JPH0689955B2 - Cryogenic refrigerator - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a cryogenic refrigerating apparatus having a cryogenic refrigerant transfer pipe, and is particularly suitable for an apparatus having a large cooled object or a large number of cooled objects. The present invention relates to a cryogenic refrigerator.

[Background of the Invention]

In a cryogenic refrigeration system having a cryogenic refrigerant transfer pipe, reducing the heat entering the cryogenic refrigerant transfer pipe is one factor that determines the success or failure of the system, so the cryogenic refrigerant transfer pipe is vacuum insulated. In addition, it is common to use laminated insulation.

Therefore, cryogenic refrigerant transfer piping is very expensive,
An important issue for the system is how to efficiently arrange the cryogenic refrigerant transfer pipes. Further, considering the case of automatically controlling the cryogenic refrigeration system, it is an important issue to simplify the system and how to efficiently perform the non-steady state operation such as precooling. Hereinafter, the case of liquid helium as the cryogenic refrigerant will be described as an example.

FIG. 1 is a system diagram of a conventional helium refrigeration system,
The figure is a cross-sectional view of a triple-tube cryogenic refrigerant transfer pipe. First
In FIG. 2 and FIG. 2, 1 is a helium refrigerator, 2 is a triple-tube cryogenic refrigerant transfer pipe, 3 is a refrigerant supply pipe, 4 is a refrigerant return pipe, 5 is a supply valve, 6 is a cryostat, 7 is a shield tank, 8 is a superconducting magnet, 9 is a liquid helium tank,
10 is a cryogenic refrigerant transfer pipe for bypass, 11 is a warmer, 12 is a bypass valve, 13 is a bypass pipe, 14 is a liquid nitrogen supply pipe to the shield tank 7, 15 is a gas nitrogen release pipe from the shield tank 7, Reference numeral 16 is an outer pipe of the triple pipe type cryogenic refrigerant transfer pipe 2.

In the above configuration, the cryogenic refrigerant generated by the helium refrigerator 1 is supplied to the cryostat 6 through the refrigerant supply pipe 3, and the liquid helium is stored in the liquid helium tank 9. In the liquid helium tank 9, the superconducting magnet 8 which is the object to be cooled is immersed, and the required cryogenic refrigerant amount is
The supply valve 5 controls the liquid level of the liquid helium in the liquid helium tank 9 to be kept constant. The gas helium gasified by absorbing the refrigeration load in the liquid helium tank 9 is used as the refrigerant return pipe 4
Return to helium refrigerator 1. Cryostat 6
Is vacuum-insulated to reduce the heat of entry into the liquid helium tank 9 from the room temperature, but in order to further reduce the heat of penetration, liquid nitrogen having an intermediate temperature between liquid helium and room temperature is assisted. It has a shield tank 7 as a heat shield mechanism as a refrigerant, and is cooled by liquid nitrogen supplied from a liquid nitrogen supply pipe 14 and gasified gas nitrogen is a gas nitrogen release pipe.
It is released into the atmosphere from 15. Refrigerant supply pipe 3 and refrigerant return pipe 4
Is arranged in the triple pipe type cryogenic refrigerant transfer pipe 2 and constitutes a triple pipe as shown in FIG. 2 together with an outer pipe 16 for vacuum heat insulation. The use of the triple-tube cryogenic refrigerant transfer pipe 2 is firstly inexpensive because it is not necessary to install two very expensive cryogenic refrigerant transfer pipes for supply and return. Secondly, since the supply side and the return side can exchange heat, the temperature of the cryogenic helium gas returning to the helium refrigerator 1 becomes almost the same as the supply refrigerant, and the stable operation of the helium refrigerator 1 is achieved. This is because there are advantages such as that

The above is the operation during steady operation, and next, the operation during precooling will be described. At the time of precooling, it is disadvantageous to use a cryogenic refrigerant transfer pipe (a triple-tube cryogenic refrigerant transfer pipe is one example) having a structure in which the supply refrigerant and the return refrigerant are in thermal contact with each other, which is a disadvantage. If used, the pre-cooling efficiency is greatly deteriorated. Therefore, during precooling, a bypass mechanism is provided, the return refrigerant is passed through the bypass cryogenic refrigerant transfer pipe 10, the temperature is restored to room temperature by the warmer 11, and then returned to the helium refrigerator 1 through the bypass pipe 13 which is a room temperature pipe. . The bypass valve 12 is used for adjusting the flow rate of the return refrigerant.

The conventional helium refrigeration system having the above-mentioned configuration and operation requires a bypass mechanism, which makes the device configuration complicated and expensive, and the operation operation is complicated. Especially, when performing automatic control, reliability is high. There was a defect such as lack of sex.

[Object of the Invention]

The object of the present invention has been made in view of the above points.
While simplifying the structure of the cryogenic refrigeration system to make it cheap,
An object of the present invention is to provide a cryogenic refrigeration apparatus suitable for facilitating driving operation and automatically controlling.

[Outline of Invention]

The cryogenic refrigerator has optimum operating conditions depending on the conditions on the load side, that is, whether it is a liquefaction load or a refrigeration load (there is also an intermediate liquefaction + refrigeration). In the case of the conventional cryogenic refrigerator, the cryogenic refrigerator is basically in the liquefaction mode when the object to be cooled is pre-cooled, and in the steady state, the refrigeration mode is the basic. Therefore, in order to automatically control the apparatus, it is necessary to change the control conditions of the cryogenic refrigerator in accordance with the conditions on the side to be cooled, and to control the bypass line, etc., which causes many difficulties. If the operating conditions of the cryogenic refrigerator can always be kept constant, the operating conditions will be easy and the reliability will be improved.

Considering the precooling conditions of the cooled object, the precooling capacity per unit flow rate when liquid helium is considered as the refrigerant is
q _r = ΔH + C _p (T-4.5). Where ΔH is the latent heat of vaporization of liquid helium (≈20 j / g), C _p is the comparison of gas helium (≈5.2 j / gK), and T is the return temperature of the gas helium from the cooled object. . Therefore, T = 30
In the case of 0K (23 ° C), q _r ≈ 1560 W / (g / s). On the other hand, if the triple-tube cryogenic refrigerant transfer pipe is used even during pre-cooling, the cooling capacity will be q _r ′ ≈ 20 W / (g / s) because only the latent heat of vaporization can be used, and pre-cooling will take a long time. It will be. As a characteristic of the helium refrigerator, in the freezing mode, about 4 times as much liquid helium can be generated as compared with the case of the liquefying mode. Therefore, precooling in the freezing mode takes about 1560/20/4 = 20 times as much precooling time. It will be.

On the other hand, as the pre-cooling load of the object to be cooled, if the liquid nitrogen temperature (about 80K) which is the auxiliary refrigerant is set to the intermediate temperature, the pre-cooling load between the room temperature and the liquid nitrogen temperature is It accounts for about 90% (because the specific heat of the metal body or the like to be cooled decreases significantly as the temperature decreases).

Therefore, during the initial precooling, it is conceivable to use the cold of liquid nitrogen used as the auxiliary refrigerant in the object to be cooled. In this case, the precooling capacity during the initial precooling is q _r ″
= 5.21j / gK (300-80) = 1140, and considering the difference in flow rate, 1560/1140/4 = 0.34 That is, the precooling capacity in the refrigeration mode becomes large near the room temperature of the cooled object. Become. Next, the temperature of the cooled object is about 10
If the auxiliary refrigerant is not used below 0K, the precooling capacity in the liquefaction mode is _qr = 20 + 5.2 (100-4.5) ≈ 520W, and the precooling capacity in the refrigeration mode is _qr '= 20 x 4 = 80W. The precooling capacity at 80/520 = 0.15 is still small, but considering that it is a temperature range that accounts for only about 10% of the total precooling load from room temperature to the temperature of liquid helium, it is a problem overall. I won't.

According to the present invention, a refrigerant supply pipe for supplying a cryogenic refrigerant from a cryogenic refrigerator into a liquid tank is connected to a liquid tank via a supply valve (a liquid surface level control valve of the liquid tank), and the refrigerant is supplied from the refrigerant supply pipe. A pre-cooling line that branches in front of the valve is provided, the pre-cooling line communicates with the object to be cooled through the pre-cooling switching valve, and heat exchange is performed with the auxiliary refrigerant having a temperature level higher than the freezing temperature of the cryogenic refrigerant in the pre-cooling line. By providing a heat exchange unit for precooling and utilizing the cooling of the auxiliary refrigerant during the initial precooling, the cryogenic refrigerator can always be operated in the same refrigeration mode without significantly changing the precooling time. .

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. In FIG. 3, the same parts as those in FIG.

In FIG. 3, 19 is a precooling line branched from the refrigerant supply pipe 3, communicated with the liquid helium tank 9 through the shield tank 7, 20 is a precooling switching valve provided in the precooling line 19, 21
Is a heat exchange section for precooling provided in the shield tank 7 of the precooling line 19.

In the above configuration, the operation during steady operation is the same as that shown in FIG. 1 and is omitted, and the operation during precooling will be described. During precooling, the supply valve 5 is closed, and the cryogenic refrigerant supplied from the helium refrigerator 1 passes through the refrigerant supply pipe 3 and exchanges heat with the return refrigerant flowing through the refrigerant return pipe 4 to rise in temperature and reach the cryostat 6. It is supplied, enters the shield tank 7 from the precooling line 19 through the precooling switching valve 20, exchanges heat with the liquid nitrogen in the precooling heat exchange section 21 and is supplied to the liquid helium tank 9 after temperature drop, and the superconducting magnet 8 is supplied. Cool down and the temperature rises,
Entering the refrigerant return pipe 4. The return refrigerant having entered the refrigerant return pipe 4 exchanges heat with the supply refrigerant flowing through the refrigerant supply pipe 3 and returns to the helium refrigerator 1 with a temperature drop. Then, when the precooling of the superconducting magnet 8 progresses to about 100K, the precooling switching valve 20 is fully closed and the supply valve 5 is opened, so that the supply refrigerant supplied to the cryostat 6 passes through the supply valve 5. It will be a regular flow.

In the above embodiment, the precooling heat exchange section 21 is provided inside the cryostat 6, but it may be provided outside the cryostat 6, and liquid nitrogen is used as an auxiliary refrigerant in the triple-tube cryogenic refrigerant transfer pipe. When the shield tube is provided, a precooling heat exchange section may be provided so as to exchange heat with the auxiliary refrigerant.

As described above, according to this embodiment, there is an effect that a bypass mechanism such as a warming device is unnecessary. Furthermore, the helium refrigerator can always be operated in the same refrigeration mode, which facilitates operation and improves reliability.

〔The invention's effect〕

As described above, according to the present invention, a bypass mechanism such as a warmer used during precooling is unnecessary, so that the device configuration can be simplified and the economical efficiency is improved. Further, the cryogenic refrigerator may be maintained in the same operating state at all times, which facilitates the operating operation and improves the reliability. Furthermore, the simplification of the device configuration and the simplification of the driving operation facilitate the automatic control.

[Brief description of drawings]

FIG. 1 is a system diagram of a conventional helium refrigerating apparatus, FIG. 2 is a sectional view of a triple-tube cryogenic refrigerant transfer pipe, and FIG. 3 is a system diagram showing an embodiment of a cryogenic refrigerating apparatus according to the present invention. . 1 ... Helium refrigerator, 2 ... Triple pipe type cryogenic refrigerant transfer pipe, 3 ... Refrigerant supply pipe, 4 ... Refrigerant return pipe, 5 ... Supply valve, 6 ... Cryostat, 7 ... Shield tank, 8
…… Superconducting magnet, 9 …… Liquid helium tank, 10 ……
Cryogenic refrigerant transfer pipe for bypass, 11 …… warmer, 12 ……
Bypass valve, 13 ... Bypass pipe, 14 ... Liquid nitrogen supply pipe, 15 ... Gas nitrogen discharge pipe, 16 ... Outer pipe, 19 ... Precooling line, 20 ... Precooling switching valve, 21 ... Precooling Heat exchange section

Claims (1)

[Claims] 1. A cryogenic refrigerator for producing a cryogenic refrigerant, a liquid tank containing a cooled object cooled by the cryogenic refrigerant produced by the cryogenic refrigerator, and an auxiliary refrigerant for the liquid tank. A cryogenic temperature which is composed of an enclosed shield tank and an outer tank accommodating the liquid tank and the shield tank, and which has a cryostat for vacuum-insulating the space between the tanks, and which is supplied from the cryogenic refrigerator into the liquid tank. In a cryogenic refrigeration system comprising a refrigerant supply pipe and a cryogenic refrigerant transfer pipe composed of a refrigerant return pipe arranged so that the refrigerant and the gasified return refrigerant returned from the liquid tank to the cryogenic refrigerator are in thermal contact The refrigerant supply pipe is connected to a liquid tank via a supply valve, and a precooling line is provided branching from the refrigerant supply pipe in a stage before the supply valve, and the precooling line is connected to a cooled object via a precooling switching valve. Communication, cooling the cryogenic refrigerant to the pre-cooling line A cryogenic refrigeration system comprising a pre-cooling heat exchange section for exchanging heat with an auxiliary refrigerant having a temperature level higher than the freezing temperature, and utilizing cold of the auxiliary refrigerant during initial pre-cooling.