U.S. patent application number 11/350537 was filed with the patent office on 2007-08-09 for leaned deswirl vanes behind a centrifugal compressor in a gas turbine engine.
This patent application is currently assigned to Honeywell International, Inc.. Invention is credited to Nick A. Nolcheff, Michon N. Plummer, John A. Slovisky.
Application Number | 20070183890 11/350537 |
Document ID | / |
Family ID | 38024292 |
Filed Date | 2007-08-09 |
United States Patent
Application |
20070183890 |
Kind Code |
A1 |
Nolcheff; Nick A. ; et
al. |
August 9, 2007 |
Leaned deswirl vanes behind a centrifugal compressor in a gas
turbine engine
Abstract
A compressor includes a deswirl assembly to improve aerodynamic
coupling with the combustor. The assembly includes an annular
housing and a plurality of vanes. The annular housing includes an
inner and an outer annular wall disposed concentric to each other,
and a flowpath defined therebetween. The plurality of vanes is
disposed in the flowpath in a substantially annular pattern. Each
vane has a leading edge, a trailing edge, a convex surface, and
concave surface, and each of the convex and concave surfaces
extends between the leading and trailing edges. Additionally, each
vane extends between and is angled relative to the inner and the
outer annular walls such that the concave surface faces the outer
annular wall and the convex surface faces the inner annular wall.
The vanes preferably have a uniform axial cross section for ease of
manufacturing.
Inventors: |
Nolcheff; Nick A.;
(Chandler, AZ) ; Slovisky; John A.; (Chandler,
AZ) ; Plummer; Michon N.; (Chandler, AZ) |
Correspondence
Address: |
HONEYWELL INTERNATIONAL INC.
101 COLUMBIA ROAD
P O BOX 2245
MORRISTOWN
NJ
07962-2245
US
|
Assignee: |
Honeywell International,
Inc.
|
Family ID: |
38024292 |
Appl. No.: |
11/350537 |
Filed: |
February 9, 2006 |
Current U.S.
Class: |
415/191 |
Current CPC
Class: |
F05D 2240/128 20130101;
F01D 9/02 20130101; F05D 2240/12 20130101; F04D 29/444 20130101;
F05D 2240/127 20130101; F05D 2240/30 20130101 |
Class at
Publication: |
415/191 |
International
Class: |
F01D 9/00 20060101
F01D009/00 |
Claims
1. A deswirl assembly for receiving air flow from a diffuser, the
deswirl assembly comprising: an annular housing including an inner
annular wall, an outer annular wall disposed concentric to the
inner annular wall, and a flowpath defined therebetween; and a
plurality of vanes disposed in the flowpath in a substantially
annular pattern, each vane having a leading edge, a trailing edge,
a convex surface, and concave surface, each of the convex and
concave surfaces extending between the leading and trailing edges,
each vane extending between and angled relative to the inner and
the outer annular walls such that the concave surface faces the
outer annular wall and the convex surface faces the inner annular
wall.
2. The deswirl assembly of claim 1, wherein each vane has an axial
cross section shape, and each axial cross section shape is
substantially the same.
3. The deswirl assembly of claim 1, further comprising a second
plurality of vanes disposed in the flowpath in a substantially
annular pattern downstream of the first plurality of vanes.
4. The deswirl assembly of claim 1, wherein the trailing edges of
the vanes of the first plurality of vanes are disposed around a
first circumferential position around the inner annular wall and
the leading edges of the vanes of the second plurality of vanes are
disposed around a second circumferential position around the inner
annular wall.
5. The deswirl assembly of claim 4, wherein the first and second
circumferential positions do not overlap.
6. The deswirl assembly of claim 4, wherein the first
circumferential position is disposed downstream of the first
circumferential position.
7. The deswirl assembly of claim 4, wherein the vanes of the second
plurality of vanes are each staggered between vanes of the first
plurality of vanes.
8. The deswirl assembly of claim 7, wherein at least one vane of
the first plurality of vanes is disposed between two vanes of the
second plurality of vanes and a first distance between the at least
one vane of the first plurality of vanes and one of the two vanes
of the second plurality of vanes is less than a second distance
between the two vanes of the second plurality of vanes.
9. The deswirl assembly of claim 8, wherein the first distance is
about 35% of the second distance.
10. A deswirl assembly for receiving air flow from a diffuser, the
deswirl assembly comprising: an annular housing including an inner
annular wall, an outer annular wall disposed concentric to the
inner annular wall, and a flowpath defined therebetween; a first
plurality of vanes disposed in the flowpath in a substantially
annular pattern, each vane having a leading edge, a trailing edge,
a convex surface, and concave surface, each of the convex and
concave surfaces extending between the leading and trailing edges,
each vane extending between and angled relative to the inner and
the outer annular walls such that the concave surface faces the
outer annular wall and the convex surface faces the inner annular
wall and each vane has an axial cross section shape, each axial
cross section shape being substantially the same; and a second
plurality of vanes disposed in the flowpath in a substantially
annular pattern downstream of the first plurality of vanes, each
vane having a leading edge, a trailing edge, a convex surface, and
concave surface, each of the convex and concave surfaces extending
between the leading and trailing edges, each vane extending between
and angled relative to the inner and the outer annular walls such
that the concave surface faces the outer annular wall and the
convex surface faces the inner annular wall and each vane has an
axial cross section shape, each axial cross section shape being
substantially the same.
11. The deswirl assembly of claim 10, wherein the trailing edges of
the vanes of the first plurality of vanes are disposed around a
first circumferential position around the inner annular wall and
the leading edges of the vanes of the second plurality of vanes are
disposed around a second circumferential position around the inner
annular wall.
12. The deswirl assembly of claim 11, wherein the first and second
circumferential positions do not overlap.
13. The deswirl assembly of claim 11, wherein the first
circumferential position is disposed downstream of the first
circumferential position.
14. The deswirl assembly of claim 11, wherein the vanes of the
second plurality of vanes are each staggered between vanes of the
first plurality of vanes.
15. The deswirl assembly of claim 14, wherein at least one vane of
the first plurality of vanes is disposed between two vanes of the
second plurality of vanes and a first distance between the at least
one vane of the first plurality of vanes and one of the two vanes
of the second plurality of vanes is less than a second distance
between the two vanes of the second plurality of vanes.
16. The deswirl assembly of claim 15, wherein the first distance is
about 35% of the second distance.
17. A system for aerodynamically coupling air flow from a
centrifugal compressor to an axial combustor, the compressor and
combustor disposed about a longitudinal axis, the system
comprising: a diffuser having an inlet, an outlet and a flow path
extending therebetween, the diffuser inlet in flow communication
with the centrifugal compressor, and the diffuser flow path
extending radially outward from the longitudinal axis; a deswirl
assembly coupled to the diffuser and comprising: an annular housing
including an inner annular wall, an outer annular wall disposed
concentric to the inner annular wall, and a flowpath defined
therebetween, the flow path in flow communication with the diffuser
outlet to receive air flowing in a radially outward direction, and
the deswirl assembly flow path configured to redirect the air in a
radially inward and axial direction through the deswirl assembly
outlet at an angle toward the longitudinal axis; and a plurality of
vanes disposed in the flowpath in a substantially annular pattern,
each vane having a leading edge, a trailing edge, a convex surface,
and concave surface, each of the convex and concave surfaces
extending between the leading and trailing edges, each vane
extending between and angled relative to the inner and the outer
annular walls such that the concave surface faces the outer annular
wall and the convex surface faces the inner annular wall; a
combustor inner annular liner disposed about the longitudinal axis,
the inner annular liner having an upstream end; a combustor outer
annular liner disposed concentric to the combustor inner annular
liner and forming a combustion plenum therebetween, the outer
annular liner having an upstream end; a combustor dome coupled to
and extending between the combustor inner and outer annular liner
upstream ends; and a curved annular plate coupled to the combustor
inner and outer annular liner upstream ends to form a combustor
subplenum therebetween, the curved annular plate having a first
opening and a second opening formed therein, the first opening
aligned with the deswirl assembly outlet to receive air discharged
therefrom.
18. The deswirl assembly of claim 17, wherein each vane has an
axial cross section shape, and each axial cross section shape is
substantially the same.
19. The deswirl assembly of claim 17, further comprising a second
plurality of vanes disposed in the flowpath in a substantially
annular pattern downstream of the first plurality of vanes.
20. The deswirl assembly of claim 17, wherein: the vanes of the
second plurality of vanes are each staggered between vanes of the
first plurality of vanes; at least one vane of the first plurality
of vanes is disposed between two vanes of the second plurality of
vanes and a first distance between the at least one vane of the
first plurality of vanes and one of the two vanes of the second
plurality of vanes is less than a second distance between the two
vanes of the second plurality of vanes; and the first distance is
about 35% of the second distance.
Description
TECHNICAL FIELD
[0001] The present invention relates to a gas turbine engine and,
more particularly, to a deswirl assembly having leaned deswirl
vanes for use in the gas turbine engine.
BACKGROUND
[0002] A gas turbine engine may be used to power various types of
vehicles and systems. A typical gas turbine engine includes a fan
section, a compressor section, a combustor section, a turbine
section, and an exhaust section. The fan section induces air from
the surrounding environment into the engine and accelerates a
fraction of the air toward the compressor section. The compressor
section compresses the pressure of the air to a relatively high
level and directs the air to the combustor section. A steady stream
of fuel is injected into the combustor section, and the injected
fuel is ignited to significantly increase the energy of the
compressed air. The high-energy compressed air then flows into and
through the turbine section, causing rotationally mounted turbine
blades therein to rotate and generate energy. The air exiting the
turbine section is exhausted from the engine via the exhaust
section, and the energy remaining in the exhaust air aids the
thrust generated by the air flowing through a bypass plenum.
[0003] In some engines, the compressor section is implemented with
a centrifugal compressor. A centrifugal compressor typically
includes at least one impeller that is rotationally mounted to a
rotor and surrounded by a shroud. When the impeller rotates, it
compresses and imparts tangential velocity to the air received from
the fan section and the shroud directs the air radially outward
into a diffuser. The diffuser decreases the radial and tangential
velocity of the air and increases the static pressure of the air
and directs the air into a deswirl assembly. The deswirl assembly
includes an annular housing having a plurality of straight radially
extending vanes mounted therein that straighten and reduce the
tangential velocity component of the air flow before it enters the
combustor section. The combustor section in some engines is
implemented with an axial through flow combustor that includes an
annular combustor disposed within a combustor housing that defines
a plenum. The straightened air enters the plenum and travels
axially through the annular combustor where it is mixed with fuel
and ignited.
[0004] Recently, conventional deswirl assemblies have included
downcanted outlets to improve aerodynamic coupling between the
diffuser and combustor. However, it has been found that these
deswirl assemblies generate greater flow angle variation across the
span of the flowpath at the deswirl vane leading edge and therefore
may not adequately condition air flow to a sufficiently low mach
number in an acceptably efficient manner unless the overall axial
length and/or radial envelope of the assembly is increased. Because
engines are continually designed to be smaller, the size increase
may not be acceptable in newer aircraft. As a result, the
configuration of the deswirl assembly has had to be redesigned. One
preferred configuration includes vanes that are shaped so that the
vane can accept a large variation in air angle at its leading edge.
The vanes may also be configured such that the pressure side of
each vane faces radially inwardly. However, although this
configuration optimizes airflow through the deswirl assembly,
manufacture of the assembly is relatively time-consuming and costly
because each vane may need to be individually formed and
shaped.
[0005] Hence, there is a need for an improved downcanted deswirl
assembly that includes a plurality of vanes that are configured to
aerodynamically couple a centrifugal compressor and an axial
through-flow combustor. Additionally, it is desirable for the
deswirl assembly to be relatively inexpensive and simple to
manufacture. Moreover, it is desirable for the deswirl assembly to
suitably direct and condition the air flowing there through for
optimal engine performance.
BRIEF SUMMARY
[0006] The present invention provides a deswirl assembly for
receiving air flow from a diffuser. The deswirl assembly includes
an annular housing and a plurality of vanes. The annular housing
includes an inner annular wall, an outer annular wall disposed
concentric to the inner annular wall, and a flowpath defined
therebetween. The plurality of vanes is disposed in the flowpath in
a substantially annular pattern. Each vane has a leading edge, a
trailing edge, a convex surface, and concave surface, and each of
the convex and concave surfaces extends between the leading and
trailing edges. Additionally, each vane extends between and is
angled relative to the inner and the outer annular walls such that
the concave surface faces the outer annular wall and the convex
surface faces the inner annular wall.
[0007] In one embodiment, and by way of example only, the deswirl
assembly including an annular housing, and a first and a second
plurality of vanes. The annular housing includes an inner annular
wall, an outer annular wall disposed concentric to the inner
annular wall, and a flowpath defined therebetween. The first
plurality of vanes is disposed in the flowpath in a substantially
annular pattern, and each vane has a leading edge, a trailing edge,
a convex surface, and concave surface, each of the convex and
concave surfaces extending between the leading and trailing edges,
each vane extends between and is angled relative to the inner and
the outer annular walls such that the concave surface faces the
outer annular wall and the convex surface faces the inner annular
wall and each vane has an axial cross section shape, and each axial
cross section shape is substantially the same. The second plurality
of vanes is disposed in the flowpath in a substantially annular
pattern downstream of the first plurality of vanes. Each vane has a
leading edge, a trailing edge, a convex surface, and concave
surface, each of the convex and concave surfaces extends between
the leading and trailing edges, and each vane extends between and
is angled relative to the inner and the outer annular walls such
that the concave surface faces the outer annular wall and the
convex surface faces the inner annular wall. Additionally, each
vane of the second plurality of vanes has an axial cross section
shape, and each axial cross section shape is substantially the
same.
[0008] In still another embodiment, a system is provided for
aerodynamically coupling air flow from a centrifugal compressor to
an axial combustor, where the compressor and combustor are disposed
about a longitudinal axis. The system includes a diffuser, a
deswirl assembly, combuster inner and outer annular liners, a
combustor dome, and a curved annular plate. The diffuser has an
inlet, an outlet and a flow path extending therebetween, where the
diffuser inlet is in flow communication with the centrifugal
compressor, and the diffuser flowpath extends radially outward from
the longitudinal axis. The deswirl assembly includes an annular
housing and a plurality of vanes. The annular housing includes an
inner annular wall, an outer annular wall disposed concentric to
the inner annular wall, and a flowpath defined therebetween. The
plurality of vanes is disposed in the flowpath in a substantially
annular pattern. Each vane has a leading edge, a trailing edge, a
convex surface, and concave surface, and each of the convex and
concave surfaces extends between the leading and trailing edges.
Additionally, each vane extends between and is angled relative to
the inner and the outer annular walls such that the concave surface
faces the outer annular wall and the convex surface faces the inner
annular wall. The combustor inner annular liner is disposed about
the longitudinal axis, and the inner annular liner has an upstream
end. The combustor outer annular liner is disposed concentric to
the combustor inner annular liner and forms a combustion plenum
therebetween. The outer annular liner has an upstream end. The
combustor dome is coupled to and extends between the combustor
inner and outer annular liner upstream ends. The curved annular
plate is coupled to the combustor inner and outer annular liner
upstream ends to form a combustor subplenum therebetween, and the
curved annular plate has a first opening and a second opening
formed therein. The first opening is aligned with the deswirl
assembly outlet to receive air discharged therefrom.
[0009] Other independent features and advantages of the preferred
deswirl assembly will become apparent from the following detailed
description, taken in conjunction with the accompanying drawings
which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a simplified cross section side view of an
exemplary multi-spool turbofan gas turbine jet engine according to
an embodiment of the present invention;
[0011] FIG. 2 is a cross section view of a portion of an exemplary
combustor that may be used in the engine of FIG. 1;
[0012] FIG. 3 is a cutaway view of a portion of an exemplary
deswirl assembly that may be implemented into the combustor shown
in FIG. 2 forward looking aft;
[0013] FIG. 4 is the portion of the exemplary deswirl assembly
shown in FIG. 3 aft looking forward; and
[0014] FIG. 5 is a top view of the exemplary deswirl assembly shown
in FIG. 3.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0015] Before proceeding with the detailed description, it is to be
appreciated that the described embodiment is not limited to use in
conjunction with a particular type of turbine engine. Thus,
although the present embodiment is, for convenience of explanation,
depicted and described as being implemented in a multi-spool
turbofan gas turbine jet engine, it will be appreciated that it can
be implemented in various other types of turbines, and in various
other systems and environments.
[0016] An exemplary embodiment of a multi-spool turbofan gas
turbine jet engine 100 is depicted in FIG. 1, and includes an
intake section 102, a compressor section 104, a combustion section
106, a turbine section 108, and an exhaust section 110. The intake
section 102 includes a fan 112, which is mounted in a fan case 114.
The fan 112 draws air into the intake section 102 and accelerates
it. A fraction of the accelerated air exhausted from the fan 112 is
directed through a bypass section 116 disposed between the fan case
114 and an engine cowl 118, and provides a forward thrust. The
remaining fraction of air exhausted from the fan 112 is directed
into the compressor section 104.
[0017] The compressor section 104 includes two compressors, an
intermediate pressure compressor 120, and a high pressure
compressor 122. The intermediate pressure compressor 120 raises the
pressure of the air directed into it from the fan 112, and directs
the compressed air into the high pressure compressor 122. The high
pressure compressor 122 compresses the air still further, and
directs the high pressure air into the combustion section 106. In
the combustion section 106, which includes an annular combustor
124, the high pressure air is mixed with fuel and combusted. The
combusted air is then directed into the turbine section 108.
[0018] The turbine section 108 includes three turbines disposed in
axial flow series, a high pressure turbine 126, an intermediate
pressure turbine 128, and a low pressure turbine 130. The combusted
air from the combustion section 106 expands through each turbine,
causing it to rotate. The air is then exhausted through a
propulsion nozzle 132 disposed in the exhaust section 110,
providing additional forward thrust. As the turbines rotate, each
drives equipment in the engine 100 via concentrically disposed
shafts or spools. Specifically, the high pressure turbine 126
drives the high pressure compressor 122 via a high pressure spool
134, the intermediate pressure turbine 128 drives the intermediate
pressure compressor 120 via an intermediate pressure spool 136, and
the low pressure turbine 130 drives the fan 112 via a low pressure
spool 138.
[0019] Turning now to FIG. 2, an exemplary cross section of the
area between the high pressure compressor 122 and annular combustor
124 is illustrated. In addition to the compressor 122 and combustor
124, FIG. 2 depicts a diffuser 204 and a deswirl assembly 206, each
disposed about a longitudinal axis 207. The high pressure
compressor 122 is preferably a centrifugal compressor and includes
an impeller 208 and a shroud 210 disposed in a compressor housing
211. The impeller 208, as alluded to above, is driven by the high
pressure turbine 126 and rotates about the longitudinal axis 207.
The shroud 210 is disposed around the impeller 208 and defines an
impeller discharge flow passage 212 therewith that extends radially
outwardly.
[0020] The diffuser 204 is coupled to the shroud 210 and is
configured to decrease the velocity and increase the static
pressure of air that is received therefrom. In this regard, any one
of numerous conventional diffusers 204 suitable for operating with
a centrifugal compressor may be employed. In any case, the diffuser
204 includes an inlet 214, an outlet 216, and a flow path 218 that
each communicates with the passage 212, and the flow path 218 is
configured to direct the received air flow radially outwardly.
[0021] The deswirl assembly 206 communicates with the diffuser 204
and is configured to substantially remove swirl from air received
therefrom, to thereby decrease the Mach number of the air flow. The
deswirl assembly 206 includes an inner annular wall 220, an outer
annular wall 222, and two pluralities of vanes 224, 226 disposed
therebetween. The walls 220, 222 define a flow path 228 that is
configured to redirect the air from its radially outward direction
to a radially inward and axially downstream direction. In this
regard, the walls 220, 222 are formed such that the flow path 228
extends between an inlet 230 and outlet 232 in an arc 233 so that
when the air exits the outlet 232, it is directed at an angle and
toward the longitudinal axis 207 and the annular combustor 124. As
the angle of the arc 233 is increased the variation of the air
angle between the inner wall 220 and out wall 222 is increased.
[0022] As briefly mentioned above, the two pluralities of vanes
224, 226 are disposed between the walls 220, 222. To secure the
vanes 224, 226 to the assembly 206, each wall 220, 222 includes two
sets of slots 234, 236, 238, 240 that are formed in annular
patterns along two axial positions. Preferably, the slots 234, 236,
238, 240 are formed downstream of the arc 233. Each of the vanes
224, 226 includes at least a top 242, 244 and a bottom 246, 248
that extend through the slots 234, 236, 238, 240. The vanes 226,
228 may be secured to the walls 220, 222 in any one of numerous
fashions, such as, for example, by brazing.
[0023] To condition the airflow to a sufficiently low Mach number,
each vane preferably has a substantially identical predetermined
shape and is positioned in the flow path 228 at a predetermined
angle relative to the walls 220, 222. Exemplary vanes 300, which
are shown as being implemented into the two pluralities of vanes
224, 226, are depicted in FIGS. 3 and 4. As briefly mentioned
above, FIG. 3 is a cutaway view of the deswirl assembly 200 looking
at the vanes 300 from forward to aft, while FIG. 4 is the deswirl
assembly shown in FIG. 3 looking at the vanes 300 from aft to
forward.
[0024] Each vane 300 includes a leading edge 302 and a trailing
edge 304. A concave pressure surface 306 and a convex suction
surface 308 extend between the leading and trailing edges 302, 304.
The vanes 300 preferably each have a uniformly shaped curved axial
cross-section from top 310 to bottom 312. In this regard, a number
of the vanes 300 having substantially identical shapes may be mass
produced from a single sheet of material. Specifically, the sheet
of material may be suitably pressed into an appropriate curve shape
to form the concave and convex surfaces 306, 308 and a plurality of
the vanes 300 may be cut from the single sheet of material.
[0025] As mentioned previously, each vane 300 of the two
pluralities of vanes 224, 226 is disposed at an angle relative to
the walls 220, 222. Preferably, the vanes 300 are each placed such
that the concave pressure surface 306 faces outwardly toward the
outer annular wall 222 and the convex suction surface 308 faces
inwardly toward the inner annular wall 220. Angling the vanes 300
in this preferred embodiment reduces the variation in air angle
between the walls 220, 222. In one exemplary embodiment, the vanes
300 are disposed such that an angle between the concave pressure
surface 208 the inner annular wall 220 is about 110.8.degree..
However, it will be appreciated that the particular angle at which
the vanes 224, 226 are disposed depends on the overall
configuration of the walls 220, 222.
[0026] The degree to which the vanes 224, 226 are angled may also
determine how the two pluralities of vanes 224, 226 are placed
relative to each another. In one example, as shown in FIGS. 3 and
4, the vanes of the first plurality of vanes 224 are equally spaced
apart from one another and the trailing edge of each vane is
disposed around a first circumferential position 242 around the
inner annular wall 220, while the vanes of the second plurality of
vanes 226 are also equally spaced apart from one another but the
leading edge of each is disposed around a second circumferential
position 244. Although the first and second circumferential
positions 242, 244 are shown in this embodiment as non-overlapping
and the first circumferential position 242 is disposed upstream of
the second circumferential position 244, the first circumferential
position 242 may alternatively be disposed downstream of the second
circumferential position 244, or may overlap.
[0027] Additionally, the second plurality of vanes 226 are
preferably staggered between the first plurality of vanes 224. For
instance, as shown in FIG. 5 viewing the vanes 300 from forward 250
to aft 252, one vane 226b of the second plurality of vanes 226 is
preferably disposed between two vanes 224a, 224b of the first
plurality of vanes 224 and biased toward the pressure surface 306
of vane 224b. In one exemplary embodiment, a distance 254 between
vane 226b of the second plurality of vanes 226 and vane 224b of the
first plurality of vanes 224 is about 35% of the distance 256
between vanes 224a, 224b of the first plurality of vanes 224. It
will be appreciated, however, that the particular distances between
all of the vanes may largely depend on the angling thereof relative
to the walls 220, 222.
[0028] It will further be appreciated that although two pluralities
of vanes 226, 228 are included in the embodiment shown in FIG. 2,
the deswirl assembly 200 may alternatively only include a single
plurality of vanes. In still other embodiments, more than two
pluralities of vanes 226, 228 may need to be employed.
[0029] An improved downcanted deswirl assembly has now been
provided that includes a plurality of vanes that are configured to
aerodynamically couple a centrifugal compressor and an axial
through-flow combustor. Additionally, the deswirl assembly is
relatively inexpensive and simple to manufacture and is capable of
directing and conditioning the air flowing there through for
optimal engine performance
[0030] While the invention has been described with reference to a
preferred embodiment, 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 invention. In addition, many modifications may be made to
adapt to a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *