Cooling device and method

Abstract

To provide a cooling device which can easily suppress closing of a flow passage of a cooling fluid in a heat exchanger caused by freezing, and to provide a method.SOLUTION: A cooling device 1 includes: a first path 2 for circulating a refrigerant; a second path 3 for flowing a cooling fluid; and a heat exchanger 4 for exchanging heat of the first path 2 and the second path 3 mutually. The first path 2 includes a compressor 5 and an expander 6 arranged further on the downstream side than the compressor 5 and further on the upstream side than the heat exchanger 4. The cooling device further includes: a bypass path 10 which flows the refrigerant from a portion further on the downstream than the compressor 5 and further on the upstream than the expander 6 to a portion further on the downstream than the heat exchanger 4 and further on the upstream than the compressor 5; and a bypass flow rate control part 11 for detecting a physical amount related to the generation of freezing of the cooling fluid in the heat exchanger 4, and for controlling the flow rate of the bypass path 10 according to the detected physical amount.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a cooling device and method.

Background Art

[0002] A cooling device is known that has a first path for circulating a refrigerant, a second path for flowing a cooling fluid, and a heat exchanger for heat exchange between the first path and the second path, and the first path has a compressor and an expander disposed downstream of the compressor and upstream of the heat exchanger (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a cooling device as described above, if subcooling by the refrigerant occurs for some reason and the cooling fluid freezes in the heat exchanger, the flow path of the cooling fluid in the heat exchanger may be blocked and the cooling fluid may stop flowing. In particular, when the cooling fluid is liquid nitrogen used for cooling a superconducting power device, it is particularly important to suppress the blockage of the flow path of the cooling fluid in the heat exchanger due to freezing.

[0005] Therefore, an object of the present invention is to provide a cooling device and method that can easily suppress the blockage of the flow path of the cooling fluid in the heat exchanger due to freezing.

Means for Solving the Problems

[0006] One aspect of the present invention is as follows.

[0007] [1] It has a first path for circulating a refrigerant, a second path for flowing a cooling fluid, and a heat exchanger for exchanging heat between the first path and the second path. The first path has a compressor and an expander disposed downstream of the compressor and upstream of the heat exchanger. A bypass path for flowing the refrigerant from a portion downstream of the compressor and upstream of the expander to a portion downstream of the heat exchanger and upstream of the compressor. A bypass flow rate control unit that detects a physical quantity related to the occurrence of freezing of the cooling fluid in the heat exchanger and controls the flow rate of the bypass path according to the detected physical quantity.

[0008] [2] The cooling device according to [1], further comprising a further heat exchanger that exchanges heat between a portion downstream of the upstream end of the bypass path and upstream of the expander and a portion downstream of the heat exchanger and upstream of the downstream end of the bypass path.

[0009] [3] The cooling device according to [1] or [2], further comprising a temperature sensor that detects the temperature of the cooling fluid as the physical quantity, or a flow rate sensor that detects the flow rate of the cooling fluid as the physical quantity.

[0010] [4] The cooling device according to any one of [1] to [3], having a turbo compressor as the compressor and an expansion turbine as the expander.

[0011] [5] The cooling device according to any one of [1] to [4], wherein the cooling fluid is liquid nitrogen.

[0012] [6] A cooling device having a first path for circulating a refrigerant, a second path for flowing a cooling fluid, and a heat exchanger for exchanging heat between the first path and the second path, wherein the first path has a compressor and an expander disposed downstream of the compressor and upstream of the heat exchanger, and a bypass path for flowing the refrigerant from a portion downstream of the compressor and upstream of the expander to a portion downstream of the heat exchanger and upstream of the compressor, and an opening degree adjusting unit for changing the opening degree of the bypass path is used. A cooling method for detecting a physical quantity related to the occurrence of freezing of the cooling fluid in the heat exchanger and changing the opening degree of the bypass path by the opening degree adjusting unit according to the detected physical quantity.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a cooling device and method that can easily suppress the blockage of the flow path of the cooling fluid in the heat exchanger due to freezing.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be illustrated with reference to the drawings.

[0016] As shown in FIG. 1, in one embodiment of the present invention, the cooling device 1 includes a first path 2 for circulating a refrigerant, a second path 3 through which a cooling fluid flows, and a heat exchanger 4 (also referred to as the first heat exchanger 4) that exchanges heat between the first path 2 and the second path 3. The first path 2 includes a compressor 5 and an expander 6 disposed downstream of the compressor 5 and upstream of the first heat exchanger 4.

[0017] The cooling device 1 has a refrigeration function of generating cold by repeating adiabatic compression, isobaric cooling, adiabatic expansion, and isobaric heating, which are the four processes of the Brayton cycle, in this order for the refrigerant. The refrigerant compressed by the compressor 5 dissipates the compression heat to, for example, the atmosphere and then undergoes adiabatic expansion in the expander 6. As a result, the temperature of the refrigerant decreases. Then, the refrigerant absorbs the surrounding heat and returns to the inlet of the compressor 5. The refrigerant is not particularly limited, but in this embodiment, it is neon gas. The cooling fluid is not particularly limited, but in this embodiment, it is liquid nitrogen.

[0018] The second path 3 constitutes part or all of a circulation path for circulating the cooling fluid. The circulation path is arranged so that superconducting power devices such as superconducting transmission cables and superconducting fault current limiters can be cooled by the cooling fluid flowing through the circulation path. When the temperature of the superconducting power device rises due to the intrusion heat or the heat generated by the device, it cannot maintain the superconducting state. Therefore, the cooling device 1 needs to stably cool the cooling fluid that cools the superconducting power device. Note that the cooling device 1 may be configured to cool devices other than the superconducting power device or cooling targets other than the devices.

[0019] The cooling device 1 includes a first temperature sensor 7a that detects the temperature of a portion downstream of the first heat exchanger 4 and upstream of the cooling target in the second path 3, and an output control unit (not shown) that controls the output (such as the rotation speed) of the compressor 5 according to the temperature detected by the first temperature sensor 7a. The output control unit is constituted by, for example, a computer. Note that the first temperature sensor 7a may be configured to detect the temperature of the second path 3 other than the above portion.

[0020] The cooling device 1 further includes a further heat exchanger 8 (also referred to as the second heat exchanger 8) that performs mutual heat exchange between a portion downstream of the compressor 5 and upstream of the expander 6 and a portion downstream of the first heat exchanger 4 and upstream of the compressor 5. According to the second heat exchanger 8, the cooling performance can be enhanced. Note that the cooling device 1 is not limited to the configuration having the second heat exchanger 8.

[0021] The cooling device 1 includes a turbo compressor as the compressor 5 and an expansion turbine as the expander 6. According to such a configuration, the cooling performance can be enhanced. Note that the cooling device 1 is not limited thereto, and for example, it may have a configuration having a compressor 5 other than a turbo compressor, or a configuration having an expander 6 other than an expansion turbine.

[0022] The electric power generated by the expander 6 is supplied to a predetermined electric circuit via the first inverter 9a and further supplied to the compressor 5 via the second inverter 9b. Note that the configuration may be such that the power recovered by the expander 6 is transmitted to the compressor 5 by another method. It is not limited to the configuration in which the power recovered by the expander 6 is used as the power source of the compressor 5, and for example, it may be used for driving other devices.

[0023] When the cooling device 1 causes subcooling by the refrigerant for some reason and the cooling fluid freezes in the first heat exchanger 4, the flow path of the cooling fluid in the first heat exchanger 4 may be blocked and the cooling fluid may stop flowing. In the case where the cooling fluid is liquid nitrogen used for cooling a superconducting power device, it is particularly important to suppress the blockage of the flow path of the cooling fluid in the first heat exchanger 4 due to freezing.

[0024] Therefore, the cooling device 1 includes a bypass path 10 for flowing the refrigerant from a portion downstream of the compressor 5 and upstream of the expander 6 to a portion downstream of the first heat exchanger 4 and upstream of the compressor 5, and a physical quantity related to the occurrence of freezing of the cooling fluid in the first heat exchanger 4 (also referred to as a freezing-related physical quantity). The bypass flow control unit 11 detects the freezing-related physical quantity and controls the flow rate of the bypass path 10 according to the detected freezing-related physical quantity so as to suppress the blockage of the flow path of the cooling fluid in the first heat exchanger 4 due to freezing.

[0025] The bypass flow rate control unit 11 includes an opening adjustment unit 11a that changes the opening of the bypass path 10, a detection unit 11b that detects a freezing-related physical quantity, and an opening adjustment unit 11a control unit (not shown) that controls the opening adjustment unit 11a to change the opening of the bypass path 10 according to the freezing-related physical quantity detected by the detection unit 11b. The opening adjustment unit 11a control unit is constituted by, for example, a computer. The opening adjustment unit 11a is constituted by a valve such as an electromagnetic valve. Note that the opening adjustment unit 11a may be constituted by a device other than a valve.

[0026] The detection unit 11b is not particularly limited, and can be constituted by, for example, a temperature sensor that detects the temperature of the cooling fluid, or a flow rate sensor 12 that detects the flow rate of the cooling fluid. In the present embodiment, the detection unit 11b is constituted by a second temperature sensor 7b that detects the temperature of a portion downstream of the expander 6 and upstream of the first heat exchanger 4 in the first path 2.

[0027] When the detected freezing-related physical quantity reaches a first threshold value (in the present embodiment, when the temperature detected by the second temperature sensor 7b drops to the first threshold value), the bypass flow rate control unit 11 increases the opening of the bypass path 10 to a first opening, and then, when the detected freezing-related physical quantity reaches a second threshold value (in the present embodiment, when the temperature detected by the second temperature sensor 7b rises to the second threshold value), the bypass flow rate control unit 11 decreases the opening of the bypass path 10 to a second opening. The second opening is, for example, an opening at which the bypass path 10 is blocked. The first opening is, for example, an opening at which the bypass path 10 is opened (for example, fully opened).

[0028] The first threshold value is set to a value at which freezing of the cooling fluid in the first heat exchanger 4 occurs or may occur. The second threshold value is set to a value at which the occurrence of freezing of the cooling fluid in the first heat exchanger 4 is less likely to occur than the first threshold value (in the present embodiment, a temperature value higher than the first threshold value).

[0029] When the opening degree of the bypass path 10 increases to the first opening degree, the flow rate of the refrigerant flowing through the bypass path 10 and flowing into the compressor 5 increases, and as a result, the pressure ratio of the compressor 5 decreases. For example, as shown in FIG. 3, when the flow rate of the compressor 5 increases at a predetermined rotational speed, the pressure ratio decreases accordingly (see the arrow in FIG. 3). When the pressure ratio of the compressor 5 decreases, the temperature detected by the second temperature sensor 7b (that is, the temperature of the refrigerant from the outlet of the expander 6 to the inlet of the first heat exchanger 4) rises, so that it is possible to suppress the blockage of the flow path of the cooling fluid in the first heat exchanger 4 due to freezing.

[0030] Therefore, for example, as shown in FIG. 5, the cold generated by the cooling device 1 can be maintained well. Note that FIG. 4 shows an example in the case where the opening degree of the bypass path 10 is not controlled by the bypass flow rate control unit 11 as described above. In the example shown in FIG. 4, the cooling fluid stops flowing due to blockage. As a result, the temperature detected by the first temperature sensor 7a continues to rise, and the output of the compressor 5 continues to increase according to the continuously rising temperature. Therefore, subcooling and blockage are not eliminated, and as a result, good generated cold cannot be obtained.

[0031] The bypass path 10 is provided to allow the refrigerant to flow from a portion downstream of the compressor 5 and upstream of the second heat exchanger 8 to a portion downstream of the second heat exchanger 8 and upstream of the compressor 5. That is, the second heat exchanger 8 is provided to perform mutual heat exchange between a portion downstream of the upstream end of the bypass path 10 and upstream of the expander 6 and a portion downstream of the first heat exchanger 4 and upstream of the downstream end of the bypass path 10. According to such a configuration, the effect of suppressing the blockage of the flow path of the cooling fluid in the first heat exchanger 4 due to freezing can be obtained with good energy efficiency.

[0032] Note that the arrangement of the bypass path 10 is not limited to this. For example, it may be provided to allow the refrigerant to flow from a portion downstream of the second heat exchanger 8 and upstream of the expander 6 to a portion downstream of the first heat exchanger 4 and upstream of the second heat exchanger 8.

[0033] The detection unit 11b may be configured by the first temperature sensor 7a as shown in FIG. 2, instead of or in addition to the second temperature sensor 7b, and the temperature detected by the first temperature sensor 7a may be used as the freezing-related physical quantity. In this case, for example, a temperature that is a predetermined value higher than the freezing temperature of the cooling fluid can be used as the first threshold value.

[0034] The detection unit 11b may be configured by a flow rate sensor 12 that detects the flow rate of a portion downstream of the first heat exchanger 4 and upstream of the object to be cooled in the second path 3 as shown in FIG. 2, instead of or in addition to the second temperature sensor 7b, and the flow rate detected by the flow rate sensor 12 may be used as the freezing-related physical quantity. In this case, for example, a flow rate corresponding to when half of the flow path cross-sectional area is blocked can be used as the first threshold value.

[0035] The detection unit 11b may be configured by the third temperature sensor 7c that detects the temperature of the first heat exchanger 4 as shown in FIG. 2, instead of or in addition to the second temperature sensor 7b, and the temperature detected by the third temperature sensor 7c may be used as the freezing-related physical quantity. In this case, for example, a temperature that is a predetermined value higher than the freezing temperature of the cooling fluid can be used as the first threshold value.

[0036] The detection unit 11b may be configured by the fourth temperature sensor 7d that detects the temperature of a portion downstream of the second heat exchanger 8 and upstream of the expander 6 in the first path 2 as shown in FIG. 2, instead of or in addition to the second temperature sensor 7b, and the temperature detected by the fourth temperature sensor 7d may be used as the freezing-related physical quantity. In this case, for example, a temperature that is a predetermined value higher than the freezing temperature of the cooling fluid can be used as the first threshold value, and for example, the first threshold value can be set in consideration of the performance and operating conditions of the expander 6.

[0037] Configure the detection unit 11b with a fifth temperature sensor 7e that detects the temperature of a portion downstream of the first heat exchanger 4 and upstream of the second heat exchanger in the first path 2 as shown in FIG. 2, instead of or in addition to the second temperature sensor 7b, and use the temperature detected by the fifth temperature sensor 7e as a freezing-related physical quantity. In this case, for example, a temperature that is a predetermined value higher than the freezing temperature of the cooling fluid can be used as the first threshold value, and the first threshold value can be set in consideration of, for example, the specifications of the cooling device 1.

[0038] Next, an example of a cooling method according to an embodiment of the present invention will be described. The cooling method according to an embodiment of the present invention uses the cooling device 1 of the above-described embodiment or a modified example thereof, detects a freezing-related physical quantity, and changes the opening degree of the bypass path 10 by the opening degree adjustment unit 11a according to the detected freezing-related physical quantity (more specifically, the bypass flow rate control unit 11 detects the freezing-related physical quantity and controls the flow rate of the bypass path 10 according to the detected freezing-related physical quantity).

[0039] Note that the cooling method of the present embodiment uses a cooling device 1 configured by removing the opening degree adjustment unit 11a control unit from the cooling device 1 of the above-described embodiment or a modified example thereof, detects a freezing-related physical quantity by the detection unit 11b, and a person operates the opening degree adjustment unit 11a to change the opening degree of the bypass path 10 (so as to suppress the blockage of the flow path of the cooling fluid in the first heat exchanger 4 due to freezing).

[0040] The present invention is not limited to the above-described embodiments and can be variously modified without departing from the gist thereof.

Example

[0041] By adjusting the opening degree of the bypass path 10 to a third opening degree smaller than the first opening degree by means of the cooling device 1 of the embodiment shown in FIG. 2, a first state in which freezing occurs is set. Then, by adjusting the opening degree of the bypass path 10 to the first opening degree, a second state in which the freezing is resolved is set. After that, a simulation was conducted in which the opening degree of the bypass path 10 was adjusted to a fourth opening degree smaller than the third opening degree to obtain a third state in which freezing occurs.

[0042] In the first state, the rotational speed of the compressor 5 was 550 rps, the flow rate of the compressor 5 was 1000 Nm 3 / h, the pressure ratio of the compressor 5 was 2.0, the inlet pressure of the expander 6 was 1000 MPaA, the outlet pressure of the expander 6 was 500 MPaA, the detected value of the second temperature sensor 7b was 62.7 K, the detected value of the third temperature sensor 7c was 62.7 K, and the detected value of the first temperature sensor 7a was 62.7 K.

[0043] In the second state, the rotational speed of the compressor 5 was 550 rps, the flow rate of the compressor 5 was 1400 Nm 3 / h, the pressure ratio of the compressor 5 was 1.88, the inlet pressure of the expander 6 was 940 MPaA, the outlet pressure of the expander 6 was 500 MPaA, the detected value of the second temperature sensor 7b was 63.7 K, the detected value of the third temperature sensor 7c was 64.2 K, and the detected value of the first temperature sensor 7a was 64.7 K.

[0044] In the third state, the rotational speed of the compressor 5 was 550 rps, the flow rate of the compressor 5 was 800 Nm 3 / h, the pressure ratio of the compressor 5 was 2.05, the inlet pressure of the expander 6 was 1025 MPaA, the outlet pressure of the expander 6 was 500 MPaA, the detected value of the second temperature sensor 7b was 62.2 K, the detected value of the third temperature sensor 7c was 62.2 K, and the detected value of the first temperature sensor 7a was 62.2 K.

[0045] Note that in any of the first state, the second state, and the third state, the detected value of the fourth temperature sensor 7d was 76 K, the detected value of the fifth temperature sensor 7e was 73 K, the detected value of the flow rate sensor 12 was 0.5 kg / s, and the efficiency of the expander 6 was 70%.

Explanation of Signs

[0046] 1 Cooling device 2 First path 3 Second path 4 First heat exchanger 5 Compressor 6 Expander 7a First temperature sensor 7b Second temperature sensor 7c Third temperature sensor 7d Fourth temperature sensor 7e Fifth temperature sensor 8 Second heat exchanger 9a First inverter 9b Second inverter 10 Bypass path 11 Bypass flow control unit 11a Opening adjustment unit 11b Detection unit 12 Flow sensor

Claims

1. A cooling device having a first path for circulating a refrigerant, a second path for flowing a cooling fluid, and a heat exchanger for exchanging heat between the first path and the second path, wherein the first path has a compressor and an expander disposed downstream of the compressor and upstream of the heat exchanger, a bypass path for flowing the refrigerant from a portion downstream of the compressor and upstream of the expander to a portion downstream of the heat exchanger and upstream of the compressor, a bypass flow rate control unit that detects a physical quantity related to the occurrence of freezing of the cooling fluid in the heat exchanger and controls the flow rate of the bypass path according to the detected physical quantity, and further having a further heat exchanger for exchanging heat between a portion downstream of the upstream end of the bypass path and upstream of the expander and a portion downstream of the heat exchanger and upstream of the downstream end of the bypass path.

2. The cooling device according to claim 1, further comprising a temperature sensor that detects the temperature of the cooling fluid as the physical quantity, or a flow rate sensor that detects the flow rate of the cooling fluid as the physical quantity.

3. The cooling device according to claim 1, having a turbo compressor as the compressor and an expansion turbine as the expander.

4. The cooling device according to claim 1, wherein the cooling fluid is liquid nitrogen.

5. A cooling device having a first path for circulating a refrigerant, a second path for flowing a cooling fluid, and a heat exchanger for exchanging heat between the first path and the second path, wherein the first path has a compressor and an expander disposed downstream of the compressor and upstream of the heat exchanger, a bypass path for flowing the refrigerant from a portion downstream of the compressor and upstream of the expander to a portion downstream of the heat exchanger and upstream of the compressor, and an opening degree adjustment unit for changing the opening degree of the bypass path, and using the cooling device, detecting a physical quantity related to the occurrence of freezing of the cooling fluid in the heat exchanger, and changing the opening degree of the bypass path by the opening degree adjustment unit according to the detected physical quantity, wherein the cooling device further has a further heat exchanger for exchanging heat between a portion downstream of the upstream end of the bypass path and upstream of the expander and a portion downstream of the heat exchanger and upstream of the downstream end of the bypass path.

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