U.S. patent application number 11/533222 was filed with the patent office on 2007-03-22 for impeller for a centrifugal compressor.
This patent application is currently assigned to INGERSOLL-RAND COMPANY. Invention is credited to Russell A. Houston, Filippo Maria Mariani, Michael O. Muller, Jay L. Robb.
Application Number | 20070065276 11/533222 |
Document ID | / |
Family ID | 37497939 |
Filed Date | 2007-03-22 |
United States Patent
Application |
20070065276 |
Kind Code |
A1 |
Muller; Michael O. ; et
al. |
March 22, 2007 |
IMPELLER FOR A CENTRIFUGAL COMPRESSOR
Abstract
An impeller for a centrifugal gas compressor includes a
stationary seal member that includes a plurality of seal tips. The
impeller is operable to produce a flow of fluid. The impeller
includes a hub having a front face and a back face. A plurality of
blades extends from the front face. Each of the blades has an
inducer portion and an exducer portion and cooperates with an
adjacent blade and the front face to at least partially define one
of a plurality of impeller channels. A portion of the flow of fluid
passes through one of the impeller channels such that the flow of
fluid defines a first pressure adjacent the inducer portion and a
second pressure that is higher than the first pressure adjacent the
exducer portion. A seal portion extends from the back face and
includes a plurality of stepped surfaces. Each of the seal tips is
disposed adjacent one of the stepped surfaces to define a plurality
of seal points.
Inventors: |
Muller; Michael O.;
(Charlotte, NC) ; Robb; Jay L.; (Rockwell, NC)
; Mariani; Filippo Maria; (Milano, IT) ; Houston;
Russell A.; (Sherrills Ford, NC) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH, LLP
100 E WISCONSIN AVENUE
MILWAUKEE
WI
53202
US
|
Assignee: |
INGERSOLL-RAND COMPANY
155 Chestnut Ridge Road
Montvale
NJ
|
Family ID: |
37497939 |
Appl. No.: |
11/533222 |
Filed: |
September 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60718438 |
Sep 19, 2005 |
|
|
|
Current U.S.
Class: |
415/170.1 |
Current CPC
Class: |
F04D 29/083 20130101;
F16J 15/406 20130101; F04D 29/284 20130101; F16J 15/447 20130101;
F01D 11/02 20130101 |
Class at
Publication: |
415/170.1 |
International
Class: |
F04D 29/08 20060101
F04D029/08 |
Claims
1. An impeller for a centrifugal gas compressor including a
stationary seal member that includes a plurality of seal tips, the
impeller operable to produce a flow of fluid, the impeller
comprising: a hub including a front face and a back face; a
plurality of blades extending from the front face, each of the
blades having an inducer portion and an exducer portion and
cooperating with an adjacent blade and the front face to at least
partially define one of a plurality of impeller channels, a portion
of the flow of fluid passing through one of the impeller channels
such that the flow of fluid defines a first pressure adjacent the
inducer portion and a second pressure that is higher than the first
pressure adjacent the exducer portion; and a seal portion extending
from the back face and including a plurality of stepped surfaces,
each of the seal tips disposed adjacent one of the stepped surfaces
to define a plurality of seal points.
2. The impeller of claim 1, wherein a bore extends from the front
face to the back face.
3. The impeller of claim 1, wherein a first stepped surface
disposed adjacent the hub has a first diameter and a second stepped
surface disposed away from the hub has a second diameter that is
smaller than the first diameter, and wherein each additional
stepped surface defines a surface diameter that is less than the
diameter of the stepped surface on the hub side of the additional
stepped surface and that is greater than the diameter of the
stepped surface on the opposite side of the additional stepped
surface.
4. The impeller of claim 1, wherein each step includes a generally
axially extending first portion and a generally radially extending
second portion.
5. The impeller of claim 4, wherein each seal tip cooperates with
one of the axially extending first portion and the radially
extending second portion to define a radial seal point and all
axial seal point.
6. The impeller of claim 1, wherein the seal portion divides the
impeller back face into a first annular area and a second annular
area, and wherein the first annular area interfaces with a first
volume of gas at a pressure substantially the same as the gas
discharged from the blades and the second annular area interfaces
with a second volume of gas at a pressure substantially less than
the gas discharged from the blades.
7. The impeller of claim 1, wherein the blades, hub, and the seal
portion are integrally-formed as a single component.
8. The impeller of claim 1, wherein a sequence defined by
corresponding radial dimensions of the steps in axial order,
starting with a step nearest the blades decreases substantially
uniformly.
9. The impeller of claim 1, wherein the exducer defines an exducer
diameter and the seal portion defines an average seal diameter that
is greater than or equal to about 50 percent of the exducer
diameter.
10. An impeller for a centrifugal compressor including a stationary
seal member having a plurality of first seal members, the impeller
operable to produce a flow of fluid, the impeller comprising: a hub
including a front side, a back side, and a bore extending from the
front side to the back side; a plurality of blades extending from
the front side, each blade including an inducer portion and an
exducer portion, the exducer portion defining an outer diameter;
and a seal portion extending from the back face and including a
plurality of second seal members, each of the first seal members
disposed adjacent one of the second seal members to define a
plurality of seal points, each of the seal points located at a seal
point diameter, the average seal point diameter being greater than
or equal to about 50 percent of the outer diameter.
11. The impeller of claim 10, wherein each second seal member has a
stepped surface, and wherein a first stepped surface is disposed
adjacent the hub and has a first diameter, and a second stepped
surface is disposed away from the hub and has a second diameter
that is smaller than the first diameter, and wherein each
additional stepped surface defines a surface diameter that is less
than the diameter of the stepped surface on the hub side of the
additional stepped surface and that is greater than the diameter of
the stepped surface on the opposite side of the additional stepped
surface.
12. The impeller of claim 10, wherein each of the second seal
members includes a generally axially extending first portion and a
generally radially extending second portion.
13. The impeller of claim 12, wherein each seal tip cooperates with
one of the axially extending first portion and the radially
extending second portion to define the radial seal point and an
axial seal point.
14. The impeller of claim 10, wherein the seal portion divides the
impeller back face into a first annular area and a second annular
area, and wherein the first annular area interfaces with a first
volume of gas at a first pressure, and the second annular area
interfaces with a second volume of gas at a second pressure
substantially less than the first pressure.
15. The impeller of claim 10, wherein the blades, hub, and the seal
portion are integrally-formed as a single component.
16. The impeller of claim 10, wherein each second seal member
includes a step, and wherein a sequence defined by corresponding
radial dimensions of the steps in axial order, starting with a step
nearest the blades decreases substantially uniformly.
17. A compressor comprising: a motor; an impeller including a hub
that is coupled to the motor, the impeller rotatable in response to
rotation of the motor and including a plurality of blades arranged
to define an inducer portion and an exducer portion, the impeller
operable to draw a flow of fluid into the inducer in a
substantially axial direction and discharge the flow of fluid from
the exducer in a substantially radial direction, a rotating seal
member extending from the impeller and spaced a non-zero distance
from the hub; and a stationary seal member positioned adjacent the
rotating seal member and cooperating with the rotating seal member
to define a plurality of seal points.
18. The compressor system of claim 17, wherein one of the rotating
seal member and the stationary seal member includes a plurality of
surfaces and the other of the rotating seal member and the
stationary seal member includes a plurality of teeth, and wherein
each tooth is disposed adjacent one of the plurality of
surfaces.
19. The compressor system of claim 18, wherein the seal portion
disposed nearest the blades defines a first diameter and each
subsequent seal portion defines a surface diameter that is smaller
is the distance of the surface from the blades increases.
20. The compressor system of claim 19, wherein the diameter of the
seal portions are substantially uniformly stepped.
21. The compressor system of claim 18, wherein two adjacent seal
portions are connected by a substantially radial surface, and
wherein one of the plurality of teeth cooperates with one of the
adjacent seal portions to define a radial seal and cooperates with
the radial surface to define an axial seal.
22. The compressor system of claim 17, wherein the exducer defines
an exducer diameter and the rotating seal portion defines an
average seal diameter that is greater than or equal to about 50
percent of the exducer diameter.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. sec. 119 to
provisional patent application Ser. No. 60/718,438, filed on Sep.
19, 2005, which is hereby fully incorporated by reference.
BACKGROUND
[0002] The invention relates to an impeller for a centrifugal
compressor. More particularly, the invention relates to an impeller
for a centrifugal compressor that includes a sealing surface on a
back portion.
[0003] Compression of a gas in centrifugal compressors, also known
as dynamic compressors, is based on the transfer of energy from a
set of rotating impeller blades to the gas. A conventional
centrifugal gas compressor includes a stationary housing and an
impeller within the housing which is rotatable about an axis. Gas,
such as air is directed in a generally axial direction to leading
edges of the impeller blades, and exits at trailing edges of the
blades in a generally radial direction, typically into a diffuser
and then a volute. The rotating blades impart energy by changing
the momentum or velocity, and the pressure of the gas. The gas
momentum, which is related to kinetic energy, is then converted
into pressure energy by decreasing the velocity of the gas in the
stationary diffuser and downstream collecting systems (e.g., the
volute). The pressure of the gas at the trailing edges of the
blades is increased compared to gas at the leading edges of the
blades. Because centrifugal compressors include both stationary and
rotating components, seals are required to contain the compressed
gas discharged from the impeller.
[0004] Due to a non-symmetric stiffness of the impeller,
mass-related body forces induced by rotation (e.g., centrifugal
forces) impart to the impeller, a characteristic displacement
directed toward the blade side of the impeller.
[0005] The net axial thrust acting on a shaft that includes one or
more impellers can be absorbed by a thrust bearing having a load
carrying capacity that generally depends on the bearing type,
design, performance and cost. During operation of the impeller,
different aerodynamically induced conditions may develop so that
the direction of the net thrust may reverse, thus requiring an
additional thrust bearing to maintain the rotor assembly in the
proper axial position with respect to the surrounding stationary
structures of the compressor.
SUMMARY
[0006] In one embodiment, the invention provides an impeller for a
centrifugal gas compressor including a stationary seal member that
includes a plurality of seal tips. The impeller is operable to
produce a flow of fluid. The impeller includes a hub having a front
face and a back face. A plurality of blades extends from the front
face. Each of the blades has an inducer portion and an exducer
portion and cooperates with an adjacent blade and the front face to
at least partially define one of a plurality of impeller channels.
A portion of the flow of fluid passes through one of the impeller
channels such that the flow of fluid defines a first pressure
adjacent the inducer portion and a second pressure that is higher
than the first pressure adjacent the exducer portion. A seal
portion extends from the back face and includes a plurality of
stepped surfaces. Each of the seal tips is disposed adjacent one of
the stepped surfaces to define a plurality of seal points.
[0007] In another embodiment, the invention provides an impeller
for a centrifugal compressor including a stationary seal member
having a plurality of first seal members. The impeller is operable
to produce a flow of fluid. The impeller includes a hub having a
front side, a back side, and a bore extending from the front side
to the back side. A plurality of blades extends from the front
side. Each blade includes an inducer portion and an exducer
portion. The exducer portion defines an outer diameter. A seal
portion extends from the back face and includes a plurality of
second seal members. Each of the first seal members is disposed
adjacent one of the second seal members to define a plurality of
seal points. Each of the seal points is located at a seal point
diameter. The average seal point diameter is greater than or equal
to about 50 percent of the outer diameter.
[0008] In yet another embodiment, the invention provides a
compressor including a motor and an impeller having a hub that is
coupled to the motor. The impeller is rotatable in response to
rotation of the motor and includes a plurality of blades arranged
to define an inducer portion and an exducer portion. The impeller
is operable to draw a flow of fluid into the inducer in a
substantially axial direction and discharge the flow of fluid from
the exducer in a substantially radial direction. A rotating seal
member extends from the impeller and is spaced a non-zero distance
from the hub. A stationary seal member is positioned adjacent the
rotating seal member and cooperates with the rotating seal member
to define a plurality of seal points.
[0009] Other features and advantages of the invention will become
apparent to those skilled in the art upon review of the following
detailed description, claims, and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a cross section view of a fluid compression system
embodying the invention and taken through an axis of rotation;
[0011] FIG. 2 is an enlarged cross section view of an impeller of
the fluid compression system of FIG. 1;
[0012] FIG. 3 is a section view of a portion of the impeller of
FIG. 2;
[0013] FIG. 4 is another section view of a portion of the impeller
of FIG. 2;
[0014] FIG. 5 is a cross section of a stationary seal ring of FIG.
1 taken through an axis of rotation;
[0015] FIG. 6 is a cross section view of two teeth of the
stationary seal ring of FIG. 5;
[0016] FIG. 7 is a cross section view of another stationary seal
ring embodying the invention and including a flow path
therethrough;
[0017] FIG. 8 is a section view of a portion of the centrifugal
compressor of FIG. 2;
[0018] FIG. 9 is a section view of another portion of the
centrifugal compressor of FIG. 2;
[0019] FIG. 10 is a schematic illustration of a pressure
distribution for a prior art impeller; and
[0020] FIG. 11 is a schematic illustration of a pressure
distribution for the impeller of FIG. 2.
DETAILED DESCRIPTION
[0021] Before any embodiments of the invention are explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangement
of components set forth in the following description or illustrated
in the following drawings. The invention is capable of other
embodiments and of being practiced or of being carried out in
various ways. Also, it is to be understood that the phraseology and
terminology used herein is for the purpose of description and
should not be regarded as limiting. The use of "including"
"comprising" or "having" and variations thereof herein is meant to
encompass the items listed thereafter and equivalents thereof as
well as additional items. The order of limitations specified in any
method claims does not imply that the steps or acts set forth
therein must be performed in that order, unless an order is
explicitly set forth in the specification.
[0022] FIG. 1 illustrates a fluid compression system 10 that
includes a prime mover, such as a motor 15 coupled to a compressor
20 and operable to produce a compressed fluid. In the illustrated
construction, an electric motor 15 is employed as the prime mover.
However, other constructions may employ other prime movers such as
but not limited to internal combustion engines diesel engines,
combustion turbines, etc.
[0023] The electric motor 15 includes a rotor 25 and a stator 30
that defines a stator bore 35. The rotor 25 is supported for
rotation on a shaft 40 and is positioned substantially within the
stator bore 35. The illustrated rotor 25 includes permanent magnets
45 that interact with a magnetic field produced by the stator 30 to
produce rotation of the rotor 25 and the shaft 40. The magnetic
field of the stator 30 can be varied to vary the speed of rotation
of the shaft 40. Of course, other constructions may employ other
types of electric motors (e.g., synchronous, induction, brushed DC
motors, etc.) if desired.
[0024] The motor 15 is positioned within a housing 50 which
provides both support and protection for the motor 15. A bearing 55
is positioned on either end of the housing 50 and is directly or
indirectly supported by the housing 50. The bearings 55 in turn
support the shaft 40 for rotation. In the illustrated construction,
magnetic bearings 55 are employed with other bearings (e.g.,
roller, ball, needle, etc.) also suitable for use. In the
construction illustrated in FIG. 1, secondary bearings 60 are
employed to provide shaft support in the event one or both of the
magnetic bearings 55 fail.
[0025] In some constructions, an outer jacket 65 surrounds a
portion of the housing 50 and defines cooling paths 70
therebetween. A liquid (e.g., glycol, refrigerant, etc.) or gas
(e.g., air, carbon dioxide, etc.) coolant flows through the cooling
paths 70 to cool the motor 15 during operation.
[0026] An electrical cabinet 75 may be positioned at one end of the
housing 50 to enclose various items such as a motor controller,
breakers, switches, and the like. The motor shaft 40 extends beyond
the opposite end of the housing 50 to allow the shaft to be coupled
to the compressor 20.
[0027] The compressor 20 includes an intake housing 80 or intake
ring, an impeller 85, a diffuser 90, and a volute 95. The volute 95
includes a first portion 100 and a second portion 105. The first
portion 100 attaches to the housing 50 to couple the stationary
portion of the compressor 20 to the stationary portion of the motor
15. The second portion 105 attaches to the first portion 100 to
define an inlet channel 110 and a collecting channel 115. The
second portion 105 also defines a discharge portion 120 that
includes a discharge channel 125 that is in fluid communication
with the collecting channel 115 to discharge the compressed fluid
from the compressor 20.
[0028] In the illustrated construction, the first portion 100 of
the volute 95 includes a leg 130 that provides support for the
compressor 20 and the motor 15. In other constructions, other
components are used to support the compressor 20 and the motor 15
in the horizontal position. In still other constructions, one or
more legs, or other means are employed to support the motor 15 and
compressor 20 in a vertical orientation or any other desired
orientation.
[0029] The diffuser 90 is positioned radially inward of the
collecting channel 115 such that fluid flowing from the impeller 85
must pass through the diffuser 90 before entering the volute 95.
The diffuser 90 includes aerodynamic surfaces 135 (e.g., blades,
vanes, fins, etc.), shown in FIG. 2, arranged to reduce the flow
velocity and increase the pressure of the fluid as it passes
through the diffuser 90.
[0030] The impeller 85 is coupled to the rotor shaft 40 such that
the impeller 85 rotates with the motor rotor 25. In the illustrated
construction, a rod 140 threadably engages the shaft 40 and a nut
145 threadably engages the rod 140 to fixedly attach the impeller
85 to the shaft 40. The impeller 85 extends beyond the bearing 55
that supports the motor shaft 40 and, as such is supported in a
cantilever fashion. Other constructions may employ other attachment
schemes to attach the impeller 85 to the shaft 40 and other support
schemes to support the impeller 85. As such, the invention should
not be limited to the construction illustrated in FIG. 1.
Furthermore, while the illustrated construction includes a motor 15
that is directly coupled to the impeller 85, other constructions
may employ a speed increaser such as a gear box to allow the motor
15 to operate at a lower speed than the impeller 85.
[0031] The impeller 85 includes a plurality of aerodynamic surfaces
or blades 150 that are arranged to define an inducer portion 155
and an exducer portion 160. The inducer portion 155 is positioned
at a first end of the impeller 85 and is operable to draw fluid
into the impeller 85 in a substantially axial direction. The blades
150 accelerate the fluid and direct it toward the exducer portion
160 located near the opposite end of the impeller 85. The fluid is
discharged from the exducer portion 160 in at least partially
radial directions that extend 360 degrees around the impeller
85.
[0032] The impeller 85 cooperates with a stationary seal ring 270
to define a seal. The seal is positioned to reduce the axial force
applied to the back face of the impeller 85, thereby reducing the
overall axial thrust toward the blades 150. The thrust is reduced
to a level that allows for the use of an active magnetic thrust
bearing 163 rather than a more conventional thrust bearing. The
magnetic thrust bearing 163 includes a thrust disc 164 having a
reduced diameter as compared to that which would be necessary
absent the aforementioned seal system.
[0033] The intake housing 80, sometimes referred to as the intake
ring, is connected to the volute 95 and includes a flow passage 165
that leads to the impeller 85. Fluid to be compressed is drawn by
the impeller 85 down the flow passage 165 and into the inducer
portion 155 of the impeller 85. The flow passage 165 includes an
impeller interface portion 170 that is positioned near the blades
150 of the impeller 85 to reduce leakage of fluid over the top of
the blades 150. Thus, the impeller 85 and the intake housing 80
cooperate to define a plurality of substantially closed flow
passages 175.
[0034] In the illustrated construction, the intake housing 80 also
includes a flange 180 that facilitates the attachment of a pipe or
other flow conducting or holding component. For example, a filter
assembly could be connected to the flange 180 and employed to
filter the fluid to be compressed before it is directed to the
impeller 85. A pipe would lead from the filter assembly to the
flange 180 to substantially seal the system after the filter and
inhibit the entry of unwanted fluids or contaminates.
[0035] Turning to FIG. 2, the impeller 85 is illustrated in greater
detail. The impeller 85 includes a hub 181 or body having a front
side 182 from which the blades extend and a back side 184 opposite
the front side 182. The inducer portion 155 is substantially
annular and draws fluid along an intake path 185 into the impeller
85. The fluid enters in a substantially axial direction and flows
through the passages 175 defined between adjacent blades 150 to the
exducer portion 160. The outlet of the exducer portion 160 defining
an outside diameter 190 of the impeller 85.
[0036] FIG. 3 illustrates the back side 184 of the impeller 85 as
including a balancing ring 195, all extension 200, and an alignment
portion 205. The alignment portion 205 is sized to fit at least
partially within a bore 210 formed as part of the shaft 40. This
provides support for the impeller 85 to inhibit mis-alignment
between the shaft 40 and the impeller 85 that can produce
undesirable vibrations. In some constructions, the shaft bore 210
and the alignment portion 205 includes alignment features (e.g.,
splines) that aid in providing the desired alignment.
[0037] The balancing ring 195 provides additional material on the
back side 184 of the impeller 85 for use during balancing. Material
can be removed from the balance ring 195 at select radial and
angular positions to statically and dynamically balance the
impeller 85 as required for the particular application. Of course,
other constructions position the balance ring 195 differently or
omit the balance ring 195 completely.
[0038] The extension 200 extends from the back side 184 in a
generally axial direction away from the blades 150. The extension
200 includes a first seal portion 215 that includes a plurality of
seal surfaces 220, and an inner surface 225 that, in some
constructions, may include another plurality of seal surfaces. The
first seal portion 215 defines an average radial diameter 230 that,
in preferred constructions is greater than about 50 percent of the
outermost diameter 190 of the impeller 85. The position of the
extension 200 divides the back side 184 of the impeller 85 into a
first annular 235 area disposed radially outside of the extension
200 and extending to the outermost diameter 190 of the impeller 85,
and a second annular area 240 disposed radially inside of the
extension 200 and extending radially inward to the alignment
portion 205.
[0039] FIG. 4 illustrates the extension 200 in greater detail. An
envelope 245 around the cantilevered extension 200 in a cross
section that includes the axis is generally trapezoidal. In three
dimensions, the outer envelope of the extension 200 includes two
frustoconical surfaces, although other shapes for the extension 200
are also possible. The plurality of seal surfaces 220 of the first
seal portion 215 are defined by a plurality of steps 250. Each step
250 includes a generally axially extending first portion 255 and a
generally radially extending second portion 260, with the first
portion 255 forming substantially a right angle with the second
portion 260. As shown in FIG. 4, the first axially-extending
surface 255 nearest the back side 184 has the largest diameter with
each subsequent axial surface 255 reducing in diameter as they move
further from the back side 184. In other words, a sequence defined
by corresponding radial dimensions of the axial surfaces 255 taken
in axial order, starting with the surface 255 nearest the blades
150 decreases substantially uniformly. The generally radial
surfaces 260 interconnect adjacent axial surfaces 255 to complete
the plurality of seal surfaces 220. In preferred constructions, the
axial surfaces 255 are substantially equal in axial length and the
radial change between any two adjacent axial surfaces 255 is
approximately equal. In other words, the radial surfaces 260 are
all substantially equal in length. In other constructions, other
step patterns are employed. For example, one construction employs
alternating high portions and low portions. Thus, the invention
should not be limited to the illustrated pattern of seal surfaces
220 alone.
[0040] In preferred constructions, the extension 200, the balance
ring 195, the alignment portion 205, and the blades 150, are
integrally-formed from a single homogeneous piece of material. Of
course other constructions, may attach or otherwise form the
various components.
[0041] Returning to FIG. 2, the illustrated construction includes a
bearing support housing 265 that attaches to the motor housing 50.
The bearing support housing 265 at least partially supports the
bearings 55, 60 and may also support other stationary components of
the fluid compression system 10. A stationary seal ring 270 that
attaches to the bearing support housing 265 includes a second seal
portion 275 that is positioned adjacent the first seal portion 215
to define a seal 280. As will be discussed in greater detail with
regard to FIG. 11, the seal 280 is preferably a labyrinth-type
seal.
[0042] FIG. 5 illustrates the stationary seal ring 270 in greater
detail than that shown in FIG. 2. The stationary seal ring 270
includes the second seal portion 275, a flange 285, a plurality of
bolt holes 290, and an alignment surface 295. The flange 285 is
arranged to abut against a substantially radial planar surface 298
to position the stationary seal ring 270 in the desired axial
position. In preferred constructions a shim 300 (shown in FIG. 2)
having a selectable or adjustable thickness is positioned between
the flange 285 and the radial planar surface 298 to set the axial
position of the stationary seal ring 270. Bolts 305 (shown in FIG.
2) pass through the bolt holes 290 and attach the stationary seal
ring 270 to the bearing support housing 265 or other stationary
component.
[0043] The alignment surface 295 fits within a bore 310 formed as
part of the bearing support housing 265 and sized to receive the
alignment surface 295. In preferred constructions, a slight
interference or press fit is employed to assure that the stationary
seal ring 270 is positioned coaxially with the bearing support
housing 265. To accommodate the press fit, the alignment surface
295 may include crush features 315 such as bumps, grooves, or other
features that allow for easier deformation during assembly. Once
the bearing support housing 265 and the stationary, seal ring 270
are coupled to one another, very little relative movement is
possible. Jack bolts may be employed for disassembly. In
constructions that employ jack bolts, additional threaded apertures
pass through the flange 285 to allow the bolts to separate the
stationary seal ring 270 and the bearing support housing 265. In
other constructions, the bearing support housing 265 and the
stationary seal ring 270 are formed as a single component or more
than two components if desired.
[0044] As illustrated in FIG. 5, the second seal portion 275
includes a plurality of teeth 320 that extend at least partially
radially inward. FIG. 6 illustrates two of the teeth 320 and a
cavity 323 therebetween in greater detail. Each tooth 320 is
substantially trapezoidal in cross-section with large fillet
radiuses between adjacent teeth 320 and between the teeth 320 and
the remainder of the stationary seal ring 270. Each tooth 320 thus
includes an upstream side 325 and a downstream side 330 that extend
at least partially radially inward and terminate at a tip surface
335. In the illustrated construction, the upstream side 325 and
downstream side 330 are not parallel. Specifically, each tooth 320
generally extends in a direction having both a radial component and
an axial component such that each tooth defines an oblique angle
331 with respect to an axis 332. The downstream side 330 of each
tooth 320 is oriented at approximately 45 degrees with respect to
the axial direction and the upstream side 325 of each tooth 320 is
oriented at approximately 30 degrees with respect to the radial
direction. However, other constructions may employ parallel
upstream sides 325 and downstream sides 330 or angles other than
those illustrated herein.
[0045] The tip surface 335 extends in a substantially axial
direction and defines a tip radius 340. In the illustrated
construction, the tip radius 340 of the tooth 320 adjacent the
impeller 85 is the largest with each adjacent tooth 320 having a
tip radius 340 that is slightly smaller as the teeth 320 get
further from the impeller 85. In other words, a sequence defined by
corresponding radial dimensions 340 of the tip surfaces 335 in
axial order, starting with a tooth 320 axially nearest the blades
150, is axially decreasing. In a preferred construction, the change
in the radius 340 of each tip surface 335 is approximately equal to
the change in radius of the plurality of axial step surfaces 255.
In other constructions, the teeth 320 have sharp or knife edge
tips, rather than the axial surface 335 illustrated herein. In
still other constructions, rounded tips are employed.
[0046] FIG. 7 illustrates another construction of a stationary seal
ring 345 that is similar to the stationary seal ring 270 of FIG. 5
but additionally includes a flow passage 350. The flow passage 350
divides the stationary seal ring 345 into a high-pressure portion
355 and a low-pressure portion 360 and is particularly suited for
use in applications where it is desirable to isolate the fluid
being compressed. A gas at a higher pressure than the expected
pressure of the compressed fluid at the point of entry of the flow
passage 350 can be introduced at the flow passage 350. The
high-pressure gas will inhibit the flow of the compressed fluid
past the flow passage 350. Rather, the introduced gas will flow
through the low-pressure portion 360 of the seal ring 345.
Alternatively, a low pressure can be applied at the flow passage
350 such that fluid being compressed passes through the
high-pressure portion 355 and air is drawn in through the
low-pressure portion 360. The air and fluid being compressed mix in
the flow passage 350 and are drawn out of the system 10.
[0047] FIG. 8 illustrates the completed labyrinth seal 280 in
greater detail. In the illustrated construction, each tip surface
335 aligns with one of the axial surfaces 255 to define a radial
seal point 365 having a narrow gap 370 between the tip surface 335
and the axial surface 255. In addition, some constructions may
position the tooth 320 adjacent the radially-extending surface 260
to define an axial seal point 375. In other constructions, other
arrangements may be employed. For example, multiple teeth 320 could
be positioned over common axial surfaces 255 Alternatively,
straight teeth could be employed.
[0048] The labyrinth seal 280 provides for an adequate seal without
undesirable contact between the rotating and the stationary
components. Should such contact inadvertently occur, the relatively
narrow teeth 320 provide little surface area for friction and
heating. Additionally, one or both of the seal surfaces 335, 255
can be made of a resilient or abradeable material to further reduce
the likelihood of damage to the impeller 85 or the stationary seal
ring 270 should undesirable contact occur.
[0049] In operation, power is provided to the motor 15 to produce
rotation of the shaft 40 and the impeller 85. As the impeller 85
rotates, fluid to be compressed is drawn into the intake housing 80
and into the inducer portion 155 of the impeller 85. The impeller
85 accelerates the fluid from a velocity near zero to a high
velocity at the exducer portion 160. In addition, the impeller 85
produces an increase in pressure between the inducer 155 and the
exducer 160.
[0050] After passing through the impeller 85, the fluid enters the
diffuser 90. The diffuser 90 acts on the fluid to reduce the
velocity. The velocity reduction converts the dynamic energy of the
flow of fluid into potential energy or high pressure. The now
high-pressure fluid exits the diffuser 90 and inters the volute 95
via the inlet channel 110. The high-pressure fluid then passes into
the collecting channel 115 which collects fluid from any angular
position around the inlet channel 110. The collecting channel 115
then directs the high-pressure fluid out of the volute 95 via the
discharge channel 125. Once discharged from the volute 95, the
fluid can be passed to several different components, including but
not limited to a drying system, an inter-stage heat exchanger,
another compressor, a storage tank, a user, an air use system,
etc.
[0051] With reference to FIG. 9, it can be seen that a space 380 is
provided between the rotating impeller 85 and the stationary
diffuser 90. While it is desirable to make this space 380 small, it
is inevitable that some compressed fluid will leak around the
impeller 85, through this space 380, and to the back side 184 of
the impeller 85. This high-pressure leakage flow 385 passes
radially inward until it reaches the labyrinth seal 280. To pass
through the labyrinth seal 280, the leakage flow must pass between
each tip surface 335 and the radial and axial surfaces 255, 260
adjacent the tooth 320. The flow 385 first must accelerate to pass
through the narrow gap 370 or openings defined between the tooth
320 and the respective radial and axial surfaces 255, 260. After
passing through these narrow gaps 370, the flow 385 is exposed to
the relatively large cavity 323 between the adjacent teeth 320 and
rapidly expands to fill the cavity 323. The expansion is
inefficient and produces a series of eddies and flow vortices that
slightly reduce the pressure of the fluid. In addition, the
rotation of the impeller 85 tends to force the fluid radially
outward into the bottom of the cavity 323 and away from the next
seal opening 370 that is disposed radially inward of the prior seal
opening 370. This process continues as the flow 385 passes each
tooth 320 until the flow 385 finally exits the labyrinth seal 280
at a pressure that is only slightly greater than atmospheric
pressure (or the ambient pressure of the compression system
10).
[0052] A flow of cooling air 390 passes through the motor 15 and
the bearings 55, 60 and enters the space between the impeller 85
and the bearing support housing 265. The cooling air 390 is also at
a pressure slightly above atmospheric pressure (or ambient
pressure) and preferably at a pressure slightly above the pressure
of the leakage flow 385 exiting the labyrinth seal 280. The two
flows 385, 390 mix and exit the system via a vent 395 formed in the
housing 50. By maintaining the cooling air 390 at a pressure
slightly higher than the leakage flow 385, the system 10 inhibits
the unwanted flow 385 of hot leakage flow into the motor 15. In
addition, the clearance space between the impeller 85 and the
bearing support housing 265 is maintained at a small value to
further inhibit the passage of hot leakage flow 385 into the
bearings 55, 60 and the motor 15.
[0053] The positioning of the extension 200 also aids in balancing
the thrust load produced by the impeller 85 during operation. FIG.
10 illustrates a prior art impeller 400 that includes a standard
seal arrangement on the shaft. Shaft seals are generally employed
as the flow area at the shaft for a given radial clearance is
smaller than the flow area for the same radial clearance at a
larger diameter. During operation, the innermost leading edge of
the impeller 400 is exposed to a pressure that is slightly above
the intake pressure of the impeller 400. The pressure increases in
a substantially linear fashion as the flow moves along the
impeller. At the exit of the impeller (exducer) the pressure is at
its highest level (prior to passage through the diffuser and the
volute). Thus, the front portion of the impeller 400 is exposed to
a pressure gradient 405 that increases with the radial distance
from the axis of rotation.
[0054] A portion of the high-pressure fluid exiting the impeller
400 flows around the outer diameter of the impeller 400 to the back
portion. There is no mechanism, other than the shaft seals on the
back portion of the prior art impeller 400 to reduce the pressure
of the leakage flow. As such, the entire back portion is exposed to
the high-pressure fluid. Thus, the back face is subjected to a
substantially uniform pressure gradient 410 across the entire area.
This results in a net thrust force toward the inlet as indicated by
arrow 415.
[0055] Turning to FIG. 11, the present impeller 85 is illustrated
for comparison. The pressure and the pressure gradient 420 applied
to the front side 182 of the impeller 85 is substantially the same
as that of the prior art impeller 400 of FIG. 10. However, the
position of the extension 200 produces a different pressure
gradient 425 on the back side 184. As can be seen, the
high-pressure leakage is applied only to the first annular portion
235 disposed radially outside of the extension 200. The pressure
level is reduced as the flow passes through the labyrinth seal 280
such that a much lower pressure (nearly atmospheric or ambient) is
applied to the remainder of the back side 184 of the impeller 85.
While the net axial thrust, as indicated by arrow 430, is still
toward the inducer 155, the magnitude of the thrust is greatly
reduced. The reduced thrust allows for the use of a smaller thrust
bearing that consumes less power and is less susceptible to
excessive heating.
[0056] While the illustrated construction employs an extension 200
positioned to maintain the direction of the net axial thrust as
illustrated in FIGS. 10 and 11, it should be readily apparent that
the position of the extension 200 could be changed to adjust, and
potentially reverse the thrust load if desired.
[0057] It should be noted that other arrangements of the
compression system 10 may be exposed or operated in pressure
regimes other than atmospheric. For example, multi-stage
compression systems may employ stages in which the outlet of the
labyrinth seal 280 is at a pressure that is much greater than
atmospheric pressure. As such, the invention should not be limited
to the pressure values disclosed herein.
[0058] Thus, the invention provides, among other things, a
compressor system 10 that includes an impeller 85 having a seal
system arranged to improve the performance of the impeller 85.
Various features and advantages of the invention are set forth in
the following claims.
* * * * *