Patent Application
20170211584
1. Technical Field
The present disclosure relates to an impeller, a centrifugal compressor, and a refrigeration cycle apparatus.
2. Description of the Related Art
Among rotating components used in centrifugal compressors, a component called an impeller applies kinetic energy to a fluid in a manner in which the fluid inhaled is accelerated mainly in a direction of the tangent of rotation. The impeller typically has an approximately truncated cone shape and rotates about a line connecting the center of its upper surface having a small diameter and the center of its lower surface having a large diameter. As disclosed in Colin Osborne et al. “AERODYNAMIC AND MECHANICAL DESIGN OF AN 8:1 PRESSURE RATIO CENTRIFUGAL COMPRESSOR”, NASA CR-134782, April 1975, an impeller has wings (blades) radially arranged.
The leading edge of each wing collides, at an angle, with a fluid inhaled into a centrifugal compressor. The collision makes a difference in velocity between the front surface (suction surface) and back surface (pressure surface) of the wing, applying kinetic energy to the fluid.
In a section from the leading edge of the wing to the trailing edge thereof, an increase in the radius of gyration of the impeller increases a velocity component of the fluid mainly in the direction of the tangent of rotation. At a position at which the impeller has the maximum outer diameter, the increase in the velocity component is at its maximum, and the total amount of the kinetic energy applied to the fluid is determined.
In the case where the impeller is designed such that the sectional area throughout the wing gradually decreases from the leading edge of the wing to the trailing edge thereof, the velocity of the fluid in the direction parallel to the front surface of the wing can be prevented from decreasing.
The velocity of the fluid in the inside (channels between the wings) of the impeller, that is, the velocity of the fluid on the front surface of the wing depends on a pressure ratio for which a compressor equipped with the impeller is required. For example, in the case where the fluid to be compressed is air, and in the case of a compressor having a pressure ratio of more than 4, the velocity (relative velocity) of the fluid when the fluid is seen from the wing side at the leading edge of the wing reaches a transonic speed. A centrifugal compressor whose target pressure ratio is 8 is described in Colin Osborne et al. “AERODYNAMIC AND MECHANICAL DESIGN OF AN 8:1 PRESSURE RATIO CENTRIFUGAL COMPRESSOR”, NASA CR-134782, April 1975. In this case, the relative velocity at the leading edge of each wing is such a high transonic speed as about a Mach number of 1.2.
The flow of the fluid in channels between the wings of the impeller is very complex. In a complex flow field, a vortex flow (vortex flow having a high vorticity of flow) having a low velocity and a high intensity is created, and accordingly, an efficient application of kinetic energy to the fluid from the wings is hindered. In addition, the friction of the fluid in the vortex flow causes a loss. This lowers the pressure ratio and an adiabatic efficiency.
One non-limiting and exemplary embodiment provides a technique for appropriately adjusting the distribution of the velocity of the fluid in the channels between the wings and for improving the efficiency of the centrifugal compressor.
In one general aspect, the techniques disclosed here feature an impeller for a centrifugal compressor including a hub that has an upper surface, a lower surface, and an outer surface, and wings that are fixed to the hub and that are arranged radially around the outer surface of the hub. A wing has a leading edge portion and a body portion. The wing is each of the wings. The leading edge portion is positioned on an upper surface side of the hub. The body portion is positioned on a lower surface side of the hub. The leading edge portion includes a leading edge. A tip of the leading edge portion and a tip of the body portion extend from the upper surface side of the hub toward the lower surface side of the hub on a side opposite to a side where the wing is fixed to the hub. In a plan view of the wing seen from a radial direction perpendicular to an axis of the impeller, a profile of the tip of the leading edge portion has a linear shape and a profile of the tip of the body portion has a curved shape.
According to the present disclosure, the distribution of the velocity of the fluid in the channels between the wings can be appropriately adjusted to improve the efficiency of the centrifugal compressor.
Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.
The present inventors have analyzed the flow of a fluid (for example, water vapor) in the inside (channels between wings) of an impeller in detail and consequently found that merging and breakdown of large vortex flows result in the production of a region in which a flow is blocked (region in which the velocity of the flow is very low) inside the impeller. The present inventors have diligently examined the shape of a wing that enables the large vortex flows to be inhibited from merging and breaking down and consequently considered the impeller according to the present disclosure.
An impeller according to a first aspect of the present disclosure is an impeller for a centrifugal compressor including a hub that has an upper surface, a lower surface, and an outer surface, and wings that are fixed to the hub and that are arranged radially around the outer surface of the hub.
A wing has a leading edge portion and a body portion. The wing is each of the wings. The leading edge portion is positioned on an upper surface side of the hub. The body portion is positioned on a lower surface side of the hub. The leading edge portion includes a leading edge.
A tip of the leading edge portion and a tip of the body portion extend from the upper surface side of the hub toward the lower surface side of the hub on a side opposite to a side where the wing is fixed to the hub.
In a plan view of the wing seen from a radial direction perpendicular to an axis of the impeller, a profile of the tip of the leading edge portion has a linear shape and a profile of the tip of the body portion has a curved shape.
The impeller according to the first aspect of the present disclosure that is expressed in another way is an impeller for a centrifugal compressor including
a hub that has an upper surface, a lower surface, and an outer surface, and
wings that are fixed to the hub and that are arranged radially around the outer surface of the hub.
A wing has a leading edge portion and a body portion. The wing is each of the wings. The leading edge portion is positioned on an upper surface side of the hub. The body portion is positioned on a lower surface side of the hub. The leading edge portion includes a leading edge. The leading edge constitutes one edge of the wing in a direction parallel to an axis of the impeller.
A tip of the leading edge portion and a tip of the body portion extend from the upper surface side of the hub toward the lower surface side of the hub. The tip of the leading edge portion and the tip of the body portion constitutes one edge of the wing opposite to the other edge of the wing where the wing is fixed to the hub in a radial direction perpendicular to the axis of the impeller.
In a plan view of the wing seen from the radial direction, a profile of the tip of the leading edge portion has a linear shape and a profile of the tip of the body portion has a curved shape.
In the impeller according to the first aspect, even when the separation of a boundary layer and/or a leakage flow at the wing edge cause high-intensity vortex flows to be produced in the inside (channels between the wings) of the impeller, the vortex flows can be inhibited from merging and becoming large. In other words, the distribution of the velocity of the fluid in the channels between the wings can be appropriately adjusted. Consequently, blocking on the inside of the impeller is inhibited, the fluid flows smoothly, and kinetic energy can be efficiently applied from the wings to the fluid. In particular, according to the first aspect, the performance of the compressor can be maintained even under operating conditions of a low Reynolds number and a low specific speed. The use of the impeller according to the first aspect enables a low-density, high-viscosity fluid (for example, water vapor) to be highly efficiently compressed.
According to a second aspect of the present disclosure, for example, each of the wings of the impeller according to the first aspect has a pressure surface and a suction surface. In the plan view of the wing seen from the radial direction, the profile of the tip of the leading edge portion includes a first upstream portion on a pressure surface side and a second upstream portion on a suction surface side, and the first upstream portion and the second upstream portion have a linear shape. In the plan view of the wing seen from the radial direction, the profile of the tip of the body portion includes a first downstream portion on the pressure surface side and a second downstream portion on the suction surface side, and the first downstream portion and the second downstream portion have a curved shape. With this structure, the effects in the first aspect can be achieved with certainty.
According to a third aspect of the present disclosure, for example, in the case where the total length of each of the wings in an axial direction parallel to the axis of the impeller according to the first or second aspect is defined as a meridional plane length in a projection view of a meridional plane that is obtained in a manner in which the wing is rotationally projected on the meridional plane containing the axis of the impeller, the leading edge portion occupies a portion of the wing extending from the leading edge to a position 5% of the meridional plane length away from the leading edge in the axial direction in the projection view of the meridional plane. The limitation of the range of the leading edge portion to a certain degree reduces the likelihood of the wings having insufficient length and accordingly enables sufficient energy to be applied to the fluid.
According to a fourth aspect of the present disclosure, for example, the wings of the impeller according to any one of the first to third aspects form respective main wings of the impeller. The impeller further includes sub wings. Each of the sub wings is disposed between the main wings that are adjacent to one another in a circumferential direction of the impeller. Considering a throat area (minimum sectional area of the channels between the wings) that can be calculated from the maximum flow rate for which the centrifugal compressor is required, the sub wings may have the sectional shape of the main wings. According to the fourth aspect, a centrifugal compressor having a wider range of the flow rate can be formed.
According to a fifth aspect of the present disclosure, for example, a ratio of the radius of the hub to the radius of each of the wings of the impeller according to any one of the first to fourth aspects ranges from 0.6 to 0.7 at the leading edge of the wing. According to the fifth aspect, the disturbance of the flow field can be effectively inhibited, and the pressure ratio can be increased.
A centrifugal compressor according to a sixth aspect of the present disclosure includes the impeller according to any one of the first to fifth aspects and a shroud wall accommodating the impeller. According to the sixth aspect, a highly efficient centrifugal compressor can be provided.
A refrigeration cycle apparatus according to a seventh aspect of the present disclosure includes the centrifugal compressor according to the sixth aspect. A material whose saturated vapor pressure is a negative pressure at a normal temperature is used as a refrigerant. According to the seventh aspect, the pressure of the refrigerant can be efficiently increased, and accordingly, the efficiency of the refrigeration cycle apparatus can be improved.
According to an eighth aspect of the present disclosure, for example, the material in the refrigeration cycle apparatus according to the seventh aspect contains water. The centrifugal compressor that uses the impeller according to the present disclosure is suitable for efficiently compressing a refrigerant containing water (water vapor).
An embodiment of the present disclosure will hereinafter be described with reference to the drawings. The present disclosure is not limited to the embodiment described below.
As illustrated in
The impeller 2 includes a hub 20, main wings 21 (full blades), and sub wings 22 (splitter blades). The hub 20 has an upper surface 20p having a small diameter and a lower surface 20q having a large diameter in the axial direction, and the diameter of the hub 20 smoothly increases from the upper surface 20p to the lower surface 20q along the axis O. The main wings 21 and the sub wings 22 are fixed to the hub 20 and arranged radially around the outer surface of the hub 20. The main wings 21 and the sub wings 22 are arranged so as to alternate in the circumferential direction of the impeller 2. The sub wings 22 are wings shorter than the main wings 21.
The sub wings 22 are not essential and may be omitted.
The housing 15 has a shroud wall 3, a peripheral member 17, and a front member 18. The shroud wall 3 has a shape extending along the impeller 2. The shroud wall 3 protrudes from the impeller 2 toward the front side and forms an inhalation port 12. The peripheral member 17 forms a scroll chamber 16 around the impeller 2, and the scroll chamber 16 is in communication with a diffuser formed between the back plate 13 and the shroud wall 3.
As illustrated in
As illustrated in
Impellers disclosed in International Publication No. 2014/073377, International Publication No. 2014/199498, Japanese Unexamined Patent Application Publication No. 2011-117346, and U.S. Patent Application Publication No. 2008/0229742 are assumed to be used under conditions in which the Reynolds number Re becomes about 106. Specifically, a centrifugal compressor as a component of a motor such as a supercharger or a gas turbine that uses air as a working fluid is assumed. The Reynolds number Re is expressed by the following formula (1).
ρ: density of the working fluid (during inhalation)
R1T: radius of a shroud at the leading edge of a wing
W1T: relative velocity on the shroud side at the leading edge of the wing
υ: kinetic viscosity of the working fluid (during inhalation)
In International Publication No. 2014/073377, International Publication No. 2014/199498, Japanese Unexamined Patent Application Publication No. 2011-117346, and U.S. Patent Application Publication No. 2008/0229742, the specific speed Ns is assumed so as to be about 0.6 to 0.8. The specific speed Ns is an index representing the size of fluid machinery and is expressed by the following formula (2).
Ns=(NQ1/2)/(H4)1/3 (2)
N: rotational speed of the axis [rpm]
Q: volume flow rate of the working fluid (entrance) [m3/sec]
H: heat drop (head) [m]
In some centrifugal compressors used in, for example, air-conditioning apparatuses, a compressible fluid other than air is used as the working fluid. In some cases, a decrease in the viscosity of the working fluid decreases Re to about 104. These cases have a problem in that high-intensity vortex flows are frequently created from the surface of the hub and the surface of the wings. Mutual influence between the high-intensity vortex flows causes a large disturbance inside the impeller. Consequently, the performance of the centrifugal compressors is greatly reduced.
As illustrated in
In contrast, in the impeller 2 according to the embodiment, each main wing 21 has the leading edge portion 24. Since the profile of the tip 35 of the leading edge portion 24 has a linear shape, the fluid is unlikely to be accelerated at the leading edge portion 24. Consequently, the boundary layer is inhibited from expanding, and a position at which a low-energy, high-intensity vortex flow due to the separation of the boundary layer is created shifts to the side that is more downstream than in the case of the conventional wing 210 (
The flows are decelerated on the side of the suction surface 21q of the leading edge portion 24 and accelerated on the side of the pressure surface 21p. Since the flows are decelerated on the side of the suction surface 21q, the boundary layer is inhibited from expanding and from being separated. Since the flows are accelerated on the pressure surface side, a low-energy flow that is created on the side of the suction surface 21q of the adjacent main wing 21 due to the separated boundary layer can be diverted. The low-energy flow can be prevented from being maintained on the pressure surface 21p and re-collides with the suction surface 21q of the main wing 21 from which the flow has been separated. This inhibits the disturbance of the velocity distribution of the fluid on the pressure surface 21p of the main wing 21 due to a secondary flow originated from the adjacent main wing 21 and enables the velocity distribution to be appropriately adjusted.
As illustrated in
As illustrated in
As illustrated in
As illustrated in
A typically designed impeller of a centrifugal compressor has a hub-tip ratio of about 0.4 to 0.5. In the embodiment, in which the hub-tip ratio ranges from 0.6 to 0.7, the inflow rate of the fluid entering the impeller 2 increases, and the pressure ratio is likely to increase. However, the disturbance of the flow field and a reduction in performance due to the disturbance are likely to manifest themselves. Accordingly, in the case where the main wings 21 having the structure described with reference to
As illustrated in
The main circuit 6 includes an evaporator 66, a first compressor 61, an intermediate refrigerator 62, a second compressor 63, a condenser 64, and an expansion valve 65. These components are connected in this order along a channel.
The evaporator 66 stores a refrigerant liquid and evaporates the refrigerant liquid in the inside thereof. Specifically, the refrigerant liquid stored in the evaporator 66 circulates through the first circulation path 7 via a heat exchanger 71 for heat absorption. For example, in the case where the refrigeration cycle apparatus 200 is an air-conditioning apparatus that cools the inside of a room, the heat exchanger 71 for heat absorption is installed inside the room and exchanges heat between air inside the room supplied from a fan and the refrigerant liquid to cool the air.
The first compressor 61 and the second compressor 63 compress refrigerant vapor through two stages. The centrifugal compressor 100 described above can be used as the first compressor 61. The second compressor 63 may be a displacement-type compressor separated from the first compressor 61 or a centrifugal compressor (for example, the centrifugal compressor 100 described above) connected to the first compressor 61 by using the shaft 11. An electric motor 67 that rotates the shaft 11 may be disposed between the first compressor 61 and the second compressor 63 or outside one of the first and second compressors. Connecting the first compressor 61 and the second compressor 63 by using the shaft 11 enables the number of the components of the first compressor 61 and the second compressor 63 to be decreased.
The intermediate refrigerator 62 cools the refrigerant vapor discharged from the first compressor 61 before the refrigerant vapor is inhaled into the second compressor 63. The intermediate refrigerator 62 may be a direct-contact-type heat exchanger or an indirect type heat exchanger.
The condenser 64 condenses the refrigerant vapor in the inside thereof and stores the refrigerant liquid. Specifically, the refrigerant liquid stored in the condenser 64 circulates through the second circulation path 8 via a heat exchanger 81 for heat dissipation. For example, in the case where the refrigeration cycle apparatus 200 is an air-conditioning apparatus that cools the inside of a room, the heat exchanger 81 for heat dissipation is installed outside the room and exchanges heat between air outside the room supplied from a fan and the refrigerant liquid to heat the air.
However, the refrigeration cycle apparatus 200 is not necessarily an air-conditioning apparatus for cooling only. For example, a first heat exchanger installed inside a room and a second heat exchanger installed outside the room are connected to the evaporator 66 and the condenser 64 with a four-way valve interposed therebetween. This achieves an air-conditioning apparatus that can change its operation between a cooling operation and a heating operation. In this case, the first heat exchanger and the second heat exchanger both function as the heat exchanger 71 for heat absorption and the heat exchanger 81 for heat dissipation. The refrigeration cycle apparatus 200 is not necessarily an air-conditioning apparatus and may be, for example, a chiller. A subject to be cooled by the heat exchanger 71 for heat absorption and a subject to be heated by the heat exchanger 81 for heat dissipation may be a gas other than air or a liquid.
The expansion valve 65 is an example of a pressure-reducing mechanism that reduces the pressure of a condensed refrigerant liquid. The pressure-reducing mechanism may be formed, for example, such that the expansion valve 65 is not disposed in the main circuit 6, and the liquid surface of the refrigerant liquid in the evaporator 66 is higher than the liquid surface of the refrigerant liquid in the condenser 64.
The evaporator 66 is not necessarily a direct-contact-type heat exchanger and may be an indirect type heat exchanger. In this case, a heating medium cooled in the evaporator 66 circulates through the first circulation path 7. Similarly, the condenser 64 is not necessarily a direct-contact-type heat exchanger and may be an indirect type heat exchanger. In this case, a heating medium heated in the condenser 64 circulates through the second circulation path 8.
In the case where water is used as the refrigerant in the refrigeration cycle apparatus 200 according to the embodiment, the first compressor 61 and the second compressor 63 compress water vapor having a negative pressure. The centrifugal compressor 100 described above is suitable for compressing a low-density, high-viscosity fluid such as water vapor. The refrigeration cycle apparatus 200 can operate under conditions in which the flow rate of the fluid is small against the required pressure ratio, that is, the Reynolds number is low and the specific speed is low. Accordingly, the centrifugal compressor 100 described above is suitable for the refrigeration cycle apparatus 200 according to the embodiment.
According to the technique disclosed in the present disclosure, the performance of the compressor can be maintained even under operating conditions of a low Reynolds number and a low specific speed. The technique disclosed in the present disclosure is suitable for a refrigeration cycle apparatus that uses a natural refrigerant such as water vapor. According to the technique disclosed in the present disclosure, in particular, the performance of a small-output refrigeration cycle apparatus can be improved, and the frequency of the maintenance of the refrigeration cycle apparatus can be decreased.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-011785 | Jan 2016 | JP | national |
