JP2008128613A - Dilution refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cost by substantially reducing the number of valves in a path to circulatingly force feed He gas, and to facilitate automatic operation by simplifying operation procedures in a dilution refrigerator. <P>SOLUTION: An oil-free vacuum pump is used as a vacuum pump for circulation He gas feeding, and a buffer tank is provided in an inlet side. By using an oil-free vacuum pump as the vacuum pump, an oil filter and an oil trap conventionally provided for removing oil mixed into circulation gas from the vacuum pump becomes unnecessary, thereby, the number of valves is reduced, and bothersome operation at shutdown is eliminated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a dilution refrigerator that uses liquid helium (3He, 4He) to obtain an ultra-low temperature of 1 to 10 ⁻³ K.

  As is well known, a mixed liquid of 3He and 4He has a 3He rich phase (hereinafter, simply referred to as “rich phase”) in which 3He is greater than 4He and 3He at a cryogenic temperature of 0.8 K (800 mK) or less. It separates into a 3He dilute phase (hereinafter simply referred to as “dilute phase”) less than 4He, and a rich phase is formed at the top and a dilute phase is formed at the bottom.

  When 3He in the rich phase enters the dilute phase, the entropy of 3He molecules in the rich phase becomes smaller in the dilute phase (this is called “dilution”), and the endotherm associated with the decrease in entropy is used. The refrigerating machine is a dilution refrigerating machine, and is used for experiments at various temperatures under ultra-low temperatures.

  The principle of the dilution refrigerator is shown in Non-Patent Document 1 and Non-Patent Document 2, and the specific configuration is shown in Patent Document 1 to Patent Document 3.

FIG. 4 is a block diagram showing an example of a conventional dilution refrigerator, in which the refrigerator main body 1 is immersed in a refrigerant 3 made of 4He liquid in a cryostat subjected to vacuum insulation, and 3He gas is circulated through the refrigerator main body 1. A circulation path 5 and a vacuum pump 7 are provided.
The circulation path 5 is an introduction path 5 a that connects the discharge port of the vacuum pump 7 and the gas introduction port of the refrigerator main body 1, and a lead-out path that connects the gas outlet port of the refrigerator main body 1 and the suction port of the vacuum pump 7. A valve Va is provided between the introduction path 5a and the lead-out path 5b.

  The vacuum pump 7 is an oil type vacuum pump (also referred to as “oil rotary vacuum pump”) that performs vacuum sealing with oil (oil), and a large amount of oil is contained on the discharge side due to the mechanism of vacuum sealing with oil. .

  The refrigerator main body 1 includes a 1K pot 11, a fractionator 13, a main heat exchanger 15, and a mixing chamber 17 in a vacuum chamber 9, and the vacuum chamber 9 itself is maintained in a vacuum state by a vacuum pump 9a.

  The 1K pot 11 is maintained in a reduced pressure state by the vacuum pump 11a, whereby the refrigerant 3 is supplied through the valve 19 and is maintained at a low temperature by the evaporation of the refrigerant 3.

  The room temperature 3He gas (also referred to as “circulation gas”) introduced into the refrigerator main body 1 from the introduction path 5a as indicated by an arrow passes through the 1K pot 11, the fractionator 13, and the main heat exchanger 15. In the process, it is cooled and liquefied sequentially and introduced into the dense phase P on the upper layer side in the mixing chamber 17.

  On the other hand, the liquid in the dilute phase Q formed in the lower layer of the rich phase P in the mixing chamber 17 is introduced into the fractionator 13 via the pipe 21, and the fractionator 13 in the 3He-4He mixed liquid 3He selectively evaporates due to the difference in saturated vapor pressure, and the evaporated 3He gas is sucked into the vacuum pump 7 from the gas outlet of the refrigerator main body 1 through the outlet passage 5b and is pressurized again by the vacuum pump 7. It is sent to the gas inlet of the refrigerator main body 1 and circulates.

  3He in the dilute phase Q decreases with the evaporation of 3He in the fractionator 13, so that 3He in the rich phase P shifts to the dilute phase Q to make up for this, and the dilution occurs in this process, The mixing chamber 17 becomes an extremely low temperature of about 10 mK due to the endothermic effect due to dilution, and is used for cooling the object to be cooled.

  Next, the flow control valve V1 provided on the suction side of the vacuum pump 7 is opened, closed, and adjusted to a predetermined opening based on the pressure detection means 23 and the control unit 25 provided on the discharge side of the vacuum pump 7. The A valve V2 is provided upstream of the flow control valve V1.

  By the way, as described above, the vacuum pump 7 of the conventional device is an oil type vacuum pump, and a large amount of oil is contained on the discharge side. When this oil enters the refrigerator main body 1, a serious failure such as blockage of the flow path is caused. Therefore, a general oil filter 27 that removes oil at room temperature is provided on the discharge side of the vacuum pump 7, and an oil trap 29 is provided at the subsequent stage. Are provided to prevent the oil from entering the refrigerator main body 1.

  In the oil trap 29, a part of the conduit of the introduction path 5a is coiled, and the coiled part is filled with activated carbon, and the coiled part is immersed in liquid nitrogen (-190 ° C. or lower) in the container. By cooling the activated carbon to a low temperature, a small amount of oil that has not been completely removed by the oil filter 27 is trapped on the activated carbon and finally removed. In addition to oil, it is easier to trap than oil. Water is also trapped and removed.

  The oil trap 29 operates when the activated carbon is kept at a low temperature, and the inlet-side valve V5 and the outlet-side valve V6 are opened to allow circulation gas to flow. When the oil trap 29 is not used for a long period of time, the valves V5 and V6 are closed to discharge liquid nitrogen in the container to heat the coiled portion, and then the valve 8 is opened to operate the vacuum pump 29a. The activated carbon is regenerated by sucking and desorbing the oil and moisture trapped in the coiled activated carbon.

  Next, in the conventional apparatus, a recovery tank 31 for recovering the circulating gas is provided, communicates with the introduction path 5a between the oil filter 27 and the valve V5 via the valve V3, and flows through the valve V4. It communicates with a lead-out path 5b between V1 and the valve V2.

  Next, an operation method of the conventional apparatus will be described. In this case, the valve V8 is opened and closed only in a special case such as regeneration of activated carbon in the oil trap 29 or exhaust of the circulating gas, and thus will not be described in the following description.

<Normal operation>
In the steady operation, the flow rate control valve V1 is set in the operating state (control state in the control unit 25), the valves V2, V5, V6 are opened, the other valves are closed, the vacuum pump 7 is operated, and the vacuum pump 7 is discharged. The circulated gas is passed through the oil filter 27 and the oil trap 29 and introduced into the refrigerator main body 1 without containing oil. The circulating gas introduced into the refrigerator main body 1 achieves the endotherm, and then returns to the suction port of the vacuum pump 7 through the lead-out path 5b.

<Stopping steady operation>
To stop the steady operation, manually close the flow control valve V1, close the valves V5 and V6, and then open the valve V4 (the valve V2 is open and the valve V3 is closed). Stop. This is because the oil in the vacuum pump 7 flows backward through the lead-out path 5b due to the pressure fluctuation when the vacuum pump 7 is stopped, or the oil is discharged from the oil filter 27 or the oil trap 29 and enters the refrigerator main body 1. Is to prevent.

  After the vacuum pump 7 is stopped, the liquid phase portion of the refrigerator main body 1 evaporates and the pressure of the outlet passage 5b increases, so that the circulating gas in the outlet passage 5b is transferred to the recovery tank 31 via the valves V2 and V4. Then, the valve Va is opened, and the circulating gas that has entered the introduction path 5a as a result of evaporation of the liquid phase portion of the refrigerator main body 1 is recovered in the recovery tank 31 via the valve V4.

  In addition, it is preferable that oil is not accompanied with the circulating gas in the recovery tank 31 as much as possible. For this reason, the valve V3 is not used at the time of recovery. When the valve V3 is opened and recovered, the circulating gas contains oil in the process of passing through the vacuum pump 7. Therefore, as described above, the flow control valve V1 is closed and recovered via V4.

  When the pressure in the circulation path becomes the same as that of the recovery tank 31, recovery to the recovery tank 31 stops, but if left in this state, oil that slightly leaks from the suction port side of the vacuum pump 7 flows back to the low-temperature refrigerator main body 1 Therefore, after the valve V4 is closed, the flow control valve V1 is manually opened (the valves V2 and Va remain open and the valve V5 remains closed), the valves V3 and V6 are opened, and the vacuum pump 7 is operated. All of the circulating gas in the circulation path 5 is recovered in the recovery tank 31 via the oil filter 27, and then the valves V2, V3, V6, Va are closed. If the oil trap 29 is recovered using the vacuum pump 7 with the valve V6 opened, the oil trap 29 is decompressed. However, during operation of the oil trap 29, the oil trapped in the low-temperature activated carbon flows out to the introduction path 5a. There is nothing.

  As described above, since the circulation gas in the circulation path 5 using the vacuum pump 7 is collected through the oil filter 27, oil that cannot be removed by the oil filter 27 is contained in the circulation gas and collected. Entering the tank 31 cannot be avoided. However, if the valve V3 is connected to the subsequent stage of the valve V6 to recover the circulating gas without oil after passing through the oil trap, this time, when the gas in the recovery tank 31 is returned to the introduction path 5a, there is no oil. It is dangerous because it is not removed.

<Resumption of operation after shutdown>
Next, to restart the operation, first, the circulating gas in the collection tank 31 is returned to the circulation path 5 to cool (pre-cool) the refrigerator main body 1. In this case, since the gas in the recovery tank 31 may contain a small amount of oil, for safety, the valves V5 and V6 are opened and the oil trap 29 is activated, and then the valve V3 is opened and the recovery tank 31 is opened. Is returned to the discharge side of the vacuum pump 7. At this time, the valve V2 is kept closed to prevent the circulating gas from flowing back into the refrigerator main body 1 through the vacuum pump 7 and the outlet passage 5b. The valve V4 is kept closed to prevent gas containing oil from entering the outlet passage 5b.

  When the circulating gas enters the introduction path 5a, the valve Va is opened, the valve V2 is opened a little, and the gas is also introduced into the outlet path 5b. When the lead-out path 5b is filled with the circulating gas and the pressure of the recovery tank 31 coincides with the circulation path, gas outflow from the recovery tank 31 stops, so the valve V3 is closed and the valve Va is also closed.

Thereafter, the valve V2 is closed, the valve V4 is opened, and the flow rate control valve V1 is manually opened, the pump 7 is operated, the residual gas in the recovery tank 31 is returned to the circulation path, and then the valve V4 is closed. The flow rate control valve V1 is set in an operating state, the valve V2 is gradually fully opened, and a steady operation is performed.
Japanese Patent No. 3338381 Japanese Patent No. 3805531 Japanese Patent No. 3644683 “Principle and Design Problem I of 3He-4He Dilution Refrigerator I”, Journal of the Physical Society of Japan, Vol. 37, No. 5 (1982), p409-418 "Principle of 3He-4He dilution refrigerator and design problems II", Journal of the Physical Society of Japan, Vol. 37, No. 7 (1982), p595-600

  As described above, a dilution refrigerator using a conventional oil-type vacuum pump requires an oil filter, an oil trap, and a recovery tank, and requires a large number of valves. Therefore, there is a disadvantage that the plurality of valves need to be automatic valves that can be remotely operated, and the cost of the entire apparatus becomes extremely high. It was also complicated that the entire amount of the circulating gas in the circulation path had to be recovered in the recovery tank when the system was stopped.

  Based on the above circumstances, the present invention provides a dilution refrigerator that eliminates the need for an oil filter and an oil trap, reduces the number of valves required for operation, and reduces costs.

  In the present invention, as the vacuum pump, an oil-free vacuum pump (also referred to as “sealed dry pump”) that mechanically seals the vacuum instead of the oil-type vacuum pump is used to make the circulation path completely oil-free, This eliminates the need for oil filters and oil traps, and uses a buffer tank that does not collect circulating gas instead of a collecting tank that collects circulating gas. As a whole, the number of valves is greatly reduced and the operating procedure is simplified. The present invention provides a dilution refrigerator that is cheaper and easier to operate than before.

The dilution refrigerator according to claim 1 of the present invention is provided in a circulation body, a circulation body for introducing a circulation gas to the refrigerator body, and discharging circulation gas from the refrigerator body. In a dilution refrigerator equipped with a vacuum pump for circulating the circulating gas;
An oil-free vacuum pump is used as the vacuum pump, and a buffer tank is provided between the suction port of the vacuum pump and the gas outlet port of the refrigerator main body to introduce a circulating gas to alleviate the pressure increase in the circulation path. It is characterized by.

  According to the dilution refrigerator of the present invention, since an oil-free vacuum pump is used as a vacuum pump, there is no mixing of oil into the circulation path, and the circulation gas does not contain oil, so an oil filter and an oil trap are unnecessary, and Since the circulation gas recovery process can be omitted as a buffer tank that does not recover the circulation gas instead of the recovery tank that recovers the circulation gas, the number of valves to be provided in the path is greatly reduced compared to the conventional, and the operation process is simplified. As a whole, the cost of the apparatus can be greatly reduced as compared with the conventional apparatus, and at the same time, automatic operation control by a computer can be easily performed at low cost.

  FIG. 1 shows the overall configuration of the dilution refrigerator according to the first embodiment of the present invention. In FIG. 1, the same components as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 1, the refrigerator main body 1 itself is the same as the conventional one in FIG. 4 except that an oil-free vacuum pump is used as the vacuum pump 7. Since the oil-free vacuum pump is used, it is not necessary to provide an oil filter or an oil trap in the introduction path 5a.

  Further, in the first embodiment of FIG. 1, a flow rate control valve V1 is provided in the lead-out passage 5b on the suction side of the vacuum pump 7, and an adsorption device 41 is provided in the introduction passage 5a on the discharge port side of the vacuum pump 7. Yes. The adsorption device 41 is filled with an adsorbent for adsorbing moisture in a container and serves to remove moisture with a conventional oil trap, but unlike a conventional oil trap, adsorbs moisture at room temperature. Is. It is easier to remove moisture than oil, and it is not necessary to cool with liquid nitrogen as in the prior art.

  Between the suction device 41 and the discharge port of the vacuum pump 7, a pressure detecting means 23 and a control unit 25 for adjusting and controlling the opening degree of the flow control valve V1 according to the pressure detected thereby are provided. . Here, the flow rate control valve V1 and the pressure detecting means 23 are the same as in the conventional example of FIG.

  Further, a buffer tank 36 is connected to the outlet path 5b upstream from the flow control valve V1. Since the buffer tank 36 is provided only to alleviate the pressure increase in the circulation path when the apparatus is stopped, the buffer tank 36 is connected to the lead-out path 5b without providing a valve. In the conventional apparatus, a recovery tank for recovering the gas in the circulation path is required, and a communication pipe must be connected to both the suction side and the discharge side of the vacuum pump, and valves must be provided for both of the communication pipes. However, this is not necessary in the apparatus of the present invention.

  A first valve Va is provided between the outlet passage 5b upstream of the flow control valve V1 and the inlet passage 5a downstream of the adsorption device 41, and is controlled according to the operation of the vacuum pump 7. It is configured to be.

  The operation method of the inventive device will be described below.

<Normal operation>
In the steady operation, the flow rate control valve V1 is in the activated state, the valve Va is closed, the vacuum pump 7 is operated, and the circulating gas discharged from the vacuum pump 7 is introduced into the refrigerator main body 1 through the adsorption device 41. .

<Stopping steady operation>
To stop the steady operation, it is only necessary to manually close the flow control valve V1 and stop the vacuum pump 7. The pressure fluctuation when the vacuum pump 7 is stopped is absorbed by the buffer tank 36.

  When the vacuum pump 7 is stopped, the liquid phase portion of the refrigerator main body 1 evaporates and the pressure in the lead-out path 5b increases, but a part of the pressure is introduced into the buffer tank 36, and the pressure in the circulation path is reduced with the buffer tank 36. Ends at the same pressure. The valve Va is also opened to allow the circulating gas on the introduction path side to communicate with the buffer tank 36. The volume of the buffer tank 36 is appropriately designed in consideration of the pressure increase in the circulation path.

<Resumption of operation after shutdown>
Next, in order to resume the operation, the valve Va is closed and the flow rate control valve V1 is activated, and then the vacuum pump 7 is operated.

  FIG. 2 shows a dilution refrigerator according to a second embodiment of the present invention.

  In the second embodiment shown in FIG. 2, a simple valve (second valve) V9 is provided in place of the flow control valve V1 in FIG. 1, and a resistor 43 is provided in parallel with the valve V9. As the body 43, a fine tube or a porous body having an appropriate flow path resistance as shown in the figure, or a valve whose opening degree is appropriately adjusted can be used.

  Unlike the case shown in FIG. 1 (detecting the pressure on the discharge side of the vacuum pump 7), the pressure detecting means 23 detects the pressure on the suction side of the vacuum pump 7, and in a steady operation, V9 is fully opened. The valve V9 whose pressure in the passage 5b is equal to or higher than a predetermined value is closed so that only the gas passing through the resistor 43 flows into the vacuum pump 7, thereby suppressing the amount of gas flowing into the vacuum pump 7, thereby reducing the vacuum pump. 7 is controlled so as not to be excessive.

  Other operations may be performed by opening the valve Va in accordance with the stop of the vacuum pump 7 as in the case of FIG.

  The embodiment of FIG. 2 may be an inexpensive opening / closing valve instead of an expensive flow rate control valve, and does not require an opening degree control, and only a simple opening / closing operation is required as compared with the embodiment of FIG. Therefore, the cost can be further reduced.

  FIG. 3 shows a dilution refrigerator according to a third embodiment of the present invention.

  The embodiment of FIG. 3 differs from the embodiment of FIG. 1 in that the control unit 25 of the vacuum pump 7 includes an inverter, and thus the flow control valve V1 is omitted.

  Thereby, during steady operation, the pressure on the discharge side of the vacuum pump 7 is inverter-controlled based on the pressure value from the pressure detection means 23 so that the rotation speed does not exceed a predetermined value. In order to prevent the discharge amount of the vacuum pump 7 and hence the amount of circulating gas sent to the refrigerator main body 1 from being excessive, the power consumption, particularly the power consumption at start-up, is controlled. The running cost can be reduced by less than the second example.

  Other operations are the same as those in FIG.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an overall configuration of a dilution refrigerator according to a first embodiment of the present invention. It is a schematic diagram which shows the whole structure of the dilution refrigerator of 2nd Example of this invention. It is a schematic diagram which shows the whole structure of the dilution refrigerator of 3rd Example of this invention. It is a schematic diagram which shows the whole structure of an example of the conventional dilution refrigerator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refrigerator main body 5 Circulation path 5a Introduction path 5b Derivation path 7 Vacuum pump 36 Buffer tank

Claims (1)

Dilution comprising a refrigerator main body, a circulation path for introduction of circulating gas to the refrigerator main body and discharge of the circulation gas from the refrigerator main body, and a vacuum pump provided in the circulation path for circulating the circulation gas In the refrigerator;
An oil-free vacuum pump is used as the vacuum pump, and a buffer tank is provided between the suction port of the vacuum pump and the gas outlet port of the refrigerator main body to introduce a circulating gas to alleviate the pressure increase in the circulation path. A dilution refrigerator characterized by.

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