BACKGROUND
Embodiments of the disclosure relate generally to a refrigeration system,
and more particularly, to a compressor.
Rotary machines are commonly used in refrigeration and turbine
applications. An example of a rotary machine includes a centrifugal compressor
having an impeller fixed to a rotating shaft. Rotation of the impeller increases a
pressure and/or velocity of a fluid or gas moving across the impeller.
In applications using new low-pressure refrigerants, the overall diameter
of the compressor is typically large to accommodate the high speeds. However,
10 these large sizes may exceed the available space within a packaging envelope.
There is therefore a need to develop a compressor having a reduced footprint and
suitable for use in low pressure refrigerant applications.
BRIEF DESCRIPTION
According to an embodiment, an impeller mountable within a centrifugal
15 compressor includes a hub having a front side and a back side, the hub being
rotatable about an axis of rotation and a plurality of vanes extending
outwardly from the front side of the hub such that a plurality of passages is
defined between adjacent vanes. The plurality of vanes is oriented such that a
flow output from the plurality of passages adjacent the back side of the impeller
20 is arranged at an angle to the axis of rotation of less than 20 degrees.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the angle of the flow output from the plurality
of passages is less than 10 degrees.
In addition to one or more of the features described above, or as an
25 alternative, in further embodiments the flow output from the plurality of passages
is arranged generally parallel to the axis of rotation.
2
According to another embodiment, a centrifugal compressor includes a
casing, an impeller arranged within the casing being rotatable about an axis, and a
diffuser section arranged within the casing. The diffuser section is positioned
axially downstream from an outlet of the impeller.
In addition to one or more of the features described above, or as 5 s an
alternative, in further embodiments the diffuser section further comprises a
diffuser structure and an axial flow passage defined between an exterior surface
of the diffuser structure and an interior surface of the casing.
In addition to one or more of the features described above, or as an
10 alternative, in further embodiments the diffuser structure is generally cylindrical
in shape.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the diffuser structure is fixed relative to the
axis.
15 In addition to one or more of the features described above, or as an
alternative, in further embodiments comprising a plurality of vanes arranged
between the diffuser structure and the casing.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the plurality of vanes are arranged at an angle
20 to the axis.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the plurality of vanes are arranged to reduce a
Mach number of a fluid flow through the compressor by at least 50%.
In addition to one or more of the features described above, or as an
25 alternative, in further embodiments the plurality of vanes includes a plurality of
first vanes extending from a first end of the diffuser structure to a central portion
3
of the diffuser structure and a plurality of second vanes extending from the
central portion of the diffuser structure to a second end of the diffuser structure.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the plurality of first vanes and the plurality of
second vanes are substantially identical or different5 .
In addition to one or more of the features described above, or as an
alternative, in further embodiments each of the plurality of second vanes axially
overlaps a corresponding vane of the plurality of first vanes.
In addition to one or more of the features described above, or as an
10 alternative, in further embodiments comprising a volute arranged axially
downstream from an outlet of the diffuser section.
In addition to one or more of the features described above, or as an
alternative, in further embodiments comprising a motor section, wherein an outlet
of the diffuser section is arranged in fluid communication with a passageway
15 formed in the motor section.
In addition to one or more of the features described above, or as an
alternative, in further embodiments at least one deswirl vane is positioned
adjacent the outlet end of the diffuser section.
In addition to one or more of the features described above, or as an
20 alternative, in further embodiments the motor section further comprises a motor
housing affixed to the casing, a motor arranged within the motor housing for
driving the impeller about the axis, the motor including a stator, and an axial
passageway extending between the motor housing and an exterior surface of the
stator.
4
In addition to one or more of the features described above, or as an
alternative, in further embodiments the centrifugal compressor is a mixed flow
compressor.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the centrifugal compressor is operable with 5 h a
low pressure refrigerant.
In addition to one or more of the features described above, or as an
alternative, in further embodiments the centrifugal compressor is operable with a
medium pressure refrigerant.
10 BRIEF DESCRIPTION OF THE DRAWINGS
The following descriptions should not be considered limiting in any way.
With reference to the accompanying drawings, like elements are numbered alike:
FIG. 1 is a cross-sectional view of a known centrifugal compressor;
FIG. 2 is a perspective cross-sectional view of a mixed flow centrifugal
15 compressor according to an embodiment;
FIG. 3A is front perspective view of an impeller of the mixed flow
centrifugal compressor according to an embodiment;
FIG. 3B is a cross-sectional view of an impeller of the mixed flow
centrifugal compressor according to an embodiment;
20 FIG. 4 is a perspective view of a diffuser structure of the mixed flow
centrifugal compressor according to an embodiment; and
FIG. 5 is a cross-sectional view of a mixed flow centrifugal compressor
according to another embodiment.
DETAILED DESCRIPTION
5
A detailed description of one or more embodiments of the disclosed
apparatus and method are presented herein by way of exemplification and not
limitation with reference to the Figures.
The term “about” is intended to include the degree of error associated
with measurement of the particular quantity based upon the equipment availabl5 e
at the time of filing the application.
The terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting of the present disclosure. As
used herein, the singular forms “a”, “an” and “the” are intended to include the
10 plural forms as well, unless the context clearly indicates otherwise. It will be
further understood that the terms “comprises” and/or “comprising,” when used in
this specification, specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the presence or
addition of one or more other features, integers, steps, operations, element
15 components, and/or groups thereof.
Referring now to FIG. 1, an example of an existing centrifugal
compressor 10 is illustrated. As shown, the centrifugal compressor 10 includes a
main casing 12 having an inlet 14 that directs refrigerant into a rotating impeller
16 through a series of adjustable inlet guide vanes 18. The impeller 16 is secured
20 to a drive shaft 20 by any suitable means to align impeller 16 along the axis of the
compressor 10. The impeller 16 has a plurality of passages 22 formed therein that
cause the incoming axial flow of a refrigerant fluid to turn in a radial direction
and discharge into an adjacent diffuser section 30. The diffuser section 30 is
disposed generally circumferentially about the impeller 16 and functions to direct
25 the compressed refrigerant fluid into a toroidal-shaped volute 32, which directs
the compressed fluid toward a compressor outlet, or alternatively, toward a
second stage of the compressor 10 (not shown), depending on the configuration
of the compressor.
6
Because the impeller 16, diffuser 30, and volute 32 are stacked radially
about the rotating shaft 20, an overall diameter of the compressor 10 defined by
these components may be large, and therefore unsuitable in applications having
size restrictions. An example of a centrifugal compressor 40 having a reduced
diameter relative to existing centrifugal compressors, such as compressor 10 5 for
example, is illustrated in FIG. 2. In, the illustrated, non-limiting embodiment, the
centrifugal compressor 40 is configured as a “mixed flow” compressor. Similar to
FIG. 1, the compressor 40 includes a main casing or housing 42 having an inlet
44 through which a fluid, such as refrigerant for example, is directed axially
10 toward a rotating impeller 46. The impeller 46 is secured to a drive shaft 48 such
that the impeller 46 is aligned with the axis X of the compressor 40.
As shown in FIGS. 2, 3A and 3B, the impeller 46 includes a hub or body
50 having a front side 52 and a back side 54. As shown, the diameter of the front
side 52 of the body 50 generally increases toward the back side 54 such that the
15 impeller 46 is generally conical in shape. A plurality of blades or vanes 56
extends outwardly from the body 50. Each of the plurality of blades 56 is
arranged at an angle to the axis of rotation X of the shaft 48 and the impeller 46.
In an embodiment, each of the blades 56 extends between the front side 52 and
the back side 54 of the impeller 46. As shown, each blade 56 includes a first end
20 58 arranged generally adjacent a first end of the hub 50 and a second end 60
located generally adjacent the back side 54 of the impeller 46. Further, the second
end 60 of the blade 56 is circumferentially offset from the corresponding first end
58 of the blade 56.
A plurality of passages 62 is defined between adjacent blades 56 to
25 discharge a fluid passing over the impeller 46 generally parallel to the axis X. As
the impeller 46 rotates, fluid approaches the front side 52 of the impeller 46 in a
substantially axial direction and flows through the passages 62 defined between
adjacent blades 56. Because the passages 62 have both an axial and radial
component, the axial flow provided to the front surface 52 of the impeller 46
7
simultaneously moves both parallel to and circumferentially about the axis of the
shaft 48. In combination, the inner surface 64 (shown in FIG. 1) of the housing
42 and the passages 62 of the impeller 46 cooperate to discharge the compressed
refrigerant fluid from the impeller 46. In an embodiment, the compressed fluid is
discharged from the impeller 46 at any angle relative to the axis X of the shaft 5 48
into an adjacent diffuser section 70. The angle may between 0°, generally parallel
to the axis of rotation X of the shaft 48, and less than 90°, less than 75°, less than
60°, less than 45°, less than 30°, less than 20°, less than 10°, or less than 5° for
example.
10 The diffuser section 70 includes a diffuser structure 72 (shown in FIGS. 1
and 4) mounted generally circumferentially about the shaft 48, at a location
downstream from the impeller 46 relative to the direction of flow through the
compressor 40. In the illustrated, non-limiting embodiment, the diffuser structure
72 is tubular in shape. When the diffuser structure 72 is mounted within the
15 compressor 40, a first end 74 of the diffuser structure 72 may directly abut the
back side 54 of the impeller 46. Further, the diffuser structure 72 may be
mounted such that an outer surface 76 thereof is substantially flush with the front
surface 52 of the impeller 46 at the interface with the back surface 54. In this
configuration, the fluid flow through the compressor 40 smoothly transitions
20 from the impeller 46 to the diffuser section 70. Although the mixed-flow impeller
illustrated and described herein is unshrouded, embodiments where a shroud is
disposed circumferentially about the impeller 46 are also within the scope of the
disclosure.
In the illustrated, non-limiting embodiment, the outer surface 76 of the
25 diffuser structure 72 is oriented generally parallel to the axis of rotation X of the
shaft 48 and the impeller 46. However, an outer surface 76 having another
configuration is also contemplated herein. In addition, the interior surface 78 of
the portion of the casing 42 within the diffuser section 70 may be oriented
generally parallel to the outer surface 76 of the diffuser structure 72. In such
8
embodiments, an axial flow channel 80 configured to receive the fluid discharged
from the impeller 46 is defined between the outer surface 76 and the casing 42.
The diffuser structure 72 may include a plurality of circumferentially
spaced vanes affixed about the outer surface 76. In the illustrated, non-limiting
embodiment, the diffuser structure 72 includes a plurality of first vanes 5 82
extending from adjacent a first, upstream end 74 of the diffuser structure 72 to a
central portion of the diffuser structure 72, and a plurality of second vanes 84
extending from a central portion of the diffuser structure 72 to generally adjacent
a downstream end 86 of the diffuser structure 72. The plurality of first vanes 82
10 may be substantially identical and/or the plurality of second vanes 84 may be
substantially identical. Alternatively, the first vanes 82 and/or second vanes 84
may vary in size and/or shape. In addition, the total number of first vanes may be
equal to or different that the total number of second vanes. Although the diffuser
structure 72 is illustrated and described as having a plurality of first vanes 82 and
15 a plurality of second vanes 84, it should be understood that embodiments having
only a single group of vanes, or alternatively, embodiments having more than two
groups of vanes are also considered within the scope of the disclosure.
As shown, both the plurality of first vanes 82 and the plurality of second
vanes 84 are oriented at an angle to the axis of rotation X of the shaft 48. The
20 angle of the plurality of first vanes 82 relative to the axis X may be the same, or
alternatively, may be different than the angle of the plurality of second vanes 84
relative to the axis X. Each of the plurality of second vanes 84 may be aligned
with a corresponding vane of the plurality of first vanes 82. Alternatively, the
plurality of second vanes 84 may be circumferentially offset from the plurality of
25 first vanes 82. In embodiments including this circumferential offset between the
plurality of first vanes 82 and the plurality of second vanes 84, adjacent ends of a
corresponding first and second vane 82, 84 may, but need not overlap one another
about the axial length of the diffuser structure 72, as shown.
9
As the refrigerant passes through the passageways 88 defined between
adjacent vanes 82, 84 of the diffuser structure 72, the kinetic energy of the
refrigerant may be converted to a potential energy or static pressure. In an
embodiment, the configuration of the plurality of vanes 82, 84 is selected to
reduce a Mach number of the fluid flow, by at least 25%, and in 5 n some
embodiments, by up to 50% or more. In an embodiment, inclusion of the vanes
82, 84 reduces the Mach number of the flow from above 1 to between about .3
and .4. Further, it should be understood that the diffuser structure 72 illustrated
and described herein is intended as an example only and that other diffuser
10 structures having an axial flow configuration and arranged in fluid
communication with the passages 62 of the impeller 46 are also contemplated
herein.
Similar to existing compressors, the diffuser section 70 may function to
direct the compressed refrigerant fluid into an adjacent toroidal volute 90, as
15 shown in FIG. 2, which directs the compressed fluid toward a compressor outlet.
Because the flow through the diffuser structure 72 is axial, the volute 90 for
receiving the flow from the diffuser structure 72 is arranged axially downstream
from the second end 86 of the diffuser structure 72. Within the volute 90, the
fluid may be directed radially toward an outlet.
20 In another embodiment, best shown in FIG. 5, the diffuser structure 72
may direct the compressed fluid flow toward a motor section 91 of the
compressor including an adjacent motor housing 92. As shown, a passageway 94
may be defined between an exterior surface 96 of a motor stator 98 and an
interior surface 100 of the motor housing 92. The passageway 94 has a generally
25 axial configuration and is generally aligned with the flow channel 80 defined
between the diffuser structure 72 and the casing 42. In addition, one or more
deswirl vanes (not shown) may be located at the interface between the flow
channel 80 and the passageway 94 to limit the rotation of the fluid flow about the
10
axis X. From the passageway 94, the fluid flow is provided to an outlet 102, such
as formed in an end of the compressor 40 for example.
A compressor 40 having a mixed flow configuration as illustrated and
described herein is suitable for use with any type of refrigerant, and may be
particularly useful with low or medium pressure refrigerants. Low pressur5 e
refrigerants typically have evaporator pressure lower than atmospheric pressure
and medium pressure refrigerants typically have evaporator pressure above
atmospheric pressure. The mixed flow compressor 40 may provide a substantial
size reduction over existing centrifugal compressors. In addition, because a high
10 pressure ratio is achieved in the single stage described, the compressor 40 may be
simplified by eliminating the need for subsequent stages. As a result, the radius of
the compressor 40 may be reduced up to about 40% and a length of the
compressor 40 may be reduced by more than 10%. Further, the performance of
the compressor 40 is improved compared to conventional centrifugal
15 compressors.
While the present disclosure has been described with reference to an
exemplary embodiment or embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be substituted for
elements thereof without departing from the scope of the present disclosure. In
20 addition, many modifications may be made to adapt a particular situation or
material to the teachings of the present disclosure without departing from the
essential scope thereof. Therefore, it is intended that the present disclosure not be
limited to the particular embodiment disclosed as the best mode contemplated for
carrying out this present disclosure, but that the present disclosure will include all
25 embodiments falling within the scope of the claims.

We Claim:
1. An impeller mountable within a centrifugal compressor,
comprising:
a hub having a front side and a back side, the hub being rotatable about an
axis of rotati5 on;
a plurality of vanes extending outwardly from the front side of the hub
such that a plurality of passages are defined between adjacent vanes, the plurality
of vanes oriented such that a flow output from the plurality of passages adjacent
the back side of the impeller is arranged at an angle to the axis of rotation, the
10 angle being less than 20 degrees.
2. The impeller of claim 1, wherein the angle of the flow output from
the plurality of passages is less than 10 degrees.
3. The impeller of claim 1, wherein the flow output from the
plurality of passages is arranged generally parallel to the axis of rotation.
15 4. A centrifugal compressor comprising:
a casing;
an impeller arranged within the casing, the impeller being rotatable about
an axis;
a diffuser section arranged within the casing, the diffuser section being
20 positioned axially downstream from an outlet of the impeller.
5. The centrifugal compressor of claim 4, wherein the diffuser
section further comprises:
a diffuser structure; and
12
an axial flow passage defined between an exterior surface of the diffuser
structure and an interior surface of the casing.
6. The centrifugal compressor of claim 5, wherein the diffuser
structure is generally cylindrical in shape.
7. The centrifugal compressor of claim 5, wherein the diffuse5 r
structure is fixed relative to the axis.
8 The centrifugal compressor of claim 5, further comprising a
plurality of vanes arranged between the diffuser structure and the casing.
9. The centrifugal compressor of claim 8, wherein the plurality of
10 vanes are arranged at an angle to the axis.
10. The centrifugal compressor of claim 8, wherein the plurality of
vanes are arranged to reduce a Mach number of a fluid flow through the
compressor by at least 50%.
11. The centrifugal compressor of claim 8, wherein the plurality of
15 vanes includes a plurality of first vanes extending from a first end of the diffuser
structure to a central portion of the diffuser structure and a plurality of second
vanes extending from the central portion of the diffuser structure to a second end
of the diffuser structure.
12. The centrifugal compressor of claim 11, wherein the plurality of
20 first vanes and the plurality of second vanes are substantially identical or
different.
13. The centrifugal compressor of claim 11, wherein each of the
plurality of second vanes axially overlaps a corresponding vane of the plurality of
first vanes.
13
14. The centrifugal compressor of claim 4, further comprising a volute
arranged axially downstream from an outlet of the diffuser section.
15. The centrifugal compressor of claim 4, further comprising a motor
section, wherein an outlet of the diffuser section is arranged in fluid
communication with a passageway formed in the motor secti5 on.
16. The centrifugal compressor of claim 15, wherein at least one
deswirl vane is positioned adjacent the outlet end of the diffuser section.
17. The centrifugal compressor of claim 15, wherein the motor section
further comprises:
10 a motor housing affixed to the casing;
a motor arranged within the motor housing for driving the impeller about
the axis, the motor including a stator; and
an axial passageway extending between the motor housing and an exterior
surface of the stator.
15 18. The centrifugal compressor of claim 4, wherein the centrifugal
compressor is a mixed flow compressor.
19. The centrifugal compressor of claim 4, wherein the centrifugal
compressor is operable with a low pressure refrigerant.
20. The centrifugal compressor of claim 4, wherein the centrifugal
20 compressor is operable with a medium pressure refrigerant.