JPH10246524A - Freezing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a cooling-down time to be shortened by a method wherein a bypass line is arranged between a downstream side of a first stage and a pipe just before member to be cooled, helium gas is flowed at the time of cooling-down and then an entire freezing machine is pre-cooled at a larger portion of freezing capability of a per-cooling expansion machine. SOLUTION: A bypass line 21 having a bypass valve 22 is arranged between a downstream side of a first stage 4 in a pre-cooling cold heat generating circuit and a part just before a cooling pipe 16 for cooling a member 20 to be cooled. At first, a first JT valve 12 is substantially closed and the bypass valve 22 is opened to start a cooling-down operation. Helium gas cooled at a first stage 4 of the pre-cooling expansion machine 1 passes through the bypass line 22 and flows into the pipe 16 for cooling the member to be cooled. Since the cooling pipe 16 and a super-conductive magnet 20 are thermally connected from each other through a magnet frame 19, the super-conductive magnet 20 is cooled with cold heat of helium gas of low temperature. After helium gas of low temperature is discharged out of the cooling pipe 16, the gas flows in an order of a second JT valve 13 and a sixth heat exchanger 11 and these members are cooled by the gas during its flowing stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a refrigeration system.

[0002]

2. Description of the Related Art Various electronic devices such as a nuclear magnetic resonance diagnostic device using a superconducting magnet, a thermophysical property measuring device, a Josephson element and various sensors, a cryopump having a high vacuum and a high pumping speed, and an electronic device using a superconducting magnet. Cryogenic liquid helium is used as a refrigerant for accelerators, synchrotron radiation generators, magnetic separators using superconducting magnets, and the like.

[0003] Generally, these devices to be cooled are provided with a liquid helium tank for storing liquid helium as a refrigerant, and the liquid helium evaporates with a small amount of heat.
Since it is expensive, a refrigeration unit that condenses the evaporated helium gas is installed.

[0004] The structure of this refrigeration system is, for example, Japanese Patent Publication No.
-49022. This is a Joule-Thomson liquefaction refrigerator consisting of a three-stage pre-cooling refrigerator, high-pressure and low-pressure pipes, and multiple heat exchangers. The high-pressure inlet of the final heat exchanger, that is, the downstream of the lowest temperature stage of the pre-cooling expander, By interposing a bypass valve with the low pressure inlet,
The cool-down time is shortened.

[0005] In the precooling expander, the helium gas supplied to the inside is expanded, for example, by the reciprocating motion of the displacer inside the precooling expander. On the other hand, the temperature of the heat exchanger can be reduced only by exchanging the temperature with the cold generation source or the low-temperature refrigerant. Therefore, in the case of this known example, the temperature of the pre-cooling expander decreases from the start of operation to the steady-state operation, that is, during the cool down, but the pipe having the heat exchanger group is the pre-cool expander. The temperature does not decrease below the three stages. That is, the temperature of the final heat exchanger does not decrease. Actually, the temperature is reduced only by the inefficiency of the heat exchanger, so that the better the temperature efficiency of the heat exchanger is, the longer it takes to cool down. Therefore, by installing the above-mentioned bypass valve, the cool-down time of the heat exchanger is hastened by flowing the low-temperature gas to the low-pressure side of the heat exchanger.

[0006]

However, in the conventional example described above, the cool-down by the bypass valve is for lowering the temperature of the final heat exchanger by utilizing the refrigerating capacity of the final expander stage. Yes, this structure is sufficient to cool only the final heat exchanger with a small heat capacity.However, if a cooling unit with a relatively large heat capacity such as a superconducting magnet body is attached, The cooldown time will be longer.

[0007]

Generally, the refrigerating capacity of a refrigerator becomes higher as the temperature becomes higher theoretically, even from the viewpoint of thermodynamics. In other words, a multi-stage expander (refrigerator) equipped for pre-cooling
The higher the temperature, the higher the refrigeration capacity of the upper stage.
For example, in the case of the three-stage pre-cooling expander shown in the known example, the temperature of the uppermost first stage is higher and the refrigerating capacity is higher, and the temperature of the lowermost third stage is lower and the refrigerating capacity is lower. Therefore, by providing a bypass line between the downstream part of the first stage having the highest refrigeration capacity and the pipe immediately before the cooled object, and flowing helium gas through the bypass line at the time of cooling down, the refrigeration capacity of the pre-cooling expander is large. Can pre-cool the entire refrigerator, thereby shortening the cool-down time. Furthermore, by providing a bypass line between the downstream part of each stage of the expander and the cooling unit, it is possible to efficiently cool down by adjusting the opening of each bypass valve.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. The cold generator 1 arranged in the cold generating circuit for pre-cooling is, for example, a two-stage Gifford McMahon expander.
(GM expander). Helium compressor unit 2
The high-pressure gas flows into the cold generator 1 and adiabatically expands therein, thereby generating cold at temperatures of about 40K and 10K in the first stage 3 and the second stage 5, respectively. The expanded gas returns to the compressor unit 2 again.

On the other hand, J isolated from a cold generation circuit for pre-cooling
The high-pressure helium gas pressurized to about 1.6 MPa by the compressor unit 3 of the T circuit passes through the high-pressure pipe 14, the first heat exchanger 6, the second heat exchanger 7, the third heat exchanger 8, The fourth heat exchanger 9 and the fifth heat exchanger 10 are entered. The first JT valve 12 is present in the high-pressure flow path after the fifth heat exchanger 10 outlet, and expands to a pressure of about 0.25 to 0.8 MPa. After that, it enters the sixth heat exchanger 11, becomes supercritical helium at a temperature of about 5K, and flows into the cooling unit piping 16.

[0010] For example, a cooled object 2 represented by a superconducting magnet
At 0, the cooling pipe 16 of the refrigerator is thermally connected to the magnet frame 19, and the cooling pipe 16 is cooled by flowing extremely low temperature helium.

The helium gas, which flows through the cooling pipe 16 and slightly rises in temperature due to a heat load caused by heat from the outside, flows into the low-pressure pipe as it is, and reaches a pressure of about 0.12 MPa by the second JT valve 13. It expands and partially liquefies, and enters the sixth heat exchanger 11. After that, it passes through the fifth heat exchanger 10, the third heat exchanger 8, and the first heat exchanger 6, and becomes almost normal temperature.
Return to the compressor unit 3 from the low pressure pipe 15.

The inside of the cryostat 18 is vacuum insulated,
The cryogenic portion shields radiant heat from the outside by a liquid nitrogen bath or a heat shield plate 17 cooled by the first stage 4 of the cold generation circuit.

A bypass line 21 having a bypass valve 22 is provided between the downstream side of the first stage 4 of the cold generation circuit for pre-cooling and immediately before the cooling pipe 16 for cooling the object 20 to be cooled.

First, the first JT valve 12 is almost closed and the bypass valve 22 is opened to start cooling down. The helium gas cooled in the first stage 4 of the precooling expander 1 flows into the cooling object cooling pipe 16 through the bypass line 22. The cooling pipe 16 and the superconducting magnet 20 are connected to the magnet frame 19
, The superconducting magnet 20 is cooled by the cold helium gas at low temperature. After the low-temperature helium gas exits the cooling pipe 16, the second JT valve 1
The third heat exchanger 11 and the sixth heat exchanger 11 flow in this order, and cool them during the passage process. If the first JT valve 12 is slightly opened in this process, the fifth heat exchanger 10 can be cooled by the helium gas cooled in the second stage 5. When the entire temperature of the cooling object cooling pipe 16, the fifth heat exchanger 10, and the sixth heat exchanger 11 drops to about 40K, the bypass valve 22 is closed and the first JT valve 12 and the second JT valve 13 are closed. After the adjustment, perform a cool down of 40K or less. In general, the specific heat of a metal material becomes extremely small at a temperature of 40 K or less, so that a certain amount of cooling can be performed without a bypass valve thereafter. The temperature of the entire refrigerator is reduced as it is, and the refrigerator enters a steady operation at a temperature around 4 to 5 K of the cryogenic cooling pipe 16.

In this embodiment, a superconducting magnet is taken as the object to be cooled 20 and the structure in which the superconducting magnet is cooled by conduction cooling using a cooling pipe is shown. The same effect can be obtained with a structure in which is immersed and cooled.

In this embodiment, the second JT valve 13 is installed downstream of the cooling pipe 16 for cooling the object 20 to be cooled. The same effect can be obtained when the cooling target 20 is cooled by generating the liquid helium of the above and flowing the liquid helium generated in the cooling pipe 16. Furthermore, even when there is one JT valve, that is, when the second JT valve 13 and the sixth heat exchanger 11 are not present, the effect of the present invention is the same.

FIG. 2 shows another embodiment of the present invention. FIG.
In addition to the structure of the embodiment shown in FIG.
A bypass line 23 including a bypass valve 24 is additionally provided between the downstream side of the pipe and the pipe immediately before the object to be cooled.

When the temperature of the first stage and below becomes about 50K or less, the bypass valve 22 is closed and a new bypass valve 24 is opened.
open. As a result, the final heat exchanger and the object to be cooled are about 1
Cool to 0K. Thereafter, the bypass valve 24 is closed to enter a steady operation.

In the above embodiment, an example of a two-stage expander has been described. However, the same effect can be obtained when three or more expanders are used and a bypass line is installed in the highest temperature stage and the final stage. . Further, if three or more expanders are provided with bypass lines in all stages and the bypass valves are sequentially operated from the high-temperature side, the effect is further enhanced.

In the above embodiment, the connection ports of the bypass lines 21 and 23 are connected immediately before the body 20 to be cooled, that is, on the upstream side. However, the effects are the same when the connection ports are connected on the downstream side.

In the above embodiment, the case where the superconducting magnet is used as the object to be cooled has been described. However, various electronic devices such as a Josephson element and various sensors, and a cryopanel having a high vacuum and a high pumping speed are used as the object to be cooled. However, the effect is the same.

Further, in the embodiment, the two-stage G
Although the explanation has been given of the example in which the M cycle expander is applied, the same effect can be obtained in a refrigeration cycle or a Brayton cycle in which a three-stage GM cycle, a Solvay cycle, a Stirling cycle, a Billmeyer cycle, a turbine type, or a Claude type expander are applied. is there.

[0023]

According to the present invention, since the circulating helium gas can be efficiently used for cool down, the cool down time of the refrigerator can be shortened.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a refrigeration apparatus according to one embodiment of the present invention.

FIG. 2 is an explanatory view of a refrigeration apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

1 ... expander, 2,3… compressor unit, 6,7,8,
9, 10, 11 ... heat exchanger, 12, 13 ... J · T valve, 1
6: cooling pipe, 17: heat shield plate, 18: vacuum vessel,
19: magnet frame, 20: superconducting coil, 21: bypass line, 22: bypass valve.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Minoru Morita 502, Kandachicho, Tsuchiura-shi, Ibaraki Pref.

Claims (1)

[Claims] 1. A cold generation circuit for pre-cooling, a pipe serving as a flow path of a circulating refrigerant, a series of heat exchangers containing the pipe,
In a refrigeration apparatus including compression means for compressing the refrigerant gas, expansion means provided with a plurality of stages for expanding the refrigerant gas, and a cooling unit for cooling the object to be cooled, most of the stages of the expansion means A refrigeration apparatus comprising a bypass valve that bypasses between a high-temperature stage and the cooling unit.