JP2016537604A - Cold head of cryogenic refrigerator - Google Patents

Abstract

The cold head of the cryogenic refrigerator includes a displacer (72, 76) attached to the working chamber (38, 40, 46) of the housing (34, 36). The cold head also includes a high pressure joint (64) that provides a highly compressed refrigerant and a low pressure joint (60) that discharges expanded refrigerant from the working chamber (38, 40, 56). Further, a valve control device (58) for controlling supply and discharge of the refrigerant is provided. In the present invention, there is a bypass channel (80) connecting the high pressure joint (64) to the low pressure joint (60).

Description

  The present invention relates to a cold head of a cryogenic refrigerator.

  WO 94/29653 discloses a cold head of a cryogenic refrigerator that operates using helium as a working gas and is connected to a high pressure source and a low pressure source. The cold head includes a multi-channel control valve. The multi-channel valve controls the piston cylinder section and the connection of the cold finger on the hot side to the high pressure inlet and the low pressure inlet, respectively. The displacer including the heat storage body defines the range of the high temperature side working chamber at one end and the range of the low temperature side working chamber at the other end. On the other hand, the displacer periodically reciprocates by the piston / cylinder part, and heat is constantly taken away from the cold head housing. By providing the cold head with a single stage displacer, the temperature can be about 30K or less. By providing a two-stage or three-stage displacer, it is possible to set the temperature below 1K. A thermodynamic periodic process (Stirling process or Gifford McMahon process) occurs in a cold head using a working gas, typically helium, which is induced in a closed circuit. As a result, heat is removed from one end of the housing surrounding the displacer.

International Publication No. 94/29653 Pamphlet

  The cold head is connected to the compressor. Since the circuit is a closed circuit, both the high pressure joint and the low pressure joint of the cold head are connected to the compressor. Such compressors typically include an overpressure valve. Similarly, an overpressure valve is provided in a return channel provided between the high pressure side and the low pressure side. Typically, the overpressure valve is a spring-loaded check valve that is generally designed for a differential pressure of, for example, 18 bar between the high pressure side and the low pressure side of the compressor, for example. If a cold head with a very high resistance is connected to the compressor, the working pressure will increase excessively on the high pressure side of the compressor. In order to release this excessive energy, the overpressure valve is opened, whereby the refrigerant, specifically helium, flows to the low pressure side of the compressor via the return flow path. The cyclic process of the cold head generates a pulse gas supply from the compressor to the cold head. Here, there is a possibility that gas vibration may occur. However, when the gas vibration occurs for a long period of time, the overpressure valve may be frequently opened and closed. In this case, since the overpressure valve is seriously overloaded, the overpressure valve may be damaged or destroyed. In addition, such overload causes serious noise generation and performance degradation. If the overpressure valve is damaged, oil can enter the cooling circuit. Another disadvantage is that performance degradation occurs due to the presence of overpressure valve hysteresis between the valve opening pressure and the valve closing pressure.

  One object of the present invention is to reduce the load on the overpressure valve.

  According to the invention, this object is solved by a cold head as defined in claim 1.

  The cold head of the cryogenic refrigerator in the present invention has a working chamber in a housing, preferably a housing divided into a plurality of parts. A single-stage or multi-stage displacer is provided in the working chamber, and the cold head further includes a high-pressure joint for supplying high-pressure refrigerant to the working chamber and a low-pressure for discharging expanded or low-pressure refrigerant. And a joint. Furthermore, a valve control device is provided. The valve control device controls the supply of the refrigerant to the working chamber and the discharge of the refrigerant from the working chamber. Here, the valve control device may include a plurality of valves, for example, an inlet valve and an outlet valve. Preferably, the valve control device includes a high-pressure joint, a low-pressure joint, and a multi-channel control valve that controls a connection between the working chamber. According to the invention, the cold head has a bypass channel connecting the two joints between the high pressure joint and the low pressure joint. If necessary, excess refrigerant may flow through the bypass channel directly from the high pressure joint to the low pressure joint without flowing through the cold head. As a result, the generated excess energy is released through the bypass channel. As a result, the overpressure valve integrated in the compressor is stable. Alternatively, the overpressure valve may be omitted from the compressor or simply provided as a safety device. As a result, it is possible to use at least a significantly lower cost overpressure valve.

  As a more preferred embodiment of the present invention, a flow control device is provided in the bypass channel. The flow control device may be, for example, a nozzle and / or a valve. The flow rate adjusting device may be adjustable. In this case, a predetermined setting is made prior to the operation, so that, for example, the valve is opened when the differential pressure is exceeded. Furthermore, the adjustment by the flow regulator can be permitted from the outside, that is, from the outside of the cold head. In this way, the corresponding adjustment can be allowed to be performed even during operation.

  The present invention provides the cold head with a bypass channel, preferably including a pressure regulator, so that a significant cost reduction of the compressor used can be achieved. Furthermore, the safe operation of the compressor is promoted and the performance of the compressor is improved. The risk of oil leakage due to damaged overpressure valves in the compressor is also reduced. Furthermore, the lifetime can be extended and noise stabilization can be achieved.

  In a more preferred embodiment of the present invention, the cold head may have a moving device for moving the displacer. The moving device may be a motor. By using a motor, such as an electric motor, for example, the displacer can move along a slotted guide. For example, by using an eccentric cam, the rotational motion of the motor can be easily converted into the linear motion of the displacer. As an alternative, a piston / cylinder part for moving the displacer may be provided. The piston / cylinder part may be driven by a separate hydraulic system, for example. However, for the purpose of its movement, it is preferred that the piston / cylinder portion be connected to the high pressure joint and the low pressure joint. In a more preferred embodiment, the operation of the piston / cylinder part and the operation of the displacer are realized by a refrigerant.

  More preferably, the cold head comprises a distributor body provided with at least a first connection channel. The first connection channel allows the high pressure joint to be connected to the working chamber. Preferably, this connection is formed by a valve control device, so that the first connection channel is provided between the valve control device and the working chamber. Preferably, the distributor body additionally has a second connection channel provided between the valve control device and the low pressure joint.

  In a particularly preferred embodiment, the valve body is designed to also include a control channel. The control channel allows the supply and release of the control medium to the moving device, specifically the piston / cylinder part. The control medium is preferably a refrigerant.

  The present invention will be described in detail below with reference to preferred embodiments and the accompanying drawings.

It is the schematic of the conventional cryogenic refrigerator. It is the schematic of the cryogenic refrigerator which concerns on this invention. 1 is a schematic cross-sectional view of one embodiment of a cold head according to the present invention.

  A conventional cryogenic refrigerator (FIG. 1) includes a compressor 10 that compresses a refrigerant such as helium. On the high pressure side, the compressor 10 is connected to the high pressure joint 14 of the cold head 16 via a conduit 12. The low pressure joint 18 of the cold head 16 is connected to the low pressure side of the compressor 10 by a conduit 20. In order to avoid overpressure in the compressor 10, a check valve 24 is provided in the return flow path 22 that connects the high pressure side of the compressor 10 to the low pressure side of the compressor 10.

  Within the cold head 16, the working chamber 26 is provided at a location where a displacer piston (not shown in FIG. 1) is installed. The inlet valve 28 is connected to the high-pressure joint 14, so that the compressed refrigerant flows into the working chamber 26 when the inlet valve 28 is opened. The expanded refrigerant is guided to the low pressure joint 18 by the outlet valve 30.

  In the basic configuration of the system according to the present invention shown in FIG. 2, the same reference numerals are given to the components that are similar or the same as those in the conventional example.

  According to the invention, the bypass channel 32, shown schematically, is provided between the inlet valve 28 of the cold head 16 and the outlet valve 30 of the cold head 16. The bypass channel 32 may be provided with a flow rate adjusting device. By providing the bypass channel 32 according to the present invention, the return flow path 22 and the overpressure valve 24 can be dispensed with, as indicated by the broken line in FIG.

  A preferred embodiment of the cold head 16 is illustrated by the cross-sectional schematic of FIG.

  The cold head 16 has a housing formed by two housing parts 34 and 36. The housing part 34 is provided with two cylindrical cold side working chambers 38 and 40 on two displacer stages 42 and 44.

  The upper displacer stage 42 delimits the hot working chamber 46 and is provided with a drive piston 48 installed in the cylinder 50 of the distributor body 52. The displacers 72 and 76 are installed in the working chambers 38, 40, and 46 formed so as to be divided into a plurality of chambers.

  The distributor body 52 defines the range of the hot working chamber 46. A control channel 54, a first connection channel 56, and a second connection channel 57 are similarly provided by drilling. The first connection channel 56 is in communication with the working chamber 46 and allows the working gas to be supplied to the working chamber 46. All three channels are controlled by control valve 58. The first connection channel 56 connects the control valve 58 to the hot working chamber 46, the control channel 54 connects the control valve 58 to the cylinder 50, and the second connection channel 57 connects the control valve 58 to the low pressure joint 60. Connecting. The control valve 58 is further connected to a chamber 62 that is connected to a high pressure joint 64. Helium gas is supplied from the high pressure joint 64 at a pressure of about 20 bar, and helium reaches the low pressure joint 18 at a pressure of about 5 bar. Either pressure is supplied to a joint (not shown) corresponding to the control valve 58 via the chamber 62 and the second connection channel 57, respectively. All of the conduits connecting them pass to the upper side of the distributor body 52 and from the upper side to the control valve 58.

  The housing part 36 houses a motor 66 that drives a control valve 58 by a shaft 68. The valve is biased by a compression spring 70.

  In the illustrated embodiment, the working gas for the thermodynamic periodic process and the driving gas for the piston / cylinder sections 48, 50 are the same. Preferably helium is used. A gas different from the working gas can be used as the driving gas.

  Instead of the piston / cylinder portions 48, 50 provided in the present embodiment for moving the displacers 72, 76, the displacers 72, 76 may be moved by a motor, for example, an electric motor. In this case, the electric motor may be provided with an eccentric cam and a slotted guide so that the rotation of the eccentric cam is a linear motion.

  Within the cylindrical working chamber 46, the displacer stage 42 includes a cylindrical displacer 72 whose interior is filled with a gas permeable heat storage 74. The heat accumulator 74 acts to accumulate cold and release the cold accumulated in warm gas passing through the inside.

  Similarly, the displacer stage 44 having a diameter smaller than that of the displacer stage 42 includes a tubular displacer 76 that can move in the axial direction within the tubular working chamber 40, and the displacer 76 is connected to the displacer 72. The interior is filled with a heat storage body 78 having gas permeability.

  During cold finger operation, the hot side working chamber 46 is first connected to the high pressure joint 64 via the first connection channel 56 and the control valve 58. At the same time, high pressure is introduced into the cylinder 50 through the control channel 54. The displacers 72 and 76 move (lower) toward the low temperature side. The gas under high pressure passes through the heat storage bodies 74 and 78 and also flows to the low temperature side. The gas under high pressure during cooling spreads and further expands by heat exchange with the heat storage body.

  In the second phase, the control channel 54 is connected to the low pressure joint. Due to the effect of the high pressure, the displacers 72 and 76 move toward the high temperature side, whereby the high temperature side working chamber 46 is contracted, and the gas passes through the heat accumulators 74 and 78 from the low temperature side in the working chamber 40.

  In the third phase, the control valve 58 connects the working chamber 40 to the low pressure joint 60 through a conduit 56. Thereby, the gas in all the working chambers of the cold head expands while being cooled.

  Thereafter, the displacers 72 and 76 move to the low temperature side, and the volume of the low temperature side working chamber 40 is reduced toward the next cycle. The gas cooled in this phase flows from the working chamber 40 toward the heat storage bodies 74 and 78 and is further cooled.

  The period of the process described above is about 2 Hz.

  In the illustrated embodiment, a bypass channel 80 according to the present invention is provided in the distributor main body 52. A bypass channel 80 connects the second connection channel 57 to the chamber 62. Thus, the bypass channel 80 connects the high pressure joint 64 to the low pressure joint 60. As shown schematically, a flow rate adjusting device such as a valve 82 is provided in the bypass channel 80. When the unnecessary high pressure in the chamber 62 increases, a portion of the refrigerant flows directly through the bypass channel 80 and is returned to the second connection channel 57 connected to the low pressure joint 60.

Claims (13)

A displacer (72, 76) attached to the working chamber (38, 40, 46) of the housing (34, 36) and a high pressure joint for providing highly compressed refrigerant to the working chamber (38, 40, 46) (64), a low pressure joint (60) that discharges expanded refrigerant from the working chamber (38, 40, 56), a supply of refrigerant to the working chamber (38, 40, 46), and the In a cold head of a cryogenic refrigerator comprising a valve controller (28, 30; 58) for controlling the discharge of refrigerant from the working chamber (38, 40, 46),
A cold head of a cryogenic refrigerator, comprising a bypass channel (80) connecting the high-pressure joint (64) to the low-pressure joint (60). The cold head of the cryogenic refrigerator according to claim 1, wherein a flow rate adjusting device (82) is provided in the bypass channel (80). The cold head of the cryogenic refrigerator according to claim 2, wherein the flow rate adjusting device (82) is adjustable during operation. The cold head of the cryogenic refrigerator according to any one of claims 1 to 3, further comprising a moving device (48, 50) for moving the displacer (72, 76). 5. The moving device is configured as a piston / cylinder part (48, 50) and is preferably connected to the high pressure joint (64) and the low pressure joint (60) during operation. Cold head of a cryogenic refrigerator. The cold head of the cryogenic refrigerator according to claim 4, wherein the moving device has a motor which is an electric motor. The cold head of the cryogenic refrigerator according to claim 6, wherein the electric motor drives an eccentric cam that moves on a slotted guide for linear movement of the displacer (72, 76). The valve control device (28, 30; 58) operates periodically and has a plurality of channels for controlling the connection of the working chamber (38, 40, 46) to the high pressure joint (64) and the low pressure joint (60). The cold head of the cryogenic refrigerator according to any one of claims 1 to 7, further comprising a control valve (58). The cold head of the cryogenic refrigerator according to claim 8, wherein the control valve (58) controls connection of the piston / cylinder part (48, 50). A distributor body (52) comprising at least a first connection channel (56) provided to connect the high pressure joint (64) to the working chamber (38, 40, 46). The cold head of the cryogenic refrigerator as described in any one of 1-8. The cryogenic refrigerator according to claim 10, wherein the first connection channel (56) is provided between the control valve (58) and the working chamber (38, 40, 46). Cold head. The pole according to claim 8 or 9, wherein the distributor body (52) includes a second connection channel (57) between the control valve (58) and the low pressure joint (60). Cold head of low-temperature refrigerator. The distributor main body (52) supplies a control medium such as a refrigerant to the piston / cylinder part (48, 50) and / or discharges the control medium (54 from the piston / cylinder part (48, 50)). The cold head of a cryogenic refrigerator as claimed in any one of claims 10 to 12, characterized in that

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