connection with the hot end polar plate (2) through direct surface contact fixed by screws;

the magnetic core (6) is of a split type design and comprises an upper magnetic core and a lower magnetic core, wherein the upper magnetic core and the lower magnetic core are symmetrically arranged by taking the superconducting material core (4) as a center, so that the superconducting material core (4) is positioned on a center connecting line of the upper magnetic core and the lower magnetic core;

the diameter of the superconducting material core (4) is the same as the diameter of the contact terminal of the cold end polar plate (1) and the diameter of the contact terminal of the hot end polar plate (2), the upper magnetic core is sleeved on the outer surface of the contact terminal of the cold end polar plate (1), and the lower magnetic core is sleeved on the outer surface of the contact terminal of the hot end polar plate (2).

2. The superconducting thermal switch according to claim 1, wherein the heat insulation supporting shell (3) connects and fixes the cold end polar plate (1) and the hot end polar plate (2) into a whole, so as to provide structural support for the whole superconducting thermal switch, and simultaneously ensure thermal insulation between the cold end polar plate (1) and the hot end polar plate (2).

3. The superconducting thermal switch according to claim 2, wherein the cold-end plate (1) is constituted by a heat-conducting plane and a contact terminal, wherein the heat-conducting plane is a cylinder with a diameter of 30mm and a thickness of 3mm, and the contact terminal is a cylinder with a diameter of 10mm and a length of 9 mm.

4. A superconducting thermal switch according to claim 3, wherein the hot-side plate (2) is constituted by a heat-conducting plane of 30 a mm a cylinder of 3 a mm a thickness and by a contact terminal of 10 a mm a cylinder of 9 a mm a length.

5. The superconducting thermal switch according to claim 4, wherein the cold-side plate (1) and the hot-side plate (2) are both made of a material with high thermal conductivity.

6. The superconducting thermal switch according to claim 5, wherein the cold end polar plate (1) and the hot end polar plate (2) are made of high-purity copper with gold-plated surfaces, the purity of the high-purity copper is more than 99.99%, one end of the high-purity copper is a flat heat conduction plane for realizing efficient heat conduction with the outside, and the other end of the high-purity copper is a contact terminal for contacting with a superconducting material block.

7. The superconducting thermal switch according to claim 1, wherein the hollow structure has an area that is more than 30% of the surface area of the cylinder.

8. The superconducting thermal switch according to claim 1, wherein the hollowed-out structure comprises more than 50% of the surface area of the cylinder.

9. The superconducting thermal switch according to claim 1, wherein the hollowed-out structure comprises more than 80% of the surface area of the cylinder.

10. Superconducting thermal switch according to claim 1, characterized in that the thermally insulating support shell (3) is made of a material having a low thermal conductivity.

11. The superconducting thermal switch according to claim 10, wherein the insulating support shell (3) is made of a material selected from at least one of titanium alloy, stainless steel, nylon resin, the insulating support shell (3) having a cylindrical wall thickness <0.2 mm.

12. The superconducting thermal switch according to claim 11, wherein the insulating support case (3) is made of nylon resin, has a wall thickness of 1.5 and mm, and has a hollowed-out structure on a side surface.

13. The superconducting thermal switch according to claim 1, wherein the core (4) of superconducting material is made of high purity metallic tin, the switching between its superconducting state and normal state being controllable by a magnetic field having a strength of about 70mT at 0.1K.

14. The superconducting thermal switch according to claim 13, wherein the superconducting wire of the superconducting winding 5 is guaranteed to be below a superconducting critical transition temperature at an operating temperature of less than 0.5K to ensure that it is in a superconducting state.

15. The superconducting thermal switch according to claim 14, wherein a gap of more than 2mm is maintained between the superconducting winding (5) and the cold-end polar plates (1), and thermal isolation is achieved in a vacuum environment of operation, so as to prevent the cold-end polar plates (1) and the hot-end polar plates (2) at two ends from conducting heat through the superconducting winding (5).

16. The superconducting thermal switch according to claim 15, wherein thermal isolation between the upper and lower cores prevents conduction of heat from the cold side plate (1) and the hot side plate (2) through the cores (6) in the off state of the superconducting thermal switch.

17. The superconducting thermal switch according to claim 16, wherein the superconducting winding (5) is an NbTi superconducting wire winding having a wire diameter of 0.2 mm.

18. The superconducting thermal switch according to claim 17, wherein a magnetic field of 75mT strength is generated at the core 4 of superconducting material at a current density of 6A/m of the superconducting winding 5; the superconducting switch works in a low-temperature vacuum environment less than 0.5 and K, and at the temperature, the superconducting winding and the support frame thereof are well connected with the hot end polar plate, so that the winding is ensured to be in a superconducting state.

19. The superconducting thermal switch according to claim 18, wherein the diameter of the superconducting core material (4) of the superconducting thermal switch is 10 mm.

20. The superconducting thermal switch according to claim 19, wherein the superconducting core material (4) is a cylinder of diameter 10mm and length 10 mm.