U.S. patent application number 09/795284 was filed with the patent office on 2001-11-01 for water heater flue system.
This patent application is currently assigned to AOS Holding Company. Invention is credited to Akkala, Marc W., Field, Kevin M., Hughes, Dennis R., Poehlman, Robert F..
Application Number | 20010035135 09/795284 |
Document ID | / |
Family ID | 27072555 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035135 |
Kind Code |
A1 |
Hughes, Dennis R. ; et
al. |
November 1, 2001 |
Water heater flue system
Abstract
A water heater includes a water tank, a combustion chamber below
the tank and communicating with the flue tube, and a flue system.
The flue system includes a flue tube, and V-shaped fins that are
metallurgically bonded to the flue tube wall to divide the flue
tube into four flue chambers extending substantially parallel to
the longitudinal axis of the flue tube. The V-shaped fins include
radially extending apertures that reduce the thermal expansion of
the V-shaped fins with respect to the flue tube to reduce stress at
the joint between the fins and the flue tube. The flue system also
includes a removable baffle hanging in each flue chamber. The
baffles include adjustable turbulation surfaces to control the
quality of combustion in the water heater. This is a
continuation-in-part of application Ser. No. 09/561,126 filed Apr.
28, 2000, the entire contents of which are herein incorporated by
reference.
Inventors: |
Hughes, Dennis R.;
(Hartford, WI) ; Akkala, Marc W.; (Cedarburg,
WI) ; Field, Kevin M.; (Oconomowoc, WI) ;
Poehlman, Robert F.; (South Milwaukee, WI) |
Correspondence
Address: |
MICHAEL BEST & FRIEDRICH, LLP
100 E WISCONSIN AVENUE
MILWAUKEE
WI
53202
US
|
Assignee: |
AOS Holding Company
Wilmington
DE
|
Family ID: |
27072555 |
Appl. No.: |
09/795284 |
Filed: |
February 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09795284 |
Feb 28, 2001 |
|
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09561126 |
Apr 28, 2000 |
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6286465 |
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Current U.S.
Class: |
122/155.2 ;
122/13.01; 122/155.1; 122/18.1 |
Current CPC
Class: |
F24H 1/205 20130101;
F24H 9/0026 20130101; F23M 9/003 20130101; F28F 13/12 20130101 |
Class at
Publication: |
122/155.2 ;
122/155.1; 122/13.01; 122/18.1 |
International
Class: |
F24H 009/18 |
Claims
1. A water heater comprising: a tank for holding water; a
combustion chamber; a flue tube extending through the tank and
communicating with the combustion chamber, the flue tube having an
inner surface; a first fin positioned within the flue tube, the fin
having a first edge that is at least partially metallurgically
bonded to the inner surface; and a first removable baffle
positioned within the flue tube, the first baffle having at least
one turbulation surface.
2. A water heater comprising: a tank for holding water; a
combustion chamber; a flue tube extending through the tank and
communicating with the combustion chamber, the flue tube having an
inner surface and a longitudinal axis; and a fin structure
positioned within the flue tube, the fin structure including at
least one fin portion that is V-shaped in cross-section and that
has a base extending substantially parallel to the longitudinal
axis, the fin portion also having two legs that extend from the
base and that are each metallurgically bonded to the inner surface
to define a joint between each of the legs and the inner surface,
and the fin portion also having at least one slot to reduce the
amount of thermal expansion of the fin structure at the joints, the
fin structure dividing the flue tube into a plurality of flue
chambers extending substantially parallel to the longitudinal
axis.
3. The water heater of claim 2 wherein the longitudinal axis is
substantially vertical, and wherein the combustion chamber is
located beneath the tank.
4. The water heater of claim 2 wherein the base is substantially
collinear with the longitudinal axis.
5. The water heater of claim 2 wherein the at least one slot
includes a plurality of slots that are equally spaced approximately
6 inches apart from each other along the length of the fin
portion.
6. The water heater of claim 2 wherein the slot extends an equal
distance from the base along each of the legs.
7. The water heater of claim 2 wherein the slot is substantially
horizontal.
8. The water heater of claim 2 wherein the at least one fin portion
includes first and second fin portions, the bases of the fin
portions being metallurgically bonded to one another such that the
legs of the first fin portion extend substantially different
directions than the legs of the second fin portion.
9. The water heater of claim 8 wherein the bases and the
longitudinal axis are all substantially coplanar.
10. The water heater of claim 2 wherein the at least one fin
portion includes first and second fin portions, the bases of the
fin portions being spaced from each other such that the legs of the
first fin portion extend substantially different directions than
the legs of the second fin portion.
11. The water heater of claim 2 further comprising a removable
baffle positioned within one of the flue chambers, the baffle
having at least one turbulation surface.
12. A water heater comprising: a tank for holding water; a
combustion chamber; a flue tube extending through the tank and
communicating with the combustion chamber, the flue tube having an
inner surface and a longitudinal axis; and a fin structure
positioned within the flue tube, the fin structure including at
least one fin portion that is V-shaped in cross-section and that
has a base extending substantially parallel to the longitudinal
axis, and the fin portions also having two legs that extend from
the base and that are each metallurgically bonded to the inner
surface to define a joint between each of the legs and the inner
surface, the legs being approximately 90 degrees apart from each
other, the fin structure dividing the flue tube into a plurality of
flue chambers extending substantially parallel to the longitudinal
axis.
13. The water heater of claim 12 wherein the longitudinal axis is
substantially vertical and the combustion chamber is located
beneath the tank.
14. The water heater of claim 12 wherein the base is substantially
collinear with the longitudinal axis.
15. The water heater of claim 12 wherein the fin portion includes
at least one slot to reduce the amount of thermal expansion of the
fin structure at the joint.
16. The water heater of claim 12 wherein the at least one fin
portion includes first and second fin portions, the bases of the
fin portions being metallurgically bonded to one another such that
the legs of the first fin portion extend substantially different
directions than the legs of the second fin portion.
17. The water heater of claim 16 wherein the bases and the
longitudinal axis are all substantially coplanar.
18. The water heater of claim 12 wherein the at least one fin
portion includes first and second fin portions, the bases of the
fin portions being spaced from each other such that the legs of the
first fin portion extend substantially different directions than
the legs of the second fin portion.
19. The water heater of claim 12 further comprising a removable
baffle positioned within one of the flue chambers, the baffle
having at least one turbulation surface.
20. A water heater comprising a water tank, a combustion chamber, a
flue extending from the combustion chamber and through the tank,
the flue having an inside and an inner surface, and a fin structure
in the flue for improving heat transfer from exhaust gases in the
flue to water in the tank, the fin structure having a longitudinal
direction, a V-shaped cross section transverse to the longitudinal
direction, a longitudinally extending point, and a pair of
longitudinally extending, spaced edges secured to the inner surface
of the flue so as to facilitate heat transfer from the fin
structure to the flue, the fin structure dividing the inside of the
flue into two longitudinally extending flue portions through which
exhaust gases can flow, and the fin structure being slotted to
reduce adverse effects of thermal expansion of the fin
structure.
21. A water heater as set forth in claim 20 wherein the edges are
welded to the inner surface of the flue.
22. A water heater as set forth in claim 20 wherein the fin
structure has two legs of substantially equal length extending from
the point, each of the legs being substantially planar and
including a respective one of the edges.
23. A water heater as set forth in claim 20 wherein the point is
located substantially in the center of the flue.
24. A water heater as set forth in claim 20 wherein the combustion
chamber is beneath the tank, wherein the flue and the point extend
substantially vertically, and wherein the fin structure has two
legs extending from the point, each of the legs defining a
substantially vertical plane and including a respective one of the
edges.
25. A water heater as set forth in claim 20 and further comprising
a baffle in one of the flue portions.
26. A water heater as set forth in claim 25 and further comprising
a baffle in the other of the flue portions.
27. A water heater as set forth in claim 20 wherein the fin
structure has therein a plurality of slots.
28. A water heater as set forth in claim 27 wherein each of the
slots extends through the point of the fin structure.
29. A water heater as set forth in claim 28 wherein the fin
structure has two legs of substantially equal length extending from
the point, each of the legs being substantially planar and
including a respective one of the edges, and wherein each of the
slots extends substantially the same distance into both legs.
30. A water heater as set forth in claim 27 wherein the slots are
substantially equally spaced along the fin structure.
31. A water heater as set forth in claim 27 wherein the combustion
chamber is beneath the tank, wherein the flue and the point extend
substantially vertically, wherein the fin structure has two legs
extending from the point, each of the legs defining a substantially
vertical plane and including a respective one of the edges, and
wherein the slots are substantially horizontal.
32. A water heater as set forth in claim 31 wherein each of the
slots has a height that is constant along substantially the entire
horizontal extent of the slot.
33. A water heater comprising a water tank, a combustion chamber, a
flue extending from the combustion chamber and through the tank,
the flue having an inside and an inner surface, and a pair of fin
structures in the flue for improving heat transfer from exhaust
gases in the flue to water in the tank, each fin structure having a
longitudinal direction, a V-shaped cross section transverse to the
longitudinal direction, a longitudinally extending point, and a
pair of longitudinally extending, spaced edges secured to the inner
surface of the flue so as to facilitate heat transfer from the fin
structure to the flue, the fin structures being arranged in
point-to-point relationship and dividing the inside of the flue
into four longitudinally extending flue portions through which
exhaust gases can flow, the flue portions being substantially
identical in size.
34. A water heater as set forth in claim 33 wherein the points of
the fin structures are spaced apart.
35. A water heater as set forth in claim 33 and further comprising
a baffle in each of the flue portions.
36. A water heater as set forth in claim 33 wherein the edges are
welded to the inner surface of the flue.
37. A water heater as set forth in claim 33 wherein each of the fin
structures has two legs of substantially equal length extending
from the associated point, each of the legs being substantially
planar and including a respective one of the associated edges.
38. A water heater as set forth in claim 33 wherein the points of
the fin structures are located substantially in the center of the
flue.
39. A water heater as set forth in claim 33 wherein the combustion
chamber is beneath the tank, wherein the flue and the points of the
fin structures extend substantially vertically, and wherein each
fin structure has two legs extending from the associated point,
each of the legs defining a substantially vertical plane and
including a respective one of the associated edges.
Description
FIELD OF THE INVENTION
[0001] The invention relates to flue systems for gas-fired water
heaters.
BACKGROUND
[0002] It is known to weld or otherwise metallurgically bond fins
inside a water heater flue tube to enhance heat conduction through
the walls of the flue tube. It is also known to hang removable
baffles in a flue tube to turbulate the exhaust gases flowing
through the flue tube.
[0003] However, known systems often do not meet the current
gas-fired water heater regulations relating to efficiency and
construction for facilitating cleaning, and many of those water
heaters that do meet the current regulations will not meet the
next, more strict regulations to be enacted. For example, under
today's regulations, the flue of a water heater has to be cleanable
to remove soot and other buildup that may be hazardous. Many known
flue systems were not designed to be easily cleaned, and therefore
may not meet this regulation.
[0004] For example, one known flue tube fin arrangement includes a
plurality of small fins extending radially inwardly into the flue
tube from the flue tube wall. Soot can collect on these small fins,
and the small fins are not easily cleaned with a brush. Another
example is a twisted fin positioned within the flue tube. A twisted
fin is not easily cleaned because a cleaning brush would have to be
twisted to follow the contour of the fin.
SUMMARY
[0005] The present invention provides a flue system for a water
heater. The flue system permits the combustion characteristics of
the water heater to be tuned or adjusted. The system also permits
relatively easy cleaning of the flue. The flue system includes a
fin that is metallurgically bonded to the flue tube, and a
removable baffle having at least one turbulation surface. The
combustion quality of the water heater is adjusted by adding or
removing baffles and by adjusting the turbulation surfaces of the
baffles. The fin may be a cruciform-shaped fin, a pair of V-shaped
fins, or a plurality of straight fins. Preferably, the fins divide
the flue tube into flue chambers extending substantially parallel
to the longitudinal axis of the flue tube, and the removable
baffles are hung in selected flue chambers.
[0006] Other features and advantages of the invention will become
apparent to those skilled in the art upon review of the following
detailed description, claims, and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a perspective, partially cut-away view of a water
heater embodying the present invention.
[0008] FIG. 2 is an enlarged exploded view of part of the flue
system of FIG. 1.
[0009] FIG. 3 is an end view of a flue tube including a first fin
construction.
[0010] FIG. 4 is an end view of a flue tube including a second fin
construction.
[0011] FIG. 5 is an end view of a flue tube including a third fin
construction.
[0012] FIG. 6 is an end view of a flue tube including a fourth fin
construction.
[0013] FIG. 7 is an end view of a flue tube including a first
baffle orientation.
[0014] FIG. 8 is an end view of a flue tube including a second
baffle orientation.
[0015] FIG. 9 is an enlarged view of the top portion of the water
heater of FIG. 1, illustrating the removal of a baffle under
low-clearance circumstances.
[0016] FIG. 10 is a perspective view of an alternative construction
of the lower end of the fin structure.
[0017] FIG. 11 is a perspective view of an alternative construction
of the fin structure.
[0018] FIG. 12 is a perspective view of an alternative construction
of the fin structure.
[0019] Before one embodiment of the invention is explained in
detail, it is to be understood that the invention is not limited in
its application to the details of construction and the arrangements
of the components set forth in the following description or
illustrated in the drawings. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways. Also, it is understood that the phraseology and terminology
used herein is for the purpose of description and should not be
regarded as limiting. The use of "including" and "comprising" and
variations thereof herein is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items. The
use of "consisting of" and variations thereof herein is meant to
encompass only the items listed thereafter. The use of letters to
identify elements of a method or process is simply for
identification and is not meant to indicate that the elements
should be performed in a particular order.
DETAILED DESCRIPTION
[0020] FIG. 1 illustrates a water heater 10 that includes a base
pan 14, a tank 18 supported by the base pan 14 and containing
water, an insulating jacket 22 surrounding the tank 18, a control
system 26, a burner 30 disposed in a combustion chamber 34 beneath
the tank 18, a water inlet pipe 38, a water outlet pipe 42, and a
flue system 50 including a flue tube 52. In operation, gas fuel is
provided to the burner 30 through a conduit 54. The gas is released
by the burner 30 in a controlled fashion, and the gas is lit by a
pilot light 58 that continually burns within the combustion chamber
34. Products of combustion from the burner 30 heat the water in the
tank 18 through the tank bottom wall 62, which is dome-shaped. The
products of combustion also flow up through the flue tube 52 and
heat the water through the wall of the flue tube 52.
[0021] FIG. 2 illustrates the flue system 50, which includes the
flue tube 52 (FIG. 1), a fin structure 66, and four removable
baffles 70. With additional reference to FIG. 3, the illustrated
fin structure 66 is a cross-shaped or cruciform fin structure
having four arms or fin portions 74 of substantially equal length
joined along a central line that is substantially coincident with
the longitudinal axis 78 of the flue tube 52.
[0022] The outer edges of the fin portions 74 are metallurgically
bonded to the inner surface of the flue tube wall as shown in FIG.
3. As used herein, "metallurgically bonded" means welded, brazed,
or otherwise joined or fused together to facilitate heat conduction
between two members. Preferably, the fin portions 74 are welded to
the flue wall from the outside by penetration, laser, arc, or
electron beam welding. Alternatively, the fin portions 74 may be
welded from inside the tube 52 with a torch. A continuous weld
along the entire length of the edge of the fin portions 74 is not
necessary. Rather, the fin portions 74 may be welded along only a
portion of each edge, either in a continuous weld or in several
segmented welds. In this regard, the fin portions 74 may be welded
along 100% or less of the length of the edges. Preferably, the fin
portions 74 are welded between about 75% and 100% of the length of
the edges to provide the desired heat transfer efficiency.
Preferably, the flue system 50 is made of mild (i.e., low carbon)
steel. In high efficiency models where corrosion caused by
condensation is a concern, the flue system 50 may be constructed of
an alloy such as stainless steel, Inconel, or an alloy of nickel.
Alternatively, any suitable material may be used to construct the
flue system 50.
[0023] The cruciform fin structure 66 provides several advantages.
First, the cruciform fin structure 66 provides structural stability
to the flue tube 52, which aids in the manufacture of the flue
system 50. The structural stability permits the flue tube 52 to
resist distortion during the glass-firing process and during
insertion of the flue tube 52 into heads during assembly.
[0024] The cruciform fin structure 66 also substantially equally
divides the inner volume of the flue tube 52 into four flue
chambers 82 that extend substantially parallel to the longitudinal
axis 78 of the flue tube 52. The four flue chambers 82 act as four
flue tubes of relatively small cross-sectional area. The hottest
gas within each flue chamber 82 is geometrically centered in the
cross-sectional area of the flue chamber 82. If there were no fin
structure 66 in the flue tube 52, the hottest gas would be centered
with respect to the cross-sectional area of the flue tube 52. A
second advantage of the cruciform fin structure 66, therefore, is
that the hottest gas is closer to the flue wall than if the fin
structure 66 were not present or if the fin structure 66 did not
divide the flue tube into separate flue chambers 82.
[0025] A third advantage of the cruciform fin structure 66 is that
it facilitates cleaning the flue tube 52. A cleaning brush may be
easily inserted into the four flue chambers 82, and no twisting of
the brush is required.
[0026] Another advantage lies in the fact that the four fin
portions 74 of the fin structure 66 are connected at the center of
the fin structure 66. In this regard, if one of the welds along one
of the edges were to fail, the fin structure 66 would still be
supported by the welds on the other fin portion 74 edges.
[0027] As shown in FIG. 1, the fin structure 66 is positioned
within the flue tube 52 to leave a space 86 between the ends of the
fin structure 66 and the ends of the tube 52. The space 86
facilitates mounting the flue tube 52 and fin structure 66 assembly
on a glass coating machine that coats the inside and outside of the
flue tube 52 and the fin structure 66 with a protective glass
coating to resist degradation of the fin structure 66 and flue tube
wall. Additionally, because the fin structure 66 is recessed with
respect to the lower end of the flue tube 52, the fin structure 66
is less likely to be overheated by the extreme temperatures in the
combustion chamber 34. The space 86 may be, for example, about
three inches, but may be more or less depending on the
circumstances.
[0028] To further facilitate the glass-coating process, one or more
fin portions 74 may include a hole 90. The hole 90 may be engaged
with a hook to suspend the fin structure 66 and flue tube 52 during
the heating procedure of glass coating. This is an advantage over
providing a hole in the flue tube 52. Holes in the flue tube 52 can
interfere with welding the flue tube 52 to the head of the tank 18
if the hole is located too far from the end of the flue tube 52. On
the other hand, if the hole is positioned too close to the end of
the tube 52, the hook may tear through the flue tube wall at the
elevated temperatures of the heating procedure. Additionally, a
hole in the flue tube 52 would have to be patched or otherwise
closed, while the hole in the fin portion 74 would not interfere
with the operation of the water heater 10.
[0029] Because the fin portions 74 are metallurgically bonded to
the flue wall, heat transfer between the fin portions 74 and the
flue wall is improved over fin portions that are not
metallurgically bonded to the flue wall. The metallurgical bonding
therefore results in more efficient transfer of heat from the
products of combustion to the water in the tank 18. The increased
heat transfer of the cruciform fin structure 66 permits a water
heater 10 to be made more compact than multiple flue designs. There
is less welding, fewer components, lower cost, and less tooling
involved in assembling a water heater 10 having the cruciform fin
structure 66 when compared to a multiple flue design.
[0030] As seen in FIG. 2, the baffles 70 are elongated and include
hangers 94 and turbulation surfaces 98. The baffles 70 may be
constructed from, for example, strips of stainless steel having
partially cut-out tabs that are bent to form the turbulation
surfaces 98. Preferably, the tabs 98 are bent in alternating
directions along the length of the baffle 70 as illustrated. The
tabs 98 may be semicircular in a shape as illustrated or any other
suitable shape. The turbulation surfaces 98 cause turbulent flow in
the products of combustion moving through the flue tube 52. The
turbulation surfaces 98 can be adjusted to provide more or less
resistance to the flow of products of combustion. The turbulation
surfaces 98 also resist downdrafts in the flue tube 52.
[0031] In this regard, the flue system 50 is adjustable, and the
quality of combustion in the water heater 10 is able to be tuned to
optimize combustion, residence time of the products of combustion
within the flue tube 52, and heat transfer to the water in the tank
18. The baffles 70 may also be removed and replaced with baffles 70
having different arrangements of turbulation surfaces 98 to
optimize these parameters and to accommodate different inputs to
the burner 30.
[0032] As can be seen in FIGS. 7 and 8, the baffles 70 may be
supported with the hangers 94 in a square or chord pattern (FIG.
7), in a radial pattern (FIG. 8), or in a combination of the chord
and radial patterns. Thus, the orientation in which the baffles 70
are hung may be used to further tune the combustion quality of the
water heater 10. Also, one or more of the baffles 70 may be removed
from the flue tube 52 to further customize the combustion
quality.
[0033] Referring now to FIG. 9, because the baffles 70 are made of
relatively narrow strips of metal, they are more easily bent than
traditional, larger baffles. As a result, the baffles 70 may be
removed from a water heater 10 under low clearance conditions,
where traditional, larger baffles could not be removed without
first tipping or otherwise moving the water heater 10. The flue 52
and fin structure 66 are easily cleaned by removing the baffles 70
from the flue tube 52 and scrubbing the flue wall and fin structure
66 with a brush.
[0034] An alternative design for the lower end of the fin structure
66 is illustrated in FIG. 10. Here it is shown that the end 102 of
the fin structure 66 may be shaped as a point (e.g., shaped as the
end of a pointed stake). As condensation forms in the flue tube 52,
water runs down the fin structure 66. In a flue system having a
flat-bottom fin structure, some of the condensation may run along
the domed bottom wall 62 of the tank 18 and drip onto the pilot
light 58, potentially extinguishing the pilot light 58. With the
pointed end 102 design shown in FIG. 10, substantially all of the
condensation runs all the way down the fin structure 66 to the
pointed end 102, and falls on the burner 30, where the condensation
is evaporated. The pointed end 102 of the fin structure 66 may
therefore help to keep the pilot light 58 from being inadvertently
extinguished.
[0035] FIG. 11 illustrates another alternative construction of the
fin structure 66. Here the fin structure 66 is provided with holes
106 to permit the cross-flow of the products of combustion through
the fin structure 66. The holes 106 do not significantly interfere
with cleaning the flue tube 52 and fin structure 66. The cross-flow
holes 106 permit better mixing of the products of combustion.
[0036] Additionally, the holes 106 in the fin structure 66
illustrated in FIG. 11 may be provided by shear-forming tabs in a
similar fashion to the tabs 98 of the baffle 70 described above.
The tabs may be bent in alternating directions. In such a
construction, the hanging baffles 70 would not be necessary, as the
bent tabs formed in the fin structure 66 would serve as turbulation
surfaces. The tabs would provide a greater and more efficient heat
transfer surface than the fin structure 66 illustrated in FIG.
11.
[0037] Alternative fin structure 66 configurations are illustrated
in FIGS. 4-6. Each alternative fin structure 66 configuration
includes a plurality of fin portions 74. In each configuration,
however, the fin portions 74 substantially divide the flue tube 52
into four flue chambers 82. In each configuration, the fin portions
74 may be sized so that they abut each other near the center of the
flue tube 52, or the fin portions 74 may be intentionally sized to
not quite touch each other. If the fin portions 74 do not touch
each other, the space between the inner edges of the fin portions
74 acts as a buffer, absorbing any distortion of the flue tube 52,
and permitting the flue tube 52 to be radially compressed before
the fin portions 74 touch each other and provide support for the
flue wall.
[0038] In FIG. 4, the outer edge of each of four fin portions 74 is
metallurgically bonded to the flue wall. The inner edge of each fin
portion 74 is positioned near the longitudinal axis 78 of the flue
tube 52.
[0039] In FIG. 5, three fin portions 74 are provided, one of which
is metallurgically bonded to the flue wall along both edges, and
two that each have one edge metallurgically bonded to the flue
wall. The two fin portions 74 that have free ends may or may not
touch the fin portion 74 that is metallurgically bonded at both
ends.
[0040] FIG. 6 illustrates a configuration with two fin portions 74,
in which the fin portions 74 are V-shaped in cross-section. The
V-shaped fin portions 74 each include a longitudinally extending
point, or base 76 and two legs 80 that extend away from the base
76. The base 76 defines a substantially vertical line that is
substantially parallel to the longitudinal axis 78 of the flue tube
52. Each leg 80 is substantially planar and includes an edge that
is metallurgically bonded to the inner surface of the flue tube 52.
The V-shaped fin portion 74 is preferably welded to the inner
surface on one side of each leg 80, but may alternatively be welded
on both sides of each leg 80. The bases 76 of the V-shaped fin
portions 74 are positioned near each other substantially along the
longitudinal axis 78 of the flue tube 52 and preferably within
approximately 0.030 inches from each other. The lines defined by
the bases 76 of the two fin portions 74 may define a plane that
includes the longitudinal axis 78. The V-shaped fin portions 74 may
alternatively be welded along the longitudinal axis 78 at their
respective bases 76.
[0041] FIG. 12 illustrates another fin structure 66 that includes
V-shaped fin portions 74 having at least one slot 92 to reduce
cracking effects caused by the thermal expansion of the fin
structure 66. The fin structure 66 is welded or otherwise
metallurgically bonded to the inside surface of the flue tube 52.
Differences between the thermal expansion of the flue tube 52 and
that of the fin structure 66 may develop thermal stresses at the
weld joint between the V-shaped fin portion 74 and the flue tube
wall. The number and the location of the slots 92 can be varied to
reduce the thermal stress on the fin portions 74 at the joints
while accommodating the actual thermal growth in the V-shaped fin
portions 74.
[0042] As shown in FIG. 12, the six slots 92 are preferably cut
horizontally across each V-shaped fin portion 74. The ends of the
slots 92 are rounded to avoid high stress concentrations that could
lead to crack propagation. The slots 92 project an equal distance
from the base 76 of the fin portion 74 along each leg 80 to within
3/8 of an inch from the edge of each leg 80. The slots 92 may
alternatively be asymmetrical with respect to the base 76, and
extend further along one leg 80 than the other leg 80. The slots 92
may also alternatively be angled with respect to horizontal and may
be longer, shorter, wider, or narrower than illustrated to optimize
heat transfer while still minimizing the stresses due to thermal
expansion. It should also be noted that the baffles 70 illustrated
in FIGS. 1, 2, and 7-9 and described above may be used with the fin
structure 66 illustrated in FIG. 12 (one baffle 70 is partially
shown in FIG. 12).
[0043] In an alternative embodiment, the total length of the
V-shaped fin portion 74 is 395/8 inches. The lowest slot 92 is
preferably 4{fraction (13/16)} inches away from the bottom end of
the fin portion 74 and all of the slots 92 are equally spaced
approximately 6 inches apart from each other such that the top slot
is also 4{fraction (13/16)} inches away from the top end of the fin
portion 74. By way of this configuration, the V-shaped fin portion
can be oriented in either direction before being inserted into the
flue tube 52 during assembly.
[0044] Although all of the fin structure 66 configurations
illustrated herein substantially divide the flue tube 52 into four
flue chambers 82, other fin structure configurations are
contemplated. For example, a fin structure configuration could be
provided in which the flue tube is divided into less than or more
than four flue chambers 82 (e.g., with only one V-shaped fin
portion or with more than two V-shaped fin portions).
* * * * *