U.S. patent application number 15/411885 was filed with the patent office on 2017-07-27 for impeller, centrifugal compressor, and refrigeration cycle apparatus.
The applicant listed for this patent is Panasonic Intellectual Property Management Co., Ltd.. Invention is credited to AKIRA HIWATA, KOTA KIMURA, KAZUYUKI KOUDA, TAKESHI OGATA, TADAYOSHI SHOYAMA, HIDETOSHI TAGUCHI.
Application Number | 20170211584 15/411885 |
Document ID | / |
Family ID | 57850964 |
Filed Date | 2017-07-27 |
United States Patent
Application |
20170211584 |
Kind Code |
A1 |
TAGUCHI; HIDETOSHI ; et
al. |
July 27, 2017 |
IMPELLER, CENTRIFUGAL COMPRESSOR, AND REFRIGERATION CYCLE
APPARATUS
Abstract
An impeller according to the present disclosure includes a hub
and wings. Each of the wings has a leading edge portion and a body
portion. 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. 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 in contact with 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.
Inventors: |
TAGUCHI; HIDETOSHI; (Osaka,
JP) ; HIWATA; AKIRA; (Shiga, JP) ; OGATA;
TAKESHI; (Osaka, JP) ; SHOYAMA; TADAYOSHI;
(Osaka, JP) ; KOUDA; KAZUYUKI; (Gunma, JP)
; KIMURA; KOTA; (Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Panasonic Intellectual Property Management Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
57850964 |
Appl. No.: |
15/411885 |
Filed: |
January 20, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 1/10 20130101; F04D
29/284 20130101; F25B 1/053 20130101; F05D 2240/307 20130101; F05D
2250/71 20130101; F01D 5/048 20130101; F04D 29/30 20130101 |
International
Class: |
F04D 29/28 20060101
F04D029/28; F25B 1/053 20060101 F25B001/053; F25B 1/10 20060101
F25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 25, 2016 |
JP |
2016-011785 |
Claims
1. An impeller for a centrifugal compressor comprising: 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, wherein a wing has a leading
edge portion and a body portion, the wing being each of the wings,
the leading edge portion being positioned on an upper surface side
of the hub, the body portion being positioned on a lower surface
side of the hub, the leading edge portion including 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, and 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.
2. The impeller according to claim 1, wherein each of the wings 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, and 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.
3. The impeller according to claim 1, wherein, in a case where a
total length of each of the wings in an axial direction parallel to
the axis of the impeller 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.
4. The impeller according to claim 1, wherein the wings form
respective main wings of the impeller, the impeller further
includes sub wings, and each of the sub wings is disposed between
the main wings that are adjacent to one another in a
circumferential direction of the impeller.
5. The impeller according to claim 1, wherein a ratio of a radius
of the hub to a radius of each of the wings ranges from 0.6 to 0.7
at the leading edge of the wing.
6. A centrifugal compressor comprising: the impeller according to
claim 1; and a shroud wall accommodating the impeller.
7. A refrigeration cycle apparatus comprising: the centrifugal
compressor according to claim 6, wherein a material whose saturated
vapor pressure is a negative pressure at a normal temperature is
used as a refrigerant.
8. The refrigeration cycle apparatus according to claim 7, wherein
the material contains water.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present disclosure relates to an impeller, a centrifugal
compressor, and a refrigeration cycle apparatus.
[0003] 2. Description of the Related Art
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
SUMMARY
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a sectional view of a centrifugal compressor
according to an embodiment of the present disclosure;
[0015] FIG. 2 is a projection view of a meridional plane of an
impeller of the centrifugal compressor illustrated in FIG. 1;
[0016] FIG. 3A is a schematic perspective view of a main wing of
the impeller;
[0017] FIG. 3B is a partially enlarged side view of the main wing
of the impeller;
[0018] FIG. 4 is a graph illustrating the relationship between a
wing angle .beta.b and a distance from a leading edge;
[0019] FIG. 5 is a diagram illustrating the hub-tip ratio of the
impeller of the centrifugal compressor illustrated in FIG. 1;
[0020] FIG. 6 is a configuration diagram of a refrigeration cycle
apparatus that uses the centrifugal compressor illustrated in FIG.
1; and
[0021] FIG. 7 is a partially enlarged side view of a main wing of a
conventional impeller.
DETAILED DESCRIPTION
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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
[0028] a hub that has an upper surface, a lower surface, and an
outer surface, and
[0029] wings that are fixed to the hub and that are arranged
radially around the outer surface of the hub.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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).
[0041] 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.
[0042] As illustrated in FIG. 1, a centrifugal compressor 100
according to the embodiment includes a shaft 11, an impeller 2, a
back plate 13, and a housing 15. The impeller 2 is fixed to the
shaft 11. The back plate 13 is disposed on the back side of the
impeller 2. The impeller 2 is accommodated in the housing 15. The
centrifugal compressor 100 is driven by rotation of the shaft 11
and compresses a working fluid. In the following description, the
front surface side of the back plate 13 in a direction (axial
direction) parallel to the axis O of the impeller 2 is also
referred to as a front side, and the back surface side thereof in
the direction is also referred to as a back side.
[0043] 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.
[0044] The sub wings 22 are not essential and may be omitted.
[0045] 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.
[0046] FIG. 2 is a projection view of a meridional plane (rotation
projection view) that is obtained in a manner in which the main
wings 21, the sub wings 22, and the shroud wall 3 are rotationally
projected on the meridional plane containing the axis O of the
impeller 2. A shape illustrated on the projection view of the
meridional plane is called "a meridional plane shape" in the field
of turbomachinery. In the embodiment, the outer circumferential
edge of each main wing 21 facing the inhalation port 12 is defined
as the leading edge 31 of the main wing 21. The outer
circumferential edge of each main wing 21 facing the shroud wall 3
is defined as the tip 32 of the main wing 21. Similarly, the outer
circumferential edge of each sub wing 22 facing the inhalation port
12 is defined as the leading edge 41 of the sub wing 22. The outer
circumferential edge of each sub wing 22 facing the shroud wall 3
is defined as the tip 42 of the sub wing 22. The leading edges 31
and 41 are positioned on the same side in the axial direction as
the upper surface 20p of the hub 20. In the embodiment, the leading
edge 31 of the main wing 21 is perpendicular to the axis O of the
impeller 2. The trailing edge 43 of the sub wing 22 is positioned
at the same position as the trailing edge 33 of the main wing 21.
The leading edge 41 of the sub wing 22 is positioned at a position
away from the leading edge 31 of the main wing 21 toward the rear
side. The leading edge 31 constitutes one edge of the main wing 21
in the direction parallel to the axis of the impeller 2.
[0047] As illustrated in FIG. 3A, each main wing 21 has a leading
edge portion 24 positioned on the side of the upper surface 20p of
the hub 20 and a body portion 25 positioned on the side of the
lower surface 20q of the hub 20. The body portion 25 is smoothly
connected to the leading edge portion 24. The tip 35 of the leading
edge portion 24 and the tip 36 of the body portion 25 extend from
the side of the upper surface 20p of the hub 20 toward the side of
the lower surface 20q of the hub 20 on a side opposite to a side
where the main wing 21 is fixed to the hub 20. As illustrated in
FIG. 3B, in a plan view of the main wing 21 seen from a radial
direction perpendicular to the axis O of the impeller 2, the
profile of the tip 35 of the leading edge portion 24 has a linear
shape, and the profile of the tip 36 of the body portion 25 has a
curved shape. A boundary 37 at which the main wing 21 is connected
to the hub 20 has a curved shape overall from the leading edge 31
to the trailing edge 33. In FIG. 3B, the axis O extends along the
boundary between the leading edge portion 24 having a linear shape
and the body portion 25 having a curved shape. The leading edge
portion 24 includes the leading edge 31. The tip 35 of the leading
edge portion 24 and the tip 36 of the body portion 25 constitute
one edge of the main wing 21 opposite to the other edge of the main
wing 21 where the main wing 21 is fixed to the hub 20 in the radial
direction perpendicular to the axis of the impeller 2.
[0048] As illustrated in FIG. 3B, each main wing 21 has a pressure
surface 21p and a suction surface 21q. The surface of the main wing
21 on the rotation direction side of the impeller 2 is the pressure
surface 21p (pressing surface), and the surface of the main wing 21
opposite to the pressure surface 21p is the suction surface 21q
(non-pressing surface). Similarly, the surface of each sub wing 22
on the rotation direction side of the impeller 2 is a pressure
surface, and the surface of the sub wing 22 opposite to the
pressure surface is a suction surface.
[0049] 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
10.sup.6. 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).
[ Formula 1 ] Re = .rho. R 1 T W 1 T v ( 1 ) ##EQU00001##
[0050] .rho.: density of the working fluid (during inhalation)
[0051] R.sub.1T: radius of a shroud at the leading edge of a
wing
[0052] W.sub.1T: relative velocity on the shroud side at the
leading edge of the wing
[0053] .upsilon.: kinetic viscosity of the working fluid (during
inhalation)
[0054] 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=(NQ.sup.1/2)/(H.sup.4).sup.1/3 (2)
[0055] N: rotational speed of the axis [rpm]
[0056] Q: volume flow rate of the working fluid (entrance)
[m.sup.3/sec]
[0057] H: heat drop (head) [m]
[0058] 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 10.sup.4.
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.
[0059] As illustrated in FIG. 7, in a conventional impeller, the
profile of the tip 210a of a wing 210 on the pressure surface side
and the profile of the tip 210b of the wing 210 on the suction
surface side have a curved shape overall. Accordingly, a fluid that
collides with a leading edge 210c is immediately accelerated. In
this case, mutual influence between the high-intensity vortex flows
is likely to cause a large disturbance inside the impeller.
[0060] 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 (FIG. 7). Since the position of the vortex
flow shifts to the downstream side, even when a low-energy vortex
flow due to the separation of the boundary layer is created near
the leading edge 31 on a surface (outer surface of the hub 20)
other than the surfaces of the main wing 21, the positions at which
the vortex flows are created are different. This inhibits the
production of a region in which a flow is blocked in the inside
(channels between the wings) of the impeller 2 due to merging and
breakdown of large vortex flows. In other words, the distribution
of the velocity of the fluid in the channels between the wings can
be appropriately adjusted. This effect is noticeable in a flow
field in which the Reynolds number is a low number of about
10.sup.4.
[0061] 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.
[0062] As illustrated in FIG. 3B, in a plan view of each main wing
21 seen from the radial direction, the profile of the tip 35 of the
leading edge portion 24 includes a first upstream portion 35a on
the side of the pressure surface 21p and a second upstream portion
35b on the side of the suction surface 21q. The first upstream
portion 35a and the second upstream portion 35b have a linear
shape. In the plan view of each main wing 21 seen from the radial
direction, the profile of the tip 36 of the body portion 25
includes a first downstream portion 36a on the side of the pressure
surface 21p and a second downstream portion 36b on the side of the
suction surface 21q. The first downstream portion 36a and the
second downstream portion 36b have a curved shape. The first
downstream portion 36a and the second downstream portion 36b have a
curvature so as to bend into a convex shape toward the side of the
suction surface 21q. This structure enables the above effects to be
achieved with certainty.
[0063] As illustrated in FIG. 2, the total length of each main wing
21 in the axial direction parallel to the axis O of the impeller 2
is defined as a meridional plane length L. The leading edge portion
24 occupies a portion of the wing 21 extending from the leading
edge 31 to a position 5% of the meridional plane length L away from
the leading edge 31 in the axial direction in the projection view
of the meridional plane in FIG. 2. The body portion 25 occupies a
portion of the main wing 21 extending from the position 5% of the
meridional plane length L away from the leading edge 31 to the
trailing edge 33. In FIG. 3A and FIG. 3B, the leading edge portion
24 is exaggeratedly illustrated. The limitation of the range of the
leading edge portion 24 to a certain degree reduces the likelihood
of the wings 21 having insufficient length and accordingly enables
sufficient energy to be applied to the fluid.
[0064] As illustrated in FIG. 4, when attention is paid to the wing
angle .beta.b of each wing (main wing) on the side on which the
wing is in contact with the hub 20, there is no large difference
between the wing angle .beta.b of the wing (main wing 21) according
to the present disclosure and the wing angle .beta.b of a
conventional wing between the position (0%) of the leading edge and
the position (100%) of the trailing edge. When attention is paid to
the wing angle .beta.b of each wing (main wing) on the side (shroud
side) opposite to the side on which the wing (main wing) is fixed
to the hub, there is a large difference between the wing angle
.beta.b of the wing (main wing 21) according to the present
disclosure and the wing angle .beta.b of the conventional wing.
Specifically, since the main wing 21 according to the present
disclosure has the leading edge portion 24 whose profile of the tip
35 has a linear shape, the absolute value of the wing angle .beta.b
is very large between the position (0%) of the leading edge and a
predetermined position (5%).
[0065] As illustrated in FIG. 5, the impeller 2 according to the
embodiment has a hub-tip ratio (D1/D2) of 0.6 to 0.7. The term
"hub-tip ratio" means a ratio (D1/D2) of the radius D1 of the hub
20 to the radius D2 of each main wing 21 at the leading edge 31 of
the main wing 21. In the case where the hub-tip ratio is in the
above range, the following effects are achieved.
[0066] 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 FIG. 3A and
FIG. 3B are used in the impeller having a hub-tip ratio of 0.6 to
0.7, the disturbance of the flow field can be effectively
inhibited, and the pressure ratio can be increased. In particular,
during high-speed rotation, blocking called inducer choking near
the leading edge 31 of the main wings 21 can be prevented.
Consequently, a centrifugal compressor having a high pressure ratio
and a wide operating range can be formed.
Embodiment of Refrigeration Cycle Apparatus
[0067] As illustrated in FIG. 6, a refrigeration cycle apparatus
200 according to the embodiment includes a main circuit 6 through
which a refrigerant circulates, a first circulation path 7 for heat
absorption and a second circulation path 8 for heat dissipation.
The main circuit 6, the first circulation path 7, and the second
circulation path 8 are filled with the refrigerant that is a liquid
at a normal temperature. Specifically, the refrigerant is a
refrigerant whose saturated vapor pressure is a negative pressure
at a normal temperature (Japanese Industrial Standards: 20.degree.
C..+-.15.degree. C./JIS Z8703). Examples of such a refrigerant
include a refrigerant whose main component is water or alcohol.
During operation of the refrigeration cycle apparatus 200, the
pressure of the inside of the main circuit 6, the first circulation
path 7, and the second circulation path 8 is a negative pressure
lower than an atmospheric pressure. The term "main component" in
the present disclosure means the most abundant component at a mass
ratio.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] 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.
* * * * *