CN112229084A

CN112229084A - Multistage compressor, electric appliance and control method

Info

Publication number: CN112229084A
Application number: CN202011158142.2A
Authority: CN
Inventors: 魏会军; 黄秦; 阙沛祯; 胡艳军; 董辉; 向柳
Original assignee: Gree Green Refrigeration Technology Center Co Ltd of Zhuhai
Current assignee: Gree Green Refrigeration Technology Center Co Ltd of Zhuhai
Priority date: 2020-10-26
Filing date: 2020-10-26
Publication date: 2021-01-15
Anticipated expiration: 2040-10-26
Also published as: CN112229084B

Abstract

The compressor comprises a low-pressure cylinder, a high-pressure cylinder, a back pressure cavity, a first liquid separator and a second liquid separator, wherein a gas inlet pipe of the compressor is communicated with a gas inlet end of the low-pressure cylinder through the first liquid separator; the second liquid separator comprises a first cavity and a second cavity, the first cavity is communicated with the backpressure cavity, the air inlet end of the high-pressure cylinder is communicated with the first cavity, the bottom of the first cavity is provided with an oil return hole, and the refrigerant oil in the first cavity is introduced into the second cavity through the oil return hole; and the air supply pipe of the compressor is communicated to the back pressure cavity through the second cavity. The second liquid separator is arranged into an upper cavity and a lower cavity, the function of separating gasoline is added before the high-pressure cylinder sucks air, the sucked air and oil of the high-pressure cylinder are reduced, the cylinder is prevented from pressing oil, and the reliability of the compressor is improved.

Description

Multistage compressor, electric appliance and control method

Technical Field

The present disclosure relates to compressor technologies, and particularly to a multi-stage compressor, an electric appliance, and a control method.

Background

A multistage compressor refers to a compressor that steps up the gas pressure in stages, and generally includes a low pressure cylinder and a high pressure cylinder, or one or more intermediate stage pressure cylinders may be provided. The two-stage enthalpy-increasing frequency-changing compressor still keeps high-efficiency characteristics under low-temperature working conditions, and occupies more and more important positions in the fields of air conditioners, heat pump water heaters, freezing and refrigerating and the like.

The conventional two-stage enthalpy-increasing compressor has the structural characteristics that high-pressure stage exhaust is communicated with a shell, and the shell has high back pressure; the high-pressure-stage cylinder is an upper cylinder, and the low-pressure-stage cylinder is a lower cylinder; the enthalpy-increasing component is communicated with the middle cavity of the pump body. Generally, in order to improve energy efficiency, the volume of the middle cavity is made as large as possible, and the hollow flange or the partition plate with a larger design size is correspondingly needed, so that the weight of the hollow flange or the partition plate is also larger. In order to reduce the mass below the welding spot and improve the structural mode, a technical worker also provides a low-pressure cylinder overhead scheme, and compressed gas of the low-pressure cylinder is directly discharged to the shell and then flows to the lower cylinder (high-pressure cylinder) from the shell to be compressed.

However, the middle-backpressure two-stage enthalpy-increasing compressor mentioned in the scheme has the problem that the refrigerant oil in the shell is easy to be sucked into the cylinder when the high-pressure cylinder sucks air, and the refrigerant oil can be discharged into a system along with a gaseous refrigerant, so that the oil quantity in the compressor is reduced, a moving part of a pump body is subjected to oil shortage abrasion, and the compressor is damaged.

Disclosure of Invention

In order to solve the technical problem that in the prior art, the technical problem that the frozen oil is sucked into the cylinder in the multi-stage compressor is solved, the application provides the multi-stage compressor, an electric appliance and a control method.

In a first aspect, the present application provides a multistage compressor, the compressor includes a low pressure cylinder and a high pressure cylinder, a back pressure cavity is included in a shell of the compressor, the compressor further includes a first liquid separator and a second liquid separator, and an air inlet pipe of the compressor is connected to an air inlet end of the low pressure cylinder through the first liquid separator; the second liquid separator comprises a first cavity and a second cavity, the first cavity is communicated with the backpressure cavity, the air inlet end of the high-pressure cylinder is communicated with the first cavity, the bottom of the first cavity is provided with an oil return hole, and the refrigerant oil in the first cavity is introduced into the second cavity through the oil return hole; and the air supply pipe of the compressor is communicated to the back pressure cavity through the second cavity.

In an embodiment of the present application, the second liquid separator includes a partition plate, the partition plate separates the second liquid separator into a first cavity above and a second cavity below, and the oil return hole is opened in the partition plate.

In an embodiment of the application, the vacuum pump further comprises a high-pressure air inlet pipe, wherein the high-pressure air inlet pipe is communicated with the first cavity, and the air inlet end of the high-pressure air inlet pipe is located on the upper portion of the first cavity.

In an embodiment of the present application, an air outlet end of the high pressure air inlet pipe is connected to an air inlet end of the high pressure cavity.

In one embodiment of the present application, the first dispenser has a volume that is less than a volume of the second dispenser.

In an embodiment of the present application, an air supply pipeline is communicated between the bottom of the second cavity and the back pressure cavity.

In an embodiment of the present application, a volume ratio of the first cavity to the second cavity is greater than or equal to 1:1 and less than 5: 1.

In an embodiment of the application, the ratio of the diameter of the cavity in the first liquid separator to the pipe diameter of the air inlet pipe or the air outlet pipe connected with the cavity is 1.2: 1-1.5: 1.

In another aspect of the present application, there is provided an appliance including the multi-stage compressor as described above. The electric appliance can be an air conditioner, a heat pump device, a water heater device or a freezing and refrigerating device.

In another aspect of the present application, a method for controlling a multistage compressor is provided, which mainly includes the steps of:

the gaseous refrigerant enters a first liquid separator;

the gaseous refrigerant enters a low-pressure cylinder of the multi-stage compressor after being processed by the first liquid separator;

the exhaust gas enters a back pressure cavity of the shell after being compressed by the low-pressure cylinder;

the medium-pressure gaseous refrigerant and the mixed refrigeration oil in the back pressure cavity enter a first cavity of a second liquid separator;

the gaseous refrigerant separated by the flash evaporator passes through a second cavity of the second liquid separator and is supplemented into the back pressure cavity;

the refrigeration oil is separated in the first cavity, enters the second cavity and is conveyed to the back pressure cavity along with the gas in the second cavity.

The multistage compressor that this application embodiment provided, to the technical problem that the frozen oil inhales the cylinder among the prior art, improve back pressure formula doublestage rotor compressor enthalpy gain part in the current casing, set to the second knockout of two upper and lower independent cavities, increase the function of petrol separation before the high-pressure cylinder is breathed in, reduce the high-pressure cylinder and breathe in and take oil, avoid the cylinder to press oil, improve compressor reliability.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and together with the description, serve to explain the principles of the application.

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a schematic view of the overall structure of a two-stage enthalpy-increasing compressor according to embodiment 1;

FIG. 2 is a schematic structural view of a two-stage enthalpy-increasing complete machine with an upper low-pressure cylinder according to embodiment 2;

FIG. 3 is a schematic diagram of a communicating tube of a two-stage enthalpy-increasing scheme with an upper low-pressure cylinder in embodiment 2;

FIG. 4 is a schematic diagram of a dual stage intermediate back pressure compressor according to an embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating piping connections for a compressor in accordance with an embodiment of the present invention;

FIG. 6 is a schematic view of a second liquid separator of the multi-stage compressor according to the embodiment of the present invention;

FIG. 7 is a schematic view of an alternative configuration of a multi-stage compressor in accordance with an embodiment of the present invention;

fig. 8 is a schematic view of an alternative second liquid separator of the compressor of the embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some embodiments of the present application, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Fig. 1 is a schematic view of the overall structure of a two-stage enthalpy-increasing compressor according to embodiment 1; the overall structure of the two-stage enthalpy-increasing compressor is shown in fig. 1, a low-temperature low-pressure refrigerant enters a lower cylinder (low pressure cylinder) 12 through a liquid distributor 11, and is discharged into an intermediate cavity formed by a lower flange 13 and a lower flange cover plate 14 after one-stage compression is completed. And the intermediate-pressure refrigerant is mixed with the refrigerant flowing in through the enthalpy increasing component in the intermediate cavity to obtain the intermediate-pressure refrigerant. After the upper cylinder (high pressure cylinder) 15 sucks the medium pressure refrigerant and completes the second-stage compression, the obtained high pressure refrigerant enters the shell 17 through an exhaust port of the upper flange 16. The conventional two-stage enthalpy-increasing compressor has the structural characteristics that high-pressure stage exhaust is communicated with a shell, and the shell has high back pressure; the high-pressure-stage cylinder is an upper cylinder, and the low-pressure-stage cylinder is a lower cylinder; the enthalpy increasing member 18 communicates with the pump body intermediate chamber.

FIG. 2 is a schematic structural view of a two-stage enthalpy-increasing complete machine with an upper low-pressure cylinder according to embodiment 2; generally, in order to improve energy efficiency, the volume of the middle cavity is made as large as possible, and the hollow flange or the partition plate with a larger design size is correspondingly needed, so that the weight of the hollow flange or the partition plate is also larger. In order to reduce the quality below the welding spot and improve the structural mode. As shown in fig. 2, a two-stage enthalpy-increasing compressor with a top low pressure cylinder (the low pressure cylinder is used as an upper cylinder 21) is provided, compressed gas in the low pressure cylinder is directly discharged to a shell 22 and then flows from the shell to a lower cylinder 23 (a high pressure cylinder) to be compressed, a refrigerant flows as shown in fig. 3, when a gaseous refrigerant is discharged from an evaporator, impurities doped in the refrigerant are filtered by a second liquid separator, the gaseous refrigerant enters the low pressure cylinder to complete first-stage compression, first-stage exhaust gas is discharged to the shell, meanwhile, gaseous refrigerant separated by a flash evaporator of a system is also fed into the shell by a first liquid separator, first-stage exhaust gas and system gas supplement are mixed in the shell to obtain medium-pressure gaseous refrigerant, the medium-pressure gaseous refrigerant and mixed refrigeration oil are sucked by the high pressure cylinder to complete second-stage compression, and the medium-pressure gaseous refrigerant is directly.

The above embodiment has at least the following two problems: 1. the second liquid separator mainly has the function of filtering impurities doped in the gaseous refrigerant, so that unnecessary material cost is increased; 2. when the first-stage exhaust and the system air supplement are mixed in the shell, the refrigeration oil in the shell is easy to mix, is sucked away by the high-pressure cylinder and is discharged out of the compressor, at the moment, the inside of the compressor is in an oil shortage state, and parts of a pump body are easy to wear.

Because the middle-backpressure two-stage enthalpy-increasing compressor has the problem that the refrigerant oil in the shell is easy to be sucked into the cylinder when the high-pressure cylinder sucks air, the refrigerant oil can be discharged into a system along with a gaseous refrigerant, so that the oil quantity in the compressor is reduced, a moving part of a pump body is subjected to oil shortage abrasion, and the compressor is damaged.

The following embodiments of the present application provide a multistage compressor, the compressor mainly includes a low pressure cylinder and a high pressure cylinder, a back pressure cavity is included in a shell of the compressor, the compressor further includes a first liquid separator and a second liquid separator, and an air inlet pipe of the compressor is connected to an air inlet end of the low pressure cylinder through the first liquid separator; the second liquid separator comprises a first cavity and a second cavity, the first cavity is communicated with the backpressure cavity, the air inlet end of the high-pressure cylinder is communicated with the first cavity, the bottom of the first cavity is provided with an oil return hole, and the refrigerant oil in the first cavity is introduced into the second cavity through the oil return hole; and the air supply pipe of the compressor is communicated to the back pressure cavity through the second cavity.

The technical problem of the cylinder is inhaled to the frozen oil among the prior art is improved to this application embodiment back pressure formula double-stage rotor compressor enthalpy gain part in the current casing, sets up the second knockout of enthalpy gain part two upper and lower independent cavities, increases the function of oil vapour separation before the high-pressure cylinder is breathed in, reduces the high-pressure cylinder and breathes in and take oil, avoids the cylinder to press oil, improves compressor reliability.

The embodiment of this application sets up to two cavitys in increasing the enthalpy part in order to solve the unstable problem of operation that current multistage enthalpy-increasing compressor easily takes place, and a cavity is equivalent to and forms the backpressure chamber of admitting air, and another cavity is equivalent to increases the enthalpy chamber of admitting air, wherein disposes oil-gas separation structure between two cavitys to in carry out effective separation with the refrigerated oil in the backpressure chamber output fluid, avoid the high-pressure cylinder to take oil problem. It will be understood by those skilled in the art that other variations in details of the technology may be made without departing from the spirit or essential characteristics of the invention as defined by the claims appended hereto.

The embodiments of the present application are described below with reference to the accompanying drawings:

FIG. 4 is a schematic diagram of a two stage intermediate back pressure compressor according to an embodiment of the present invention, FIG. 5 is a schematic diagram of the piping connection of the compressor according to an embodiment of the present invention, and FIG. 6 is a schematic diagram of the second liquid separator of the multi-stage compressor according to an embodiment of the present invention; in a first aspect, the present application provides a multi-stage compressor, where the compressor includes a low pressure cylinder 47 and a high pressure cylinder 48, a casing 46 of the compressor includes a back pressure cavity, and further includes a first liquid separator 41 and a second liquid separator 42, and an air inlet pipe of the compressor is connected to an air inlet end of the low pressure cylinder 47 through the first liquid separator 41; the second liquid divider 42 comprises a first cavity 63 and a second cavity 64, the first cavity 63 is communicated with the back pressure cavity, the air inlet end of the high pressure cylinder 48 is communicated with the first cavity 63, the bottom of the first cavity 63 is provided with an oil return hole 62, and the frozen oil in the first cavity 63 is introduced into the second cavity 64 through the oil return hole 62; the compressor inlet pipe 65 is connected to the back pressure chamber via the second cavity 64.

The enthalpy-increasing component is arranged as a second liquid distributor 42 with an upper cavity and a lower cavity, the function of oil-gas separation is added before the high-pressure cylinder 48 sucks air, the sucked air and oil carrying of the high-pressure cylinder 48 are reduced, the cylinder is prevented from pressing oil, and the reliability of the compressor is improved.

In a specific embodiment of the present application, the second liquid separator includes a partition 61, the partition 61 divides the second liquid separator 42 into an upper first cavity 63 and a lower second cavity 64, and the oil return hole 62 is opened in the partition 61. The partition 61 may be formed by stamping as a whole, and a circle of inverted V-shaped rib is formed on the partition 61, on one hand, the strength of the partition 61 can be enhanced, and on the other hand, the oil return hole 62 may be configured at the top of the V-shaped rib, so as to form an oil pool on the top surface of the partition 61, so as to deposit and filter the impurities in the refrigeration oil on the top surface of the partition 61. The frozen oil output through the oil return hole 62 reduces the heavy impurities.

In a specific embodiment of the present application, a high pressure intake pipe is further included to supply air to the high pressure cylinder 48, the high pressure intake pipe is introduced into the first cavity 63, and the air inlet end of the high pressure intake pipe is located on the upper portion of the first cavity 63. And the top of the high-pressure air inlet pipe can be provided with a filtering component so as to filter the inlet air.

In a specific embodiment of the present application, an air outlet end of the high pressure air inlet pipe is connected to an air inlet end of the high pressure cavity.

In one embodiment of the present application, the first liquid separator 41 has a volume smaller than the volume of the second liquid separator 42. In the illustrated embodiment, the first liquid separator 41 has a volume of between about 3% and about 6% of the volume of the second liquid separator 42, and in the illustrated embodiment the volume fraction is about 4.6%.

In a specific embodiment of the present application, an air supply line 43 is connected between the bottom of the second cavity 64 and the back pressure chamber.

As shown in fig. 4, the present invention provides an improved embodiment, in which the liquid distributor before the suction of the low pressure cylinder 47 is reduced and replaced with the first liquid distributor 41, and a second liquid distributor 42 is added before the suction of the high pressure cylinder 48, and the second liquid distributor 42 is divided into an upper cavity and a lower cavity by a partition 61.

As shown in fig. 6, the partition plate 61 has a plurality of oil return holes 62, so that the refrigerant oil in the first cavity 63 can flow back into the second cavity 64, and the enthalpy increasing component 18 before being replenished is eliminated, and an air replenishing pipeline 43 is communicated between the bottom of the second cavity and the housing, so that the system air replenishing pipe 65 directly passes through the second cavity 64 of the second liquid separator, then enters the housing 46 to be mixed with the medium-pressure refrigerant gas discharged from the low-pressure cylinder 47, passes through the pipeline 44 at the top of the housing, enters the first cavity 63 of the second liquid separator 42, is sucked by the high-pressure cylinder 48 to be compressed, and finally is discharged from the exhaust pipe 45 into the system.

As shown in fig. 5, when the gaseous refrigerant is discharged from the evaporator, impurities doped in the refrigerant are filtered by the first liquid separator 41, the filtered gaseous refrigerant enters the low-pressure cylinder 47 to complete first-stage compression, first-stage exhaust gas is discharged into the shell 46, meanwhile, the gaseous refrigerant separated by the system flash evaporator is also fed into the shell 46 through the second cavity 64 of the second liquid separator 42, the first-stage exhaust gas and the system make-up gas are mixed in the shell to obtain medium-pressure gaseous refrigerant, the medium-pressure gaseous refrigerant and a part of mixed refrigerant oil are discharged into the first cavity 63 of the second liquid separator 42, the medium-pressure gaseous refrigerant is separated by the first cavity 63 of the second liquid separator 42, the refrigerant oil flows into the second cavity 64 of the second liquid separator 42 and returns to the shell 46 together with the gaseous refrigerant discharged from the system flash evaporator, and the gaseous refrigerant is sucked by the high-pressure cylinder 48 to complete second-stage compression.

Because the first liquid separator 41 only filters impurities, the diameter of the inner cavity of the first liquid separator 41 only needs to be slightly larger than the air inlet pipe and the air outlet pipe, and the air inlet pipe and the air outlet pipe can be effectively welded with the first liquid separator 41, namely the ratio of the diameter of the inner cavity of the first liquid separator 41 to the pipe diameters of the air inlet pipe and the air outlet pipe is 1.2: 1-1.5: 1; because the upper cavity of the second liquid separator 42 functions to separate the oil-gas mixture discharged from the housing, in order to realize the sufficient separation of the gaseous refrigerant and the refrigeration oil, the volume of the first cavity 63 needs to be increased as much as possible, and the second cavity 64 functions to filter impurities and return oil doped during the gas supply of the system, and has little requirement on the volume, so that in order to fully realize the functions and leave a welding space, the volume ratio of the first cavity to the second cavity of the second liquid separator 42 needs to be ensured to be more than or equal to 1:1 and less than 5: 1.

The second liquid separator structure arranged on the enthalpy-increasing gas-supplementing side is shown in fig. 6, a partition plate 61 is arranged inside the second liquid separator 42 to divide the liquid separator into an upper cavity and a lower cavity, a middle hole of the partition plate 61 is an avoiding hole for avoiding a straight pipe (high-pressure inlet pipe), and a plurality of oil return holes 62 are arranged around the avoiding hole to enable the refrigerant oil accumulated in the upper cavity of the liquid separator to enter the lower cavity through the oil return holes and finally return to the shell 46. The gas inlet pipe and the gas outlet pipe of the liquid separator only extend into the upper cavity of the liquid separator, the enthalpy-increasing gas inlet pipe extends into the lower cavity, and a communicating pipe is arranged at the bottom of the lower cavity and used for communicating the lower cavity of the liquid separator with the interior of the shell.

Fig. 7 is a schematic view showing an alternative structure of a multi-stage compressor according to an embodiment of the present invention, and fig. 8 is a schematic view showing a second liquid separator according to an alternative structure of a compressor according to an embodiment of the present invention. The enthalpy-increasing air inlet pipe of the second liquid separator passes through the upper cavity from the upper cover but is not communicated with the upper cavity and directly extends into the lower cavity. On the other hand, the oil return holes can also be arranged in three and are annularly arranged, and the oil return holes are also evenly spaced on the central angle.

the gaseous refrigerant enters a first liquid separator;

Compared with the prior art, the embodiment of the application has the technical effects that:

1. the back pressure type double-stage rotor compressor enthalpy increasing component in the existing shell is improved and is arranged into a large liquid separator with an upper cavity and a lower cavity, the function of gasoline separation is added before the high-pressure cylinder sucks air, the sucked air and oil of the high-pressure cylinder are reduced, the cylinder is prevented from pressing oil, and the reliability of the compressor is improved.

2. The liquid distributor before the low-pressure cylinder inhales is improved, the discharge of the refrigerant oil of the compressor to a system can be reduced based on the improved mode provided by the point 1, namely the low-pressure cylinder inhales without separating excessive refrigerant oil, the volume of the air suction liquid distributor of the low-pressure cylinder can be reduced, and the material cost of the compressor is reduced.

3. The volume of the middle cavity is increased, namely the ratio of the volume of the middle cavity to the displacement is increased, and the performance of the multi-stage rotor compressor can be improved.

4. The air inlet of the enthalpy-increasing port and the air suction of the high-pressure cylinder need to pass through a cavity similar to the expansion chamber type silencer, so that the air flow pulsation can be reduced, and the running noise of the compressor can be reduced.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The above description is merely exemplary of the present application and is presented to enable those skilled in the art to understand and practice the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multistage compressor comprising a low pressure cylinder and a high pressure cylinder, the compressor comprising a back pressure chamber within its housing,

the air inlet pipe of the compressor is communicated to the air inlet end of the low-pressure cylinder through the first liquid separator;

the second liquid separator comprises a first cavity and a second cavity, the first cavity is communicated with the backpressure cavity, the air inlet end of the high-pressure cylinder is communicated with the first cavity, the bottom of the first cavity is provided with an oil return hole, and the refrigerant oil in the first cavity is introduced into the second cavity through the oil return hole; and the air supply pipe of the compressor is communicated to the back pressure cavity through the second cavity.

2. The multi-stage compressor according to claim 1, wherein the second liquid separator includes a partition plate dividing the second liquid separator into an upper first cavity and a lower second cavity, the oil return hole opening in the partition plate.

3. The multi-stage compressor of claim 1, further comprising a high pressure inlet pipe, the high pressure inlet pipe opening into the first cavity, the high pressure inlet pipe inlet end being located at an upper portion of the first cavity.

4. The multi-stage compressor of claim 3, wherein an outlet end of the high pressure inlet pipe communicates to an inlet end of the high pressure chamber.

5. The multi-stage compressor of claim 1, wherein the first knockout volume is less than the second knockout volume.

6. The multi-stage compressor according to claim 1, wherein a gas supply line is communicated between a bottom of the second cavity and the back pressure cavity.

7. The multi-stage compressor according to any one of claims 1 to 6, wherein a volume ratio of the first cavity to the second cavity is 1:1 or more and less than 5: 1.

8. The multi-stage compressor according to any one of claims 1 to 6, wherein the ratio of the diameter of the cavity in the first liquid separator to the diameter of the inlet pipe or the outlet pipe connected thereto is 1.2:1 to 1.5: 1.

9. An electrical appliance comprising a multistage compressor according to any one of claims 1 to 8.

10. A control method of a multistage compressor, wherein the multistage compressor is a multistage compressor according to any one of claims 1 to 8, characterized by comprising the steps of:

the gaseous refrigerant enters a first liquid separator;