JPH03105162A - Cryogenic freezer - Google Patents

Abstract

PURPOSE:To keep a high freezing capability for a long period of time by a method wherein a cold heat accumulation device has a spring mechanism in its inside for stably holding a cold heat accumulating material. CONSTITUTION:During operation of a freezer, a cold heat accumulation device 10 is moved up and down within a cylinder. Herium gas flows through the cold heat accumulation material 22 in both directions under a pressure difference between a high pressure and a low pressure, resulting in that the cold heat accumulation material 22 is severely oscillated. When the cold heat accumulation material 22 is severely oscillated due to unavoidable non-uniform particle diameter of the cold heat accumulating material 22, small particles enter the large particles and a changing volume of the cold heat accumulation material 22 is decreased. However, since the cold heat accumulation material 22 is always restricted to a lower temperature end by a resilient force of a disc spring 26, a pressor plate 25 and a metallic net 23, the cold heat accumulation material 22 is stably held irrespective of a severe flow of herium gas as well as vibration of the cold heat accumulator 10. Even if the cold heat accumulation material 22 is severely oscillated, the cold heat accumulation material 22 is kept stably, so that it is possible to avoid some disadvantages such as a reduction of freezing capability caused by a frictional heat generation between the particles of the cold heat accumulation material 22, a damage of the cold heat accumulation device 10 caused by an external flow of the cold heat accumulation material 22 and a solidification of relative fixing of the cold heat accumulation material 22.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to improvements in cryogenic refrigerators widely used for cooling superconducting magnets, cryopumps, and the like.

(Prior art) This is a small refrigerator that freezes to extremely low absolute temperatures of about 10 to 20 [K]. Gift McMahon (
(hereinafter abbreviated as GM) cycle, reverse Stirling cycle,
There are refrigerators that utilize principles such as the Solvay cycle, and are widely used for cooling semiconductor manufacturing equipment and magnetic diagnostic kits, as well as for cryopumps, which are high-vacuum pumps.

As an example, the basic structure of a cryogenic refrigerator based on the GM cycle will be explained using FIGS.

A gas cooler■ and an oil separator■ are installed on the discharge side of the compressor (1).
This machine is equipped with the following equipment and is connected to the GM type cold head (■) via the intake valve (■) with piping 0. GM type cold head ■ has cylinder 0, 1st stage regenerator ■, 1st stage gas seal 0, 2nd stage regenerator (10), 2nd stage gas seal (l1
), and a regenerator drive mechanism (l2). The first stage regenerator (8) is connected in series with the second regenerator (IO) through a connecting pin (13), and both are connected to the regenerator drive mechanism (i).
2) causes the cylinder 0 to reciprocate simultaneously between the top dead center and the bottom dead center at a constant cycle.

Gas seals 0 and (11) are provided in both the first and second stage regenerators (8) and (10), respectively.
(10) prevents the flow of refrigerant helium gas in the gap between cylinder 0, and the refrigerant helium gas is transferred to the regenerator ■,
The structure is such that the cold storage materials (14) and (15) that are placed inside the (LO) flow through them. Cold storage material (14), (is
), the first-stage regenerator (2) is usually made of a layered copper alloy wire mesh, and the second-stage regenerator (10) is usually filled with lead pellets. The GM type cold head (2) is equipped with an exhaust valve (16), a surge tank (17), etc. between the gas suction side of the compressor (2), and is connected to the gas intake side of the compressor (2) through a pipe 0.

The refrigerant that has been pressurized and heated by the compressor (1) is cooled by the gas cooler ■, and impurities such as oil mist mixed in the refrigerant are removed by the oil separator ■, and then passed from the intake valve ■ to the GM type cold head. ■Flow inwards. Helium gas, which does not liquefy even at extremely low temperatures, is commonly used as a refrigerant. Intake valve (4
), the opening/closing timing of the exhaust valve (16) and the regenerator (6),
The positional relationship of (10) within the cylinder ω is as shown in FIG.

That is, when the regenerator (10) is at the bottom dead center, the intake valve (4) opens and high pressure helium gas at room temperature flows into the space above the cylinder ω. At this time, the exhaust valve (16) remains closed. While the intake valve ■ is open, the regenerator ■, (
io) moves to the top dead center, the refrigerant helium gas exchanges heat with the cold storage material (■4) of the first stage regenerator (■4) that stores cold, and flows into the first stage expansion chamber (18) while being cooled. Next, it exchanges heat with the regenerator material (15) of the second stage regenerator (10), is further cooled to a low temperature, and flows into the second stage expansion chamber (19). At the same time as the regenerators (8) and (10) reach top dead center, the intake valve (■) closes and the exhaust valve (16) opens. Then the exhaust valve (1
6) is connected to the suction side of the compressor (1), which has low pressure, so the helium gas expands adiabatically and flows into the first and second stages.
Stage expansion chamber (18). Cold occurs in (19). The exhaust valve (16) is open until the regenerators (8) and (10) reach the bottom dead center, and the cooled helium gas in the second stage expansion chamber (19) is transferred to the second stage regenerator (10). cold storage material (l
5), the cold is stored in the cold storage material (l5), the temperature of the refrigerant rises, and it flows into the first stage expansion chamber (l8).

Similarly, the regenerator material (14) of the first stage regenerator (8) and helium gas exchange heat, and the temperature rises to room temperature, and the exhaust valve (
16), flows out of the GM type cold head ■, and returns to the suction side of the compressor (1). By repeating the above cycle, the first stage and second stage expansion chambers (18), (1
9) is cooled to a cryogenic temperature. The first stage expansion chamber (18) performs cooling to a liquid nitrogen temperature level of approximately 80 [K], and the second stage expansion chamber (19) performs cooling to a temperature of 20 [K] or less for cryopumps and superconducting magnets. This is the normal usage of cryogenic refrigerators when used for cooling. Refrigeration cycles such as the GM cycle, reverse Stirling cycle, and Solvay cycle are collectively called regenerative cycles (R
As is clear from the fact that they are called generative cycles, regenerators that store the cold heat of refrigerants play a very important role. The following three properties are required for the cold storage material to be filled into the cold storage device. That is,
(a) High heat capacity per unit volume at the temperature level used.

(b) High heat exchange efficiency with refrigerant gas and low gas ventilation resistance. (c) There is a large temperature difference between both ends of the cold storage material, so the thermal conductivity is low.

(a) is because the regenerator acts as a regenerative heat exchanger and therefore needs to have a much larger heat capacity than the refrigerant gas. Since the specific heat of ordinary metal materials generally decreases with temperature, it is necessary to use a material that has a large specific heat at the operating temperature level. Therefore, copper or a copper alloy such as brass or phosphor bronze is generally used for the first stage. Since the second stage is used in an extremely low temperature region, lead is used, which has a lower specific heat than copper alloy at room temperature.

In addition, in recent years, rare earth metals have been developed that have a higher specific heat than buttons in the cryogenic region, and such materials are also being used.

Although (b) is a mutually contradictory condition, it is a condition that must always be taken into consideration in a regenerator type heat exchanger. The first method was selected due to the ease of manufacturing due to the material of the cold storage material.
The stage has a structure in which a large amount of wire mesh cold storage material is laminated,
The second stage is generally filled with small spherical regenerator material. With this structure, (c)
This is intended to reduce the apparent thermal conductivity of the cryocooler, reduce the amount of heat that enters the cryogenic area, and improve the refrigeration capacity.

The structure of the second stage regenerator will be explained in more detail with reference to FIG. 5.9 A hole (20) for gas circulation is provided at one end of the container of the cylindrical regenerator (10). The opposite end is also provided with a hole (21) for gas flow.
The inside of the regenerator is densely filled with button balls (22). The diameter of the small balls (22) is approximately 0.1 to 0.2 mm, and lead is used with a uniform particle size. and gas flow holes (2
In order to prevent the small balls (22) from leaking out from the small balls (22), wire mesh (23) that is finer than the diameter of the small balls (22) is used.
) (e.g. 200 mesh copper alloy wire gauze) are placed at both ends.

(References above: “Cryoco” by G. Walker
olers”, Plenum Press (1983
), etc.) (Problems to be Solved by the Invention) When manufacturing such a regenerator, one end of the regenerator (10) shown in FIG. It is common to assemble the regenerator by pouring it in, then filling it with small lead balls (22), then laying a wire mesh (23), and then gluing the lid (24) to the regenerator (10). be. Methods for making small metal balls that serve as cold storage materials include dropping molten metal into oil and allowing it to settle and solidify, but metals with low melting points, such as lead, cannot be made into relatively perfect spheres. Similar grains can be easily produced. These particles are sieved to collect small balls of uniform particle size and used as a cold storage material.However, O. Even if small spheres of about 1 mm size can be separated by sieving, very fine mesh sieves must be used in several stages, which increases the cost of manufacturing and reduces yield. Due to physical limitations, it is difficult to obtain particles of uniform particle size. For example, 0.1mm"0.
Lead particles in the range of 2a+w will be used as the cold storage material.

By the way, as mentioned earlier when explaining the operation of a cryogenic refrigerator, while the refrigerator is operating, the regenerator moves up and down inside the cylinder, and due to the pressure difference between high and low pressure, helium gas is absorbed into the regenerator material. As it circulates in both directions, the cold storage material is shaken violently. If the regenerator material is a perfect sphere, has exactly the same diameter, and is packed close-packed inside the regenerator, no matter how violently the gas flows and the regenerator is shaken, the regenerator material will remain intact. Since it is firmly fixed, no problems will occur. However, in reality, as mentioned earlier, it is impossible to make a regenerator material with a completely uniform spherical diameter, and during long periods of shaking, small particles may get stuck between the large particles. As a result, a space gradually forms inside the regenerator, which causes the regenerator material to shake even more rapidly. As a result, there is a problem in that the refrigerating capacity is significantly reduced due to loss due to frictional heat generation between particles. In addition, after being shaken for a long period of time, there is a risk that the wire mesh for preventing leakage may be damaged and an accident may occur where the cold storage material leaks out of the cold storage device. In this case, foreign matter will get mixed in between the regenerator and the cylinder, resulting in fatal damage to the cryogenic refrigeration unit, such as damage to the regenerator drive mechanism due to galling. In addition, since lead is a soft metal, as it is violently shaken and repeatedly collided with each other, it sticks to each other inside the regenerator and solidifies, obstructing gas flow and significantly increasing the apparent thermal conductivity. Accidents may also occur where the material no longer functions as a material. Recently, attempts have been made to use rare earth metals as high-performance cold storage materials in place of lead. Even when this material is used as a cold storage material, rare earth intermetallic compounds are generally hard;
Because it is difficult to manufacture a perfect sphere, the above-mentioned problems arise, almost the same as in the case of lead.

In view of these points, the cryogenic refrigerator of the present invention is equipped with a regenerator that can stably hold a regenerator material for a long period of time even if the particle size of the regenerator material is somewhat uneven. The purpose of the present invention is to provide a highly reliable cryogenic refrigerator that can maintain its refrigerating capacity.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the cryogenic refrigerator of the present invention has the following features:
The present invention is characterized in that it includes a regenerator having a spring mechanism that holds a regenerator material.

(Function) In the cryogenic refrigerator of the present invention, even if the filling volume decreases during long-term shaking because the particle size of the regenerator material in the regenerator is somewhat uneven or not a perfect sphere, the spring mechanism Because the cold storage material is pressed down and held stably, there is no generation of frictional heat due to friction between the cold storage material particles. Able to maintain high refrigeration capacity.

In addition, by being held stably by the spring mechanism, it is possible to prevent accidents such as the cold storage material leaking out of the cold storage device or small balls of the cold storage material sticking to each other and solidifying, thereby improving long-term reliability. We can provide high-quality refrigerators.

(Example) FIG. 1 shows an example of the present invention. A lid (24) with gas flow holes (20) is provided on the high temperature end side of the container of the regenerator (10).
), and small balls (22), which are cold storage materials, are densely packed inside. A disc spring (26) is disposed between the lid (24) and the cold storage material (22) via a wire mesh (23) for preventing the cold storage material from flowing out and a holding plate (25) made of porous material. The regenerator material (22) is pressed against the low temperature end side of the regenerator (10) by the elastic force of the disc spring (26). Cool storage device (l
A wire mesh (23) for preventing cold storage material from flowing out and gas flow holes (21) are provided on the low-temperature end side of O), which has the same structure as the conventional device.

Next, the operation of this embodiment will be described.

During operation of the refrigerator, the regenerator (10) moves up and down within the cylinder, and the helium gas flows in both directions through the regenerator (22) due to the pressure difference between high and low pressures.
22) is shaken violently. Unavoidable cold storage material (22
) Due to the non-uniformity of the particle size, while being shaken for a long time, small particles get stuck between the large particles, and the filling volume of the regenerator material (22) gradually decreases. However, the elastic force of the disc spring (26) and the presser plate (25). Wire mesh (
23), the regenerator material (22) is always held at the low temperature end side, so the regenerator material (22) is stably held despite vibrations of the regenerator (10) and violent outflow of helium gas.

In this way, even if the cold storage material (22) is shaken violently,
According to this embodiment, since the structure is such that the cold storage material (22) is stably held, the refrigerating capacity decreases due to frictional heat generation between the cold storage material (22) particles, and the cold storage material (22) (10) It is possible to avoid problems such as damage caused by leakage and the cold storage materials (22) sticking together and solidifying.

FIG. 2 shows another embodiment of the invention. As a spring mechanism, a spiral spring (27) is used instead of a disc spring. In this case as well, the same action and effect as in the above embodiment can be obtained. In addition to the above, coil springs and plate springs can also be used as spring mechanisms. It is also possible to use a spring or the like.

〔Effect of the invention〕

As described above, in the cryogenic refrigerator according to the present invention, the reduction in the filling volume of the cold storage material caused by the unavoidable non-uniformity of the particle size of the cold storage material or the non-perfect spherical shape,
The spring mechanism holds the regenerator material stably inside the regenerator,
It is possible to provide a highly reliable cryogenic refrigerator that can maintain high refrigerating capacity over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a regenerator structure of a cryogenic refrigerator according to an embodiment of the present invention, and FIG. 2 is a diagram showing a regenerator structure of a cryogenic refrigerator according to another embodiment of the present invention. , FIG. 3 is a diagram showing the structure of a cryogenic refrigerator using the GM cycle, FIG. 4 is a diagram showing the operation of the device shown in FIG. 3, and FIG. 5 is a diagram showing the structure of a regenerator of a conventional device. 1... Compressor 2... Gas cooler 3.
・・Oil separator 4・Intake valve 5・GM type cold head

Claims (1)

[Claims] A cryogenic refrigerator equipped with a regenerator filled with a regenerator as a means for achieving an extremely low temperature, characterized in that the regenerator has a spring mechanism that stably holds the regenerator filled inside. Machine.