Refrigeration system and its oil return method

Abstract

The present invention provides a refrigeration system and an oil return method thereof. The refrigeration system includes: a compressor, a condenser, a throttling device, and an evaporator connected in sequence to form a refrigeration circuit; wherein, the refrigeration system further includes an oil recovery system, the oil recovery system includes at least two ejectors connected in series, and each of the at least two ejectors includes a high-pressure fluid inlet, a suction fluid inlet, and a fluid outlet; wherein, the high-pressure fluid inlet of each of the at least two ejectors is connected to a high-pressure refrigerant source, the fluid outlet of the front ejector in any two adjacent ejectors among the at least two ejectors is connected to the suction fluid inlet of the rear ejector; and wherein, the suction fluid inlet of the foremost ejector among the at least two ejectors is connected to the oil-rich layer region of the refrigeration system, and the fluid outlet of the last ejector among the at least two ejectors is connected to the bearing chamber of the compressor. The refrigeration system and the oil return method according to the embodiments of the present invention provide stable oil return pressure and amount.

Description

Technical Field

[0001] The present invention relates to a refrigeration system, and more particularly, to an oil return device and an oil return method for a refrigeration system. Background Art

[0002] In a refrigeration system, components of a compressor such as bearings require oil for lubrication. In an oil-free refrigeration system, the compressor itself does not have a lubricating oil passage, but rather, by recovering the liquid rich in oil (also known as a gas-liquid two-phase) that accumulates at the bottom of an evaporator, for example, to the bearing chamber of the compressor, the oil present in the refrigerant is thus used to lubricate, anticorrode, and cool the bearings in the compressor. In such a system, there are certain requirements for the amount and pressure of the returned refrigerant to ensure that sufficient oil can reach the desired lubricated position of the compressor bearings and does not affect the design of the bearing chamber.

[0003] Ejectors are commonly used in commercial power recovery or heat recovery systems. An ejector typically includes a high-pressure fluid that is converted into a high-momentum gas-liquid two-phase fluid through a high-pressure fluid nozzle. The suction fluid is sucked in with the high-momentum gas-liquid two-phase fluid and mixed with the high-momentum gas-liquid two-phase fluid in a mixing chamber, and momentum exchange occurs, and then diffuses in a diffuser chamber to increase the pressure of the fluid and is then delivered to a downstream device. Summary of the Invention

[0004] The object of the present invention is to solve or at least alleviate the problems existing in the prior art.

[0005] According to some aspects, there is provided a refrigeration system, which includes: a compressor, a condenser, a throttling device, and an evaporator that are connected in sequence to form a refrigeration circuit;

[0006] Wherein, the refrigeration system further includes an oil recovery system, and the oil recovery system includes at least two ejectors connected in series, and each of the at least two ejectors includes a high-pressure fluid inlet, a suction fluid inlet, and a fluid outlet;

[0007] Wherein, the high-pressure fluid inlet of each of the at least two ejectors is connected to a high-pressure refrigerant source, the fluid outlet of the front ejector in any two adjacent ejectors among the at least two ejectors is connected to the suction fluid inlet of the rear ejector; and wherein, the suction fluid inlet of the foremost ejector among the at least two ejectors is connected to the rich oil layer region of the refrigeration system, and the fluid outlet of the last ejector among the at least two ejectors is connected to the bearing cavity of the compressor.

[0008] Optionally, in the refrigeration system described above, the mass flow rate ratio Mr of the suction fluid inlet to the high-pressure fluid inlet of each of the at least two ejectors is in the range of 0 - 2, or in the range of 0.1 - 1.2, or in the range of 0.2 - 0.8, or is approximately 0.5. Optionally, the mass flow rate ratio Mr of each of the at least two ejectors is substantially the same, thus simplifying the design of the ejector system.

[0009] Optionally, in the refrigeration system described above, the pressure rise ratio Pr of the fluid outlet of each of the at least two ejectors to the pressure of the suction fluid inlet is in the range of 1 - 3, or in the range of 1.1 - 2.5, or in the range of 1.15 - 2, or in the range of 1.2 - 1.8, or is approximately 1.5. Optionally, the pressure rise ratio Pr of each of the at least two ejectors is substantially the same, thus simplifying the design of the ejector system.

[0010] Optionally, in the refrigeration system described above, the mass flow rate of the high-pressure fluid inlet of the subsequent ejector among any two adjacent ejectors of the at least two ejectors is greater than the mass flow rate of the high-pressure fluid inlet of the preceding ejector. Optionally, the mass flow rate of the high-pressure fluid inlet of the subsequent ejector among any two adjacent ejectors of the at least two ejectors is 2 - 11 times, optionally 2.25 - 6 times, the mass flow rate of the high-pressure fluid inlet of the preceding ejector.

[0011] Optionally, in the refrigeration system described above, the high-pressure refrigerant source is taken from the condenser, and optionally, the refrigerant taken from the condenser is pressurized by a pressurizing device such as a liquid pump.

[0012] Optionally, in the refrigeration system described above, the refrigeration system further includes a bypass channel directly connecting the liquid pump to the bearing cavity of the compressor.

[0013] Optionally, in the refrigeration system described above, the fluid outlet of the last ejector among the at least two ejectors communicates with a through hole of the compressor facing the bearing cavity of the compressor, and / or the suction fluid inlet of the foremost ejector among the at least two ejectors communicates with the oil-rich layer region of the evaporator.

[0014] On the other hand, an oil return method in a refrigeration system is provided, the method including: pumping and pressurizing the oil-rich liquid in the oil-rich layer region of the refrigeration system through an oil recovery system and then transporting it to the bearing cavity of the compressor, the oil recovery system including at least two ejectors connected in series.

[0015] Optionally, in the method, connecting at least two ejectors in series includes:

[0016] Connect the high-pressure fluid inlet of each of the at least two ejectors to a high-pressure refrigerant source;

[0017] Connect the fluid outlet of the front ejector in any two adjacent ejectors among the at least two ejectors to the suction fluid inlet of the rear ejector; and

[0018] Connect the suction fluid inlet of the foremost ejector among the at least two ejectors to the rich oil layer region of the refrigeration system, and connect the fluid outlet of the last ejector among the at least two ejectors to the bearing cavity of the compressor.

[0019] Optionally, the method further includes taking liquid refrigerant from the condenser as the high-pressure refrigerant source and optionally pressurizing the liquid refrigerant.

[0020] Optionally, the method further includes directly passing a part of the liquid refrigerant to the bearing cavity of the compressor.

[0021] The refrigeration system and the oil return method according to the embodiments of the present invention provide stable oil return pressure and amount. Brief Description of the Drawings

[0022] Referring to the accompanying drawings, the disclosure of the present invention will become more understandable. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the protection scope of the present invention. In addition, similar numbers in the figures are used to represent similar components, where:

[0023] Figure 1 Shows a schematic structural diagram of a refrigeration system according to an embodiment of the present invention;

[0024] Figure 2 Shows a schematic structural diagram of a refrigeration system according to another embodiment of the present invention;

[0025] Figure 3 Shows a schematic structural diagram of a refrigeration system according to another embodiment of the present invention; and

[0026] Figure 4 Shows a schematic diagram of an embodiment of an ejector. Detailed Description of the Embodiments

[0027] Reference Figure 1, which shows a refrigeration system according to an embodiment of the present invention. The refrigeration system includes: a compressor 1, a condenser 2, a throttling device 3, and an evaporator 4 that are connected in sequence to form a refrigeration circuit. The refrigeration circuit can operate in various ways known in the art. In the illustrated example, the compressor 1 includes an inlet 12 and an outlet 11. The compressor outlet 11 is connected to the inlet of the condenser 2, the outlet of the condenser 2 is connected to the throttling device 3. The throttling device 3 can be, for example, an expansion valve or other device, which is then connected to the inlet of the evaporator 4, and the outlet of the evaporator 4 is finally connected to the inlet 12 of the compressor 1 to form a refrigeration circuit. It should be understood that in addition to the components shown, the refrigeration circuit may also include other components, such as various valves, bypass flow paths, and / or other heat exchangers, etc. The refrigeration circuit according to an embodiment of the present invention can be used in combination with an oil-free compressor, where the oil-rich liquid (oil-rich refrigerant) in the oil-rich layer region in the refrigeration system is provided to the compressor bearing chamber to provide functions such as lubrication and anti-corrosion. Therefore, the refrigeration system further includes an oil recovery system. The oil recovery system includes at least two ejectors 6, 7, 8 connected in series. Each of the at least two ejectors 6, 7, 8 includes a high-pressure fluid inlet 61, 71, 81, a suction fluid inlet 62, 72, 82, and a fluid outlet 63, 73, 83. The high-pressure fluid inlets 61, 71, 81 of each ejector are connected to a high-pressure fluid source. For example, in the illustrated embodiment, the high-pressure fluid inlets 61, 71, 81 of each ejector are connected to a pressurizing device 5. The pressurizing device 5 can be, for example, a liquid pump, and the pressurizing device 5 is further connected to a position P between the outlet of the condenser 2 and the throttling device 3. Thus, the pressurizing device 5 can divert a part of the liquid refrigerant taken from the condenser 2 to the high-pressure fluid inlets 61, 71, 81 of each ejector. In addition, the series connection of the ejectors means that the fluid outlet of the preceding ejector in any two adjacent ejectors among the at least two ejectors 6, 7, 8 is connected to the suction fluid inlet of the succeeding ejector. For example, for the adjacent first ejector 6 and second ejector 7, the fluid outlet 63 of the first ejector 6 is connected to the suction fluid inlet 72 of the second ejector 7. And for the adjacent second ejector 7 and third ejector 8, the fluid outlet 73 of the second ejector 6 is connected to the suction fluid inlet 82 of the third ejector 8, and so on.In addition, the suction fluid inlet 62 of the foremost ejector among at least two ejectors, i.e., the first ejector 6 in the illustrated embodiment, is connected to the oil-rich layer region of the refrigeration system. For example, in the illustrated embodiment, it is connected to the evaporator 4, such as the oil-rich layer region near the bottom of the evaporator 4, to extract the refrigerant containing oil (such as in a gas-liquid two-phase state) located at the bottom of the evaporator 4. And the fluid outlet 83 of the last ejector among at least two ejectors, i.e., the third ejector 8 in the illustrated embodiment, leads to the bearing chamber of the compressor 1, that is, the pressurized refrigerant with oil is led to the bearing chamber of the compressor 1, such as the through hole 13 of the compressor 1 facing its bearing cavity, so that the refrigerant can be sprayed onto the bearing for functions such as cooling, lubrication, and anti-corrosion. The through hole 13 can be located on the compressor housing to communicate the bearing cavity of the compressor with the outside of the bearing cavity. At the through hole 13, devices such as one or more nozzles can be provided, for example, to guide the fluid to various positions in the bearing cavity. It should be understood that although in the illustrated embodiment, the oil-rich layer region is selected as the bottom of the evaporator 4, in alternative embodiments, the oil-rich liquid can also be extracted from other oil-rich layer regions in the refrigeration system, such as other heat exchangers like economizers or liquid storage devices (if any). The refrigeration system according to the embodiment of the present invention extracts and pressurizes the oil-rich liquid by using at least two ejectors connected in series, so that it has sufficient pressure when entering the compressor 1 to provide better lubrication.

[0028] It should be understood that although three ejectors 6, 7, and 8 are shown connected in series in the figure, depending on the desired pressure at the compressor, the pressurizing ability of the ejectors themselves, and / or on-site conditions (such as the space for arranging the ejectors), more ejectors can be used, such as four, five, six, or only two ejectors. For example, in Figure 2 the embodiment, a case is shown where the oil recovery system only has two ejectors connected in series. In addition, another difference from Figure 1 the embodiment is that if there is a sufficient pressure difference between the liquid refrigerant taken from the condenser 2 and the oil-rich liquid, the pressurizing device 5 can be omitted.

[0029] In some embodiments, the mass flow rate at the high-pressure fluid inlet of the subsequent ejector among any two adjacent ejectors among at least two ejectors is greater than the mass flow rate at the high-pressure fluid inlet of the preceding ejector. In Figure 1 the illustrated embodiment, the mass flow rate at the high-pressure fluid inlet 81 of the third ejector 8 is greater than the mass flow rate at the high-pressure fluid inlet 71 of the second ejector 7, and the mass flow rate at the high-pressure fluid inlet 71 of the second ejector 7 is greater than the mass flow rate at the high-pressure fluid inlet 61 of the first ejector 6, and so on. In some embodiments, the mass flow rate at the high-pressure fluid inlet of the subsequent ejector is 2 - 11 times, optionally 2.25 - 6 times, the mass flow rate at the high-pressure fluid inlet of the preceding ejector. For example, inFigure 1 In the illustrated embodiment, 2 times is taken as an example. Then, the mass flow rate at the high-pressure fluid inlet 71 of the second ejector 7 is 2 times that at the high-pressure fluid inlet 61 of the first ejector 6, and the mass flow rate at the high-pressure fluid inlet 81 of the third ejector 8 is 2 times that at the high-pressure fluid inlet 71 of the second ejector 7. Therefore, the high-pressure fluid at the high-pressure fluid source is distributed to the high-pressure fluid inlets 61, 71, and 81 of the first ejector 6, the second ejector 7, and the third ejector 8 in a ratio of 1:2:4. Additionally, the pressures of the fluids at the high-pressure fluid inlets 61, 71, and 81 of the first ejector 6, the second ejector 7, and the third ejector 8 are substantially equal, and this pressure depends on the pressure of the fluid at the condenser outlet itself and the capacity of the pressurizing device 5. In some other embodiments, different mass flow rate ratios at the high-pressure fluid inlets of the subsequent ejectors and the preceding ejectors can be designed according to different specific system requirements.

[0030] In some embodiments, the mass flow rate ratio of the suction fluid inlet and the high-pressure fluid inlet of each ejector can be defined as the mass flow rate ratio Mr. Then, the mass flow rate ratio Mr of each of at least two ejectors 6, 7, and 8 can be substantially the same, thereby simplifying the design of the ejector system. In some other embodiments, the mass flow rate ratio Mr of each ejector can be within the range of 0 - 2, or within the range of 0.1 - 1.2, or within the range of 0.2 - 0.8, or approximately 0.5.

[0031] In some embodiments, the ratio of the pressure at the fluid outlet of each ejector to the pressure at the suction fluid inlet is defined as the pressure rise ratio Pr. In some embodiments, the pressure rise ratio Pr of the pressure at the fluid outlet to the pressure at the suction fluid inlet of each of at least two ejectors 6, 7, and 8 can be substantially the same, thereby simplifying the design of the ejector system. In some other embodiments, the pressure rise ratio Pr of each of at least two ejectors 6, 7, and 8 can be within the range of 1 - 3, or within the range of 1.1 - 2.5, or within the range of 1.15 - 2, or within the range of 1.2 - 1.8, or approximately 1.5.

[0032] It should be understood that the mass flow rate ratio Mr and the pressure rise ratio Pr of at least two ejectors can be set differently, and specifically can be set according to factors such as the requirement of the oil return amount. The larger the mass flow rate ratio Mr, the more fluid can be ejected. However, due to the characteristics of the ejector itself, the larger the mass flow rate ratio Mr, the smaller the pressure rise ratio Pr. Therefore, for the final design of the ejector, including the mass flow rate ratio Mr and the pressure rise ratio Pr, the oil return requirement, the pressure rise requirement, and system characteristics such as the actually selected refrigerant, etc. should be comprehensively considered.

[0033] In a specific embodiment, the suction fluid inlet 62 of the first ejector 6 extracts an oil-rich liquid (in this embodiment, R1233ZD refrigerant containing oil) from the evaporator at a flow rate of 0.05 GPM (gallons per minute), which includes 500 PPM of oil and has a pressure of approximately 6.21 psi. The refrigerant containing oil is pressurized to 10.557 psi by the first ejector 6, to 17.94 psi by the second ejector, and to 30.5 psi by the third ejector, and is provided to the compressor. On the other hand, the high-pressure fluid pumped by the pressurizing device 5 such as a pressure pump is provided to the high-pressure fluid inlets of each ejector at a flow rate of 2.1 GPM. For example, it is provided to the high-pressure fluid inlet 61 of the first ejector 6 at a flow rate of approximately 0.125 GPM, to the high-pressure fluid inlet 71 of the second ejector 7 at a flow rate of 0.437 GPM, and to the high-pressure fluid inlet 81 of the third ejector 8 at a flow rate of 1.53 GPM. The high-pressure fluid may have a pressure of, for example, 34.6 psi. It should be understood that the specific data in the above embodiments are only exemplary and not restrictive, and suitable pressure pump and ejector parameters can be selected according to the actual working conditions.

[0034] Continue to refer to Figure 3 , where components identical to those in the Figure 1 embodiment are labeled with the same numerals. In the Figure 3 embodiment, the refrigeration system further includes a bypass channel 51 directly connected from the pressurizing device 5 to the compressor 1. The bypass channel 51 is used to provide additional refrigerant for cooling to the compressor 1. Although not shown, a valve such as a flow valve may also be arranged on the bypass channel 51 to regulate the flow rate of this refrigerant stream, etc.

[0035] Continue to refer to Figure 4An embodiment of an ejector that can be used in a refrigeration system according to an embodiment of the present invention will be introduced. The ejector may include: a high-pressure fluid passage 901; a suction fluid passage 902; a mixing chamber 93 that is in fluid communication with the high-pressure fluid passage 901 and the suction fluid passage 902 respectively; and a diffuser chamber 94 downstream of the mixing chamber 93. In some embodiments, the high-pressure fluid passage 901 includes: a high-pressure fluid inlet 91 and a high-pressure fluid nozzle, and the high-pressure fluid nozzle sequentially includes a converging section 911 with a gradually decreasing cross-sectional area, a throat 912, a diverging section 913 with a gradually increasing cross-sectional area, and a high-pressure fluid outlet 914, and the high-pressure fluid outlet 914 faces the mixing chamber 93. The suction fluid passage 902 includes a suction fluid inlet 92 and a suction chamber 921 surrounding the high-pressure fluid nozzle, and the suction chamber 921 is in communication with the mixing chamber 93. For example, there is a tapered structure transition section 922 between the suction chamber 921 and the mixing chamber 93. In some embodiments, the mixing chamber 93 may be a cylindrical shape with a constant cross-sectional area, in which the high-pressure fluid entering through the high-pressure fluid passage 901 and the suction fluid sucked through the suction fluid passage 902 are fully mixed to form a subsonic fluid, and this fluid diffuses in the diffuser chamber 94 to recover the kinetic energy therein into pressure, thereby forming a medium-pressure fluid, and leaving from the fluid outlet 95. Therefore, as Figure 1 and Figure 2 shown, the series-connected ejectors can gradually increase the pressure of the suction fluid, thereby providing a refrigerant with sufficient pressure and oil content to the compressor to provide functions such as lubrication, anti-corrosion, and cooling.

[0036] On the other hand, a method for oil return in a refrigeration system is also provided, including: pressurizing the refrigerant at the evaporator through an oil recovery system including at least two series-connected ejectors and then transmitting it to the compressor.

[0037] The device and method according to an embodiment of the present invention provide a refrigerant with stable pressure and oil content to the compressor. The number of ejectors in the device according to an embodiment of the present invention can be flexibly selected. The device of the present invention can be applied to the transformation of an existing refrigeration system, that is, only an oil recovery device needs to be added on the basis of the existing refrigeration system. In addition, the ejectors in the recovery system are pure mechanical components, with high stability and little need for maintenance.

[0038] The specific embodiments described above are only for more clearly describing the principle of the present invention, in which each component is clearly shown or described to make the principle of the present invention easier to understand. Without departing from the scope of the present invention, those skilled in the art can easily make various modifications or changes to the present invention. Therefore, it should be understood that these modifications or changes should be included within the scope of the patent protection of the present invention.

Claims

1. A refrigeration system, comprising: A compressor, a condenser, a throttling device and an evaporator that are sequentially connected to form a refrigeration circuit; characterized in that the refrigeration system further includes an oil recovery system, and the oil recovery system includes at least two ejectors connected in series, and each of the at least two ejectors includes a high-pressure fluid inlet, a suction fluid inlet and a fluid outlet; Wherein, the high-pressure fluid inlet of each of the at least two ejectors is connected to a high-pressure refrigerant source, and the fluid outlet of the preceding ejector in any two adjacent ejectors among the at least two ejectors is connected to the suction fluid inlet of the subsequent ejector; and wherein, the suction fluid inlet of the foremost ejector among the at least two ejectors is connected to the oil-rich layer region of the refrigeration system, and the fluid outlet of the last ejector among the at least two ejectors is connected to the bearing cavity of the compressor; Wherein, the mass flow ratio Mr of the suction fluid inlet and the high-pressure fluid inlet of each of the at least two ejectors is in the range of 0-2.

2. The refrigeration system according to claim 1, characterized in that, The mass flow ratio Mr of the suction fluid inlet and the high-pressure fluid inlet of each of the at least two ejectors is in the range of 0.1-1.

2.

3. The refrigeration system according to claim 2, characterized in that, The mass flow ratio Mr of the suction fluid inlet and the high-pressure fluid inlet of each of the at least two ejectors is in the range of 0.2-0.

8.

4. The refrigeration system according to claim 3, wherein The mass flow ratio Mr of the suction fluid inlet and the high-pressure fluid inlet of each of the at least two ejectors is basically the same and is 0.

5.

5. The refrigeration system according to claim 1, characterized in that, The pressure rise ratio Pr of the pressure at the fluid outlet and the pressure at the suction fluid inlet of each of the at least two ejectors is in the range of 1-3.

6. The refrigeration system according to claim 5, wherein, The pressure rise ratio Pr of the pressure at the fluid outlet and the pressure at the suction fluid inlet of each of the at least two ejectors is in the range of 1.1-2.

5.

7. The refrigeration system according to claim 6, wherein, The pressure rise ratio Pr of the pressure at the fluid outlet and the pressure at the suction fluid inlet of each of the at least two ejectors is in the range of 1.15-2.

8. The refrigeration system according to claim 7, characterized in that, The pressure rise ratio Pr of the pressure at the fluid outlet and the pressure at the suction fluid inlet of each of the at least two ejectors is in the range of 1.2-1.

8.

9. The refrigeration system according to claim 8, wherein The pressure rise ratio Pr of the pressure at the fluid outlet and the pressure at the suction fluid inlet of each of the at least two ejectors is basically the same and is 1.

5.

10. The refrigeration system according to claim 1, wherein The mass flow rate of the high-pressure fluid inlet of the subsequent ejector in any two adjacent ejectors among the at least two ejectors is greater than the mass flow rate of the high-pressure fluid inlet of the preceding ejector.

11. The refrigeration system according to claim 10, characterized in that, The mass flow rate of the high-pressure fluid inlet of the subsequent ejector in any two adjacent ejectors among the at least two ejectors is 2-11 times the mass flow rate of the high-pressure fluid inlet of the preceding ejector.

12. The refrigeration system according to claim 11, characterized in that, The mass flow rate of the high-pressure fluid inlet of the subsequent ejector in any two adjacent ejectors among the at least two ejectors is 2.25-6 times the mass flow rate of the high-pressure fluid inlet of the preceding ejector.

13. The refrigeration system according to any one of claims 1-12, characterized in that, The high-pressure refrigerant source is taken from the condenser, and wherein, the refrigerant taken from the condenser is pressurized by a pressurizing device, and the pressurizing device is a liquid pump.

14. The refrigeration system according to claim 13, characterized in that, The refrigeration system further includes a bypass passage directly connected from the liquid pump to the bearing cavity of the compressor.

15. The refrigeration system according to any one of claims 1-12, characterized in that, The fluid outlet of the last ejector among the at least two ejectors communicates with a through hole of the compressor facing the bearing chamber of the compressor, and / or the suction fluid inlet of the foremost ejector among the at least two ejectors communicates with the oil-rich layer region of the evaporator.

16. A method for oil return in a refrigeration system, characterized in that, The method includes: extracting and pressurizing the oil-rich liquid in the oil-rich layer region of the refrigeration system through an oil recovery system and then transmitting it to the bearing chamber of the compressor, the oil recovery system including at least two ejectors connected in series, wherein connecting at least two ejectors in series includes: Connecting the high-pressure fluid inlet of each of the at least two ejectors to a high-pressure refrigerant source; Connecting the fluid outlet of the preceding ejector among any two adjacent ejectors of the at least two ejectors to the suction fluid inlet of the succeeding ejector; and Connecting the suction fluid inlet of the foremost ejector among the at least two ejectors to the oil-rich layer region of the refrigeration system, and connecting the fluid outlet of the last ejector among the at least two ejectors to the bearing chamber of the compressor; wherein, the method further includes setting the mass flow ratio Mr of the suction fluid inlet and the high-pressure fluid inlet of each of the at least two ejectors within the range of 0-2.

17. The oil return method according to claim 16, wherein The method further includes taking liquid refrigerant from the condenser as the high-pressure refrigerant source, and wherein, the method further includes pressurizing the liquid refrigerant.

18. The oil return method according to claim 17, wherein, The method further includes directly passing a part of the liquid refrigerant to the bearing chamber of the compressor.

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