Centrifugal compressor and its impeller

Abstract

This invention provides a centrifugal compressor and its impeller, wherein the impeller includes a plurality of blades arranged circumferentially, with a flow channel formed between each pair of adjacent blades; each blade is backward-curved, gradually bending away from the impeller's rotation direction from its inlet end to its outlet end; and in the direction from the inlet end to the outlet end, the thickness of each blade first gradually increases and then gradually decreases. The impeller of this invention has higher aerodynamic efficiency, which is beneficial for miniaturizing the centrifugal compressor.

Description

Technical Field

[0001] This invention relates to the field of compressor technology, and in particular to a centrifugal compressor and its impeller. Background Technology

[0002] Centrifugal compressors offer significant advantages such as energy efficiency, high performance, stable operation, and long lifespan. However, in the refrigeration field, centrifugal compressors are suitable for high-flow, low-pressure-ratio applications and struggle to achieve high-efficiency operation at low flow rates and high pressure ratios. Therefore, centrifugal compressors are primarily used in large-capacity chiller units. Smaller and medium-sized refrigeration systems more commonly utilize screw compressors, scroll compressors (such as in small central air conditioning systems, including multi-split systems), and rotary compressors. However, the operating efficiency of these types of compressors is far lower than that of centrifugal compressors. Furthermore, these types of compressors mostly use lubricating oil. This easily leads to problems such as lubricating oil accumulation in the heat exchanger, hindering oil return to the compressor, resulting in poor lubrication of compression components and increased thermal resistance in the heat exchanger.

[0003] Therefore, solving the various challenges arising from the miniaturization of centrifugal compressors, enabling their application in small and medium-sized refrigeration systems to replace screw compressors, scroll compressors, and even rolling rotor compressors, will make these refrigeration systems more energy-efficient and have a profound impact on the refrigeration industry. Summary of the Invention

[0004] One object of the present invention is to provide a centrifugal compressor and its impeller to solve or at least partially solve the aforementioned problems existing in the prior art.

[0005] The purpose of this invention is to provide a centrifugal compressor and its impeller, which improves the aerodynamic efficiency of the impeller.

[0006] On one hand, the present invention provides an impeller for a centrifugal compressor, comprising a plurality of blades arranged circumferentially thereon, with a flow channel formed between each pair of adjacent blades;

[0007] Each blade is a backward-curved type, gradually bending away from the impeller's rotation direction from its inlet end to its outlet end; and

[0008] In the direction from the inlet to the outlet, the thickness of each blade first gradually increases and then gradually decreases.

[0009] Optionally, the side of each blade facing the rotation direction of the impeller is the pressure surface, and the side facing away from the rotation direction is the suction surface;

[0010] In the direction from the inlet to the outlet, the pressure surface of each blade includes a first concave section and a first convex section that are smoothly connected in sequence, and each suction surface includes a second convex section and a second concave section that are smoothly connected in sequence.

[0011] Optionally, in the direction from the inlet end to the outlet end, the installation angles of the pressure surface and suction surface of each blade gradually increase and then gradually decrease.

[0012] The installation angle is the angle between the tangent at any point on the pressure or suction surface and the impeller tangent at that point.

[0013] Optionally, the installation angle of the pressure surface at the outlet end is between 0° and 10°;

[0014] The installation angle of the suction surface at the outlet end is between 20° and 40°.

[0015] Optionally, the installation angle of the pressure surface at the inlet end is between 5° and 15°;

[0016] The installation angle of the suction surface at the inlet end is smaller than that of the pressure surface at the inlet end, and is between 0° and 10°.

[0017] Optionally, the ratio of the length of the first convex segment to the length of the first concave segment is between 3 and 5.

[0018] Optionally, the ratio of the length of the second concave segment to the length of the second convex segment is between 1 and 2.

[0019] Optionally, each blade may have a tip structure at both its inlet and outlet ends.

[0020] Optionally, both the pressure surface and the suction surface are parallel to the axis of the impeller.

[0021] On the other hand, the present invention provides a centrifugal compressor including an impeller, said impeller being an impeller as described in any of the above claims.

[0022] This invention involves a special design of the blade shape of the centrifugal compressor impeller. For example, each blade is made to be backward-curved, gradually bending away from the impeller's rotation direction from its inlet end to its outlet end. Furthermore, the thickness of each blade gradually increases and then gradually decreases in the direction from the inlet end to the outlet end. This increases the blade's reaction degree, reduces the absolute Mach number of the airflow at the blade outlet, and reduces flow losses. This significantly improves the impeller's aerodynamic efficiency, making it more suitable for low-flow, high-pressure ratio operating conditions. Consequently, it is suitable for application in small chillers or multi-split systems and other small central air conditioning units, thus achieving the miniaturization of centrifugal compressors.

[0023] Furthermore, the impeller of the present invention features a specially designed structural detail, including the shape and mounting angle of its pressure and suction surfaces. For example, in the direction from the inlet to the outlet, each blade's pressure surface includes a first concave section and a first convex section that are smoothly connected in sequence, and each suction surface includes a second convex section and a second concave section that are smoothly connected in sequence. The mounting angles of both the pressure and suction surfaces are further designed to gradually increase and then gradually decrease. The mounting angle ranges of the pressure and suction surfaces at the inlet and outlet ends are also specifically defined. These special designs significantly improve the impeller's aerodynamic efficiency, making it more suitable for low-flow-rate, high-pressure-ratio operating conditions.

[0024] 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 of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0025] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0026] Figure 1 This is a schematic diagram of the impeller profile according to an embodiment of the present invention;

[0027] Figure 2 yes Figure 1 A schematic diagram showing the mounting angle of the pressure surface of one blade in the impeller.

[0028] Figure 3 yes Figure 1 A schematic diagram showing the mounting angle of the suction surface of one blade in the impeller.

[0029] Figure 4 This is a schematic diagram of the impeller structure according to an embodiment of the present invention;

[0030] Figure 5 yes Figure 4 An exploded view of the impeller shown.

[0031] Figure 6 yes Figure 5 A schematic diagram of the structure of the second impeller body;

[0032] Figure 7 This is a schematic diagram of the overall structure of a centrifugal compressor according to an embodiment of the present invention;

[0033] Figure 8 Yes Figure 7 A schematic cross-sectional view of the centrifugal compressor shown, obtained by cutting along the axis of the impeller.

[0034] Figure 9 yes Figure 8 Enlarged view of point A;

[0035] Figure 10 yes Figure 7 A schematic diagram of the structure of a compression unit;

[0036] Figure 11 yes Figure 10 Another angle view of the compression unit shown;

[0037] Figure 12 yes Figure 10 An exploded view of the compression unit shown. Detailed Implementation

[0038] The following reference Figures 1 to 12 The centrifugal compressor and its impeller 200 according to an embodiment of the present invention are described below. In some figures, the x-axis represents the axial direction of the impeller 200, which is also the axial direction of the motor 40 and its stator 41 and rotor 42; solid arrows represent the airflow direction.

[0039] Figure 1 This is a schematic diagram of the impeller profile according to an embodiment of the present invention; Figure 2 yes Figure 1 A schematic diagram showing the mounting angle of the pressure surface 241 of one blade 240 in the impeller 200; Figure 3 yes Figure 1 The diagram shows the mounting angle of the suction surface 242 of one blade 240 in the impeller.

[0040] The impeller 200 of this embodiment is used in a centrifugal compressor, such as... Figure 1 As shown, the impeller 200 includes a plurality of blades 240 arranged circumferentially, with a flow channel 250 formed between each pair of adjacent blades 240. Each blade 240 is backward-curved, gradually curving away from the impeller's rotation direction from its inlet end (end A) to its outlet end (end B). The arrows in the figure indicate the impeller's rotation direction. The inlet end (end A) refers to the radially inner end of the blade 240, which is also the end adjacent to the air inlet side of the flow channel 250. The outlet end (end B) refers to the radially outer end of the blade 240, which is also the end adjacent to the air outlet side of the flow channel 250. In the direction from the inlet end (end A) to the outlet end (end B), the thickness of each blade 240 first gradually increases and then gradually decreases. For example... Figure 1As shown, each blade 240 has a pointed tip structure at its inlet end (end A) and outlet end (end B). This increases the reaction degree of the blade 240, reduces the absolute Mach number of the airflow at the outlet of the blade 240, and reduces flow losses. This significantly improves the aerodynamic efficiency of the impeller 200, making the impeller more suitable for low flow rate and high pressure ratio conditions. Consequently, it is suitable for application in small chillers or multi-split central air conditioning systems, enabling the miniaturization of centrifugal compressors.

[0041] like Figures 1 to 3 As shown, the side of each blade 240 facing the rotation direction of the impeller 200 is the pressure surface 241, and the side facing away from the rotation direction is the suction surface 242. Both the pressure surface 241 and the suction surface 242 can be parallel to the axial direction of the impeller 200.

[0042] In the direction from the inlet end (end A) to the outlet end (end B), the pressure surface 241 of each blade 240 includes a first concave section AG and a first convex section GB that are smoothly connected in sequence, and each suction surface 242 includes a second convex section AH and a second concave section HB that are smoothly connected in sequence. Specifically, in the direction from the inlet end to the outlet end, the mounting angle of the pressure surface 241 and suction surface 242 of each blade 240 gradually increases and then gradually decreases. The mounting angle is the angle between the tangent at any point on the pressure surface 241 or suction surface 242 and the tangent direction of the impeller 200 at that point. The larger the mounting angle at a point on the pressure surface 241 or suction surface 242, the closer the tangent at that point is to the radial direction.

[0043] Preferably, the length ratio of the first convex segment GB to the first concave segment AG is between 3 and 5, and more preferably between 3.5 and 4.5. Preferably, the length ratio of the second concave segment HB to the second convex segment AH is between 1 and 2, and more preferably between 1.2 and 1.8.

[0044] like Figure 2 and Figure 3 As shown, the installation angle α1 of the pressure surface 241 at the outlet end (the angle between the tangent BD1 of the pressure surface 241 at end B and the impeller tangent BC at end B) is made smaller to achieve a strong backward bending effect; preferably, α1 is between 0° and 10°. The installation angle α2 of the suction surface 242 at the outlet end (the angle between the tangent BD2 of the suction surface 242 at end B and BC) is greater than α1; preferably, α2 is between 20° and 40°. The installation angle β1 of the pressure surface 241 at the inlet end (the angle between the tangent AF1 of the pressure surface 241 at end A and the impeller tangent AE at end A) can be between 5° and 15°, and the installation angle β2 of the suction surface 242 at the inlet end (the angle between the tangent AF2 of the suction surface 242 at end A and the impeller tangent AE at end A) is smaller than the installation angle β1 of the pressure surface 241 at its inlet end, and is between 0° and 10°.

[0045] The embodiments of the present invention have made special designs on the shape and installation angle of the pressure surface 241 and suction surface 242 of the impeller blade 240, and made the above-mentioned special limitations on key dimensions, all of which have a significant effect on improving the aerodynamic efficiency of the impeller 200, making the impeller 200 more suitable for low flow and high pressure ratio working conditions.

[0046] Figure 4 This is a schematic diagram of the impeller structure according to an embodiment of the present invention; Figure 5 yes Figure 4 An exploded view of the impeller shown. Figure 6 yes Figure 5 A schematic diagram of the structure of the second impeller body.

[0047] like Figures 4 to 6 As shown, the impeller 200 in this embodiment of the invention can be a split type. Specifically, the impeller 200 includes a first impeller body 210 and a second impeller body 220. The second impeller body 220 is provided with an inlet 201 of the impeller 200. Both the first impeller body 210 and the second impeller body 220 are disc-shaped and connected end-to-end. A plurality of first sub-blades 2401 are formed on the first impeller body 210, and a plurality of second sub-blades 2402 are formed on the second impeller body 220. The plurality of first sub-blades 2401 and the plurality of second sub-blades 2402 are spliced ​​together to form a plurality of complete blades 240.

[0048] Each first sub-blade 2401 can be provided with a threaded hole 214, and each second sub-blade 2402 can be provided with a screw hole 224, so that the first impeller body 210 and the second impeller body 220 can be connected and fastened by multiple screws 230.

[0049] Each first sub-blade 2401 can be provided with a positioning groove 213, and each second sub-blade 2402 can be provided with a positioning protrusion 223, so that each positioning protrusion 223 can be inserted into a positioning groove 213, thereby making the position between the first impeller body 210 and the second impeller body 220 more stable and making the alignment of each first sub-blade 2401 and each second sub-blade 2402 more accurate.

[0050] Traditional impellers are typically cast in one piece, resulting in suboptimal surface finish that affects compression efficiency and generates noise. This is especially true for enclosed impellers, where the blades are internal, making it even more difficult to guarantee blade surface precision. This embodiment addresses this by designing the impeller 200 as a split type, allowing for the separate fabrication of two impeller bodies. This exposes the sub-blades of each impeller body, enabling surface treatment for a smoother finish.

[0051] On the other hand, embodiments of the present invention provide a centrifugal compressor, which includes an impeller, said impeller being the impeller 200 as described in any of the above embodiments.

[0052] Figure 7 This is a schematic diagram of the overall structure of a centrifugal compressor according to an embodiment of the present invention; Figure 8 Yes Figure 7 A schematic cross-sectional view of the centrifugal compressor shown, obtained by cutting along the axis of the impeller 200. Figure 9 yes Figure 8 Enlarged view of point A.

[0053] like Figures 7 to 9 As shown, the centrifugal compressor of this embodiment generally includes a housing 10, a motor 40, and at least one compression unit 20, 30.

[0054] The housing 10 defines a receiving space within which the motor 40 is mounted. 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 compression units 20 and 30 can be one or more. For example, the centrifugal compressor can be a single-stage compressor with only one compression unit. Alternatively, the centrifugal compressor can be a multi-stage compressor with multiple compression units 20 and 30. Each compression unit 20 or 30 includes a volute 100 mounted on the housing 10 and an impeller 200 disposed within the volute 100. The 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.

[0055] Traditional centrifugal compressors typically have a diffuser downstream of the impeller in each stage. The impeller discharges the airflow into the diffuser, where it is diffused before entering the volute.

[0056] Compared to traditional centrifugal compressors, the centrifugal compressor of this invention omits the diffuser, directly mounting the impeller 200 within the volute 100. This avoids significant diffusion losses caused by large airflow vorticity within the diffuser, thereby improving the overall efficiency of the centrifugal compressor and making its structure more compact. Therefore, this structure facilitates the miniaturization of centrifugal compressors while maintaining high efficiency, making them suitable for applications in small chiller units or multi-split systems and other small central air conditioning systems.

[0057] In some embodiments, for example Figure 7 and Figure 8 As shown, the centrifugal compressor can be a two-stage compression type, with two compression units. It can be deduced that one of the two compression units, 20 and 30, must be a low-pressure stage and the other a high-pressure stage, as... Figure 7 and Figure 8In the diagram, the compression unit 20 on the left is the low-pressure stage, and the compression unit 30 on the right is the high-pressure stage. The outlet of the volute 100 of the low-pressure stage compression unit 20 is connected to the inlet of the volute 100 of the high-pressure stage compression unit 30 via a connecting pipe 90. Specifically, a flange 91 is provided at the inlet end of the connecting pipe 90 to connect to the flange 130 at the outlet of the volute 100 of the low-pressure stage compression unit 20, and a flange 92 is provided at the outlet end of the connecting pipe 90 to connect to the volute 100 of the high-pressure stage compression unit 30. Preferably, the low-pressure stage compression unit 20 and the high-pressure stage compression unit 30 are located on opposite sides of the axial direction of the motor 40, so that the impellers 200 of the two compression units 20 and 30 are directly connected to the motor 40, and this facilitates partial cancellation of the axial forces of the two impellers 200.

[0058] In some embodiments, the centrifugal compressor further includes at least one radial magnetic bearing 60 and / or at least one axial magnetic bearing 80, which are mounted within the housing 10 to support the rotor 42 of the motor 40. Figure 8 As shown, the centrifugal compressor includes two radial magnetic bearings 60 to support the rotor 42 in the radial direction. The centrifugal compressor also includes an axial magnetic bearing 80 to counteract the axial force generated by the movement of the impeller 200 on the rotor 42. The magnetic bearings are made using the principle of magnetic levitation and are oil-free. Therefore, there is no need to add lubricating oil to the centrifugal compressor, thus completely avoiding the oil return problem in small and medium-sized refrigeration systems (traditionally, screw compressors, scroll compressors, and rolling rotor compressors are basically all oil-lubricated), improving the heat exchanger's heat exchange efficiency. Furthermore, the use of magnetic bearings results in less mechanical wear, lower energy consumption, lower noise, enhanced stability, and a longer lifespan for the centrifugal compressor.

[0059] Furthermore, such as Figure 9 As shown, in addition to the magnetic levitation bearings mentioned above, ordinary radial bearings 70 can also be provided at the axial end of the rotor 42 to provide key support for the end of the rotor 42, making it more stable and improving the operational reliability of the centrifugal compressor.

[0060] Figure 10 yes Figure 7 A schematic diagram of the structure of a compression unit 20 in the image; Figure 11 yes Figure 10 Another angle view of the compression unit 20 shown; Figure 12 yes Figure 10 An exploded view of the compression unit 20 shown.

[0061] Each compression unit 20, 30 includes a volute 100 mounted on the housing 10 and a centrifugal impeller 200 disposed within the volute 100. The volute 100 defines an inlet channel 101, a volute-shaped channel 102, and an outlet channel 103 connected sequentially along the airflow direction, i.e., the volute 100 flow channels are divided into three sections. The inlet of the inlet channel 101 constitutes the inlet of the volute 100 as described herein, and the outlet of the outlet channel 103 constitutes the outlet of the volute 100. The inlet channel 101 extends along the axial direction (x-axis direction) of the centrifugal impeller 200. The volute-shaped channel 102 is flat and its thickness direction is parallel to the axial direction of the centrifugal impeller 200. The outlet channel 103 gradually transitions from a flat shape to a cylindrical shape from its junction with the volute-shaped channel 102 to the outlet of the volute 100. The centrifugal impeller 200 has its inlet 201 facing the inlet flow channel 101 and its outlet facing the volute flow channel 102, so that air is drawn in from the inlet flow channel 101, compressed and discharged into the volute flow channel 102.

[0062] In this embodiment, the flattened volute 102 flattens the overall shape of the volute 100, which helps to reduce the axial dimension of the centrifugal compressor and achieve compressor miniaturization. More importantly, since the outlet airflow passage 103 gradually transitions from a flat shape to a cylindrical shape from its junction with the volute 102 to the outlet of the volute 100, the airflow can achieve a very good diffusion effect as it enters the cylindrical and wider outlet airflow passage 103 from the thinner, flattened volute 102. Moreover, since the outlet airflow passage 103 gradually transitions from a flat shape to a cylindrical shape from its junction with the volute 102 to the outlet of the volute 100, the transition is very smooth, reducing unnecessary airflow resistance loss. At the same time, the cylindrical shape is also suitable for connection with downstream pipelines.

[0063] In some embodiments, such as Figure 12 As shown, the volute 100 can be a split structure, comprising a volute body 110 assembled along the axial direction of the inlet air passage 101 and a cover plate 120. The volute body 110 defines the aforementioned inlet air passage 101, a first half of the volute flow passage 102, and an outlet air passage 103, wherein the volute flow passage 102 is open on the side facing the cover plate 120. The cover plate 120 is disposed on one axial side of the volute body 110 to cover the open side of the first half of the volute flow passage 102, and defines a second half of the volute flow passage 102. The first half and the second half of the volute flow passage 102 relative to each other constitute the completed volute flow passage 102.

[0064] In this embodiment, the volute 100 is configured as a split structure, with the volute body 110 and the cover plate 120 being machined separately to form the inlet air passage 101, the volute flow passage 102, and the outlet air passage 103. Compared to the existing one-piece cast volute, in this embodiment, the surfaces of the inlet air passage 101, the volute flow passage 102, and the outlet air passage 103 are smoother, which better satisfies the uniformity of the internal flow field, reduces flow loss caused by excessively rough flow passage surfaces, and improves the operating efficiency of the centrifugal compressor.

[0065] Furthermore, such as Figure 9 As shown, the two planes in the thickness direction of the volute 102 can be transitioned to the circumferential volute side surface with rounded corners. Figure 9 The radius (R) is used to increase the strength of the volute, alleviate local stress concentration, eliminate angular vortices, and ensure the uniformity of the flow field. The value of R can be selected according to the thickness of the volute channel 102. The split structure of the volute 100 facilitates the machining of the aforementioned radius.

[0066] In this embodiment of the invention, the impeller 200 is designed with a strong backward curve, so that more of the work done by the impeller 200 on the airflow is converted into static pressure increase, and less into velocity increase. Because the outlet absolute airflow angle of a strongly backward-curved impeller is large, using a traditional diffuser would result in greater airflow vortex and diffusion losses. This embodiment of the invention uses a specially designed volute 100 directly connected to the impeller 200, effectively avoiding this problem. Therefore, the improvements in this embodiment of the invention are not isolated but work together. Specifically, this embodiment of the invention comprehensively combines the improvements of directly installing the impeller 200 inside the volute 100, specially designing the flow channel of the volute 100, and using a strongly backward-curved impeller 200. This not only achieves the beneficial effects of each structural improvement but also greatly avoids their respective adverse effects, resulting in higher overall efficiency of the centrifugal compressor and a more compact structure, facilitating miniaturization.

[0067] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. An impeller for a centrifugal compressor, comprising a plurality of blades arranged circumferentially thereon, wherein a flow channel is formed between each pair of adjacent blades; Each blade is a backward-curved type, gradually bending away from the direction of impeller rotation from its inlet end to its outlet end; and In the direction from the inlet end to the outlet end, the thickness of each blade first gradually increases and then gradually decreases; The side of each blade facing the rotation direction of the impeller is the pressure surface, and the side facing away from the rotation direction is the suction surface. In the direction from the inlet end to the outlet end, the pressure surface of each blade includes a first concave section and a first convex section that are smoothly connected in sequence, and each suction surface includes a second convex section and a second concave section that are smoothly connected in sequence. The installation angle of the pressure surface at the outlet end is between 0° and 10°; The installation angle of the suction surface at the outlet end is between 20° and 40°; The installation angle of the pressure surface at the inlet end is between 5° and 15°; The installation angle of the suction surface at the inlet end is smaller than that of the pressure surface at the inlet end, and is between 0° and 10°.

2. The impeller according to claim 1, wherein... In the direction from the inlet end to the outlet end, the installation angle of the pressure surface and the suction surface of each blade gradually increases and then gradually decreases. The installation angle is the angle between the tangent at any point on the pressure surface or the suction surface and the impeller tangent at that point.

3. The impeller according to claim 1, wherein... The ratio of the length of the first convex segment to the length of the first concave segment is between 3 and 5.

4. The impeller according to claim 1, wherein The ratio of the length of the second concave segment to the length of the second convex segment is between 1 and 2.

5. The impeller according to claim 1, wherein Both the pressure surface and the suction surface are parallel to the axis of the impeller.

6. The impeller according to claim 1, wherein Each blade has a tip structure at its inlet and outlet ends.

7. A centrifugal compressor comprising an impeller, said impeller being the impeller as claimed in any one of claims 1 to 6.

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