Centrifugal compressor and refrigeration device

Abstract

Provided is a technology for making it possible to improve the performance of a closed impeller of a centrifugal compressor. A compressor 10 according to one embodiment of the present disclosure comprises an impeller 200 and a casing 100 that accommodates the impeller 200. The impeller 200 has a hub 210 having a meridional surface 211, a plurality of blades 220 provided on the meridional surface 211, and a shroud 230 provided to the leading ends of the plurality of blades so as to cover the meridional surface 211. The shroud 230 is provided with a through-hole 235 that penetrates therethrough to extend between the inner surface of the shroud 230 on the opposite of the meridional surface 211 and the outer surface of the shroud 230 on the opposite of the inner surface of the casing 100 and that has an opening 235B on the outer surface side and an opening 235A on the inner surface side. The through-hole 235 is inclined such that, on a cross-section including an axial center AX of a rotation shaft 250 of the impeller 200, a center 235Bc of the opening 235B is positioned on the inlet 200-in side of the impeller 200 relative to a center 235Ac of the opening 235A.

Description

Centrifugal compressor, refrigeration device

[0001] The present disclosure relates to a centrifugal compressor and the like.

[0002] Conventionally, a technique related to a closed impeller of a centrifugal compressor is known (for example, see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2009-156122

[0004] By the way, regarding the closed impeller of the centrifugal compressor, for example, it is desirable to suppress performance degradation associated with backflow, separation, etc., and improve performance.

[0005] An object of the present disclosure is to provide a technique capable of improving the performance of a closed impeller of a centrifugal compressor.

[0006] In a first aspect of the present disclosure, there is provided a centrifugal compressor including an impeller (200) and a casing (100) that houses the impeller (200). The impeller (200) has a hub (210) having a meridional plane (211), a plurality of blades (220) provided on the meridional plane (211), and a shroud (230) provided at the tips of the plurality of blades (220) so as to cover the meridional plane (211). The shroud (230) is provided with a first passage (235) that penetrates between the inner surface facing the meridional plane (211) and the outer surface facing the inner surface of the casing (100), and has a first opening (235B) on the outer surface side and a second opening (235A) on the inner surface side. In a cross-section including the axis (AX) of the rotation axis (250) of the impeller (200), the first passage (235) is inclined such that the center (235Bc) of the first opening (235B) is located closer to the inlet (200in) side of the impeller (200) than the center (235Ac) of the second opening (235A).

[0007] According to this embodiment, the centrifugal compressor can, for example, allow a portion of the fluid passing through the impeller to flow into the gap between the shroud and the casing through a first passage, and circulate the fluid to the inlet side of the impeller through that gap. As a result, the centrifugal compressor can suppress the upward slope of the pressure-flow characteristic by increasing the work coefficient (i.e., impeller work) on the high-pressure, low-flow side, while slightly reducing the peak efficiency of the impeller. As a result, the centrifugal compressor can expand its operating range (so-called wide range). Furthermore, the centrifugal compressor can suppress mild surges caused by the upward slope of the pressure-flow characteristic, and can also suppress the generation of humming noise associated with mild surges. In addition, the centrifugal compressor can circulate fluid from the outlet side of the impeller through, for example, the gap between the shroud and the casing and the first passage. As a result, the centrifugal compressor can suppress wakes near the outlet of the impeller. Thus, the centrifugal compressor can improve the performance of a closed impeller.

[0008] Furthermore, according to this embodiment, since the first passage of the centrifugal compressor is inclined toward the inlet side of the impeller, pressure loss due to separation during fluid circulation can be suppressed, and the effect of performance improvement can be further enhanced.

[0009] Furthermore, in a second aspect of the present disclosure, based on the first aspect described above, the plurality of blades (220) comprises a first blade (220a) and a second blade (220b) adjacent to the first blade (220a) in the direction of rotation (RT) of the impeller (200), and when a line segment (225) making the minimum distance between the inlet (200in) side of the first blade (220a) and the second blade (220b) is defined as a first virtual point (P1) located 40 percent of the length of the line segment from the end on the first blade (220a) side and a second virtual point (P2) located 60 percent of the length of the line segment from the end on the first blade (220a) side, The second opening (235A) may be located between a first virtual line (VL1) extending circumferentially through the first virtual point (P1) and a second virtual line (VL2) extending circumferentially through the second virtual point (P2).

[0010] Furthermore, in a third aspect of this disclosure, based on the first or second aspect described above, a second passage (110B) is formed by the inlet (200in) end of the shroud (230) and the casing (100) facing each other in the axial direction, and the second passage (110B) may be inclined toward the outlet (200out) side of the impeller (200) with respect to a direction perpendicular to the inner surface of the shroud (230) in a cross section including the axis (AX).

[0011] Furthermore, in a fourth aspect of this disclosure, based on the third aspect described above, the end of the shroud (230) on the inlet (200 in) side may be chamfered.

[0012] Furthermore, in a fifth aspect of the present disclosure, based on the third or fourth aspect described above, the axial width of the second passage (110B) may narrow from the outer side to the inner side of the shroud (230).

[0013] Furthermore, in a sixth aspect of the present disclosure, based on any one of the third to fifth aspects described above, the inner diameter (D2) of the inlet (200in) end of the shroud (230) may be smaller than the inner diameter (D1) of the casing (100) at a location axially opposite to the inlet (200in) end of the shroud (230).

[0014] Furthermore, in a seventh aspect of the present disclosure, based on any one of the first to sixth aspects described above, the plurality of blades (220) do not have to have their tip portions on the shroud (230) side overlap with the second opening (235A).

[0015] Furthermore, in an eighth aspect of the present disclosure, based on any one of the first to seventh aspects described above, a sealing portion (240) may be provided between the outer surface of the shroud (230) and the casing (100).

[0016] Furthermore, in a ninth aspect of the present disclosure, based on the eighth aspect described above, the first opening (235B) may be provided on the inlet (200in) side of the seal portion (240).

[0017] Furthermore, in a tenth aspect of the present disclosure, based on any one of the first to ninth aspects described above, the first passage (235) may be provided to extend in the circumferential direction.

[0018] Furthermore, in an eleventh aspect of the present disclosure, based on any one of the first to tenth aspects described above, a second passage (110B) is formed by the inlet (200in) end of the shroud (230) and the casing (100) facing each other in the axial direction along the axis (AX), a third passage (110A) is formed between the outer surface of the shroud (230) and the inner surface of the casing (100) communicating with the first passage (235) and the second passage (110B), and in the second passage (110B) or the third passage (110A), the inner surface of the casing (100) may have projections (114, 115) extending in a direction perpendicular to the circumferential direction, grooves (113) extending in a direction perpendicular to the circumferential direction, or a rough surface rougher than the inner surface of the shroud (230).

[0019] Furthermore, in a twelfth aspect of the present disclosure, based on the eighth aspect described above, the first opening (235B) may be provided on the outlet (200out) side of the impeller (200) rather than the seal portion (240).

[0020] Furthermore, in a thirteenth aspect of the present disclosure, based on any one of the first to twelfth aspects described above, the present invention includes a first compression section for compressing an incoming fluid and a second compression section into which a fluid discharged from the first compression section flows and compresses the fluid, wherein the first compression section includes another impeller having another shroud without the first passage (235), and the second compression section may include the impeller (200) having the shroud (230) with the first passage (235).

[0021] Furthermore, a fourteenth aspect of the present disclosure provides a refrigeration system comprising a centrifugal compressor (10) according to any one of the first to thirteenth aspects described above.

[0022] According to the above-described embodiment, it is possible to improve the performance of the closed impeller of a centrifugal compressor.

[0023] This is a diagram showing the configuration of an example of a refrigeration system. This is a diagram showing the configuration of an example of a compressor. This is a diagram showing the first example of the structure of a compressor. This is a diagram showing the first example of the structure of a compressor. This is a diagram showing the pressure-flow characteristics of a compressor according to an embodiment and a comparative example. This is a diagram showing the second example of the structure of a compressor. This is a diagram showing the pressure-flow characteristics of the second example of the structure of a compressor. This is a diagram showing the third example of the structure of a compressor. This is a diagram showing the fourth example of the structure of a compressor. This is a diagram showing the fifth example of the structure of a compressor. This is a diagram showing the sixth example of the structure of a compressor. This is a diagram showing the seventh example of the structure of a compressor. This is a diagram showing the eighth example of the structure of a compressor. This is a diagram showing the ninth example of the structure of a compressor. This is a diagram showing the tenth example of the structure of a compressor. This is a diagram showing the eleventh example of the structure of a compressor. This is a diagram showing the twelfth example of the structure of a compressor. This is a diagram showing the thirteenth example of the structure of a compressor. This is a diagram showing the fourteenth example of the structure of a compressor. This is a diagram showing the fifteenth example of the structure of a compressor. This is a diagram showing the sixteenth example of the structure of a compressor. This is a diagram showing the seventeenth example of the structure of a compressor. This is a diagram showing the nineteenth example of the structure of a compressor.

[0024] The embodiments will be described below with reference to the drawings.

[0025] [Configuration of the Refrigeration System] The configuration of the refrigeration system 1 according to this embodiment will be described with reference to Figure 1.

[0026] Figure 1 shows an example of the configuration of a refrigeration device 1.

[0027] The refrigeration device 1 circulates a refrigerant through the refrigerant circuit RC and uses a compression refrigeration cycle to cool or heat the target liquid or gas.

[0028] Refrigeration device 1 is, for example, a chiller that cools a target liquid (cooled liquid) by heat exchange between a refrigerant and the target liquid using a compression refrigeration cycle. The cooled liquid is, for example, water or brine. Alternatively, refrigeration device 1 may be a water heater that generates hot water by heat exchange between a refrigerant and water using a compression refrigeration cycle. Alternatively, refrigeration device 1 may be an air conditioner that cools or heats a target space by heat exchange between a refrigerant and air. The following explanation will focus mainly on the case where refrigeration device 1 is a chiller.

[0029] As shown in Figure 1, the refrigeration system 1 includes refrigerant paths L1 to L4, a compressor 10, a heat exchanger 20, an expansion mechanism 30, and a heat exchanger 40 as components of the refrigerant circuit RC.

[0030] Refrigerant pathways L1 to L4 are paths through which the refrigerant flows. Refrigerant pathways L1 to L4 are, for example, metal pipes made of steel or similar material.

[0031] Refrigerant path L1 connects the heat exchanger 40 to the suction port of the compressor 10. Refrigerant path L2 connects the discharge port of the compressor 10 to the heat exchanger 20. Refrigerant path L3 connects the heat exchanger 20 to the expansion mechanism 30. Refrigerant path L4 connects the expansion mechanism 30 to the heat exchanger 40.

[0032] The compressor 10 compresses the low-pressure refrigerant flowing in from the refrigerant path L1 and discharges the high-pressure refrigerant into the refrigerant path L2.

[0033] The heat exchanger 20 performs heat exchange between a refrigerant flowing through its interior and an external heat transfer medium (for example, cooling water).

[0034] The heat exchanger 20 is a so-called condenser, which cools the high-temperature and high-pressure refrigerant that flows in from the refrigerant path L2 and is compressed by the compressor 10 through heat exchange with an external heat transfer medium, thereby condensing it and releasing the high-pressure liquid refrigerant into the refrigerant path L3.

[0035] The expansion mechanism 30 expands the high-pressure liquid refrigerant, causing the low-pressure gas-liquid mixture of refrigerant to flow out. The expansion mechanism 30 is, for example, an expansion valve or an orifice.

[0036] The expansion mechanism 30 expands the high-pressure liquid refrigerant that flows in from the refrigerant path L3 and has passed through the heat exchanger 20, causing the low-pressure gas-liquid mixed refrigerant to flow out into the refrigerant path L4.

[0037] The heat exchanger 40 performs heat exchange between the refrigerant flowing through its interior and the external liquid to be cooled.

[0038] The heat exchanger 40 is a so-called evaporator, which evaporates the low-pressure gas-liquid mixed refrigerant that has flowed in from the refrigerant path L4 and has been expanded by the expansion mechanism 30 by absorbing heat from the coolant to be cooled, and discharges the low-pressure gas refrigerant to the refrigerant path L1. Thereby, the refrigeration device 1 can cool the coolant to be cooled.

[0039] [Configuration of Compressor] Next, the configuration of the compressor 10 according to the present embodiment will be described with reference to FIG. 2.

[0040] FIG. 2 is a diagram showing a configuration example of the compressor 10.

[0041] In addition, in FIG. 2, a cross-sectional view taken by a plane including the axis AX of the rotating shaft 250 is shown so that the contents inside the casing 100 are exposed.

[0042] Hereinafter, the direction along the axis AX of the rotating shaft 250, that is, the parallel direction will be referred to as the "axial direction", and the description may be made using the names of the "axial direction", the "radial direction", and the "circumferential direction" with respect to the axis AX as a reference.

[0043] As shown in FIG. 2, in this example, the compressor 10 is a centrifugal compressor (centrifugal compressor).

[0044] The number of stages of the compressor 10 is, for example, one stage (single stage) as shown in FIG. 2. Further, the number of stages of the compressor 10 may be two or more stages. In the multi-stage compressor 10, a plurality of compression units including the impeller 200 are provided in series.

[0045] The compressor 10 includes a casing 100, an impeller 200, a rotating shaft 250, an electric motor 300, a radial magnetic bearing 400, a thrust magnetic bearing 500, and a touchdown bearing 600.

[0046] The casing 100 is a housing for housing and attaching the components of the compressor 10 inside.

[0047] The impeller 200 is housed in an impeller chamber 110 formed inside the casing 100.

[0048] The impeller 200 is attached to the rotating shaft 250 and rotates about the axis AX of the rotating shaft 250. The impeller 200 is formed such that the outer diameter of its outer surface (the meridian plane 211 described later) increases from one end in its axial direction (in this example, the right end in the figure) to the other end (in this example, the left end in the figure). The impeller 200 causes the refrigerant flowing axially from the suction pipe 120 to flow radially outward at the other end in its axial direction at the circumferential center portion at one end in its axial direction. A diffuser 111 is provided on the outer side in the radial direction at the other end in the radial direction of the impeller 200. In the diffuser 111, the dynamic pressure (i.e., kinetic energy) of the refrigerant flowing out from the impeller 200 is converted into static pressure (i.e., pressure energy), and the compressed refrigerant flows out from the diffuser 111 to the discharge pipe 130.

[0049] The electric motor 300 is housed in a motor chamber 140 formed inside the casing 100.

[0050] The electric motor 300 rotationally drives the impeller 200 using electric power supplied from the outside. The electric motor 300 is, for example, a permanent magnet synchronous motor. The electric motor 300 is of an inner rotor type and includes a rotor 310 attached to the rotating shaft 250 and a stator 320 disposed on the outer side in the radial direction of the rotor 310 and fixed to the inner peripheral surface of the motor chamber 140 in the casing 100.

[0051] The radial magnetic bearing 400 supports the radial load of the rotating shaft 250 in a non-contact manner by electromagnetic force. Two radial magnetic bearings 400 are provided and are respectively fixed to the inner surface of the casing 100. The two radial magnetic bearings 400 are arranged so as to be adjacent to both ends of the electric motor 300 in the axial direction.

[0052] The thrust magnetic bearing 500 supports the thrust load of the rotating shaft 250 non-contact by electromagnetic force. The thrust magnetic bearing 500 includes a pair of electromagnets 510, each fixed to the inner surface of the casing 100. The pair of electromagnets 510 are positioned adjacent to each of the axial ends of a disc-shaped collar 260, which is provided on the rotating shaft 250 and is centered on the axis AX. The collar 260 is made of a magnetic material, and the thrust magnetic bearing 500 maintains the position of the rotating shaft 250, which is integrated with the collar 260, non-contact by the magnetic attraction force of the pair of electromagnets 510 to the collar 260.

[0053] The touchdown bearing 600 is provided to suppress contact between the rotating shaft 250 and the radial magnetic bearing 400, and between the collar 260 and the electromagnet 510 of the thrust magnetic bearing 500. The touchdown bearing 600 is, for example, mainly composed of angular contact ball bearings.

[0054] [First example of compressor structure] Next, a first example of the structure of the compressor 10 according to this embodiment will be described with reference to Figures 3 to 5.

[0055] Figures 3 and 4 show a first example of the compressor 10. Specifically, Figure 3 is a perspective view of the impeller 200 of the compressor 10 according to this example. Figure 4 is a cross-sectional view of the compressor 10 according to this example, including the axis AX of the rotating shaft 250. The following cross-sectional views are of the same type as those shown in Figures 8 to 17 and 20 to 24. Figure 5 shows the pressure-flow characteristics of the compressor 10 according to the embodiment and the compressor according to the comparative example. In Figure 5, the surge line 501 and the pressure-flow characteristic line 502 are drawn for the compressor according to the comparative example, and the surge line 511 and the pressure-flow characteristic line 512 are drawn for the compressor 10 according to the embodiment.

[0056] The compressor in the comparative example differs from the compressor 10 in this example in that it does not have the through-hole 235 described later, but is otherwise the same as the compressor 10 in this example.

[0057] As shown in Figure 4, the impeller 200 is positioned in an impeller chamber 110 formed inside the casing 100. The impeller 200 is rotationally driven by an electric motor 300 via a rotating shaft 250, causing the refrigerant from the suction pipe 120 to flow in through an inlet 200in at one axial end and to flow out towards the radially outer diffuser 111 through an outlet 200out at the other axial end.

[0058] As shown in Figures 3 and 4, in this example, the impeller 200 is a so-called closed impeller and includes a hub 210, blades 220, and a shroud 230.

[0059] The blades 220 are provided on the meridional plane 211, which is the outer surface of the hub 210. There are multiple blades 220, and the multiple blades 220 are arranged in the circumferential direction. The multiple blades 220 may be arranged at equal intervals in the circumferential direction or at unequal intervals.

[0060] The shroud 230 is provided so as to be connected to the tip of the blade 220 so as to cover the meridional plane 211 of the hub 210. The shroud 230 is formed such that, in the axial direction, its outer diameter around the axis AX expands as a whole from the inlet 200in side of the impeller 200 toward the outlet 200out. For example, as shown in Figure 4, the shroud 230 has, in the axial direction, a first section having a constant outer diameter around the axis AX of the rotating shaft 250, starting from the inlet 200in of the impeller 200, and a second section where the outer diameter around the axis AX expands, starting from the rear end of the first section. Alternatively, the shroud 230 may be formed such that, in the axial direction, its outer diameter around the axis AX of the rotating shaft 250 expands continuously from the inlet 200in toward the outlet 200out of the impeller 200.

[0061] In this example, the suction pipe 120 is formed inside the casing 100. For example, the inner surface 100A of the casing 100 corresponding to the suction pipe 120 has a constant diameter (inner diameter) centered on the axis AX of the rotating shaft 250. The inner diameter of the inner surface 100A of the casing 100 is the same as the inner diameter (inner diameter) of the inner surface of the shroud 230 at the inlet 200in of the impeller 200, as shown in Figure 4.

[0062] A stepped surface 100C is provided between the inner surfaces 100A and 100B of the casing 100, and the stepped surface 100C faces the end surface 230A on the inlet 200in side of the shroud 230. In this example, the stepped surface 100C is a plane perpendicular to the axial direction.

[0063] The end face 230A of the shroud 230 is a plane perpendicular to the axial direction, similar to the stepped surface 100C. Therefore, the distance between the stepped surface 100C and the shroud 230 is constant in the radial direction.

[0064] The shroud 230 is provided with through holes 235 that penetrate between its inner and outer surfaces.

[0065] As shown in Figure 4, the through-hole 235 is located relatively close to the inlet 200in of the impeller 200 in the shroud 230 in a cross-section including the axis AX, and is formed to penetrate linearly between the inner and outer surfaces of the shroud 230. In this example, the through-hole 235 is provided in the first section of the shroud 230 described above. As a result, the through-hole 235 can communicate the space inside the shroud 230 with the inlet 200in of the impeller 200 through the space 110A between the shroud 230 and the inner surface 100B of the casing 100, and the space 110B between the end face 230A of the shroud 230 and the stepped surface 100C. Therefore, a portion of the refrigerant flowing into the impeller 200 can be circulated through the through-hole 235, space 110A, and space 110B to the inlet 200in of the impeller 200 and merged with the main flowing into the impeller 200.

[0066] As a result, for example, as shown in Figure 5 (pressure-flow characteristic line 512), the compressor 10 can obtain high pressure in a region where the discharge flow rate Q is relatively low, compared to the pressure-flow characteristic 502 of the compressor in the comparative example that does not have through holes 235 (see pressure difference 513). Furthermore, the compressor 10 can achieve an expanded operating range (i.e., a wider range) compared to the pressure-flow characteristic 502 of the compressor in the comparative example that does not have through holes 235 (see region 514).

[0067] Furthermore, as shown in Figure 5, for example, the pressure-flow characteristics 502 of the compressor in the comparative example include a region 503 of the discharge flow rate Q that has an upward-sloping characteristic in which the pressure P increases in accordance with the increase in the discharge flow rate Q. In the region 503 with an upward-sloping characteristic, a localized backflow phenomenon called a mild surge occurs, and as a result, a humming sound may be generated from the impeller 200.

[0068] In contrast, in this example, as described above, the pressure in the region where the discharge flow rate Q is relatively low can be increased, thereby increasing the work of the impeller 200. As a result, the upward slope characteristic in region 503 can be suppressed (in the example of Figure 5, the upward slope characteristic can be eliminated). Therefore, the humming noise of the impeller 200 can be suppressed.

[0069] As shown in Figure 3, the through-holes 235 are provided along the entire circumference, i.e., the entire circumference, and are formed in a slit shape that extends in the circumferential direction. This makes it possible to increase the flow rate circulating through the through-holes 235 to the inlet 200in of the impeller 200.

[0070] The through-hole 235 includes an opening 235A on the inner surface side of the shroud 230 and an opening 235B on the outer surface side of the shroud 230. In this example, the through-hole 235 has a constant width (axial dimension) in a cross-section including the axis AX, and the widths of openings 235A and 235B are the same.

[0071] A sealing member 240 is provided in the gap between the shroud 230 and the inner surface 100B of the casing 100 corresponding to the impeller chamber 110. The sealing member 240 is a non-contact type sealing member, such as a labyrinth seal. Alternatively, the sealing member 240 may be a sliding type sealing member.

[0072] In this example, the sealing member 240 is provided on the outlet 200out side of the impeller 200 beyond the opening 235B of the through hole 235. As a result, the sealing member 240 can partition the space between the shroud 230 and the inner surface 100B of the casing 100 between the inner surface 100B that communicates with the through hole 235 and the space on the outlet 200out side of the impeller 200 beyond the sealing member 240. Therefore, the sealing member 240 can suppress the circulation of refrigerant from the outlet 200out to the inlet 200in of the impeller 200 through the space between the shroud 230 and the inner surface 100B of the casing 100. Thus, the compressor 10 can suppress the increase in losses due to the generation of excessive circulation flow and achieve both the above-mentioned effect of the through hole 235 and efficiency.

[0073] Furthermore, the through-hole 235 is provided so as to be inclined toward the inlet 200in side of the impeller 200, with respect to a direction perpendicular to the inner surface of the shroud 230. Specifically, in a cross-section including the axis AX, the center 235Bc of the opening 235B of the through-hole 235 is positioned toward the inlet 200in side of the impeller 200 than the center 235Ac of the opening 235A. This suppresses the separation that occurs at the outer edge of the opening 235B of the through-hole 235 when refrigerant flows into the space 110B from the through-hole 235, and as a result, the reduction in the effective flow path cross-sectional area can be suppressed. Therefore, the compressor 10 can increase the flow rate circulating to the inlet 200in of the impeller 200 through the through-hole 235, and further improve the effect of the through-hole 235.

[0074] Furthermore, for example, if the opening 235B of the through hole 235 is positioned closer to the outlet 200out of the impeller 200 in the axial direction, it may become necessary to position the sealing member 240 at a location where the expansion rate of the outer diameter of the shroud 230 along the axial direction is relatively large. In this case, the gap between the sealing member 240 and the outer surface of the shroud 230 increases, and as a result, the amount of refrigerant flowing in from the outlet 200out side of the impeller 200 to the inlet 200in side of the impeller 200 through the gap between the shroud 230 and the inner surface 100B of the casing 100 increases, which may lead to a decrease in the efficiency of the compressor 10. In addition, in order to reduce the gap between the sealing member 240 and the outer surface of the shroud 230, it may be necessary to modify the shape of the outer surface of the shroud 230, which may result in an increase in the inertia of the impeller 200 and an increase in cost.

[0075] In contrast, in this example, since the through-hole 235 is inclined toward the inlet 200in side of the impeller 200, the position of the opening 235B of the through-hole 235 can be positioned axially closer to the inlet 200in of the impeller 200. Therefore, the sealing member 240 can be positioned axially closer to the inlet 200in of the impeller 200, and as a result, it is less likely that the sealing member 240 will be positioned in a location where the expansion rate of the outer diameter of the shroud 230 along the axial direction is relatively large. Thus, the compressor 10 can suppress the occurrence of problems such as decreased efficiency due to increased leakage of fluid from the outlet 200out side of the impeller 200 into the space between the shroud 230 and the inner surface 100B of the casing 100 toward the inlet 200in side of the impeller 200, increased inertia of the impeller 200, and increased costs.

[0076] The degree of inclination of the through-hole 235 (for example, the inclination angle θ1) is determined by considering, for example, the viewpoint of suppressing delamination occurring at the outer edge of the opening 235B of the through-hole 235, and the viewpoint of facilitating the flow of refrigerant from the main flow inside the impeller 200 into the through-hole 235. The greater the degree of inclination of the through-hole 235, the less likely delamination is to occur at the outer edge of the opening 235B of the through-hole 235, while the smaller the degree of inclination of the through-hole 235, the easier it is for the main flow of refrigerant passing inside the shroud 230 to flow into the through-hole 235.

[0077] The inclination angle θ1 is the angle formed between a straight line (reference line) perpendicular to the inner or outer surface of the shroud 230 at the location where the through-hole 235 is positioned, in a cross-section including the axis AX, and the center line of the through-hole 235. The reference line is, for example, a straight line that passes through the center 235Ac of the opening 235A in a cross-section including the axis AX and is perpendicular to the line segment connecting both ends of the opening 235A. The center line of the through-hole 235 is a line that continuously connects the centers of each position along the reference line between the opening 235A and the opening 235B in the through-hole 235 in a cross-section including the axis AX. In this example, the center line of the through-hole 235 is a straight line connecting the center 235Ac of the opening 235A and the center 235Bc of the opening 235B.

[0078] For example, prioritizing the ease of flow of the main stream of refrigerant into the through-hole 235, the inclination angle θ1 of the through-hole 235 is defined in a range of 10 degrees or more. Alternatively, prioritizing the suppression of delamination occurring at the outer edge of the opening 235B of the through-hole 235, the inclination angle θ1 of the through-hole 235 may be defined in a range of 30 degrees or more. Furthermore, balancing the ease of flow of the main stream of refrigerant into the through-hole 235 with the suppression of delamination occurring at the outer edge of the opening 235B of the through-hole 235, the inclination angle θ1 of the through-hole 235 may be defined in a range of 20 degrees or more.

[0079] Furthermore, the compressor 10 may be a multi-stage type as described above. In this case, as the pressure increases, that is, as the operating point moves towards lower flow rates, the load on the later stage compressor becomes higher than the load on the earlier stage compressor. As a result, generally, the later stage compressor tends to be more prone to mild surges or surges than the earlier stage compressor. Therefore, from the viewpoint of widening the operating range of the compressor, the impeller 200 of this embodiment is used in the later stage compressor, and through holes 235 are provided in the shroud 230, while from the viewpoint of improving efficiency, through holes 235 do not need to be provided in the shroud of the impeller in the earlier stage compressor. Specifically, through holes 235 in the shroud 230 may be provided only in at least one of the compressors that are later than the first stage compressor among the multiple stages of the compressor. For example, the compressor 10 includes a first compressor into which refrigerant flows, and a second compressor into which refrigerant discharged from the first compressor flows. Furthermore, the first compression section uses an impeller without through holes 235 in the shroud, while the second compression section uses an impeller 200 having through holes 235 in the shroud 230. Alternatively, to prioritize widening the compression range, an impeller 200 with through holes 235 in the shroud 230 may be used in all of the multiple compression sections.

[0080] [Second example of compressor structure] Next, a second example of the structure of the compressor 10 according to this embodiment will be described with reference to Figures 6 and 7.

[0081] In the following, components identical to or corresponding to the first example described above will be denoted by the same reference numerals. The explanation will focus on the parts that differ from the first example, and explanations of parts that are identical to or corresponding to the first example may be omitted. The same approach will be taken in the explanations of the third to twentieth examples described later, in relation to the examples already explained.

[0082] Figure 6 shows a second example of the compressor structure 10. Specifically, Figure 6 is an unfolded view of the meridional plane 211 of the impeller 200 and the base end of the blade 220 around the axis AX. Figure 7 shows the pressure-flow characteristics related to the second example of the compressor structure 10. Figure 7 includes the pressure-flow characteristics 701 of the compressor 10 according to this example and the pressure-flow characteristics 702 and 703 of compressors according to two comparative examples. Pressure-flow characteristics 702 corresponds to a comparative example in which the entire opening 235A of the through hole 235 is located in region 602 adjacent to the inlet 200in side of the impeller 200 than region 601 in Figure 6, and pressure-flow characteristics 703 corresponds to a comparative example in which the entire opening 235A of the through hole 235 is located in region 603 adjacent to the outlet 200out side of the impeller 200 than region 601. Furthermore, Figure 7 also includes a comparative example of Figure 5, namely, the pressure-flow characteristics 502 of a compressor without the through-hole 235.

[0083] In Figure 6, two of the multiple blades 220 are shown as representative examples, and for convenience, the blade 220 on the rear side in the rotational direction RT is designated as "blade 220a," and the blade 220 on the front side in the rotational direction RT is designated as "blade 220b."

[0084] The compressor 10 in this example differs from the first example described above in that the position of the opening 235A of the through hole 235 is determined in relation to the arrangement of the blades 220 of the impeller 200, but may be the same as the first example described above in other respects.

[0085] As shown in Figure 6, in this example, the through hole 235 is provided such that part or all of the opening 235A is located on a region 601 that includes a virtual line VL0 extending circumferentially from the center P0 of the throat 225.

[0086] The throat 225 is a line segment that corresponds to the shortest distance between the blade 220b and one end of the blade 220a on the inlet 200in side (virtual point Ps) on the meridional plane 211. In other words, the throat 225 is a line segment that connects the virtual point Ps on the blade 220a and the virtual point Pe on the blade 220b, which corresponds to the position at the shortest distance from the virtual point Ps, on the meridional plane 211.

[0087] Region 601 is the region between virtual lines VL1 and VL2 that extend in the circumferential direction, and virtual lines VL1 and VL2 are arranged so as to sandwich virtual line VL0 in the axial direction. For example, virtual line VL1 is a virtual line that extends in the circumferential direction from virtual point P1, which is located 40% of the length of the throat 225 with virtual point Ps as the starting point, on the throat 225. Also, for example, virtual line VL2 is a virtual line that extends in the circumferential direction from virtual point P1, which is located 60% of the length of the throat 225 with virtual point Ps as the starting point, on the throat 225.

[0088] For example, as shown in Figure 7, in the comparative example pressure-flow characteristics 702 and 703, where the entire opening 235A of the through-hole 235 is included in regions 602 and 603 respectively, the pressure in the low-flow region is relatively low. This is because, when the opening 235A of the through-hole 235 is in region 602, region 602 is relatively close to the inlet 200in of the impeller 200, so the pressure of the refrigerant circulating through the through-hole 235 is relatively low, and the effect of the pressure increase of the impeller 200 due to the circulating flow is limited. Also, when the opening 235A of the through-hole 235 is in region 603, region 603 is relatively close to the outlet 200out of the impeller 200, so the pressure of the refrigerant circulating through the through-hole 235 becomes relatively high, and as a result, the efficiency of the impeller 200 itself decreases significantly.

[0089] In contrast, in this example, the flow rate of the circulating flow can be optimized by arranging the region 601 so that part or all of the opening 235A of the through hole 235 is included above it. As a result, as shown in Figure 7, the pressure-flow characteristics 701 of the compressor 10 show that the pressure is relatively high in the low flow rate region. Therefore, by increasing the pressure in the low flow rate region, the aforementioned upward slope characteristic can be suppressed.

[0090] [Third example of compressor structure] Next, a third example of the compressor 10 according to this embodiment will be described with reference to Figure 8.

[0091] Figure 8 shows a third example of the compressor 10.

[0092] As shown in Figure 8, the compressor 10 in this example differs from the first and second examples described above in that the through-hole 235 penetrates between the inner and outer surfaces of the shroud 230 in a curved path, but may be the same as the first or second example described above in other respects.

[0093] In this example, the through-hole 235 is formed in a curved shape such that its centerline slopes toward the inlet 200in side of the impeller 200 as it moves from opening 235A toward opening 235B. In other words, the through-hole 235 is formed in a curved shape such that the inclination angle θ1 increases as it moves from opening 235A toward opening 235B. This allows the inclination angle θ1 at opening 235B to be set to be relatively large. Therefore, separation when the refrigerant inside the shroud 230 flows into the space 110A through the through-hole 235 can be further suppressed. Furthermore, within the manufacturing constraints of the through-hole 235, the inclination angle θ1 at opening 235A and the inclination angle θ1 at opening 235B can be set separately. Therefore, within the manufacturing constraints of the through-hole 235, the inclination angle θ1 at opening 235A can be set to be relatively small, while the inclination angle θ1 at opening 235B can be set to be relatively large. Therefore, it is possible to optimize the ease of flow of the main refrigerant into the through-hole 235 and the suppression of peeling that occurs at the outer edge of the opening 235B of the through-hole 235.

[0094] [Fourth example of compressor structure] Next, with reference to Figure 9, a fourth example of the structure of the compressor 10 according to this embodiment will be described.

[0095] Figure 9 shows a fourth example of the compressor 10.

[0096] As shown in Figure 9, the compressor 10 in this example differs from the first to third examples described above in that the corners of the outer edges of the openings 235A and 235B of the through hole 235 are chamfered in a curved shape, and may be the same as the first or second example described above in other respects.

[0097] In this example, chamfers 235C and 235D are applied to the corners of the outer edges of the openings 235A and 235B of the through hole 235 on the side of the inlet 200in of the impeller 200. The chamfers 235C and 235D are, for example, rounded chamfers.

[0098] This makes it possible to suppress peeling at the outer edge of the opening 235A when the main flow of refrigerant inside the shroud 230 flows into the through hole 235, and also suppresses peeling at the outer edge of the opening 235B when refrigerant flows from the through hole 235 into the space 110A.

[0099] [Fifth example of compressor structure] Next, with reference to Figure 10, a fifth example of the structure of the compressor 10 according to this embodiment will be described.

[0100] Figure 10 shows the structure of a fifth example of the compressor 10.

[0101] As shown in Figure 10, the compressor 10 in this example differs from the first to fourth examples described above in that the end face 230A of the shroud 230 is inclined toward the inside of the impeller 200, and may be the same as any one of the first to fourth examples described above in other respects.

[0102] The end face 230A of the shroud 230 is a plane that is inclined such that, in a cross-section including the axis AX, the inner end point of the shroud 230 is on the inside side of the impeller 200 (in other words, on the outlet 200out side of the impeller 200) than the outer end point.

[0103] This allows the circulating flow in space 110B to have a component in the same direction as the main flow near the inlet 200in of the impeller 200. Therefore, separation at the end face 230A of the shroud 230 when the circulating flow of refrigerant through the through hole 235 merges with the main flow of refrigerant near the inlet of the impeller 200 from space 110B can be suppressed, and pressure loss can be reduced. In addition, the circulating flow that merges with the main flow near the inlet 200in of the impeller 200 from space 110B can suppress backflow that occurs at the ends of the blades 220 of the impeller 200.

[0104] The greater the degree of inclination of the end face 230A of the shroud 230 (for example, the inclination angle θ2), the smaller the difference in flow direction between the main flow and the circulating flow, and as a result, the more effective it is at suppressing losses associated with the merging of the main flow and the circulating flow and the mixing of the refrigerant that accompanies the merging of the flows. On the other hand, the smaller the degree of inclination of the end face 230A of the shroud 230, the smaller the angle at which the circulating flow changes direction from space 110A to space 110B, and as a result, the more effective it is at suppressing losses associated with separation at the corner between the outer surface of the shroud 230 and the end face 230A.

[0105] The inclination angle θ2 is the angle formed by a line perpendicular to the inner surface of the shroud 230 and the end face 230A of the shroud 230 in a cross-section containing the axis AX.

[0106] For example, prioritizing the suppression of losses associated with the merging of the main flow and the circulating flow, the inclination angle θ2 of the end face 230A of the shroud 230 is defined in a range of 30 degrees or more. Alternatively, prioritizing the suppression of losses associated with separation at the corner between the outer surface of the shroud 230 and the end face 230A in the circulating flow, the inclination angle θ2 of the end face 230A of the shroud 230 may be set in a range of 10 degrees or more. Furthermore, to strike a balance between suppressing losses associated with the merging of the main flow and the circulating flow and suppressing losses associated with separation at the corner between the outer surface of the shroud 230 and the end face 230A in the circulating flow, the inclination angle θ2 of the end face 230A of the shroud 230 may be defined in a range of 20 degrees or more.

[0107] Furthermore, the degree of inclination of the end face 230A of the shroud 230 may be indirectly determined by the degree of inclination of the space 110B as a refrigerant passage (for example, the inclination angle θ3).

[0108] In this example, the inclination of the end face 230A of the shroud 230 causes the direction of the refrigerant circulation flow passing through the space 110B to be inclined toward the outlet 200out of the impeller 200, from the outer surface to the inner surface of the shroud 230, with reference to the direction perpendicular to the inner surface of the shroud 230. Therefore, the space 110B, which serves as a passage for the refrigerant, can be considered to be inclined toward the outlet 200out of the impeller 200, from the outer surface to the inner surface of the shroud 230, with reference to the direction perpendicular to the inner surface of the shroud 230.

[0109] The inclination angle θ3 is defined, for example, as the angle between a line perpendicular to the inner surface of one end of the impeller 200 on the inlet 200in side of the shroud 230 (reference line) and the center line of the space 110B as a refrigerant passage in a cross-section including the axis AX. The center line of the space 110B as a refrigerant passage is a line that continuously connects the centers of the width of the space 110B at each position along the reference line between one end of the space 110B on the outer surface side and the other end on the inner surface side of the shroud 230. The width of the space 110B is the width of the space 110B in the direction perpendicular to the reference line. In this example, the center line of the space 110B as a refrigerant passage is a straight line connecting the center of the width of the space 110B at one end of the space 110B on the outer surface side and the center of the width of the space 110B at the other end of the space 110B on the inner surface side.

[0110] For example, prioritizing the suppression of losses associated with the merging of the main flow and the circulating flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage is defined to be in the range of 30 degrees or more. Alternatively, prioritizing the suppression of losses associated with separation at the corner between the outer surface and the end face 230A of the shroud 230 in the circulating flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage may be set to be in the range of 10 degrees or more. Furthermore, to strike a balance between suppressing losses associated with the merging of the main flow and the circulating flow and suppressing losses associated with separation at the corner between the outer surface and the end face 230A of the shroud 230 in the circulating flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage may be defined to be in the range of 20 degrees or more.

[0111] In this example, since the inclination angle θ2 is twice the inclination angle θ3, the inclination angle θ2 can be defined as twice the previously defined inclination angle θ3.

[0112] [Sixth Example of Compressor Structure] Next, with reference to Figure 11, a sixth example of the compressor 10 according to this embodiment will be described.

[0113] Figure 11 shows a sixth example of the structure of the compressor 10.

[0114] As shown in Figure 11, the compressor 10 in this example differs from the fifth example described above in that the end face 230A of the shroud 230 is curved, but may be the same as the fifth example described above in other respects.

[0115] The end face 230A of the shroud 230 is inclined in the same way as in the fifth example described above, and has a curved shape such that the degree of inclination (for example, inclination angles θ2, θ3) increases from the outer surface to the inner surface of the shroud 230.

[0116] As a result, the compressor 10 can improve its ability to suppress separation when the circulating flow of refrigerant merges from the space 110B into the main flow, and to suppress backflow at the ends of the blades 220 of the impeller 200.

[0117] In this example, the degree of inclination (inclination angles θ2, θ3) of the end face 230A of the shroud 230 and the space 110B serving as a passage for the refrigerant is evaluated at one end on the inner side of the shroud 230, that is, near the confluence with the main flow of the refrigerant, and may be defined in the same manner as in the sixth example described above.

[0118] [Seventh example of compressor structure] Next, with reference to Figure 12, a seventh example of the compressor 10 according to this embodiment will be described.

[0119] Figure 12 shows a seventh example of the structure of the compressor 10.

[0120] As shown in Figure 12, the compressor 10 in this example differs from the first to sixth examples described above in that a curved chamfer is applied to the corner of the outer edge of the end face 230A of the shroud 230, and may be the same as the fifth example described above in other respects.

[0121] Chamfers 230B and 230C are provided at the corners between the end face 230A of the shroud 230 and the outer and inner surfaces of the shroud 230, respectively.

[0122] This makes it possible to suppress the separation of the refrigerant circulation flow and also suppress pressure loss.

[0123] [Eighth example of compressor structure] Next, with reference to Figure 13, the eighth example of the structure of the compressor 10 according to this embodiment will be described.

[0124] Figure 13 shows an eighth example of the structure of the compressor 10.

[0125] As shown in Figure 13, the compressor 10 in this example differs from the first to seventh examples described above in that the stepped surface 100C is inclined to approach the end face 230A of the shroud 230 from the inner surface 100B side to the inner surface 100A side, and in other respects it may be the same as any one of the first to fourth examples described above.

[0126] In this example, the stepped surface 100C is a plane that forms an acute angle with respect to both the inner surface 100A corresponding to the suction pipe 120 and the inner surface 100B corresponding to the impeller chamber 110, in a plane containing the axis AX.

[0127] This allows the circulating flow in space 110B to have a component in the same direction as the main flow near the inlet 200in of the impeller 200. Therefore, separation at the end face 230A of the shroud 230 when the circulating flow of refrigerant through the through hole 235 merges with the main flow of refrigerant near the inlet of the impeller 200 from space 110B can be suppressed, and pressure loss can be reduced. In addition, the circulating flow that merges with the main flow near the inlet 200in of the impeller 200 from space 110B can suppress backflow that occurs at the ends of the blades 220 of the impeller 200.

[0128] Furthermore, as the stepped surface 100C approaches the end face 230A of the shroud 230 from the inner surface 100B side towards the inner surface 100A side, the width of the space 110B as a refrigerant passage decreases as it approaches the point where it merges with the main flow of the refrigerant circulation. Specifically, the width t2 at one end of the space 110B as a refrigerant passage on the inner surface 100A side is smaller than the width t2 at the other end on the inner surface 100A side.

[0129] This increases the dynamic pressure of the circulating flow, promoting the merging of the main flow and the circulating flow. Furthermore, by increasing the dynamic pressure of the circulating flow, the effect of the circulating flow pushing back against the flow attempting to reverse in the main flow is enhanced, and as a result, the reverse flow in the main flow can be suppressed.

[0130] The greater the degree of inclination of the stepped surface 100C (for example, the inclination angle θ4), the smaller the difference in flow direction between the main flow and the circulating flow, and as a result, the more effective it is at suppressing losses associated with the merging of the main flow and the circulating flow and the mixing of the refrigerant that accompanies the merging of the flows. On the other hand, the smaller the degree of inclination of the stepped surface 100C, the smaller the angle at which the circulating flow changes direction from space 110A to space 110B, and as a result, the more effective it is at suppressing losses associated with separation at the corner between the outer surface of the shroud 230 and the end surface 230A.

[0131] The inclination angle θ4 is the angle formed by a line perpendicular to the inner surface of the shroud 230 at one end of the impeller 200 on the inlet 200in side, and the stepped surface 100C, in a cross-section including the axis AX.

[0132] For example, prioritizing the suppression of losses associated with the merging of the main flow and the circulating flow, the inclination angle θ4 of the stepped surface 100C is defined in a range of 30 degrees or more. Alternatively, prioritizing the suppression of losses associated with separation at the corner between the outer surface of the shroud 230 and the end surface 230A in the circulating flow, the inclination angle θ4 of the stepped surface 100C may be set in a range of 10 degrees or more. Furthermore, to strike a balance between suppressing losses associated with the merging of the main flow and the circulating flow and suppressing losses associated with separation at the corner between the outer surface of the shroud 230 and the end surface 230A in the circulating flow, the inclination angle θ4 of the stepped surface 100C may be defined in a range of 20 degrees or more.

[0133] Furthermore, the degree of inclination of the stepped surface 100C may be indirectly determined by the degree of inclination of the space 110B as a refrigerant passage (for example, the inclination angle θ3).

[0134] In this example, the inclination of the stepped surface 100C causes the direction of the refrigerant circulation flow passing through the space 110B to be inclined toward the outlet 200out side of the impeller 200, from the outer surface to the inner surface of the shroud 230, with reference to the direction perpendicular to the inner surface of the shroud 230. Therefore, the space 110B, which serves as a passage for the refrigerant, can be considered to be inclined toward the outlet 200out side of the impeller 200, from the outer surface to the inner surface of the shroud 230, with reference to the direction perpendicular to the inner surface of the shroud 230.

[0135] For example, prioritizing the suppression of losses associated with the merging of the main flow and the circulating flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage is defined to be in the range of 30 degrees or more. Alternatively, prioritizing the suppression of delamination at the corner between the outer surface of the shroud 230 and the end face 230A in the circulating flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage may be set to be in the range of 10 degrees or more. Furthermore, balancing the manufacturability of the casing 100 with the suppression of losses associated with delamination when the circulating flow merges with the main flow, the inclination angle θ3 of the space 110B serving as the refrigerant passage may be defined to be in the range of 20 degrees or more.

[0136] In this example, since the inclination angle θ4 is twice the inclination angle θ3, we can define the inclination angle θ4 as twice the previously defined inclination angle θ3.

[0137] [Ninth example of compressor structure] Next, with reference to Figure 14, a ninth example of the structure of the compressor 10 according to this embodiment will be described.

[0138] Figure 14 shows the ninth example of the structure of the compressor 10.

[0139] As shown in Figure 14, the compressor 10 in this example differs from the first to eighth examples described above in that the stepped surface 100C is a curved surface, but in other respects it may be the same as the eighth example described above.

[0140] In this example, the stepped surface 100C of the casing 100 is inclined in the same way as in the eighth example described above, and has a curved shape such that the degree of inclination (for example, the inclination angle θ4) increases from the inner surface 100B side to the inner surface 100A side in a cross section including the axis AX.

[0141] As a result, the compressor 10 can improve its ability to suppress separation when the circulating flow of refrigerant merges from the space 110B into the main flow, and to suppress backflow at the ends of the blades 220 of the impeller 200.

[0142] In this example, the degree of inclination (inclination angles θ3, θ4) of the end face 230A of the shroud 230 and the space 110B serving as a passage for the refrigerant is evaluated at one end on the inner surface side of the shroud 230, that is, near the confluence with the main flow of the refrigerant, and may be defined in the same manner as in the eighth example described above.

[0143] [Tenth example of compressor structure] Next, with reference to Figure 15, a tenth example of the structure of the compressor 10 according to this embodiment will be described.

[0144] Figure 15 shows a tenth example of the structure of the compressor 10.

[0145] As shown in Figure 15, the compressor 10 in this example differs from the first to ninth examples described above in that the connection portion with the inner surface 100A and the connection portion with the inner surface 100B on the stepped surface 100C are formed in a curved shape, but it may be the same as the ninth example described above in other respects.

[0146] In this example, a curved surface 100D is formed at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100B, and a curved chamfer 100E is formed at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100A.

[0147] This suppresses separation of the refrigerant flow as it passes through spaces 110A and 110B, and also reduces pressure loss.

[0148] [Eleventh example of compressor structure] Next, with reference to Figure 16, an eleventh example of the structure of the compressor 10 according to this embodiment will be described.

[0149] Figure 16 shows an eleventh example of the structure of the compressor 10.

[0150] As shown in Figure 16, the compressor 10 in this example differs from the first to tenth examples described above in that both the end face 230A and the stepped surface 100C of the shroud 230 are formed in a curved shape, and may be the same as the sixth or ninth example described above in other respects.

[0151] In this example, the end face 230A of the shroud 230 has a curved shape similar to that of the sixth example described above. Also, the stepped surface 100C of the casing 100 has a curved shape similar to that of the ninth example described above.

[0152] As a result, similar to the sixth and ninth examples described above, the compressor 10 can improve the effect of suppressing separation when the circulating refrigerant flow merges from the space 110B into the main flow, and the effect of suppressing backflow at the ends of the blades 220 of the impeller 200.

[0153] Furthermore, in this example, the curved shape of the end face 230A of the shroud 230 and the stepped surface 100C of the casing 100 is defined such that the width of the space 110B, which serves as a passage for the refrigerant, decreases as it approaches the confluence point with the main flow of the refrigerant circulation. For example, in a cross-section including the axis AX, the curved shape of the end face 230A of the shroud 230 and the stepped surface 100C of the casing 100 is defined such that the width t2 at one end on the inner surface 100A side of the space 110B, which serves as a passage for the refrigerant, is smaller than the width t1 at the other end on the inner surface 100B side.

[0154] This increases the dynamic pressure of the circulating flow, promoting the merging of the main flow and the circulating flow. Furthermore, increasing the dynamic pressure of the circulating flow can suppress backflow in the main flow.

[0155] [Twelfth Example of Compressor Structure] Next, with reference to Figure 17, a twelfth example of the structure of the compressor 10 according to this embodiment will be described.

[0156] Figure 17 shows a twelfth example of the structure of the compressor 10.

[0157] As shown in Figure 17, the compressor 10 in this example differs from the first to eleventh examples described above in that the suction pipe 120 and the area extending 200 in from the inlet 200 in the impeller 200 are formed in a bell mouth shape, but in other respects it may be the same as the eleventh example described above.

[0158] In this example, the inner diameter of the inner surface 100A of the casing 100 corresponding to the suction pipe 120 is formed to decrease as it approaches the inlet 200in of the impeller 200. For example, as shown in Figure 17, the inner surface 100A of the casing 100 is formed in a bell mouth shape.

[0159] This allows the refrigerant flow towards the inlet 200in of the impeller 200 to be accelerated. As a result, the circulating refrigerant flow from space 110B can be merged with the accelerating region of the main refrigerant flow, promoting the mixing of the main refrigerant flow and the circulating refrigerant flow merging from space 110B into the main flow, thereby suppressing losses due to interference between the main flow and the recirculating flow.

[0160] In this example, the inner diameter (inner diameter D2) of the shroud 230 at the inlet 200in of the impeller 200 is set to be smaller than the inner diameter (inner diameter D1) of the connection between the inner surface 100A and the stepped surface 100C of the casing 100.

[0161] This allows the refrigerant flow to be further accelerated between one end of the inner surface 100A of the casing 100 and the inlet 200in of the impeller 200. As a result, the mixing of the main flow of refrigerant and the circulating flow of refrigerant joining the main flow from space 110B is further promoted, improving the effect of suppressing losses due to interference between the main flow and the recirculating flow.

[0162] [13th Example of Compressor Structure] Next, with reference to Figure 18, a 13th example of the structure of the compressor 10 according to this embodiment will be described.

[0163] Figure 18 shows a thirteenth example of the structure of the compressor 10. Specifically, Figure 18 is a perspective view of the impeller 200 of the compressor 10 according to this example.

[0164] As shown in Figure 18, the compressor 10 in this example differs from the first to twelfth examples described above in that the slit-shaped through holes 235 extending in the circumferential direction are provided only in a part of the circumferential direction, and may be the same as any one of the first to twelfth examples described above in other respects.

[0165] In this example, multiple through holes 235 are arranged spaced apart in the circumferential direction. Connecting portions 236 that separate adjacent through holes 235 in the circumferential direction connect the portion of the shroud 230 on the inlet 200in side and the portion on the outlet 200out side of the through holes 235.

[0166] For example, the impeller 200 may experience a blade vibration mode in which the leading edge of the tip of the blade 220 vibrates.

[0167] In contrast, in this example, the connecting portion 236 connects the portion of the shroud 230 on the inlet 200in side of the through hole 235, which corresponds to the leading edge of the tip of the blade 220, to the portion on the outlet 200out side. This suppresses the decrease in eigenvalues ​​and improves the strength against wing vibration.

[0168] [14th Example of Compressor Structure] Next, with reference to Figure 19, the 14th example of the structure of the compressor 10 according to this embodiment will be described.

[0169] Figure 19 shows a 14th example of the structure of the compressor 10. Specifically, Figure 19 is a perspective view of the impeller 200 of the compressor 10 according to this example.

[0170] As shown in Figure 19, the compressor 10 in this example differs from the 13th example described above in the structure of the connecting portion 236, but may be the same as the 13th example described above in other respects.

[0171] In this example, in some or all of the multiple through holes 235 provided in the circumferential direction, the openings 235B are positioned so as not to overlap with the tips of the blades 220. In other words, the inner surface of the connecting portion 236 may be connected to the blades 220. For example, as shown in Figure 19, the connecting portion 236 is formed to overlap with the blades 220 when viewed from the radially outside. This prevents the blades 220 from reducing the flow path cross-sectional area of ​​the through holes 235, and as a result, it is possible to suppress a decrease in the flow rate circulating to the inlet 200in of the impeller 200 through the through holes 235. Therefore, it is possible to ensure both sufficient flow circulating to the inlet 200in of the impeller 200 through the through holes 235 and sufficient strength against blade vibration.

[0172] [Fifteenth example of compressor structure] Next, with reference to Figure 20, this is a diagram showing the fifteenth example of the structure of the compressor 10 according to this embodiment.

[0173] Figure 20 shows the 15th example of the structure of the compressor 10.

[0174] As shown in Figure 20, the compressor 10 in this example differs from the first to sixteenth examples described above in that a groove 113 is provided on the inner surface 100B of the casing 100 corresponding to the space 110A, and may be the same as the twelfth example described above in other respects.

[0175] The groove 113 is provided on the inner surface 100B of the casing 100 corresponding to the space 110A, that is, in the portion of the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240, and extends in a direction perpendicular to the circumferential direction. In other words, the groove 113 is provided on the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240, and extends along a plane that includes the axial and radial directions (i.e., a plane that includes the axis AX). In this example, the groove 113 is provided on the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240, and extends in the axial direction. For example, there are multiple grooves 113, and the multiple grooves 113 are arranged in a circumferential direction along the entire circumferential direction, that is, around the whole circumference. The spacing between the multiple grooves 113 may be equal or unequal.

[0176] As a result, when the circulating flow of refrigerant flowing from the through-hole 235 into the space 110A passes through the groove 113, the groove 113 restricts the circumferential flow and suppresses the rotational (swirling) velocity component (forward swirling component) included in the circulating flow. Therefore, it is possible to prevent a situation in which the pressure increase of the impeller 200 associated with the merging of the circulating flow into the main flow is reduced due to the forward swirling component included in the circulating flow.

[0177] [16th example of compressor structure] Next, with reference to Figure 21, the 16th example of the structure of the compressor 10 will be described.

[0178] Figure 21 shows the 16th example of the structure of the compressor 10.

[0179] As shown in Figure 21, the compressor 10 in this example differs from the first to fifteenth examples described above in that a projection 114 is provided on the inner surface 100B of the casing 100 corresponding to the space 110A, and may be the same as the twelfth example described above in other respects.

[0180] The projection 114 is provided so as to extend in a direction perpendicular to the circumferential direction in the portion of the inner surface 100B of the casing 100 corresponding to the space 110A, that is, in the portion of the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240. In other words, the groove 113 is provided so as to extend along a plane including the axial and radial directions (i.e., a plane including the axis AX) in the portion of the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240. In this example, the groove 113 is provided so as to extend in the axial direction in the portion of the inner surface 100B of the casing 100 that is on the side of the inlet 200in of the impeller 200 that is on the side of the seal member 240. For example, there are multiple projections 114, and the multiple projections 114 are arranged in a circumferential direction along the entire circumferential direction, that is, around the whole circumference. The spacing between the multiple protrusions 114 may be equal or unequal.

[0181] As a result, when the circulating flow of refrigerant flowing from the through-hole 235 into the space 110A passes near the projection 114, the projection 114 restricts the circumferential flow, thereby suppressing the rotational (swirling) velocity component (forward swirling component) included in the circulating flow. Therefore, it is possible to prevent a situation in which the pressure increase of the impeller 200 associated with the merging of the circulating flow into the main flow is reduced due to the forward swirling component included in the circulating flow.

[0182] [17th example of compressor structure] Next, with reference to Figure 22, the 17th example of the structure of the compressor 10 will be described.

[0183] Figure 22 shows the 17th example of the structure of the compressor 10.

[0184] As shown in Figure 22, the compressor 10 in this example differs from the first to sixteenth examples described above in that a projection 115 is provided on the stepped surface 100C, but may be the same as the twelfth example described above in other respects.

[0185] The projections 115 are provided on the stepped surface 100C so as to extend radially. For example, there may be multiple projections 115, and these multiple projections 115 are arranged in a circumferential direction over the entire circumference, i.e., the entire circumference. The spacing between the multiple projections 115 may be equal or unequal.

[0186] As a result, when the circulating flow of refrigerant flowing from space 110A to space 110B passes near the projection 115, the projection 115 restricts the circumferential flow, thereby suppressing the rotational (swirling) velocity component (forward swirling component) included in the circulating flow. Therefore, it is possible to prevent a situation in which the pressure increase of the impeller 200 associated with the merging of the circulating flow into the main flow is reduced due to the forward swirling component included in the circulating flow.

[0187] [Example 18 of Compressor Structure] Next, with reference to Figure 23, an example 18 of the structure of the compressor 10 will be described.

[0188] Figure 23 shows the 18th example of the structure of the compressor 10.

[0189] As shown in Figure 23, the compressor 10 in this example differs from the first to seventeenth examples described above in that the through hole 235 is provided on the outlet 200out side of the sealing member 240 in the shroud 230, but may be the same as the first example described above in other respects.

[0190] The sealing member 240 is positioned between the inlet 200in end of the impeller 200 in the shroud 230 and the inner surface 100B of the casing 100.

[0191] As described above, the through-hole 235 is provided on the shroud 230 on the outlet 200out side, beyond the inlet 200in side and the outlet 200out side of the impeller 200, and beyond the sealing member 240. For example, the inner opening 235A of the through-hole 235 is provided on the outlet 200out side of the center between the inlet 200in side and the outlet 200out side of the inner surface of the shroud 230 in a cross section including the axis AX. In this example, the through-hole 235 is provided in a position relatively close to the outlet 200out of the impeller 200 in the shroud 230 in a cross section including the axis AX, and is formed to penetrate linearly between the inner and outer surfaces of the shroud 230.

[0192] As a result, as shown in Figure 23, a portion of the refrigerant discharged from the outlet 200out of the impeller 200 can be allowed to flow into the through-hole 235 through the space 110C between the inner surface 100B of the casing 100 and the shroud 230, and circulated inside the impeller 200. Therefore, the compressor 10 can suppress the wake, which is a low-energy refrigerant accumulation region that occurs near the outlet of the impeller 200, by the circulating flow that merges with the main flow of the impeller 200 through the through-hole 235.

[0193] Furthermore, the through-hole 235 is provided so as in the first example described above, that it is inclined toward the inlet 200in side of the impeller 200 with respect to a direction perpendicular to the inner surface of the shroud 230. In a cross-section including the axis AX, the center 235Bc of the opening 235B of the through-hole 235 is positioned toward the inlet 200in side of the impeller 200 than the center 235Ac of the opening 235A. This suppresses the separation that occurs at the outer edge of the opening 235A of the through-hole 235 when refrigerant flows from the through-hole 235 into the main flow of the impeller 200. The compressor 10 can suppress losses when the quasi-downstream flow merges from the through-hole 235 into the main flow of the impeller 200, and further improve the effect of the through-hole 235.

[0194] The degree of inclination of the through-hole 235 (for example, the inclination angle θ1) is determined by considering, for example, the viewpoint of suppressing delamination occurring at the outer edge of the opening 235A of the through-hole 235, and the viewpoint of facilitating the flow of refrigerant circulating in the space 110C into the through-hole 235. This is because a larger degree of inclination of the through-hole 235 makes it less likely for delamination to occur at the outer edge of the opening 235A of the through-hole 235, while a smaller degree of inclination of the through-hole 235 makes it easier for the flow of refrigerant circulating in the space 110C to flow into the through-hole 235.

[0195] For example, prioritizing the ease of refrigerant flow from the space 110C into the through-hole 235, the inclination angle θ1 of the through-hole 235 is defined in a range of 10 degrees or more. Alternatively, prioritizing the suppression of delamination occurring at the outer edge of the opening 235A of the through-hole 235, the inclination angle θ1 of the through-hole 235 may be defined in a range of 30 degrees or more. Furthermore, balancing the ease of refrigerant flow from the space 110C into the through-hole 235 with the suppression of delamination occurring at the outer edge of the opening 235A of the through-hole 235, the inclination angle θ1 of the through-hole 235 may be defined in a range of 20 degrees or more.

[0196] [Nineteenth example of compressor structure] Next, with reference to Figure 24, the ninth example of the structure of the compressor 10 according to this embodiment will be described.

[0197] Figure 24 shows the 19th example of the structure of the compressor 10.

[0198] As shown in Figure 24, the compressor 10 in this example differs from the first to eighteen examples described above in that it is provided on both the inlet 200in side and the outlet 200out side of the impeller 200 in the shroud 230 with respect to the sealing member 240, but may be the same as the twelfth example described above in other respects.

[0199] As a result, the compressor 10 can achieve high pressure and a wide range in the low flow rate region and suppress mild surges of the impeller 200 through the action of the through hole 235 on the inlet 200in side of the impeller 200, while suppressing wake of the impeller 200 through the action of the through hole 235 on the outlet 200out side of the impeller 200.

[0200] Furthermore, in this example, similar to the first example described above, the through-hole 235 on the inlet 200in side of the impeller 200 is provided so as to be inclined toward the inlet 200in side of the impeller 200, with reference to a direction perpendicular to the inner surface of the shroud 230.

[0201] As a result, the compressor 10 can suppress separation at the outer edge of the opening 235B when the refrigerant flows into the space 110B through the through hole 235, and increase the flow rate circulating to the inlet 200in of the impeller 200. Therefore, the compressor 10 can further improve the mild surge suppression effect due to the action of the through hole 235.

[0202] Furthermore, in this example, similar to the 18th example described above, the through hole 235 on the outlet 200out side of the impeller 200 is provided to be inclined toward the inlet 200in side of the impeller 200, with reference to a direction perpendicular to the inner surface of the shroud 230.

[0203] As a result, the compressor 10 can suppress separation at the outer edge of the opening 235A when the refrigerant merges with the main refrigerant flow from the through-hole 235, and the compressor 10 can suppress losses when the quasi-downstream flow merges with the main flow of the impeller 200 from the through-hole 235. Therefore, the compressor 10 can further improve the wake suppression effect due to the action of the through-hole 235.

[0204] [Other examples of compressor structure] Next, other examples of the structure of the compressor 10 will be described.

[0205] The first to 19 examples of the structure of the compressor 10 described above may be modified or altered as appropriate. Hereinafter, for convenience, examples of modifications or alterations will be referred to as "modified versions."

[0206] <First Modification> In the fourth example of the structure of the compressor 10 described above (Figure 9), the chamfers 235C and 235D may be straight chamfers (for example, C-chamfers).

[0207] <Second Modification> In the fourth example of the structure of the compressor 10 described above (Figure 9) and in the first modification, either the chamfer 235C or 235D may be omitted.

[0208] <Third Modification> In the third example of the structure of the compressor 10 described above (Figure 8), chamfers 235C and 235D of the fourth example (Figure 9) or the first modification described above may be provided on at least one outer edge of the openings 235A and 235B.

[0209] <Fourth Modification> In the fifth example (Figure 10) to twelfth example (Figure 17) and fifteenth example (Figure 20) to seventeenth example (Figure 22) of the structure of the compressor 10 described above, the through hole 235 may be replaced with the through hole 235 of the form of the fourth example (Figure 9) described above.

[0210] <Fifth Modification> In the 18th and 19th examples of the structure of the compressor 10 described above, the through hole 235 provided on the outlet 200out side of the impeller 200 from the sealing member 240 may be formed in a curved shape in a cross section including the axis AX. In this case, unlike the through hole 235 of the third example (Figure 8) described above, the through hole 235 is formed in a curved shape such that its center line slopes toward the inlet 200in side of the impeller 200 as it moves from the opening 235B toward 235A.

[0211] <Sixth Modification> The chamfers 230B and 230C in the seventh example of the structure of the compressor 10 described above (Figure 12) may be straight chamfers (for example, C-chamfers).

[0212] <Seventh Modification> In the seventh example (Figure 12) and the sixth modification of the structure of the compressor 10 described above, either the chamfer 230B or 230C may be omitted.

[0213] <Eighth Modification> In the sixth example of the structure of the compressor 10 described above (Figure 11), chamfers 230B and 230C of the seventh example (Figure 12) or the fifth modification may be provided at the connection points (corners) between the end face 230A of the shroud 230 and the outer and inner surfaces, respectively.

[0214] <Ninth Modification> In the tenth example of the structure of the compressor 10 described above (Figure 15), instead of a curved surface 100D, a flat surface may be provided at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100B to fill the corner. Also, in the tenth example of the structure of the compressor 10 described above, the chamfer 100E at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100A may be a flat chamfer (for example, a C-chamfer).

[0215] <Tenth Modification> In the tenth example of the structure of the compressor 10 described above (Figure 15) and the ninth modification, either the curved surface 100D or the flat surface, or the chamfer 100E, provided at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100B may be omitted.

[0216] <11th Modification> In the first (Figure 4) to seventh (Figure 12), ninth (Figure 14), eleventh (Figure 16), twelfth (Figure 17), fifteenth (Figure 20) to seventeenth (Figure 22), and nineteenth (Figure 24) examples of the structure of the compressor 10 described above, the corner corresponding to the connection between the stepped surface 100C and the inner surface 100B may be provided with the curved surface 100D of the tenth example (Figure 15) described above or the flat surface of the ninth modification described above. Similarly, in the first (Figure 4) to seventh (Figure 12), ninth (Figure 14), eleventh (Figure 16), twelfth (Figure 17), fifteenth (Figure 20) to seventeenth (Figure 22), and nineteenth (Figure 24) examples of the structure of the compressor 10 described above, a chamfer 100E, as in the tenth example (Figure 15) or a modified example of the ninth described above, may be provided at the corner corresponding to the connection between the stepped surface 100C and the inner surface 100A.

[0217] <Twelfth Modification> In the fifteenth example of the structure of the compressor 10 described above (Figure 20) and its various modifications, a relatively rough surface (rough surface) may be used on the inner surface 100B of the casing 100 instead of, or in addition to, the groove 113. For example, the inner surface 100B of the casing 100 is rougher than the inner or outer surface of the shroud 230. The roughness of the inner surface 100B of the casing 100 can suppress the rotational (swirling) velocity component (forward swirling component) included in the circulating flow of refrigerant flowing from the through hole 235 into the space 110A.

[0218] <13th Modification> In the 16th example of the structure of the compressor 10 described above (Figure 21) and its various modifications, a relatively rough surface may be used on the inner surface 100B of the casing 100 instead of, or in addition to, the projection 114. For example, the inner surface 100B of the casing 100 is rougher than the inner or outer surface of the shroud 230. The roughness of the inner surface 100B of the casing 100 can suppress the rotational (swirling) velocity component (forward swirling component) included in the circulating flow of refrigerant flowing from the through hole 235 into the space 110A.

[0219] <14th Modification> In addition, in the first example (Figure 4) to the 19th example (Figure 24) of the structure of the compressor 10 described above, and in the first to 11th modifications described above, the through-holes 235 may not be slit-shaped with a relatively long dimension in the circumferential direction, but may be shaped with a relatively short dimension in the circumferential direction (for example, a round hole, an oval hole, a rectangular hole, etc.). In this case, there are multiple through-holes 235, and the multiple through-holes 235 are arranged in a line in the circumferential direction at equal or unequal intervals. In this case, in some or all of the multiple through-holes 235 provided in the circumferential direction, the openings 235B may be arranged so as not to overlap with the tips of the blades 220. This makes it possible to suppress a situation in which the cross-sectional area of ​​the flow path of the through-holes 235 is reduced by the blades 220, and as a result, it is possible to suppress a reduction in the flow rate circulating to the inlet 200in of the impeller 200 through the through-holes 235.

[0220] [Operation] Next, the operation of the centrifugal compressor and refrigeration system according to this embodiment will be described.

[0221] In a first aspect of this embodiment, the centrifugal compressor comprises an impeller and a casing housing the impeller. The centrifugal compressor is, for example, the compressor 10 described above. The impeller is, for example, the impeller 200 described above. The casing is, for example, the casing 100 described above. Specifically, the impeller has a hub having a meridional plane, a plurality of blades provided on the meridional plane, and a shroud provided at the tips of the plurality of blades so as to cover the meridional plane. The meridional plane is, for example, the meridional plane 211 described above. The hub is, for example, the hub 210 described above. The blades are, for example, the blades 220 described above. The shroud is, for example, the shroud 230 described above. More specifically, the shroud is provided with a first passage that penetrates between an inner surface facing the meridional plane and an outer surface facing the inner surface of the casing, and has a first opening on the outer surface side and a second opening on the inner surface side. The first opening is, for example, the opening 235B described above. The second opening is, for example, the opening 235A described above. The first passage is, for example, the through hole 235 described above. The first passage is inclined such that, in a cross-section including the axis of rotation of the impeller, the center of the first opening is located on the inlet side of the impeller than the center of the second opening. The rotation axis is, for example, the rotation axis 250 described above. The axis is, for example, the axis AX described above. The center of the first opening is, for example, the center 235Bc described above. The center of the second opening is, for example, the center 235Ac described above. The inlet is, for example, the inlet 200in described above.

[0222] As a result, the centrifugal compressor can, for example, allow a portion of the fluid passing through the impeller to flow into the gap between the shroud and the casing through a first passage, and circulate the fluid back to the impeller inlet through that gap. Therefore, while the peak efficiency of the impeller may decrease slightly, the centrifugal compressor can suppress the upward slope of the pressure-flow characteristic by increasing the work coefficient (i.e., impeller work) on the high-pressure, low-flow side. Consequently, the centrifugal compressor can achieve an expanded operating range (so-called wide-range operation). Furthermore, the centrifugal compressor can suppress mild surges caused by the upward slope of the pressure-flow characteristic, as well as the generation of humming noise associated with mild surges. In addition, the centrifugal compressor can circulate fluid from the impeller outlet to the impeller through, for example, the gap between the shroud and the casing, and the first passage. Therefore, the centrifugal compressor can suppress wakes near the impeller outlet. Thus, the centrifugal compressor can improve the performance of closed impellers.

[0223] Furthermore, in a second aspect of this embodiment, based on the first aspect described above, the plurality of blades include a first blade and a second blade adjacent to the first blade on the front side in the rotational direction of the impeller. The first blade is, for example, the blade 220a described above. The rotational direction is, for example, the rotational direction RT described above. The second blade is, for example, the blade 220b described above. Specifically, starting from one end of the first blade on the inlet side, and on a line segment that makes the minimum distance between it and the second blade, a first virtual point is defined as a point 40 percent of the length of the line segment from one end of the first blade, and a second virtual point is defined as a point 60 percent of the length of the line segment from one end of the first blade. The second opening may be located between a first virtual line extending circumferentially through the first virtual point and a second virtual line extending circumferentially through the second virtual point. The inlet end of the first blade is, for example, the virtual point Ps described above. The line segment is, for example, the throat 225 described above. The first virtual point is, for example, the virtual point P1 described above. The second virtual point is, for example, the virtual point P2 described above. The first virtual line is, for example, the virtual line VL1 described above. The second virtual line is, for example, the virtual line VL2 described above.

[0224] This allows the centrifugal compressor to optimize the flow rate circulated through the first passage to the impeller inlet, thereby appropriately suppressing the upward slope of the pressure-flow characteristic.

[0225] Furthermore, in a third aspect of this embodiment, based on the first or second aspect described above, a second passage may be formed by the inlet end of the shroud and the casing facing each other in the axial direction. The second passage is, for example, the space 110B described above. The second passage may be inclined toward the outlet side of the impeller, with respect to a direction perpendicular to the inner surface of the shroud, in a cross-section including the axis, from the outer surface to the inner surface of the shroud. The outlet is, for example, the outlet 200out described above.

[0226] As a result, the centrifugal compressor can return the circulating flow that flows into the gap between the shroud and the casing through the first passage back to the main fluid at the impeller inlet through the second passage. Furthermore, because the second passage is inclined toward the impeller outlet, the centrifugal compressor can suppress separation of the circulating flow and reduce pressure loss when the circulating flow merges with the main flow. In addition, because the second passage is inclined toward the impeller outlet, the centrifugal compressor can introduce the circulating flow into the main flow while retaining a component in the direction of the main flow, and as a result, the backflow phenomenon that occurs at the blade ends of the impeller can be suppressed.

[0227] Furthermore, in the fourth aspect of this embodiment, based on the third aspect described above, the inlet end of the shroud may be chamfered.

[0228] This makes it possible to suppress separation in the circulating flow and to suppress pressure loss due to the reduction in the effective cross-sectional area of ​​the flow path that occurs when separation occurs.

[0229] Furthermore, in a fifth aspect of this embodiment, based on the third or fourth aspect described above, the axial width of the second passage may narrow from the outer surface side to the inner surface side of the shroud.

[0230] As a result, the centrifugal compressor has a second passage formed in a nozzle shape toward the main flow at the impeller inlet, which increases the dynamic pressure of the recirculated flow when it merges with the main flow. Therefore, the centrifugal compressor can enhance its ability to suppress the backflow phenomenon that occurs at the ends of the impeller blades.

[0231] Furthermore, in the sixth aspect of this embodiment, assuming any one of the third to fifth aspects described above, the inner diameter of the inlet end of the shroud may be smaller than the inner diameter of the casing at a location axially opposite to the inlet end of the shroud. The inner diameter of the inlet end of the shroud is, for example, the inner diameter D2 described above. The inner diameter of the casing at a location axially opposite to the inlet end of the shroud is, for example, the inner diameter D1 described above.

[0232] As a result, the centrifugal compressor has a bell-mouth-shaped flow path near the impeller inlet, which allows the main flow to be accelerated at the impeller inlet. Therefore, the centrifugal compressor can merge the circulating flow from the second passage into the main flow's acceleration region, thereby promoting the mixing of the main flow and the circulating flow and suppressing losses caused by interference between the two flows.

[0233] Furthermore, in the seventh aspect of this embodiment, assuming any one of the first to sixth aspects described above, the multiple blades do not need to have their shroud-side tip portions overlap with the second opening.

[0234] This allows the centrifugal compressor to enlarge the flow path cross-sectional area of ​​the first passage and increase the flow path for the circulating flow.

[0235] Furthermore, in the eighth aspect of this embodiment, based on any one of the first to seventh aspects described above, a sealing portion may be provided between the outer surface of the shroud and the casing. The sealing portion is, for example, the sealing member 240 described above.

[0236] This allows the centrifugal compressor to guide, for example, fluid flowing into the gap between the shroud and the casing through the first passage towards the impeller inlet. Furthermore, the centrifugal compressor can guide fluid flowing from the impeller outlet into the gap between the shroud and the casing through the first passage.

[0237] Furthermore, for example, if the opening on the outer surface of the shroud in the first passage (the first opening) is positioned closer to the impeller outlet in the axial direction, it may become necessary to position the seal at a location where the expansion rate of the shroud's outer diameter along the axial direction is relatively large. In this case, the gap between the seal and the outer surface of the shroud increases, which can lead to increased leakage of fluid flowing into the space between the shroud and the casing to the opposite side of the seal, potentially resulting in a decrease in the efficiency of the centrifugal compressor. In addition, modifications to the shape of the outer surface of the shroud may be necessary to reduce the gap between the seal and the outer surface of the shroud, which may result in increased impeller inertia and increased costs.

[0238] In contrast, in this embodiment, as described above, since the first passage is inclined toward the impeller inlet, the position of the opening on the outer surface of the first passage (the first opening) can be positioned closer to the impeller inlet in the axial direction. As a result, the seal portion can be positioned closer to the impeller inlet in the axial direction, and consequently, it becomes less likely that the seal portion will be positioned in a location where the expansion rate of the outer diameter of the shroud along the axial direction is relatively large. Therefore, the centrifugal compressor can suppress problems such as decreased efficiency due to increased leakage of fluid flowing into the gap between the shroud and the casing to the opposite side of the seal portion, increased impeller inertia, and increased costs.

[0239] Furthermore, in the ninth aspect of this embodiment, based on the eighth aspect described above, the first opening may be provided on the inlet side of the sealing portion.

[0240] This allows the centrifugal compressor to circulate the fluid flowing into the gap between the shroud and the casing through the first passage towards the impeller inlet. As a result, the centrifugal compressor can suppress the upward slope of the pressure-flow characteristic, thereby suppressing mild surges and reducing the generation of humming noise.

[0241] Furthermore, in the tenth aspect of this embodiment, based on any one of the first to ninth aspects described above, the first passage may be provided to extend in the circumferential direction. Alternatively, the first passage may be provided in only a part of the entire circumferential direction.

[0242] This allows the centrifugal compressor to increase the flow path cross-sectional area of ​​the first passage. Furthermore, by providing the first passage in only a portion of the circumferential direction, the centrifugal compressor can prevent the shroud from being divided by the first passage, which would reduce the eigenvalues, and ensure appropriate impeller blade vibration intensity.

[0243] Furthermore, in the eleventh aspect of this embodiment, a second passage may be formed by the inlet end of the shroud and the casing facing each other in the axial direction along the axis, based on any one of the first to tenth aspects described above. Also, a third passage communicating with the first passage and the second passage may be formed between the outer surface of the shroud and the inner surface of the casing. The third passage is, for example, space 110A. In the second passage or the third passage, the inner surface of the casing may have projections extending in a direction perpendicular to the circumferential direction, grooves extending in a direction perpendicular to the circumferential direction, or a rough surface rougher than the inner surface of the shroud. The inner surface of the casing is, for example, the inner surface 100B described above. The projections are, for example, the projections 114 and 115 described above. The grooves are, for example, the groove portion 113 described above.

[0244] This allows the centrifugal compressor to reduce the swirling component (i.e., the circumferential velocity component) of the fluid flow into the gap between the casing and the shroud through the first passage. As a result, the centrifugal compressor can prevent a situation where the effect of the pressure increase on the impeller due to the circulating flow is diminished by the influence of the swirling component in the circulating flow.

[0245] Furthermore, in the twelfth embodiment of this embodiment, based on the eighth embodiment described above, the first opening may be provided on the outlet side of the impeller rather than the sealing portion.

[0246] This allows the centrifugal compressor to circulate a portion of the fluid at the impeller outlet by allowing fluid to flow from the impeller outlet side into the gap between the casing and the shroud, and then through the first passage into the main flow of the impeller. As a result, the centrifugal compressor can suppress wake near the impeller outlet.

[0247] Furthermore, in a thirteenth embodiment of this embodiment, based on any one of the first to twelfth embodiments described above, the centrifugal compressor may include a first compression section for compressing the incoming fluid, and a second compression section into which the fluid discharged from the first compression section flows and compresses the fluid. The first compression section may include another impeller having another shroud without the first passage, and the second compression section may include the impeller having the shroud with the first passage.

[0248] As a result, by providing the first passage only in the downstream compression section where mild surges are likely to occur, the centrifugal compressor can balance the suppression of mild surges through high pressure and wide pressure range in the low flow rate region with efficiency.

[0249] Furthermore, in the 14th aspect of this embodiment, the refrigeration system may include a centrifugal compressor of any one of the first to 13 aspects described above. The refrigeration system is, for example, the refrigeration system 1 described above.

[0250] This makes it possible to improve the performance of the closed impeller of the centrifugal compressor installed in the refrigeration system.

[0251] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims.

[0252] Finally, this application claims priority based on Japanese Patent Application No. 2024-161492, filed on 18 September 2024, and the entire contents of the Japanese Patent Application are incorporated herein by reference.

[0253] 1 Refrigeration unit 10 Compressor 20 Heat exchanger 30 Expansion mechanism 40 Heat exchanger 100 Casing 100A Inner surface 100B Inner surface 100C Stepped surface 100D Curved surface 110 Impeller chamber 110A Space 110B Space 110C Space 111 Diffuser 113 Groove 114 Projection 115 Projection 120 Intake pipe 130 Discharge pipe 140 Motor chamber 200 Impeller 200in Inlet 200out Outlet 210 Hub 211 Meridian plane 220 Blade 220a Blade 220b Blade 225 Throat 230 Shroud 230A End face 235 Through hole 235A Opening 235Ac Center 235B Opening 235Bc Center 236 Connecting part 240 Seal member 250 Rotating shaft 260 Collar 300 Motor 310 Rotor 320 Stator 400 Radial magnetic bearing 500 Thrust magnetic bearing 510 Electromagnet 600 Touchdown bearing AX Axis center D1 Inner diameter D2 Inner diameter P0 Center P1 Virtual point P2 Virtual point Pe Virtual point Ps Virtual point t1 Width t2 Width VL0 Virtual line VL1 Virtual line VL2 Virtual line θ1 Inclination angle θ2 Inclination angle θ3 Inclination angle θ4 Inclination angle

Claims

Impeller (200), The device comprises a casing (100) that houses the impeller (200), The impeller (200) is A hub (210) having a meridional plane (211), A plurality of blades (220) are provided on the meridional plane (211), The system includes a shroud (230) provided at the tip of the plurality of blades (220) so as to cover the meridional plane (211), The shroud (230) is provided with a first passage (235) that penetrates between the inner surface facing the meridional plane (211) and the outer surface facing the inner surface of the casing (100), and has a first opening (235B) on the outer surface side and a second opening (235A) on the inner surface side. In a cross-section including the axis (AX) of the rotation axis (250) of the impeller (200), the first passage (235) is inclined such that the center (235Bc) of the first opening (235B) is located closer to the inlet (200in) of the impeller (200) than the center (235Ac) of the second opening (235A). Centrifugal compressor. 　 The plurality of blades (220) are, The first blade (220a) and The impeller (200) has a first blade (220a) and a second blade (220b) adjacent to the front side in the rotational direction (RT) of the impeller (200), Starting from one end (Ps) of the first blade (220a) on the inlet (200in) side, and considering the line segment (225) that makes the minimum distance between it and the second blade (220b), the first virtual point (P1) is defined as a point 40 percent of the length of the line segment away from the end on the first blade (220a) side, and the second virtual point (P2) is defined as a point 60 percent of the length of the line segment (225) away from the end on the first blade (220a) side. The second opening (235A) is located between a first virtual line (VL1) extending circumferentially through the first virtual point (P1) and a second virtual line (VL2) extending circumferentially through the second virtual point (P2). The centrifugal compressor according to claim 1. 　 The end of the shroud (230) on the inlet (200 in) side and the casing (100) face each other in the axial direction, thereby forming a second passage (110B). The second passage (110B), in a cross-section including the axis (AX), is inclined toward the outlet (200out) side of the impeller (200) with respect to a direction perpendicular to the inner surface of the shroud (230), with respect to the direction perpendicular to the inner surface of the shroud (230). A centrifugal compressor according to claim 1 or 2. 　 The end of the shroud (230) on the inlet (200 in) side is chamfered. The centrifugal compressor according to claim 3. 　 The axial width of the second passage (110B) narrows from the outer side to the inner side of the shroud (230). The centrifugal compressor according to claim 3 or 4. 　 The inner diameter (D2) of the inlet (200in) end of the shroud (230) is smaller than the inner diameter (D1) of the casing (100) at the location axially opposite to the inlet (200in) end of the shroud (230). A centrifugal compressor according to any one of claims 3 to 5. 　 The plurality of blades (220) are arranged such that the tip portion on the shroud (230) side does not overlap with the second opening (235A). A centrifugal compressor according to any one of claims 1 to 6. 　 A sealing portion (240) is provided between the outer surface of the shroud (230) and the casing (100). A centrifugal compressor according to any one of claims 1 to 7. 　 The first opening (235B) is provided on the inlet (200in) side of the sealing portion (240). The centrifugal compressor according to claim 8. 　 The first passage (235) is provided so as to extend in the circumferential direction. A centrifugal compressor according to any one of claims 1 to 9. 　 The end of the shroud (230) on the inlet (200 in) side and the casing (100) face each other in the axial direction along the axis (AX), thereby forming a second passage (110B). A third passage (110A) is formed between the outer surface of the shroud (230) and the inner surface of the casing (100), communicating with the first passage (235) and the second passage (110B). In the second passage (110B) or the third passage (110A), the inner surface of the casing (100) has projections (114, 115) extending in a direction perpendicular to the circumferential direction, grooves (113) extending in a direction perpendicular to the circumferential direction, or a rough surface rougher than the inner surface of the shroud (230). A centrifugal compressor according to any one of claims 1 to 10. 　 The first opening (235B) is provided on the outlet (200out) side of the impeller (200) than the sealing portion (240). The centrifugal compressor according to claim 8. A first compression section that compresses the incoming fluid, The system includes a second compression section into which the fluid discharged from the first compression section flows and compresses the fluid, The first compression section includes another impeller having another shroud in which the first passage (235) is not provided, The second compression section includes the impeller (200) having the shroud (230) through which the first passage (235) is provided. A centrifugal compressor according to any one of claims 1 to 12. 　 A centrifugal compressor (10) according to any one of claims 1 to 13, Refrigeration equipment.

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