Refrigeration equipment

Abstract

To provide a freezer that can achieve both reduction in mechanical loss in a compressor and securement of reliability, thereby achieving ultra-low temperature of -60°C.SOLUTION: A freezer 100 according to the present disclosure comprises a low-temperature side refrigeration cycle CL in which a first refrigerant circulates, a high-temperature side refrigeration cycle CH in which a second refrigerant circulates, and an intermediate heat exchanger 10 connecting the low-temperature side refrigeration cycle and the high-temperature side refrigeration cycle so as to exchange heat between the first refrigerant and the second refrigerant, where the first refrigerant is a mixed refrigerant containing CO2 and R32, the second refrigerant is CO2, and refrigeration oil having a kinetic viscosity of 5.2 mm2 / s or more and 19.8 mm2 / s or less at 40°C is stored in a compressor 2 of the low-temperature side refrigeration cycle.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to refrigeration systems, particularly cascade cycle type refrigeration systems. [Background technology]

[0002] In recent years, there has been a growing demand for refrigerants with low GWP (Global Warming Potential) values ​​from an environmental protection perspective. Refrigerants capable of achieving low GWP include HFC refrigerants and carbon dioxide (CO2) refrigerants. R23 and R32 are well-known HFC refrigerants. The GWP of R23 is 14,800. The GWP of R32 is 675. The GWP of CO2 refrigerant is 1.

[0003] Using such low-GWP refrigerants can impair the cooling capacity of refrigeration systems. This effect is particularly pronounced in refrigeration systems targeting ultra-low temperatures of around -45°C to -70°C.

[0004] One possible measure when using low-GWP refrigerants is to increase the compression ratio of the compressor used in the refrigeration system. However, simply increasing the compression ratio may cause the compressor's discharge temperature to become excessively high, potentially preventing the desired refrigeration capacity from being achieved.

[0005] Patent Document 1 describes a refrigeration system that achieves both low GWP and high refrigeration capacity by employing a cascade cycle configuration. The cascade cycle type refrigeration system mainly comprises a low-temperature refrigeration cycle, a high-temperature refrigeration cycle, and an intermediate heat exchanger provided between them. In Patent Document 1, the refrigerant circulating in the low-temperature refrigeration cycle is a mixed refrigerant containing CO2 and R32, while the refrigerant circulating in the high-temperature refrigeration cycle is CO2 only.

[0006] Conventionally, common HFC refrigerants are paired with refrigeration oils of ISO viscosity grades such as VG32, VG68, and VG75. CO2 refrigerants are paired with refrigeration oil of ISO viscosity grade VG68.

[0007] For example, conventional ultra-low temperature refrigeration equipment uses R23 in combination with the alkylbenzene oil ISO VG32 (Barrel Freeze 32SAM, manufactured by Matsumura Oil Co., Ltd.).

[0008] For example, in the cascade cycle type refrigeration system described in Patent Document 1, refrigeration oil with ISO viscosity grade VG68 is used in both refrigeration cycles. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2022-55607 [Overview of the project] [Problems that the invention aims to solve]

[0010] The refrigeration system described in Patent Document 1 is capable of operation with ultra-low temperatures as the target temperature. When operated at ultra-low temperatures, the fluidity of the refrigeration oil that exits the compressor decreases, and the return of oil to the compressor becomes poor. This increases mechanical losses and reduces the mechanical efficiency of the compressor. The decrease in fluidity can be suppressed by using a low-viscosity refrigeration oil. However, lowering the viscosity of the refrigeration oil reduces the oil film load capacity, raising concerns about lubrication problems such as bearing wear, reduced lifespan, and seizure. Such problems reduce the reliability of the refrigeration system.

[0011] This disclosure is made in view of these circumstances and aims to provide a refrigeration system that can achieve ultra-low temperatures of -60°C while simultaneously reducing mechanical losses in the compressor and ensuring reliability. [Means for solving the problem]

[0012] To solve the above problems, the refrigeration apparatus of this disclosure employs the following means. The refrigeration device according to the present disclosure includes a low-temperature refrigeration cycle in which a first refrigerant circulates, a high-temperature refrigeration cycle in which a second refrigerant circulates, and an intermediate heat exchanger that connects the low-temperature refrigeration cycle and the high-temperature refrigeration cycle so that the first refrigerant and the second refrigerant exchange heat. The first refrigerant 16% to 22% by weight contains R32 The remaining part is CO 2 That is is a mixed refrigerant, the second refrigerant is CO2, and the compressor of the low-temperature refrigeration cycle The base oil is at least one selected from the group consisting of ester oils, ether oils, glycol oils, and mineral oils. has a kinematic viscosity of 5.2 mm , [Figure 4] , , [Figure 3] , , [Figure 6] , [Figure 5] ,

[0016] , ,

[0015] , , , , , , / s or more and 19.8 mm 2 / s or less of To achieve ultra-low temperatures of -60℃ refrigeration oil stored therein.

Advantages of the Invention

[0013] According to the present disclosure, it is possible to achieve both reduction of mechanical loss in the compressor and ensuring of reliability, and it becomes a refrigeration device for realizing an ultra-low temperature of -60°C.

Brief Description of the Drawings

[0017] In the low-temperature refrigeration cycle, heat exchange occurs between the indoor air and the refrigerant (the first refrigerant, described later). In the high-temperature refrigeration cycle CH, heat exchange occurs between the outside air and the refrigerant (the second refrigerant, described later). The refrigerant (second refrigerant) that has exchanged heat with the outside air then exchanges heat with the refrigerant (first refrigerant) on the low-temperature refrigeration cycle side in the intermediate heat exchanger 10.

[0018] (Configuration of the low-temperature refrigeration cycle) The low-temperature refrigeration cycle CL includes an evaporator 1, a first compressor 2, a low-temperature expansion valve 3 (a first low-temperature expansion valve 31 and a second low-temperature expansion valve 32), and a low-temperature receiver 81.

[0019] The first compressor 2, the first low-temperature expansion valve 31, the low-temperature receiver 81, the second low-temperature expansion valve 32, and the evaporator 1 are arranged sequentially from upstream to downstream in the flow direction of the first refrigerant and are connected in a ring by the low-temperature piping P1.

[0020] The cold-side piping P1 is filled with a primary refrigerant. The primary refrigerant is a mixed refrigerant containing carbon dioxide (CO2, GWP: 1) and R32 (difluoromethane, GWP: 675). The main component of the mixed refrigerant is CO2. R32 may be included in an amount of 16% to 22% by weight relative to the total weight of the mixed refrigerant. In the mixed refrigerant, CO2 and R32 may be mixed in a ratio of CO2:R32 = 78:22 (by weight).

[0021] The first compressor 2 compresses the low-pressure gaseous refrigerant supplied from the evaporator 1 to produce a high-temperature, high-pressure gaseous refrigerant. The first compressor 2 has a larger capacity than the compressor of the high-temperature side refrigeration cycle (the second compressor 4, described later).

[0022] The first compressor 2 is a two-stage compressor, for example, called a scroll rotary (registered trademark). In the first compressor 2, a rotary compressor 21 is used on the low-pressure side (suction side), and a scroll compressor 22 is used on the high-pressure side (discharge side). The rotary compressor 21 and the scroll compressor 22 are connected coaxially.

[0023] The first compressor 2 is equipped with a radial upper bearing and a radial lower bearing (not shown). The radial upper bearing (drive bearing) is located at the rear end of the orbiting scroll and rotatably supports the drive bush. The radial lower bearing (main bearing) rotatably supports the drive shaft. In the first compressor 2, the sliding surface area of ​​the bearings is larger in the rotary compressor 21 than in the scroll compressor 22.

[0024] The first compressor 2 is equipped with a reservoir (not shown) in which the first refrigeration oil is stored. The base oil of the first refrigeration oil stored in the reservoir is one or more oils selected from the group consisting of ester oil, ether oil, glycol oil, and mineral oil. The first refrigeration oil acts as a lubricant on the sliding surfaces of the bearings in the first compressor 2. The first refrigeration oil operates in a medium temperature and medium pressure atmosphere.

[0025] In combination with a mixed refrigerant containing CO2 and R32, the refrigerant dissolution viscosity of the first refrigeration oil is 0.32 cP or higher, preferably 0.43 cP to 0.51 cP, and more preferably 0.47 cP, at a temperature of 4.4°C and an absolute pressure of 2.5 MPa.

[0026] If the refrigerant's dissolution viscosity at a temperature of 4.4°C and an absolute pressure of 2.5 MPa is 0.32 cP or higher, an oil film of sufficient thickness to meet the criteria can be formed on the sliding surface of the bearing.

[0027] If the refrigerant dissolution viscosity at a temperature of 4.4°C and an absolute pressure of 2.5 MPa is 0.43 cP or higher, a 20% margin of the oil film thickness difference according to the criteria can be secured. If the refrigerant dissolution viscosity at a temperature of 4.4°C and an absolute pressure of 2.5 MPa is 0.51 cP or lower, approximately 90% of the current machine's mechanical efficiency can be secured.

[0028] In combination with a mixed refrigerant containing CO2 and R32, the refrigerant-dissolved viscosity of the first refrigeration oil is 0.32 cP or more and 0.8 cP or less, preferably 0.70 cP or more and 0.78 cP or less, and preferably 0.74 cP at a temperature of 12.3 °C and an absolute pressure of 2.5 MPa.

[0029] For ensuring reliability in a compressor, it is advantageous that the viscosity of the first refrigeration oil is higher. However, if the viscosity of the first refrigeration oil is too high, the mechanical efficiency will decrease. If the refrigerant-dissolved viscosity of the first refrigeration oil is 0.8 cP or less at a temperature of 12.3 °C and an absolute pressure of 2.5 MPa, an oil film about twice the thickness of the criteria is formed on the sliding surface of the bearing, and a significant efficiency decrease compared to the current machine can be avoided from the viewpoint of mechanical efficiency. Therefore, reliability and mechanical efficiency can be compatible in a relatively wide range of the operating points required for the low-stage side refrigeration cycle.

[0030] The kinematic viscosity of the first refrigeration oil is 5.2 mm 2 / s or more and 19.8 mm 2 / s or less, preferably 6.12 mm 2 / s or more and 16.5 mm 2 / s or less, more preferably 6.12 mm 2 / s or more and 11.0 mm 2 / s or less, still more preferably 7.14 mm 2 / s or more and 8.14 mm 2 / s or less, most preferably 7.64 mm 2 / s. The kinematic viscosity is a value measured by a method conforming to JIS-K2283.

[0031] The density of the first refrigeration oil at 15 °C is​​​​​​​​​​​​​The flash point of the first refrigeration oil is 179°C to 185°C, preferably 179°C to 181°C, and more preferably 181°C. The flash point is a value measured according to the method in accordance with JIS-K2265.

[0033] The high-temperature, high-pressure gaseous refrigerant produced in the first compressor 2 flows into the intermediate heat exchanger 10. In the intermediate heat exchanger 10, heat exchange takes place between the second refrigerant (low-temperature, low-pressure liquid refrigerant) in the high-temperature refrigeration cycle CH and the first refrigerant (high-temperature, high-pressure gaseous refrigerant) in the low-temperature refrigeration cycle. As a result, in the low-temperature refrigeration cycle CL, the gaseous refrigerant flowing through the intermediate heat exchanger 10 condenses, generating high-pressure liquid refrigerant.

[0034] The high-pressure liquid-phase refrigerant passes through the low-temperature side first expansion valve 31, the low-temperature side receiver 81, and the low-temperature side second expansion valve 32 in that order. As the high-pressure liquid-phase refrigerant passes through the low-temperature side first expansion valve 31, its pressure drops to a certain extent, becoming a medium-pressure, medium-temperature liquid-phase refrigerant. This liquid-phase refrigerant is stored in the low-temperature side receiver 81 and separated into gas and liquid phases. Of this, the gas phase component is supplied to the first compressor 2 (specifically, upstream of the high-pressure side scroll compressor 22) through the low-temperature side circuit 91, which acts as a gas injection circuit 9. In other words, the low-temperature first refrigerant (gas phase component) before compression is sent to the first compressor 2 through the low-temperature side circuit 91.

[0035] The medium-temperature, medium-pressure liquid phase refrigerant that has passed through the low-temperature receiver 81 passes through the low-temperature second expansion valve 32, where its pressure decreases further, resulting in a low-temperature, low-pressure liquid phase refrigerant.

[0036] The liquid phase refrigerant, which has become low temperature and low pressure after passing through the low-temperature side second expansion valve 32, flows into the evaporator 1. The evaporator 1 is installed inside the freezer (the room to be frozen). Heat exchange takes place in the evaporator 1 between the air in the freezer and the first refrigerant.

[0037] Furthermore, it is desirable to forcibly supply air from the freezer compartment to the evaporator 1 using a fan. The low-temperature liquid-phase refrigerant absorbs heat from the freezer compartment, causing the temperature inside the freezer compartment to decrease. In other words, the freezer compartment is cooled. Consequently, the liquid-phase refrigerant flowing through the evaporator 1 increases in temperature and changes from liquid to gaseous.

[0038] The refrigerant, having passed through evaporator 1 and become a gas, is then drawn back into the first compressor 2. This cycle is repeated continuously, adjusting the temperature of the freezer to the desired value.

[0039] The specifications for the low-temperature refrigeration cycle are exemplified below. Evaporation temperature -62°C (LP = 0.2 MPaA*) HP / MP = 2.4 / 0.6 [MPaA] Nc = 10⁴ [rps] Ts / Td = -55 / 95 [°C], oil temperature (inside the compressor) = 0 [°C], etc.

[0040] *Since the load side (LP side) remains almost constant, and the HP side (high-temperature LP side) also remains almost constant, the pressure conditions do not change significantly.

[0041] HP: Discharge pressure of scroll compressor 42 MP: Discharge pressure of rotary compressor 41 LP: Suction pressure of rotary compressor 41 Nc: Actual rotational speed Ts: Suction temperature Td:Discharge temperature

[0042] (Configuration of the high-temperature side refrigeration cycle) The high-temperature side refrigeration cycle CH includes a second compressor 4, a heat sink 5, a high-temperature side expansion valve 6 (high-temperature side first expansion valve 61 and high-temperature side second expansion valve 62), and a high-temperature side receiver 82.

[0043] The second compressor 4, radiator 5, high-temperature side first expansion valve 61, high-temperature side receiver 82, and high-temperature side second expansion valve 62 are arranged sequentially from the upstream side to the downstream side in the flow direction of the second refrigerant and are connected in a ring by the high-temperature side piping P2.

[0044] The high-temperature side piping P2 is filled with a secondary refrigerant. This secondary refrigerant contains only carbon dioxide (CO2).

[0045] The second compressor 4 compresses the low-pressure gaseous refrigerant supplied from the intermediate heat exchanger 10 to produce a high-temperature, high-pressure gaseous refrigerant. The second compressor 4 is a two-stage compressor known as a scroll rotary type. A rotary compressor 41 is used on the low-pressure side, and a scroll compressor 42 is used on the high-pressure side. The rotary compressor 41 and the scroll compressor 42 are connected coaxially.

[0046] The second compressor 4 is equipped with a radial upper bearing and a radial lower bearing (not shown). The radial upper bearing (drive bearing) is located at the rear end of the orbiting scroll and rotatably supports the drive bush. The radial lower bearing (main bearing) rotatably supports the drive shaft. In the second compressor 4, the sliding surface area of ​​the bearings is larger in the rotary compressor 41 than in the scroll compressor 42.

[0047] The second compressor 4 is equipped with a reservoir (not shown) in which the second refrigeration oil is stored. The second refrigeration oil stored in the reservoir is based on one or more oils selected from the group consisting of ester oil, ether oil, glycol oil, and mineral oil. The ester oil may be, for example, a polyol ester oil. The second refrigeration oil acts as a lubricant on the sliding surfaces of the bearings in the second compressor 4. The second refrigeration oil operates in a medium temperature and medium pressure atmosphere.

[0048] In combination with CO2 refrigerant, the refrigerant dissolution viscosity of the second refrigeration oil is 9.96 cP or more and 10.04 or less, preferably 10 cP, at a temperature of 4.4°C and an absolute pressure of 2.5 MPa.

[0049] In combination with CO2 refrigerant, the refrigerant dissolution viscosity of the second refrigeration oil is 12.16 cP or more and 12.24 or less, preferably 12.2 cP, at a temperature of 12.3°C and an absolute pressure of 2.5 MPa.

[0050] The kinematic viscosity of the second refrigeration oil is 61.2 mm at 40°C. 2 / s or more 74.8mm 2 / s, preferably 68mm 2 It is / s.

[0051] The density of the second refrigeration oil at 15°C is 0.96 g / cm³. 3 That is the case.

[0052] The flash point of the second refrigeration oil is 254°C.

[0053] The high-temperature, high-pressure gaseous refrigerant generated in the second compressor 4 flows into the radiator 5. The radiator 5 is located outside the freezer (the room to be frozen). Heat exchange takes place in the radiator 5 between the second refrigerant and the outside air.

[0054] Furthermore, it is desirable that outside air be forcibly supplied to the heat sink 5 by a fan (not shown). This causes the gaseous refrigerant to condense in the heat sink 5, generating high-pressure liquid refrigerant.

[0055] The high-pressure liquid-phase refrigerant passes through the high-temperature side first expansion valve 61, the high-temperature side receiver 82, and the high-temperature side second expansion valve 62 in that order. As the high-pressure liquid-phase refrigerant passes through the high-temperature side first expansion valve 61, its pressure drops to a certain extent, becoming a medium-pressure, medium-temperature liquid-phase refrigerant. This liquid-phase refrigerant is stored in the high-temperature side receiver 82 and separated into gas and liquid phases. Of this, the gas phase component is supplied to the second compressor 4 (specifically, upstream of the high-pressure side scroll compressor 42) through the high-temperature side circuit 92, which acts as a gas injection circuit 9. In other words, the low-temperature second refrigerant (gas phase component) before compression is sent to the second compressor 4 through the high-temperature side circuit 92.

[0056] The medium-temperature, medium-pressure liquid phase refrigerant that has passed through the high-temperature side receiver 82 passes through the high-temperature side second expansion valve 62, where its pressure decreases further, becoming a low-temperature, low-pressure liquid phase refrigerant.

[0057] The liquid-phase refrigerant, which has become low-temperature and low-pressure after passing through the high-temperature side second expansion valve 62, flows into the intermediate heat exchanger 10. In the intermediate heat exchanger 10, heat exchange takes place between the second refrigerant (low-temperature, low-pressure liquid-phase refrigerant) in the high-temperature side refrigeration cycle CH and the first refrigerant (high-temperature, high-pressure gaseous refrigerant) in the low-temperature side refrigeration cycle, which will be described later. As a result, in the high-temperature side refrigeration cycle CH, the temperature of the liquid-phase refrigerant flowing through the intermediate heat exchanger 10 rises and it changes from liquid to gaseous.

[0058] The refrigerant, having passed through the intermediate heat exchanger 10 and become a gas, is then drawn back into the second compressor 4. In the high-temperature refrigeration cycle CH, this cycle is carried out continuously.

[0059] (Effects and Benefits) In a cascade cycle type refrigeration system, the compression ratios required for the first compressor 2 and the second compressor 4 can be kept low. As a result, the temperature of the refrigerant discharged from these compressors (discharge temperature) can be further reduced. In other words, the refrigeration capacity of the refrigeration system 100 can be further increased.

[0060] Figure 2 shows the cycle diagram of the refrigeration system according to the above embodiment. In this figure, the horizontal axis represents specific enthalpy, the vertical axis represents pressure, the solid line represents the high-temperature refrigeration cycle CH, and the dashed line represents the low-temperature refrigeration cycle CL. As shown in Figure 2, in a cascade cycle type refrigeration system, the cycle diagrams of the high-temperature refrigeration cycle CH and the low-temperature refrigeration cycle CL are superimposed on each other at an intermediate position (intermediate heat exchanger 10).

[0061] This allows the refrigerant temperature to be lowered to a lower temperature compared to using only the high-temperature refrigeration cycle CH. For example, if the radiator outlet temperature of the high-temperature refrigeration cycle CH is 34°C, the evaporation temperature of the low-temperature refrigeration cycle CL can be set to an ultra-low temperature of around -68°C.

[0062] In cascade cycle refrigeration systems, it is possible to use different types of refrigerants in the low-temperature refrigeration cycle (CL) and the high-temperature refrigeration cycle (CH). Low GWP (Gross Warming Point) can be achieved by primarily using CO2 as the refrigerant. A mixed refrigerant containing R32 (a mixture of CO2 and R32) can further enhance refrigeration capacity compared to using CO2 alone.

[0063] By adjusting the R32 content to between 16% and 22% by weight, the GWP can be kept below 150, thus meeting international regulatory limits. This makes it possible to provide a refrigeration system 100 that achieves both low GWP and high refrigeration capacity.

[0064] In the high-temperature refrigeration cycle CH, only CO2 is used as the secondary refrigerant, so the density does not become excessively low compared to when R32 is mixed in. This also allows the compression ratio required by the second compressor 4 to be kept low.

[0065] In the low-temperature refrigeration cycle CL, the kinematic viscosity was 5.2 mm at 40°C. 2 / s or more 19.8mm 2 By applying / s refrigeration oil to the first compressor 2, it becomes possible to achieve both reliability and reduced mechanical losses.

[0066] In the low-temperature refrigeration cycle CL, applying refrigerant oil with a refrigerant dissolution viscosity of 0.43 cP to 0.51 cP at a temperature of 4.4°C and an absolute pressure of 2.5 MPa to the first compressor 2 makes it possible to achieve both reliability and reduced mechanical losses, even when operating at -60°C.

[0067] Figure 3 shows the relationship between the refrigerant dissolution viscosity of the refrigerant oil and the oil film thickness formed on the sliding surfaces of the bearings at the operating temperature of the first compressor 2. The operating conditions were a temperature of 4.4°C or 12.3°C and an absolute pressure of 2.5 MPa. In Figure 3, the horizontal axis represents the refrigerant dissolution viscosity (cP), the vertical axis represents the oil film thickness (μm), the solid line represents the oil film thickness of the main bearing, and the dashed line represents the oil film thickness of the drive bearing.

[0068] The oil film thickness criteria for the main bearings is 0.68 μm, and for the drive bearings, it is 0.61 μm. The criteria are the oil film thickness required to ensure stable oil film formation during operation and prevent lubrication failure of the bearing due to oil film breakdown. The oil film thickness criteria are determined by bearing specifications (bearing clearance, bearing surface properties), rotational speed, temperature conditions, etc. If the oil film thickness is too thin, the oil film will not be stable, leading to lubrication failure due to oil film breakdown, which can cause bearing failure.

[0069] As shown in Figure 3, these criteria can be met with a refrigerant dissolution viscosity of 0.32 cP or higher. In other words, bearing reliability can be ensured by using refrigerant oil with a refrigerant dissolution viscosity of 0.32 cP or higher at a temperature of 4.4°C and an absolute pressure of 2.5 MPa. Using refrigerant oil with a refrigerant dissolution viscosity of 0.43 cP to 0.51 cP at a temperature of 4.4°C and an absolute pressure of 2.5 MPa allows for a margin of safety, thus ensuring reliability more reliably.

[0070] As the operating temperature increases, the refrigerant dissolution viscosity also increases. If the refrigerant dissolution viscosity becomes too high, it leads to a decrease in mechanical efficiency. As shown in Figure 3, refrigerant oil with a refrigerant dissolution viscosity of 0.8 cP can form an oil film on the bearing sliding surface that is about twice the thickness of the criterion. From this result, it can be seen that if the refrigerant dissolution viscosity is 0.8 cP or less at a relatively high temperature range (12.3°C) and an absolute pressure of 2.5 MPa, an oil film of sufficient thickness can be obtained.

[0071] The relationship between the refrigerant dissolution viscosity at a temperature of 4.4°C and an absolute pressure of 2.5 MPa, and the kinematic viscosity at 40°C was investigated.

[0072] The kinematic viscosity (40°C, 100°C) of arbitrary ester-based refrigerant oils A and B was measured according to the method compliant with JIS K2283. Based on the measurement results, the kinematic viscosity (4.4°C, 12.3°C) was calculated. Next, for refrigerant oil A, the refrigerant solubility (%) and refrigerant solubility (cP) under operating conditions of 2.5 MPa pressure and 4.4°C or 12.3°C were obtained from temperature-pressure, refrigerant solubility, and refrigerant solubility charts. The refrigerant solubility of refrigerant oil B was calculated from the kinematic viscosity ratio of B / A at each temperature and the refrigerant solubility of refrigerant oil A.

[0073] The results are shown in Figures 4 and 5. The kinematic viscosity of refrigerant oil A was 64.2 mmHg at 40°C. 2 / s, 8.0mm at 100℃ 2 / s, 363mm at 12.3℃ 2 / s, 697mm at 4.4℃ 2 The value was / s. The kinematic viscosity of refrigerant oil B was 7.6 mm at 40°C. 2 / s, 2.1mm at 100℃ 2 / s, 22mm at 12.3℃ 2 / s, 33mm at 4.4℃ 2 It was / s.

[0074] At an absolute pressure of 2.5 MPa and a temperature of 12.3°C, the refrigerant solubility of refrigerant oil A was 19.1%, and the refrigerant solubility was 12.2 cP. At an absolute pressure of 2.5 MPa and a temperature of 4.4°C, the refrigerant solubility of refrigerant oil A was 22.9%, and the refrigerant solubility was 10.0 cP.

[0075] The refrigerant dissolution viscosity of refrigerant oil B at an absolute pressure of 2.5 MPa and a temperature of 12.3°C was 0.74 cP. The refrigerant dissolution viscosity of refrigerant oil B at an absolute pressure of 2.5 MPa and a temperature of 4.4°C was 0.47 cP.

[0076] Multiply the ratio of 0.32 cP to the refrigerant dissolution viscosity of refrigerant oil B at an absolute pressure of 2.5 MPa and a temperature of 4.4°C by the kinematic viscosity of refrigerant oil B at 40°C to obtain the kinematic viscosity mm at 40°C. 2 Converted to / s. The kinematic viscosity at 40°C for a refrigerant with a dissolution viscosity of 0.32 cP is 5.202 mm². 2 It was / s.

[0077] From the above results, the kinematic viscosity at 40°C is 5.2 mm³. 2 By using refrigerant oil with a performance rating of / s or higher, the reliability of the bearings can be ensured.

[0078] In the above, the kinematic viscosity of refrigerant oil B at 40°C is calculated from the refrigerant dissolution viscosity. However, this calculation method is only valid for the combination of the above embodiments: "refrigerant for the low-temperature side refrigeration cycle of a cascade cycle type refrigeration system," "mixed refrigerant of CO2 and R32," and "refrigerant oil based on ester oil, ether oil, glycol oil, and mineral oil." The inventors conducted prior studies, including measuring the refrigerant dissolution viscosity of refrigerant oils A and B for single refrigerants, CO2 and R32, and concluded that the kinematic viscosity can be calculated from the refrigerant dissolution viscosity in the combination of the above embodiments: "refrigerant for the low-temperature side refrigeration cycle of a cascade cycle type refrigeration system," "mixed refrigerant of CO2 and R32," and "refrigerant oil based on ester oil, ether oil, glycol oil, and mineral oil." The above relationship between refrigerant dissolution viscosity and kinematic viscosity may not hold true under conditions that deviate from the above combination of embodiments.

[0079] Figure 6 shows the relationship between viscosity grade and compressor mechanical efficiency ratio. In this figure, the horizontal axis represents viscosity grade, the vertical axis represents mechanical efficiency ratio, ● represents rotary mechanical efficiency ratio (refrigerant: CO2 + R32, temperature: -45°C), ○ represents scroll mechanical efficiency ratio (refrigerant: CO2 + R32, temperature: -45°C), ▲ represents rotary mechanical efficiency ratio (refrigerant: CO2, temperature: -10°C), and △ represents scroll mechanical efficiency ratio (refrigerant: CO2 + R32, temperature: -10°C). In this figure, the mechanical efficiency ratio on the vertical axis is set to 1, where 96% of the actual value of the rotary mechanical efficiency (refrigerant: CO2, temperature: -10°C) of the current CO2 compressor is set. Viscosity grade is ISO viscosity grade. The refrigerant oil is ester-based.

[0080] The high-temperature refrigeration cycle using CO2 as the sole refrigerant (refrigerant: CO2, temperature: -10°C) had a higher mechanical efficiency ratio than the low-temperature refrigeration cycle using a mixed refrigerant of CO2 and R32 (CO2 + R32, temperature: -45°C). In the low-temperature refrigeration cycle, rotary compressors tended to have a higher mechanical efficiency ratio than scroll compressors, and this tendency became more pronounced as the viscosity grade decreased.

[0081] It is preferable that the mechanical efficiency ratio be 80% of the mechanical efficiency of the current CO2 compressor (efficiency ratio of 0.8 or higher). As shown in Figure 6, the rotary mechanical efficiency ratio of the low-temperature refrigeration cycle is 0.8 or higher when the viscosity grade is 20 or lower. The kinematic viscosity of viscosity grade 20 is 19.8 mm² / s or lower at 40°C. Therefore, by using refrigeration oil with a kinematic viscosity of 19.8 mm² / s or lower at 40°C, an efficiency ratio of 0.8 or higher can be achieved compared to the current machine.

[0082] In the refrigeration system according to the above embodiment, the gas injection circuit 9 supplies a low-temperature first refrigerant or second refrigerant before compression to at least one of the first compressor 2 and the second compressor 4. This makes it possible to further lower the final refrigerant discharge temperature by supplying a low-temperature refrigerant to an intermediate position between these multiple stages, for example, when the first compressor 2 and the second compressor 4 are configured as multi-stage compressors.

[0083] The gas injection circuit 9 is provided in both the low-temperature refrigeration cycle CL and the high-temperature refrigeration cycle CH. This makes it possible to lower the discharge temperature of the compressors (first compressor 2 and second compressor 4) in both the low-temperature refrigeration cycle CL and the high-temperature refrigeration cycle CH.

[0084] The gas injection circuit 9 is configured to supply refrigerant to the upstream side of the high-pressure scroll compressors 22 and 42. In the scroll compressors 22 and 42, the refrigerant circulating inside the casing is configured to flow into the compression chamber without being significantly restricted by flow direction or other factors. In other words, compared to the rotary compressors 21 and 41, it is easier to add other refrigerants to the outside of the compression chamber in the scroll compressors 22 and 42. This makes it possible to add refrigerant more easily and smoothly using the gas injection circuit 9.

[0085] <Note> The refrigeration apparatus described in the above-described embodiment can be understood, for example, as follows. A refrigeration system (100) according to a first aspect of the present disclosure comprises a low-temperature refrigeration cycle (CL) through which a first refrigerant circulates, a high-temperature refrigeration cycle (CH) through which a second refrigerant circulates, and an intermediate heat exchanger (10) connecting the low-temperature refrigeration cycle and the high-temperature refrigeration cycle so as to exchange heat between the first refrigerant and the second refrigerant, wherein the first refrigerant is a mixed refrigerant containing CO2 and R32, the second refrigerant is CO2, and the compressor (2) of the low-temperature refrigeration cycle contains a refrigerant with a kinematic viscosity of 5.2 mm at 40°C. 2 / s or more 19.8mm 2 / s of refrigeration oil is stored here.

[0086] In the refrigeration system described above, by employing a cascade cycle type with a low-temperature side refrigeration cycle and a high-temperature side refrigeration cycle, the compression ratio required for the compressor in each refrigeration cycle can be kept low. As a result, the temperature of the refrigerant discharged from these compressors (discharge temperature) can be further reduced, and the refrigeration capacity of the refrigeration machine can be further increased.

[0087] In the refrigeration system described above, the first refrigerant in the low-temperature refrigeration cycle and the second refrigerant in the high-temperature refrigeration cycle exchange heat in an intermediate heat exchanger. This allows the refrigerant temperature to be lowered to a lower level compared to using only the high-temperature refrigeration cycle. As a result, a refrigeration system capable of ultra-low temperatures, achieving a freezer chamber temperature of -60°C, can be provided.

[0088] In the refrigeration system described above, it is possible to use different types of refrigerants in the low-temperature refrigeration cycle CL and the high-temperature refrigeration cycle CH.

[0089] A mixed refrigerant containing CO2 and R32 is used as the primary refrigerant circulating in the low-temperature refrigeration cycle. Using CO2 as the refrigerant enables a low GWP (Gross Wave Pressure). A mixed refrigerant containing R32 can further enhance refrigeration capacity compared to using CO2 alone. By using CO2 as the main component of the refrigerant and adjusting the R32 blend, a GWP of 150 or less and a coefficient of performance (COP) of 0.5 can be achieved. This allows for the provision of a refrigeration system that achieves both low GWP and high refrigeration capacity.

[0090] In the high-temperature refrigeration cycle, since only CO2 is used as the secondary refrigerant, the density does not become excessively low compared to when R32 is mixed in. This also allows for a lower compression ratio to be required in the compressor of the high-temperature refrigeration cycle.

[0091] By applying refrigerant oil with the above kinematic viscosity to the compressor of the low-temperature side refrigeration cycle, an oil film of sufficient thickness to meet the criteria can be formed on the sliding parts, ensuring reliability. Furthermore, the application of refrigerant oil with the above kinematic viscosity can reduce mechanical losses.

[0092] In the refrigeration apparatus according to the second aspect of the present disclosure, the refrigerant dissolution viscosity of the refrigerant oil may be 0.43 cP or more and 0.51 cP or less at a temperature of 4.4°C and an absolute pressure of 2.5 MPa.

[0093] By setting the refrigerant dissolution viscosity of the refrigeration oil within the above range, it is possible to further reduce mechanical losses while ensuring a margin for oil film thickness.

[0094] In the third aspect of the present disclosure, the refrigeration apparatus may, in the first aspect described above, have a refrigerant dissolution viscosity of the refrigeration oil of 0.70 cP or more and 0.78 cP or less at a temperature of 12.3°C and an absolute pressure of 2.5 MPa.

[0095] By setting the refrigerant dissolution viscosity of the refrigeration oil within the above range, it is possible to further reduce mechanical losses while ensuring a margin for oil film thickness. [Explanation of Symbols]

[0096] 1. Evaporator 2. First Compressor (Compressor) 3. Low-temperature expansion valve 4. Second Compressor 5 Heat sink 6. High-temperature side expansion valve 9. Gas injection circuit 10 Intermediate heat exchanger 21 Rotary Compressor 22 Scroll Compressor 31 Low-temperature side first expansion valve 32 Low-temperature side second expansion valve 41 Rotary Compressor 42 Scroll Compressor 61 High temperature side first expansion valve 62 High temperature side second expansion valve 81 Low-temperature receiver 82 High-temperature side receiver 91 Low-temperature circuit 92 High temperature side circuit 100 Refrigeration equipment CH High-Temperature Refrigeration Cycle CL Low-temperature refrigeration cycle P1 Low-temperature side piping P2 High-temperature side piping

Claims

1. The low-temperature refrigeration cycle in which the first refrigerant circulates, A high-temperature refrigeration cycle in which a second refrigerant circulates, An intermediate heat exchanger connects the low-temperature side refrigeration cycle and the high-temperature side refrigeration cycle so that the first refrigerant and the second refrigerant exchange heat, Equipped with, The first refrigerant is a mixed refrigerant containing 16% to 22% by weight of R32, with the remainder being CO2. The second refrigerant is CO ２ And, The compressor of the low-temperature refrigeration cycle uses at least one base oil selected from the group consisting of ester oil, ether oil, glycol oil, and mineral oil, with a kinematic viscosity of 5.2 mm at 40°C. ２ / s or more 19.8mm ２ A refrigeration system that stores refrigerant oil with a flow rate of less than / s and is designed to achieve ultra-low temperatures of -60°C.

2. The refrigeration apparatus according to claim 1, wherein the refrigerant dissolution viscosity of the refrigerant oil is 0.43 cP or more and 0.51 cP or less at a temperature of 4.4°C and an absolute pressure of 2.5 MPa.

3. The refrigeration apparatus according to claim 1, wherein the refrigerant dissolution viscosity of the refrigerant oil is 0.70 cP or more and 0.78 cP or less at a temperature of 12.3°C and an absolute pressure of 2.5 MPa.

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