JPH02302563A - Ultra-cryo freezer - Google Patents

Abstract

PURPOSE:To reduce a minimum temperature of a freezer and realize an increased freezing power at a low temperature by a method wherein a temperature sensor for use in sensing a temperature at the lower temperature part is provided and a controlling means for use in controlling, basing upon the detected temperature change, an operating frequency of a displacer of the freezer is provided. CONSTITUTION:A temperature sensor 41, a controller 42 and an inverter are provided in a GM freezer, for example. The temperature sensor 41 is arranged near a second stage 17 acting as a low temperature part to detect a temperature at this location and then its detected signal is sent to a controller (a controlling means) 42. The controller 42 may control the number of revolution of a motor 13 through the inverter 43 arranged at an intermediate part between a power supply 44 and a motor 13 in response to a variation of temperature. Accordingly, an operating frequency of the displacer acting as a refrigerant compressing member for the freezer cooperating with the motor. As the operating frequency is delayed, the minimum temperature is decreased and an amount of freezing at a low temperature is high. However, as the temperature is increased, the frequency is delayed and then a freezing amount is low. Accordingly, the operating frequency at each of the temperature levels is varied to cause the temperature to be decreased to a low value and thus it is possible to realize a freezer having a high freezing capability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a cryogenic refrigerator, and particularly to a regenerator refrigerator.

(Prior art) Among cryogenic refrigerators, there are various types of regenerator refrigerators with regenerators, such as Gifford-McMahon (GM) refrigerators and Stalin refrigerators, which are used for cooling superconducting magnets and infrared sensors. or as a cold IA source for cryopumps. Among these, G.M.
Figure 4 shows the configuration for each type of refrigeration. This GM refrigerator consists of a cold head 1 and a refrigerant gas guide/discharge system 2. A displacer 12, which is installed in the cold head 1 and operates at two constant speeds, is connected to the refrigerant gas guide/discharge system 2. This is a refrigerator that repeatedly expands and cools refrigerant gas in conjunction with each other to reach extremely low temperatures.

That is, the cold head 1 includes a closed cylinder 11, a displacer 12 housed in the cylinder so as to be able to reciprocate, and a motor 13 that is disposed in a room communicating with the cylinder 11 and provides the displacer 12 with the power necessary for the reciprocating motion. It is made up of.

The cylinder 11 includes a large-diameter first cylinder 14 and a small-diameter second cylinder 15 coaxially connected to the first cylinder 14.
It is made up of. Then, the first cylinder 14 and the second cylinder
The boundary wall portion with the cylinder 15 constitutes a first stage 16 as a cooling surface, and the tip wall portion of the cylinder 15 constitutes a second stage 17 having a lower temperature than the first stage 16.

The displacer 12 includes a first displacer 18 that reciprocates within the first cylinder 14 and a second displacer 19 that reciprocates within the second cylinder 15. The first displacer 18 and the second displacer 19 are
They are connected in the axial direction by a connecting member 20. A fluid passage 21 extending in the axial direction is formed inside the first displacer 18 to constitute a first regenerator 35.
Inside the regenerator 35 is a regenerator material 22 made of copper mesh or the like.
is accommodated. Similarly, a fluid passage 23 extending in the axial direction is also formed inside the second displacer 19, and constitutes a second regenerator 36. The second regenerator 36 houses a regenerator material 24 made of balls or powder of lead, other metals, intermetallic compounds, or the like. Seal mechanisms 25 are provided between the outer circumferential surface of the first displacer 18 and the inner circumferential surface of the first cylinder 14 and between the outer circumferential surface of the second displacer 19 and the inner circumferential surface of the second cylinder 15, respectively. ．．
26 is installed.

The upper end of the first disk brainer 18 in the figure is connected to a connecting rod 27.
, is connected to the rotating shaft of the motor 13 via a Scotch choke or crankshaft 28.

Therefore, when the rotating shaft of the motor 13 rotates, the displacer 12 reciprocates in synchronization with this rotation as shown by the solid line arrow 29 in the figure.

A refrigerant gas inlet 30 is provided at the upper side wall of the first cylinder 14.
and a discharge port 31 are provided, and these inlet port 30 and discharge port 31 are connected to the refrigerant gas introduction and discharge system 2.

The refrigerant gas introduction and discharge system 2 constitutes a helium gas circulation system via the cylinder 11, and the discharge port 31 is connected to the low pressure valve 3.
2. Inlet 30 via compressor 33 and high pressure valve 34
It is connected to. Also, this refrigerant gas introduction and discharge system 2 compresses low pressure (approximately 5 atm) helium gas to high pressure (approximately 18 atm) with a compressor 33 and supplies it to the cylinder 1.
1. The opening and closing of the low-pressure valve 32 and the high-pressure valve 34 are controlled according to the relationship described later in relation to the reciprocating movement of the displacer 12.

A brief explanation of the operation of the refrigerator configured as described above is as follows. In this refrigerator, the first stage 16 and the second stage 17 are the parts where cold occurs, that is, the parts that serve as cooling surfaces.

They cool down to 1 in 30 and 8 degrees Celsius, respectively, in the absence of a heat load. Therefore, there is a temperature gradient from room temperature (300K) to 30K between the upper and lower ends of the first regenerator 35, and a temperature gradient from 30K to 8K between the upper and lower ends of the second regenerator 36 in the figure. .

However, this temperature changes depending on the heat load of each stage, and normally the temperature ranges from 30 to 80 in the first stage 16.
So it's about 8-20.

When the motor 13 starts rotating, the displacer 12 reciprocates between the dead center and the bottom dead center. When the displacer 12 is at the bottom dead center, the high pressure valve 34 opens and high pressure helium gas flows into the cold head 1. Next, the displacer 12 moves to top dead center. As described above, seals are provided between the outer circumferential surface of the first displacer 18 and the inner circumferential surface of the first cylinder 14 and between the outer circumferential surface of the second displacer 19 and the inner circumferential surface of the second cylinder 15, respectively. Mechanism 25.
26 is installed. For this reason, the distributor 12
When the gas heads toward the top dead center, the high-pressure helium gas passes through the first regenerator 35 and the second regenerator 36 and enters the first regenerator formed between the first displacer 18 and the second displacer 19. A second expansion chamber 40 formed between the expansion chambers 3 and 9 and the second displacer 19 and the tip wall of the second cylinder 15
flows to. Along with this flow, the high-pressure helium is cooled by the cold storage material 22, 24, and eventually the high-pressure helium gas that has flowed into the first-stage expansion chamber 39 is reduced to about 30%.
The high pressure helium gas that has flowed into the expansion chamber 40 is cooled to about 80 ℃. Here, the high pressure valve 34 is closed and the low pressure valve 32
opens. When the low pressure valve 32 listens in this way, the first expansion chamber 3
High-pressure helium gas within the chamber and the second expansion chamber 40 expands to generate cold. Due to this cold, the first stage 1
6 and the second stage 17 are cooled. Then, the displacer 12 moves to the bottom dead center again, and along with this, the helium gas in the first expansion chamber 39 and the second expansion chamber 40 is removed. 8 Helium gas is stored in a regenerator 35.3
6, it is warmed by the cold storage materials 22 and 24, reaches room temperature, and is discharged through the discharge port 31. Hereinafter, the refrigeration operation is performed by repeating the amount shown in (a) above.

In addition, in these types of refrigeration, the displacer operating frequency during operation is always constant, and the lowest temperature produced by the refrigerator is about 8.

In addition, the number of units that can be expected to have good refrigerating capacity as a refrigerator was about 10 or more. This is because the heat capacity of the regenerator material 24 used in the second regenerator 36 decreases as the temperature decreases, so the ability to store heat declines and the heat exchange efficiency as a regenerator decreases significantly.

On the other hand, in order to lower the minimum temperature and improve the refrigerating capacity at low temperatures, a material such as a magnetic material with a high specific heat may be used for the cold storage material 24 in the second refrigerator 36, or the second expansion stage may be further multistaged. However, high refrigerating capacity has not been achieved at temperatures below 10%.

(Problem to be solved by the invention) -As mentioned above, in the conventional crystal cooling type low temperature refrigerator,
The operating frequency of the displacer remains constant regardless of the temperature level, and no improvement in refrigerating capacity at extremely low temperatures could be expected.

Therefore, the present invention is a display! The purpose is to provide a cryogenic refrigerator with increased cooling capacity and a low minimum temperature by changing the operating frequency of the dog depending on the temperature level.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the present invention generates cold by cooling compressed refrigerant gas using a regenerator and then expanding it in a low temperature section. In the cryogenic refrigerator that
A temperature sensor is provided to detect the temperature of the low-temperature section, and a control means is provided to control the operating frequency of the displacer of the refrigerator based on the detected temperature change so as to improve the refrigerating capacity.

(Function) The temperature sensor detects temperature changes in the low temperature section, and controls the operating frequency of the compression member of the refrigerator based on the results.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 shows an embodiment of this invention, in which GM refrigeration is
Temperature sensor 41. This is an example in which a controller 42 and an inverter are provided. Therefore, the same components as those in FIG. 4 are designated by the same reference numerals and their explanations will be omitted.

The temperature sensor 41 is provided adjacent to the second stage 17, which is a low-temperature part, and detects the temperature of this part.
The detection signal is sent to the control means) 42. controller 4
2 controls the rotation speed of the motor 13 according to changes in temperature via an inverter 43 provided between the power source and the motor. Therefore, the operating frequency of the displacer 12, which is a refrigeration-like refrigerant compression member that operates in conjunction with the displacer, can be changed in accordance with the detected temperature.

Fig. 3 shows the refrigerating capacity curve of the refrigerator when the operating frequency is changed. 6Qrpm as a typical operating frequency
, 36 rpm, and 18 rpm. A normal refrigerator has an operating frequency of about 60 r11ffl. Third
As can be seen from the figure, the slower the operating frequency is, the lower the minimum temperature (temperature when freezing *+ Ific5 w) is, and the amount of refrigeration at low temperatures is also large. However, as the temperature increases, the lower the frequency, the smaller the freezing excitation. Therefore, by changing the operating frequency at each temperature level, it is possible to realize a refrigerator with a low temperature and a large refrigerating capacity. Second
The figure shows the refrigeration capacity according to an embodiment of the invention. 8.
5 and above, 60 rpm, 6.3K to 8.5, 36 rpm, and 6.3 and below, 18 rpm. The broken line is the refrigeration capacity of a conventional refrigerator, which is 60
It is an rpm only operation. It can be seen that according to the embodiments of the present invention, a refrigerator has been realized which can be heated to a lower temperature than the conventional one and has a large refrigerating capacity at low temperatures.

In the embodiments described above, the present invention is configured with a GM refrigerator, but it can be configured with a regenerator type refrigerator such as a Stirling cycle or a Birmya cycle. Further, in the detailed embodiment, an inverter is used to change the operating frequency of the displacer, but the operating frequency may be changed by other methods. Further, in the above-mentioned embodiment, the operating frequency is 60 rpm, 36 rpm,
It is limited to 18 rpm, and its temperature range is 8.5 and 6.
．． Although it was limited to 3K, other frequencies and temperature levels may be used.

[Effect of the invention 1] As described above, according to the present invention, it is possible to slow down the operating frequency of the refrigerant compression member of the refrigerator as the temperature decreases, lower the minimum temperature of the refrigerator, and increase the refrigerating capacity at low temperatures. increase can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway configuration diagram of a refrigerator according to an embodiment of the present invention, FIG. 2 is a diagram showing the characteristics of the refrigerator according to an embodiment of the present invention in comparison with that of a conventional refrigerator, and FIG. The figure shows the refrigerating capacity of the refrigerator when the operating frequency of the displacer is changed, and FIG. 4 is a schematic diagram of the conventional refrigerator. 19...Second display (refrigerant compression member) 41.
... Temperature sensor 42 ... Controller (control means) 43 ... Inverter

Claims (2)

[Claims] (1) After cooling the compressed refrigerant gas using a regenerator,
A cryogenic refrigerator that generates cold by expanding in a low-temperature section includes a temperature sensor that detects the temperature of the low-temperature section, and a system that improves the refrigerating capacity based on the temperature change detected by this temperature sensor. A cryogenic refrigerator characterized by comprising: control means for controlling the operating frequency of a displacer. (2) The cryogenic refrigerator according to claim 1, wherein the control means controls the operating frequency of the displacer of the refrigerator to be lowered as the temperature decreases at a cryogenic temperature.