U.S. patent application number 09/960753 was filed with the patent office on 2003-03-27 for waffle cooling.
This patent application is currently assigned to Honeywell International, Inc.. Invention is credited to Hadder, James Lolnell.
Application Number | 20030056516 09/960753 |
Document ID | / |
Family ID | 25503573 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030056516 |
Kind Code |
A1 |
Hadder, James Lolnell |
March 27, 2003 |
WAFFLE COOLING
Abstract
Walls that require cooling, including combustor walls of jet
engines, having two members forming a waffle shaped structure are
described. The dual member structure comprises passages for
incoming air, which zigzag through part of the waffle structure.
The air is then released to the combustor or exhausted elsewhere.
Additionally, the need for a cool film on one side of the wall may
be eliminated. The waffle shaped structure disclosed is relative
easy to manufacture.
Inventors: |
Hadder, James Lolnell;
(Scottsdale, AZ) |
Correspondence
Address: |
Honeywell International, Inc.
Law Dept. AB2
P.O. Box 2245
Morristown
NJ
07962-9806
US
|
Assignee: |
Honeywell International,
Inc.
Law Dept. AB2 P.O. Box 2245
Morristown
NJ
07962-9806
|
Family ID: |
25503573 |
Appl. No.: |
09/960753 |
Filed: |
September 21, 2001 |
Current U.S.
Class: |
60/772 ;
60/752 |
Current CPC
Class: |
Y02T 50/675 20130101;
F23R 3/06 20130101; Y02T 50/60 20130101; F23R 3/005 20130101 |
Class at
Publication: |
60/772 ;
60/752 |
International
Class: |
F23R 003/42 |
Claims
We claim:
1. An apparatus for cooling, comprising: a first member having a
smooth surface; a second member having an uneven surface disposed
to form a plurality of cavities by affixing the uneven surface onto
the smooth surface of the first member; a plurality of openings
having an airflow connecting together at least a first cavity and a
second cavity; at least one opening in the first cavity for
receiving incoming air; and at least another opening in the second
cavity for disposing outgoing air, whereby a temperature of, as
well as the temperature difference between, the first and second
members is reduced.
2. The apparatus of claim 1, wherein sides of the first and second
cavities are bonded to the smooth surface of the first member.
3. The apparatus of claim 1, wherein the first and second cavities
form an airflow passage.
4. The apparatus of claim 1, wherein the first and second members
form a plurality of airflow passages.
5. The apparatus of claim 4, wherein the plurality of airflow
passages are airflow independent of one another.
6. The apparatus of claim 4, wherein at least two of the airflow
passages are airflow connected to one another.
7. The apparatus of claim 1, wherein the first member comprises a
first side free of a cold film.
8. An apparatus for cooling walls, comprising: a first wall having
a first surface and a corresponding second surface; a second wall
having a waffle shape with a plurality of cavities being formed
therein; each cavity being defined by a plurality of sides with a
part of the cavity sides rigidly affixed to the first surface of
the first wall; and a plurality of gaps formed at sides of the
cavities that are non-rigidly affixed to the first surface of the
first wall; said gaps form a passage for air to flow from one end
of the apparatus to another end through at least some of the
cavities, whereby the first wall and the second wall are cooled or
the stress thereupon released.
9. The apparatus of claim 8, wherein the second surface covers only
a portion of the first wall.
10. The apparatus of claim 8, wherein the second surface of the
first wall is heated by a heat source abuts the second surface.
11. The apparatus of claim 8, wherein at least one gap is formed
for air in-take.
12. The apparatus of claim 8, wherein the passage flows air in a
tortuous pattern.
13. The apparatus of claim 12, wherein the passage flows air in a
zigzag pattern.
14. A combustor, comprising: an inflow of air having a primary air
flow flowing into an inner cylinder and a secondary air flow
flowing into an air casing defined and limited by the inner
cylinder and an outer cylinder; a first wall being part of an outer
limit of the inner cylinder and having a first surface and a second
surface; a second wall being part of the outer limit of the inner
cylinder and having a waffle shape that forms a plurality of
cavities; each cavity being defined by four sides with part of the
cavity sides rigidly affixed to the first surface of the first
wall; and a plurality of gaps formed at the sides of the cavities
that are non-rigidly affixed to the first surface of the first wall
to provide a passage for air to flow from one end of the apparatus
to another end of the apparatus through at least some of the
cavities, whereby the first wall and the second wall are cooled or
stress thereon are released.
15. The combustor of claim 14, wherein the combustor is comprised
of a can-type combustion chamber.
16. The combustor of claim 14, wherein the combustor is comprised
of an annular type combustion chamber.
17. The combustor of claim 14, wherein the combustor is comprised
of a can-annular-type combustion chamber.
18. A method for cooling walls, comprising the steps of: providing
a first wall having a smooth surface; providing a second wall
having a waffle shape with a plurality of cavities each having a
plurality of sides; affixing at least some of the sides to the
first member; and flowing air through said cavities along a
tortuous passage, whereby said first and second walls are cooled or
stress thereon are released.
19. The method of claim 18, further comprising the step of flowing
the air from one cavity to an adjacent cavity.
20. The method of claim 19, further comprising the step of flowing
the air through a plurality of air passages.
21. The method of claim 20, further comprising the step of flowing
the air in a plurality of tortuous patterns.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to the cooling of thin walls for
various aerospace applications and, more specifically, this
invention relates to the cooling of thin walls using a waffle
structure.
[0002] Various devices such as combustor liners, other exhaust
structures or similar structures, and walls of rocket engine, need
cooling. The air used for air/fuel mixtures can be used
advantageously for that purpose. It is known that efficient burning
of fuel is a goal for good turbine engine designs but the burning
of fuel necessarily involves heat generation. Further, the burning
of fuel also necessarily causes environmental problems
necessitating the reduction of dangerous emissions. How to
dissipate the generated heat and how to use the cooling air
effectively becomes an important design issue. In addition, the
difference in temperature in various parts of the thin walls
challenges designers in that they need to consider both the
efficiency of fuel burning and the structural integrity of the thin
walls. Structural design of thin walls such as those for combustion
liners is generally based on experience with previous systems.
Various patents have addressed the issue.
[0003] U.S. Pat. No. 4,642,993, entitled Combustor Liner Wall,
teaches a combustor liner wall with an interior wall, an exterior
wall, and a honeycomb structure disposed therebetween. The
honeycomb structure is formed with generally radially aligned
cells. The patent teaches a structure known in the art as licolite.
However, it does not address the issue of thermal growth
differences between the hot and cold walls of a panel structure,
which may result in high stresses for even moderately sized
combustors. To solve the above problem, the walls are divided into
small panels where spent cooling air is dumped. This may result in
release of dangerous emissions.
[0004] U.S. Pat. No. 4,864,827, entitled Combustor, teaches a gas
turbine engine combustor with a semi-spherical upstream wall
comprised of two correspondingly shaped skins spaced apart by
pedestals attached to one of the skins to define a space between
them. In other words, this patent maintains a space between two
walls by the use of pedestals. The two walls float, or move,
relative to each other so as to relieve the geometrical changes
that result from temperature variations. However, this does not
allow a stable gap between the two walls. Further, for relatively
large structures this patent may be impractical in that no stable
gap can be maintained because the pedestals are not rigidly affixed
to at least one of the walls.
[0005] U.S. Pat. No. 5,822,853, entitled Method for Making
Cylindrical Structures with Cooling Channels, teaches a gas turbine
having a double wall with a plurality of cooling channels
therebetween. The cooling channels are formed between the inner
member of the structure and the outer member thereof. In other
words, the patent addresses a method of manufacturing, involving a
sandwiched panel. However, the walls are not rigidly connected to
each other and, therefore, the problem of thermal growth difference
between the two walls is not resolved. Also, as can be appreciated,
the fact that there is no rigid connection between the walls causes
at least a reduction in efficiency with regard to heat transfer.
Further, the lack of connection between the walls may make the
concept impractical for larger structures.
[0006] As can be seen, there is a need for a method and apparatus
to deal with thermal growth differences occurring between
adjacently located hot and cold walls of panel structures, and
which does not result in high stresses during operation. Further,
it is desirable to have a simple structure that is easy to
fabricate, and at the same time fulfills the need of cooling the
apparatus. The waffle cooling satisfies that need. The second wall
is an irregular non smooth surface that responds somewhat like a
bellows, and expands and contracts with respect to the thermal
expansion of the first surface thus reducing the stresses that are
generated by the difference in temperatures between the two
surfaces.
SUMMARY OF THE INVENTION
[0007] In one aspect of the present invention, there is disclosed
an apparatus for cooling thin walls that comprises a first member,
which has a smooth surface; a second member, which has an uneven
surface disposed to form a plurality of cavities by rigidly
affixing part of the uneven surface onto the smooth surface of the
first member, and a plurality of openings connecting at least two
cavities; and at least one opening in a first cavity for receiving
incoming air, as well as at least one opening in a second cavity
for disposing out-going air, whereby the temperature, as well as
the temperature difference between the members, is reduced.
[0008] In another aspect of the present invention, there is
disclosed an apparatus for cooling thin walls that comprises a
first wall having a generally smooth shape with a first surface,
and a second surface; a second wall having a waffle shape, wherein
a plurality of cavities are formed, each cavity being defined by
four sides with part of the cavity sides rigidly affixed to the
first surface of the first wall; and a plurality of gaps formed at
the sides of the cavities that are non-rigidly affixed to the first
surface of the first wall, thereby forming a passage for air to
flow from one end of the apparatus to the other through at least
some cavities, whereby the first wall and the second wall are
cooled.
[0009] In a further aspect of the present invention, a combustor is
described comprising an inflow of air having a primary flow into an
inner cylinder, and a secondary flow into an air casing defined and
limited by the inner cylinder and an outer cylinder. The combustor
further comprises a first wall that is part of the outer limit of
the inner cylinder, which has a generally smooth shape, and which
includes a first surface, and a second surface. A second wall is
also provided that is part of the outer limit of the inner
cylinder, which has a waffle shape within which there is a
plurality of waffle shaped cavities. Further, each cavity is
defined by four sides with part of the cavity sides being rigidly
affixed to the first surface of the first wall, whereby a plurality
of gaps is formed at the sides of the cavities that are non-rigidly
affixed to the first surface of the first wall, thus forming a
passage for air to flow from one end of the apparatus to the other
end through at least some cavities. Thereby, the first wall and the
second wall are cooled.
[0010] In yet another aspect of the present invention, a method for
making a cooling device comprises the steps of providing a first
member that has a generally smooth surface, providing a second
member having a waffle shape with a plurality of trapezoidal shaped
cavities each having four sides, and affixing at least some of the
four sides onto the first member.
[0011] These and other features, aspects and advantages of the
present invention will become better understood with reference to
the following drawings, description and claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 depicts a schematic diagram of one embodiment of the
present invention;
[0013] FIG. 2 depicts a perspective view of the present
invention;
[0014] FIG. 3 depicts a schematic flow of a combustion chamber;
and
[0015] FIG. 4 depicts an embodiment of the present invention for a
can-type combustor.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The following detailed description is of the best currently
contemplated modes of carrying out the invention. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention,
since the scope of the invention is best defined by the appended
claims.
[0017] Referring to FIG. 1, numeral 100 denotes a waffle cooling
apparatus embodying the present invention. A first or inner member
102 may be generally smooth in that it has at least one smooth
(i.e., even or planar) surface made of flexible material, such as
HA230 or HS188 made by Haynes International, such that the inner
member 102 can be bent (not shown) to form a curve along with a
second or outer member 103. The outer member 103 may also be made
of generally flexible material, such as HA230, HS188 or HastX made
by Haynes International, but is not smooth (i.e., not even or
planar) in form or shape. For example, the outer member 103 may
have indentations such that a set of cavities can be formed
utilizing the concave volume generated by the indentations. Thus,
air can pass between the inner member 102 and the outer member
103.
[0018] The outer member 103 can be formed by a plurality of airflow
units of which at least one allows an airflow 114 therethrough.
Each unit can comprise a plurality of cavities, with one
representative cavity being intermediate cavity 104. Intermediate
cavity 104 may generally have four sides for ease of fabrication.
However, intermediate cavity 104 may have a lesser or greater
number of sides. Some considerations in determining the number of
sides are ease of fabrication, and rigidity of the connection
between the inner member 102 and the outer member 103 for efficient
heat transfer between them. The intermediate cavity 104 can further
comprise or define an air gap 106 such as for air intake into such
cavity 104 when air flows out of one cavity and then flows into an
adjacent cavity 104. The intake gap 106 may be an opening having a
circumference (not shown) formed by portions of the inner member
102 and the outer member 103.
[0019] Intermediate cavity 104 can also have an air opening or gap
108 such as for air outflow from the cavity 104 when air flows out
of one cavity 104 and into an adjacent downstream cavity 104.
Similarly arranged cavities can thereby define at least part of an
air passage which will be described below. The shape and
circumference of the air outflow gap 108 can be identical to that
of the intake gap 106, or it could be different. But the particular
shape, size, and circumference of the openings or gaps 106 and 108
are based on the goal of efficient cooling of the walls or the
inner and outer members 102, 103, thus precluding undue stresses on
the inner member 102 since a heat source (not shown) may cause the
inner member 102 to be at a relatively higher temperature than that
of the outer member 103. It is evident that one wall may be cooler
than the other and it is desirous to have a suitable structure that
reduces this temperature difference as well as cools the inner and
outer members 102,103.
[0020] Still referring to FIG. 1, and for purposes of illustration,
incoming air 110 can form an initial airflow through an initial
inflow gap 112. Incoming air 110 can define an airflow 114 that
traverses a plurality of cavities 104. In other words, the cavities
are interconnected such that the airflow 114 may traverse through
the cavities via gaps on the sides of cavities such as at the
intake gap 106 and air outflow gap 108. Desirably, the airflow 114
follows a tortuous path as opposed to a straight one for greater
cooling.
[0021] Outer member 103 may be subdivided into a plurality of
independent airflow units. In each unit, an air passage can exist
through which an airflow 114 can pass. For example, air passages
may zigzag through units of similar shape and form as that of air
passage 104. Other than the gaps 106 and 108, the sides of the
cavities on the outer member 103 can be rigidly attached to inner
member 102. The inner and outer members 102 and 103 may be made of
iron, aluminum, nickel, cobalt or related alloys. The inner and
outer members 102 and 103 may be bonded to each other using bonding
techniques know in the art and made of iron, aluminum, nickel,
cobalt, or related alloys. A primary goal is to have a
predetermined amount of air flowing through a particular area of
the apparatus 100 that is comprised of inner member 102 and outer
member 103. Once the inner and outer members 102 and 103 are bonded
to each other, the combined structure may be formed to achieve a
desired shape. The bonding process increases the thermal unity
between the inner member 102 and the outer member 103 because heat
transfers more readily between the members. This is primarily
because there are no other elements or materials existing between
the inner member 102 and the outer member 103.
[0022] Another feature of the invention is that air passage 104 may
be adjusted in size and shape to achieve an optimal cooling effect.
For example, the zigzag pattern of air passage 104 may be modified
at different portions of the structure to address heat intensity
variations.
[0023] Referring to FIG. 2, numeral 200 generally depicts a
perspective view of the structure depicted in FIG. 1. First or
inner member 202 can comprise an inner surface 204 and an outer
surface 206. Generally, a heat source (not shown) may be located at
the side of the inner surface 204, Thereby, heat may be dissipated
geometrically first to the inner surface 204, then to the outer
surface 206 of the inner member 202, and then to a second or outer
member 208. A plurality of cavities, such as cavities 210, can form
part of an interconnection path (not shown) wherein an air
passageway (not shown) is defined. It is contemplated that a
plurality of interconnection paths may be formed.
[0024] Incoming air (depicted by arrows 212, 214 and 216) can flow
through respective openings or gaps in the cavities 210. For
example, incoming air 212 may flow into gap 218, incoming air 214
may flow into gap 220, and incoming air 216 may flow into gap
222.
[0025] The sides 224 of cavities 210 may be rigidly affixed to the
outer surface 206. For instance, the sides 224 of cavities 210 can
be made out of the same material as the outer member 208, and may
be bonded onto the outer surface 206, which may be made out of
similar materials. As can be appreciated, some cavities 210 may be
interconnected to each other, whereby an interconnect (not shown)
is formed as a subset of all the cavities. This may be demonstrated
by referring back to FIG. 1, wherein the outer member 103 comprises
a plurality of independent zigzag sub-units or subsets. This
necessarily requires openings on some sides of some cavities 210.
Hence, the opening portions (not shown) in between cavities of the
sides 224 of cavities 210 are not rigidly affixed upon the outer
surface 206. This is also true for the inflow gaps 218, 220, 222
since the members are not rigidly affixed to each other as there is
an opening in between. However, other than the inflow gaps 218,
220, and 222, and the openings on the sides (not shown), the sides
may be affixed rigidly onto a smooth surface of the first member or
the outer surface 206.
[0026] The instant invention is described as waffle cooling because
the cavities 210, and the sides 224 of cavities 210, together form
a structure that is similar in configuration to a waffle, and its
purpose is for cooling. However, the sides 224 of cavities 210 do
not have to be equal in length, and the angle between the adjacent
sides does not have to be ninety degrees or the same angle. In
addition, since the finished waffle shaped structure may need to be
bent in the shape of a curve, the resultant shape of the waffle
cooling pattern may be trapezoidal, albeit on a non-flat plane.
[0027] As can be appreciated, the outer member 208 may comprise a
plurality of units such the independent zigzag airflow patterns.
Each unit can further comprise an interconnect wherein an air
passage (not shown), such as air passage 104 of FIG. 1, is defined.
Each unit may be independent in that no connections exist between
units or, alternatively, each unit may be dependent and connected
to each other. It is evident that more than one unit may exist in
the apparatus.
[0028] An air outlet 226 can be provided at the end of each airflow
passage 104. The air inflow can be any one of the air inflows 212,
214, 216. The function of this air outlet 226 may be to serve as an
outlet for cooling air, as well as other purposes. For example,
with a combustor, expended cooling air coming out of air outlet 226
may mix with fuel in a primary zone and be utilized for combustion
purposes.
[0029] Since one the main purposes of the invention is cooling, it
follows that the volume of air passing through any interconnect can
increase, or reduce the cooling. A working definition of the
interconnect is the space wherein each subset of cavities 210 is
interconnected by openings. Therefore, the geometric configuration
of the interconnect can determine the amount of airflow that passes
through it. The geometric configuration includes, but is not
limited to, the size of the inflow gaps 218, 220, 222, and other
openings (not shown) between cavities 210. In addition, heat
conduction characteristics of the material constituting the
apparatus may also be significant.
[0030] FIGS. 1 and 2 illustrate only one embodiment of the instant
invention. Variations in the heat intensity of various regions of
the inventive waffle cooling apparatus may vary. It follows,
therefore, that the amount of air passing through any interconnect
can be increased or decreased depending on the extent of the
cooling required. As a result, it may be desirable to modify some
of the dimensional parameters of the inventive waffle cooling
apparatus. Examples include increasing the opening of the initial
airflow gap 112, the incoming air flows 212, the interconnecting
intake gap 106, and the air outflow gap 108.
[0031] Referring now to FIG. 3, there is shown a schematic flow 300
of a combustion chamber wherein the instant invention can be used.
A compressor (not shown) can discharge airflow at a velocity of
about 490 ft/sec for purposes of illustration. This velocity may
not be suitable for combustion and must be reduced. Air flowing
into the combustion chamber can comprise primary airflow 302 and
secondary airflow 304. Upon reaching a suitable velocity, with a
concomitant increase in pressure as well, the primary airflow 302
can enter the combustion chamber. The secondary airflow 304 may
then flow into air casing 306 defined as the space between an inner
cylinder having a radius r and an outer cylinder having a radius R.
On the inner cylinder wall 308, the structure of the instant
invention may be applied. For example, the present invention may be
applied at areas 310, 312, and 314 which are located on regions
316, 318, and 320, respectively. It is known in the art that the
primary airflow 302 contributes about 10-20% of the total air mass
used for combustion. The balance comes from other sources including
the secondary airflow 304. Therefore, the waffle structure of this
invention may be used for the combustion chamber at areas 310, 312,
314 that are located on regions 316, 318, and 320 respectively. As
can be appreciated, the secondary airflow 304 can be used both for
combustion as well as for cooling purposes.
[0032] A typical combustion chamber receives 20% of its air from
the primary airflow 302, predominantly within region 316. The
balance of the air comes from the secondary airflow 304, from which
10% goes into region 318 and about 70-80% goes into region 320.
Because different regions require different amounts of air, and
there may be variations of pressure at various locations within the
air casing 306, the opening that takes the air in, for example
areas 310, 312, 314 having the waffle structure for air intake and
the opening that disposes of the air, needs to be suitably
designed. For example, the dimension or specifically the diameter
of the openings such as the inflow gaps 218, 220, 222, the
direction of the openings, and the size of the interconnect, need
to be designed accordingly for optimal performance including
sufficient air for sufficient cooling. The design must take into
consideration various factors such as: sufficient air be fed into
the combustion chamber at various locations or regions; air passing
through be sufficient such that the walls 308 of the inner cylinder
such as 204 and 206 of FIG. 2 be adequately cooled; the apparatus
used be easy to fabricate; and the structure of the apparatus be
sufficient for a limited air intake. Certain locations of the
combustion chamber cylindrical wall 308 may need no cooling, and
would not benefit from the use of the present invention. The
present invention may accordingly be selectively applied on an as
needed basis at locations where other forms of cooling are
insufficient.
[0033] Referring now to FIG. 4, there is shown a can-type combustor
400, wherein the present invention may be applied. An atomizer
swirler assembly 402, having a generally cylindrical shape, is
located at a first end 408 of the can-type combustor 400. The
atomizer swirler assembly 402 comprises a coupling element 404 that
circumferentially couples with a wall portion 406 that forms part
of an inner cylindrical wall. The atomizer swirler assembly 402
typically receives primary airflow at a first end 408 at a high
velocity, processes the air, and inputs the same into an inner
cylindrical space 410 at a reduced velocity. Wall portion 406
extends to first member region 412, wherein the inventive waffle
cooling structure is desirable.
[0034] The waffle cooling structure comprises a second member 414
that has concave regions 413 disposed to form a plurality of
cavities in combination with the outer smooth surface the first
member 412. It should be noted that the present invention is an
improvement over prior art in that there is no need for any other
structural component other than the first member 412 and the second
member 414. For example, there is no need for a third element
between the first member 412 and the second member 414. Air 416,
418 from secondary air source enters the waffle cooling structure
via slots 422 and 420 respectively.
[0035] Air 416 enters slot 422 defining the beginning of a first
passage 424 that traverses an interconnect comprised of a subset of
a plurality of cavities interconnected together, slot 422, and
first passage 424. First passage 424 comprises an opening 426 on
wall portion 406 and an outlet channel 427. Outlet channel 427 is
limited by wall portion 406 and an extension member 428. Expended
air cools the first member 412 (and to some extent cools the second
member 414) and comes out of the outlet channel 427. The expended
air, in turn, mixes with fuel in the primary zone of the inner
cylindrical space 410. At the end of the combustor, turbine
transition duct 434 of a generally cylindrical shape is coupled to
the end 436 of the first member 412.
[0036] Similarly, air 418 enters slot 420 that defines a beginning
of a second passage 425 that traverses an interconnect comprised of
a subset of cavities interconnected together, slot 420, and outlet
430. The outlet 430 is comprised of an opening 432 on first member
412. Expended air cools the first member 412. The expended air
also, to some extent, cools the second member 414. Further,
expended air comes out of the outlet 430 at the combustor exit
segment.
[0037] Similar inventive waffle cooling structures may be provided
at other locations or regions of the combustor where cooling is
desired. The specific geometric configurations of such additional
waffle cooling structures may be varied as necessary to provide the
requisite cooling characteristics.
[0038] As can be appreciated, the present invention provides
cooling to thin walls (e.g., about 0.015 to 0.100 inches thick) of
structures such as, but without limitation, combustor liners.
Cooling passages are formed by a subset of cavities between two
bonded pieces of sheet metal. The first piece comprises at least
one smooth surface and forms the structural wall that is to be
cooled. The second piece is waffled to form cavities on at least
one smooth surface. The cavities are interconnected with gaps to
form a passage for air to zigzag from a first end to a second end
of a panel as needed. In the present form of the invention, the
narrow gap between the cavities accelerates the air, increases the
turbulence, correspondingly increasing the heat transfer
coefficient. Air enters the passageways through gaps at one end of
the passages and exits to the hot flow path at the other end. It
should be noted that there may be one opening at the exit of each
passage such as 426 or 430, but may merge into a common slot such
as 427.
[0039] One notable feature of the present invention is that this
type of cooling may allow walls such as the first member 412 of
FIG. 4 to be cooled without a cold film on the hot side of the
combustor. This may reduce hydrocarbon and carbon monoxide
emissions. As can be appreciated, cool boundary layers along the
walls are known to have the tendency to quench the combustion
reaction, thus producing by-products of incomplete combustion such
as CO and UHC. However, as an alternative, the cold film may be
introduced in such cases to further enhance cooling, or if
emissions are not of primary concern.
[0040] As a general matter, with regard to the waffle cooling of
the present invention in relation to other types of cooling, the
amount of air used should be comparable to that of effusion
cooling. However, the need for the introduction of the cold film on
the inner side of the wall or first member 412 may not be required.
Furthermore, the first member generally a thin wall having a
limited thickness of about 015 to 100 inches.
[0041] It should be understood, of course, that the foregoing
relates to preferred embodiments of the invention and that
modifications may be made without departing from the spirit and
scope of the invention as set forth in the following claims. For
example, the present invention can be applied not only in a
can-type combustor, but in an annular-type combustor and
can-annular-type combustor as well. Furthermore, other exhaust
system structures may benefit from use of this invention as
well.
* * * * *