EP3071903B1 - Cold head for cryogenic refrigerating machine - Google Patents

Description

The invention relates to a cold head for a low-temperature refrigerator.

WO 94/29653 describes a cold head for a low-temperature refrigerator, which is operated with helium as the working gas and is connected to a high pressure source and a low pressure source. The cold head contains a multi-channel control valve, which controls the connection of a high-pressure inlet and a low-pressure inlet, each with a piston-cylinder unit and with a warm-side working area of the cold finger. The displacer, which can contain a regenerator, delimits a warm-side working space at one end and a cold-side working space at the opposite end. As the displacer is periodically moved back and forth by the piston-cylinder unit, heat is constantly extracted from the housing of the cold head. With a cold head with a single-stage displacer, temperatures down to around 30 K can be generated. With two- or three-stage displacers, temperatures down to 1 K can be generated. A thermodynamic cycle (Stirling process or Gifford-McMahon process) is carried out in the cold head with the process gas, usually helium, the process gas being conducted in a closed cycle. The result is that heat is extracted from one end region of the housing enclosing the displacer.

The cold head is connected to a compressor. Since it is a closed circuit, both the high pressure connection and the low pressure connection of the cold head are connected to the compressor. Such compressors usually have an overflow valve. This is arranged in a return flow channel arranged between the high pressure side and the low pressure side. Usually, overflow valves are spring-loaded check valves, which are usually designed for a differential pressure between high and low pressure of the compressor of, for example, 18 bar. If a cold head with a very high resistance is connected to the compressor, the working pressure on the high-pressure side of the compressor is increased. To discharge this excess energy, the overflow valve opens so that the refrigerant, in particular helium, flows via the return line to the low-pressure side of the compressor. Due to the cyclical process of the cold head, there is a pulsed gas supply from the compressor to the cold head. Gas vibrations can occur here. This can lead to frequent opening and closing of the overflow valve, especially over a long period of time. This causes considerable overloading of the overflow valve. These can damage or even destroy the valve seat of the overflow valve. Furthermore, considerable noise and performance losses occur. If the overflow valve is damaged, oil can also get into the refrigeration circuit. Another disadvantage is that power losses occur due to the existing hysteresis of the overflow valve between the opening and closing pressure.

A cold head for low-temperature chillers with the features of the preamble of claim 1 is from WO 03/036191 known.

The object of the invention is to reduce the load on the overflow valve.

According to the invention, this object is achieved by a cold head according to claim 1.

The cold head according to the invention for a low-temperature refrigeration machine has a working space in an optionally multi-part housing. A single or multi-stage displacer is arranged in the work space. Furthermore, the cold head has a high-pressure connection for supplying highly compressed cooling medium to the work space and a low-pressure connection for removing relaxed or low-pressure cooling medium. A control valve device is also provided. The control valve device is used to control the supply and discharge of refrigerant into or out of the work space. In this case, the control device can have a plurality of valves, such as, for example, an inlet and an outlet valve. It is preferred that the control valve device has a multi-channel control valve through which the connection between the high-pressure connection, the low-pressure connection and the work space is controlled.

According to the invention, the cold head has a distribution body in which at least one first connecting channel is provided. The first connection channel is used to connect the high pressure connection to the work area. This connection is preferably made via the control valve device, so that the first connection channel is arranged between the control valve device and the work space. The distributor body preferably additionally has a second connecting channel, which is arranged between the control valve device and the low-pressure connection.

In a particularly preferred embodiment, the distribution body is designed such that it also has a control channel. The control channel serves to supply and discharge control medium to the movement device, ie in particular to the piston-cylinder unit. The control medium is preferably the cooling medium. According to the cold head a bypass channel arranged between the high-pressure connection and the low-pressure connection or connecting the two connections, which is provided in the distribution body. If necessary, excess refrigerant can flow directly from the high-pressure connection to the low-pressure connection without it flowing through the cold head. Such excess energy can thus be derived via the bypass. This means that the overflow valve integrated in the compressor is relieved. If necessary, the overflow valve in the compressor can even be completely omitted or can only be provided as a safety device. This means that at least one significantly cheaper overflow valve can be used.

In a particularly preferred development of the invention, a flow regulation device is arranged in the bypass channel. This is, for example, a nozzle and / or a valve. The flow regulation device can be adjustable. It is possible that a fixed setting is carried out before operation, so that the valve opens, for example, when a pressure difference is exceeded. Furthermore, it is possible to adjust the flow regulating device from the outside, i. H. from outside the cold head. In this respect, it may be possible to make appropriate settings even during operation.

Due to the provision according to the invention of a bypass in the cold head, preferably having a pressure regulating device, a considerable cost reduction can be achieved in the compressors used. Furthermore, the operational reliability of the compressors can be improved and an increase in the compressor output can be achieved. The risk of oil breakthroughs due to a damaged overflow valve in the compressor is also reduced. Furthermore, the service life is increased and a constant noise behavior can be achieved.

In a preferred development of the invention, the cold head has a movement device for moving the displacer. The movement device can be a motor. With the help of the motor, which can be an electric motor, for example, the displacer can be moved with the aid of a link guide. This can take place, for example, via an eccentric, so that the rotary movement of the motor is converted into a linear movement of the displacer in a simple manner. Alternatively, a piston-cylinder unit can be provided for moving the displacer. The piston-cylinder unit can be operated, for example, via a separate hydraulic system. However, it is preferred to connect the piston-cylinder unit to the high-pressure connection and the low-pressure connection for actuation. The actuation of the piston-cylinder unit and thus the movement of the displacer is thus carried out in a preferred embodiment by means of the refrigerant.

The invention is explained in more detail below on the basis of a preferred embodiment with reference to the attached drawings.

Figur 1

eine schematische Darstellung einer Tieftemperatur-Kältemaschine nach dem Stand der Technik,

Figur 2

eine schematische Darstellung einer Tieftemperatur-Kältemaschine gemäß der Erfindung und

Figur 3

eine schematische Schnittansicht einer erfindungsgemäßen Ausführungsform eines Kaltkopfes.

Show it:

Figure 1

1 shows a schematic representation of a cryogenic refrigerator according to the prior art,

Figure 2

is a schematic representation of a cryogenic refrigerator according to the invention and

Figure 3

is a schematic sectional view of an embodiment of a cold head according to the invention.

A low-temperature chiller according to the state of the art ( Figure 1 ) has a compressor 10, by which refrigerant, such as helium, is compressed.

On the high pressure side, the compressor 10 is connected via a line 12 to a high pressure connection 14 of a cold head 16. A low pressure connection 18 of the cold head 16 is connected to the low pressure side of the compressor 10 via a line 20. In order to avoid overloading the compressor 10, a check valve 24 is arranged in a return flow line 22, which connects the high pressure side of the compressor 10 to the low pressure side of the compressor 10.

Within the cold head 16, a work space 26 is provided, in which an in Figure 1 Displacement piston, not shown, is arranged. An inlet valve 28 is connected to the high-pressure connection 14, so that compressed refrigerant flows into the working space 26 when the inlet valve 28 is open. Expanded refrigerant can be led to the low pressure connection 18 via an outlet valve 30.

At the in Figure 2 illustrated basic structure of a system according to the invention, similar and identical components are identified by the same reference numerals.

According to the invention, a bypass channel 32 is provided in a schematic representation between the inlet valve 28 of the cold head 16 and the outlet valve 30 of the cold head 16, in which a flow regulating device is optionally arranged. As in Figure 2 Shown in dashed lines, by providing the bypass channel 32 according to the invention, the backflow line 22 and the overflow valve 24 can be omitted.

A preferred embodiment of the cold head 16 is shown in a schematic sectional view in FIG Figure 3 shown.

The cold head 16 has a housing which consists of the two housing parts 34 and 36. In the housing part 34, two cylindrical cold-side working spaces 38 and 40 for the two displacement stages 42 and 44 are accommodated.

The upper displacement stage 42 delimits a warm-side work space 46 and it is equipped with a drive piston 48, which is accommodated in a cylinder 50 of a distribution body 52. The displacer 42, 44 is thus arranged in a work space 38, 40, 46 consisting of several subspaces.

The distribution body 52 delimits the working chamber 46 on the warm side. It is equipped with bores which form a control channel 54, a first connecting channel 56 and a second connecting channel 57. The first connecting channel 56 opens into the working space 46 and serves to supply this space with the working gas. All three channels are controlled by the control valve 58. The first connecting channel 56 connects the control valve 58 to the warm-side working space 46, the control channel 54 connects the valve 58 to the cylinder 50 and the second 57 connects the valve 58 to a low-pressure connection 60. The control valve 58 is also connected to a space 62 which communicates with a high pressure connection 64. The high-pressure connection 64 supplies helium gas at a pressure of approximately 20 bar, while helium is present at the low-pressure connection 18 at a pressure of approximately 5 bar. Through the space 62 or the second connecting channel 57, both pressures are supplied to corresponding connections (not shown) of the control valve 58. All lines lead into the top of the distribution body 52 and from there to the valve 58.

A motor 66 is housed in the housing part 36 and drives the control valve 58 via a shaft 68. This is under the action of a compression spring 70.

In the exemplary embodiment shown, the process gas which is subjected to the thermodynamic cycle and the drive gas for the piston-cylinder unit 48, 50 are identical. Helium is expediently used. A gas other than the process gas can also be used as the drive gas.

Instead of the piston-cylinder unit 48, 50 arranged in the illustrated embodiment for moving the displacers 72, 76, a motor movement of the displacers 72, 76 can also take place, for example with the aid of an electric motor. For this purpose, the electric motor can be provided with an eccentric and a link guide, so that the rotation of the eccentric is converted into a linear movement.

The displacer stage 42 has a tubular displacer 72 in the cylindrical working space 46, which is filled with a thermal regenerator 74 which is gas-permeable. The regenerator 74 is used to store cold and to release stored cold to the inflowing warm gas.

In the same way, the displacer stage 44, which has a smaller diameter than the displacer stage 42, contains a tubular displacer 76 which is axially displaceable in the cylindrical working space 40, which is connected to the displacer 72 and is also filled with a gas-permeable regenerator 78.

When the cold finger is in operation, the warm-side working space 46 is first connected to the high-pressure connection 64 via the first connecting duct 56 and the control valve 58. At the same time, the high pressure is let into the cylinder 50 via the control channel 54. The displacers 72 and 76 are shifted to the cold side (downwards). The high pressure gas also flows through the regenerators 74 and 78 to the cold side. It relaxes with cooling, with further relaxation through heat exchange with the regenerators.

In the second phase, the control channel 54 is connected to the low pressure connection. Under the effect of the high pressure, the displacers 72 and 76 are shifted towards the warm side, so that the warm-side working space 46 is located reduced and gas flows through the regenerators 74 and 78 into the cold-side working space 40.

In the third phase, the control valve 58 causes the working space 46 to be connected to the low-pressure connection 60 via the line 56. As a result, the gas relaxes in all work rooms of the cold head while cooling.

The displacers 72 and 76 are then moved to the cold side, as a result of which the volume of the cold-side working space 40 is reduced in order to be prepared for the next cycle. In this phase, the cold gas flows from the working space 40 into the regenerators 74 and 78, which are thereby further cooled.

The frequency of the described working cycle is approximately 2 Hz.

Furthermore, in the exemplary embodiment shown, a bypass duct 80 according to the invention is provided in the distribution body 52. The bypass duct 80 connects the second connecting duct 57 to the space 62. The bypass duct 80 thus connects the high-pressure connection 64 to the low-pressure connection 60. A flow regulating device, such as a valve 82, is shown schematically within the bypass duct 80. In the event of an undesirably high pressure rise in the space 62, part of the refrigerant thus flows directly through the bypass duct 80 back into the duct 57 connected to the low-pressure connection 60.

Claims (12)

1. Cold head for cryogenic refrigeration machines, comprising
   a housing (34, 36),
   a displacer (72, 76) mounted in a working chamber (38, 40, 46) of the housing (34, 36),
   a high-pressure connection (64) for supplying highly compressed refrigerant into the working chamber (38, 40, 46),
   a low-pressure connection (60) for discharging expanded refrigerant from the working chamber (38, 40, 46), and
   a control valve device (28, 30; 58) for controlling the supply and discharge of refrigerant into and from the working chamber (38, 40, 46),
   a distributor body (52) in which at least a first connecting channel (56) is provided for connecting the high-pressure connection (64) to the working chamber (38, 40, 46),
   characterized by
   a bypass channel (80) connecting the high-pressure connection (64) to the low-pressure connection (60) and provided in the distributor body (62).
2. Cold head for cryogenic refrigeration machines of claim 1, characterized in that the first connecting channel (56) is arranged between the control valve (58) and the working chamber (38, 40, 46).
3. Cold head for cryogenic refrigeration machines of one of claims 1 -2, characterized by the distributor body (52) has a second connecting channel (57) between the control valve (58) and the low-pressure connection (60).
4. Cold head for cryogenic refrigeration machines of one of claims 1-3, characterized in that the distributor body (52) has a control channel (54) for supplying and/or discharging a control medium, in particular a refrigerant, to and/or from the piston-cylinder unit (48, 50).
5. Cold head for cryogenic refrigeration machines of one of claims 1-4, characterized in that a throughflow regulation device (82) is arranged in the bypass channel (80).
6. Cold head for cryogenic refrigeration machines of claim 5, characterized in that the throughflow regulation device (82) is adjustable in particular during operation.
7. Cold head for cryogenic refrigeration machines of one of claims 1-6, characterized by a movement device (48, 50) for moving the displacer (72, 76).
8. Cold head for cryogenic refrigeration machines of claim 7, characterized in that the movement device is configured as a piston-cylinder unit (48, 50) which, for actuation, is preferably connected to the high-pressure connection (64) and the low-pressure connection (60).
9. Cold head for cryogenic refrigeration machines of claim 7, characterized in that the movement device has a motor, in particular an electric motor.
10. Cold head for cryogenic refrigeration machines of claim 9, characterized in that the electric motor drives an eccentric that acts on a slotted guide to cause a linear movement of the displacer (72, 76).
11. Cold head for cryogenic refrigeration machines of one of claims 1 - 9, characterized in that the control valve device (28, 30; 58) has a cyclically operating, multi-channel control valve (58) that controls the connection of a working chamber (38, 40, 46) to a high-pressure connection (64) and to a low-pressure connection (60).
12. Cold head for cryogenic refrigeration machines of claim 11, characterized in that the control valve (58) controls the connection of the piston-cylinder unit (48, 50).

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