JPH0788981B2 - Cryogenic refrigerator - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cryogenic refrigerator for obtaining cryogenic temperatures at an absolute temperature of 4K.

(Prior Art) Conventionally, as disclosed in JP-A-61-235650 and as shown in FIG. 4, a Joule-Thomson valve is provided in front of a cooler (R) of a final heat stage (Z) for obtaining 4K. (V) is interposed, and this valve (V) allows the helium cooled by the Joule-Thomson heat exchangers (A, B, C) and the heat stage (X, Y) of the pre-cooling refrigeration circuit (S). I'm trying to expand.

A bypass circuit (W) having a throttle mechanism (D) and an on-off valve (K) is connected between the high pressure gas pipe (H) and the low pressure gas pipe (L) of the Joule-Thomson circuit (J). Even when the valve (V) is set to an extremely narrowed opening from the beginning, by opening and closing the on-off valve (K) and performing bypass during the cooldown in which the temperature is lowered from room temperature to extremely low temperature. A situation in which the return pressure of the low-pressure gas pipe (L) is abnormally lowered due to excessive throttling is avoided, adjustment of the opening of the valve (V) is unnecessary, and rotation of the operation can be achieved.

Then, the helium temperature after passing through the Joule-Thomson valve (V) is detected, and when the detected value drops to a predetermined temperature,
The on-off valve (K) is closed to stop the bypass, the entire amount is allowed to flow to the side of the Joule-Thomson valve (V), the final heat stage (Z) is cooled to the 4K level, and normal operation is started. .

(Problems to be solved by the invention) However, in the above-mentioned conventional one, the on-off valve (K) is detected by detecting the helium temperature after passing through the Joule-Thomson valve (V).
Since the temperature detector is closed, the temperature detector detects a very low temperature of helium after passing through the valve (V), which makes it difficult to detect the temperature itself and has a problem of poor controllability.

The Joule-Thomson valve (V) is a heat exchanger (A).
And a heat stage (X), etc. are provided in a vacuum container, so a temperature detector is provided at the outlet of the valve (V), that is, in the vacuum container, and a bypass circuit provided outside the vacuum container. The distance from (W) increases, and it becomes a remote control,
There is a problem that it is difficult to perform highly accurate control.

The object of the present invention is to close the on-off valve of the bypass circuit by detecting the low pressure at the downstream side of the connection portion of the bypass circuit, improve the controllability, and set the low pressure according to the temperature condition of the final heat stage. Considering that there is a possibility that the on-off valve will not be closed without reaching the value, it is an object of the present invention to provide a cryogenic refrigerator that can solve this problem by using timer control together.

(Means for Solving the Problem) Therefore, in the present invention, in order to achieve the above object, a Joule equipped with a Joule-Thomson valve (7) in front of a cooler (30) for cooling the final heat stage (3). A Thomson circuit (20) and a precooling refrigeration circuit (30) for cooling the helium gas flowing through this circuit, and a high pressure gas pipe (21) and a low pressure gas pipe (22) in the Joule-Thomson circuit (20). In a cryogenic refrigerator in which a bypass circuit (4) having a throttle mechanism (41) and an opening / closing valve (42) which is opened during a cool down operation is connected between the bypass circuit () in the low pressure gas pipe (22). A low pressure detector (PS) is provided on the downstream side of the connection portion of 4), and a valve control means (6) for closing the opening / closing valve (42) when the detection value of the detector (PS) exceeds a set value. Provided.

Further, in the above structure, the timer (TM) for measuring the set time is provided, and the combination means (60) for closing the on-off valve (42) when the set time is measured by the timer (TM) is provided.

(Operation) The low pressure detector (PS) detects the low pressure after joining the Joule-Thomson valve (7) side and the bypass circuit (4),
When this detected value exceeds the set value, it is possible to detect that the cooldown is near the end. By closing the open / close valve (42) by detecting this low pressure, it is possible to compare with the closing control by detecting the cryogenic temperature. Therefore, the control can be easily performed.

If the combined means (60) is used, the low pressure detector (PS)
Even if the detector (PS) cannot perform the valve closing control because the detected value at 2 does not reach the set value, the on-off valve (42) is closed after the set time is measured by the timer (TM). Then, the final heat stage (3) can be lowered to the target temperature.

(Embodiment) The cryogenic refrigerator shown in FIG. 1 comprises a Joule-Thomson circuit (20) using helium as a circulating refrigerant and a precooling refrigerating circuit (30) also using helium. In the following description, the acronym Jules Thomson is abbreviated as JT.

The JT circuit (20) is a large capacity low stage compressor (23),
A high-pressure gas pipe (21) and a low-pressure gas pipe (21) are attached to a compression unit (200) equipped with a small capacity post-stage compressor (24), an oil separator (25), an adsorber (26), and a gas ballast tank (27). twenty two)
First to third J-Ts arranged in the vacuum container (10) via
Heat exchanger (51, 52, 53), first and second coolers (54,5
5), adsorber (56), JT valve (7), and final third
It is configured by connecting the coolers (30) of the heat stage (3). The adsorbers (26) (56) remove impurities from each state of helium, and the gas ballast tank (27) circulates helium under the control of the high pressure control valve (28) and the intermediate pressure control valve (29). It regulates the quantity.

Further, between the high pressure gas pipe (21) and the low pressure gas pipe (22) in the compression unit (200) of the JT circuit (20), a throttle mechanism (41) composed of a capillary tube.
And a bypass circuit (4) having an on-off valve (42) composed of a solenoid valve that is opened during the cool-down operation are connected, and during the cool-down, bypass is performed to supply helium to the JT valve (7) side. By limiting the amount, even if the valve (7) is fixed to the extremely narrowed opening during steady operation, the low pressure lower limit switch (LPS) attached to the low pressure gas pipe (22) operates to operate. By avoiding the situation of stopping, the cooldown operation by fixing the opening can be automated.

On the other hand, the pre-cooling refrigeration circuit (30) includes a pre-cooling compressor (33), a compression unit (300) including an oil separator (34), an adsorber (35) and a surge bottle (36), and a high-pressure gas pipe. (3
1) and low-pressure gas pipe (32), steady operation 60 ~ 70K
The expander (37) having the first heat stage (1) and the second heat stage (2) of about 15K is connected.

In addition, in each compression unit (200) (300), (210)
(310) is a cooling water coil, and each discharge gas coil (21
1,212) and (311) and the injection oil coils (213,214) and (312) are cooled.

With the above configuration, the low pressure gas pipe (22) in the JT circuit (20), which is a low pressure pressure detector (P) configured by a pressure switch, is provided downstream of the connection portion of the bypass circuit (4).
S) is additionally provided, and valve control means (6) is provided for closing the on-off valve (42) and stopping bypass when the detection value of the detector (PS) exceeds a set value.

Specifically, the valve control means (6) turns on / off the solenoid (SV) of the on-off valve (42) by the operation of the low pressure detector (PS), as shown in FIG. , The detector (PS) is connected in series to the excitation line of the control relay (R1), and the make contact (R1-a) of the control relay is connected.
Is connected in series to the excitation line of the solenoid (SV). Thus, when the detector (PS) reaches the set pressure and operates, and its contact is switched, the control relay (R1) is turned off, the make contact (R1-a) is released, and the solenoid (SV) is turned on. It is turned off and the on-off valve (42) is closed. The operating pressure of the detector (PS), that is, the set pressure (Pset) (see FIG. 3) is 0.5 k in gauge pressure.
It is about g / cm ² .

With the above configuration, the on-off valve (42) is provided at the start of cool down.
On the other hand, the opening of the JT valve (7) is fixed from the beginning to an extremely narrowed opening corresponding to, for example, 4.2K during steady operation. Therefore, most of the helium gas discharged into the high pressure gas pipe (21) is bypassed via the bypass circuit (4), and the helium gas supplied to the JT valve (7) side remains with the rest. Become. As a result, even if the temperature of the helium gas flowing through the J-T valve (7) is still high and its density is low, the supply amount itself to the valve (7) is small,
It is possible to suppress an abnormal decrease in outlet pressure due to excessive throttling, and the low pressure after joining the bypass circuit (4) is, as shown in FIG. 3, a value that is approximately the same as the pressure value during steady operation. The lower limit switch (LPS) operates due to an abnormal decrease in the low-pressure pressure, and it is possible to avoid a situation in which the engine cannot be operated.

Then, as the cooldown progresses, the helium gas supplied to the J-T heat exchanger (51) ... side heats with the low-pressure helium on the return side in each heat exchanger (51, 52, 53). Helium temperature supplied to the J-T valve (7) while being exchanged and cooled and being cooled by the first and second heat stages (1) and (2) through the coolers (54, 55). Is gradually reduced. Due to this temperature decrease, the density of helium supplied to the JT valve (7) increases, and the amount of helium gas passing through the valve (7) also gradually increases. In this way, the pressure drop after passing through the J-T valve (7) is gradually reduced along with the temperature drop, and when the cool down is near the end, the bypass circuit (4) is bypassed and the pressure after the merging is reduced. The return pressure will gradually increase.

Thus, when the low pressure return pressure exceeds the set value (Pset) of the detector (PS), the on-off valve (42) is closed, the bypass is stopped, and the total amount of helium gas is on the JT valve (7) side. Soon after, the final 3rd heat stage (3) will drop to the target of 4.2K, and it will shift to steady operation.

As described above, the open / close valve (4
Since 2) is controlled, it is possible to easily shift from cooldown to steady operation and improve the controllability as compared with the control by cryogenic temperature detection.

By the way, the opening of the JT valve (7) is set according to the target temperature of the final third heat stage (3), and even if the control can be performed at 4.2K as described above, the target When the temperature is lowered a little to 4.1K, the opening of the valve (7) becomes smaller, so as shown by the dotted line in FIG. In some cases, the low-pressure pressure after the merging of the helium that has passed through) and the helium that is bypassed by the bypass circuit (4) does not reach the set pressure (Pset) and is saturated below this. In this case, since the detector (PS) does not operate, the bypass cannot be stopped and the JT valve (7) cannot supply the entire amount of helium, and the final third heat stage There is a problem that (3) cannot reach the target of 4.1K. Here, it is possible to slightly lower the set pressure (Pest), but this time, at the setting of 4.2K or higher of 4,3K, the bypass is stopped and the entire amount is stopped before the helium temperature falls sufficiently. Since the supply is switched to the supply, it is not possible to reliably prevent an abnormal decrease in the low-pressure return pressure, which is not a good idea.

Therefore, as shown in FIG. 1, a timer (TM) for measuring a set time is provided, and a combination means (60) for closing the on-off valve (42) when the set time is measured by the timer (TM) is provided.

Specifically, as shown in FIG. 2, the combination means (60) turns on the solenoid (SV) of the opening / closing valve (42) by the operation of the timer (TM), as in the low pressure detector (PS). The control relay (R1) and the pressure detector (P
S) in series with timed break contact (T) of the timer (TM)
It is configured by connecting Mb). In this way, the timer (TM) measures the set time and break contact (TM
When -b) is released, the control relay (R1) is turned off, the make contact (R1-a) is released, the solenoid (SV) is turned off, and the opening / closing valve (42) is closed. The time measured by the timer (TM) (Tset) (see Fig. 3) is the final third
It is set based on the heat capacity of the heat stage (3) and the like.

As described above, when the combined means (60) is used, the valve closing control by the low pressure detector (PS) can be performed as in the case where the final target temperature of the third heat stage (3) is 4.1K. Even if it is not necessary, after the fixed time (Tset) measured by the timer (TM) has passed, the on-off valve (42) can be closed and the bypass can be stopped, and by supplying the full amount of helium gas, the final third heat stage (3 ) Can get 4.1K.

(Advantages of the Invention) According to the present invention, a low pressure detector (PS) is provided on the low pressure gas pipe (22) of the Joule-Thomson circuit (20) at the downstream side of the connection portion of the bypass circuit (4). Since the valve control means (6) that closes the opening / closing valve (42) when the detection value of the detector (PS) exceeds the set value is provided, compared to the valve closing control by detecting the extremely low temperature, the automatic cool down operation is performed. The transition control to the steady operation can be easily performed, and the controllability thereof can be improved.

Also, when the combination means (60) is used, even if the valve closing control by the low pressure detector (PS) cannot be performed, the timer (T
The bypass can be stopped by M) and the final heat stage (3) can be lowered to the target temperature.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a cryogenic refrigerator according to the present invention, FIG. 2 is an electric circuit diagram of valve control means, FIG. 3 is an operation characteristic diagram, and FIG.
The figure is a circuit diagram of a conventional example. (3) …… Final heat stage (4) …… Bypass circuit (6) …… Valve control means (7) …… Joule-Thomson valve (20) …… Joule-Thomson circuit (21) …… High-pressure gas pipe ( 22) …… Low pressure gas pipe (30) …… Pre-cooling refrigeration circuit (41) …… Throttle mechanism (42) …… Open / close valve (60) …… Combined means (PS) …… Low pressure pressure detector (TM) …… Timer

Claims (2)

[Claims] 1. A Joule-Thomson circuit (20) having a Joule-Thomson valve (7) in front of a cooler (30) for cooling a final heat stage (3) and helium gas flowing through this circuit. A pre-cooling refrigeration circuit (30) that opens and closes between the high pressure gas pipe (21) and the low pressure gas pipe (22) in the Joule-Thomson circuit (20) and the throttle mechanism (41) during cooldown operation. In a cryogenic refrigerator connected with a bypass circuit (4) having a valve (42), a low-pressure pressure detector (PS) is provided downstream of the connection part of the bypass circuit (4) in the low-pressure gas pipe (22). A cryogenic refrigerator, which is provided with valve control means (6) for closing the on-off valve (42) when the detection value of the detector (PS) exceeds a set value. 2. A timer (TM) for measuring a set time is provided,
When this timer (TM) measures the set time, the on-off valve (4
The cryogenic refrigerator according to claim 1, further comprising: a combination means (60) for closing the above item (2).