JPH0289963A - Super-low temperature refrigerating machine - Google Patents

Abstract

PURPOSE:To utilize effectively coldness by only simple opening and closing of a valve and attempt to reduce the precooling time a great deal by a very simple operation by bypassing the helium gas which is most cooled by a piping during precooling to a maximum thermal load such as a body to be cooled, etc. and providing the piping with a valve. CONSTITUTION:Since the helium that is cooled in a second cooling stage 142 can be flowed not to a high pressure flow channel of a third heat exchanger 133 but directly to a body 16 to be cooled through a precooling flow channel 19 by opening a precooling valve 20 in a precooling flow channel 19 during precooling, the body 16 to be cooled can be cooled in a short time. And, the flow of the helium gas in the third heat exchanger 133 is almost only on the low pressure side, and heat exchange between the high pressure helium gas and low pressure helium gas is not made, and the third heat exchanger 133 also can be cooled by the helium gas out of the body 16 to be cooled. If at the time when the temperature at the entrance of a Joule-Thomson valve 15 reaches about 20K at which the effect can be fully exhibited the precooling valve 20 is closed, all the helium gas starts to flow to the third heat exchanger 133, and finally the body 16 to be cooled is cooled to about 4.2K.

Description

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

(Prior Art) As a conventional cryogenic refrigerator, one having a configuration shown in the flow diagram of FIG. 2 is known. That is, 1 in the figure is a cold generation device for pre-cooling, and 11 is a Joule-Thompson loop. As the cold generation device 1, for example, a Gifford-McMahon (GM) refrigerator is used. This GM refrigerator is composed of a compressor 2, a cold head 3, and a helium gas pipe 4, and the cold head 3 is equipped with first-stage and second-stage cooling chambers 51 and 52. - way,
The Joule-Thomson loop 11 mainly includes a Joule-Thomson loop compressor 12 and first to third heat exchangers 1.
3. ~133, the first and second cooling stages 14 in contact with the first and second stage cooling heads 51% 52 of the cold generation device 1 ] s 142 , Joule-Thompson valve 1
It consists of 5.

The operation of the cryogenic refrigerator shown in FIG. 2 will be explained.

First, helium gas (approximately 18 aLm) compressed by the compressor 2 of the cold generator 1 for precooling is supplied to the cold head 3 via the helium gas pipe 4, and is expanded to a low pressure (approximately 5ate) within the head 3. This produces cold.

At this time, the first stage cooling head 51 is cooled to about 40K, and the second film cooling head 52 is cooled to about 15K. In this state, compressed helium gas (approximately 18 atm) is passed through the first heat exchanger 131 by the compressor 12 of the Joule or Thomson loop 11, and then passed through the first cooling stage +4. Then, it is cooled to about 40K in the first stage cooling head 51 of the cold generation device 1. Subsequently, it passes through the second heat exchanger 132 and is cooled to about 15 K at the second cooling stage 142 at rad 5□ of the cold generation device (■). Then,
It passes through the third heat exchanger 133, and at the high-pressure outlet of the third heat exchanger 133, the temperature decreases to about 5 degrees, and Joule-Thompson expands to about 1 ati in the Joule-Thomson valve 15, and the temperature of the helium gas expands. It is cooled to the helium saturation temperature (approximately 4.2 K) at a later pressure. The state of the helium gas at this time is a gas-liquid two-phase flow at a saturation temperature, and the cold generated in this two-phase flow is used to cool the object to be cooled (for example, a superconducting magnet, helium gas, etc.) IB. The helium gas after passing through the object to be cooled 1B is transferred to the third heat exchanger 133.
, second heat exchanger 132, and first heat exchanger] 31, the high-pressure helium gas is cooled down to room temperature in each heat exchanger 133, 13□, and 131, and then returned to the compressor 12.
The pressure is boosted by

However, in order for the helium gas to generate refrigeration through Joule-Thompson expansion in the Joule-Thompson valve 15, the temperature of the helium gas at the outlet side of the third heat exchanger 5133, which is the final stage, must be sufficiently lowered (approximately 45 below)
It is necessary to be present. This can also be understood from the inversion curve of the Joule-Thomson effect of helium gas shown in FIG.

Therefore, when cooling down from room temperature, the third heat exchanger 133, the Joule-Thompson valve 15, the object to be cooled 16
becomes a heat load and prevents the Joule-Thompson valve from lowering the temperature of the helium gas sufficiently. Moreover, since the helium gas cooled in the second cooling stage 142 is warmed by exchanging heat with the heated reflux low-pressure helium gas in the third heat exchanger 133, more time is required for cooling.

Therefore, in order to shorten the precooling time, as shown in FIG. The outlet (low-pressure side flow path of the room temperature section) is connected to the flow path 17 by a precooling channel 17, and a precooling valve 18 is provided near the room temperature section of the flow channel 17. According to this configuration, during precooling (until the Joule-Thomson effect appears), the precooling valve 18 is opened to cool the object 16 to be cooled, and then the warmed helium gas flows to the low pressure side of the third heat exchanger 133. By reducing the amount of helium gas flowing into the heat exchanger 133 and reducing the degree to which the high-pressure helium gas is heated by exchanging heat with the helium gas on the low-pressure side in the heat exchanger 133, the precooling time can be shortened.

However, the conventional cryogenic refrigerator described above has the following problems. That is, the second cooling stage 142
In order to return the cooled helium gas to the room temperature through the precooling channel 17, by adjusting the valve 18 provided in the precooling channel 17, if too much cooled helium gas is allowed to flow into the precooling channel 17, the valve 18 freezes. There is a risk of helium gas leaking. For this reason, there is a problem in that it is necessary to pay close attention to the operation, and the driving work becomes complicated. Furthermore, it was inefficient to return a portion of the helium gas that has been cooled in the second cooling stage 142 to room temperature without using it for cooling the object to be cooled 1B.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and it is possible to simplify the operation in order to shorten the pre-cooling time, and to eliminate wasteful discharge of cold. The purpose is to provide a cryogenic refrigerator that can be used effectively.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a cryogenic refrigerator that generates cold by precooling compressed helium gas using a cold generator for precooling and then subjecting it to Joule-Thomson expansion. Cryogenic refrigeration characterized in that the high-pressure side inlet of the final stage heat exchanger before Joule-Thompson expansion is connected to the outlet of the Joule-Thompson valve by a pipe, and a valve is provided in the middle of the pipe. It is a machine.

(Function) According to the present invention, the high-pressure side inlet of the final stage heat exchanger before Joule-Thompson expansion and the outlet of the Joule-Thompson valve are connected by a pipe, and a valve is provided in the middle of the pipe,
By opening the valve during precooling, the coldest helium gas can flow into the low-pressure flow path of the object to be cooled and the final stage heat exchanger. Therefore, with a simple valve operation, all the cold obtained during precooling can be effectively used to cool the body to be cooled, which is the main heat load, and the final stage heat exchanger, thereby shortening the precooling time. .

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIG. In addition, in FIG. 1, the same members as those in FIG. 2 described above are given the same reference numerals, and explanations thereof will be omitted.

As shown in the flow diagram of FIG. 1, the cryogenic refrigerator of this embodiment has a high-pressure side inlet of the third heat exchanger IA3, which is the final stage heat exchanger before Joule-Fist-Thomson expansion, and a Joule-Fist
The outlet of the Thomson valve 15 is connected to the outlet of the Thomson valve 15 by a pipe (precooling channel) 19, and a precooling valve 20 is provided in the middle of the precooling channel 19.

According to such a configuration, by opening the precooling valve 20 of the precooling passage I9 during precooling, the Joule-Thompson loop 11
Since the Joule-Thomson valve 15 has a much larger pressure loss than the precooling valve 20, most of the helium gas cooled in the second cooling stage 142 does not flow into the high pressure flow path of the third heat exchanger 133. Helium gas pre-cooling channel 19
can be passed to. Therefore, the helium cooled in the second cooling stage 142 can be directly flowed to the object to be cooled 16 through the pre-cooling channel 19, so that the weight to be cooled 6 can be cooled in a short time. Furthermore, during such precooling, the flow of helium gas into the third heat exchanger 133 is almost only on the low pressure side, and heat exchange between high and low pressure helium gases is not performed, so that the helium gas flows out from the object to be cooled 16. The third heat exchanger 133 can also be cooled by the helium gas. Joule-Thomson Valve 15 Temperature at which the Joule-Thomson effect can be fully exerted (approximately 20K)
When the pre-cooling valve 20 is closed when the pre-cooling valve 20 is closed, all the helium gas starts to flow into the third heat exchanger 133, and the temperature at the outlet of the Joule-Thomson valve 15 decreases more and more due to the Joule-Thomson effect, eventually reaching about 4 Cooled object 16 up to .2K
is cooled. Therefore, the Joule Thomson loop 11
By connecting the pre-cooling channel 19 to a specific location,
By simply opening and closing the pre-cooling valve 20 provided in the pre-cooling channel 19, cold can be used for appetizing purposes, and the pre-cooling time can be significantly shortened.

Note that the present invention is not limited to the configuration shown in FIG. 1 described in the above embodiment. For example, the cold generation device for precooling may use a Stirling refrigerator, liquid nitrogen, or liquid hydrogen.

Furthermore, even if the cycle of the cryogenic refrigerator is a Claude cycle having two expansion engines, for example, it is possible to achieve the same effects as in the above embodiment.

[Effects of the Invention] As detailed above, according to the present invention, the helium gas, which is the coldest during precooling, is bypassed by the piping to the maximum heat load of the object to be cooled, etc., and the piping is provided with a valve. By doing so, it is possible to provide a cryogenic refrigerator that can effectively utilize cold by simply opening and closing the valve, and can achieve a significant reduction in precooling time with extremely simple operations.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of a cryogenic refrigerator showing an embodiment of the present invention, FIG. 2 is a flow diagram showing a conventional cryogenic refrigerator, and FIG. 3 is a flow diagram showing a conventional cryogenic refrigerator.
The figure is a characteristic diagram for explaining the Joule-Thomson effect of helium gas. l...Cold generator for pre-cooling, 2...Compressor, 3...Cold head, 51%52...Cooling head, U...Joule-Thomson loop, 12...Joule-Thomson loop controller Bread, 131-133
...Heat exchanger, 141.142...Cooling stage,
15... Joule-Thompson valve, 1B... object to be cooled, 19... pre-cooling channel (piping), 20... pre-cooling valve. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] In a cryogenic refrigerator that generates refrigeration by precooling compressed helium gas using a precooling refrigeration generator and then subjecting it to Joule-Thompson expansion, the high-pressure side inlet of the final stage heat exchanger before Joule-Thompson expansion. A cryogenic refrigerator characterized in that a pipe connects an outlet of a Joule-Thomson valve with a valve, and a valve is provided in the middle of the pipe.