CN114542488A

CN114542488A - Centrifugal compressor

Info

Publication number: CN114542488A
Application number: CN202011329616.5A
Authority: CN
Inventors: 俞国新; 桂幸民; 李思茹; 陈锦践; 朱万朋; 韩聪; 殷纪强; 常云雪; 毛守博; 宋强; 魏伟
Original assignee: Qingdao Haier Smart Technology R&D Co Ltd; Haier Smart Home Co Ltd
Current assignee: Qingdao Haier Smart Technology R&D Co Ltd; Haier Smart Home Co Ltd
Priority date: 2020-11-24
Filing date: 2020-11-24
Publication date: 2022-05-27
Also published as: WO2022111411A1

Abstract

The invention provides a centrifugal compressor, which comprises a shell; the motor is arranged in the shell; and at least one compression unit, each compression unit comprises a volute installed on the housing and a centrifugal impeller arranged in the volute, and the centrifugal impeller is configured to rotate under the driving of a motor so as to compress the airflow entering the volute and discharge the airflow through an outlet of the volute. The invention is beneficial to realizing the miniaturization of the centrifugal compressor and can keep high efficiency.

Description

Centrifugal compressor

Technical Field

The invention relates to the technical field of compressors, in particular to a centrifugal compressor.

Background

The centrifugal compressor has the remarkable advantages of energy conservation, high efficiency, stable operation and long service life. However, in the refrigeration field, the centrifugal compressor is suitable for large-flow and low-pressure-ratio working occasions, and the efficient low-flow and high-pressure-ratio operation is difficult to realize. Therefore, the centrifugal compressor is applied to a large-cooling-capacity water chilling unit. Medium and small-sized refrigeration systems are increasingly using screw compressors, scroll compressors (such as small central air conditioners including multi-split air conditioners) and rolling rotor compressors. These types of compressors, however, operate far less efficiently than centrifugal compressors. Most of these compressors are lubricated with lubricating oil. The problems that the lubricating oil is accumulated in the heat exchanger, the oil is disadvantageously returned to the compressor, the lubrication of related compression parts is poor, the heat exchange resistance of the heat exchanger is increased and the like are easily caused.

Therefore, if the centrifugal compressor can be miniaturized and applied to small and medium-sized refrigeration systems to replace a screw compressor, a scroll compressor and even a rolling rotor compressor, the energy efficiency of the refrigeration systems is higher, and the refrigeration industry is influenced profoundly.

Disclosure of Invention

An object of the present invention is to solve or at least partially solve the above problems of the prior art and to provide a centrifugal compressor which can maintain high efficiency while achieving miniaturization.

The invention further aims to avoid the oil return problem of the compressor of a small and medium-sized refrigerating system.

It is a further object of the present invention to reduce the diffuser loss of the compressed gas stream in a centrifugal compressor.

In particular, the present invention provides a centrifugal compressor comprising:

a housing;

the motor is arranged in the shell; and

at least one compression unit, each compression unit includes a volute mounted to the housing and a centrifugal impeller disposed within the volute, the centrifugal impeller configured to rotate under drive of the motor to compress and discharge an airflow entering the volute through an outlet of the volute.

Optionally, the volute defines an inlet flow channel, a volute flow channel and an outlet flow channel which are connected in sequence along the airflow direction; the air inlet flow channel extends along the axial direction of the centrifugal impeller; the volute flow channel is flat with the thickness direction parallel to the axial direction of the centrifugal impeller; the air outlet flow channel gradually transits from the connection part with the volute flow channel to the outlet of the volute from a flat shape to a cylindrical shape; the inlet of the centrifugal impeller faces the air inlet flow passage, and the outlet of the centrifugal impeller faces the volute flow passage.

Optionally, the volute flow passage has a thickness greater than the outlet width of the centrifugal impeller.

Optionally, the ratio of the thickness of the volute to the outlet width of the centrifugal impeller is between 1.5 and 2.

Optionally, the inlet conduit comprises a tapered section that tapers in cross-section in the direction of airflow.

Alternatively, the tapered section is a truncated cone as a whole, and the generatrix of the tapered section is arc-shaped with the concave side facing the central axis direction of the intake runner.

Optionally, the centrifugal impeller is a strong back-curved shrouded impeller.

Optionally, the centrifugal compressor is of a two-stage compression type, the number of the at least one compression unit is two, and the outlet of the volute of the compression unit of the low-pressure stage is communicated with the inlet of the volute of the compression unit of the high-pressure stage through a connecting pipe.

Optionally, the compression unit of the low-pressure stage and the compression unit of the high-pressure stage are respectively located at two axial sides of the motor.

Optionally, the centrifugal compressor further comprises: at least one radial magnetic bearing and/or at least one axial magnetic bearing mounted within the housing to support the rotor of the electric machine.

Compared with the traditional centrifugal compressor, the centrifugal compressor of the invention omits a diffuser, and the centrifugal impeller is directly arranged in the volute, so that the larger diffusion loss caused by the larger rotation degree of the airflow in the diffuser is avoided, the overall efficiency of the compressor is improved, and the structure of the centrifugal compressor is more compact. Therefore, this configuration is advantageous for achieving a compact centrifugal compressor, and is suitable for application to a small central air conditioner such as a small chiller or a multi-split air conditioner, while maintaining high efficiency.

Furthermore, the centrifugal compressor can adopt a radial magnetic suspension bearing and an axial magnetic suspension bearing, and the magnetic suspension bearing is an oilless bearing, so that lubricating oil does not need to be added into the centrifugal compressor, the oil return problem of the compressor of a medium and small refrigeration system is thoroughly avoided (a screw compressor, a scroll compressor and a rolling rotor compressor which are conventionally adopted are basically lubricated by oil), and the heat exchange efficiency of the heat exchanger is improved; and the mechanical abrasion is small, the energy consumption is low, the noise is small, the stability of the whole machine is enhanced, and the service life is longer.

Furthermore, the volute flow channel defined by the volute is flat in the thickness direction parallel to the axial direction of the centrifugal impeller, and the flat volute flow channel enables the volute to be flat integrally, so that the compressor is favorably miniaturized. More importantly, the air outlet flow channel is gradually transited from a flat shape to a cylindrical shape from the joint of the air outlet flow channel and the volute flow channel to the outlet of the volute. Therefore, the air flow enters the cylindrical and wide air outlet flow channel from the thin and flat volute flow channel, and the excellent diffusion effect can be achieved. And because the air outlet flow channel gradually transits from the flat shape to the cylindrical shape from the joint of the air outlet flow channel and the volute flow channel to the outlet of the volute, the transition is smooth, the unnecessary resistance loss of the air flow is reduced, and meanwhile, the cylindrical shape is also suitable for being connected with a downstream pipeline.

Further, the invention recognizes that the direct exhaust of the centrifugal impeller to the volute causes the mach number of the airflow to be increased and the centrifugal effect of the airflow to be large, so that the airflow is accumulated to the radial outer side, the flow field is not uniform, and the larger flow loss is caused. In order to eliminate or at least relieve the adverse effects, the thickness of the volute flow channel is specially made to be larger than the width of the outlet of the centrifugal impeller, so that after the airflow enters the volute flow channel of the volute, the pressure and the speed are expanded and reduced, the Mach number of the airflow is reduced, the centrifugal effect is reduced, finally, the uniformity of the flow field at the outlet of the volute is obviously increased, and finally, the efficiency of the centrifugal compressor is improved.

Furthermore, the centrifugal impeller is a strong backward-bending type closed impeller, so that the centrifugal impeller does more work on airflow and is converted into static pressure lifting, and the work is converted into speed increase. Because the absolute airflow angle of the outlet of the strong backward-bending centrifugal impeller is larger, if the traditional diffuser is adopted, the airflow rotation degree is larger, and the diffusion loss is larger. The volute with the special design is directly connected with the centrifugal impeller, so that the problem can be effectively avoided. Therefore, the centrifugal impeller is comprehensively and directly arranged in the volute, the volute flow channel is specially designed, and the improvements of the strong backward-bending type centrifugal impeller are combined together, so that the beneficial effects of various structural improvements are obtained, the respective adverse effects are avoided, the overall efficiency of the centrifugal compressor is higher, the structure is more compact, and the miniaturization of the centrifugal compressor is favorably realized.

The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments thereof, taken in conjunction with the accompanying drawings.

Drawings

Some specific embodiments of the invention will be described in detail hereinafter, by way of illustration and not limitation, with reference to the accompanying drawings. The same reference numbers in the drawings identify the same or similar elements or components. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the drawings:

fig. 1 is a schematic view of the overall structure of a centrifugal compressor according to an embodiment of the present invention;

fig. 2 is a schematic sectional view of the centrifugal compressor shown in fig. 1 taken along the axial direction of the centrifugal impeller;

FIG. 3 is an enlarged view at A of FIG. 2;

FIG. 4 is a schematic diagram of the structure of one of the compression units of FIG. 1;

FIG. 5 is another angular schematic view of the compression unit shown in FIG. 4;

FIG. 6 is an exploded schematic view of the compression unit shown in FIG. 4;

FIG. 7 is a schematic structural view of a centrifugal impeller in the compression unit shown in FIG. 6;

FIG. 8 is a blade profile schematic of the centrifugal impeller of FIG. 7;

FIG. 9 is an exploded schematic view of the centrifugal impeller of FIG. 7;

fig. 10 is a schematic structural view of the second sheave body in fig. 9.

Detailed Description

A centrifugal compressor according to an embodiment of the present invention will be described with reference to fig. 1 to 10. In the partial figures, the x-axis represents the axial direction of the centrifugal impeller 200, and also the axial direction of the motor 40 and its stator 41 and rotor 42; the direction of airflow is indicated by the solid arrows.

Fig. 1 is a schematic view of the overall structure of a centrifugal compressor according to an embodiment of the present invention; fig. 2 is a schematic sectional view of the centrifugal compressor shown in fig. 1, taken along the axial direction of the centrifugal impeller 200; fig. 3 is an enlarged view of fig. 2 at a.

As shown in fig. 1 to 3, a centrifugal compressor of an embodiment of the present invention may generally include a casing 10, a motor 40, and at least one

compression unit

20, 30.

The cabinet 10 defines an accommodation space, and the motor 40 is installed in the cabinet 10. The motor 40 includes a stator 41 and a rotor 42, the stator 41 is fixed to the housing 10, and the rotor 42 is rotatable relative to the stator 41. The number of the

compression units

20, 30 may be one or more. For example, the centrifugal compressor may be of a single-stage compression type, and only one compression unit may be provided. The centrifugal compressor may be of a multistage compression type in which a plurality of

compression units

20 and 30 are provided. Each

compression unit

20, 30 includes a volute 100 mounted to the casing 10 and a centrifugal impeller 200 disposed within the volute 100. The centrifugal impeller 200 is configured to rotate under the drive of the motor 40 to compress the airflow entering the volute 100 and discharge it through the outlet of the volute 100.

In a conventional centrifugal compressor, a diffuser is basically disposed downstream of a centrifugal impeller at each stage, the centrifugal impeller discharges an air flow into the diffuser, and the air flow is diffused by the diffuser and then enters a volute.

Compared with the traditional centrifugal compressor, the centrifugal compressor of the invention omits a diffuser, and the centrifugal impeller 200 is directly arranged in the volute 100, so that the larger diffusion loss caused by the larger rotation degree of the airflow in the diffuser is avoided, the overall efficiency of the centrifugal compressor is improved, and the structure of the centrifugal compressor is more compact. Therefore, this structure is advantageous for the miniaturization of the centrifugal compressor and for the application to a small central air conditioner such as a small chiller or a multi-split air conditioner while maintaining high efficiency.

In some embodiments, such as shown in fig. 1 and 2, the centrifugal compressor may be of the two-stage compression type, with two compression units. It can be seen that one of the two

compression units

20, 30 is necessarily a low pressure stage, and the other is a high pressure stage, as shown in fig. 1 and 2, the compression unit 20 on the left side of the drawing is a low pressure stage, and the compression unit 30 on the right side is a high pressure stage. The outlet of the volute 100 of the compression unit 20 of the low pressure stage communicates with the inlet of the volute 100 of the compression unit 30 of the high pressure stage through a connection pipe 90. Specifically, the inlet end of the connection pipe 90 is provided with a flange 91 to interface with the flange 130 of the outlet of the volute 100 of the compression unit 20 of the low pressure stage, and the outlet end of the connection pipe 90 is provided with a flange 92 to connect with the volute 100 of the compression unit 30 of the high pressure stage. It is preferable that the compression unit 20 of the low pressure stage and the compression unit 20 of the high pressure stage are respectively located at both axial sides of the motor 40, so that the centrifugal impellers 200 of the two

compression units

20, 30 are respectively directly connected to the motor 40, and it is advantageous to partially cancel the axial forces of the two centrifugal impellers 200.

In some embodiments, the centrifugal compressor further comprises at least one radial magnetic bearing 60 and/or at least one axial magnetic bearing 80 mounted within the casing 10 to support the rotor 42 of the motor 40. As shown in fig. 2, the centrifugal compressor comprises two radial magnetic bearings 60 to support the rotor 42 in the radial direction. The centrifugal compressor further comprises an axial magnetic bearing 80 to counteract the axial force generated by the movement of the centrifugal impeller 200 on the rotor 42. The magnetic suspension bearing is made by adopting a magnetic suspension principle and is an oilless bearing. Therefore, lubricating oil does not need to be added into the centrifugal compressor, so that the oil return problem of the compressor of a small and medium-sized refrigeration system is thoroughly solved (the conventional screw compressor, the scroll compressor and the rolling rotor compressor which are usually adopted are basically lubricated by oil), and the heat exchange efficiency of the heat exchanger is improved. And the magnetic suspension bearing is adopted, so that the centrifugal compressor has the advantages of small mechanical wear, low energy consumption, small noise, enhanced stability and longer service life.

Further, as shown in fig. 3, on the basis of the magnetic suspension bearing, a common radial bearing 70 may be further disposed at an axial end of the rotor 42 to support the end of the rotor 42 in an important manner, so that the end is more stable and the operational reliability of the centrifugal compressor is improved.

FIG. 4 is a schematic diagram of the construction of one of the compression units 20 of FIG. 1; FIG. 5 is another angular schematic view of the compression unit 20 shown in FIG. 4; fig. 6 is an exploded schematic view of the compression unit 20 shown in fig. 4.

In the embodiment of the present invention, the gas flow enters the flow passage defined by the volute 100 from the inlet of the volute 100, then enters the centrifugal impeller 200 in the flow passage of the volute 100, and finally flows out of the outlet of the volute 100 to enter the next-stage compression unit 30 or discharge compressor.

In some embodiments, as shown in fig. 4 to 6, the volute 100 defines an inlet flow passage 101, a volute flow passage 102 and an outlet flow passage 103 which are connected in sequence in the direction of the gas flow, i.e., the volute 100 flow passage is divided into three sections. The inlet of inlet flow path 101 forms the inlet of volute 100 as described herein, and the outlet of outlet flow path 103 forms the outlet of volute 100. The intake runner 101 extends in the axial direction (x-axis direction) of the centrifugal impeller 200. The scroll flow path 102 is flat in a thickness direction parallel to the axial direction of the centrifugal impeller 200. The outlet flow channel 103 gradually changes from flat to cylindrical from the junction with the volute flow channel 102 to the outlet of the volute 100. The centrifugal impeller 200 has an inlet 201 (see fig. 8) facing the inlet flow path 101 and an outlet 202 (see fig. 8) facing the scroll flow path 102 to introduce air from the inlet flow path 101 and compress the air to discharge it to the scroll flow path 102.

In this embodiment, the flat volute flow channel 102 flattens the whole volute 100, which is beneficial to reducing the axial size of the centrifugal compressor and realizing the miniaturization of the compressor. More importantly, as the outlet flow channel 103 gradually changes from flat to cylindrical from the junction with the volute flow channel 102 to the outlet of the volute 100, the gas flow can have a very good diffusion effect in the process of entering the cylindrical and wide outlet flow channel 103 from the thin and flat volute flow channel 102. Moreover, as the outlet flow channel 103 gradually transits from the flat shape to the cylindrical shape from the joint with the volute flow channel 102 to the outlet of the volute 100, the transition is very smooth, unnecessary resistance loss of the air flow is reduced, and the cylindrical shape is also suitable for being connected with a downstream pipeline.

In some embodiments, as shown in FIG. 2, the intake runner 101 may include a tapered section 1011 with a gradually decreasing cross-section in the direction of airflow to improve the efficiency of air induction. Specifically, the tapered section 1011 may be made in the shape of a truncated cone as a whole, with a generatrix in the shape of an arc with a concave side facing the central axis direction of the intake runner 101. Further, the generatrix of the tapered section 1011 may be a straight line or a combination of various shapes. The intake runner 101 may be tapered as a whole, or may be a tapered section in a partial section, and a straight section in a partial section, whose cross section does not change with the change in the axial position.

In some embodiments, as shown in FIG. 6, the volute 100 may be a split structure including a volute body 110 and a cover plate 120 that are split along the axial direction of the inlet flow channel 101. The volute body 110 defines the aforementioned inlet flow passage 101, a first half of the volute flow passage 102 and an outlet flow passage 103, wherein the volute flow passage 102 is open to one side of the cover plate 120. The cover plate 120 covers an axial side of the volute body 110 to cover an open side of a first half of the volute 102 and define a second half of the volute 102, the first half of the volute 102 and the second half of the volute 102 opposing each other to form the completed volute 102. The rotation shaft 214 of the centrifugal impeller 200 is connected to the rotor 42 of the motor 40 through the center hole of the cover plate 120. In the present embodiment, the volute casing 100 is provided as a separate structure, and the volute casing body 110 and the cover plate 120 are separately machined to form the inlet flow passage 101, the volute flow passage 102 and the outlet flow passage 103 by machining. Compared with the existing integrally cast volute, in the embodiment, the surfaces of the inlet flow channel 101, the volute flow channel 102 and the outlet flow channel 103 are smoother, the uniformity of an internal flow field can be better met, the flow loss caused by the fact that the surfaces of the flow channels are too rough is reduced, and the operating efficiency of the centrifugal compressor is improved.

Further, as shown in fig. 3, two planes in the thickness direction of the volute flow channel 102 and the circumferential volute side face may be transited by a fillet (R angle in fig. 3) so as to increase the volute strength, relieve the local stress concentration, eliminate the corner vortex and ensure the uniformity of the flow field. The size of R can be selected based on the thickness of the volute 102. The split configuration of the volute 100 facilitates the machining of the aforementioned rounded corners.

Fig. 7 is a schematic structural view of the centrifugal impeller 200 in the compression unit 20 shown in fig. 6; fig. 8 is a blade profile schematic of the centrifugal impeller 200 shown in fig. 7.

In some embodiments, the thickness of the volute 102 is made greater than the outlet width of the centrifugal impeller 200. The thickness of the volute 102 refers to the dimension of the volute in the axial direction (x-axis) of the centrifugal impeller 200, and the outlet width B of the centrifugal impeller 200 refers to the dimension of the outlet 202 of the centrifugal impeller 200 in the axial direction of the centrifugal impeller 200, and is specifically marked in fig. 7. Specifically, the inventors have confirmed through a plurality of experiments that the optimum effect can be obtained by setting the ratio of the thickness of the scroll flow passage 102 to the outlet width of the centrifugal impeller 200 to 1.5 to 2.

The inventors have recognized that exhausting the centrifugal impeller 200 directly to the volute 100 results in an increase in the mach number of the airflow, a large centrifugal effect of the airflow accumulating radially outward, resulting in a non-uniform flow field, resulting in large flow losses. In order to eliminate or at least alleviate the above adverse effects, in the embodiment of the present invention, the thickness of the volute 102 is especially made larger than the outlet width B of the centrifugal impeller 200, so that after the airflow enters (the volute 102 of) the volute 100, the pressure expansion and the speed reduction are performed, the mach number is reduced, the centrifugal effect is reduced, finally, the uniformity of the flow field at the outlet of the volute 100 is significantly increased, and finally, the efficiency of the compressor is improved.

In some embodiments, centrifugal impeller 200 is a strong back-curved shrouded impeller. As shown in fig. 8, the centrifugal impeller 200 has a plurality of blades 203 arranged along its circumferential direction, a flow channel 212 is formed between every two adjacent blades 203, and the airflow enters the radial inner side of each flow channel 212 through the inlet 201 of the centrifugal impeller 200, and is rotated by the centrifugal impeller 200 so that the airflow flows to the radial outer side thereof in each flow channel to flow out of the centrifugal impeller 200 to the volute flow channel 102 of the volute 100. During which each vane 203 applies work to the airflow to raise the pressure of the airflow. Fig. 8 illustrates the rotation direction of the centrifugal impeller 200 by an arrow. Each blade 203 of the centrifugal impeller 200 has a backward-curved structure, and the tip (end adjacent to the radially outer edge of the centrifugal impeller 200) of each blade is bent backward compared to the remaining section, so that each blade of the centrifugal impeller 200 has a strong backward-curved structure, as shown in fig. 8.

In the embodiment of the present invention, the centrifugal impeller 200 is strongly backward curved, so that the centrifugal impeller 200 applies more work to the air flow and converts the work into static pressure lifting, and the work is converted into speed increase. Because the absolute airflow angle of the outlet of the strong backward-bending centrifugal impeller is larger, if a traditional diffuser form is adopted, the airflow rotation degree is larger, and the diffusion loss is larger. The embodiment of the present invention employs the specially designed volute 100 to directly connect with the centrifugal impeller 200, which can effectively avoid this problem. It follows that the various improvements of the embodiments of the present invention do not act in isolation from each other, but act in combination. Specifically, in the embodiment of the present invention, the centrifugal impeller 200 is integrally and directly installed in the volute 100, the flow channel of the volute 100 is specially designed, and the improvements of the strong backward-bending centrifugal impeller 200 are combined together, so that the beneficial effects of various structural improvements are obtained, the respective adverse effects are greatly avoided, the overall efficiency of the centrifugal compressor is high, the structure is more compact, and the miniaturization is facilitated.

FIG. 9 is an exploded schematic view of the centrifugal impeller 200 shown in FIG. 7; fig. 10 is a schematic structural view of the second impeller body 220 in fig. 9.

In some embodiments, as shown in fig. 8-10, the centrifugal impeller 200 may be split. Specifically, the centrifugal impeller 200 includes a first impeller body 210 and a second impeller body 220, wherein the first impeller body 210 and the second impeller body 220 are both disc-shaped and are in butt joint, and blade halves are formed on opposite surfaces of the first impeller body 210 and the second impeller body 220, and the blade halves are connected to form a complete blade 203.

The first impeller body 210 and the second impeller body 220 may be coupled and fastened by a plurality of fasteners, such as rivets 230. One or more positioning grooves 2113 can be formed on the first impeller body 210, the same number of positioning protrusions 2214 are formed on the second impeller body 220, and each positioning protrusion 2214 is clamped into one positioning groove 2113, so that the position between the first impeller body 210 and the second impeller body 220 is more stable, the alignment between the blade halves is more accurate, and the performance of the centrifugal impeller 200 is prevented from being influenced by the misalignment of the blades 203.

The first impeller body 210 is provided with a rotation shaft 214 having a mounting hole 215 formed at the center thereof so as to be coupled to the rotor 42 by a screw 300. The second impeller body 220 is provided with an inlet 201 for the centrifugal impeller 200. The traditional centrifugal impeller is of an integrally cast type, and the surface precision of the traditional centrifugal impeller is not ideal, so that the compression efficiency and the adverse noise of the traditional centrifugal impeller are influenced. Especially for a closed impeller, the blades are inside, and the precision of the blade surface is more difficult to guarantee. In the present embodiment, the centrifugal impeller 200 is configured as a split type as described above, so that the two impeller bodies are separately manufactured, and the blades of each impeller body are exposed to the outside to process the surfaces of the impeller bodies, so that the impeller bodies are smoother.

Thus, it should be appreciated by those skilled in the art that while a number of exemplary embodiments of the invention have been illustrated and described in detail herein, many other variations or modifications consistent with the principles of the invention may be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Accordingly, the scope of the invention should be understood and interpreted to cover all such other variations or modifications.

Claims

1. A centrifugal compressor characterized by comprising:

a housing;

the motor is arranged in the shell; and

at least one compression unit, each compression unit comprising a volute mounted to the housing and a centrifugal impeller disposed within the volute, the centrifugal impeller configured to rotate under the drive of the motor to compress and discharge an airflow entering the volute through an outlet of the volute.

2. The centrifugal compressor according to claim 1,

the volute defines an air inlet flow channel, a volute flow channel and an air outlet flow channel which are sequentially connected along the air flow direction;

the intake runner extends in an axial direction of the centrifugal impeller;

the volute flow channel is flat with the thickness direction parallel to the axial direction of the centrifugal impeller; and is

The air outlet flow channel gradually transits from a flat shape to a cylindrical shape from the joint of the air outlet flow channel and the volute flow channel to the outlet of the volute;

the inlet of the centrifugal impeller faces the air inlet flow channel, and the outlet of the centrifugal impeller faces the volute flow channel.

3. The centrifugal compressor according to claim 2,

the thickness of the volute flow passage is larger than the outlet width of the centrifugal impeller.

4. The centrifugal compressor according to claim 3,

the ratio of the thickness of the volute to the outlet width of the centrifugal impeller is between 1.5 and 2.

5. The centrifugal compressor according to claim 2,

the inlet flow channel comprises a tapered section with gradually-reduced section along the airflow direction.

6. The centrifugal compressor according to claim 5,

the whole tapered section is in a truncated cone shape, and a generatrix of the tapered section is in an arc shape with a concave side facing the direction of the central axis of the air inlet flow channel.

7. The centrifugal compressor according to claim 1,

the centrifugal impeller is a strong backward-bending closed impeller.

8. The centrifugal compressor according to claim 1,

the centrifugal compressor is of a two-stage compression type, the number of the at least one compression unit is two, and the outlet of the volute of the compression unit of the low-pressure stage is communicated with the inlet of the volute of the compression unit of the high-pressure stage through a connecting pipe.

9. The centrifugal compressor according to claim 8,

the compression unit of the low-pressure stage and the compression unit of the high-pressure stage are respectively positioned at two axial sides of the motor.

10. The centrifugal compressor according to claim 1, further comprising:

at least one radial magnetic bearing and/or at least one axial magnetic bearing mounted within the housing to support a rotor of the electric machine.