Note: Descriptions are shown in the official language in which they were submitted.
CA 02590905 2007-05-31
67363-1209D
IMPROVED WATER HEATER FLUE SYSTEM
This is a divisional of Application Serial
No. 2,345,487, filed April 27, 2001.
FIELD OF THE INVENTION
The invention relates to flue systems for gas-
fired water heaters.
BACKGROUND
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.
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.
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.
-1-
CA 02590905 2007-05-31
67363-1209D
SUNIMARY
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.
According to one aspect of the present invention,
there is provided 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.
-2-
CA 02590905 2007-05-31
67363-1209D
According to another aspect of the present
invention, there is provided 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 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, 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, wherein the fin portion includes at least
one slot to reduce the amount of thermal expansion of the
fin structure at the joint.
According to still another aspect of the present
invention, there is provided 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
-2a-
CA 02590905 2007-05-31
67363-1209D
reduce adverse effects of thermal expansion of the fin
structure.
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
Fig. 1 is a perspective, partially cut-away view
of a water heater embodying the present invention.
Fig. 2 is an enlarged exploded view of part of the
flue system of Fig. 1.
Fig. 3 is an end view of a flue tube including a
first fin construction.
Fig. 4 is an end view of a flue tube including a
second fin construction.
Fig. 5 is an end view of a flue tube including a
third fin construction.
Fig. 6 is an end view of a flue tube including a
fourth fin construction.
Fig. 7 is an end view of a flue tube including a
first baffle orientation.
Fig. 8 is an end view of a flue tube including a
second baffle orientation.
-2b-
CA 02590905 2007-05-31
67363-1209D
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.
Fig. 10 is a perspective view of an alternative construction of the lower
end of the fin structure.
Fig. 11 is a perspective view of an alternative construction of the fin
structure.
Fig. 12 is a perspective view of an alternative construction of the fin
structure.
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
perfoimed in a particular order.
DETAILED DESCRIPTION
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
-3-
CA 02590905 2007-05-31
67363-1209D
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.
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 eruciform 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.
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 poi-tions 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%
-4-
CA 02590905 2007-05-31
67363-1209D
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.
The ciuciform 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.
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.
-5-
CA 02590905 2007-05-31
67363-1209D
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.
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.
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.
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.
-6-
CA 02590905 2007-05-31
67363-1209D
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.
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.
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 turbu(ent flow in the products of combustion moving through the flue
tube
52. The turbulation sur-faces 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.
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
-7-
CA 02590905 2007-05-31
67363-1209D
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.
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.
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.
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 tun 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
-8-
CA 02590905 2007-05-31
67363-1209D
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.
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.
Additionally, the holes 106 in the fin structure 66 illustrated in Fig. 11 may
.10 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.
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.
-9-
CA 02590905 2007-05-31
67363-1209D
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.
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.
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.
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
-10-
CA 02590905 2007-05-31
67363-1209D
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 thei7nal growth in the V-shaped fin portions 74.
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).
In an alternative embodiment, the total length of the V-shaped fin portion
74 is 39 5/8 inches. The lowest slot 92 is preferably 4 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
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.
-11-
CA 02590905 2007-05-31
67363-1209D
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).
-12-
