U.S. patent application number 09/851792 was filed with the patent office on 2002-04-11 for heat exchanger with enhancements.
Invention is credited to Jia, Shaobo, Tomlinson, Ronald S..
Application Number | 20020040777 09/851792 |
Document ID | / |
Family ID | 26930276 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020040777 |
Kind Code |
A1 |
Tomlinson, Ronald S. ; et
al. |
April 11, 2002 |
Heat exchanger with enhancements
Abstract
A heat exchanger for use with a furnace, each heat exchanger
includes a plurality of heat exchanger elements. Each heat
exchanger element includes a pair of clamshells sealingly attached
to one another. The heat exchanger element includes a longitudinal
axis. A pair of depressions are disposed in each respective said
pair of clamshells. The depressions face one another to form a
passageway wall and a serpentine fluid passageway therebetween. At
least a portion of the serpentine fluid passageway extends along
the longitudinal axis. A plurality of enhancements are formed in
the depressions and are disposed within the portion of the
serpentine fluid passageway. The plurality of enhancements project
into the serpentine fluid passageway. Each enhancement constitutes
a corrugation having a substantially trapezoidal longitudinal
cross-section. A longitudinally positioned passageway wall portion
is extended between each adjacently positioned enhancements within
each clamshell.
Inventors: |
Tomlinson, Ronald S.; (Mt.
Juliet, TN) ; Jia, Shaobo; (Lilburn, GA) |
Correspondence
Address: |
BAKER & DANIELS
111 E. WAYNE STREET
SUITE 800
FORT WAYNE
IN
46802
|
Family ID: |
26930276 |
Appl. No.: |
09/851792 |
Filed: |
May 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60236969 |
Sep 29, 2000 |
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Current U.S.
Class: |
165/163 |
Current CPC
Class: |
F28D 1/035 20130101;
F28D 9/0031 20130101; F28F 2250/102 20130101; F28F 3/04 20130101;
F24H 3/105 20130101 |
Class at
Publication: |
165/163 |
International
Class: |
F28D 001/00 |
Claims
What is claimed is:
1. A heat exchanger for use with a furnace, each heat exchanger
comprising: a plurality of heat exchanger elements, each said heat
exchanger element including a pair of clamshells sealingly attached
to one another, said heat exchanger element having a longitudinal
axis, a pair of depressions disposed in each respective said pair
of clamshells, said depressions facing one another to form a
passageway wall and a serpentine fluid passageway therebetween, at
least a portion of said serpentine fluid passageway extending along
said longitudinal axis, a plurality of enhancements in said
depressions and disposed within said portion of said serpentine
fluid passageway, said plurality of enhancements projecting into
said serpentine fluid passageway, each said enhancement comprising
a transversely extending corrugation having a substantially
trapezoidal longitudinal cross-section, a longitudinally positioned
passageway wall portion is extended between adjacently positioned
enhancements within each clamshell, whereby said plurality of
enhancements being structured and arranged with said passageway
wall portions to direct a flow of products of combustion received
in said heat exchanger element along said passageway wall at a
non-zero velocity.
2. The heat exchanger of claim 1, wherein said serpentine fluid
passageway includes an inlet and an outlet and a plurality of
longitudinally arranged channels fluidly connecting said inlet and
said outlet, said channels fluidly connected by bend portions.
3. The heat exchanger of claim 1, further comprising a first
manifold wherein said each heat exchanger element is fixed relative
to an adjoining said heat exchanger element through said first
manifold.
4. The heat exchanger of claim 3, further comprising a second
manifold, said first manifold is attached to either said inlets or
outlets of said serpentine passageway and said second manifold is
attached to the remaining of said inlets or outlets.
5. The heat exchanger of claim 3, further comprising a support
member attached to a periphery portion of each said heat exchanger
element.
6. The heat exchanger of claim 1, wherein said corrugations on one
of said pair of clamshells are offset and interested relative to
the other corrugations of the other said clamshell to form a
continuous saw-toothed passageway disposed in said portion of said
longitudinally arranged serpentine fluid passageway.
7. The heat exchanger of claim 6 wherein said passageway includes a
substantially uniform longitudinal cross-section.
8. The heat exchanger of claim 6, wherein said passageway
longitudinally tapers in the direction of the flow through said
serpentine fluid passageway.
9. A heat exchanger element for use with a furnace, each heat
exchanger element comprising: a pair of clamshells sealingly
attached to one another, said heat exchanger element having a
longitudinal axis, a pair of depressions disposed in said pair of
clamshells, said depressions facing one another to form a
passageway wall and a serpentine fluid passageway therebetween, at
least a portion of said serpentine fluid passageway extending along
said longitudinal axis, a plurality of enhancements in said
depressions and disposed within said portion of said serpentine
fluid passageway, said plurality of enhancements projecting into
said serpentine fluid passageway, each said enhancement comprising
a corrugation having a substantially trapezoidal longitudinal
cross-section, a longitudinally positioned passageway wall portion
extended between each adjacently positioned enhancements within
each clamshell, whereby said plurality of enhancements being
structured and arranged with said passageway wall portions to
direct a flow of products of combustion received in said heat
exchanger element along said passageway wall at a non-zero
velocity.
10. The heat exchanger element of claim 9, wherein one of said pair
of depressions includes said corrugations being internested with
the other said corrugations on the other said depression.
11. The heat exchanger element of claim 9, further comprising at
least one enhancement channel defined by a portion of said
serpentine passageway which includes said trapezoidally shaped
corrugations, said corrugations disposed on one of said pair of
depressions including ramping surfaces in fluid communication with
ramping surfaces defined by the corrugations disposed on the other
depression, whereby a flow velocity of hot products of combustion
is registerable through substantially all of the said enhancement
channel at positions proximate to said ramping surfaces.
12. The heat exchanger element of claim 11, wherein each of said
ramping surfaces includes an angle of inclination followed by an
angle of declination, said angle of inclination is greater than
said angle of declination.
13. The heat exchanger element of claim 11, wherein each of said
ramping surfaces includes an angle of inclination followed by an
angle of declination, each said angle of inclination is
substantially similar to each said angle of declination.
14. The heat exchanger element of claim 9, wherein said serpentine
fluid passageway includes an inlet channel, a first enhancement
channel and a second enhancement channel, said corrugations are
confined to said first and second enhancement channels.
15. The heat exchanger element of claim 14, wherein said first and
second enhancement channels longitudinally extend and said
corrugations are transversely disposed within said first and second
enhancement channels.
16. The heat exchanger element of claim 15, wherein said first
enhancement channel longitudinally tapers in the direction of
internal flow and said second enhancement channel is substantially
longitudinally uniform.
17. A heat exchanger for use with a furnace including at least one
heat exchanger element which receives hot products of combustion
therein and having room air being forced externally thereover, the
heat exchanger comprising: a pair of clamshells each having a
depression disposed therein and sealingly attached to one another,
said depressions defining an inlet and an outlet in fluid
communication through a serpentine flow passageway, a portion of
said flow passageway defining an inlet channel, at least one
enhancement channel disposed in said flow passageway and positioned
downstream relative to said inlet channel, a plurality of
enhancements provided on said depressions and extended inwardly
into said enhancement channel, said enhancements reducing zones of
recirculation of the hot products of combustion flowed internally
through said passageway whereby heat transfer is increased between
the hot products of combustion and room air urged externally over
each heat exchanger element.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to furnaces and in particular to heat
exchangers for use in furnaces.
[0003] 2. Description of the Related Art
[0004] In one form of a conventional domestic furnace, air to be
heated is passed in heat transfer association with a plurality of
stacked serpentine heat exchanger elements forming a heat exchanger
encased in a cabinet. Each heat exchanger element defines a flow
path for hot products of combustion produced by combustion of fluid
fuel, typically, such fuel may include, for example, oil or natural
gas. The hot products of combustion, in passing through the heat
exchanger elements, transfer their heat energy to the air to be
heated, conventionally referred to as the room air, and are then
exhausted through a suitable flue.
[0005] Prior art serpentine heat exchangers are typically
manufactured from either a continuous tube or in two halves joined
together, e.g., "clam-shell", by known bending and/or joining
techniques. To increase the heat transfer between the combustion
products, contained within the heat exchanger, and the ambient
environment residing at the exterior of the same, it is known that
forcing the flow to become non-laminar, especially at the latter
portion of the exchanger, greatly improves heat transfer.
[0006] Flow diverters and separators of many types were added to
the interior structure of the exchangers to increase the flow
turbulence, however such methods significantly increased
manufacturing costs of the heat exchangers. To lessen the expense
yet retain acceptable levels of exchanger performance both
continuous tube and clamshell type heat exchanger elements included
external deformations to create internal flow "turbulators" to
increase heat transfer performance at an acceptable additional
cost. However, the need has arisen to decrease the size of furnace
cabinet and accompanying heat exchanger assembly therein while
sustaining equal or increased heat transfer characteristics of the
heat exchanger assembly.
[0007] U.S. Pat. No. 5,346,001 issued to Rieke et al. discloses a
heat exchanger which employs a turbulator region comprised of
multiple, interfacing and closely arranged deformations within the
clamshells. The deformations are successively and contiguously
arranged within each clamshell to promote turbulence, and
consequently, enhanced heat transfer within this region. However,
the turbulator region causes a significant decrease in flow
velocity along portions of the interior walls of the turbulator
region which corresponds to a decrease of heat transfer along these
wall portions.
[0008] A clamshell type heat exchanger assembly which causes
turbulent flow, however increases flow velocity at the site of
passageway walls to increase heat transfer between the heat
exchanger elements and room air would be desirable.
[0009] Further, a clamshell type heat exchanger utilizing
conventional materials of construction which sealably contains flue
gases while using less heat exchanger materials, consequently
providing a significant cost decrease, as compared to prior art
exchangers, would be desirable.
SUMMARY OF THE INVENTION
[0010] The present invention overcomes the disadvantages of prior
art furnaces by employing a heat exchanger including a plurality of
clamshell elements having trapezoidal enhancements to significantly
increase the heat transfer and provide an overall smaller or
compact furnace corresponding to a reduction of manufacturing and
assembly costs.
[0011] The present invention provides a heat exchanger for use with
a furnace including a plurality of heat exchanger elements having
internal structures which receive hot products of combustion and
transfer heat to room air being externally forced over each heat
exchanger element. Each heat exchanger element includes a pair of
clamshells, having depressions facing one another. The depressions
are sealingly clamped to one another and form a passageway wall and
a serpentine fluid passageway therebetween. The depressions within
the clamshells define an inlet and an outlet in fluid communication
through the serpentine flow passageway. A plurality of enhancements
are disposed within the depressions defined in the clamshells and
extend into the flow passageway. Each enhancement is provided with
a corrugation and each corrugation includes a substantially
trapezoidal cross-section. Longitudinally positioned passageway
wall portions extend between adjacently positioned enhancements
within each clamshell. The plurality of enhancements are structured
and arranged with the passageway wall portions to direct a flow of
products of combustion received in the heat exchanger element along
the passageway wall at a non-zero velocity.
[0012] The present invention heat exchanger, in one form thereof,
includes a heat exchanger element having enhancements in one
clamshell coacting with enhancements in the other clamshell to
increase the heat transfer between the flow of hot products of
combustion through the element with room air flowing externally
over the element. Each enhancement defines upstream and downstream
ramping portions separated by a plateau and having respective
angles of inclination and declination.
[0013] The heat exchanger of the present invention further provides
at least one heat exchanger element having a pair of clamshells.
The clamshells include a serpentine fluid passageway therein which
receives hot products of combustion. The fluid passageway includes
an inlet channel and at least one enhancement channel positioned
downstream relative to the inlet channel. The inlet and enhancement
channels are in fluid communication with one another and a
plurality of enhancements are disposed within the enhancement
channel. The enhancements reduce zones of recirculation formed by
the hot products flowed through the passageway and correspondingly
increase the heat transfer between the hot products of combustion
and room air being urged externally over the heat exchanger
element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above-mentioned and other features and advantages of the
present invention, and the manner of attaining them, will become
more apparent and the invention will be better understood by
reference to the following description of embodiments of the
invention taken in conjunction with the accompanying drawings,
wherein:
[0015] FIG. 1 is a perspective view of a furnace adapted with a
plurality of heat exchanger elements according to the present
invention showing the heat transfer enhancements thereon;
[0016] FIG. 2 is a perspective view of a first embodiment of a
right-hand half section of the heat exchanger with enhancements
according to the present invention;
[0017] FIG. 3 is a plan view of one of the heat exchanger elements
of the heat exchanger element of FIG. 1, showing the right-hand
half section;
[0018] FIG. 4 is a plan view of the heat exchanger element of FIG.
3, showing the left-hand half section;
[0019] FIG. 5 is a sectional view of the heat exchanger according
to the present invention taken along line 5-5 of FIG. 3, showing a
first enhancement channel;
[0020] FIG. 6 is a sectional view of the first embodiment heat
exchanger according to the present invention taken along line 6-6
of FIG. 3, showing the enhancements within a second enhancement
channel;
[0021] FIG. 6A is an enlarged view of the encircled area of FIG. 6,
illustrating a pair of interfacing enhancements;
[0022] FIG. 6B is an enlarged fragmentary view of a second
embodiment heat exchanger according to the present invention,
showing a pair of enhancements;
[0023] FIG. 6C is an enlarged fragmentary view of a third
embodiment heat exchanger according to the present invention,
showing a pair of interfacing enhancements;
[0024] FIG. 7 is a sectional view of the heat exchanger element of
FIG. 3 taken along line 7-7;
[0025] FIG. 8 is an end view of the heat exchanger element of FIG.
3 viewed along line 8-8;
[0026] FIG. 9 is a top view of the heat exchanger element of FIG. 3
viewed along line 9-9;
[0027] FIG. 10 is a bottom view of the heat exchanger element of
FIG. 3 viewed along line 10-10;
[0028] FIG. 11 is a flow model of a heat exchanger having angled
symmetrical enhancements, showing the stream-line contours of the
hot products of combustion flowing therethrough;
[0029] FIG. 12 is a flow model of the first embodiment heat
exchanger according to the present invention, showing the stream
line contours of the hot products of combustion flowing
therethrough;
[0030] FIG. 13 is a plan view of the heat exchanger bank according
to the present invention, showing the inlet and outlet ports;
and
[0031] FIG. 14 is an enlarged fragmentary sectional view of the
heat exchanger according to the present invention, viewed along
line 14-14 of FIG. 13.
[0032] Corresponding reference characters indicate corresponding
parts throughout the several views. Although the drawings represent
embodiments of the present invention, the drawings are not
necessarily to scale and certain features may be exaggerated in
order to better illustrate and explain the present invention. The
exemplifications set out herein illustrate embodiments of the
invention, and such exemplifications are not to be construed as
being exhaustive or to limit the scope of the invention in any
manner.
DETAILED DESCRIPTION OF THE INVENTION
[0033] Referring to FIG. 1, furnace 10 is shown including outer
housing, or cabinet 12. Mounted within cabinet 12 is heat exchanger
bank generally designated 14. Air to be conditioned, hereinafter
referred to as room air, is delivered to heat exchanger bank 14 by
blower 16. Heat exchanger bank 14 is defined by a plurality of
side-by-side heat exchanger elements 18 providing therebetween a
plurality of air flow passages 20 for passing air delivered from
blower 16 in heat transfer association with each heat exchanger
element 18. Hot products of combustion or flue gases are flowed
through the interiors of heat exchanger elements 18 from a burner
means (not shown) having a plurality of individual burners (not
shown) and each burner is associated with a respective heat
exchanger element 18. The products of combustion from the
respective heat exchanger elements are forcibly exhausted by an
exhaust blower (not shown), for example, from the furnace through a
discharge flue (not shown) by known means.
[0034] Blower 16 is adjacently disposed relative to horizontal
divider wall 17 so as to deliver the air to be conditioned upwardly
through an inlet opening (not shown) in divider wall 17 which
thereafter communicates with heat exchanger flow passages 20. After
passing in external heat exchange relationship with the heat
exchanger elements 18, the heated air is conducted to the space to
be heated by suitable duct means (not shown). Subsequently, the
room air may be recirculated through the furnace by suitable return
ducts (not shown) to blower 16.
[0035] Referring to FIGS. 2-4, each heat exchanger element 18 is
formed by preforming a pair of individual plates or "clamshells."
Each element includes right-hand clamshell 19 (FIGS. 1-3) and
left-hand clamshell 21 (FIG. 4). Clamshells 19 and 21 include
depressions 29, 31 forming the serpentine configuration illustrated
in FIGS. 2-4, having peripheral edge 23 of heat exchanger element
18 secured together in sealed relationship by a turned end portion
or crimp 25 (FIG. 5). The crimped engagement of clamshells 19 and
21 is the subject of U.S. Pat. Nos. 4,298,061; 4,441,241;
4,510,660; 4,538,338; 4,547,943; 4,649,894; 4,663,837; 4,718,484;
and 4,893,390 and are hereby incorporated herein by reference.
Referring to FIGS. 3-4, it may be seen that eyelets 39 are arranged
about inner portions of clamshells 19, 21 specifically along
passageway 24, to prevent combustion products from escaping through
the interior of clamshells 19, 21. Each eyelet 39 is comprised of
material from one clamshell protruding through a hole extended
through the other clamshell (FIG. 7). The material protruding
through is then "rolled over" to produce a secure engagement
between clamshells. Clamshells 19 and 21 of heat exchanger element
18 may be comprised of corrosion resistant metallic materials, such
as aluminized steel, stainless steel, or a coated metal material,
for example.
[0036] Referring to FIGS. 1-4, each pair of depressions 29, 31 of
heat exchanger element 18 defines a serpentine products of
combustion passageway 24, formed by passageway walls 27 (FIG. 6A),
having an inlet 26 and an outlet 28. Referring to FIG. 3, the hot
products of combustion received from the respective burners enter
passageway 24 through inlet 26. Serpentine fluid passageway 24
includes an inlet channel 30 which is U-shaped and extends in a
direction coincident with longitudinal reference axis 33. Inlet
channel 30 is transversely arranged relative to air flow passages
20 defined between the respective heat exchanger elements 18 and
walls 32 comprising cabinet 12 (FIGS. 1 and 2). As best seen in
FIG. 3, each heat exchanger element 18 includes two enhanced heat
transfer channels, namely, first enhancement channel 34 and second
enhancement channel 36. Channels 30, 34, and 36 longitudinally
extend along longitudinal axis 33 and are generally parallel to
each other. Further, it may be seen that enhancement channels 34
and 36 are perpendicularly arranged relative to the direction of
air flow from blower 16 (FIG. 1).
[0037] Referring to FIG. 3, serpentine fluid passageway 24 is
formed from an interfaced relation between depression 29 of
clamshell 19 and depression 31 of matching clamshell 21.
Depressions 29, 31 define inlet 26, outlet 28, and passageway 24
extended therebetween. Passageway 24 fluidly connects inlet and
outlet 26 and 28. Inlet and outlet manifolds 42, 43 (FIG. 1) are
attached to respective inlets and outlets 26, 28 of heat exchanger
elements 18 to accommodate connection to a burner assembly (not
shown) and an exhaust blower assembly (not shown).
[0038] Attached to inlet manifold 42 (FIG. 1) is inlet channel 30
provided with U-shaped bend 44 at peripheral edge 23 of heat
exchanger element 18. Inlet channel 30, generally circular in
cross-section (FIG. 7), is provided with a converging nozzle
portion 37 (FIG. 2) and is connected to first enhancement channel
34 through U-shaped bend 46 (FIG. 5). Bend 46, transitions from a
generally circular cross-section at its connection with inlet
channel 30, to a non-circular cross-section 35 (FIGS. 7-8) as it
merges into first enhancement channel 34. Referring to FIG. 2,
first enhancement channel 34 becomes increasingly flat and connects
with flat U-shaped bend 48 through reduction connector 49 (FIG. 2).
Bend 48 is substantially uniformly flat and connects first and
second enhancement channels 34, 36 (FIGS. 5-6). Flat bend 48
provides a decreased flow area corresponding to an increase in
velocity of flow of hot products of combustion in preparation for
urging the flow through second enhancement channel 36. In the
exemplary embodiment, the "flatness" or reduction in height of
first enhancement channel 34 may be 5.9 mm over a 275.4 mm length,
for example.
[0039] Referring to FIGS. 1-4, serpentine fluid passageway 24
includes trapezoidally shaped, spaced corrugations or enhancements
transversely arranged relative to longitudinal reference axis 33,
provided on first and second enhancement channel portions 34, 36,
respectively. First enhancement channel portion 34 includes
enhancements 50-54 (FIG. 3) formed on clamshell 19 internested or
staggered with enhancements 55-59 (FIG. 4) formed on clamshell 21.
The staggered relationship is best seen in FIG. 5 as the
alternating enhancements form a generally saw-toothed passageway
for hot products of combustion to turbulently flow therethrough.
Similarly, second enhancement channel 36 includes enhancements
60-64 (FIG. 3), formed in clamshell 19, in an internested
relationship with enhancements 65-69 (FIG. 4) formed in clamshell
21, to provoke flow turbulence and increased heat transfer. In
contrast to first enhancement channel 34 illustrated in FIG. 5,
passageway walls 27 (FIG. 6) of second enhancement channel 36 do
not taper and are generally uniformly spaced relative to the space
formed between clamshells 19, 21.
[0040] Referring to FIG. 6A, second enhancement channel 36 of the
first embodiment heat exchanger 18 is shown, illustrating
asymmetrically arranged enhancements 62 and 68. Specifically,
second enhancement channel 36 includes enhancement 68 having
upstream ramp 71 and downstream ramp 72 respectively positioned at
angles of inclination and declination .alpha. and .theta. measured
relative to longitudinal reference line 74. Arrow 75 illustrates
the direction of flow for the hot products of combustion flowing
therethrough (FIGS. 5 and 6). Further, it may be seen that located
between wall 27 of passageway 24 and ramp 71 is arced intersection
76. Plateau 78 is provided between ramps 71 and 72 and a pair of
rounded edges 80, 82 are provided at the intersection of plateau 78
and respective ramps 71, 72. Additionally, arced intersection 84,
positioned downstream relative to engagement portion 68, is
provided between the intersection of ramp 72 and passageway wall
27.
[0041] In the exemplary embodiment, upstream and downstream ramps
71 and 72 may have angles of inclination and declination of .alpha.
and .theta. of 63.degree. and 47.degree., respectively. Further,
rounded edges 80, 82 may each include an inside radius of 6.9 mm
and arced intersections 76 and 84 may have respective inside radii
of 7.6 mm and 15.2 mm. Accordingly, each raised enhancement may
extend into passageway 24 depth "D" of 14 mm, for example.
[0042] Referring to FIGS. 6 and 6A, enhancement 62 is generally a
mirror image of enhancement 68, however enhancement 62 is arranged
offset, relative to enhancement 68. In the exemplary embodiment
substantially all of the enhancements are of similar construction
and include each upstream ramp 71 positioned upstream of each
counterpart downstream ramp 72 (FIG. 6A). However, an infinite
selection of ramp angles and enhancement contours are possible
which may be common or differ between individual enhancements to
provide enhanced heat transfer characteristics.
[0043] Referring to FIGS. 6B and 6C, shown are additional exemplary
embodiments of the present invention which also provide enhanced
heat transfer characteristics between hot products of combustion
and room air. Specifically, and with reference to FIG. 6B, shown is
a second embodiment heat exchanger including second enhancement
channel 36b of heat exchanger element 18b. Heat exchanger element
18b includes a similar number and spacing of enhancements as
compared to heat exchanger 18, however differs therefrom in several
aspects. One such difference corresponds to enhancement 68b which
includes upstream and downstream ramps 71b, 72b, provided with
respective angles .alpha..sub.b and .theta..sub.b, measured from
longitudinal reference line 74b. Angles .alpha..sub.b and
.theta..sub.b are substantially similar. Yet, it may be seen that
enhancement 68b is asymmetrical due to arced intersection 84b
having a significantly larger radius relative to arced intersection
76b. For example, angles .alpha..sub.b and .theta..sub.b, may each
be 63.degree. and arced intersections 76b and 84b may have 4.6 mm
and 15.2 mm inside radii, respectively. Rounded edges 80b, 82b may
each be provided with a 4.6 mm inside radius and depth D.sub.b of
enhancements 62b, 68b may be 16.3 mm, for example.
[0044] Referring to FIG. 6C, shown is a third embodiment heat
exchanger provided with enhancements 62c, 68c within second
enhancement channel 36c of heat exchanger element 18c. Enhancement
68c differs from enhancement 68 in that it is symmetrically
arranged and angles .alpha..sub.c and .theta..sub.c of ramps 71c,
72c are substantially identical. Also, it may be seen that arced
intersection 76c is substantially similar to that of arced
intersection 84c. For example, angles .alpha..sub.c and
.theta..sub.c may each be 63.degree., arced intersections 76c and
84c each may include an inside radius of 3.8 mm and rounded edges
80c, 82c may be 4.6 mm measured at their respective inside radii.
Further, enhancements 62c, 68c may include depth D.sub.c of 16.3
mm, for example.
[0045] Referring to FIG. 11, shown is a first flow model with
uniform and sharply formed enhancements 90. Passageway 88
accommodates the flow of hot products of combustion which are
illustrated by flow arrow 101 and flow streamline contour 102.
First flow model 86 does not directly correspond to any of the
described embodiments of heat exchangers of the present invention,
however the disclosure of its structure and function is fundamental
to understanding the operation of the exemplary embodiments of the
inventive heat exchangers according to the present invention. Flow
model 86 includes uniform enhancements 90 which are intersected to
form generally saw-toothed shaped passageway 88 therebetween. First
flow model 86 includes intersections 92 formed between each ramp 94
and adjacently positioned wall portion 96. Each enhancement 90
includes a pair of edge portions 98 separated by a generally planar
plateau portion 100. It may be seen that the hot products of
combustion flowing through passageway 88, indicated by arrow 101,
form flow streamline contour 102. Streamline contour 102 represents
a velocity gradient of flow through passageway 88 wherein an
increased number of lines represents an increased flow velocity.
Those having ordinary skill in the art will appreciate that
increased velocity of the combustion products is directly related
to increased heat transfer. Proximate to edge portions 98, contour
102 illustrates an increased velocity region. In contrast,
proximate to the intersections 92 the velocity is generally
insignificant shown by a lack of streamlines, and moreover this
deficiency of streamlines corresponds to "recirculation zones" 104.
Recirculation zones 104 represent flow stagnation corresponding to
low flow velocity and insignificant heat transfer.
[0046] Referring to FIG. 12, shown is second flow model 106 which
corresponds to the first embodiment heat exchanger 18 according to
the present invention. In contrast to flow model 86 shown in FIG.
11, second flow model 106 illustrates a flow of hot products of
combustion indicated by flow by arrow 107, forming streamline curve
108 having little or no recirculation zones. Flow streamline curve
108 in FIG. 12 discloses a generous number of streamlines in close
proximity to passageway walls 27 corresponding to increased flow
velocity and enhanced heat transfer between the hot products of
combustion flowing through passageway 24 and room air circulating
over external surfaces of passageway walls 27. Similarly, the
second and third embodiment heat exchangers include respective heat
exchanger elements 18b, 18c exhibiting substantially similar flow
performance and heat transfer characteristics to that of flow
contour 108 of FIG. 12.
[0047] Referring to FIGS. 1 and 13, arrangement of the heat
exchanger elements to form a heat exchanger or bank 14 will now be
described. As best seen in FIG. 13, each heat exchanger element 18
is supported by being attached to inlet manifold 42, outlet
manifold 43 and L-shaped support member 110 (FIG. 1). The distance
between any two adjacent each heat exchanger elements is
predetermined by the spacing of inlet holes 112, in inlet manifold
42, and outlet holes 114, in outlet manifold 43 (FIG. 13). Each
heat exchanger element 18 includes an annular inlet rim 116 (FIG.
2) and outlet rim 118 (FIG. 2), which respectively attach to inlet
and outlet manifolds 42, 43. Each outlet rim 118, as best
illustrated in FIG. 14, is sealingly attached to outlet manifold 43
utilizing a crimping relationship to form a gas-tight seal
therebetween. U-shaped sleeve 120, which includes slot 122, is
engaged by annular protrusion 124 provided by heat exchanger
element 18. Sleeve 120 extends into passageway 24 of heat exchanger
element 18 and is bent over at bend 126 to sealably join outlet
manifold 43 with heat exchanger element 18. Outlet manifold 43
includes flange portion 128 extended radially, outwardly from each
outlet hole 114 and includes a perpendicular bend 130, to provide
access for the exhaust fan assembly (not shown). It will be
understood that the sealed engagement of inlet manifold 42 with
each heat exchanger 18 is similar to the sealed engagement of
outlet manifold 43 with each heat exchanger 18 previously
described.
[0048] While this invention has been described as having exemplary
designs, the present invention can be further modified within the
spirit and scope of this disclosure. This application is therefore
intended to cover any variations, uses, or adaptations of the
invention using its general principles. Further, this application
is intended to cover such departures from the present disclosure as
come within known or customary practice in the art to which this
invention pertains and which fall within the limits of the appended
claims.
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