Note: Descriptions are shown in the official language in which they were submitted.
CA 02496656 2007-04-17
FINNED TUBE HEAT EXCHANGER AND METHOD
BACKGROUND OF THE INVENTION
B. Field of the Invention:
The present invention relates generally to heat exchange devices and to
components therefor, such
devices being used in a variety of heat exchange applications including water
heaters and boilers,
as well as fluid heat rejection devices.
C. Description of the Prior Art
The present invention deals with heat exchange devices generally. A common
example of such a
device is a water heater or boiler, although as will become apparent, the
principles of the invention
can also be applied to other heat exchange applications. Water heaters and
boilers (referred to
collectively as water heaters in the discussion which follows) typically have
a water heater tank,
often of the vertical tube type which utilizes fire tubes located above a
combustion chamber. The
typical prior art gas, oil or gas/oil fired water heater featured a non-
pressurized, external combustion
chamber which was typically located on the bottom exterior of the water
heater. Vertical shell or
V-shell heat exchangers of the above type are well-known in the industry.
Water heaters of the above type generally provide for the flow of hot gas
through a series of tubes
mounted in vertical fashion between top and bottom support plates within the
water heater tank. The
products of combustion from the combustion chamber pass vertically upward
through the upward
interiors of the vertical tubes and out a flue outlet. Water is circulated
into and out of a chamber in
the prior art devices located between the tube support plates. The water
contacts and circulates about
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the exterior of the vertical tubes to effect heat transfer to heat the water.
In U.S. Patent Nos. 4,465,024; 4,545,329 and 4,938,204, water heater designs
are shown which
feature one or more submergible, pressurized combustion chambers so that all
combustion takes
place in the water heater tank interior in a chamber surrounded by water.
These improved water
heater designs featured an externally mounted, forced draft burner unit
mounted on the exterior of
the closed tank at a tank opening so that the burner nozzle extends in the
direction of the combustion
chamber for heating the combustion chamber. The resulting designs decrease
heat loss and increase
the thermal efficiency of the water heater many times over that which was
achievable with the prior
art tube and plate arrangement.
A variety of'heat exchanger designs are also known which feature, e.g., coiled
tube heat exchangers.
In such designs as the Legend Burkay from A. O. Smith Corporation of
Milwaukee, Wisconsin,
water flows through the interior of the heat exchanger tubes while hot
products of combustion flow
over the outside of the heat exchanger. Certain of the prior art designs in
which the water flow was
through the tube interior featured finned copper tubes in combination with
separate baffle elements.
Other manufacturers of similar products, besides A.O. Smith Corporation,
include Teledyne LARS
Corporation, Lochinvar Corporation, RBI Water Heaters, Ray Pak, and Patterson-
Kelley
Corporation.
The field of the present invention is not limited to water heater and boiler
applications, although
those type devices provide a convenient setting for explaining the principles
of the invention. Other
heat exchanger applications for the present invention include fluid heat
rejection devices which
feature water cooling and air heating, for example.
A need exists for an improved heat exchanger coil design which is simple in
design and economical
to manufacture and which exhibits improved efficiency over existing designs.
Also, despite the above noted improvements in heat exchanger, water heater and
boiler designs, a
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need has continued to exist for an improved water heater of the finned copper
tuber variety which
could be produced economically and which would be effective for heating
potable water for end use
applications, or for heating non-potable water for the purpose of, e.g.,
transferring heat to an air
space or to a process, such as for food or chemical processing or other
similar water heater and boiler
applications.
A need also exists for improvements in condensing water heater designs
featuring heat exchange
components of the finned copper tube variety, in which the metallic components
are treated for
corrosion protection in order to protect them from acidic condensation and
other forms of corrosion
or contamination which can damage untreated copper or cupronickel materials.
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SUMMARY OF THE INVENTION
A finned tube water heater which may be used to heat water or other heat
transfer fluid and may be
used as a heating boiler is shown which includes at least one, and preferably
two flow manifolds,
each having a water inlet and a water outlet and a plurality of connecting
openings. A plurality of
circular flow tubes are arranged in stacked fashion to form a tube bundle
which surrounds an initially
open interior space. Each flow tube has a pair of opposing connecting ends
which connect to
selected ones of the openings provided in the flow manifolds. A burner is also
provided having a
burner outlet which communicates with the interior space within the stacked
tube bundle for
producing products of combustion for heating water flowing in the flow tubes.
The flow tubes have
external fins located on an exterior surface thereof. The external fins are
crushed to form upper and
lower flat stacking surfaces for stacking the tubes to form the tube bundle.
The external fins are also
crushed to form angled baffled surfaces about an external periphery of the
flow tubes. The baffle
surfaces serve to retain heat from the products of combustion which are
released into the interior
space within the stacked tube bundle.
Preferably, the external fins which are crushed to form the angled baffled
surfaces on each flow tube
present a continuous exposed surface on the exterior of the tube bundle when
the flow tubes are
stacked in vertical fashion. The continuous exposed surface comprises an
integral baffle surface for
the tube bundle when the tubes are stacked with the flat stacking surfaces in
contact, thereby
eliminating the need for a separate baffle member to assist in retaining and
more uniformly
distributing heat from the products of combustion in the interior space within
the stacked tube
bundle. In the most preferred embodiment, each finned flow tube is formed with
a forming die
which creates four facets on the exterior of each tube. Two of the facets form
the stacking surfaces
and two of the facets form the baffle surface.
In the preferred embodiment of the invention, a pair of vertically arranged
flow manifolds are
provided, each having connecting openings for receiving a connecting end of
the finned flow tubes
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making up the tube bundle as previously described. The pair of vertically
arranged flow manifolds
have internal passageways for cross communication between the flow manifolds,
whereby water
enters an inlet of the first manifold of the pair and circulates through an
internal passageway and
through a connected flow tube to the second manifold of the pair. Each
traverse of water from one
manifold to the other is characterized as a "pass" and the number of passes
may range from one to
many. The water then circulates through an internal passageway and through a
second flow tube
back to the first flow manifold. The circulation continues through all of the
flow tubes until the
water exits an outlet of one of the selected flow manifolds. A flow control
switch can be located
within a selected one of the vertically arranged manifolds in-line with the
flow path of water through
the flow manifold.
The tube bundle is constructed by positioning at least one brazing ring about
each flow tube
connecting end. The brazing ring is received upon an internal landing area of
the flow opening in
the flow manifold for brazing the tubes to the flow manifold. Preferably, the
vertically arranged
manifold and connected flow tubes are brazed in an furnace as a unit in a one-
step brazing operation.
Preferably, the tube bundle is brazed in a furnace in an oxygen starved
atmosphere at a temperature
in the range of about 1400 Fahrenheit.
The tube bundle is sandwiched between a base pan and bulkhead, each of which
can be provided
with an insulating refractory disk for reducing heat loss through the base pan
and bulkhead. The
base pan and the bulkhead are joined by a plurality of connecting rods which
hold the tube bundle,
base pan and bulkhead in tension. In this embodiment, a one piece jacket,
which can be insulated,
circumscribes the tube bundle, base pan and bulkhead. The one piece jacket may
be segmented to
facilitate manufacture, assembly or services. The jacket seals against
peripheral surfaces of the base
pan and bulkhead to create a flue space when installed about the tube bundle.
The flue space
receives products of combustion produced by the burner. The jacket also has a
flue outlet opening
for exhausting products of combustion and may have an opening or openings for
other piping
penetrations. The one piece jacket can be held in place by a mechanical clasp
and connectors,
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whereby the jacket is easily removable to expose the tube bundle and other
components of the
assembly for maintenance operations.
A blower/mixing box is mounted on an upper surface of the bulkhead. A burner
retention flange is
sandwiched between the blower/mixing box and the bulkhead. The blower/mixing
box contains an
internal scroll and an orifice member which together form a venturi passage.
The internal scroll and
orifice member have side tabs which are received within mating holes provided
in the opposing sides
of the blower/mixing box, alignment of the tabs and holes serving to provide
the desired shape for
the scroll within the blower/mixing box. Air and gas mixing, necessary for
proper combustion, takes
place within the blower/mixing box assembly, thus eliminating the need for
separate down stream
mixing contrivances. The blower/mixing box has an air inlet which may be
fitted with an inlet
damper system capable of responding to operational controls and which may
provide indication of
damper position. One embodiment of this inlet damper system has an internal
butterfly member
which is angularly positionable to control the flow of air through the
assembly. The butterfly is
movable between an open position for high fire conditions and a closed
position for low fire
conditions of the water heater, whereby the damper, in conjunction with a low
and high fire valve
or valves serves as a staging mechanism for the water heater.
An electrical control box with opposing sidewalls is mounted on the bulkhead.
The one-piecejacket
is provided with a control panel opening and a control panel is mounted within
the opening. The
control panel has a pair of opposing tabs at an upper end thereof which are
received within mating
T-slots provided in the opposing sides of the electrical control box. In this
way, the control panel
is positionable between a lowered positioned and an upwardly raised and locked
position which
provides access to electrical connections located within the electrical box. A
transparent cover panel
fits over the control panel within the control panel opening. The transparent
cover panel is formed
of a flexible plastic which allows the panel to be secured within the control
panel opening by flexing
the sides of the plastic material.
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The gas train consists of one or more gas circuits with one or more gas valves
per circuit. In one
embodiment, the gas train consists of a one inch main control train for single
stage models and an
additional three-quarter inch control train for two-stage models. Both gas
trains inject gas into the
blower/mixing box where it is mixed with a combustion air supply. The
combustion process is
initiated by a hot surface spark or gas pilot ignitor adjacent to the burner.
Desired water temperature
is monitored to provide a controlling signal to turn on, control, and turn off
the water heater.
The present invention also contemplates an improved finned tube heat exchanger
which maybe used
in other applications besides that of a water heater or boiler. The improved
heat exchanger
comprises at least one flow manifold having a water inlet and a water outlet
and a plurality of
connecting openings. A plurality of circular flow tubes are arranged in
stacked fashion to form a
tube bundle which surrounds an initially open interior space, each flow tube
having a pair of
opposing connecting ends which connect to selected connecting openings
provided in the at least one
flow manifold. The flow tubes have extemal fins located on an exterior surface
thereof, the external
fins being crushed to form upper and lower flat stacking surfaces for stacldng
the tubes to form the
tube bundle. The external fins are also crushed to form angled baffle surfaces
about an external
periphery of the tubes when the tubes are stacked to form a tube bundle.
The circular flow tubes are preferably formed of a material selected from the
group consisting of
copper, aluminum, stainless steel, mild steel and cupronickel. The circular
flow tubes can be
provided with a corrosion resistant coating which is formed by priming an
exterior surface of the
flow tubes with a noble metal primer, followed by applying a corrosion
protective monomeric or
polymeric topcoat. The preferred noble metal is selected from the group
consisting of platinum,
gold, silver, electroless nickel, titanium, and alloys including HastelloyTM,
InconelTM, Mone1TM and IncoloyTM.
The circular flow tubes can also first be anodized prior to applying the
corrosion protective
monomeric or polymeric topcoat. The preferred monomeric or polymeric topcoat
can comprise a
fluropolymer. The heat exchanger can be incorporated within a water heater
having a burner having
a bumer outlet which communicates with the interior space within the stacked
tube bundle for
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producing products of combustion for heating water flowing in the flow tubes.
The heat exchanger
can also be incorporated within a fluid heat rejection device having a blower
having a blower outlet
which communicates with the interior space within the stacked tube bundle for
producing an air flow
in heat exchange relationship with water being cooled as it flows through the
interior of the tube
bundle.
A method of corrosion protecting a finned tube heat exchanger is also shown
which includes the
steps of providing a heat exchanger having:
a pair of flow manifolds, each having a water inlet and a water outlet and a
plurality of
connecting openings;
a plurality of circular flow tubes arranged in stacked fashion to form a tube
bundle which
surrounds an initially open interior space, each flow tube having a pair of
opposing
connecting ends which connect to selected connecting openings provided in a
selected one
of the flow manifolds; and
wherein the flow tubes have external fins located on an exterior surface
thereof, the external
fins being crushed to form upper and lower flat stacking surfaces for stacking
the tubes to
form the tube bundle, the external fins also being crushed to form angled
baffle surfaces
about an external periphery of the tubes, the angled baffle surfaces on each
flow tube
presenting a continuous exposed surface on the exterior of the tube bundle
when the flow
tubes are stacked in vertical fashion which comprises an integral baffle
surface for the tube
bundle; and
wherein the circular flow tubes are formed of a material selected from the
group consisting of
copper, aluminum, stainless steel, mild steel and cupronickel; and
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wherein the circular flow tubes are provided with a corrosion resistant
coating which is formed by
priming an exterior surface of the flow tubes with a noble metal primer,
followed by applying a
corrosion protective monomeric or polymeric topcoat.
The preferred noble metal is selected from the group consisting of platinum,
gold, silver, electroless
nickel, titanium, and alloys including HastelloyTM, InconelTM, MonelTM and
IncoloyTM. The preferred
monomeric or polymeric topcoat can comprise a fluropolymer.
Additional objects, features and advantages will be apparent in the written
description which follows.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of the finned tube water heater embodiment of
the invention with the
outer removable jacket shown in phantom lines
Figure 2 is a side, cross-sectional view of a finned tube prior to being
formed in the forming process
of the invention.
Figure 3 is an end view taken along lines III-III in Figure 2.
Figure 4 is a perspective view of one of the circular flow tubes which has
been formed in the
forming process of the invention.
Figure 5 is a partial view of one of the vertically arranged flow manifolds
showing the openings
which receive the connecting ends of the circular flow tubes.
Figure 6 is a partial, perspective view of one of the formed flow tubes
showing the crushed fins
thereof.
Figure 7 is an isolated view of three brazing rings which are positioned on
the connecting end of the
flow tube of Figure 6.
Figure 8 is a side, partial cross-sectional view of a portion of the vertical
flow manifold showing one
opening thereof with the connecting end of flow tube inserted in the opening
and with the brazing
rings positioned on the landing of the opening.
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Figure 9 is an end view of the flow tube of the invention showing the crushed
fins which form the
stacking surfaces and the angular baffled surfaces thereof.
Figure 10 is an isolated view of the tube bundle of the invention showing the
vertically arranged
flow manifolds and the circular flow tubes making up the tube bundle.
Figure 11 is a top view of the tube bundle showing the connecting ends of the
flow tubes within the
vertically arranged flow manifold.
Figure 12 is an isolated view of the removable jacket for the water heater of
the inanition.
Figure 13 is a simplified partial view of the lower portion of the assembled
water heater showing
the removable jacket supported upon the horizontal runners of the assembly.
Figure 14 is a simplified, perspective view of the water heater assembly with
portions removed for
ease of illustration and showing the burner located within the blower/mixing
box assembly.
Figure 15 is an isolated view of the blower/mixing box.
Figure 16 is a view of the mixer box in exploded fashion showing the internal
components thereof.
Figure 17 is a simplified, isolated view of the control panel which is located
within the control panel
opening of the electrical control box.
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Figures 18 and 19 illustrate the movement of the control panel within the
mating T slots provided
in the opposing sidewalls of the electrical control box of the assembly.
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DETAILED DESCRIPTION OF THE INVENTION
It will be understood from the description which follows that the finned tube
heat exchanger of the
invention may be utilized in a variety of applications including water heaters
and boilers as well as,
for example, fluid heat rejection devices in which water passing through the
device is being cooled
and air passing in heat exchange relationship is being heated. The water
heater application provides
a convenient illustration of the principles of the invention, however.
Figure 1 thus shows a finned tubed water heater of the invention designated
generally as 11. The
water heater 11 includes a heat exchanger or "tube bundle assembly",
designated generally as 13,
and a gas delivery and firing section, designated generally as 14. The tube
bundle assembly will
typically be formed of copper, but in some embodiments of the invention may be
formed of
aluminum, stainless steel, mild steel and cupronickel. The tube assembly 13 is
shown in isolated
fashion in Figure 10. The tube bundle assembly preferably includes at least
two perpendicular flow
manifolds 15, 17, which, in this case, are arranged in a vertical
configuration. The flow manifolds
15, 17 are "perpendicular" to the circular flow tubes 25. In some embodiments
of the invention,
however, the flow manifolds may be arranged in horizontal fashion, as if the
unit 11 were tipped on
its side. Also, while the manifold 15 is taller than the manifold 17 in Figure
1, appliances may also
be designed with identical height manifolds. One of the two manifolds 15 has a
water inlet 19 and
a water outlet 21. Figure 5 shows a portion of one of the vertically arranged
flow manifolds 15, the
manifold having a plurality of connecting openings 23. The manifold 15 also
has oppositely
arranged closed ends 22, 24. The closed ends 22, 24 together with metal caps
or disks brazed to an
outer or inner surface of the flow manifolds, form dividers for the flow of
water in alternate flow
paths, as will be described in greater detail.
A plurality of circular flow tubes (25 in Figures 10 and 11) are arranged in
stacked fashion to form
the tube bundle which surrounds an initially open interior space (27 in Figure
11). As shown in
Figure 4, each flow tube 25 is "circular" in the sense that it is an
incomplete arc of a circle, the
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opening or gap ("g" in Figure 4) allowing the flow tube to be connected to the
flow manifolds (see
Figure 11). Each flow tube has a pair of opposing connecting ends (29, 31 in
Figures 4 and 11)
which connect to the openings provided in the flow manifolds 15, 17.
With reference to Figures 2-9, the circular flow tubes 25 are initially
provided as straight finned
tubes having the cross-sectional structure illustrated in Figures 2 and 3.
Figure 2 shows the fins 35
which circumscribe the tube 25 and which are arranged in a plane generally
perpendicular to the
exterior surface 37 of the tube. The straight finned tube 25 is then fed
through a rolling or forming
die (not shown) which crushes the external fins in a predetermined pattern. In
the particular example
illustrated, a 7/8 inch finned copper tube is formed into a twenty inch
diameter circle with the fins
formed to create an angular baffle surface around the outer circumference. In
the most preferred
form of the invention, the external fins 35 are crushed in the forming die to
form upper and lower
flat stacking surfaces (39, 41 in Figure 9) for stacking the tubes to form the
tube bundle. The
external fins are also crushed to form angled baffle surfaces 43, 45 about an
external periphery of
the tubes.
As shown in Figures 6 and 10, the external fins of the flow tubes 25 which are
crushed to form the
angled baffled surfaces on each flow tube present a continuous exposed surface
on the exterior of
the tube bundle 13. When the flow tubes are stacked in vertical fashion, the
continuous exposed
surface comprises an integral baffle surface for the tube bundle with the flat
stacking surfaces 39,
41 (Figure 9) in contact, thereby eliminating the need for a separate baffle
member to assist in
retaining and more uniformly distributing heat from the products of combustion
in the interior space
27 (Figure 11) within the stacked tube bundle 13. In the most preferred form
of the invention, each
finned flow tube 25 is formed with a forming die which creates four facets
(39, 41, 43, 45 in Figure
9) on the exterior of each tube. Two of the facets 39, 41 form the stacking
surfaces and two of the
facets 43, 45 form the baffle surface.
As best seen in Figure 8, each of the vertically arranged flow manifolds 15
has a flow opening (23
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in Figure 5) for receiving the connecting end 31 of the finned flow tubes.
Rather than using a T-drill
or round hole puncher, the flow openings 23 are machined or punched with
tooling to provide an
oval opening having a particularlypreferred shape. Each of the openings is
preferably formed having
a circumferential landing area (47 in Figure 8) which leads to an internal
draw region 49. At least
one brazing ring of filler metal and preferably three brazing rings (51 in
Figure 7) are positioned
about each flow tube connecting end. The brazing rings are received upon the
internal landing area
47 of the flow opening for brazing the tubes to the flow manifold when the
tube connecting end 31
is positioned as shown in Figure 8. Once the filler metal (brazing ring) is
preplaced, the assembly
is then furnace brazed in an oxygen starved environment at a temperature of a
approximately 1400
Fahrenheit. Other brazing furnaces and techniques can also be utilized in
addition to the described
preferred brazing method. In addition to brazing rings, other braze filler
metal such as brazing paste,
brazing strips/foil, cast braze filler metal, etc., can be utilized.
Preferably, liquid nitrogen is injected
into the furnace to shield the copper of the tube bundle assembly from
oxidation and to provide rapid
cooling of the assembly. With reference to Figures 1 and 10, it is important
to note header pipes (16,
18 in Figure 1) may be hand brazed at the joints 20, 22.
In the completed tube bundle assembly as shown in Figure 10, each of the flow
manifolds 15, 17 has
connecting openings for receiving a connecting end 29, 31 of the finned flow
tubes making up the
tube bundle. The pair of vertically arranged flow manifolds 15, 17 have
internal passageways (not
shown) for cross-communication between the flow manifolds. In this way, for
example, water enters
the inlet 19 in the flow manifold 15 and passes through a connected flow tube
or tubes such as tubes
51, 53 to the second manifold 17. The water then passes through an internal
passageway (not shown)
in the second manifold 17 and out flow tubes 55, 57 back to the first
manifold. The circulation
continues through all of the flow tubes until the water exits the outlet 21 of
the first flow manifold.
Although the preferred tube bundle assembly has a pair or vertically arranged
flow manifolds 15, 17,
a heat exchanger arrangement can also be visualized in which only a single
flow manifold is utilized.
With reference to Figure 10, one can visualize the vertical flow manifolds 15,
17 being combined
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as a single vertical flow manifold having connecting openings, as has been
described, for the
connected flow tubes. The single vertical flow manifold would have a series of
internal walls or
baffles which would create flow passages for directing the water from the
inlet 19 to the outlet 21.
As best seen in Figure 1, the tube bundle assembly 13 is sandwiched between a
base pan 59 and a
bulkhead 61, each of which can be provided with an insulating refractory disk
or lining (shown
broken away as 63 in Figure 1) for insulating the tube bundle. The base pan 59
and the bulkhead 61
are joined by a plurality of threaded connecting rods (65, 67 shown in Figure
1) which hold the tube
bundle, base pan and bulkhead in tension. In this way, the tube bundle
assembly can be provided
in a "package fashion" for subsequent maintenance or replacement operations.
Although the preferred device is described with reference to the use of
insulating refractory disks to
seal the ends of the heat exchanger, the refractory disks could be replaced by
a pumped water cavity
or a series of tubes. This would help to minimize heat loss, increase the heat
transfer and minimize
or eliminate the use of refractory.
As shown in Figures 1, 14 and 15, a blower/mixing box 69 is mounted on an
upper surface (71 in
Figure 1) of'the bulkhead. Figures 15 and 16 show the blower/mixing box in
isolated and exploded
fashion, respectively. The blower/mixing box 69 contains an internal scroll 73
which has a plurality
of side tabs 75 which are received within mating holes 77 provided in the
opposing sides 79, 81 of
the blower/mixing box 69. Alignment of the tabs and holes serves to provide
the desired shape for
the scroll and allows assembly within the blower/mixing box. The assembly also
includes an orifice
element 83. The orifice element 83 has a polygonal upper extent 84 and
downwardly extending
flanges 86, 88. The orifice element 83 sits behind the gas ports 78, 80. Upon
assembly, the orifice
element 83 together with the scroll 73 forms a venturi shaped passageway
within the blower/mixing
box.
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The preferred burner illustrated in the drawings has a generally cylindrical
exterior surface which
is formed of a woven metal fabric. The burner also has a conically tapered
interior, as shown in
Figure 14. Other burner styles can also be utilized, if desired. Such burners
include those having
a woven metal fabric covered tubular burner, with an internal distributor that
is not conical in shape,
in addition to burners which have neither a conical tapered center nor a woven
metal cover. Thus,
the burner could be a punched port, porous mat, porous or ported ceramic or
woven metallic mat,
with properly sized air fuel passageways or porosity and with a conically
tapered, variable airfoil or
ported air/fuel distribution system.
As shown in Figure 16, the blower/mixing box 69 is received upon a planar base
member 85. The
base member 85 acting as a strengthening member to hold the bulkhead 61 flat
when assembled as
shown in Figures 1 and 14. The exposed flange region of the base member 85 and
holes 89, 91, 93
serve as a mounting surface for the ignition source (generally at 81 in Figure
1). The oppositely
arranged holes 90, 92, 94 are provided for mounting a sight glass (not shown).
A fiberglass ceramic
gasket fits between the base member 85 and the bulkhead and clamps the sight
glass assembly in
place.
A burner (95 in Figure 14) has a burner outlet 96 which communicates with the
interior space 27
within the stacked tube bundle for producing products of combustion for
heating water flowing in
the flow tubes. As shown in Figure 14, the burner 95 is inserted into bulkhead
61 where it is
surrounded by and concentrically located within the tube bundle assembly 13.
High temperature
gaskets of material such as glass fiber or refractory are used to seal the
burner 95 to the bulkhead and
the blower assembly to the burner.
The gas train and ignition system will now be described in terms of one
preferred embodiment of
the invention, namely a two stage unit with hot surface ignition. However, it
will be appreciated
from the discussion which follows, that units may also be manufactured with
single stage operation,
full range air/fuel modulation, and with alternate flame ignition means such
as direct ignition or
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spark pilot.
In the preferred embodiment of the device shown in Figure 1, the gas train
consists of a one inch
main control train 97 and a three-quarter inch control train 99 for two stage
water heater operation.
Both gas trains inject gas into the blower/mixing box 69 where it is mixed
with the combustion air
supply. As shown in Figure 14, the blower/mixing box 69 has an air inlet 100
which is fitted with
an air inlet damper 101. The damper 101 has an internal butterfly member 103
which is angularly
positionable to control the flow of air through the assembly. The butterfly
103 can be moved
angularly between a fully open position for high fire conditions and a fully
closed position for low
fire conditions of the water heater. The air damper in the preferred
embodiment is described as being
a butterfly which is used for staging. The butterfly 103 can also be an
operative element which takes
another convenient shape for controlling the air or air/fuel flow. Thus, the
butterfly may assume a
variety of shapes and may be used for staging or modulation.
The combustion process in initiated by a hot surface ignitor adjacent to the
burner and is monitored
by appropriate electrical controls. In use, the damper acts as a switch
mechanism. The second stage
will only fire if on high flame. The second stage then fires and begins to
increase the internal
temperature. When the process temperature reaches a first set point, the
damper butterfly closes.
This action cuts off the air supply (except for leakage around the damper) and
a gas valve shuts off
to the high side. Only the low side gas is now being admitted. As demand
increases, the damper
opens to again turn on the high side. In this way, the damper serves as a
staging mechanism for the
water heater. The water temperature is monitored at the inlet of the flow
manifold by means of a
temperature sensor 105 (Figure 14). A flow control switch, such as paddle 107
in Figure 4, is
located within a section of the vertically arranged manifold 15 in-line with
the flow path through the
flow manifold and is furnace brazed in position during the brazing of the tube
bundle assembly. This
eliminates any labor associated with pipe fittings downstream of the flow
manifold 15.
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CA 02496656 2005-02-10
While a preferred embodiment of the control system has been described, other
traditional blower and
control systems may be utilized, as well. For example, in another embodiment,
the inlet damper
controls the flow of air through the assembly by means of a movable restrictor
plate, tube or member
whose area is increased or decreased. This variable damper, in conjunction
with a variable gas valve
or valves, serves as a modulation mechanism for the water heater. The amount
of gas released by
the gas valve is proportional to the amount of combustion air drawn into the
blower inlet. The air
and gas are unifromly mixed in the blower of the blower mixing box. The
combustion process is
initiated by a hot surface igniter, electrical spark or gas pilot igniter
adjacent to the burner. The
desired water temperature is monitoried to provide a controlling signal to
turn the water heater up,
down, or off.
As shown in figures 12 and 13, the water heater also includes a one-piece
jacket 109 which can be
insulated or uninsulated. The j acket 109 circumscribes the tube bundle 13,
base pan 59 and bulkhead
61 and seals against peripheral surfaces thereof, such as surface 111 in
Figure 1, to thereby form a
flue space when installed about the tube bundle. The flue space receives
products of combustion
produced by the burner. The jacket also has flue outlet opening 113 for
exhausting products of
combustion through a flue outlet conduit (not shown).
As shown in Figure 13, the one-piecejacket 109 is held in place initially by a
mechanical clasp 115,
whereby the jacket is easily installed and removable to expose the tube bundle
and other internal
components for maintenance operations by opening the mechanical clasp. In the
preferred method
of assembly, a pair of runners (115, 116 in Figure 13) are provided beneath
the base pan 59 and
extend beneath the base pan in order to support the base pan. The runners each
have an exposed
length 119 which also serves to support the one-piece insulated jacket 109 as
the jacket is being
installed about the tube bundle. Once the j acket has been drawn up tight by
means of the mechanical
clasp 115, a series of mechanical connectors, such as threaded screws 121, can
further be installed
to secure the jacket in position. To remove the jacket and completely expose
the internal
components, it is only necessary to unscrew the screws 121 and detach the
clasp 115.
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CA 02496656 2005-02-10
As shown in Figures 17, an electrical control box with opposing sidewalls 123,
125 is mounted on
the bulkhead 61. The one-piece jacket 109 is provided with a control panel
opening 127. A control
panel 129 is mounted within the opening. The control panel 129 has a pair of
opposing tabs (131
shown in Figures 17-19) at an upper end thereof which are received within
mating T slots 133
provided in the opposing sidewalls of the control box. In this way, the
control panel is positionable
between a lowered position (shown in phantom lines as 129 in Figure 17) and an
upwardly raised
and locked position indicated as 135 in Figure 17. The upwardly raised
position provides access to
the electrical components located within the electrical control box in case of
maintenance or other
operational needs.
A transparent cover panel 137 fits over the electrical control panel within
the control panel opening.
The transparent cover panel 137 is formed of a flexible plastic material which
allows the panel to
be secured within the control panel opening 127 by flexing the sides of the
plastic material and
inserting the transparent cover within the opening. The cover can then be
retained by tension within
the opening 127 or can be secured with a screw or other fixture.
The firing operation will now be briefly described with respect to one
preferred embodiment of the
invention using hot surface ignition. The operating thermostat senses a return
water temperature
below a first set point and the operating circuit is energized. If no
intervening control device opens
the circuit, such as an energy management system, the combustion control will
be energized. The
flame control checks for an open safety proving circuit and if an open
condition exists, the ignition
sequence will begin. The flame control begins by energizing the blower circuit
and subsequently
checking the safety proving circuit for a positive air, water pressure,
overfire and flue conditions.
When the safety circuit has been proved and a 15 second pre-surge is complete,
the warm-up period
begins. When the ignitor current reaches the acceptable threshold, the valve
circuit will energize and
ignition of the main flame occurs. The presence of the flame is continuously
monitored by flame
rectification through the hot surface igniter. If the flame is lost or fails
to ignite the system will retry
for three attempts before locking out and requiring reset. In the case of the
two stage construction
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CA 02496656 2005-02-10
firing cycle, the two stage operating control will open and close the inlet
dampers so as to stage the
burner between high and low fire conditions. The damper then stages the second
stage (main gas
train) while leaving the first stage operational until the system water
temperature exceeds the first
set point on the operating control. When the demand for heat has ended, the
flame control will de-
energize the valve circuit and allow the combustion air blower to operate for
a post purge period of
about 30 seconds.
The improved heat exchanger or tube bundle 13 has been described with respect
to a preferred
embodiment of its use as the heat exchange element of a finned tube water
heater or boiler.
However, other applications for the improved heat exchanger can also be easily
visualized. For
example, with reference to Figure 1 of the drawings, one can easily visualize
the heat exchanger tube
bundle 13 being used in a fluid heat rejection device used for water cooling
and air heating. In such
an embodiment of the invention, hot water would be introduced into the tube
bundle through the
inlet 19 and cooled water would pass out the exit 21 (Figure 10). The burner
gas delivery and firing
section 14 would be replaced with a commercially available blower which would
be used to
introduce a stream of air in heat exchange relationship with the tubes by
forcing the air through the
open interior space (27 in Figure 11) of the tube bundle. If desired, a
cooling water cascade could
be pumped across the coils of the tube bundle to increase heat transfer.
The preferred water heater of the invention has been described in a non-
condensing embodiment.
In other embodiments of the invention, the heat exchanger or tube bundle 13
may be utilized in a
condensing environment. A condensing environment can arise in various ways.
Generally speaking,
when a water heater increases in efficiency, the temperature of the flue gas
decreases and when the
flue gas temperature drops below the dew point, flue gas condensation forms.
This condensation is
typically acidic and can damage unprotected copper or cupronickel of the type
used in the
manufacture of the preferred heat exchanger of the invention, as previously
described. Although a
number of condensate resistive polymer coatings are known which could be used
to protect such heat
exchangers or other copper components, they are difficult or impossible to
successfully apply
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because naturally forming copper oxidation 'inhibits successful bonding of the
polymer to the copper
surface. Where copper oxidation forms on clean copper at room temperatures,
the speed and severity
of copper oxide formation is dramatically accelerated at temperatures
frequently required to cure
such polymers.
Successful polymer bonding requires that the copper remain clean and virtually
oxide free
throughout the polymer coating and curing process. Previously, this has been
achieved by methods
such as conducting cleaning, polymer coating and oven curing in a vacuum
environment. Use of this
process has been limited, however, due to the high cost, complexity and
physical limitations inherent
in processing in a vacuum environment. These limitations are dramatically
reduced by the use of
a noble metal primer to limit post cleaning oxidation before and during the
polymer application
process. By applying a noble metal primer surface, the copper oxidation that
traditionally forms is
avoided and a successful polymer to copper bond is easily achieved. Since
noble metals are
relatively expensive, it is significant to note that the bonding benefit can
be achieved with a very thin
layer, sometimes calla flash coat. The layer need only be thick enough to
prevent copper oxidation
from occurring during the condensate protective polymer application process.
However due
consideration must be given to increasing the thickness to minimize copper
oxidation when there
is extended dwell time between cleaning, polymer coating and curing.
The noble metal which is used to prime the exterior surface of the heat
exchanger is preferably
selected from the group consisting of platinum, gold, silver, electroless
nickel, titanium, and alloys
including HastelloyTM, InconelTM, MonelTM and IncoloyTM. In some embodiments
of the invention, the
exterior surfaces of the heat exchanger can also be anodized prior to applying
the corrosion
protective monomeric or polymeric topcoat. The top coat can be any suitable
monomer or polymer
which provides corrosion protection and which is capable of withstanding the
combustion process
and the acidic effects of flue gas condensate on a surface enhanced heat
exchanger. A number of
members of the fluropolymer family of polymers can be utilized, for example.
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CA 02496656 2005-02-10
In one embodiment of the corrosion protection process of the invention, the
copper heat exchanger
receives a 0.5 mil thick primer of electroless nickel to maintain a copper
oxide free surface over
which a 7 to 10 mil Polytetrafluoroethylene (PTFE) condensate protective
polymer is applied. The
condensate protective PTFE polymer is then cured and bonded to the copper heat
exchanger at
approximately 700 degrees F in a high temperature curing oven.
An invention has been provided with several advantages. The finned tube water
heater of the
invention features a tube bundle with an integral baffle construction which
eliminates the need for
additional baffle components. The circular flow tube and vertical manifold
arrangement provide
effective cross flow of water through the assembly to facilitate heat
exchange. The blower/mixing
assembly is constructed of simple, easily fabricated components which simplify
assembly and reduce
cost. A "build up" method of assembling the blower/mixing box and associated
components on the
bulkhead reduces assembly costs. Costs are further reduced because the
blower/mixing box achieves
integral air/fuel mixing, without the use of a secondary mechanism or device.
The vertical flow
manifolds have oval holes with a landing area and an inward draw which allows
filler metal to be
assembled about the flow tube connecting ends and positioned on the landing
areas. The tube bundle
can then brazed as a unit in a brazing furnace to produce an ASME certifiable
joint of high
reliability.
The one-piece, insulating jacket performs the cosmetic function of surrounding
the internal
components of the device and also forms a flue collection chamber for the tube
bundle. This jacket
is initially restrained by a mechanical clasp which can be easily released to
remove the jacket for
maintenance operations on the internal components of the assembly. The
frequently required flow
indication device can be installed in the run of the manifold flow, thereby
eliminating labor for pipe
fittings downstream. A damper, interlocked with two or more independent gas
circuits, can be added
to the blower/mixing box inlet to form a staging mechanism to provide a low
cost control scheme
for two or more stage firing of the burner. A damper, electrically, optically,
pneumatically or
mechanically liked to a gas control valve can be added to the blower/mixing
box inlet to form a low
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CA 02496656 2007-10-16
cost control scheme for maintaining the appropriate air to fuel ratio over a
wide range of burner
firing. The control panel and transparent cover panel provide a water
resistant assembly in those
cases where the water heater is exposed to the elements.
The corrosion protection process employed in some embodiments of the invention
provides
corrosion protection for condensing water heaters, boilers and heat exchanger
components. The
method introduces an oxidation inhibiting substrate preparation from a noble
metal including but not
limited to platinum, gold, silver, electroless nickel and titanium or alloys
such as HastelloyTM, InconelTM,
MonelTM and IncoloyTM, or anodizing to preserve the heat transfer and other
metallurgical properties of
the base metal where the base metal includes copper, aluminum, stainless
steel, mild steel and
cupronickel. With the base metal preserved by the first step in the method,
the base metal then easily
accepts a corrosion protective monomer or polymer topcoat capable of
withstanding the combustion
process and the acidic effects of flue gas condensate on a surface enhanced
heat exchanger.
While the invention has been shown in several of its forms, it is not thus
limited but is susceptible
to various changes and modifications without departing from the spirit
thereof.
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