JPH068708B2 - Small cryogenic refrigerator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a small cryogenic refrigerating apparatus using magnetic refrigeration applicable to a cryopump, a He liquefying apparatus, and the like.

[Prior Art] In a conventional small cryogenic refrigeration system, a piston-shaped displacer is slidably fitted in a cylinder, and the displacer is reciprocated to move the displacer and the low temperature end of the cylinder. It is common to increase or decrease the volume of the expansion chamber formed between them and expand and contract the expansion chamber to sequentially expand the gas to carry out a predetermined refrigeration cycle. 20K
-15K is the temperature limit for pumping heat. Therefore, in order to realize the cryogenic temperature of liquid helium temperature (4.2K), it is necessary to combine it with a refrigerating means capable of pumping heat from 4K to 20K. Is.

As one of the refrigerating means to be combined with the small refrigerator of such a gas cycle, the use of a magnetic refrigerator using a magnetic refrigerating material (a substance whose entropy change characteristics differ depending on the strength of the magnetic field at extremely low temperatures) was devised. There is. That is,
In this magnetic refrigerator, when the magnetic refrigerating material is subjected to a cycle of repeating demagnetization-excitation, the temperature drops due to adiabatic demagnetization during demagnetization, and heat is absorbed as the entropy increases,
During excitation, it is possible to exert the effect of a heat pump that radiates heat as the temperature rises due to adiabatic excitation and entropy decreases, and recent research has demonstrated that it can be used for pumping heat from 4K to 20K. There is.

Therefore, the cryogenic refrigerating device currently proposed as a device utilizing this magnetic refrigerator is configured such that the small refrigerator of the gas cycle as described above and the magnetic refrigerator are each configured independently, and both are appropriately arranged. By connecting with a thermal anchor, heat is drawn from the magnetic refrigerator to room temperature. Specifically, the cold head of the gas refrigerator and the magnetic refrigerating material of the magnetic refrigerator are thermally coupled via heat conduction of metal and heat transfer of He gas. However, in the case where the two are separately configured and combined in this way, the mechanism is inevitably complicated, and not only is the size of the entire apparatus increased, but also the heat transfer section from outside However, there is a problem in that the refrigerating capacity is greatly reduced due to the heat transfer loss because the heat intrusion is unavoidable.

[Problems to be Solved by the Invention] The present invention has been made by focusing on the above-mentioned problems, and it is possible to combine a gas refrigerator and a magnetic refrigerator with H
e As a refrigerating device capable of realizing an extremely low temperature equal to or lower than the liquefaction temperature, a refrigerating device capable of simultaneously solving the above-mentioned problems, that is, downsizing of the entire device can be achieved, and a gas refrigerator and a magnetic refrigerator can be combined. The heat transfer mechanism between is simply configured,
Moreover, it is an object of the present invention to newly provide a cryogenic refrigeration system which has a small heat transfer loss and can be expected to improve the refrigeration performance.

[Means for Solving the Problems] In order to achieve such an object, the present invention forms the outer wall of the final stage expansion chamber on the cryogenic side with a magnetic refrigerating material and the inner surface of the magnetic refrigerating material. And a reciprocating refrigerator configured to bring the end surface of the piston member that expands and contracts the expansion chamber into contact with the inner surface of the magnetic refrigerating material for each exhaust step of the expansion chamber, and a magnetic field to the magnetic refrigerating material. And a magnetic field varying means for variably applying the magnetic refrigerating material to the magnetic field varying means when the piston member approaches, and when the piston member separates. A feature is that a timing control unit for degaussing is provided.

[Operation] With such a configuration, the magnetic refrigerating material forming the outer wall of the final stage expansion chamber serves as the piston member regardless of the model of the reciprocating gas refrigerator and the type of refrigerating cycle operated therein. A heat cycle similar to the reverse Carnot cycle is carried out using the contact and separation of the heat switch as a heat switch to absorb heat from the cryogenic region around the magnetic refrigeration material and radiate it directly to the piston member of the gas refrigerator. That is, since the magnetic refrigerating material that also serves as the outer wall of the expansion chamber is excited by the magnetic field varying means controlled by the timing control section when the piston member approaches, at this time, it is first adiabatically excited to raise the temperature. Then, when the piston member comes into contact with the inner surface of the piston member and both of them come into contact with each other, the heat is conducted to the piston member so as to be isothermally excited. Also, when the piston member separates, it is demagnetized by the magnetic field varying means controlled by the timing control unit, so at this time, the magnetic refrigeration material is first adiabatically demagnetized and the temperature goes down, and then the temperature becomes extremely low. When it reaches the temperature of the region, it takes heat from its surroundings and is demagnetized isothermally. The heat pumped out in such a cycle is pumped to the room temperature side in the refrigeration cycle of the reciprocating gas refrigerator.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are schematic diagrams of a cryogenic device according to the present invention, in which a reciprocating gas refrigerator 1 is arranged on the upper normal temperature side and a magnetic refrigerator 2 is arranged on the lower cryogenic side. It will be installed.

The reciprocating gas refrigerator 1 is a movable shell type that has recently been developed and proposed by the present inventor, and a two-stage type of this type is shown in the figure. Therefore, first, the structure of the gas refrigerator 1 will be briefly described.
The internal regenerators 3b and 4b, the cylindrical movable shell 5 that surrounds the regenerators 3b and 4b and is slidable in the axial direction, and the shell 5 is surrounded by the external regenerators 3a and 4a. And a cylindrical casing 6 that is disposed therein, and corresponds to a piston space member in this case, which is a volume space formed between the movable shell 5 and a member facing inside and outside thereof at the lower end of each step. Expansion chambers 7b, 7a, 8b, 8a are formed which expand and contract alternately inside and outside by the reciprocating movement of the movable shell 5 in the vertical direction. More specifically, first, the internal regenerator 3b of the first stage is connected to the base 9 at the room temperature end by being connected by a communication pipe 10 which also functions as a member for flowing gas in and out of the movable shell 5. The second internal regenerator 4b is supported by the internal regenerator 3b of the first stage and positioned and fixed. The external regenerators 3a, 4a of the first stage and the second stage are fixed to the casing 6, respectively, and positioned and fixed together with the casing 6 supported by the base 9. Needless to say, each of the above-mentioned regenerators has gas permeability and is for heat exchange with the circulating gas. Further, the movable shell 5 has a lid portion at the upper end on the base 9 side, and the communicating pipe 10 is provided from the lid portion.
Through the chamber 11b. 11a is formed. Inside the movable shell 5, gas can be sucked and discharged from the inflow / outflow port 12 provided in the base 9 through the communication pipe 10 into the internal regenerator 3b of the first stage (in the chamber 11b). It is also filled with gas), and the movable shell 5
Gas can be sucked and discharged from the outside of the chamber through an inflow / outflow port 13 provided in the base 9 through a chamber 11a.

Then, in the movable shell type gas refrigerator having such a configuration, it is made of, for example, GGG (gadolinium gallium garnet) in order to integrally configure the magnetic refrigerator 2 on the cold head side together with the magnetic field varying means described later. A magnetic refrigeration material 18 is provided. That is, this magnetic refrigerating material 18 is provided so as to form an outer wall at the lower end of the expansion chamber 8a at the final stage, which is on the cryogenic side of the gas refrigerator, and in the case of the illustrated example, the lower end is open. The thick magnetic refrigeration material 1 is placed in the opening of the casing 6
8 is fitted to seal the opening airtightly,
The inner surface is exposed to the final stage expansion chamber 8a, and the outer surface is exposed to the outer cryogenic atmosphere. Further, at the lower end of the movable shell 5 facing the inner surface of the final stage expansion chamber 8a made of the magnetic refrigeration material 18, this portion is made of, for example, thick heat storage made of Pb in order to increase the heat storage capacity of the shell lower end portion 19. It is made of a member. Specifically, in the illustrated example, a separate heat storage member 19 is fitted into the opening of the movable shell 5 whose lower end is open, and the opening is hermetically closed. Although the heat storage member 19 should not be breathable by itself, it should be possible to promote heat exchange with the gas in the inner and outer expansion chambers 8b and 8a as much as possible, for example, by forming a gas entry hole. Is preferred. As described above, the magnetic refrigerating material 18 and the heat storage member 19 are arranged with the final stage expansion chamber 8a interposed therebetween, and the expansion chambers 8a and 7a outside the movable shell 5 are exhausted, that is, the shell lower end. Each time the portion 19 descends and approaches the magnetic refrigerating material 18, as shown in FIG. 1, the reciprocating motion of the gas refrigerator 1 is performed so that the two come into direct contact with each other at the top dead center and are brought into surface contact with each other. I am adjusting.

The drive means of the movable shell refrigerator 1 having the above-described structure will be briefly described. The inflow / outflow ports 12 and 13 provided in the base 9 on the room temperature end side are respectively connected to the discharge port and the intake port of the compressor 14. Supply system passage 15 and exhaust system passage 1
6 and 6 are switchably connected via a timing valve 17, and by switching the valve 17, intake and exhaust necessary for the expansion chambers 7b, 8b, 7a, 8a inside and outside the movable shell 5 are alternately performed, and at the same time, the movable shell is moved. 5 is automatically reciprocated by the suction gas pressure inside and outside thereof. That is, when the high pressure gas is introduced into the movable shell 5, the movable shell 5 is urged downward due to the difference in pressure receiving area between the low temperature side and the normal temperature side (specifically, the cross-section integral of the communication pipe 10 in the chamber 11b). On the contrary, when the high-pressure gas is introduced to the outside, it is also urged upward due to the difference in the pressure receiving area between the low temperature side and the normal temperature side (specifically, the cross-section integral of the communication pipe 10 in the chamber 11a). -ing Then, with such one reciprocating movement of the movable shell 5, the inner expansion chambers 7b and 8b and the outer expansion chambers 7a and 8a are expanded and contracted by shifting the half-cycle phase.

Next, the structure of the magnetic refrigerator 2 will be described. In the magnetic refrigerator 2, the magnetic refrigerator 18 is provided at the lower end of the gas refrigerator 1 also as the outer wall of the final expansion chamber 8a, and the magnetic refrigerator 18. The magnetic field varying means 20 is provided around the material 18. In this case, the magnetic field changing means 20
A superconducting magnet 21 is internally provided in an annular movable case 20a having a liquid reservoir 20b for storing liquefied He and the like, and the superconducting magnet 21 is integrated with the movable case 20a in the gas freezing chamber 1. The magnetic refrigeration material 18 can be excited or demagnetized at a predetermined timing by reciprocating up and down in synchronization with the switching of the timing valve 17. That is, the timing valve 17 which gives the timing for switching the driving direction to the driving mechanism (not shown) that controls the vertical reciprocating movement constitutes the timing control section of the present invention. That is, when approaching the magnetic refrigerating material 18 of the movable shell 5, the superconducting magnet 21 is moved up to bring it close to the magnetic refrigerating material 18 to excite the magnetic refrigerating material 18 (first
(State shown in the figure), and conversely, the movable shell 5 is the magnetic refrigeration material 1
When separating from 8, the superconducting magnet 21 is lowered to move it away from the magnetic refrigerating material 18 so that the magnetic refrigerating material 18 is demagnetized (state of FIG. 2). Then, at the time of this descending, the superconducting magnet 21 has its case 20a.
Each of them is immersed in the liquefied gas 23 stored in the lower dewar 22, and at this time, LHe or the like is successively replenished to the liquid reservoir 20b. In FIG. 1, 24 is a gas liquefaction chamber, and 25 is a vacuum chamber surrounding the low temperature side of the magnetic refrigerator 2 and the gas refrigerator 1.

The case where the operation of the refrigerating apparatus having the above-described configuration is used for He liquefaction will be described as an example.

When the volume of the outer expansion chambers 7a, 8a of each stage is the maximum and the volume of the inner expansion chambers 7b, 8b is the minimum (the state of FIG. 2), the timing valve 17 is set to the B position to supply the inside of the movable shell 5. When the outside of the system passage 15 is communicated with the exhaust system passage 16, high pressure gas is introduced into the inside expansion chambers 7b and 8b while precooling through the regenerators 3b and 4b, while the outside expansion chambers 7a and 8a are outside. From this, the gas cooled by adiabatic expansion is discharged while cooling the regenerators 3a, 4a. At the same time, however, the movable shell 5 descends due to the imbalance of the gas pressure acting on the movable shell 5 as described above. Finally, the shell lower end portion 19 comes into contact with the inner surface of the magnetic refrigerating material 18 in the final stage expansion chamber 8a.
On the other hand, at the same time as the switching of the timing valve 17, the superconducting magnet 21 is moved up from the lower liquid He to a close position around the magnetic refrigerating material 18 so that the magnetic refrigerating material 18 has a magnetic field strength B = 0. It will excite up to strength B = B ₁ . Then, at this time, as shown by I-II in FIG. 3, the magnetic refrigerating material 18 first rises in temperature by adiabatic excitation (isentropic change without heat exchange with the outside), and then the shell lower end portion. When 19 abuts on the inner surface of the magnetic refrigerating material 18 and both come into surface contact, the magnetic refrigerating material 18 is deprived of heat by the shell lower end portion 19 by contact heat conduction, so that if the temperature of the shell lower end portion 19 is 15K, The refrigerating material 18 is maintained at this temperature, and is II-II in FIG.
As indicated by I, it will be excited isothermally.

Next, the lower end portion 19 of the shell is in contact with the inner surface of the magnetic refrigerating material 18 as shown in FIG. 1, that is, the outer expansion chambers 7a and 8a of each stage have the smallest volume and the inner expansion chambers 7b and 8b have the largest volume. Therefore, when the timing valve 17 is set to the A position so that the outside of the movable shell 5 communicates with the air supply system passage 15 and the inside of the movable shell 5 communicates with the exhaust system passage 16, the gas cooled by adiabatic expansion from the inside expansion chambers 7b, 8b. Is discharged while cooling the regenerators 3b and 4b, while high-pressure gas is introduced from the outside expansion chambers 7a and 8a while precooling through the regenerators 3a and 4a. Movable shell 5
Of the movable shell 5 due to the imbalance of the gas pressure acting on the
Then, as shown in FIG. 2, the lower end 19 of the shell finally reaches the bottom dead center position farthest from the inner surface of the magnetic refrigerating material 18 in the final stage expansion chamber 8a as shown in FIG. on the other hand,
Simultaneously with the switching of the timing valve 17, the superconducting magnet 21 is now lowered away from around the magnetic refrigerating material 18 and immersed in the liquefied He 23 below, so that the magnetic refrigerating material 18 is removed. Magnetic field strength B =
The demagnetization will be from B ₁ to B = 0. Then, at this time, as shown by III-IV in FIG. 3, the magnetic refrigerating material 18 first lowers its temperature by adiabatic demagnetization (isentropic change with no heat exchange with the outside), and then the temperature is changed to LHe. When the temperature drops to 4.2K, the magnetic refrigeration material 1
8 draws heat from the He gas in the surrounding gas liquefaction chamber 24 to liquefy it and is demagnetized isothermally as shown by IV-I in FIG.

Therefore, according to the above cycle, the magnetic refrigeration material 18
Performs a heat cycle similar to the reverse Carnot cycle and plays a role of a heat pump for pumping heat from the gas liquefaction chamber 24 (4.2K) on the cryogenic side to the cold head (15K) of the gas refrigerator 1 ( Endothermic with IV-I, II-III
To radiate heat). Moreover, the transfer of heat from the magnetic refrigerating material 18 to the gas refrigerator 1 realizes an effective heat switch by the difference between the contact heat conduction between the magnetic refrigerating material 18 and the lower end of the shell and the heat transfer when they are separated. Will be done efficiently. Then, the heat pumped up to the cold head side through the heat conduction from the temperature level of 4.2K to the shell lower end portion 19 at the temperature level of 15K by the magnetic refrigerating material 18 in this way is refrigerated in the gas refrigerator 1. It will be pumped to the room temperature side by the cycle. The gas refrigerator 1 of the movable shell type is not limited to the Gifford-McMahon cycle as described in the operation description, but may be another refrigeration cycle such as a solve cycle.

If it is a refrigerating device having such a configuration and action,
The following effects can be obtained. First of all,
Compared to the conventional structure in which a gas refrigerator and a magnetic refrigerator are independently configured and are thermally connected via these heat transfer members, both are organically integrated and configured. Therefore, it is possible to realize a very small cryogenic refrigerating apparatus having a refrigerating capacity from the LHe temperature (4.2 K) or so, which has not been heretofore available. Secondly, as described above, this does not require a separate heat transfer member, and heats and separates the magnetic refrigerating material that forms the outer wall of the final expansion chamber of the gas refrigerator from the lower end of the shell. Since heat is directly transmitted to the cold head side of the gas refrigerator as a switch, the mechanism is not complicated due to the thermal connection as in the conventional system, and at the same time heat enters from the outside to the heat transfer section. Since the risk of heat loss is also eliminated, the reduction in refrigeration efficiency due to heat transfer loss can be minimized.

Although one embodiment has been described above, the small cryogenic refrigeration system of the present invention is not limited to this, and can be modified into various modes for implementation. To illustrate this, first, the magnetic refrigerating material used in the present invention is not necessarily limited to the above GGG, and in short, it can be widely used as long as it is a substance whose entropy change characteristic greatly fluctuates depending on the strength of the magnetic field at cryogenic temperature. Expected to be available.

Further, in the embodiment, as the magnetic variable means, the superconducting magnet is moved with respect to the magnetic refrigeration material at the fixed position to change the magnetic field strength of the magnetic refrigeration material. Alternatively, the coil current of the electromagnet disposed in the above may be turned on / off to excite and demagnetize. In this case, the timing control unit may be any device that measures the timing of the ON-OFF switch.
For example, the timing valve 17 can be used.

Also, regarding the type of the gas refrigerator used in the present invention, basically, it is considered that the reciprocating type can be similarly implemented. That is, it is not necessarily limited to the case of combining with the movable shell type. However, particularly in the case of being combined with the movable shell type gas refrigerator as in the embodiment, the utility value of the present invention can be further enhanced for the following reasons. That is, in comparison with the type that reciprocates the displacer which has a conventional general regenerator integrally in this new type, the inner and outer expansion chambers each perform one cycle in one reciprocating movement of the movable shell, and substantially Not only has the feature of doubling the refrigeration capacity, but the movable shell with a small inertial mass is reciprocated, so even if the internal space is filled with a regenerator and the volume is maximized, problems such as vibration will occur. Therefore, the most compact gas refrigerating machine of the same performance can be provided. In other words, this is very convenient for maximizing miniaturization in combination with the magnetic refrigerator.

It is needless to say that the movable shell type is not limited to the two-stage type as in the case of the embodiment, and the number of stages can be increased or decreased as necessary. Further, in the case of the embodiment, the constituent material of the shell lower end portion forming the end surface of the piston member that abuts against the magnetic refrigerating material is such that the contact surface side with the magnetic refrigerating material is made of a material having good thermal conductivity and light weight. The composite material may be used, or a fin may be provided at a portion in contact with the expansion gas in order to promote heat exchange with the expansion gas.

EFFECTS OF THE INVENTION Since the present invention is provided with the above-mentioned configuration, it can be particularly compactly configured as a small cryogenic refrigeration apparatus used for refrigeration at a liquid helium temperature, and It is possible to provide a product having a simple structure and a high refrigerating capacity in which the efficiency does not decrease due to heat transfer loss from the magnetic refrigerating material.

[Brief description of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a cross-sectional view showing a schematic configuration of a refrigerating apparatus according to the present invention, and FIG. 2 is the same when its movable shell is at a position different from that of FIG. FIG. 3 is a partial cross-sectional view, and FIG. 3 is a temperature-entropy diagram showing a heat cycle of this refrigeration system. DESCRIPTION OF SYMBOLS 1 ... Gas refrigerator 2 ... Magnetic refrigerator 3a, 4a ... External regenerator 3b, 4b ... Internal regenerator 5 ... Movable shell (piston member) 6 ... Casing 7a , 8a ... outer expansion chamber (8a ... final expansion chamber) 7b, 8b ... inner expansion chamber 9 ... base 10 ... communication pipe 12, 13 ... inflow / outflow port 15 ...・ Supply system path 16 ・ ・ ・ Exhaust system path 17 ・ ・ ・ Timing control unit (timing valve) 18 ・ ・ ・ Magnetic refrigerating material 19 ・ ・ ・ Shell lower end (Heat storage member) 21 ・ ・ ・ Superconducting magnet (Variable magnetic field) means)

Claims (1)

[Claims] 1. An outer wall of a final stage expansion chamber on the cryogenic side is formed of a magnetic refrigerating material, and an end surface of a piston member facing the inner surface of the magnetic refrigerating material to expand and contract the expansion chamber is exhausted from the expansion chamber. A reciprocating gas refrigerator configured to be brought into contact with the inner surface of the magnetic refrigerating material in each step, and magnetic field varying means for variably applying a magnetic field to the magnetic refrigerating material, A small cryogenic temperature characterized in that the magnetic field varying means is provided with a timing control unit for exciting the magnetic refrigeration material when the piston member approaches and demagnetizing the magnetic refrigeration material when the piston member separates. Refrigeration equipment.