JP2024059364A - Oil-lubricated compressor for cryogenic refrigerator and method of operating same - Google Patents

Abstract

[Problem] To provide a compressor for a cryogenic refrigerator that enables a reduction in the load on the cooler. [Solution] A compressor 12 for an oil-lubricated cryogenic refrigerator that compresses refrigerant gas in a cryogenic refrigerator 10 is provided. The compressor 12 includes a liquid-cooled heat exchanger 24 that cools the refrigerant gas and/or oil by heat exchange with a cooling liquid, and a cooling controller 70 configured to acquire a supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24, and to control the flow rate of the cooling liquid in the liquid-cooled heat exchanger 24 and/or the amount of heat exhausted from the compressor 12 based on the acquired supply temperature of the cooling liquid. [Selected Figure] Figure 2

Description

The present invention relates to an oil-lubricated compressor for a cryogenic refrigerator and a method for operating the same.

An oil-lubricated helium compressor with dual aftercoolers has been proposed (see, for example, Patent Document 1). This compressor has two built-in aftercoolers for cooling the helium and oil, namely a water-cooled aftercooler and an air-cooled aftercooler. The air-cooled aftercooler is arranged in series or parallel with the water-cooled aftercooler. The fan of the air-cooled aftercooler is operated to provide redundancy in case the cooling water circuit of the water-cooled aftercooler is blocked.

JP 2019-505751 A

Cryogenic refrigerators are commonly used to provide cryogenic cooling for cryogenic devices that operate at extremely low temperatures, such as superconducting magnets. A cryogenic device may contain a variety of heat-generating components, such as a cryogenic refrigerator compressor. These heat-generating components are often cooled by a common chiller attached to the cryogenic device. The chiller may typically take the form of an air-cooled chiller that provides a cooling fluid to each of the heat-generating components.

The cooling capacity of a chiller can be affected by external factors such as the ambient temperature. For example, when the ambient temperature is high in summer, the cooling capacity can drop significantly compared to when the temperature is low in winter (for example, in the case of air-cooled chillers, the drop can reach several tens of percent). There is a risk that the cooling capacity of the chiller will become strained or insufficient due to such external factors, or due to factors such as increased heat generation caused by the operating conditions of the cryogenic equipment. If the temperature of the heat-generating equipment rises excessively due to insufficient cooling capacity, there is a concern that the performance of the equipment will decrease or abnormal operation will occur. This can undesirably interfere with the operation of the cryogenic equipment.

One exemplary objective of an embodiment of the present invention is to provide a compressor for a cryogenic refrigerator that allows for reduced load on the cooler.

According to one aspect of the present invention, there is provided an oil-lubricated cryogenic refrigerator compressor that compresses refrigerant gas for the cryogenic refrigerator. The cryogenic refrigerator compressor includes a liquid-cooled heat exchanger that cools the refrigerant gas and/or oil by heat exchange with a cooling liquid, and a cooling controller configured to acquire the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger and control the cooling liquid flow rate of the liquid-cooled heat exchanger and/or the amount of heat exhausted from the cryogenic refrigerator compressor based on the acquired supply temperature of the cooling liquid.

According to one aspect of the present invention, there is provided a method for operating an oil-lubricated cryogenic refrigerator compressor that compresses refrigerant gas for the cryogenic refrigerator. The cryogenic refrigerator compressor includes a liquid-cooled heat exchanger that cools the refrigerant gas and/or oil by heat exchange with a cooling liquid. The method includes acquiring a supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger, and controlling the flow rate of the cooling liquid in the liquid-cooled heat exchanger and/or the amount of heat exhausted from the cryogenic refrigerator compressor based on the acquired supply temperature of the cooling liquid.

In addition, any combination of the above components or mutual substitution of the components or expressions of the present invention between methods, devices, systems, etc. are also valid aspects of the present invention.

The present invention provides a compressor for a cryogenic refrigerator that reduces the load on the cooler.

1 is a diagram illustrating a schematic diagram of a cryogenic device according to an embodiment; 1 is a diagram illustrating a schematic diagram of a cryogenic refrigerator according to an embodiment; FIG. 13 is a diagram illustrating a schematic diagram of another example of a cooling controller according to an embodiment. FIG. 13 is a diagram illustrating a schematic diagram of another example of a cooling controller according to an embodiment. FIG. 13 is a diagram illustrating a schematic diagram of another example of a cooling controller according to an embodiment.

Below, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate explanation, and should not be interpreted as being limiting unless otherwise specified. The embodiments are illustrative and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

Figure 1 is a schematic diagram of a cryogenic device 100 according to an embodiment. The cryogenic device 100 may be, for example, a superconducting magnet device. The superconducting magnet device is mounted in a high magnetic field device as a magnetic field source for, for example, a single crystal pulling device, an NMR (Nuclear Magnetic Resonance) system, an MRI (Magnetic Resonance Imaging) system, an accelerator such as a cyclotron, a high energy physics system such as a nuclear fusion system, or other high magnetic field device (not shown), and can generate the high magnetic field required for the device.

The cryogenic device 100 includes a cryogenic refrigerator 10 for cryogenic cooling of a superconducting magnet. The cryogenic refrigerator 10 includes an oil-lubricated cryogenic refrigerator compressor (hereinafter also simply referred to as the compressor) 12 and a cold head 14.

The compressor 12 generates heat of compression when compressing the refrigerant gas. In addition to the compressor 12, the cryogenic device 100 may also include at least one device 102_1 to 102_n that can generate heat. For example, if the cryogenic device 100 is an MRI system (or part thereof), the device 102 may include a gradient magnetic field coil, a gradient magnetic field amplifier, an RF amplifier, etc.

In order to cool the compressor 12 and other equipment 102 that may generate heat, the cryogenic device 100 is provided with a cooler 110 configured to adjust the temperature of the cooling liquid and circulate it. The cooler 110 is shared by the compressor 12 and the equipment 102. The cooler 110 is, for example, a chiller, and may be, for example, an air-cooled chiller or a chiller using another cooling method. As an exemplary configuration, the cooler 110 is configured to supply cooling liquid (for example, cooling water) to a heat exchanger 104 provided in the cryogenic device 100. The cooler 110 is also configured to recover the cooling liquid used for cooling from the heat exchanger 104 and cool it again.

A coolant line 106 is connected to each of the compressor 12 and the equipment 102 to the heat exchanger 104. Heat exchange between the cooled coolant supplied from the cooler 110 and the coolant in the coolant line 106 is carried out in the heat exchanger 104, thereby cooling the coolant in the coolant line 106. The coolant is supplied to the compressor 12 and the equipment 102 to cool them. The coolant used for cooling is returned to the heat exchanger 104 through the coolant line 106 and is cooled again.

Figure 2 is a schematic diagram of a cryogenic refrigerator 10 according to an embodiment.

The compressor 12 is configured to recover the refrigerant gas of the cryogenic refrigerator 10 from the cold head 14, pressurize the recovered refrigerant gas, and supply the refrigerant gas to the cold head 14 again. The compressor 12 is also called a compressor unit. The cold head 14 is also called an expander, and has a room temperature section 14a and a low temperature section 14b, also called a cooling stage. The refrigerant gas is also called a working gas, and is typically helium gas, although other suitable gases may be used. The compressor 12 and the cold head 14 form the refrigeration cycle of the cryogenic refrigerator 10, thereby cooling the low temperature section 14b to a desired cryogenic temperature. The low temperature section 14b can cool an object to be cooled, such as a superconducting magnet.

The cryocooler 10 is, by way of example, a single-stage or two-stage Gifford-McMahon (GM) refrigerator, but may also be a pulse tube refrigerator, a Stirling refrigerator, or other types of cryocooler. The cold head 14 has a different configuration depending on the type of cryocooler 10, but the compressor 12 may have the configuration described below regardless of the type of cryocooler 10.

In general, the pressure of the refrigerant gas supplied from the compressor 12 to the cold head 14 and the pressure of the refrigerant gas recovered from the cold head 14 to the compressor 12 are both significantly higher than atmospheric pressure and can be referred to as the first high pressure and the second high pressure, respectively. For ease of explanation, the first high pressure and the second high pressure are also simply referred to as the high pressure and the low pressure, respectively. Typically, the high pressure is, for example, 2 to 3 MPa. The low pressure is, for example, 0.5 to 1.5 MPa, e.g., about 0.8 MPa.

The compressor 12 includes a compressor body 16, a refrigerant gas line 18, an oil circulation line 20, and a compressor cooling system 22. In FIG. 2, for ease of understanding, the refrigerant gas line 18 is shown by a solid line, and the oil circulation line 20 is shown by a dashed line. As will be described in detail later, the compressor cooling system 22 includes a liquid-cooled heat exchanger 24 and an air-cooled heat exchanger 26, and is configured to cool the refrigerant gas line 18 and the oil circulation line 20. The compressor 12 also includes a compressor housing 28 that houses each of the components of the compressor 12, such as the compressor body 16, the refrigerant gas line 18, the oil circulation line 20, and the compressor cooling system 22.

The compressor body 16 is configured to compress the refrigerant gas drawn in from its intake port and discharge it from its discharge port. The compressor body 16 uses oil for cooling and lubrication, and the drawn refrigerant gas is directly exposed to this oil inside the compressor body 16. Therefore, the refrigerant gas is discharged from the discharge port with a small amount of oil mixed in.

The compressor body 16 may be, for example, a scroll type, rotary type, or other pump that pressurizes the refrigerant gas. The compressor body 16 may be configured to discharge a fixed, constant flow rate of refrigerant gas. Alternatively, the compressor body 16 may be configured to discharge a variable flow rate of refrigerant gas. The compressor body 16 may also be referred to as a compression capsule.

The refrigerant gas line 18 includes a discharge port 30, a suction port 31, a discharge flow path 32, and a suction flow path 33. The discharge port 30 is an outlet port for the refrigerant gas installed in the compressor housing 28 to send out the refrigerant gas pressurized to a high pressure by the compressor body 16 from the compressor 12, and the suction port 31 is an inlet port for the refrigerant gas installed in the compressor housing 28 to receive the low-pressure refrigerant gas into the compressor 12. The discharge flow path 32 and the suction flow path 33 are housed in the compressor housing 28. The discharge port of the compressor body 16 is connected to the discharge port 30 by the discharge flow path 32, and the suction port 31 is connected to the suction port of the compressor body 16 by the suction flow path 33.

The discharge flow path 32 is provided with a liquid-cooled heat exchanger 24 and an air-cooled heat exchanger 26 that constitute the compressor cooling system 22. In addition, the discharge flow path 32 is provided with an oil separator 34 and an adsorber 35 downstream of the compressor cooling system 22.

The oil separator 34 is provided to separate the oil that is mixed into the refrigerant gas as it passes through the compressor body 16 from the refrigerant gas. The adsorber 35 is provided to remove remaining contaminants in the refrigerant gas, such as vaporized oil, from the refrigerant gas by adsorption. The oil separator 34 and the adsorber 35 are connected in series. In the discharge flow path 32, the oil separator 34 is disposed on the compressor body 16 side, and the adsorber 35 is disposed on the discharge port 30 side.

An oil return line 21 is provided to connect the oil separator 34 to the compressor body 16. The oil recovered by the oil separator 34 can be returned to the compressor body 16 through the oil return line 21. A filter for removing dust contained in the oil separated by the oil separator 34 and an orifice for controlling the amount of oil returned to the compressor body 16 may be provided midway along the oil return line 21.

On the other hand, a storage tank 36 is provided in the intake passage 33. The storage tank 36 is provided as a volume for removing pulsation contained in the low-pressure refrigerant gas returning from the cold head 14 to the compressor 12.

The refrigerant gas line 18 is also provided with a refrigerant gas bypass valve 38 that connects the discharge passage 32 to the suction passage 33 so as to bypass the compressor body 16. As an example, the refrigerant gas bypass valve 38 branches off from the discharge passage 32 between the oil separator 34 and the absorber 35, and is connected to the suction passage 33 between the compressor body 16 and the storage tank 36. The refrigerant gas bypass valve 38 is provided for refrigerant gas flow rate control and/or for equalizing the pressure between the discharge passage 32 and the suction passage 33 when the compressor 12 is stopped.

The refrigerant gas line 18 of the compressor 12 is connected to the cold head 14. A high-pressure port 40 and a low-pressure port 41 are provided in the room temperature section 14a of the cold head 14. The high-pressure port 40 is connected to the discharge port 30 by a high-pressure pipe 42, and the low-pressure port 41 is connected to the suction port 31 by a low-pressure pipe 43.

The oil circulation line 20 connects the oil outlet of the compressor body 16 to the oil inlet so as to pass through the compressor cooling system 22 (i.e., the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26). Therefore, the oil flowing out of the compressor body 16 can be cooled by the compressor cooling system 22 and flow back into the compressor body 16.

In this embodiment, the oil circulation line 20 branches into multiple oil flow paths (two in this example) in the compressor cooling system 22, as described below. These branched oil flow paths merge again between the compressor cooling system 22 and the oil inlet of the compressor body 16.

The oil circulation line 20 may be provided with an orifice that controls the flow rate of oil flowing therethrough. The oil circulation line 20 may also be provided with a filter that removes dust particles contained in the oil. Such an orifice and filter may be provided, for example, downstream of the oil circulation line 20, that is, between the compressor cooling system 22 and the oil inlet of the compressor body 16.

As described above, the compressor cooling system 22 includes the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26. The liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26 are connected in series, and the liquid-cooled heat exchanger 24 is provided upstream of the air-cooled heat exchanger 26. Thus, the oil and high-pressure refrigerant gas heated by the heat of compression generated by the compression of the refrigerant gas in the compressor body 16 first flow from the compressor body 16 into the liquid-cooled heat exchanger 24 to be cooled, and then flow into the air-cooled heat exchanger 26.

In this embodiment, the liquid-cooled heat exchanger 24 is mounted on the compressor 12 as the main cooling device of the compressor 12, and the air-cooled heat exchanger 26 is mounted on the compressor 12 as a backup cooling device of the compressor 12. Thus, the liquid-cooled heat exchanger 24 operates all the time while the compressor 12 is in operation, and the air-cooled heat exchanger 26 does not operate when the liquid-cooled heat exchanger 24 is operating normally, and may operate when the liquid-cooled heat exchanger 24 does not operate due to a malfunction or the like, or when its cooling capacity is reduced. Therefore, the air-cooled heat exchanger 26 may be configured to switch itself on and off based on the output of a sensor provided on the compressor 12, such as an oil or refrigerant gas temperature sensor.

The liquid-cooled heat exchanger 24 includes a first portion 24a that cools the refrigerant gas by heat exchange between the refrigerant gas and the cooling liquid, and a second portion 24b that cools the oil by heat exchange between the oil and the cooling liquid. The first portion 24a is disposed between the compressor body 16 and the oil separator 34 in the discharge flow path 32, more specifically, between the discharge port of the compressor body 16 and the air-cooled heat exchanger 26, and cools the refrigerant gas flowing through the discharge flow path 32. The second portion 24b is disposed between the oil outlet of the compressor body 16 and the air-cooled heat exchanger 26 in the oil circulation line 20, and cools the oil flowing through the oil circulation line 20.

Typically, water (e.g., tap water, industrial water, etc.) is used as the cooling liquid, but other suitable cooling liquids may be used. The supply side of the cooling liquid line 106 is connected to the cooling liquid inlet port 60 of the compressor 12, and the recovery side of the cooling liquid line 106 is connected to the cooling liquid outlet port 61 of the compressor 12. Thus, the cooling liquid is supplied from the supply side of the cooling liquid line 106 to the compressor 12 through the cooling liquid inlet port 60. The cooling liquid from the cooling liquid inlet port 60 is supplied to the first part 24a and the second part 24b of the liquid-cooled heat exchanger 24 for cooling the refrigerant gas and oil. The cooling liquid used for cooling in the liquid-cooled heat exchanger 24 is discharged from the compressor 12 to the recovery side of the cooling liquid line 106 through the cooling liquid outlet port 61. In this way, the compression heat generated in the compressor body 16 is removed outside the compressor 12 together with the cooling liquid. The coolant may be cooled by a coolant circulation device such as a known water chiller (e.g., the cooler 110 shown in FIG. 1) and supplied again to the compressor 12 through the coolant line 106.

The air-cooled heat exchanger 26 also includes a cooling fan 50, a first oil line 46 arranged to be forcibly cooled by the cooling fan 50, and a second oil line 48 arranged to bypass the first oil line 46 and be forcibly cooled by the cooling fan 50.

The first oil line 46 and the second oil line 48 are part of the oil circulation line 20 arranged in the air-cooled heat exchanger 26. The second oil line 48 branches off from the oil circulation line 20 upstream of the air-cooled heat exchanger 26, i.e., between the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26, and rejoins the first oil line 46 downstream of the air-cooled heat exchanger 26, i.e., between the air-cooled heat exchanger 26 and the oil inlet of the compressor body 16.

As an exemplary configuration, the cooling fan 50 is installed in the compressor housing 28 so that, when activated, it discharges air from the air-cooled heat exchanger 26 to the outside. Two air intakes 52 are provided in the compressor housing 28 in a portion surrounding the air-cooled heat exchanger 26, and when the cooling fan 50 is activated, air is taken in from the outside through these air intakes 52 into the air-cooled heat exchanger 26. The air flow blown into the air-cooled heat exchanger 26 from one air intake 52 is used for forced air cooling of the refrigerant gas line 18 and the first oil line 46, and the other air flow blown into the air-cooled heat exchanger 26 from the other air intake 52 is used for forced air cooling of the second oil line 48. In FIG. 2, these air flows are shown diagrammatically with thick arrows for ease of understanding.

The cooling fan 50 of the air-cooled heat exchanger 26 may generate an air flow in the opposite direction to that of the above example, and may be configured to blow air from the outside into the air-cooled heat exchanger 26. The cooling fan 50 may be configured to blow air onto the refrigerant gas line 18, the first oil line 46, and the second oil line 48.

During operation of the cryogenic refrigerator 10, the refrigerant gas recovered from the cold head 14 to the compressor 12 flows from the low pressure port 41 through the low pressure piping 43 into the suction port 31 of the compressor 12. The refrigerant gas passes through the storage tank 36 on the suction passage 33 and is recovered to the suction port of the compressor body 16. The refrigerant gas is compressed and pressurized by the compressor body 16. The refrigerant gas discharged from the discharge port of the compressor body 16 is cooled by the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26, and then passes through the oil separator 34 and the absorber 35 before leaving the compressor 12 from the discharge port 30. The refrigerant gas is supplied to the inside of the cold head 14 through the high pressure piping 42 and the high pressure port 40.

Oil flowing out from the oil outlet of the compressor body 16 flows through the oil circulation line 20 into the liquid-cooled heat exchanger 24, where it is cooled by heat exchange between the oil and the cooling liquid. The cooled oil flows from the liquid-cooled heat exchanger 24 into the air-cooled heat exchanger 26. The oil branches into the first oil line 46 and the second oil line 48 within the air-cooled heat exchanger 26. When the cooling fan 50 is operating, the oil is cooled by air as it flows through the first oil line 46 and the second oil line 48. The oil flowing out from the air-cooled heat exchanger 26 is returned to the oil inlet of the compressor body 16 through the oil circulation line 20.

In this embodiment, the compressor 12 includes a cooling controller 70 configured to acquire the supply temperature of the coolant supplied to the liquid-cooled heat exchanger 24 and control the flow rate of the coolant in the liquid-cooled heat exchanger 24 based on the acquired supply temperature of the coolant. The cooling controller 70 is configured to compare the acquired supply temperature of the coolant with a temperature threshold and limit the flow rate of the coolant in the liquid-cooled heat exchanger 24 if the supply temperature exceeds the temperature threshold.

The cooling controller 70 includes a temperature sensor 72 that measures the supply temperature of the coolant supplied to the liquid-cooled heat exchanger 24. The temperature sensor 72 is provided on the supply side of the coolant line 106, in this example, between the coolant inlet port 60 and the liquid-cooled heat exchanger 24 in the compressor 12. The temperature sensor 72 may be provided in the coolant inlet port 60. The temperature sensor may be, for example, a thermistor.

In addition, the cooling controller 70 includes a coolant bypass valve 74 connected in parallel with the liquid-cooled heat exchanger 24 and a valve controller 76 configured to open or increase the opening of the coolant bypass valve 74 when the supply temperature of the coolant exceeds a temperature threshold.

The cooling controller 70 and/or valve controller 76 are realized as hardware components using elements and circuits including a computer's CPU and memory, and as software components using computer programs, etc., but are depicted in the diagram as functional blocks realized by the cooperation of these components. Those skilled in the art will understand that these functional blocks can be realized in various ways by combining hardware and software.

The valve controller 76 may be a valve driver and may be built into the coolant bypass valve 74 or other valve. Alternatively, the valve controller 76 may be installed outside the valve and connected to the valve.

The cooling controller 70 operates, for example, as follows. First, the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24 is acquired. This cooling liquid temperature is measured by the temperature sensor 72. A signal indicating the measured temperature is output from the temperature sensor 72 and transmitted to the valve controller 76. The valve controller 76 receives the measured temperature signal from the temperature sensor 72. In this way, the valve controller 76 can acquire the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24.

The valve controller 76 controls the coolant flow rate of the liquid-cooled heat exchanger 24 based on the acquired coolant supply temperature. Specifically, for example, the valve controller 76 compares the acquired coolant supply temperature with a temperature threshold value. The coolant bypass valve 74 may be an on-off valve. In this case, the valve controller 76 opens and closes the coolant bypass valve 74 based on the comparison result. Alternatively, the coolant bypass valve 74 may be a flow control valve. In this case, the valve controller 76 may open and close the coolant bypass valve 74 or adjust its opening degree based on the comparison result.

The temperature threshold may be set based on the upper limit temperature (e.g., about 30°C) of the specifications for the temperature of the cooling liquid supplied by the cooler 110, or may be equal to this upper limit temperature. The temperature threshold can be set appropriately based on the designer's empirical knowledge or on experiments or simulations performed by the designer. The temperature threshold may be set in advance and stored in the valve controller 76.

When the coolant supply temperature falls below the temperature threshold, the valve controller 76 closes the coolant bypass valve 74. In this case, the coolant supplied from the coolant line 106 flows into the liquid-cooled heat exchanger 24. Thus, the coolant is used to cool the refrigerant gas and oil in the liquid-cooled heat exchanger 24.

On the other hand, when the supply temperature of the coolant exceeds the temperature threshold, the valve controller 76 opens the coolant bypass valve 74. In this case, the coolant supplied from the coolant line 106 can flow to both the coolant bypass valve 74 and the liquid-cooled heat exchanger 24. However, since the flow resistance of the liquid-cooled heat exchanger 24 is generally large, in practice, most or substantially all of the coolant flows to the coolant bypass valve 74 instead of the liquid-cooled heat exchanger 24.

If the coolant bypass valve 74 is of a type whose opening can be controlled, the valve controller 76 may increase the opening of the coolant bypass valve 74 when the supply temperature of the coolant exceeds the temperature threshold value. When the supply temperature of the coolant falls below the temperature threshold value, the valve controller 76 may decrease the opening of the coolant bypass valve 74. Even in this way, the cooling of the liquid-cooled heat exchanger 24 can be restricted when the temperature of the coolant supplied to the liquid-cooled heat exchanger 24 is high. Furthermore, if the coolant temperature drops, the restriction can be relaxed or lifted.

As described above, the cooling capacity of the cooler 110 may be insufficient due to external factors such as the ambient temperature or other factors, causing the temperature of the coolant supplied from the cooler 110 to the compressor 12 to increase. According to an embodiment, the cooling controller 70 can use the coolant bypass valve 74 to limit the flow rate of the coolant in the liquid-cooled heat exchanger 24. The coolant bypasses the liquid-cooled heat exchanger 24 through the coolant bypass valve 74, so that little (or no) coolant is supplied to the liquid-cooled heat exchanger 24, and the cooling effect of the liquid-cooled heat exchanger 24 is limited or virtually nonexistent. The compressor 12 can reduce the amount of heat dissipated to the cooler 110, i.e., the load on the cooler 110 can be reduced.

The surplus power of the cooler 110 thus created can be used to cool other equipment 102 in the cryogenic device 100 that requires heat dissipation. In this way, possible cooling capacity shortages in the cooler 110 and problems resulting from this can be addressed, and the operation of the cryogenic device 100 can be continued.

Furthermore, the cooling controller 70 may be configured to operate the air-cooled heat exchanger 26 when the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24 exceeds a temperature threshold. In this way, despite the above-mentioned limitations on the supply of cooling liquid to the liquid-cooled heat exchanger 24, the compressor 12 can maintain cooling using the air-cooled heat exchanger 26, or using the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26 together.

In this case, for example, the valve controller 76 may be configured to control not only the coolant bypass valve 74 but also the cooling fan 50. The valve controller 76 may operate the cooling fan 50 in conjunction with the operation of the coolant bypass valve 74 described above based on the supply temperature of the coolant.

That is, when the coolant supply temperature exceeds the temperature threshold, the valve controller 76 opens the coolant bypass valve 74 and operates the air-cooled heat exchanger 26 (turns on the cooling fan 50). On the other hand, when the coolant supply temperature falls below the temperature threshold, the valve controller 76 closes the coolant bypass valve 74 and does not operate the air-cooled heat exchanger 26 (turns off the cooling fan 50). This temperature threshold may be the same value as the above-mentioned temperature threshold used to open and close the coolant bypass valve 74.

By operating the air-cooled heat exchanger 26, the heat generated by the compressor 12 is released to the surroundings of the compressor 12 together with the air flow of the air-cooled heat exchanger 26. In some cases, this may cause an excessive rise in the surrounding temperature, which may adversely affect surrounding equipment.

To address this, the cooling controller 70 may be configured to obtain the ambient temperature and stop the air-cooled heat exchanger 26 based on the obtained ambient temperature. Additionally or alternatively, the cooling controller 70 may be configured to obtain the ambient temperature and release the restriction on the flow rate of the cooling liquid in the liquid-cooled heat exchanger 24 based on the obtained ambient temperature.

To obtain the ambient temperature, the cooling controller 70 may include an ambient temperature sensor 54 that measures the ambient temperature. The ambient temperature sensor 54 may be disposed, for example, in the compressor housing 28 near the air-cooled heat exchanger 26. The ambient temperature sensor 54 may be installed in the cooling fan 50.

For example, the cooling controller 70 (e.g., valve controller 76) obtains the ambient temperature measured by the ambient temperature sensor 54 and compares the ambient temperature to a predetermined ambient temperature threshold. When the ambient temperature falls below the ambient temperature threshold, the cooling controller 70 activates the air-cooled heat exchanger 26. Additionally or alternatively, the cooling controller 70 limits the coolant flow rate of the liquid-cooled heat exchanger 24 as described above (e.g., opens the coolant bypass valve 74). On the other hand, when the ambient temperature exceeds the ambient temperature threshold, the cooling controller 70 does not activate the air-cooled heat exchanger 26. Additionally or alternatively, the cooling controller 70 releases the limit on the coolant flow rate of the liquid-cooled heat exchanger 24 (e.g., closes the coolant bypass valve 74).

FIG. 3 is a diagram showing another example of the cooling controller 70 according to the embodiment. In addition to the temperature sensor 72 and the valve controller 76 described above, the cooling controller 70 may include a control valve 75 connected in series with the liquid-cooled heat exchanger 24. The control valve 75 may be an on-off valve. Alternatively, the cooling liquid bypass valve 74 may be a flow control valve. The cooling controller 70 may be configured to open/close the control valve 75 or adjust the opening degree thereof based on the supply temperature of the cooling liquid obtained from the temperature sensor 72, thereby controlling the flow rate of the cooling liquid in the liquid-cooled heat exchanger 24.

For example, the valve controller 76 compares the supply temperature of the coolant obtained from the temperature sensor 72 with the temperature threshold value. When the supply temperature of the coolant falls below the temperature threshold value, the valve controller 76 opens the control valve 75. In this case, the coolant supplied from the coolant line 106 flows into the liquid-cooled heat exchanger 24. Thus, the coolant is used to cool the refrigerant gas and oil in the liquid-cooled heat exchanger 24. On the other hand, when the supply temperature of the coolant exceeds the temperature threshold value, the valve controller 76 closes the control valve 75. In this case, the coolant supplied from the coolant line 106 is cut off. Thus, the coolant is not used for cooling in the liquid-cooled heat exchanger 24.

Even in this way, the compressor 12 can reduce the amount of heat dissipated to the cooler 110 to deal with the rise in the temperature of the cooling liquid, thereby reducing the load on the cooler 110.

If the control valve 75 is of a type whose opening can be controlled, the valve controller 76 may decrease the opening of the control valve 75 when the supply temperature of the coolant exceeds the temperature threshold value. When the supply temperature of the coolant falls below the temperature threshold value, the valve controller 76 may increase the opening of the control valve 75. Even in this way, the cooling of the liquid-cooled heat exchanger 24 can be restricted when the temperature of the coolant supplied to the liquid-cooled heat exchanger 24 is high. Furthermore, if the coolant temperature drops, the restriction can be relaxed or lifted.

Also, as shown by the dashed line in FIG. 3, the above-mentioned coolant bypass valve 74 may be used in combination with the control valve 75. The cooling controller 70 may be configured to link the coolant bypass valve 74 and the control valve 75 based on the supply temperature of the coolant. For example, the valve controller 76 may control both the coolant bypass valve 74 and the control valve 75. The valve controller 76 may control the control valve 75 in conjunction with the operation of the above-mentioned coolant bypass valve 74 based on the supply temperature of the coolant. That is, when the supply temperature of the coolant exceeds the temperature threshold, the valve controller 76 may open the coolant bypass valve 74 and close the control valve 75. On the other hand, when the supply temperature of the coolant falls below the temperature threshold, the valve controller 76 may close the coolant bypass valve 74 and open the control valve 75.

FIG. 4 is a diagram showing a schematic diagram of another example of the cooling controller 70 according to the embodiment. The cooling controller 70 includes a first temperature sensor 72 on the supply side, as well as a second temperature sensor 73 and a flow rate sensor 78 on the recovery side. The second temperature sensor 73 measures the discharge temperature of the cooling liquid discharged from the liquid-cooled heat exchanger 24. The second temperature sensor 73 may be provided between the cooling liquid outlet port 61 and the liquid-cooled heat exchanger 24, or at the cooling liquid outlet port 61. The flow rate sensor 78 measures the cooling liquid flow rate of the liquid-cooled heat exchanger 24. The flow rate sensor 78 is provided on the supply side of the cooling liquid line 106, in this example, between the first temperature sensor 72 and the control valve 75.

As described below, the cooling controller 70 may be configured to acquire the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24, the discharge temperature of the cooling liquid discharged from the liquid-cooled heat exchanger 24, and the cooling liquid flow rate of the liquid-cooled heat exchanger 24, calculate the amount of heat dissipation to the liquid-cooled heat exchanger 24 based on the acquired supply temperature, discharge temperature, and cooling liquid flow rate, and limit the cooling liquid flow rate of the liquid-cooled heat exchanger 24 so that the calculated amount of heat dissipation is equal to or less than the allowable heat dissipation amount.

For example, the valve controller 76 first obtains the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24 from the first temperature sensor 72, obtains the discharge temperature of the cooling liquid discharged from the liquid-cooled heat exchanger 24 from the second temperature sensor 73, and obtains the cooling liquid flow rate of the liquid-cooled heat exchanger 24 from the flow rate sensor 78.

Next, the valve controller 76 calculates the amount of heat dissipated to the liquid-cooled heat exchanger 24 based on the acquired supply temperature, discharge temperature, and coolant flow rate. The amount of heat dissipated from the compressor 12 to the liquid-cooled heat exchanger 24 can be calculated by a known method from the temperature difference between the inlet and outlet of the liquid-cooled heat exchanger 24 and the coolant flow rate flowing through the liquid-cooled heat exchanger 24.

The valve controller 76 then limits the flow rate of the cooling liquid in the liquid-cooled heat exchanger 24 so that the calculated amount of heat dissipation is equal to or less than the allowable amount of heat dissipation. The allowable amount of heat dissipation is the amount of heat dissipation permitted to be dissipated from the compressor 12 to the cooler 110 by the liquid-cooled heat exchanger 24, and may be, for example, a value that correlates with the supply temperature of the cooling liquid or a constant value. The allowable amount of heat dissipation can be set appropriately based on the designer's empirical knowledge or on experiments, simulations, etc. performed by the designer.

The valve controller 76 compares the calculated amount of heat dissipation with this allowable amount of heat dissipation. When the calculated amount of heat dissipation falls below the allowable amount of heat dissipation, the valve controller 76 opens the control valve 75. In this case, the coolant supplied from the coolant line 106 flows into the liquid-cooled heat exchanger 24. Thus, the coolant is used to cool the refrigerant gas and oil in the liquid-cooled heat exchanger 24. On the other hand, when the calculated amount of heat dissipation exceeds the allowable amount of heat dissipation, the valve controller 76 closes the control valve 75. In this case, the coolant supplied from the coolant line 106 is cut off. Thus, the coolant is not used for cooling in the liquid-cooled heat exchanger 24.

In this way, the compressor 12 can reduce the amount of heat dissipated to the cooler 110 and reduce the load on the cooler 110.

If the control valve 75 is of a type whose opening can be controlled, the valve controller 76 may decrease the opening of the control valve 75 when the calculated amount of heat dissipation exceeds the allowable amount of heat dissipation. If the calculated amount of heat dissipation falls below the allowable amount of heat dissipation, the valve controller 76 may increase the opening of the control valve 75. Even in this way, when the amount of heat dissipation from the compressor 12 to the liquid-cooled heat exchanger 24 is large, the cooling by the liquid-cooled heat exchanger 24 can be restricted. Furthermore, if the amount of heat dissipation decreases, the restriction can be relaxed or lifted.

Also, in the embodiment of FIG. 4, the above-mentioned coolant bypass valve 74 may be used in combination with the control valve 75, as in the embodiment of FIG. 3. The cooling controller 70 may be configured to link the coolant bypass valve 74 and the control valve 75 based on the calculated amount of heat dissipation. For example, the valve controller 76 may control both the coolant bypass valve 74 and the control valve 75. The valve controller 76 may control the coolant bypass valve 74 in linkage with the operation of the above-mentioned control valve 75 based on the calculated amount of heat dissipation. That is, when the calculated amount of heat dissipation exceeds the allowable amount of heat dissipation, the valve controller 76 may open the coolant bypass valve 74 and close the control valve 75. On the other hand, when the calculated amount of heat dissipation falls below the allowable amount of heat dissipation, the valve controller 76 may close the coolant bypass valve 74 and open the control valve 75.

Figure 5 is a schematic diagram of another example of a cooling controller 70 according to an embodiment. The compressor 12 is equipped with a compressor motor 80 whose operating frequency (i.e., rotation speed) is variable, and the compressor body 16 is driven by the compressor motor 80. The compressor motor 80 may be, for example, an electric motor or any other suitable type of motor. By increasing the operating frequency of the compressor motor 80, the discharge flow rate of the compressor body 16 is increased. At this time, the amount of exhaust heat of the compressor 12 also increases. Conversely, by decreasing the operating frequency of the compressor motor 80, the discharge flow rate of the compressor body 16 is decreased. At this time, the amount of exhaust heat of the compressor 12 also decreases.

The cooling controller 70 includes an inverter 82 that controls the operating frequency of the compressor motor 80. The compressor motor 80 and the inverter 82 are powered from an external power source such as a commercial power source (three-phase AC power source). The inverter 82 is configured to adjust the frequency of the power input from the external power source under the control of the cooling controller 70 as described below, and output the power to the compressor motor 80 at any frequency. The operating frequency of the compressor motor 80 corresponds to the output frequency of the inverter 82, and can be adjusted, for example, in the range of 30 Hz to 100 Hz, or 40 Hz to 70 Hz.

The cooling controller 70 is configured to acquire the supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger 24, and to control the amount of heat discharged from the compressor 12 based on the acquired supply temperature of the cooling liquid. The cooling controller 70 is configured to compare the acquired supply temperature of the cooling liquid with a temperature threshold, and to limit the operating frequency of the compressor motor 80 if the supply temperature exceeds the temperature threshold.

For example, the cooling controller 70 compares the coolant supply temperature obtained from the temperature sensor 72 with a temperature threshold value. When the coolant supply temperature falls below the temperature threshold value, the cooling controller 70 maintains the operating frequency of the compressor motor 80. Alternatively, the cooling controller 70 allows the operating frequency of the compressor motor 80 to increase. In other words, the amount of heat exhausted by the compressor 12 is allowed to increase.

On the other hand, when the supply temperature of the coolant exceeds the temperature threshold, the cooling controller 70 reduces the operating frequency of the compressor motor 80. The amount of reduction in the operating frequency may be a constant value, or may be determined according to the difference between the supply temperature of the coolant and the temperature threshold. In this case, the amount of exhaust heat of the compressor 12 can be reduced.

In this way, the compressor 12 can reduce the heat it generates, thereby reducing the load on the cooler 110.

The above-described embodiment of limiting the operating frequency of the compressor motor may be used in conjunction with the embodiment of limiting the cooling liquid flow rate of the liquid-cooled heat exchanger 24 described with reference to Figures 1 to 4.

The present invention has been described above based on examples. Those skilled in the art will understand that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination will have the combined effects of each of the combined embodiments.

In the above-described embodiment, the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26 are connected in series in the compressor cooling system 22, and the liquid-cooled heat exchanger 24 is provided upstream of the air-cooled heat exchanger 26. However, the compressor cooling system 22 may have other configurations. For example, the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26 may be connected in series, and the air-cooled heat exchanger 26 may be provided upstream of the liquid-cooled heat exchanger 24. Alternatively, the liquid-cooled heat exchanger 24 and the air-cooled heat exchanger 26 may be connected in parallel.

The liquid-cooled heat exchanger 24 may be configured to cool only one of the refrigerant gas and the oil. Alternatively, the liquid-cooled heat exchanger 24 may include a first liquid-cooled heat exchanger that cools the refrigerant gas and a second liquid-cooled heat exchanger that cools the oil. Similarly, the air-cooled heat exchanger 26 may be configured to cool only one of the refrigerant gas and the oil. Alternatively, the air-cooled heat exchanger 26 may include a first air-cooled heat exchanger that cools the refrigerant gas and a second air-cooled heat exchanger that cools the oil.

In the above-described embodiment, the cooling controller 70 is provided within the compressor 12, i.e., within the compressor housing 28 of the compressor 12. Alternatively, the cooling controller 70 may be provided outside the compressor 12. For example, the cooling controller 70 may be housed in a housing separate from the compressor housing 28, and may be located adjacent or close to the compressor housing 28, or away from the compressor 12.

The temperature sensor 72 for measuring the coolant supply temperature may be disposed at a location separate from the compressor 12. For example, the temperature sensor 72 may be provided in the cooler 110. Alternatively, the temperature sensor 72 may be provided in a coolant line to the other equipment 102. The cooling controller 70 may obtain the coolant supply temperature from the temperature sensor 72 provided in the cooler 110 and/or the other equipment 102.

To mitigate or prevent sudden changes in the coolant flow rate of the liquid-cooled heat exchanger 24 due to operation of the coolant bypass valve 74 and/or the control valve 75, the cooling controller 70 may include an orifice or constant flow valve in series with the coolant bypass valve 74 and/or in series with the control valve 75.

The present invention has been described using specific terms based on the embodiment, but the embodiment merely illustrates one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiment without departing from the concept of the present invention as defined in the claims.

10 cryogenic refrigerator, 12 compressor, 16 compressor body, 24 liquid-cooled heat exchanger, 26 air-cooled heat exchanger, 70 cooling controller, 75 control valve, 76 valve controller, 80 compressor motor.

Claims (9)

An oil-lubricated compressor for a cryogenic refrigerator that compresses a refrigerant gas for the cryogenic refrigerator,
a liquid-cooled heat exchanger that cools the refrigerant gas and/or oil by heat exchange with a cooling liquid;
and a cooling controller configured to acquire a supply temperature of the cooling liquid supplied to the liquid-cooled heat exchanger, and to control a flow rate of the cooling liquid in the liquid-cooled heat exchanger and/or an amount of exhaust heat of the compressor for the cryogenic refrigerator based on the acquired supply temperature of the cooling liquid. The compressor for a cryogenic refrigerator according to claim 1, characterized in that the cooling controller is configured to compare the acquired coolant supply temperature with a temperature threshold, and limit the coolant flow rate of the liquid-cooled heat exchanger if the supply temperature exceeds the temperature threshold. The cooling controller includes:
a control valve connected in series with the liquid-cooled heat exchanger;
3. The compressor for a cryogenic refrigerator according to claim 2, further comprising: a valve controller configured to close the control valve or reduce an opening degree of the control valve when the supply temperature of the coolant exceeds the temperature threshold value. The cooling controller includes:
a bypass valve connected in parallel to the liquid-cooled heat exchanger;
3. The compressor of claim 2, further comprising: a valve controller configured to open the bypass valve or increase the opening of the bypass valve when the supply temperature of the coolant exceeds the temperature threshold. The cooling system further includes an air-cooled heat exchanger that cools the refrigerant gas and/or the oil,
5. The compressor for a cryogenic refrigerator according to claim 2, wherein the cooling controller is configured to operate the air-cooled heat exchanger when the supply temperature exceeds the temperature threshold. The compressor for a cryogenic refrigerator according to claim 5, characterized in that the cooling controller is configured to acquire an ambient temperature and stop the air-cooled heat exchanger and/or release the restriction on the coolant flow rate based on the acquired ambient temperature. The cooling controller includes:
Acquire a discharge temperature of the cooling liquid discharged from the liquid-cooling heat exchanger and a flow rate of the cooling liquid in the liquid-cooling heat exchanger;
Calculating the amount of heat dissipated to the liquid-cooled heat exchanger based on the acquired supply temperature, discharge temperature, and coolant flow rate;
2. The compressor for a cryogenic refrigerator according to claim 1, wherein a flow rate of the cooling liquid in the liquid-cooled heat exchanger is limited so that a calculated amount of heat radiation is equal to or less than an allowable amount of heat radiation. The compressor further includes a compressor body that compresses the refrigerant gas, and a compressor motor that drives the compressor body and has a variable operating frequency.
2. The compressor for a cryogenic refrigerator according to claim 1, wherein the cooling controller is configured to compare the acquired coolant supply temperature with a temperature threshold, and to limit an operating frequency of the compressor motor if the acquired coolant supply temperature exceeds the temperature threshold. A method for operating an oil-lubricated cryogenic refrigerator compressor that compresses a refrigerant gas for the cryogenic refrigerator, the cryogenic refrigerator compressor having a liquid-cooled heat exchanger that cools the refrigerant gas and/or oil by heat exchange with a cooling liquid, the method comprising the steps of:
Obtaining a supply temperature of a cooling liquid supplied to the liquid-cooled heat exchanger;
and controlling the coolant flow rate of the liquid-cooled heat exchanger and/or the amount of heat exhausted from the compressor for the cryogenic refrigerator based on the acquired supply temperature of the coolant.

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