Multi-stage compression refrigeration unit

Abstract

To provide a refrigeration device capable of operating stably with improved efficiency of a refrigeration cycle.SOLUTION: A refrigeration device comprises: a compression unit including a compression mechanism of three or more stages; a first heat exchanger; a decompression unit; a second heat exchanger; a plurality of intermediate-pressure injection flow paths that is provided between a high-pressure decompression mechanism and a low-pressure decompression mechanism, and supplies a refrigerant of an intermediate pressure between a high pressure and a low pressure between the compression mechanisms; a gas-liquid separator that supplies a gas-phase refrigerant to relatively high-pressure side high-pressure intermediate-pressure injection flow paths among the plurality of intermediate-pressure injection flow paths; and an inside heat exchanger that supplies, to low-pressure side intermediate-pressure injection flow paths relative to the high-pressure intermediate-pressure injection flow paths, a refrigerant that is obtained by exchanging heat between a liquid refrigerant that is a liquid-phase refrigerant supplied from the gas-liquid separator and a two-phase refrigerant, which is obtained by decompressing a part of the liquid refrigerant, to absorb heat from the liquid refrigerant.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a refrigeration device that compresses a refrigerant in multiple stages. [Background technology]

[0002] Patent Document 1 discloses a refrigeration device equipped with a two-stage compression mechanism. The refrigeration device includes an electric compressor equipped with a low-stage compression mechanism and a high-stage compression mechanism in a sealed housing, a radiator, a high-pressure expansion valve, a gas-liquid separator, a low-pressure expansion valve, an evaporator, and a gas injection pipe. The gas refrigerant introduced from the gas-liquid separator into the housing of the electric compressor is sucked into the high-stage compression mechanism together with the refrigerant discharged from the low-stage compression mechanism into the housing by the gas injection pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-44420 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to reduce the global warming potential (GWP) and improve the coefficient of performance (COP), refrigerants with low GWP are being adopted, and the development and commercialization of refrigeration equipment including two-stage compression mechanisms is progressing. When a refrigerant containing CO2 is used as the refrigerant, it is effective to introduce an intermediate pressure refrigerant between the high pressure set in the radiator and the low pressure set in the evaporator from the gas-liquid separator between the low-stage compression mechanism and the high-stage compression mechanism (intermediate pressure injection) in order to suppress the high refrigerant discharge temperature associated with high-pressure operation to an allowable limit. With this configuration, the discharge temperature can be suppressed by injecting a refrigerant with a lower temperature than the temperature of the refrigerant discharged from the low-stage compression mechanism. In addition, by supplying liquid refrigerant from the gas-liquid separator to the low-pressure expansion valve, the enthalpy obtained by the evaporator is increased compared to the case of single-stage compression, so that the refrigeration capacity can be increased and the COP can be improved.

[0005] In a refrigeration system that employs a low GWP refrigerant, it is desirable to realize a refrigeration system that has an increased COP while suppressing the discharge temperature from the compressor by further increasing the number of stages in the compression mechanism. However, according to experimental research by the inventors of the present disclosure, it has been found that when the number of stages is increased to three or more, the liquid levels in each of the multiple gas-liquid separators are not stable. In general, to avoid the occurrence of flash (the generation of bubbles in the refrigerant), liquid refrigerant is stored in the gas-liquid separator, and the refrigerant is supercooled by a supercooling heat exchanger. For example, in a refrigeration system that operates with a four-stage compression-four-expansion cycle by increasing the number of stages of the compression mechanism and expansion valve to "4," local fluctuations in refrigerant pressure can cause unevenness in the liquid refrigerant levels stored in each of the three gas-liquid separators. If the uneven distribution of liquid refrigerant makes it impossible to secure liquid in the low-pressure gas-liquid separator that allows refrigerant to flow into the evaporator, and the refrigerant flows into the low-pressure pressure reducing mechanism and the evaporator in a two-phase state, the efficiency may deteriorate and the operation of the refrigeration system may become unstable. To avoid this, it is possible to detect the liquid level in each of the three gas-liquid separators and control the operation of the compressor based on the liquid level, but such control is difficult.

[0006] In view of the above, an object of the present disclosure is to provide a refrigeration device that can operate stably while improving the efficiency of the refrigeration cycle. [Means for solving the problem]

[0007] The present disclosure relates to a refrigeration device that circulates a refrigerant through a refrigeration cycle, the refrigeration device including a compression section including three or more compression mechanisms connected in series and each compressing a refrigerant, a first heat exchanger that dissipates heat of the refrigerant discharged from the compression section to outside air, a high-pressure pressure reduction mechanism on a relatively high pressure side, and a low-pressure pressure reduction mechanism on a relatively low pressure side, and a pressure reduction section that reduces the pressure of the refrigerant that has passed through the first heat exchanger by the high-pressure pressure reduction mechanism and the low-pressure pressure reduction mechanism, a second heat exchanger that absorbs heat from a thermal load from the refrigerant that has passed through the pressure reduction section, a high pressure provided between the high-pressure pressure reduction mechanism and the low-pressure pressure reduction mechanism and set in the first heat exchanger, the high-pressure intermediate pressure injection flow path being a relatively high-pressure side among the plurality of intermediate pressure injection flow paths; and an internal heat exchanger that exchanges heat between a liquid refrigerant, which is a liquid phase refrigerant, supplied from the gas-liquid separator and a two-phase refrigerant formed by reducing the pressure of a portion of the liquid refrigerant, and supplies the refrigerant, which has absorbed heat from the liquid refrigerant, to the intermediate pressure injection flow path on the low pressure side relative to the high-pressure intermediate pressure injection flow path. Effect of the Invention

[0008] In the present disclosure, by combining one or more gas-liquid separators and one or more internal heat exchangers as two types of intermediate pressure injection means, the required number of stages (N-1) of intermediate pressure injection corresponding to the number of compression stages N (3 or more) is satisfied, and the gas-liquid separator is arranged on the high pressure side of the internal heat exchanger. In this way, the number of gas-liquid separators is smaller than when a gas-liquid separator is arranged at each stage of intermediate pressure injection, and therefore it is possible to suppress efficiency reduction and unstable operating conditions caused by uneven distribution of liquid refrigerant. In addition, since the gas-liquid separator is disposed on the high pressure side of the internal heat exchanger, saturated liquid can be made to flow from the gas-liquid separator into the internal heat exchanger to provide supercooling to the refrigerant. The supercooling allows stable and efficient operation, and there is no need to provide a supercooling heat exchanger into which the refrigerant that has passed through the internal heat exchanger flows, which contributes to cost reduction and reduction in size and weight of the device. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a circuit configuration of a refrigeration device according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a Moliere diagram of the refrigeration system shown in FIG. [Diagram 3] FIG. 4 is a Moliere diagram of a refrigeration device according to a comparative example. [Figure 4] FIG. 13 is a diagram showing a circuit configuration of a refrigeration device according to a modified example of the present disclosure. [Diagram 5] FIG. 4 is a Moliere diagram of the refrigeration system shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the accompanying drawings. [Basic elements of the refrigeration cycle] A multi-stage compression refrigeration device 1 shown in FIG. 1 circulates a refrigerant through a refrigeration cycle, thereby cooling an appropriate heat load (for example, air and stored items inside a device housing) using outside air as a heat source. The refrigeration device 1 includes, as basic elements forming a refrigeration cycle, a compression section 10 that compresses a refrigerant, a radiator E1 (first heat exchanger) that radiates heat from the refrigerant to the outside air, a pressure reduction section 20 that reduces the pressure of the refrigerant, and a heat absorber E2 (second heat exchanger) that absorbs heat from a thermal load into the refrigerant. The refrigerant compressed by the compression section 10 flows through the radiator E1, the pressure reduction section 20, and the heat absorber E2 in this order, and is sucked into the compression section 10.

[0011] The refrigerant circuit of the refrigeration device 1 of this embodiment is filled with a single refrigerant or a mixed refrigerant arbitrarily selected from, for example, HFC (Hydro Fluoro Carbon) refrigerants, HFO (Hydro Fluoro Olefin) refrigerants, carbon dioxide (CO2) refrigerants, hydrocarbon-based refrigerants, etc. From the viewpoint of reducing GWP, this embodiment employs a refrigerant that contains at least a portion of carbon dioxide (CO2).

[0012] [Multi-stage compression and decompression mechanism] The compression section 10 includes multiple-stage compression mechanisms 11-14 connected in series. The first stage compression mechanism 11, the second stage compression mechanism 12, the third stage compression mechanism 13, and the fourth stage compression mechanism 14 sequentially compress the refrigerant over multiple steps from the low pressure side L to the high pressure side H. The number of stages N of the compression section 10 is 3 or more, and as an example, the number of stages N is "4". The first to fourth stages are indicated by the symbols n1, n2, n3, and n4.

[0013] 2 is a Moliere diagram showing the relationship between the pressure and specific enthalpy of the refrigerant in the refrigeration device 1. Symbols such as r1, r2, ... shown in FIG. 2 correspond to the same symbols shown in FIG. As shown in FIG. 2, the refrigeration system 1 operates on a four-stage compression, two-stage expansion refrigeration cycle.

[0014] The refrigeration device 1 of this embodiment includes two electric compressors 101, 102, a control device 15 capable of controlling the operation of the electric motors and expansion valves of the electric compressors 101, 102, and an intermediate cooling heat exchanger 16 provided between the electric compressors 101, 102. The first electric compressor 101 includes a first stage compression mechanism 11 and a second stage compression mechanism 12 connected in series, a housing 101A that houses the compression mechanisms 11, 12, and an electric motor 101B that drives the compression mechanisms 11, 12 to rotate. The second electric compressor 102 includes a third stage compression mechanism 13 and a fourth stage compression mechanism 14 connected in series, a housing 102A that houses the compression mechanisms 13, 14, and an electric motor 102B that drives the compression mechanisms 13, 14 to rotate.

[0015] The intermediate cooling heat exchanger 16 cools the refrigerant discharged from the second-stage compression mechanism 12 by radiating heat to the outside air and supplies it to the suction part of the third-stage compression mechanism 13 (from the operating point r4 to r5 in FIG. 2).

[0016] The first-stage compression mechanism 11 corresponds to, for example, a rotary compression mechanism including a piston rotor and a cylinder. The same applies to the third-stage compression mechanism 13. The second-stage compression mechanism 12 corresponds to, for example, a scroll compression mechanism including a pair of scroll members. The same applies to the fourth-stage compression mechanism 14.

[0017] The pressure reducing part 20 includes a low-pressure pressure reducing mechanism 21 on the relatively low-pressure side L and a high-pressure pressure reducing mechanism 22 on the relatively high-pressure side H. The pressure reducing mechanisms 21 and 22 may each be an expansion valve or a capillary tube, etc. In particular, it is preferably an expansion valve capable of adjusting the opening degree of the throttle. The high-pressure pressure reducing mechanism 22 and the low-pressure pressure reducing mechanism 21 sequentially reduce the pressure of the refrigerant passing through the radiator E1 in this order.

[0018] As shown in FIG. 2, the refrigerant is compressed by the compression mechanisms 11 to 14 of multiple stages n1, n2, n3, n4, so that the pressure of the refrigerant increases step by step. Along with this, the discharge temperature of the refrigerant rises. By reducing the temperature of the refrigerant by the action of the intermediate cooling heat exchanger 16 that radiates heat of the refrigerant to the outside air (from r4 to r5), it is possible to contribute to suppressing the discharge temperature of the entire compression part 10.

[0019] The pressure between the suction pressure to the first stage n1 of compression and the discharge pressure from the second stage n2 is referred to as the first intermediate pressure P1. Similarly, the pressure between the suction pressure to the second stage n2 and the discharge pressure from the third stage n3 is referred to as the second intermediate pressure P2, and the pressure between the suction pressure to the third stage n3 and the discharge pressure from the fourth stage n4 is referred to as the third intermediate pressure P3. The relationship of P1 < P2 < P3 holds. The critical temperature of CO2 is lower than that of other refrigerants, for example, HFC (Hydro Fluoro Carbon). Therefore, during steady operation of the refrigeration device 1, the CO2 refrigerant is compressed to a critical pressure P C However, the pressure (r12, r13, r14) of the refrigerant passing through the radiator E1 and the high-pressure pressure reducing mechanism 22, i.e., the third intermediate pressure P3, is higher than the critical pressure P C Stay below.

[0020] (Medium pressure injection) The refrigeration system 1 performs intermediate pressure injection, which supplies intermediate-pressure refrigerant obtained by gas-liquid separation of the refrigerant between the low-pressure pressure reduction mechanism 21 and the high-pressure pressure reduction mechanism 22 between the first to fourth stage compression mechanisms 11 to 14. To this end, the refrigeration system 1 includes N-1 intermediate pressure injection means (31-33) provided between the low-pressure pressure reduction mechanism 21 and the high-pressure pressure reduction mechanism 22, and N-1 intermediate pressure injection flow paths 41-43 corresponding to the intermediate pressure injection means (31-33), respectively.

[0021] By supplying refrigerant at intermediate pressures P1, P2, P3 between the serially connected compression mechanisms 11-14 through the intermediate pressure injection passages 41-43, the discharge temperatures of the second-stage, second-stage, and fourth-stage compression mechanisms 12-14 can be reduced. Valves may be provided as necessary in each of the intermediate pressure injection channels 41 to 43. The valves may be switched between open and closed depending on the operating conditions.

[0022] 1, the intermediate pressure injection means (31-33) is composed of a single gas-liquid separator 33 (receiver) and internal heat exchangers 32, 31. The gas-liquid separator 33 is disposed on the high pressure side H with respect to the internal heat exchangers 32, 31. The high pressure internal heat exchanger 32 is disposed on the high pressure side H with respect to the low pressure internal heat exchanger 31. The gas-liquid separator 33, the internal heat exchanger 32, and the internal heat exchanger 31 supply intermediate-pressure refrigerant to the second- to fourth-stage compression mechanisms 12-14 through the corresponding intermediate-pressure injection passages 41-43, respectively.

[0023] The refrigerant discharged from the fourth stage compression mechanism 14 is depressurized by the high-pressure decompression mechanism 22 and flows into the gas-liquid separator 33. The refrigerant that flows into the gas-liquid separator 33 is separated into a gas phase and a liquid phase based on the density difference inside the storage tank 33A. This corresponds to a state change from r12 to r13 and r14, as shown in Fig. 2. A third intermediate pressure injection flow path 43 is connected to the gas phase region 33B above the liquid level in the storage tank 33A.

[0024] The gas phase refrigerant at the third intermediate pressure P3 separated from the liquid phase in the gas-liquid separator 33 is supplied to the high pressure side H for intermediate pressure injection through the third intermediate pressure injection passage 43. salary (r13 to r8). The temperature of the refrigerant at the third intermediate pressure P3 supplied to the fourth stage compression mechanism 14 by the third intermediate pressure injection passage 43 is lower than the temperature of the refrigerant discharged from the third stage compression mechanism 13. Therefore, the temperature of the refrigerant supplied by the third intermediate pressure injection passage 43 and the refrigerant discharged from the third stage compression mechanism 13 as a whole to be drawn into the fourth stage compression mechanism 14 decreases (from r7 to r8). As a result, the temperature of the refrigerant discharged from the fourth stage compression mechanism 14 also decreases, so that the intermediate pressure gas injection contributes to reducing the discharge temperature.

[0025] On the other hand, the liquid phase refrigerant (liquid refrigerant) stored in the storage tank 33A is supplied to the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31, and while the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31 provide supercooling, a part of the refrigerant is provided to the low-pressure side L for the third intermediate pressure injection through the second intermediate pressure injection flow path 42 and the first intermediate pressure injection flow path 41, respectively. With the injection of the intermediate pressures P1, P2, and P3, the flow rate of the refrigerant is sequentially reduced. Therefore, the capacity of the high-pressure internal heat exchanger 32, which is upstream of the refrigerant flow from the high-pressure pressure reducing mechanism 22 to the low-pressure pressure reducing mechanism 21, is greater than the capacity of the low-pressure internal heat exchanger 31, which is downstream. Under the rated conditions of the refrigeration device 1, the capacity of the high-pressure internal heat exchanger 32 is, for example, about 2.5 times greater than the capacity of the low-pressure internal heat exchanger 31.

[0026] Both the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31 exchange heat between the liquid refrigerant supplied from the gas-liquid separator 33 and a two-phase refrigerant obtained by reducing the pressure of a portion of the liquid refrigerant supplied from the gas-liquid separator 33 using a pressure reduction mechanism (321, 311). The high-pressure internal heat exchanger 32 includes a main flow path 320 through which the liquid refrigerant supplied from the inside of the gas-liquid separator 33 in a saturated state flows in, a pressure reduction mechanism 321, a branch flow path 322 through which a portion of the liquid refrigerant supplied from the gas-liquid separator 33 flows into the pressure reduction mechanism 321, and a heat absorption flow path 323 through which the two-phase refrigerant that has been reduced in pressure by the pressure reduction mechanism 321 from the third intermediate pressure P3 to the second intermediate pressure P2 (from r14 to r15 in Figure 2) flows in.

[0027] The refrigerant flowing through the heat absorption flow passage 323 absorbs heat from the refrigerant flowing through the main flow passage 320 and is gasified (from r15 to r16), and is sucked into the third stage compression mechanism 13 through the second intermediate pressure injection flow passage . On the other hand, the refrigerant flowing through the main flow path 320 is supercooled by dissipating heat to the refrigerant flowing through the heat absorption flow path 323 (from r14 to r17) and flows into the low-pressure internal heat exchanger 31.

[0028] When the refrigerant at the second intermediate pressure P2 is supplied to the suction section of the third stage compression mechanism 13 through the second intermediate pressure injection passage 42 (from r16 to r6), the temperature of the refrigerant flowing out of the intermediate cooling heat exchanger 16 and sucked into the third stage compression mechanism 13 decreases (from r5 to r6). Between the second stage compression mechanism 12 and the third stage compression mechanism 13, in addition to the injection action of the intermediate pressure P2, the suction temperature to the third stage compression mechanism 13 also decreases due to the action of the intermediate cooling heat exchanger 16 (from r4 to r5), so that the discharge temperature can be further suppressed.

[0029] The low-pressure internal heat exchanger 31 includes a main flow path 310 through which the liquid refrigerant in a supercooled state (supercooled liquid) flowing out from the high-pressure internal heat exchanger 32 flows, a pressure reducing mechanism 311, a branch flow path 312 through which a part of the supercooled liquid flows into the pressure reducing mechanism 311, and a heat absorbing flow path 313 through which the two-phase refrigerant that has been depressurized from the second intermediate pressure P2 to the first intermediate pressure P1 (from r17 to r18) by the pressure reducing mechanism 311 flows. The refrigerant flowing through the heat absorbing flow path 313 is gasified (from r18 to r19) by absorbing heat from the refrigerant flowing through the main flow path 310, and is drawn into the second-stage compression mechanism 12 through the first intermediate pressure injection flow path 41 (from r19 to r3). ​​This causes the temperature of the refrigerant drawn into the second-stage compression mechanism 12 to decrease (from r2 to r3).

[0030] On the other hand, the refrigerant flowing through the main flow path 310 dissipates heat to the refrigerant flowing through the heat absorption flow path 313, thereby increasing the degree of supercooling (from r17 to r20), and flows into the low-pressure decompression mechanism 21. The liquid refrigerant at the first intermediate pressure P1 flowing out from the low-pressure internal heat exchanger 31 is sufficiently subcooled, so it flows directly into the low-pressure pressure reduction mechanism 21 without passing through a subcooling heat exchanger, and is reduced in pressure by the low-pressure pressure reduction mechanism 21 (from r20 to r21). The refrigerant that has passed through the low-pressure pressure reduction mechanism 21 evaporates by absorbing heat from the thermal load in the heat absorber E2, and is drawn into the first stage compression mechanism 11 (from r21 to r22).

[0031] The pressures of the liquid refrigerant flowing from the gas-liquid separator 33 to the internal heat exchanger 32, the liquid refrigerant flowing from the high-pressure internal heat exchanger 32 to the low-pressure internal heat exchanger 31, and the refrigerant flowing from the low-pressure internal heat exchanger 31 to the low-pressure pressure reduction mechanism 21 correspond to the third intermediate pressure P3 (r14, r17, and r20). H to the third intermediate pressure P3, and the third intermediate pressure P3 to low pressure P L In other words, the refrigeration device 1 is operated in a state in which the number of expansion stages is less than the number of compression stages N, that is, in a four-stage compression and two-stage expansion cycle.

[0032] [Major actions and effects] In order to improve the COP while using a refrigerant with a low GWP, it is effective to increase the number of stages N, such as from single-stage compression to two-stage compression, and then to three-stage compression or four-stage compression. The operation and effects of the refrigeration system 1 of this embodiment will be described below with reference to a comparative example. When adopting three or more stages of multi-stage compression, based on the example of two-stage compression (for example, the above-mentioned Patent Document 1), it is conceivable to provide the refrigeration device with the same number of pressure reduction mechanisms as the number of compression stages N and N-1 gas-liquid separators. In the case of such a refrigeration device having, for example, four stages, a pressure reduction mechanism, gas-liquid separator, pressure reduction mechanism, gas-liquid separator, pressure reduction mechanism, gas-liquid separator, and pressure reduction mechanism are arranged in this order from the high pressure side H to the low pressure side L, and intermediate pressure gas-phase refrigerant is supplied from each gas-liquid separator through an intermediate pressure injection flow path to the suction section of the compression mechanism. The refrigeration device of this comparative example operates in a cycle of N-stage compression and N-stage expansion, as shown by the solid line in Fig. 3. N is, for example, "4". The refrigeration device of the comparative example may include a subcooling heat exchanger that exchanges heat between the liquid refrigerant flowing out of the gas-liquid separator on the lowest pressure side L and outside air. In that case, the refrigerant is subcooled as shown by the dashed arrow in FIG.

[0033] The refrigeration device of the comparative example includes N-1 gas-liquid separators, and therefore includes two or more gas-liquid separators when the number of stages N is 3 or more. In that case, it is difficult to secure liquid refrigerant in a predetermined gas-liquid separator among the multiple gas-liquid separators. Even if a subcooling heat exchanger is provided on the lowest pressure side L, it is desirable to secure liquid refrigerant at least in the gas-liquid separator located on the lowest pressure side L and supply liquid refrigerant from the gas-liquid separator to the low-pressure decompression mechanism 21 in order to prevent the refrigerant from flowing into the low-pressure decompression mechanism 21 and the heat absorber E2 in a two-phase state. For that purpose, it is necessary to control the rotation speed of the compression mechanisms 11 to 14 based on the liquid levels of each of the N-1 gas-liquid separators. At least two liquid level sensors are required to grasp the liquid levels of each of the N-1 gas-liquid separators.

[0034] Unlike the comparative example, when increasing the number of stages N, the refrigeration system 1 of this embodiment does not include a number of pressure reduction mechanisms and gas-liquid separators corresponding to the number of stages N, or does not include a number of internal heat exchangers corresponding to the number of stages N, but includes a single gas-liquid separator 33 on the high pressure side H and internal heat exchangers 32, 31 on the low pressure side L. In other words, the refrigeration system 1 of this embodiment does not include the same number of gas-liquid separators as the number of stages (N-1) required for intermediate pressure injection, and includes a number of gas-liquid separators 33 that is fewer than the number of stages (N-1) required for intermediate pressure injection. Since the number of gas-liquid separators 33 provided in the refrigeration system 1 is small relative to the number of stages (N-1) required for intermediate pressure injection, the degree of uneven distribution of refrigerant between the gas-liquid separators that may occur when multiple gas-liquid separators are provided is reduced. As a result, the effect of improving efficiency by increasing the number of compression stages N is ensured while suppressing efficiency reduction and unstable operating conditions caused by uneven distribution of liquid refrigerant, and also contributing to stabilizing the operating conditions of the refrigeration system 1.

[0035] In particular, since the refrigeration system 1 of this embodiment includes only a single gas-liquid separator 33 as a gas-liquid separator, it is possible to ensure that the liquid refrigerant is stored in a specific gas-liquid separator 33 without the liquid amount running out in some of the multiple gas-liquid separators. This makes it unnecessary to perform control based on the liquid level of the gas-liquid separator, and also makes a liquid level sensor unnecessary. Even if liquid level sensors are installed, the number of them can be reduced.

[0036] As described above, according to the refrigeration device 1 of the present embodiment, the following effects can be obtained. (1) Since only a single gas-liquid separator 33 is provided as the gas-liquid separator, unlike a case in which multiple gas-liquid separators are provided, it is possible to ensure that liquid refrigerant is stored in a specific gas-liquid separator 33 without liquid refrigerant moving between the gas-liquid separators. Therefore, there is no need to perform control based on the liquid level in the gas-liquid separator. The simplified control allows the cost of the refrigeration device 1 to be reduced.

[0037] (2) Since the gas-liquid separator 33 is disposed on the high pressure side H relative to the internal heat exchangers 32, 31, saturated liquid flows from the gas-liquid separator 33 to the internal heat exchangers 32, 31. This allows the refrigerant to be supercooled. This not only improves the COP and suppresses the occurrence of flashes, allowing the refrigeration system 1 to operate stably and efficiently, but also ensures that the refrigerant is supercooled, eliminating the need to cause the refrigerant that has passed through the internal heat exchangers 32, 31 to flow into the supercooling heat exchanger. In other words, it is sufficient to cause the refrigerant that has passed through the internal heat exchangers 32, 31 to flow directly into the low-pressure decompression mechanism 21. In this way, unlike the comparative example, a subcooling heat exchanger is not necessary, and the refrigerant circuit configuration can be simplified, which can contribute to reducing costs and the size and weight of the device. In this embodiment, a sufficient degree of subcooling can be obtained by sequentially flowing the liquid refrigerant from the gas-liquid separator 33 into the two internal heat exchangers 32, 31. Therefore, in addition to the significant effects of improving efficiency and stabilizing operation, there is no need to add a high-capacity subcooling heat exchanger to increase the degree of subcooling, and therefore the effects of reducing costs and making the device smaller and lighter are also significant.

[0038] (3) By providing the high-pressure internal heat exchanger 32 and / or the low-pressure internal heat exchanger 31 with an expansion valve as a pressure reducing mechanism, it becomes possible to perform intermediate pressure injection of two-phase refrigerant by adjusting the opening degree of the expansion valve, as shown in Fig. 2. For example, when the high-pressure internal heat exchanger 32 is provided with an expansion valve as the pressure reducing mechanism 321, it becomes possible to perform injection of the second intermediate pressure P2 (from r16 to r6) of the two-phase refrigerant to the third stage compression mechanism 13 through the second intermediate pressure injection passage 42 by adjusting the opening degree of the expansion valve. Alternatively, if the low-pressure internal heat exchanger 31 is equipped with an expansion valve as the pressure reduction mechanism 311, by adjusting the opening degree of the expansion valve, it becomes possible to inject the first intermediate pressure P1 using two-phase refrigerant (from r19 to r3) into the second stage compression mechanism 12. Injection of two-phase refrigerant reduces the intake temperature of the refrigerant into the compression mechanism, thereby keeping the discharge temperature within acceptable limits.

[0039] (4) In general, a heat insulating material is provided in the gas-liquid separator to keep the refrigerant at a low temperature. By arranging the gas-liquid separator 33 on the high-pressure side H of the internal heat exchangers 31, 32, the pressure saturation temperature in the gas-liquid separator is higher than when the gas-liquid separator is arranged on the low-pressure side L, and therefore the temperature difference between the gas-liquid separator 33 and the outside air temperature is smaller. Therefore, the thickness of the heat insulating material provided in the gas-liquid separator 33 can be made thinner, which contributes to reducing costs and making the device smaller and lighter.

[0040] For example, under the rated conditions of the refrigeration system 1, in the case where a single gas-liquid separator 33 corresponding to the third intermediate pressure P3 is provided, and two internal heat exchangers 32, 31 corresponding to the second intermediate pressure P2 and the first intermediate pressure P1, respectively, are provided as shown in Fig. 1, the temperature of the liquid outlet of the gas-liquid separator 33 is 20°C, and in this case, the temperature difference with the outside air temperature is the smallest. The temperature of the liquid outlet is calculated by cycle calculation. The same applies below. Although not shown in the figure, in the case where a single gas-liquid separator corresponding to the second intermediate pressure P2 is provided and two gas-liquid separators corresponding to the third intermediate pressure P3 and the first intermediate pressure P1, respectively, the temperature of the liquid outlet of the gas-liquid separator is 2°C. Furthermore, when a single gas-liquid separator corresponding to the first intermediate pressure P1 is provided and two gas-liquid separators corresponding to the third intermediate pressure P3 and the second intermediate pressure P2, respectively, are provided, the temperature of the liquid outlet of the gas-liquid separator is -12°C.

[0041] The fact that the closer the gas-liquid separator is to the higher pressure side, the higher the pressure saturation temperature is, and therefore the smaller the temperature difference between the gas-liquid separator and the outside air, can also be explained by the Moliere diagram in Figure 3 relating to the comparative example. As can be seen from Figure 3, if the pressure saturation temperature of the high-pressure gas-liquid separator (r12) is T1, the pressure saturation temperature of the medium-pressure gas-liquid separator (r15) is T2, and the pressure saturation temperature of the low-pressure gas-liquid separator (r18) is T3, it is clear that T1>T2>T3. The higher the pressure saturation temperature, the smaller the temperature difference between the gas-liquid separator and the outside air.

[0042] As described above, according to the refrigeration device 1 of this embodiment, by combining one or more gas-liquid separators 33 and one or more internal heat exchangers 31, 32 as two types of intermediate pressure injection means, the required number of stages (N-1) of intermediate pressure injection corresponding to the number of compression stages N (3 or more) is satisfied, and by arranging the gas-liquid separator 33 on the high pressure side H relative to the internal heat exchangers 31, 32, it is possible to improve the COP while using a refrigerant with a low GWP, such as CO2, and to stably operate the refrigeration device 1 while maintaining the discharge temperature below the allowable limit.

[0043] [Modifications] The refrigeration device 1 does not necessarily have to include the high-pressure internal heat exchanger 32 and the low-pressure internal heat exchanger 31, and may include only a single internal heat exchanger or three or more internal heat exchangers depending on the number of stages N. Even in such a case, the same effects as those obtained by the above embodiment can be obtained.

[0044] The refrigeration system 1-2 shown in Fig. 4 includes N-stage (four-stage) compression mechanisms 11-14, and includes, as N-1 (three) intermediate-pressure injection means, two gas-liquid separators 33, 32-2 and a single internal heat exchanger 31. Fig. 5 is a Moliere diagram of the refrigeration system 1-2. The refrigeration device 1-2 includes three decompression mechanisms 21-23 that configure the decompression section 20, including the decompression mechanism 22 located between the two gas-liquid separators 33, 32-2. Therefore, the refrigeration device 1-2 is operated according to a four-stage compression and three-stage expansion cycle.

[0045] As with the refrigeration system 1 of the above embodiment, the refrigeration system 1-2 also includes two gas-liquid separators 33, 32-2, which is a smaller number than the number of stages (N-1) required for intermediate pressure injection, thereby reducing the degree of uneven distribution of liquid refrigerant between the gas-liquid separators 33, 32-2. As a result, it is possible to ensure the effect of improving efficiency by increasing the number of compression stages N while suppressing the decrease in cycle efficiency and the instability of the operating state, and also to contribute to the stabilization of the operating state of the refrigeration system 1-2.

[0046] In addition, since the gas-liquid separators 33 and 32-2 are disposed on the high pressure side H of the internal heat exchanger 31, saturated liquid flows from the gas-liquid separator 32-2 into the internal heat exchanger 31, so that the refrigerant can be supercooled (from r17 to r20 in FIG. 4). The supercooling allows stable and efficient operation, and there is no need to add a supercooling heat exchanger to obtain supercooling, which contributes to cost reduction and size and weight reduction of the device.

[0047] In addition, by adjusting the opening of the expansion valve provided as the pressure reducing mechanism 311 in the internal heat exchanger 31, it becomes possible to inject the first intermediate pressure P1 using two-phase refrigerant (from r19 to r3). ​​This reduces the suction temperature of the refrigerant to the second stage compression mechanism 12, so that the discharge temperature of the refrigerant from the compression section 10 can be kept within the allowable limit. Furthermore, by arranging the gas-liquid separators 33, 32-2 on the high-pressure side H of the internal heat exchanger 31, the thickness of the insulation material can be reduced compared to when the gas-liquid separators 33, 32-2 are arranged on the low-pressure side L of the internal heat exchanger 31, which contributes to making the device smaller and lighter.

[0048] In addition to the above, it is possible to select and discard the configurations given in the above embodiment, or to change them to other configurations as appropriate.

[0049] (Additional Note) The refrigeration apparatus described above can be understood as follows. [1] A refrigeration device 1, 1-2 that circulates a refrigerant by a refrigeration cycle includes a compression section 10 including three or more compression mechanisms 11-14 connected in series and each compressing a refrigerant, a first heat exchanger (E1) that dissipates heat of the refrigerant discharged from the compression section 10 to the outside air, a high-pressure pressure reduction mechanism 22 on a relatively high pressure side, and a low-pressure pressure reduction mechanism 21 on a relatively low pressure side, and includes a pressure reduction section 20 that reduces the pressure of the refrigerant that has passed through the first heat exchanger E1 by the high-pressure pressure reduction mechanism 22 and the low-pressure pressure reduction mechanism 21, a second heat exchanger (E2) that absorbs heat from a heat load from the refrigerant that has passed through the pressure reduction section 20, and a high-pressure P H and a plurality of intermediate pressure injection passages 41-43 which supply refrigerant of intermediate pressures P1, P2, P3 between the compression mechanisms and a low pressure PL set in the second heat exchanger (E2), between the compression mechanisms; a gas-liquid separator 33 (or 33, 32-2) which supplies gas phase refrigerant to a high pressure intermediate pressure injection passage (43, or 43, 42) on the relatively high pressure side H among the plurality of intermediate pressure injection passages 41-43; and an internal heat exchanger 32, 31 (or 31) which exchanges heat between a liquid refrigerant, which is a liquid phase refrigerant supplied from the gas-liquid separator 33, and a two-phase refrigerant obtained by reducing the pressure of a portion of the liquid refrigerant, and supplies the refrigerant obtained by absorbing heat from the liquid refrigerant to the intermediate pressure injection passage 42, 41 (or 41) on the low pressure side L for the high pressure intermediate pressure injection passage (43, or 43, 42). [2] The refrigeration device 1 is provided with only one gas-liquid separator 33, and one or more internal heat exchangers 32, 31 are provided between the gas-liquid separator 33 and the low-pressure decompression mechanism 21. [3] The refrigeration system 1 includes a maximum pressure gas-liquid separator 33 located on the highest pressure side H, to which the refrigerant is directly supplied from the high pressure pressure reducing mechanism 22 . [4] The refrigeration devices 1, 1-2 include a lowest-pressure internal heat exchanger 31 located on the lowest-pressure side L, which directly causes the refrigerant to flow into the low-pressure pressure reducing mechanism . [5] The internal heat exchangers 31, 32 each include an expansion valve (311, 321) that reduces the pressure of a portion of the liquid refrigerant to expand it. [6] The refrigeration device 1 is equipped with two or more internal heat exchangers 31, 32, and the capacity of the internal heat exchanger 32 located on the relatively high pressure side H is the same as that of the relatively low pressure side L The capacity of the internal heat exchanger 31 located at [7] The refrigerant contains at least a portion of carbon dioxide. [Explanation of symbols]

[0050] 1,1-2 Refrigeration equipment 10 Compression section 11 No. One-stage compression mechanism 12 No. Two-stage compression mechanism 13 No. 3-stage compression mechanism 14 No. 4-stage compression mechanism 15 Control device 16 Intercooled heat exchanger 20 Pressure reduction section 21 Low pressure reduction mechanism 22 High pressure reduction mechanism 21~23 Pressure reducing mechanism 31 Low pressure internal heat exchanger (lowest pressure internal heat exchanger) 32 High pressure internal heat exchanger 32-2 Gas-liquid separator 33 Gas-liquid separator (highest pressure gas-liquid separator) 33A Storage tank 33B Gas Phase Region 41 First intermediate pressure injection passage 42 Second intermediate pressure injection passage 43 Third intermediate pressure injection passage (high-pressure intermediate pressure injection passage) 101 First electric compressor 101A Housing 101B Electric motor 102 Second electric compressor 102A Housing 102B Electric motor 310 Main channel 311 Pressure reducing mechanism 312 Branch Channel 313 Endothermic channel 320 Main channel 321 Pressure reducing mechanism 322 Branch Channel 323 Endothermic flow path E1 radiator (1st heat exchanger) E2 heat absorber (second heat exchanger) H High pressure side L Low pressure side N number of stages P1, P2, P3 intermediate pressure PC Critical Pressure PH High Pressure PL Low Pressure n1,n2,n3,n4 stages

Claims

1. A refrigeration device that circulates a refrigerant through a refrigeration cycle, a compression unit including four or more compression mechanisms connected in series to compress the refrigerant, a first heat exchanger that dissipates heat of the refrigerant discharged from the compression section to outside air; a pressure reducing unit including a high-pressure pressure reducing mechanism on a relatively high pressure side and a low-pressure pressure reducing mechanism on a relatively low pressure side, the pressure of the refrigerant having passed through the first heat exchanger being reduced by the high-pressure pressure reducing mechanism and the low-pressure pressure reducing mechanism; a second heat exchanger that absorbs heat from a thermal load through the refrigerant that has passed through the pressure reducing section; a plurality of intermediate pressure injection flow paths provided between the high pressure reduction mechanism and the low pressure reduction mechanism, for supplying the refrigerant at an intermediate pressure between the high pressure set in the first heat exchanger and the low pressure set in the second heat exchanger between the compression mechanisms; a first gas-liquid separator that supplies the refrigerant in a gas phase to a third intermediate pressure injection flow path on a relatively high pressure side among the plurality of intermediate pressure injection flow paths; a second gas-liquid separator that supplies the gas-phase refrigerant to a second intermediate-pressure injection flow path that is a lower pressure side of the third intermediate-pressure injection flow path, among two-layer refrigerants obtained by reducing the pressure of the liquid refrigerant that is the liquid phase refrigerant supplied from the first gas-liquid separator; a first intermediate-pressure injection flow path that is on the low-pressure side relative to the second intermediate-pressure injection flow path, and an internal heat exchanger that exchanges heat between a liquid refrigerant, which is the refrigerant in the liquid phase supplied from the second gas-liquid separator, and a two-phase refrigerant obtained by reducing the pressure of a portion of the liquid refrigerant, thereby absorbing heat from the liquid refrigerant, and supplies the refrigerant to a first intermediate-pressure injection flow path that is on the low-pressure side relative to the second intermediate-pressure injection flow path.

2. The first gas-liquid separator is located on the highest pressure side and includes a maximum pressure gas-liquid separator to which the refrigerant is directly supplied from the high pressure pressure reducing mechanism.

2. The refrigeration system of claim 1.

3. The internal heat exchanger is located on the lowest pressure side and includes a lowest pressure internal heat exchanger that causes the refrigerant to flow directly into the low pressure pressure reducing mechanism.

2. The refrigeration system of claim 1.

4. The internal heat exchanger is an expansion valve for reducing the pressure of a portion of the liquid refrigerant to expand it; A refrigeration apparatus according to any one of claims 1 to 3.

5. Two or more of the internal heat exchangers are provided, The capacity of the internal heat exchanger located on the relatively high pressure side is greater than the capacity of the internal heat exchanger located on the relatively low pressure side.

5. A refrigeration system according to any one of claims 1 to 4.

6. The refrigerant contains at least a portion of carbon dioxide.

6. A refrigeration system according to any one of claims 1 to 5.

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