Centrifugal compressor

Abstract

The purpose of the present invention is to suppress leakage flow in a gap between the tip of a blade and a housing. A centrifugal compressor is provided with: an open impeller having a hub and blades provided on the outer periphery of the hub; a drive shaft connected to the impeller, and a bearing supporting the drive shaft; and a housing covering the impeller, in which a movable range of the drive shaft with respect to a radial direction of the bearing is larger than a movable range of the drive shaft with respect to an axial direction of the bearing, and a first gap between an outer peripheral edge of the blade on a gas inlet side and an inner wall of the housing is larger than a second gap between an outer peripheral edge of the blade on a gas outlet side and the inner wall of the housing.

Description

Technical Field

[0001] This invention relates to a centrifugal compressor. Background Technology

[0002] For example, a refrigeration unit used in an air conditioning system includes a compressor, a condenser, an expansion valve, and an evaporator. Patent Document 1 discloses a centrifugal compressor as a compressor. The centrifugal compressor described in Patent Document 1 includes a rotor having a hub and blades, and a housing surrounding the rotor.

[0003] <Prior art documents>

[0004] <Patent Documents>

[0005] Patent Document 1: International Publication No. 2018 / 146752 Summary of the Invention

[0006] <Problem to be solved by this invention>

[0007] During the operation of a centrifugal compressor, a leakage flow occurs, where gas flows from the high-pressure side to the low-pressure side through the gap between the blade tip and the housing. This leakage flow reduces the operating efficiency of the centrifugal compressor. The object of this invention is to provide a centrifugal compressor capable of suppressing the leakage flow in the gap between the blade tip and the housing.

[0008] <Methods for solving problems>

[0009] One aspect of the present invention relates to a centrifugal compressor comprising: an open impeller having a hub and blades disposed on the outer periphery of the hub; a rotating shaft connected to the impeller; a bearing supporting the rotating shaft; and a housing covering the impeller, wherein the radial movable range of the rotating shaft relative to the bearing is greater than the axial movable range of the rotating shaft relative to the bearing, and a first gap between the outer periphery of the gas inlet side of the blades and the inner wall of the housing is greater than a second gap between the outer periphery of the gas outlet side of the blades and the inner wall of the housing.

[0010] In this centrifugal compressor, the second gap between the outer periphery of the blade on the gas outlet side and the inner wall of the casing is narrower than the first gap between the outer periphery of the blade on the gas inlet side and the inner wall of the casing. In this centrifugal compressor, in the gas flow direction, a second gap narrower than the first gap on the inlet side (lower pressure) is formed on the outlet side (higher pressure). Therefore, leakage flow in the gap between the outer periphery of the blade and the casing can be suppressed on the outlet side (higher pressure).

[0011] In a centrifugal compressor according to one aspect of the present invention, the minimum point of the blade angle exists in the rear half of the blade.

[0012] In this centrifugal compressor, the blade load is high at the point where the blade angle is at its minimum. In the portion of the blade with high load, the pressure difference between the positive and negative pressure surfaces of the blade is large. In this centrifugal compressor, the pressure difference between the positive and negative pressure surfaces of the blade is also large in the rear half of the blade.

[0013] In a centrifugal compressor according to one aspect of the present invention, the minimum point of the blade angle exists at a position where the length m relative to the meridional plane is more than 0.6m and less than 1.0m.

[0014] In addition, the so-called "meridian length" is the length specified on the meridional plane (a diagram in which the shape of the blade after being rotated and projected about the axis of rotation is superimposed in a section along the axis of rotation).

[0015] In a centrifugal compressor according to one aspect of the present invention, when the direction perpendicular to the meridional length m along the blade direction is defined as the span direction, and the length from the outer peripheral surface of the hub to the outer peripheral edge of the blade in the span direction is defined as the span length s, the minimum point of the blade angle may exist in the rear half of the blade at a position that is 0.5s or more relative to the span length s.

[0016] In a centrifugal compressor according to one aspect of the present invention, the minimum point of the blade angle may also exist in the rear half of the blade at a position with a span length s of 0.9s or more.

[0017] In a centrifugal compressor according to one aspect of the present invention, the bearing may be an air bearing, a foil bearing, a controlled magnetic bearing, a rolling bearing, or a sliding bearing.

[0018] In a centrifugal compressor according to one aspect of the present invention, the bearing is a control type magnetic bearing, which can control the position of the rotating shaft such that the radial distance of the rotating shaft to the landing point is greater than the axial distance of the rotating shaft to the landing point.

[0019] In a centrifugal compressor according to one aspect of the present invention, the distance of the first gap can be more than twice the distance of the second gap.

[0020] In a centrifugal compressor according to one aspect of the present invention, the impeller rotation speed can be 30,000 rpm or higher. Attached Figure Description

[0021] Figure 1 This is a schematic diagram showing a refrigeration machine equipped with a centrifugal compressor according to one embodiment.

[0022] Figure 2 This is a schematic diagram illustrating a centrifugal compressor according to one embodiment.

[0023] Figure 3 This is a side view of the impeller.

[0024] Figure 4 This is a longitudinal sectional view showing the gap between the outer periphery of the impeller and the inner wall of the casing.

[0025] Figure 5 It is a graph showing the relationship between the meridional plane length and the blade angle.

[0026] Figure 6 It is a diagram showing the outer periphery of the impeller and the length of the meridional plane.

[0027] Figure 7 It is a graph showing the relationship between the meridional length and the hydrostatic coefficient.

[0028] Figure 8 It is a graph showing the relationship between meridional length and static pressure.

[0029] Figure 9 This is a schematic diagram illustrating a centrifugal compressor according to one embodiment.

[0030] Figure 10 It is a diagram that superimposes the shape of the blade onto a cross section along the rotation axis C1, showing the shape after rotating and projecting it around the rotation axis C1. Detailed Implementation

[0031] Referring to the accompanying drawings, non-limiting embodiments of the present invention will be described. Furthermore, in the drawings, identical or corresponding components or parts are labeled with identical or corresponding reference numerals. Additionally, repeated descriptions of identical or corresponding components or parts will be omitted below. Furthermore, in the drawings, components or parts are not necessarily drawn to scale. Therefore, those skilled in the art can arbitrarily determine specific dimensions by referring to the following non-limiting embodiments. Furthermore, the following embodiments are for illustrative purposes and are not intended to limit the invention. Moreover, the features and combinations thereof described in the embodiments are not necessarily the essential content of the invention.

[0032] [Overview of the refrigeration machine involved in the implementation]

[0033] Reference Figure 1 The refrigeration unit 100 equipped with the centrifugal compressor described in the embodiments will be described. Figure 1 The refrigeration unit 100 shown can be used, for example, in air conditioning units, refrigeration equipment, and cold storage equipment. The refrigeration unit 100 can also be used in other equipment. The refrigeration unit 100 performs a refrigeration cycle. The refrigeration cycle of the refrigeration unit 100 is a vapor compression refrigeration cycle. The refrigeration unit 100 includes a centrifugal compressor 10, a condenser 20, an expansion valve 30, and an evaporator 40. The centrifugal compressor 10 is a turbo compressor.

[0034] The refrigerant used as the working fluid in the refrigeration unit 100 is not particularly limited. The centrifugal compressor 10 compresses the refrigerant gas. The condenser 20 condenses the refrigerant gas compressed by the centrifugal compressor 10. The expansion valve 30 expands the refrigerant condensed in the condenser 20. The evaporator 40 evaporates the refrigerant expanded by the expansion valve 30. The refrigerant gas evaporated in the evaporator 40 is then drawn into the centrifugal compressor 10.

[0035] Centrifugal compressor 10 performs reversible adiabatic compression on the refrigerant gas. The refrigerant gas supplied to condenser 20 dissipates heat and liquefies under constant pressure. The liquefied refrigerant irreversibly expands at constant enthalpy in expansion valve 30, and a portion of the refrigerant evaporates. The refrigerant absorbs heat under constant pressure in evaporator 40.

[0036] The refrigeration unit 100 includes piping L11 to L14 for refrigerant flow. Piping L11 is the suction pipe connecting the evaporator 40 to the centrifugal compressor 10. Piping L12 connects the centrifugal compressor 10 to the condenser 20. Piping L13 connects the condenser 20 to the expansion valve 30. Piping L14 connects the expansion valve 30 to the evaporator 40.

[0037] Refrigerant gas flows through pipe L11 and is drawn into centrifugal compressor 10. After being compressed in centrifugal compressor 10, the refrigerant gas flows through pipe L12 and is supplied to condenser 20. After being liquefied in condenser 20, the refrigerant liquid flows through pipe L13 and into expansion valve 30. After expanding in expansion valve 30, the refrigerant flows through pipe L14 and is supplied to evaporator 40. After absorbing heat in evaporator 40, the refrigerant gas flows through pipe L11 and is supplied to centrifugal compressor 10.

[0038] Centrifugal compressor

[0039] Next, the centrifugal compressor 10 will be described. The centrifugal compressor 10 is, for example, a two-stage compressor. The centrifugal compressor 10 can also be a single-stage compressor. Figure 2 As shown, the centrifugal compressor 10 includes a housing 11, impellers 12A and 12B, a drive shaft 13, bearings 14A and 14B, and a motor 50. The housing 11 houses the impellers 12A and 12B, the drive shaft 13, the bearings 14A and 14B, and the motor 50. The centrifugal compressor 10 has a back-to-back structure where the back surfaces of the impellers 12A and 12B face each other. Figure 9 As shown, the centrifugal compressor 10 may also have an in-line structure in which impellers 12A and 12B are connected in the same orientation.

[0040] The housing 11 includes: a compression chamber 11a housing an impeller 12A; a compression chamber 11b housing an impeller 12B; and a motor chamber 11c housing an electric motor 50. The centrifugal compressor 10 includes a piping L11B connecting the compression chambers 11a and 11b. The piping L11B supplies refrigerant gas ejected from the low-pressure side compression chamber 11a to the high-pressure side compression chamber 11b.

[0041] [Drive shaft]

[0042] Impellers 12A and 12B are disposed at both ends of the drive shaft 13. Impeller 12A is disposed at one end of the drive shaft 13, and impeller 12B is disposed at the other end of the drive shaft 13. Impellers 12A and 12B are axially separated on the drive shaft 13. The drive shaft 13 includes the rotating shaft of the motor 50. The rotating shaft of the motor 50 includes the portion of the drive shaft 13 between impellers 12A and 12B.

[0043] [Bearings]

[0044] Bearings 14A and 14B rotatably support the drive shaft 13. Bearings 14A and 14B are fixed to the housing 11. Bearings 14A, 14B, and 14C are radial bearings and thrust bearings, respectively. The centrifugal compressor 10 has multiple bearings 14A, 14B, and 14C. Bearings 14A, 14B, and 14C are, for example, oil-free bearings. Bearings 14A and 14B can be sliding bearings or rolling bearings. Bearings 14A, 14B, and 14C can also be hydrostatic bearings. Oil-free bearings are bearings that do not require lubrication. Examples of oil-free bearings include gas bearings, air bearings, foil bearings, and magnetic bearings.

[0045] Bearings 14A, 14B, and 14C can also be air bearings. Air bearings are a type of hydrostatic bearing; compressed air is blown between the drive shaft 13 and the bearing surface, causing the drive shaft 13 to float and support the load. Bearings 14A and 14B can also be gas bearings that cause the drive shaft 13 to float by blowing compressed gas between it and the bearing surface. Gas bearings can be those that use refrigerant gas as compressed gas to blow onto the drive shaft 13, causing it to float.

[0046] Bearings 14A, 14B, and 14C can also be foil bearings, a type of pneumatic bearing. Foil bearings have a thin film (foil) as the bearing surface. The film has low stiffness to bending and is flexible. Foil bearings support loads by allowing the foil to flex. During rotation of the drive shaft 13, a fluid film (air film) is formed between the drive shaft 13 and the bearing surface, which is the foil. The foil bearing uses the foil and the fluid film to support the drive shaft 13. Due to the flexibility of the foil, the foil bearing can form a bearing clearance corresponding to the rotational speed of the drive shaft 13, the load on the drive shaft 13, the ambient temperature of the drive shaft 13, and other operating conditions.

[0047] Bearings 14A, 14B, and 14C can also be magnetic bearings that support the rotating shaft using magnetic attraction or repulsion. Bearings 14A, 14B, and 14C can also be active magnetic bearings (AMB). In active magnetic bearings, for example, bearings 14A and 14B can be radial magnetic bearings, and bearing 14C can be a thrust magnetic bearing. The radial magnetic bearing includes an electromagnet disposed around the drive shaft 13. The electromagnet has an iron core and a coil. The thrust magnetic bearing includes an axial disk extending radially outward from the drive shaft 13, and an electromagnet disposed axially opposite the axial disk.

[0048] The type, location, and quantity of bearings 14A, 14B, and 14C are not limited to those described above. The centrifugal compressor 10 may also include a touch-down bearing. The touch-down bearing is also called an auxiliary bearing or a backup bearing. The touch-down bearing limits the range of motion of the drive shaft 13. The touch-down bearing can limit the radial range of motion of the drive shaft 13. The touch-down bearing can limit the axial range of motion of the drive shaft 13. The touch-down bearing allows the stator and rotor to not contact each other. The touch-down bearing can support the drive shaft 13 even when the magnetic bearing is not energized.

[0049] The control-type magnetic bearing can control the position of the drive shaft 13, ensuring that the radial distance from the drive shaft 13 to the landing bearing is greater than the axial distance from the drive shaft 13 to the landing bearing. The distance to the landing bearing can be the distance from the drive shaft 13 to the landing bearing until they make contact. It can also be the movable range of the drive shaft 13, or its maximum movable range.

[0050] The centrifugal compressor 10 may also include a control unit 70 capable of controlling the movable range of the drive shaft 13. The control unit 70 can control the current supplied to the coils of the bearings 14A, 14B, and 14C, which are control-type magnetic bearings. By controlling the current supplied to the coils, the control unit 70 can control both the radial and axial movable range of the drive shaft 13. The control unit 70 can control the position of the drive shaft 13 such that its radial movable range is greater than its axial movable range.

[0051] [Electric motor]

[0052] The electric motor 50 is the drive source for the centrifugal compressor 10. The electric motor 50 has a rotor 51 and a stator 52. The rotor 51 is fixed to the drive shaft 13 and rotates together with the drive shaft 13. The stator 52 is fixed to the housing 11 and is arranged around the rotor 51.

[0053] The refrigerator 100 includes an inverter 60. The inverter 60 controls the speed of the motor 50. The inverter 60 is a controller that controls the operating frequency of the motor 50. The speeds of the impellers 12A and 12B and the drive shaft 13 can be above 30,000 rpm. By controlling the operating frequency of the motor 50, the inverter 60 can change the speeds of the impellers 12A and 12B and the drive shaft 13.

[0054] The impellers 12A and 12B of the centrifugal compressor 10 rotate under the rotational driving force of the electric motor 50. The refrigerant gas is compressed by the rotation of the impellers 12A and 12B. Impeller 12A is the low-pressure side impeller, and impeller 12B is the high-pressure side impeller. The refrigerant gas compressed by impeller 12A is supplied to impeller 12B. Impeller 12B further compresses the refrigerant gas discharged from impeller 12A.

[0055] [Control Department]

[0056] The control unit 70 includes a CPU 71 and a storage unit 72. The CPU (Center Processing Unit) 71 manages the overall processing in the refrigerator 100. The CPU 71 can control the speed of the motor 50 via the inverter 60. The CPU 71 can also control the opening and closing of the expansion valve 30.

[0057] The storage unit 72 includes a ROM (Read Only Memory) 73 and a RAM (Random Access Memory) 74. The ROM 73 stores various programs used by the CPU 71 to perform control processing, as well as various data required for the operation of the refrigerator 100. The RAM 74 can temporarily store data obtained from various sensors.

[0058] [impeller]

[0059] Next, the impeller 12A will be described. Impeller 12A is as follows... Figure 3 As shown, it has a hub 121 and blades 122 disposed on the outer periphery of the hub 121. The hub 121 is connected to the end of the drive shaft 13.

[0060] The hub 121 has a generally conical shape that expands in diameter from its front to its rear. The hub 121 rotates integrally with the drive shaft 13. From a weight reduction point of view, the inner side of the hub 121, except for the axle periphery and outer edge, can also be hollow.

[0061] Blade 122 extends radially outward from the outer circumferential surface of hub 121. Blade 122 is arranged in a spiral shape along the outer circumferential surface of hub 121. Impeller 12B is the same as impeller 12A, and its description is omitted here.

[0062] [Range of movement of the drive shaft]

[0063] Next, the movable range of the drive shaft 13 will be explained. In the centrifugal compressor 10, the radial movable range of the drive shaft 13 is greater than its axial movable range. The radial movable range of the drive shaft 13 relative to bearings 14A, 14B, and 14C is greater than its axial movable range relative to bearings 14A, 14B, and 14C. For example, the movable range of the drive shaft 13 can be the actual movable range of the drive shaft 13, or it can be the movable range of the impellers 12A and 12B connected to the drive shaft 13. The movable range of the drive shaft 13 can also be the movable range of the rotor 51 fixed to the drive shaft 13. The movable range of the drive shaft 13 can be the movable range at any point, or it can be the average value of multiple points.

[0064] [The gap between the impeller blades and the inner wall of the casing]

[0065] Next, refer to Figure 4 The gap between the blades 122 of the impellers 12A and 12B and the inner wall 15 of the housing 11 will be explained. Figure 4 It is a longitudinal sectional view showing the gap between the outer periphery 123 of the impellers 12A and 12B and the inner wall 15 of the housing 11, including the meridional section of the impellers 12A and 12B.

[0066] The blade end clearance t1 between the outer periphery 123a of the gas inlet side of blade 122 and the inner wall 15 of housing 11 is greater than the blade end clearance t2 between the outer periphery 123b of the gas outlet side of blade 122 and the inner wall 15 of housing 11. Blade end clearance t1 is an example of the first clearance. Blade end clearance t2 is an example of the second clearance.

[0067] The outer peripheral edges 123a and 123b are the leading edges of the blade 122. The outer peripheral edges 123a and 123b are located radially away from the outer peripheral surface of the hub 121 of the impellers 12A and 12B. The outer peripheral edges 123a and 123b are the radial ends of the impellers 12A and 12B.

[0068] The gas inlet side is the small diameter side of the hub 121, and the gas outlet side is the large diameter side of the hub 121. The small diameter side of the hub 121 is the side away from the motor 50 in the axial direction of the drive shaft 13, and the large diameter side of the hub 121 is the side closer to the motor 50 in the axial direction of the drive shaft 13.

[0069] The blade tip clearance t1 on the gas inlet side can be more than twice the blade tip clearance t2 on the gas outlet side. The blade tip clearance t1 on the gas inlet side can also be the blade tip clearance at a position near the leading edge 122a of the gas inlet, or it can be the blade tip clearance located axially behind the leading edge 122a. The blade tip clearance t1 can also be the position where the blade tip clearance is at its maximum. The blade tip clearance can also be the distance between the curve representing the shape of the outer periphery 123 and the curve representing the shape of the inner wall 15 of the housing 11 in a cross-section along the axial direction of the impellers 12A and 12B. For example, the blade tip clearance can also be the length along the normal to the curve representing the shape of the outer periphery 123.

[0070] The blade tip clearance t2 on the gas outlet side can be the blade tip clearance located near the trailing edge 122b of the gas outlet, or it can be the blade tip clearance located axially forward of the trailing edge 122b. The blade tip clearance t2 on the gas outlet side can also be the position where the blade tip clearance is minimum. The blade tip clearance t2 on the gas outlet side can also be the blade tip clearance located at a position 0.5m or more and 1.0m or less relative to the meridional length m (described later). Furthermore, 0.5m and 1.0m refer to lengths of 0.5 times and 1.0 times the meridional length m, respectively. The blade tip clearance t2 can also be the blade tip clearance located at a position 0.6m or more and 1.0m or less relative to the meridional length m, or it can be the blade tip clearance located at a position 0.75m or more and 0.95m or less relative to the meridional length m, for example, 0.8m, or it can be the blade tip clearance located at a position 0.9m or less relative to the meridional length m.

[0071] [Relationship between meridional plane length and blade angle]

[0072] Next, the relationship between the length of the meridional plane and the blade angle will be explained. Figure 5 This is a graph showing the relationship between meridional length and blade angle. Figure 5 In the diagram, the horizontal axis represents the normalized meridional length, and the vertical axis represents the blade angle. The "meridional length" is a diagram of the blade shape projected around the axis of rotation C1 onto a cross-section along the meridional plane (see reference...). Figure 10 The length specified on the axis of rotation. The axis of rotation C1 is the axis of rotation of the drive shaft 13, and the axis of rotation of the impellers 12A and 12B. The blade shape refers to the shape along the outer periphery of the blade 122.

[0073] In addition, Figure 5The horizontal axis shown represents the proportions (normalized values) when the total length of the meridional plane is set to "m". "0" represents the length equivalent to 0 times the meridional plane length m at the gas inlet side end, which is the position of the leading edge 122a of blade 122; "1" represents the length equivalent to 1 times the meridional plane length m at the gas outlet side end, which is the position of the trailing edge 122b of blade 122. In the following... Figures 6-9 The same applies to China.

[0074] The minimum point βmin of the blade angle β of blade 122 is the value of the blade angle located in the latter half of the meridional length m of blade 122. The latter half of the meridional length m refers to the portion above 0.5m and below 1.0m. The minimum point βmin of the blade angle β can also be located above 0.6m and below 1.0m. The minimum point βmin of the blade angle β can also be located above 0.75m and below 0.95m. For example, the minimum point βmin of the blade angle β can be 0.8m or 0.9m.

[0075] The blade angle β is represented by the following formula (1).

[0076] tanβ=rdθ / dm··· (1)

[0077] like Figure 6 As shown, "r" is the radial length from the rotation axis (center) C1 of impellers 12A and 12B to the outer periphery 123 of blade 122. "θ" is the angle between the radial line segment connecting the outer periphery 123a and the rotation axis C1 when viewed along the rotation axis C1, and the radial line segment connecting any point J on the outer periphery 123 to the rotation axis C1. "m" is the meridional length.

[0078] [Relationship between meridional length, hydrostatic coefficient, and hydrostatic pressure]

[0079] Figure 7 This is a graph showing the relationship between meridional length and hydrostatic coefficient. Figure 7 In the diagram, the horizontal axis represents the normalized meridional length m, and the vertical axis represents the hydrostatic coefficient. Figure 7 The static pressure coefficient P1 of the positive pressure surface of blade 122 and the static pressure coefficient P2 of the negative pressure surface of blade 122 are shown in the figure. Figure 8 This is a graph showing the relationship between hydrostatic pressure distribution and meridional length. Figure 8 In the diagram, the horizontal axis represents the normalized meridional length in meters (m), and the vertical axis represents static pressure. Figure 8 The static pressure P3 on the positive pressure surface of blade 122 and the static pressure P4 on the negative pressure surface of blade 122 are shown in the figure.

[0080] like Figure 7As shown, in impellers 12A and 12B, ΔP1 (=P1-P2) reaches its maximum when the value of the horizontal axis is approximately 0.85. Furthermore, as... Figure 8 As shown, in impellers 12A and 12B, ΔP2 (=P3-P4) reaches its maximum when the value of the horizontal axis is approximately 0.85. Since ΔP1 and ΔP2 are small in the part with large blade tip clearance (near the value of the horizontal axis is 0), and large in the part with small blade tip clearance (near the value of the horizontal axis is 0.85), blade tip leakage loss can be reduced.

[0081] [Wingspan Direction S]

[0082] Next, we will explain the wingspan direction S. Figure 10 This is a diagram superimposed on a section along the rotation axis C1, showing the shape of the blade after rotation and projection around C1. The wingspan direction S is orthogonal to the direction along the meridional plane length m, and is along the blade 122. "Wingspan length s" is the length along the wingspan direction S from the outer peripheral surface 124 of the hub 121 to the outer peripheral edge 123 of the blade 122. The position where the wingspan length s is 0 in the wingspan direction S is on the outer peripheral surface 124 of the hub 121. The position where the wingspan length s is 1 in the wingspan direction S is on the outer peripheral edge 123. The position where the wingspan length s is 0.5s in the wingspan direction S is the midpoint between the outer peripheral surface 124 of the hub 121 and the outer peripheral edge 123. Positions where the wingspan length s exceeds 0.5s are positions closer to the outer peripheral edge 123 than the position of 0.5s.

[0083] [The relationship between wingspan s and the minimum point of blade angle]

[0084] As described above, the minimum point βmin of the blade angle β of blade 122 exists in the latter half of the meridional length m of blade 122. The minimum point βmin of the blade angle β exists at a position greater than 0.5s relative to the wingspan length s. The minimum point βmin of the blade angle β can also exist at a position greater than 0.9s relative to the wingspan length s.

[0085] [Operation of a centrifugal compressor]

[0086] Refer again Figure 1 The operation of the centrifugal compressor 10 will be explained below. When the centrifugal compressor 10 is running, the electric motor 50 is energized. Power is supplied to the electric motor 50, driving the drive shaft 13 to rotate. The rotation of the drive shaft 13 causes the impellers 12A and 12B to rotate.

[0087] Refrigerant gas flows from pipe L11 into compression chamber 11a through the rotation of impeller 12A. The refrigerant gas in compression chamber 11a is compressed and pressurized by the rotation of impeller 12A. The refrigerant gas flowing into compression chamber 11a is compressed to, for example, an intermediate pressure. The refrigerant gas compressed to an intermediate pressure is then supplied to impeller 12B through pipe L11B.

[0088] The refrigerant gas in pipe L11B is drawn into compression chamber 11b as impeller 12B rotates. The refrigerant gas in compression chamber 11b is compressed and pressurized by the rotation of impeller 12B. The compressed refrigerant gas is then ejected into the interior of pipe L12. The refrigerant gas ejected from centrifugal compressor 10 flows through the interior of pipe L12 and into condenser 20.

[0089] [Effects of the centrifugal compressor described in the implementation method]

[0090] Centrifugal compressor 10 has such Figure 3 The open impellers 12A and 12B shown have a hub 121 and blades 122 disposed on the outer periphery of the hub 121, as shown in the figure. Figure 1 The drive shaft 13 connected to impellers 12A and 12B, the bearings 14A and 14B supporting the drive shaft 13, and the housing 11 covering the impellers 12A and 12B are shown. The radial movable range of the drive shaft 13 relative to the bearings 14A and 14B is greater than the radial movable range of the drive shaft 13 relative to the bearings 14A and 14B. Figure 4 As shown, the blade end gap t1 (first gap) between the outer periphery 123a of the gas inlet side of the blade 122 and the inner wall 15 of the housing 11 is greater than the blade end gap t2 (second gap) between the outer periphery 123b of the gas outlet side of the blade 122 and the inner wall 15 of the housing 11.

[0091] In this centrifugal compressor 10, the blade end clearance t2 between the outer periphery 123b of the blade 122 on the gas outlet side and the inner wall 15 of the housing 11 is narrower than the blade end clearance t1 between the outer periphery 123a of the blade 122 on the gas inlet side and the inner wall 15 of the housing 11. In this centrifugal compressor 10, in the gas flow direction, a blade end clearance t2 narrower than the blade end clearance t1 on the lower pressure inlet side is formed on the outlet side. Therefore, leakage flow in the blade end clearance t2 between the outer periphery 123b of the blade 122 and the inner wall 15 of the housing 11 can be suppressed on the higher pressure outlet side. By suppressing blade end leakage, the reduction in operating efficiency of the centrifugal compressor 10 can be suppressed.

[0092] In the centrifugal compressor 10, the minimum point of the blade angle β of the blade 122 exists in the latter half of the meridional length m of the blade 122. This centrifugal compressor 10 enables the realization of a compressor with an impeller having a blade load distribution type of the latter half of the load. In the centrifugal compressor 10, contact between the outer periphery 123a on the gas inlet side and the casing 11 can be suppressed, and leakage flow in the blade tip clearance can be reduced. The centrifugal compressor 10 achieves a balance between avoiding contact at the inlet blade tips and reducing blade tip leakage losses.

[0093] In the centrifugal compressor 10, the larger blade end clearance t1 on the gas inlet side can suppress fluid stripping on the negative pressure side and suppress surge. In addition, since impellers 12A and 12B are open impellers, they are easier to manufacture than closed impellers.

[0094] In the centrifugal compressor 10, the blade load is high at the point where the blade angle β is at its minimum. In the portion of the blade with high load, the pressure difference between the positive and negative pressure surfaces of blade 122 is large. In this type of centrifugal compressor 10, the pressure difference between the positive and negative pressure surfaces of blade 122 is large in the rear half of blade 122. The positive pressure surface is the surface with higher pressure in the thickness direction of blade 122, and the negative pressure surface is the surface with lower pressure.

[0095] In the centrifugal compressor 10, the minimum point of the blade angle β exists at a position that is more than 0.6m and less than 1.0m relative to the meridional length m.

[0096] In the centrifugal compressor 10, when the direction perpendicular to the meridional length m along the blade 122 is defined as the span direction S, and the length from the outer peripheral surface 124 of the hub 121 to the outer peripheral edge 123 of the blade 122 in the span direction S is defined as the span length s, the minimum point of the blade angle β exists in the rear half of the blade 122 at a position greater than or equal to the span length s. According to this structure, the centrifugal compressor 10 has a larger pressure difference between the positive and negative pressure surfaces of the blade 122 in the span direction S, at a position greater than or equal to the span length s. In such a centrifugal compressor 10, leakage flow in the gap between the leading edge of the blade 122 and the housing can be suppressed. As a result, the reduction in operating efficiency in the centrifugal compressor 10 can be suppressed.

[0097] Furthermore, in the centrifugal compressor 10, it can also be configured such that the minimum point of the blade angle β exists in the rear half of the blade 122 at a position with a span length s of 0.9s or more.

[0098] In the centrifugal compressor 10, bearings 14A, 14B, and 14C can also be air bearings. In the centrifugal compressor 10, bearings 14A, 14B, and 14C can also be foil bearings. In the centrifugal compressor 10, bearings 14A and 14B can also be control-type magnetic bearings. With such bearings 14A, 14B, and 14C, the centrifugal compressor 10 can support the drive shaft 13, which rotates at high speed. With bearings 14A and 14B, the maintenance of bearings 14A, 14B, and 14C can be reduced.

[0099] In the centrifugal compressor 10, bearings 14A, 14B, and 14C, which are control type magnetic bearings, can control the position of the drive shaft 13, so that the radial distance of the drive shaft 13 to the landing is greater than the axial distance of the drive shaft 13 to the landing.

[0100] In the centrifugal compressor 10, the impellers 12A and 12B can rotate at speeds of 30,000 rpm or higher. The centrifugal compressor 10 can be used as a compressor with impellers that require high-speed rotation and a high-head pressure. In the centrifugal compressor 10, the impellers 12A and 12B can also rotate at speeds of less than 30,000 rpm.

[0101] Compared to conventional centrifugal compressors, this centrifugal compressor 10 can tolerate larger unsteady vibrations. The centrifugal compressor 10 can tolerate unsteady vibrations of impellers 12A and 12B. The centrifugal compressor 10 can be used, for example, as an air-cooled high-pressure turbo compressor. The centrifugal compressor 10 can also be used as a small-capacity compressor. While most existing centrifugal compressors are used for large-capacity, low-differential-pressure applications, the centrifugal compressor 10 of this type can be used as a small-capacity, high-differential-pressure compressor.

[0102] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Various modifications and substitutions can be applied to the above embodiments without departing from the scope of the present invention. Furthermore, the features described separately can be combined as long as they do not create technical contradictions.

[0103] In the above embodiment, a refrigeration unit 100 equipped with a centrifugal compressor 10 is illustrated, but the centrifugal compressor 10 can also be used for purposes other than refrigeration units 100. The internal fluid of the centrifugal compressor 10 is not limited to a refrigerant.

[0104] One aspect of the present invention is summarized as follows.

[0105] <1>

[0106] A centrifugal compressor comprising:

[0107] An open impeller has a hub and blades disposed on the outer periphery of the hub;

[0108] A rotating shaft is connected to the impeller;

[0109] Bearings, supporting the rotating shaft; and

[0110] Casing, covering the impeller,

[0111] The radial range of motion of the rotating shaft relative to the bearing is greater than the axial range of motion of the rotating shaft relative to the bearing.

[0112] The first gap between the outer periphery of the gas inlet side of the blade and the inner wall of the housing is greater than the second gap between the outer periphery of the gas outlet side of the blade and the inner wall of the housing.

[0113] <2>

[0114] According to the centrifugal compressor described in <1> above, wherein,

[0115] The minimum point of the blade angle exists in the rear half of the blade.

[0116] <3>

[0117] According to the centrifugal compressor described in <2> above, wherein,

[0118] The minimum point of the blade angle exists at a position where the length m relative to the meridional plane is greater than 0.6m and less than 1.0m.

[0119] <4>

[0120] According to the centrifugal compressor described in <2> or <3> above, wherein,

[0121] When the direction perpendicular to the meridional length m along the blade is defined as the wingspan direction, and the length along the wingspan direction from the outer peripheral surface of the hub to the outer peripheral edge of the blade is defined as the wingspan length s,

[0122] At a position where the blade angle is greater than or equal to the wingspan length s by 0.5s, the minimum point of the blade angle exists in the rear half of the blade.

[0123] <5>

[0124] According to the centrifugal compressor described in <4> above, wherein,

[0125] At a position where the blade angle is greater than or equal to the wingspan length s by 0.9s, the minimum point of the blade angle exists in the rear half of the blade.

[0126] <6>

[0127] The centrifugal compressor according to any one of <1> to <5> above, wherein,

[0128] The bearing is an air bearing, a foil bearing, a controlled magnetic bearing, a rolling bearing, or a sliding bearing.

[0129] <7>

[0130] According to the centrifugal compressor described in <6> above, wherein,

[0131] The bearing is a controlled magnetic bearing.

[0132] The control type magnetic bearing controls the position of the rotating shaft such that the radial distance of the rotating shaft to the landing point is greater than the axial distance of the rotating shaft to the landing point.

[0133] <8>

[0134] The centrifugal compressor according to any one of <1> to <7> above, wherein,

[0135] The distance of the first gap is more than twice the distance of the second gap.

[0136] <9>

[0137] The centrifugal compressor according to any one of <1> to <8> above, wherein,

[0138] The impeller rotates at a speed of 30,000 rpm or higher.

[0139] This international application claims priority to Japanese Patent Application No. 2023-058713, filed on March 31, 2023, and incorporates the entire contents of Japanese Patent Application No. 2023-058713 into this international application.

[0140] Label Explanation

[0141] 10: Centrifugal compressor

[0142] 12A, 12B: Impeller

[0143] 13: Drive shaft (rotary shaft)

[0144] 14A, 14B: Bearings (air bearings, foil bearings, controlled magnetic bearings)

[0145] 15: Inner wall

[0146] 121: Wheel hub

[0147] 122: Blade

[0148] t1: Blade tip clearance (first clearance)

[0149] t2: Blade tip clearance (second clearance).

Claims

1. A centrifugal compressor, comprising: An open impeller has a hub and blades disposed on the outer periphery of the hub; A rotating shaft, which is connected to the impeller; Bearings that support the rotating shaft; and Casing that covers the impeller, The radial range of motion of the rotating shaft relative to the bearing is greater than the axial range of motion of the rotating shaft relative to the bearing. The first gap between the outer periphery of the gas inlet side of the blade and the inner wall of the housing is greater than the second gap between the outer periphery of the gas outlet side of the blade and the inner wall of the housing.

2. The centrifugal compressor according to claim 1, wherein, The minimum point of the blade angle exists in the rear half of the blade.

3. The centrifugal compressor according to claim 2, wherein, The minimum point of the blade angle exists at a position where the length m relative to the meridional plane is greater than 0.6m and less than 1.0m.

4. The centrifugal compressor according to claim 2 or 3, wherein, When the direction perpendicular to the meridional length m along the blade is defined as the wingspan direction, and the length along the wingspan direction from the outer peripheral surface of the hub to the outer peripheral edge of the blade is defined as the wingspan length s, At a position where the blade angle is greater than or equal to the wingspan length s by 0.5s, the minimum point of the blade angle exists in the rear half of the blade.

5. The centrifugal compressor according to claim 4, wherein, At a position where the blade angle is greater than or equal to the wingspan length s by 0.9s, the minimum point of the blade angle exists in the rear half of the blade.

6. The centrifugal compressor according to any one of claims 1 to 5, wherein, The bearing is an air bearing, a foil bearing, a controlled magnetic bearing, a rolling bearing, or a sliding bearing.

7. The centrifugal compressor according to claim 6, wherein, The bearing is a controlled magnetic bearing. The control type magnetic bearing controls the position of the rotating shaft such that the radial distance of the rotating shaft to the landing point is greater than the axial distance of the rotating shaft to the landing point.

8. The centrifugal compressor according to any one of claims 1 to 7, wherein, The distance of the first gap is more than twice the distance of the second gap.

9. The centrifugal compressor according to any one of claims 1 to 8, wherein, The impeller rotates at a speed of 30,000 rpm or higher.

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