Note: Descriptions are shown in the official language in which they were submitted.
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Air Inlets for Gas Water Heaters
Field of the invention
The present invention relates to air inlets gas fired water heaters,
particularly to improvements to gas fired water
heaters adapted to render them safer for use. The present invention also
relates to ignition inhibiting water heaters
Background of the invendon
The most commonly used gas-fired water heater is the storage type, generally
including an assembly of a water
tank, a gas bumer to provide heat to the tank, a pilot burner to initiate the
main burner on demand, an air inlet
adjacent the burner near the base of the jacket, an exhaust flue and a jacket
to cover these components. Another
type of gas-fired water heater is the instantaneous type which has a water
flow path through a heat exchanger
heated, again, by a main butner initiated from a pilot burner flame. For
convenience, the following description is in
terms of storage type water heaters but the invention is not limited to this
type. Thus, reference to "water
container," "water containment and flow means," "means for storing or
containing water" and similar such terms
includes water tanks, reservoirs, bladders, bags and the like in gas-fired
water heaters of the storage type and water
flow paths such as pipes, tubes, conduits, heat exchangers and the like in gas-
fired water heaters of the
instantaneous type.
A particular difficulty with many locations for water heaters is that the
locations are also used for storage of other
equipment such as lawn mowers, trimmers, snow blowers and the like. It is
common for such machinery to be
refuelled in such locations.
There have been a number of reported instances of spilled gasoline and
associated extraneous fumes being
accidentally ignited. There are many available ignition sources, such as
refrigerators, running engines, electric
motors, electric light switches and the like.
However, gas water heaters have sometimes been suspected because they often
have a pilot flame.
Vapours from spilled or escaping flammable liquid or gaseous substances in a
space in which an ignition source is
present provides for ignition potential. The expression "fumes," '4extraneous
gases" or "extraneous fumes" is
sometimes hereinafter used to encompass gases, vapours or fumes generated by a
wide variety of liquid volatile or
semi-volatile substances such as gasoline, kerosene, turpentine, alcohol,
insect repellent, weed killer, solvents and
the like as well as non-liquid substances such as propane, methane, butane and
the like. Many inter-related factors
influence whether a particular fuel spillage leads to ignition, These factors
include, among other things, the
quantity, nature and physical properties of the particular type of spilled
liquid fuel. Also influential is whether air
currents in the room, either natural or artificially created, are sufficient
to accelerate the spread of fumes, both
laterally and in height, from the spillage point to an ignition point yet not
so strong as to ventilate such fumes
harmlessly, that is, such that air to fuel ratio ranges are capable of
enabling ignition are not reached given all the
surrounding circumstances.
One surrounding circumstance is the relative density of the fumes. When a
spilled liquid fuel spreads on a floor,
normal evaporation occurs and fumes from the liquid form a mixture with the
surrounding air that may, at some
time and at some locations, be within the range that will ignite. For example.
the range for common gasoline vapour
is between about 3% and 8% gasoline with air, for butane between about 1% and
10%. Such mixtures form and
spread by a combination of processes including natural diffusion, forced
convection due to air current drafts and by
gravitationally affected upward displacement of molecules of one less dense
gas or vapour by those of another more
dense. Most common fuels stored in households are, as used. either gases with
densities relatively close to that of
air (e.g.. propane and butane) or liquids which form fumes having a density
close to that of air, (e.g. gasoline.
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which may contain butane and pentane among other components is very typical of
such a liquid fuel).
In reconstructions of accidental ignition situations, and when gas water
heaters are sometimes suspected and which
involved spilled fuels typically used around households, it is reported that
the spillage is sometimes at floor level
and it is reasoned that it spreads outwardly from the spill at first close to
floor level. Without appreciable forced
mixing, the air/fuel mixture would tend to be at its most flammable levels
close to floor level for a longer period
before it would slowly diffuse towards the ceiling of the room space. The
principal reason for this observation is
that the density of the fumes typically involved is not greatly dissimilar to
that of air. Combined with the tendency
of ignitable concentrations of the fumes being at or near floor level is the
fact that many gas appliances often have
their source of ignition at or near that level.
The invention aims to substantially lower the probability of ignition in
typical liquid fuel spillage circumstances.
The invention also aims to substantially raise the probability of successful
confinement of ignition of spilled
tlammable substances from typical spillage situations to the inside of the
combustion chamber.
Summary of the invention
The present invention provides a water heater including: a water container; a
combustion chamber located adjacent
said container; a burner located inside said combustion chamber; at least one
inlet positioned at an opening in said
combustion chamber, said inlet permitting ingress of admit air and extraneous
fume species into said combustion
chamber and prevent egress of flames from said water heater
The air inlet is or includes a flame arrestor positioned at said opening in
said combustion chamber to block ingress
of admit air and extraneous fume species when the temperature in said
combustion chamber adjacent said flame
trap exceeds a predeternuned temperature.
A blocking plate can be positioned within said combustion chamber and spaced
above said opening.
The water heater can further include a heat sensor positioned within said
combustion chamber and adjacent said
flame trap and capable of shutting off fuel to said bumer when said the
temperature in said combustion chamber
adjacent said flame trap exceeds said predetermined temperature.
The flame arrestor can also include a blocking plate supported by at least one
leg formed from a temperature
sensitive fusible material adapted to melt when said predetermined temperature
is exceeded, thereby permitting said
blocking plate to move toward and over said opening.
Preferably the temperature sensitive fusible material is a thermoplastic, and
more specifically low density
polyethylene having a melting temperature of about 100 C to 200 C.
The air inlet can be formed from a ceramic material having a thickness of
about 12 mm or more and having
openings of about 36.5 to 73 openings per square centimetre and wherein said
openings include about 64% to 80%
of the surfaces of said air inlet.
Preferably the openings are square and the ceramic material is extruded.
The air inlet can altemative(y be formed from two layers of woven metal mesh
arranged to be in contact with each
other over substantially all of their respective contacting surfaces and being
formed in a non-planar orientation to
facilitate substantially even layer contact during expansion and contraction.
The layers of woven metal mesh can be dome-shaped if desired.
The water heater can include a flame arrestor positioned at said opening and
adapted to direct a flame extinguishing
substance toward a surface of said flame trap in said combustion chamber.
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The flame arrestor can include a container having at least one nozzle and
contains said flame extinguishing
substance. The at least one nozzle can contains a plug made from a fusible
material, having material has a melting
temperature of about 150 C to 300 C, that maintains said flame extinguishing
substance inside said container
unless the temperature in said combustion chamber adjacent said flame trap
exceeds a predetermined temperature.
The flame extinguishing substance is selected from the group consisting of
sodium bicarbonate and fire blanketing
foams mixed with a propellant.
Preferably fire blanketing foams are mixed with a propellant are activated
when the temperature adjacent said flame
trap is 300 C -500 C.
The container preferably has two nozzles extending from opposite end portions
thereof, each nozzle being directed
to opposing edge portions of said at least one inlet.
The at least one inlet can have a plurality of ports, each port having a
limiting dimension less than a minimum
quenching distance applicable to said extraneous fume species, thereby
confining ignition and combustion of said
extraneous fume species within said combustion chamber.
Preferably said at least one inlet is constructed such that peak natural
frequencies of vibration of said at least one
inlet, in combination with said combustion chamber structure, are different
from peak frequencies generated by an
extraneous fume combustion process on the inlet within the combustion chamber.
During combustion of said extraneous fume species over a prolonged period, a
surface of said at least one inlet
located outside of said combustion chamber remains sufficiently cool so as to
prevent heating the extraneous fume
species and air with it before it passes through said at least one inlet to a
temperature above an ignition temperature
of said extraneous fumes species and air.
The ports of said at least one inlet can be spaced apart on said at least one
inlet by a distance which enables the
temperature of mixtures of extraneous fume species with air adjacent to the
surface of the walls of said ports to
remain below the ignition temperature of said mixtures.
The ports of said at lest one inlet can be spaced apart from each other so
that a closest point between boundaries of
adjacent ports is a distance of no less than about 1.1 mm. The shortest
distance between adjacent ports can be
substantially the same.
Preferably at least one of said ports of said at least one inlet is adjacent a
pilot bumer associated with said
combustion chamber to ignite said extraneous fume species as the fume species
passes into said combustion
chamber and before there is a potentially explosive accumulation of fumes in
said combustion chamber.
The ports of said at least one inlet include slots and wherein said limiting
dimension is the width of said slots.
Preferably said ports include slots which have an L/W ratio of between about 2
to about 15, wherein L is the length
of said slots and W is the width of said slots
Preferably said ports of said at least one inlet are arranged in rows. It is
preferable that a first port in every atternate
row has its location offset with respect to a port of an adjacent row.
Alterrtatively the ports of said at least one inlet are slots arranged in
rows, with at least one peripheral row of said at
least one inlet including slots arranged parallel to each other and which have
their longitudinal axes at an angle of
about 90" the orientation of each of the longitudinal axes of slots in other
rows.
Preferably at least one of said rows of ports of said at least one inlet is a
peripheral row having a larger interport
spacing than others of said rows.
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Preferably the at least one inlet is constructed from a sheet material with
ports that are elongated and spaced apart,
said ports being arranged so that there are at least two regions of ports, an
inner region which is included of a group
of said ports, and an outer region which is comprised of the remainder of said
ports, said outer region having an
interport spacing between adjacent ports which is greater than the interport
spacing of said ports in said inner
region.
Preferably said ports include slots about 0.5 mm in width and if said ports
include circular holes, the circular holes
are 0.5 mm in diameter.
The water heater can eniit an audible signal when said extraneous fumes pass
through said at least one inlet and are
buming inside said combustion chamber. The audible signal can be produced by
the action of the burning of said
extraneous fumes near to said at least one inlet, inside of said combustion
chamber.
The ports of said alt least one inlet can be formed in a metal plate by
photochemical machining.
The water heater combustion chamber can be formed with a surrounding skirt
having an end cap joined at one end
thereof, with another end of said surrounding skirt being a surface of said
combustion chamber. An enclosure can
be provided which encloses said container and which also forms both of said
surrounding skirt and said end cap.
Alternatively said surrounding skirt and said end cap are formed separate from
the enclosure which encloses said
container and said combustion chamber.
The water heater will include an outlet spaced apart from said at least one
inlet allowing products of combustion to
exit said combustion chamber.
Thew at least one inlet preferably includes a plate having a plurality of
ports. The plate is preferably made of metal.
The at least one inlet can have a heat dissipation region at its periphery.
The heat dissipation region can include a
metal to metal overlap portion between a peripheral edge of a plate forming
said at least one inlet and a peripheral
edge of an opening in the combustion chamber.
The plate can include a skirt; while said combustion chamber has an opening
which sealingly receives said plate,
said opening having a surrounding skirt; and said skirts are sized so that
inwardly facing surfaces of said skirt of
said plate engage outwardly facing surfaces of said surrounding skirt.
The plate can altematively include a skirt; while said combustion chamber has
an opening which sealingly receives
said plate, said opening having a surrounding skirt; and said skirts are sized
so that outwardly facing surfaces of
said skirt of said plate engage inwardly facing surfaces of said surrounding
skirt.
If desired, the heat dissipation region can include an additional surface area
in the form of at least one fin extending
from the inlet.
The heat dissipation region can include an increased interport spacing
adjacent its periphery.
Preferably the plate is a ferrous based material about 0.5 mm thick.
The interport spacing of the ports of said at least one inlet adjacent a
peripheral portion of the ports in said plate is
in the range of about 2 mm to 4 mm and the interport spacing of remaining
ports is in the range of about 1 mm to
1.5 mm.
The plate can be a ceramic plate having a thickness in the range about 9 mm to
12 mm and ports in the range of
about 1.1 mm to 1.3 mm diameter.
Flame lift promoters can be provided at edge portions of the pons. The flame
lift promoters can be sharp edges at
upstream extremities of the ports. Altematively the flame lift promoters can
be undercut cross-sectional profiles
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wherein the intersection of the ports with at least an inside surface of the
plate is an angle of less than 90".
Altematively the flame lift promoters are interport spacings of at least about
3 mm.
The ports of said at least one inlet can be constructed so that in cross-
section, said ports have substantially parallel
sides.
5 The ports can be consttucted so that in cross-section said ports have sides
which converge. The ports can converge
in an upstream direction, and may terminate with substantially parallel sides.
Preferably the ports are slot shaped and not more than about 0.6 mm wide and
spaced apart from each other at least
about 1.1 mm.
The ports can include peripheral extrusions extending inwardly into the
combustion chamber to act as flame lift
promoters.
The ports can be formed in a plate in a pattern, said pattem acting as a flame
lift promoter.
The ports can be arranged in a pattem comprising solely apertures in the form
of an aligned and spaced array of
slots.
If desired a first pattern of slots can be located in a centre portion of said
inlet and a second pattem of slots at a
peripheral portion, with said second pattem comprising a larger interport
distance than said first pattern.
The ports can be arranged in a radial pattern or altematively in a
circumferential pattem.
The water heater can include a cooling mechanism in cooperating with said at
least one inlet. The cooling
mechanism can include a water applicator for said inlet. Preferably the water
applicator directs water to a face of
the inlet external to the combustion chamber.
The at least one inlet is preferably constructed such that the peak resonant
frequencies of said intet are different
from peak resonant frequencies of a combination of said combustion chamber and
an exhaust gas flow path when
extraneous fumes are being combusted at the inlet.
the heat dissipation region includes an additional surface area in the form of
at least one fin extending from the
combustion chamber.
If desired the ports can be formed with cross-sections which, within a single
port, both converge and diverge.
The said at least one inlet can be formed from a metal plate which is deformed
from a flat form to include stiffening
members extending across at least a portion containing said plurality of
ports. Preferably said stiffening members
intersect with ports. Alternatively stiffening members are provided extending
across unported portions which
subdivide said plurality of ports into an integral number of sub-portions
The invention also provides a control valve for supplying fuel to a water
heater containing a main bumer and a
pilot burner including: a fuel inlet adapted to connect to a supply of fuel;
at least one fuel outlet adapted to connect
to the main bumer; a conduit for fuel flow between the inlet and outlet; a
closure associated with the conduit to
control flow of fuel from the inlet to the outlet: a circuit associated with
the valve and including a thermally
actuated device associated with the closure, said device, when heated by the
pilot burner providing a signal to the
closure to open or close the closure; and a combustion sensitive fuse
connected to the circuit and positioned to be
exposed to extraneous sources of flame and/or heat extemal to and adjacent the
control valve.
The control valve can further include an externally accessible socket in the
circuit into which the fuse is removably
insertable. Alternatively the socket is adapted to receive the fuse
independently separate from the thermally
actuated device. Preferably the socket is accessible from an underside of the
valve, while the fuse is positioned at
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an underside of the valve.
The closure of the control valve includes a member located in a portion of the
conduit and is normally resiliently
biased in a closed position.
Preferably the circuit further includes a solenoid associated with the
closure, the solenoid being capable of
receiving an electrical signal from the thermally actuated device and opening
said closure in response.
Preferably the fuse is temperature sensitive and the circuit further includes
an over temperature energy cut out
switch associated with a temperature sensitive thermostat probe, said energy
cut out switch being capable of
interrupting gas flow through said control valve to the main bumer and the
pilot burner.
Preferably the thermally actuated device is a thermocouple.
The circuit can further include a manual switch connected to the thermally
actuated device and having on, off and
pilot positions, said pilot position causing the closure to open until such
time as the thermally actuated device is
capable of providing a signal to open the closure.
The closure can include a member located in a portion of the conduit and which
is normally resiliently biased in a
closed position.
Preferably said circuit associated with the valve includes a solenoid
associated with the closure, the solenoid being
capable of receiving output from the thermocouple and maintaining open said
closure in response to output
indicative of a flame at said pilot burner.
The control valve can include an energy cut out switch associated with a
temperature sensitive thermostat, the
energy cut out switch being associated with a temperature sensitive thermostat
probe, said energy cut out switch
being capable of interrupting gas flow through said control valve to the main
bumer and the pilot bumer.
Preferably the control valve includes a combustion sensitive fuse connected to
the control valve circuit and
positioned to be exposed to extraneous sources of flame and/or heat extemal to
and adjacent the control valve.
The invention further provides a water heater as described above having a
control valve as also described above.
Said at least one inlet can be positioned below and adjacent said pilot
burrter and with said water heater further
including a venturi extending into said combustion chamber to supply
combustion air to said main burner.
Preferably the water heater further includes a lint trap positioned exteriorly
of said at least one inlet and across said
opening.
The invention provides a gas water heater including a water container adapted
to be heated by a gas burrter. An
enclosure surrounds the burner and the water container. The water heater has
at least one opening adapted to allow
air for combustion or extraneous fumes to enter the enclosure without igniting
flammable extraneous fumes outside
of the enclosure.
In another aspect the invention encompasses a water heater including a water
container and a combustion chamber
located adjacent the container. The combustion chamber has a floor portion
with an opening. An upwardly
extending conduit is substantially air tightly sealed to the edge of the
opening. A bumer is located inside the
combustion chamber and a flame trap is positioned across the conduit, the
flame trap pernutting ingress of air and
extraneous gases. if present, into the combustion chamber and prevent egress
of flames from the structure. A flame
arrestor is positioned at the opening and is actuated when the temperature in
the combustion chamber adjacent the
flame trap exceeds a predetermined temperature.
In other embodiments, the water heater includes specially constructed flame
traps. One is a ceramic material having
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a thickness of about 12 mm or more and having openings of about 36.6 to 73
openings pet square centimetre
(openings/cmZ) and wherein the openings are about 64% to 80% of the surface of
the flame trap. Another has two
layers of woven mesh arranged to be in contact with each other over
substantially all of their respective contacting
surfaces and in formed in a non-planar orientation to facilitate substantially
even layer contact during expansion
and contraction.
The invention also provides a water heater including a water container,
adjacent which is, a combustion chamber
having one or more inlets to admit air and any extraneous flammable fume
species which may have escaped in the
vicinity of the water heater into its combustion chamber. In one particularly
preferred form, an inlet comprises a
metal plate of thickness about 0.4 to 0.6 millimetres and through which pass
many ports, each of which has a
quenching distance as will be defined within 10% of the thickness of the
plate. Because of choice of the quenching
distance appropriate to several types of inlet plate the water heater is able
to confine ignition and combustion of
extraneous fume species within the combustion chamber; despite the presence of
a burner(s) in the combustion
chamber to combust fuel to heat the water in container.
In an alternative form the inlet can take the form of a ceramic plate having a
thickness in the range about 9 mm to
12 mm through which passes many ports each having a quenching distance of 1.1
to 1.3mm, which can likewise
confine ignition and combustion of extraneous fumes to the combustion chamber.
Brief description of the drawings
Seiected embodiments of the invention will now be described, by way of example
only, by reference to the
accompanying drawings in which:
Figure 1 is a schematic partial cross-sectional view of a gas water heater
embodying aspects of the invention.
Figure 2 is a schematic partial cross-sectional view of a gas water heater
similar to Figure 1, with additional safety
features.
Figure 3 is a cross-sectional view of the water heater of Figure 2 taken
through the line 1II-III.
Figure 3A is a cross-sectional view of the base region of the water heater of
Figure 1.
2 5 Figure 4 is a schematic partial cross-sectional view of a gas water heater
similar to that of Figure 2.
Figure 5 is a cross-sectional view of the water heater of Figure 4 taken
through line V-V.
Figure 6 is a schematic partial cross-sectional view of a gas water heater
with a safety feature in accordance with
aspects of the invention.
Figure 7 is a schematic partial cross-sectional view of a gas water heater of
another embodiment of the invention.
Figure 8 is a schematic partial cross-sectional view of a gas water heater of
yet another embodiment of the
invention.
Figure 9 is a schematic partial cross-sectional view of still another
embodiment of the invention.
Figure 10 is a cross-sectional view of the water heater of Figure 9 taken
through the line X-X.
Figure 1 I is an upright elevational view taken from the rear of a gas valve
according to the aspects of invention.
Figure 12 is an upright elevatiorial showing the left side of the gas valve
shown in Figure 11.
Figure 13 is an upright perspective view of the valve of Figure 1 1 and Figure
12.
Figure 14 is a schematic partial cross-sectional view of a water heater with
the gas valve as shown in Figure 11 to
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Figure 13.
Figure 15 is an electrical circuit embodied in the gas valve shown in Figure 1
1 to Figure 13.
Figure 16 is a cross-sectional view of the gas valve shown in Figure I 1 to
Figure 13.
Figure 17 is a schematic elevation, taken partly in section, of a portion of
the bottom end of a water heater of the
type shown in Figure 14 including further means for dampening combustion.
Figure 18 show the first extinguishing means of Figure 17 following actuation
in the event of combustion on the
flame trap illustrated.
Figure 19 is a further embodiment of a means for extinguishing fire similar to
that shown in Figure 17.
Figure 20 shows the first extinguishing means of Figure 19 following actuation
in the event of combustion on the
flame trap.
Figure 21 is a detailed schematic elevation, taken partly in section, of a
bottom end portion of a water heater of the
type shown in Figure 14 substituting a different type of flame trap.
Figure 22 is a detailed schematic elevatiort, taken partly in section.
including a heat actuated chemical fire
extinguishing means operative with the flame trap.
Figure 23 is a detailed schematic elevation, taken in section and similar to
Figure 22, including an embodiment of
flame trap material arranged in two contacting layers.
Figure 24 is a schematic partial cross-sectional view of a gas-fuelled water
heater having a single large air inlet
according to the invention..
Figure 25 is a cross-sectional view of a water heater of Figure 24 taken
through the line 11-11 in Figure 24.
Figure 26 is a schematic plan view depicting a portion of the base of a
combustion chamber of a water heater
including an air inlet.
Figure 27 is a schematic plan view of an air inlet according to the invention
of a type which could be included in
the Figure 26. arrangement.
Figure 28 is a schematic plan view depicting a portion of the base of a
combustion chamber of a water heater
substituting an air inlet of different shape and hole pattern.
Figure 29 is a schematic plan view of an air inlet according to the invention
of a type which could be included in
the Figure 28 arrangement.
Figure 30 is a plan view of an inlet plate showing a hole pattern applicable
to an air inlet of the type shown in
Figure 29.
Figure 31 is a plan view of an inlet plate showing a further hole pattern
applicable to an air inlet of the type shown
in Figure 29.
Figure 32 is a plan view of ports on an inlet plate according to the invention
of the embodiment shown in Figure
26.
Figure 33 to Figure 41 are each a further plan view of additional alternative
patterrts of ports on an inlet plate
according to the invention of the embodiment shown in Figure 26.
Figure 42 illustrates a plan view of a single port as shown in Figure 33 to
Figure 41.
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Figure 43 and Figure 44 are each a detail view of the spacing of part of the
arrangement of ports on the inlet plate of
Figure 33 and Figure 34 respectively.
Figure 45 is a cross-section of an embodiment of a port in an air inlet
according to the invention.
Figure 46 is a schematic cross-section of a water heater having a ported inlet
connected to a remotely positioned clean-
in-place lint filter, according to the invention.
Figure 47 and Figure 48 illustrate alternative forms of attachments according
to the invention of two shapes of inlet to a
wall of a combustion chamber of a water heater.
Figure 49 a plan view of one version of an air inlet plate and its attachment
to a combustion chamber.
Figure 50 is a side view of the air inlet plate of Figure 49.
Figure 51 is a partial cross of the air inlet plate of Figure 49 at the lines
LI-LI.
Figure 52 is an attachment detail cross section of the air inlet plate of
Figure 49 and its attachment to a combustion
chamber.
Figure 53 is a perspective view of a version of an embodiment of an air inlet
plate.
Figure 54 is a perspective view of a version of another embodiment of an air
inlet plate.
Figure 55 is a cross-sectional view of the version of air inlet plate shown in
Figure 54.
Figure 56 to Figure 58 are schematic cross-section views of three embodiments
of water heater showing relative
positions of air inlet plates to other components including the combustion
chamber walls.
Figure 59 is a detail of an inlet in cross section.
Figure 60 is a perspective view of one port in the inlet as shown in Fig 36.
Figure 61 is a perspective view of one port of an inlet with an adjacent bead
of solder.
Figure 62 is a cross section of an air inlet plate coated with an intumescent
coating.
Figure 63 is a cross section identical with Figure 62 with the addition of
combustion of extraneous fumes on one
surface.
Figure 64 is a cross section showing the aftermath of the combustion shown in
Figure 63.
Figure 65 is a perspective schematic view of an inlet plate with a sliding
mechanism to occlude ports in an inlet plate.
Figure 66 is a cross section along the line A-A through the arrangement of
Figure 65 with ports aligned.
Figure 67 is the same cross section of Figure 65 when the ports are occluded.
Figure 68 is a perspective schematic view of an inlet plate with a rotary
mechanism to occlude ports in an inlet plate.
Figure 69 is a cross section along the line B-B through the arrangement of
Figure 68 with ports aligned.
Figure 70 is the same cross section of Figure 68 when the ports are occluded.
Figure 71 is a partial cross section of the lower portion of a water heater
with a spray nozzle at an air inlet according to
the invention and including an audible alarm.
Figure 72 to Figure 75 are partial cross-sections of ports in inlet plates.
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Figure 76 is a plan view of an air inlet plate stiffened by cross-broken
diagonal folds.
Figure 77 is front elevation of the air inlet plate of Figure 76.
Figure 78 is a side elevation of the air inlet plate of Figure 76.
Figure 79 is a plan view of an air inlet plate stiffened and divided into
separate perforated portions with stiffening
5 formations between those separate portions.
Figure 80 is a front elevation of the air inlet plate of Figure 79.
Figure 81 is a side elevation of the air inlet plate of Figure 79.
Figure 82 is a schematic elevation of a bottom half of a water heater with an
inlet plate mounted in the base of the
combustion chamber, the base being dampened by contact with resilient damping
materials sandwiched between
10 the external surface of the combustion chamber and a pan forming the base
of the water heater's protective jacket.
Figure 83 is a plan view of an air inlet in the base of a water heater
enclosure.
Figure 84 is a side view of the base of Figure 83.
Figure 85 is a detail cross sectional view of a portion of Figure 84.
Detailed description of the embodiments
It will be understood that the invention disclosed and defined herein extends
to all alternative combinations of two
or more of the individual features mentioned or evident from the text or
drawings. All of these different
combinations constitute various alternative aspects of the invention.
It will be appreciated that the following description is intended to refer to
the specific embodiments of the
invention selected for illustration in the drawings and is not intended to
define or limit the invention other than in
the appended claims.
Figure 1 illustrates a storage type gas water heater 2 including jacket 4
which surrounds a water tank 6, a main
bumer 14 in a combustion chamber 15. Water tank 6 is preferably of mains
pressure capability and capable of
holding heated water. Water tank 6 is preferably insulated by foam insulation
8. Altemative insulation may include
fibreglass or other types of fibrous insulation and the like.
Located underneath water tank 6 is main butner 14 which preferably uses
natural gas or other gases such as LPG,
for example. Main bumer 14 combusts a gas and air mixture and the hot products
of combustion resulting rise up
through flue 10. Flue 10, in this instance, contains a series of baffles 12 to
better transfer heat generated by main
butner 14. Near pilot burner 49 is a sheath 52, preferably made of copper,
containing wires from a flame detecting
thermocouple 51 which is a known safety measure to ensure that in the absence
of a flame at pilot bumer 49 the gas
control valve 48 shuts off the gas supply.
The products of combustion pass upwardly and out the top of jacket 4 via flue
outlet 16 after heat has been
transferred from the products of combustion. Flue outlet 16 discharges
conventionally into a draught diverter 17
which in tum connects to an exhaust duct 19 leading outdoors.
Close to the height of the top of' jacket 4 and flue outlet 16 is an air inlet
18 through which air is drawn down duct
22 to main bumer 14. Duct 22 is preferably constructed from sheet metal 20. In
a non-illustrated alterrtative
construction, a part or all of duct 22 may be inside the external cylindrical
envelope of jacket 4.
Water heater 2 is preferably mounted on legs 24 to raise the base 26 off the
floor. In base 26 is an aperture 28
which is closed, but not gas tightly, by a flame trap device 30 which operates
on a flame quenching principle.
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II
Flame trap 30 is preferably made from two substantially parallel sheets of
mesh each about 0.010 inch diameter
metal wire strands woven into mesh having about 30 to 40 strands per inch.
Altematively, inlet could be a woven
metal mesh having transverse wires of thickness about 0.2 to 0.5 millimetres
defining a plurality of ports, so that
each port has a quenching distance equal to the greater of the side lengths of
four-sided open areas between the
woven wires and in a range of about 0.3 to 0.5 mm, being thereby able to
confine ignition and combustion of said
extraneous fume species within said combustion chamber. Mild steel or
stainless steel wire are suitable.
Altematively, a ported ceramic tile of the SCHWANK type (registered trade
mark) can be utilised although the
recognised flame quenching ability of metallic woven or knitted mesh together
with its robustness and ease of
forming generally commends its use. A ported ceramic tile functions as a flame
quenching trap as long as the
porosity is suitable. If a ported ceramic tile is used, preferably it has a
thickness in the range about 9 nun to 12
mm and having openings of about 36.5 to 73 openings per square centimetre.
Preferably the openings include
about 64% to 80% of the surfaces of the tile or aperture which the tile will
cover. Preferably the tile is made of
extruded ceramic material and can have openings which are square, or
altematively the openings can be slots
having an length to width ratio (L1W) of between about 3 to about 20. Circular
holes could also be used but
preferably these will have a quenching distance which is a diameter of about
1.1 mm to 1.3mm.
A single layer of mesh or a porous ceraniic tile may be susceptible to
clogging by lint or other "blocking" materials
such as dust or the like. Lint caught in the openings of a single mesh or a
tile might act as a wick which may allow
flame, which would not otherwise pass through the flame trap, to do so. In
this situation the flame trap device
would tend not to function as efficiently. To prevent this tendency, the flame
trap is preferably constructed with
either two layers of mesh or a layer of mesh and a tile. The mesh layers are
most preferably in contact with one
another. In this way the layer of mesh further from the source of fumes acts
as a flame trap and the layer closer to
the source of fumes acts as a lint trap.
Where base 26 meets jacket 4, mating surfaces 32 (made up from surfaces of
base 26 and jacket 4) can be sealed
thoroughly to prevent ingress of air or flammable gas or vapour. In Figure 1,
mating surfaces 32 extend upwardly
from base 26 around jacket 4. The cyiindrical wall of jacket 4 (the majority
of gas water heaters are cylindrical;
however, a cubic or other shaped jacket 4 may be utilised) can be sealed gas
tightly so no openings or breaks
remain upon assembly and installation. In particular, gas, water, electrical,
control or other connections, fittings or
plumbing, wherever they pass through jacket 4 or base 26 to jacket 4 and all
service entries or exits to jacket 4 or
duct 22 need not be sealed airtight providing they are designed and
constructed to have only minor surface to
surface clearances or gaps, each of which is capable of acting as flame
quenching traps. The structure of such
service entries or exits are known in the art and not described herein. It is
preferred, however, that the space around
the burrter be substantially air/gas tight except for means to supply
combustion air.
Pilot flame establishment can be achieved by a piezoelectric igniter. A pilot
flame observation window sealed to the
jacket 4 can be provided. Altematively, if the pilot 49 is to be lit by
removing or opening an access, safety
interlocks (not illustrated) are included to ensure complete closure against
unprotected fume access during water
heater operation.
During normal operation, water heater 2 operates in the same fashion as
conventional water heaters except that
most air for combustion enters at air inlet 18 and a small proportion through
flame trap 30. However, if spilt fuel is
in the vicinity of water heater 2 then some gas or vapour from the spilled
fuel may be drawn through flame trap 30
before it builds up to a level to enter via air inlet 18. Flame trap 30 allows
the combustible gas or vapour and air to
enter but prevents flame escaping jacket 4 or duct 22. The spilled fuel is
bumed within combustion chamber 15 and
exhausted either through flue 10 via outlet 16 and duct 19 or through duct 22
and inlet 18 (which in this case will
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12
act as an outlet). Because flame is restricted from passing outwardly through
flame trap 30, spilled fuel external to
water heater 2 will not be ignited.
If desired, the embodiment of illustrated could, as in Figure 3A. include a
flame sensitive switch 50A located near
to the flame trap 30 so that it can detect the existence of flame on the flame
trap 30 and subsequently close valve 48
to shut down the gas supply to the burner l4 and pilot 49. If desired, the
flame sensitive switch 50A may be
substituted by a light detector or a heat detector, or a gas, fume or vapour
detection switch, or an oxygen depletion
sensor, so as to close off gas control valve 48 when either a flammable fume
or a flame is detected.
Figure 2 and Figure 3 show an embodiment similar to that of Figure 1. Like
parts use the same reference numbers
as those of Figure 1. In Figure 2, there is adjacent gas control valve 48, a
flame sensitive switch 50 which may be
inserted in the same circuit as pilot flame detecting thermocouple 51 and
located close thereto.
With reference to the cross section depicted in Figure 3, duct 22 contains gas
control valve 48 and flame trap 30 is
shown fomting a bottom end of the duct 22. In fact, flame trap 30 can be
arranged and installed spanning the
bottom end of duct 22 and an adjacent portion of base 26. An advantage from
such a positioning of flame trap 30,
including that shown in Figure 2 and Figure 3, by comparison with the centre
position of base 26 shown in
Figure 1, is that it permits positioning of flame sensitive switch 50 (Figure
2) directly below gas control valve 48
which is also an ideal position to detect flame spillage from combustion
chamber 15 which can occur if, for
example, flue 16, or exhaust duct becomes blocked. Similarly, it is ideally
positioned to detect flame spillage such
as would occur due to air starvation if inlet 18 were inadvertently blocked.
As shown in Figure 2 and Figure 3, opening 28 and flame trap 30 (including a
lint trap device as mentioned above)
are at the base of duct 22 below gas control valve 48 and flame detecting
switch 51 (see Figure 2). In this way,
should fumes which enter through flame trap 30 be ignited, a flame forms and
burns on the inside surface of the
flame trap and flame detecting switch 50 actuates the gas control valve 48 to
shut off the gas supply, thus removing
it as a continuing source of ignition. After the pilot and main flames have
been extinguished, any vapours of spilled
fuel continuing to enter through flame trap 30 may continue to burn because of
the initial ignition and resulting
suction of air (which may also be due to how water in tank 6) and may continue
to butn until there is insufficient
flammable vapour remaining to be drawn in from the vicinity of water heater 2.
By providing an air inlet 18 at a high position above the base 26, for the
more commonplace liquid fuels there will
be a lesser likelihood of flammable gases and vapours being available for
ignition by bumer or pilot flame.
In the water heater 2 of Figure 4 and Figure 5, the path for air entry to main
butner 14 is provided by a combined
air inlet and duct 54 fabricated of metallic mesh 21. This arrangement
provides that combustion air passes through
the air inlet which is constructed from a flame quenching surface 21 and the
height of duct 54 need not be as high
as jacket 4 nor need it necessarily extend upwardly. As evident in Figure 5,
it is preferably composed of separated
layers 21a and 21b of metallic mesh. This two layer construction avoids a
layer of lint, deposited externally,
providing a possible combustion path through the mesh, as previously
explained.
Lint deposition in the openings of the mesh may be a cause of gradual
blockage. In due course such linting may
cause starvation of combustion air. Therefore, an extended surface area (along
the full height of water heater 2 as
depicted for instance) of the combined air inlet and air duct 54 may be of
advantage for prolonging the time taken
for duct 54 to become occluded with lint and for providing an adequate path
for free induction of the air normally
required for combustion.
The gas valve 48 is illustrated in its preferted position outside of duct 54
as shown in Figure 5. The entry of the gas
pipe and thermocouple sheath into duct 54 is effected so that if a hole is
left it is small enough either to be totally
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13
sealed or to act as a flame quenching trap.
The preference for gas valve 48 outside duct 54 is that it provides one way of
providing user access to the control
knob and any buttons on gas control valve 48. It would be equally applicable
in cases where duct 22 is made of
imperforate sheet metal 20 as shown in Figure 1 and Figure 2.
For ease of construction one option is that the gas pipe and thermocouple
sheath can enter water heater 2 via an
opening in jacket 4, completely bypassing duct 54. This opening can then be
sealed or if a gap is left, the gap is
sized to act as a flame trap. However, whichever way the thermocouple sheath
passes to enter the combustion
chamber, if it includes a flame sensitive switch 50 or other equivalent sensor
(eg item 50A from figure 3A), then it
is greatly preferred that the flame sensitive switch 50 or other sensor is
located in relation to the position of flame
trap 30 so that the relative positions co-operate in, the event that a flame
from spilled fuel forms on the flame trap.
Illustrated in Figure 6 is another embodiment of the present invention,
similar to that of Figure 1, with like parts
like numbered. This embodiment includes an anchor 34 which anchors a nylon
line 36 which is a heat sensitive
frangible member. The nylon line 36 passes close to the upper surface of flame
trap 30 and around a lower pulley
38 then continues on to an upper pulley 40 around which it passes though 180
degrees, to make connection with a
flap 42. Flap 42 is connected by hinge 44 either to the inside of passage 22
or to a flange 46.
Flange 46, if it is utilised, can have a sealing medium (not illustrated)
around it so that when flap 42 makes contact
with it, an air tight seal or a flame trap is formed. If flange 46 is not
utilised, flap 42 can carry a seal so that, when
released to move to a closed position, it will seal the inside of duct 22 to
air tight quality, or, in the altemative to
form a flame trap. Flap 42 can be biased towards the closed position by a
spring, which is a preferred method, or
alternatively the biasing can be by other means. If desired, flap 42 can be
constructed from mesh, as described
above to act as a flame trap.
In the embodiment of Figure 6, when fumes from spilled fuel passing through
the flame trap 30 are ignited, the heat
of ignition breaks nylon line 36, which is heat sensitive and frangible,
thereby causing flap 42 to move to a closed
position, shutting off the air supply to main bumer 14. This leaves no path
down duct 22 for air or combustible
fumes which may have built up around water heater 2 to sufficiently gain
access to main burner 14 and so pilot
burner 49 and main burner 14 may not have enough air available through flame
trap 30 to continue burning in
which case flame detection thermocouple 50 will cut off the gas supply until
manual intervention can restore it
when a safe atmosphere is restored.
In Figure 7 and Figure 8 are illustrated a gas water heater 2 constructed
similarly to that illustrated in Figure 1, and
illustrated with like parts being numbered. Water heater 2 includes a base 26
and jacket 4 which are either
completely sealed (not illustrated) to air tight and flammable gas or vapour
tight quality or, alternatively, unsealed
gas paths are fine (small) enough to act as flame traps. In this instance,
when completely sealed, air for combustion
is drawn in from the air inlet 18, and there is no means present to ignite
spilled fuel at the lower portions of water
heater 2.
The embodiments shown in Figure 7 and Figure 8 have no flame trap 30 or
opening 28. However, an appreciable
time delay will occur before gases or vapours from spilled fuel rise to the
elevated level of air inlet 18. Only once
the gases or vapours from spilled fuel rise to the level of air inlet 18 could
the gases or vapours be drawn down
passage 22 to main bumer 14. Many spillages, nevertheless are quite minor in
terms of volume of liquid spilled and
in such cases the embodiment of Figure 7 would tend to provide an adequate
level of protection and that of Figure
8 even more so. The air inlet 18, if it does not include a flame trap 30,
should be at least about 500 rnillimetres (20
inches) from base 26 (if base 26 is near to the ground), in the presence of
gasoline fumes (a different height may be
required for other fumes). However, for added protection a greater distance is
preferred.
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14
The more frequently used typical flammable fumes of spilled liquid fuels are
far less likely to be available to a gas
water heater flame by providing an air inlet 18 at a high position above base
26.
If base 26 and jacket 4 has small gaps or openings limited in their size to
act as flame traps, then its operation will
be similar to the embodiment of Figure 1. The features of Figure 6 can be
incorporated also with the embodiments
described in Figure 7 and Figure 8 when base 26 and jacket 4 are sealed. In
this instance, because the water heater
now includes a heat sensitive frangible member 36 located in an air passage in
the vicinity of the main burner 14, if
gases or vapours ignite having flowed down the passage 22 (which would
indicate that the volume of gases or
fumes had risen to the level of air entry of the air inlet 18), the resulting
flame would melt a frangible member such
as nylon line 36 in the vicinity of main bumer 14. Nylon line 36 can be
connected in tutn to a non-flammable and
non-frangible section which in turn makes connection with a spring biased flap
similar to flap 42 capable of sealing
passage 22. The distance between nylon line 36 and flap 42 is sufficiently
long to close passage 22 before a flame
travelling back up passage 22 reaches flap 42. If flap 42 is.hinged so that
its closing motion is in the direction that
flame would have to travel to exit passage 22, the hinging arrangement may be
aided in closing by the movement of
flame in a closing direction.
A further improvement to the above embodiments shown in Figure 1 to Figure 6
is to provide a snorkel 60 as
shown in Figure 8 extending the air inlet upwardly. Snorkel 600 allows air to
be drawn to main burner 14 but, by
taking air from a height above the top of jacket 4, will further reduce the
risk of water heater 2 being an ignition
source of flammable gases or vapours from spilled fuel. If the height of
jacket 4 is not greater than about 500
nullimetres (20 inches) above base 26, snorkel 60 can be used to draw
combustion air from a more appropriate
height, depending upon the spillage which may occur.
In conjunction with any form of the invention as shown in Figure 1 to Figure
6, a gas shut down facility siniilar to
the above mentioned gas shut down ability can be provided. In another form,
the gas shut down facility can be
initiated by a flame sensitive switch 50 or thermocouple 5 1. Such a
thermocouple is preferably located just inside
of the flame trap 30 where ever it appears. Flame sensitive switches may also
be used in circuit with the
thermocouple (e.g., thermocouple 51 of Figure 1) provided for confirming the
establishment and retention of a pilot
flame by raising an electric current flow to a level capable of keeping open a
gas supply to the pilot burner.
Flame sensitive switches may also be used to reduce fire hazards in
circumstances where flame of the bumer can
"spill" through an air access opening adjacent the main and pilot burners. In
known flame sensitive switches, the
heat sensor is externally positioned and in some embodiments of the invention
a flame sensitive switch is
positioned above flame trap 30 to sense flame heat input resulting from
spilled flammable vapour burning on the
inside of flame trap 30 after having entered the combustion chamber through a
possible entry path. In the
embodiment of Figure 3A, the preferred position of the flame sensitive switch
50A is immediately above the flame
trap and it is preferred that a small heat shield (not shown) be placed above
the flame sensitive switch to shield it
from the normal radiant heat associated with the main burner 14. In Figure 2,
the flame sensitive switch 50 is
positioned a short way above flame trap 30.
An additional level of safety is provided by the addition of an oxygen
depletion sensor in conjunction with pilot
burner 49. This makes available the entire air requirement for the pilot flame
to the pilot bumer only through a pilot
air duct (not illustrated), gas tightly separate from air supply duct 22 and
combustion chamber 15. The pilot air duct
has an air intake external to the remainder of the water heater assembly,
preferably low to floor level where water
heaters are generally installed, standing upright on a floor. At any
convenient location in the pilot air duct between
the air intake end and the pilot burner is a flame quenching insert, composed
of one or more of a variety of high
thermal capacity gas porous heat resistant materials such as described in
relation to ftame trap 30. Locating the
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flame quenching insert at or near the air intake end is advantageous to make
it accessible for cleaning of lint or dust
that may accumulate in it. An element sensitive to oxygen depletion is also
located in the pilot air duct.
With these features added to the embodiments of Figure 1 to Figure 7, use of
the oxygen depletion sensor reduces
the risk of ignition of flammable vapour in particular when pilot bumer 49 is
alight but main burner 14 is not, by
5 sensing oxygen depletion in the incoming pilot air supply if a flammable
component ignites in which case it would
cause a gas control valve 48 of the type referred to in Figures 1 to Figure 7
to shut down gas flow to the pilot
burner. The shut down provides a time period for flanunable vapour to safely
ventilate. Resumption of normal
operation of the water heater requires human intervention but, even if done
ill-advisedly, in any event the oxygen
depletion sensor would continue to deny pilot burner 49 of gas and the
arrangement would behave safely even with
10 extraneous flammable fumes remaining near water heater 2. An oxygen
depletion sensor can be used altematively
in place of or in conjunction with the previously described flame sensitive
switch 50, and can be located similarly.
The invention thus far described can function at three levels of safety. The
first level is illustrated in relation to
Figure 7 and Figure 8, wherein there is added height and distance so that
fumes from spilled fuel must travel to
reach main bumer 14 or pilot bumer 49.
15 The second level. as illustrated in Figure 1, Figure 2, Figure 3 and Figure
6, adds not only height and distance but
also allows some, and advantageously all, the extraneous fumes to enter the
base of water heater 2 and be consumed
safely, conceivably until all residual risk of fire and explosion is avoided
by dissipation of the spillage.
The third level, as illustrated in Figure 4 and Figure 5, adds a further level
of confidence by protecting all air entry
with a flame arrestor, recognising that high levels of airborne lint or other
dust may tend to block the air intake and
starve the burrter of air for combustion if the air entry were not
periodically cleared of that lint or other dust. The
embodiment of Figure 4 and Figure 5 can be constructed to protect against
ignition of flammable gases and vapours
outside of the enclosure or jacket regardless of the density of those gases
and vapours relative to air.
In a prefened form the water heater 2 contains at least some of the following
features: the opening includes an
aperture which is covered by a flame trap, which prevents the bumer from
igniting extraneous fumes outside of the
enclosure, and an air inlet through which air for combustion purposes is
drawn; the opening is remote from the
burner and includes a duct for passage of air to the butner; the opening and
the aperture are collocated or are a
single item; the at least one opening is covered by a flame trap; the aperture
is in the enclosure; the aperture is
positioned close to a lower end of the enclosure; the aperture is positioned
in a lower end of the enclosure; the
aperture is positioned below the burner; the aperture is positioned to allow
air and fumes outside of the water heater
to enter into an air passage leading to the burner; the aperture is positioned
to allow air and fumes outside of the
water heater to enter into an air passage leading to the burtter; the aperture
allows air and fumes to enter the lowest
point of the air passage; one of or a combination of: a light detection or
sensitive device; a flame detecting or
sensitive device; a temperature sensitive or detecting device; a heat
detecting or sensitive device; and an oxygen
depletion sensitive or detection device, is located in the water heater to
detect flame from the fumes if they have
been ignited inside the enclosure; the opening includes an air inlet which is
not covered by a flame trap, the air inlet
having its lowest opening at a height of not less than about 500 millimetres
or about 20 inches or more from the
bottom of the enclosure; the opening is located at or adjacent to the highest
point of the enciosure, if the enclosure
has a height of about 500 millimetres (mm) or greater, from the bottom of the
enclosure; a snorkel device is
provided to extend the at least one opening at a height above the highest
point of the enclosure; the flame trap
includes a heat resistant permeable material having high thermal capacity; the
flame trap includes a screen selected
from either woven or knitted mesh: the flame trap is made of metal: the flame
trap is made from a metal selected
from the group consisting of: steel, stainless steel, copper and alurninium; a
lint trap is included to wholly cover the
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16
aperture and the flame trap; the lint trap is formed by mesh placed in the
path of lint or dust travelling to the flame
trap means; the water heater includes a gas shut off means which shuts off the
gas supply to the bumer and or a
pilot burner if the air and fumes are ignited after entering the enclosure;
the gas shut off means includes a heat
sensitive means; the gas shut off means includes a flame sensitive switch: the
gas shut off means includes an
oxygen depletion sensitive means; the enciosure includes a separable jacket
and base; the flame trap is provided at
or as part of the construction of joining areas of the base to the jacket, or
the jacket to other component or the base
to other component or at any location where the fumes could enter the
enclosure; the flame trap is inherent in or is
formed by the joining areas including either only gaps or apertures of a size
small enough to act as a flame trap; the
flame trap has been added to the joining area or is deliberately incorporated
as part of the joining area; the flame
trap is a layer of metallic mesh cooperating with the joining area to achieve
the flame quenching or arresting
function; the flame trap is inside of the water heater; and the gas shut off
means includes a light detection means.
One advantage provided by the invention is the provision of a barrier to
unprotected entry, at the lower end of the
jacket or enclosure, of flammable extraneous fumes. In altemative embodiments
it provides a protected entry means
for such fumes near or at the base of the enclosure in which case these
extraneous fumes are consumed in a
controlled manner. The protected entry is, in the most preferred form, an air
inlet or a flame trap preventing ignition
of the remaining fumes in the surrounding atmosphere or of any liquid
remaining nearby.
An advantage of locating the air intake for combustion purposes above the
midpoint of the gas water system is that
it reduces the chance of extraneous fumes entering the heater via the air
intake because generally such flammables
are heavier than air, which in the main do not attain dangerous levels at the
air intake level.
The use of air close-off means and gas shut-off means activated by a trigger
provides the advantage of suffocating
any flame in the heater, or switching off the gas supply, or preventing
uncontrolled or undirected ignition of gases
or vapours from exiting the heater environment.
By providing an extended air intake, the risk of lint or dust affecting the
efficiency of the water heater is reduced.
Still further advantages of the invention are provided by the structure shown
in Figure 9 and Figure 10. Figure 9
and Figure 10 show water heater 2 wherein aperture 28 having flame trap 30
across its mouth and positioned below
pilot bumer 49, pilot bumer 49 being located adjacent one edge of main burner
14. Aperture 28 is positioned
immediately undemeath pilot burner 49, preferably the closer the better to
assist in achieving smooth and or early
ignition. Aperture 28 is connected to the lower end of the enclosure by an
upwardly extending tube 70, the
upwardly extending portion of tube 70 being preferably impermeable to air, gas
or fumes. Tube 70 is preferably
constructed of sheet metal, although other suitable materials may be
substituted. It is also possible that tube 70 as
shown in Figure 9 can be made either partially or completely from flame trap
materials, especially the upper
portion.
Locating flame trap 30 above base 26 minimises the possibility of water
condensate occluding the pores or
openings in flame trap 30 or water splashing from, for example, hosing the
floor near base 26 of water heater 2.
Thusõ the length of tube 70 is not especially critical so long as it performs
the function of preventing pore or port
occlusion. In Figure 9 a horizontal blocking plate 74 is located above flame
trap 28 to prevent water condensate or
particulate matter such as steel scale flakes falling on the flame trap,
thereby reducing the chance of occluding it.
It has also been discovered that a two layer construction of flame trap 30
with a lint filter is highly advantageous.
Figure 9 illustrates a lint filter 72 in addition to a double layer flame trap
30. Filter 72 may be a different material
from flame trap 30. The potential for accumulation of lint over time has been
a concem. However, it has been
unexpectedly discovered that structure such as that shown in Figure 9 and
Figure 10 is surprisingly free of lint
accumulation problems. It is believed that the horizontal and very close
positioning of flame trap 30 to main bumer
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17
14 results in small pressure pulses associated with main bumer 14 igniting on
each occasion. Apparently, the pulses
blow away any lint from the face of flame trap 30. This appears to provide a
repeating self-cleaning effect.
Another significant advantage can be provided to the water heaters described
above by providing an improved gas
control valve which is better illustrated in figures I i to 16. In
conventional gas valves, the thermocouple and over-
temperature fuse have been inconveniently located in an integrated structure
sheathed in a copper capillary tube
with significant thermal inertia. If either the thermocouple or the
temperature fuse require replacement then it is not
immediately apparent which one has failed and, because both are replaced as an
integrated unit, unnecessary cost is
involved. The thermal fuse is a relatively low cost item compared to the
entire integrated structure and, therefore, it
is advantageous to be able to test the circuit by merely removing the suspect
fuse and replacing it. This test does not
involve removal of the thermocouple which requires awkward access into the
water heater combustion chamber.
Thus, there can be a considerable reduction in the time a water heater service
person needs to identify and correct a
problem in the many cases where an open circuit is related to the fuse rather
than the thermocouple. Therefore, the
reason for replacement being necessary can be ascertained more directly and,
thus, safe operation resumed more
certainly.
Figure I I to Figure 14 show a gas control valve 48 supplying main burner,l4
having an adjacent pilot burner 49 in
water heater 2 with combustion chamber 15 The valve 48, illustrated in figure
11 to 16 include a gas inlet 120 for
connection to a supply (not shown) of combustible gas. Valve 48 has a gas
outlet 124 for connection to a conduit
(not shown) leading to main burner 14 and an outlet 126 to connect to pilot
burner 49. Internal components of the
valve include an orifice or conduit 127 for gas flow between the inlet 120 and
outlet 124 and a closure 154
normally resiliently biased to close the orifice to prevent or permit flow of
gas from the inlet 120 to the outlet 124
as required.
Incorporated in valve 48 is an electrical circuit 128 such as shown in Figure
15 and 16, including thermocouple 51
connected to a solenoid 132. Thermocouple 51 provides an electrical potential,
sometimes hereinafter referred to as
"signal", when heated by a flame established at pilot bumer 49, typically 12
to 15 mV, to solenoid 132 which is
sufficient to maintain solenoid 132 open against the normally closing bias of
a spring 156 associated with closure
154. Specifically, the electrical potential is provided to solenoid 32,
creating a magnetic force which, via an
armature connected to closure 154, maintains closure 154 open. It should be
noted that the electrical potential is
not sufficient to open closure 154 from its closed position except when valve
passage 127 is first opened by manual
switch 142 being manually position in the "pilot" or "on" positions and the
potential is adequate to maintain closure
154 in its open position.
When a flame is absent at pilot burner 49, valve 48 remains shut except during
a start up procedure. The circuit has
a manual switch 142 with three positions, "off', "pilot" and "on". In the
"pilot" position the switch may be
depressed to hold open valve 48 while thermocouple 51 heats sufficiently to
power circuit 128. Manual switch 142
is depressed in the "pilot" and "on" positions to lift closure 154 off its
seat against the closing bias force of spring
156. In the open position, an electrical current passing through the coil of
solenoid 158 generated by the
thermocouple 51 when heated by the flame of the pilot burner 49 (Figure 4) is
adequate to maintain closure 154 in
the open position during normal use of water heater 2, Normal use of water
heater 2 involves pilot burrter 49 being
alight at all times.
An over-temperature energy cut out 144 is instalied inside a temperature
sensitive thermostat probe 146 (shown in
Figure 12) which interrupts all gas flow through the valve in the event that
an unsafe temperature develops inside
the tank.
As best seen in Figure l 1 and Figure 15, valve 48 has a fuse 134 connected in
electrical circuit 128 and exposed at
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18
the bottom surface of valve 48 to be sensitive to extraneous sources of flame
and heat external to and in the region
of the valve, particularly undemeath it.
Valve 48 features an externally accessible socket 136 in electrical circuit
128 in which thermal fuse 134 is
removably inserted. Socket 136 is positioned to receive thermal fuse 134
independently and separate from
thermocouple 51.
Socket 136 and fuse 134 are accessible from the underside of valve 48 as shown
in Figure 11 and Figure 14
wherein valve 48 is mounted on an extemal vertical wall of water heater 2.
This leads to the advantage of rapid
response time since the underside is more likely to be impinged upon by
extraneous flame because valve 48 is also
vertically above access point 138 to main bumer 14 and pilot burner 49 such as
for lighting, inspection and
combustion air entry. Extraneous flame and heat within water heater 2 may
result from accidental combustion of a
flammable substance near water heater 2, the flame being likely to establish
itself firstly adjacent to access point
138.
Another advantage of mounting fuse 134 to be accessible at a downward facing
surface of valve 48 is that fuse 134
would not be as noticeable upon a casual inspection of water heater 2 and
valve 48 and, therefore, not so likely to
invite removal by personnel unaware of its safety-motivated purpose. Water
heater 2 will not continue to function if
it were removed and not replaced.
Despite the preferred downward facing position of fuse 134, positions on other
faces of valve 48 are possible. Fuse
134 has minimal thermal inertia and to that end involves minimal mass and is
not enclosed in a copper or similar
sheath. A preferred fuse 134 is one encapsulated only in a small quantity of
organic polymer resin. One presently
preferred form of thermal fuse 134 is manufactured by Therm-O-Dis, Inc.,
Mansfield, Ohio, USA. The radial lead
type is the most suitable for insertion into a socket 136 and a model
available with a maximum rated opening
temperature of 102 C has a suitably rapid response time.
Further advantageous embodiments of the invention are described below in
relation to Figure 17 to and those
following. The embodiments in Figure 17 to Figure 23 are particularly
advantageous in situations where it is
desired that water heaters embodying to the invention do not function to
consume substantial quantities of spilled
fuel but rather to prevent all combustion of extraneous fumes around a water
heater, leaving spilled flammable
vapours or fumes to be dispersed by ventilation rather than controlled
combustion in the combustion chamber.
One important reason why this may be a preferred option is that if a
considerable amount of spilled flammable
vapour is available to be consumed, then the flame established on the flame
trap or air inlet porous surface inside
the combustion chamber of the water heater could last long enough to
substantially heat the conductive flame trap
material so that the side of it exposed to the source of flammable vapours
("upstream" side) may become
sufficiently heated to reach the auto-ignition temperature of the particular
spilled vapour such that the vapour could
be ignited outside the water heater without actual transference of the flame
through the flame trap. The
embodiments shown in Figure 17 to Figure 23 address this unlikely but
potential difficulty according to several
broad strategies.
The first such strategy involves mechanical devices triggered to operate by
the heat of the flame burning on the face
of the flame trap in the combustion chamber. The devices operate to starve
flames of air for continuing combustion
which flames are established on the flame trap surface.
The second strategy is to extinguish flames established on the flame trap
quickly by a combined chemical and
physical reaction to the heat o the flame trap by generating, releasing and
propelling a flame extinguishment
substance into the intake of the flame upstream of the flame trap.
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The third strategy involves selecting specific tlame trap materials and
coating them with an ablative or intumescent
substance that, when subjected to heat of combustion of split flammable
vapours on the "downstream" surface of
the flame trap, expands to occlude the pores of the flames trap thereby
extinguishing the flame.
The fourth strategy is to select a thick, low heat conductive flame trap
material such that heating at the downstream
surface of the flame trap results in a much longer or infinite period before
the temperature on the upstream face of
the flame trap could reach a temperature able to cause ignition of the spilled
vapours upstream of the flame trap
entry.
With reference to Figure 17, base 226 of the water heater has an aperture to
which an upstanding tube 270 is
joined, the tube terminating approximately 5 cms above the base 270 to create
a hole spanned by a flame trap 229.
Above tube 270 and flame trap 229 is a substantially horizontal blocking plate
274 adjacent combustion chamber
2B which may be conical or curved so as to be able to deflect any condensation
water falling upon its upper surface
outwardly beyond the flame trap area. Fixed to the underside of horizontal
blocking plate 274 is a temperature
sensitive fuse 234 connected to the gas valve 48 (see, for example Figure 1)
arranged to enable flow of gas through
the gas valve to be shut off in the event of fuse 234 being open circuited by
formation of a flame on the upper
surface of the flame trap. A drop tube 302 is provided to create a smooth
sliding fit inside the tube 270. Drop tube
302 is held in the upward position illustrated in Figure 17 by a ring of
fusible sealant 304 which acts as a hot melt
adhesive to support tube 302 for normal operation in an upward position.
Fusible sealant 304 most preferably has a
melting temperature of about 100 C to 200 C.
Opening 271 in the drop tube 302 may be spanned by a lint filter 272 if
desired. As shown in Figure 18 in the event
of a flame forming on flame trap 229 the fiusible sealant 304 melts allowing
drop tube 302 to fall until it reaches a
flat surface such as a floor or mating stop 303 upon which the heater is
installed. The distance between the floor
303 and the base 226 of the heater must be not more than the vertical height
of drop tube 302 so that, as illustrated,
there is no space for sufficient air to enter the tube 270 to enable
combustion on the upper surface of the flame trap.
Such combustion effectively triggers the falling of drop tube 302, which
substantially closes opening 271 and
thereby starves the flame of any further vapour or fumes and air and
extinguishing it.
A different arrangement performing a similar function to that shown in Figure
17 and Figure 18 is provided in
Figure 19 and Figure 20. In this case a horizontal blocking plate 274 is
supported above flame trap 229 (Figure 19)
by three legs 320 made from readily fusible material, preferably a
thermoplastic material such as low density
polyethylene. The readily fusible material most preferably has a melting
temperature of 100 C to 200 C. Of
course, other readily fusible materials may be substituted. With this
arrangement, in the event that combustion of
spilled flammable vapour or fumes occurs on the flame trap 229, legs 320 melt
as shown in Figure 20 so that
horizontal blocking plate 274 falls onto the top of tube 270, thus blocking
the flow of further vapour or fumes and
air to continue combustion, thereby extinguishing combustion.
With reference to Figure 21, an altemative type of flame trap material 329 is
illustrated. The flame trap 329 may be
in a number of forms, the common feature of which is a much greater dimension
in the direction of through flow of
air or fumes than previously disclosed in the illustrated embodiments. The
main purpose of the thicker flame trap
material 329 is to delay and/or reduce the conduction of heat from the top
surface of flame trap 329 to the
underside of flame trap 329 in the event of combustion being established due
to flammable fumes and vapour
igniting on the upper surface of flame trap 329. One type of flame trap is
constructed of stainless steel foil, which is
corrugated and joined to an uncorrugated strip of stainless steel foil of
similar thickness and the first and second
tapes joined together and spirally wound as disclosed in Hayakawa et al. U.S.
Patent 5,588,822. Then, the time
taken for the inlet side of the flame trap to become heated to a temperature
sufficient to ignite flammable vapours
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external to the water heater is considerably increased. This configuration can
be rearranged if the overall shape of
the flame trap is other than circular.
Even longer delay times are provided when the flame trap material 329 is
constructed of ceramic materials such as
Celcor (registered trade mark of Corning Incorporated of Houghton Part,
Coming, NY 14831) extruded ceramic
5 having a thickness of about 12 mm or greater being preferred. It is
preferably provided with an open frontal area
between about 64% and 80% and with between about 36.6square openings/cm2 and
73 square openings/cm2. Flame
trap 329 may be in any desired shape and may be built up to a total required
area by using smaller modules of the
ceramic material. Adjacent modules of cerarnic can be sealed to each other
using a flexible sealant 330 or the like
as required.
10 With reference to Figure 22, an alternative means of extinguishing flames
on flame trap 229 is shown. Upstanding
tube 270, water heater base 226 and optional lint filter 272 are as previously
illustrated as in Figure 23. Flame trap
229 may be made from any of the materials as herein mentioned. Additional
structure in Figure 22 includes a
container 306 charged with a substance capable of extinguishant flame which is
restrained from leakage by fusible
plugs 310 inserted in one or more outlets 308 to the container. Ends of the
tubes 308 distant from the attachment to
15 the container 306 may terntinate in nozzles 312 to increase the mixing of
flame extinguishant from the nozzles.
Flame extinguishing in container 306 may include one or more of many known
substances decomposable under the
effect of elevated temperature occasioned by the formation of flames on the
flame trap 229 including, for example
sodium bicarbonate. Sodium bicarbonate decomposes under the effect of elevated
temperature to give off carbon
dioxide gas which when mixed into the air stream, including flammable vapour
entering the open end of tube 270,
20 is able to extinguish flames on the upper (or inside) surface of the flame
trap 229. Whilst the fusible plug or plugs
310 closing container 306 may have quite a wide range of suitable fusing
temperatures, it is prefeaed that the range
be sufficiently high so that fuse 234 is more likely to open the circuit and,
therefore, shut off the gas flow before
fusible plug(s) 310 melt. Accordingly, a preferred melting temperature of the
fusible plug(s) is in the range of about
150 C to 300 T.
Thetmal fuse 234 is positioned in such a way that the presence of container
306 does not impede the fuse's
function of shutting down supply of fuel gas to the main and pilot bumers as
elsewhere illustrated. The flame
extinguishant encapsulated in container 306 may include fire blanketing foams
together with a propellant which,
under the effect of a temperature attained (typically in the range of 300 C
to 500 C) just above the flame trap
when a flame is burning thereon, would create high vapour pressure to propel
the flame suppressant foam out
through the nozzles 312 and into the fume/air intake travelling upwardly
through tube 270.
With reference to Figure 23, an alternativeiy shaped flame trap 332 is shown.
Support tube 270, water heater base
226 and optional lint filter 272 are as previously illustrated, for example as
in Figure 23. With reference to the
flame trap material 332, this includes a double layer of woven metal mesh as
previously described except that in
Figure 23 the two component layers are formed in a non-planar upwardly domed
shape (for a circular aperture tube
or an upwardly corrugated shape for a square or rectangular aperture at the
top of tube 270). The advantage of the
flame trap 332 over flat woven mesh constructions is that the two layers can
be reliably manufactured substantially
in contact and will remain substantially in contact because of the way they
expand when so curved and do not form
localised areas of contact between the two layers of mesh. A disadvantage
obtained with localised contact is that
hot spots form quickly at such areas of contact and these nught initiate
ignition of unburned flammable fuels on the
outside of the flame trap structure. Thus, the flame trap illustrated in
Figure 23 can sustain combustion on its upper
surface for a greater length of time than a sirnilar flat structure without
causing ignition on the lower or outward
side of the flame trap.
CA 02338078 2006-11-03
21
Whilst the above embodiments are directed to room or indoor installed gas
water heaters, the improvements
described will function in an outdoor environment, if spillages occur nearby
and fumes enter the gas water heater.
If desired the flame trap or air inlet may be located at various positions
other than those shown in the drawings and
deseribed above. One altemative position is in the side of the combustion
chamber opposite the gas supply. In such
a construction the flame trap or air inlet would be located in an opening in
the skirt below the water tank and
extending through the corresponding portion of insulation.
In a further option the flame trap is positioned above the height of entry to
the combustion chamber and a flame
sensitive switch is positioned above that height of entry in the flow path of
combustion air toward the burner. 7tte
aperture covered by the flame trap is in radiant heat communication with a
flame sensitive switch also positioned to
be sensitive to flame roll out from flue blockage or combustion air
starvation.
Further, the flame trap may be made from a variety of materials such as those
described above, but can be
fabricated from others not specifically identified so long as they permit
passage of air and fumes in one direction
but prevent flames from travelling in the opposite direction.
Suitable flame trap materials include those being porous. gas permeable and
possessing sufficiently high thermal
capacity to quench flame under typical conditions of use. Metallic sttuctures
having holes of sizes described below,
made from, for example, mild steel, stainless steel, copper or aluminium as
described below are suitable and porous
ceramics including glass or mineral wool woven or non-woven constructions are
also suitable. Fibre tnatrix ceramic
is suitable as is flexible or rigid constructions.
Also, the air passage for combustion air, such as in the structure labelled 22
in Figure I. can be located between
water tank 6 and jacket 4. The passageway can be of a variety of shapes and
sizes and can be fonned in and
bounded by the insulation or can be formed by tubes, pipes conduits and the
like.
It should also bc understood that utilisation of the flame sensitive switch or
simiiar devices may be used with all
types of gas fired water heaters, including those not equipped with flame
traps. Further, devices other than
thermocouples 51 providing electrical potentials may be employed so long as
they are capable of converting heat
energy to assist in actuating closure 154. Heat to mechanical, heat to
optical, heat to magnetic and the like types of
conversions are all within the scope of the invention. Accordingly, "signaP"
as used in the claims refers not only to
"electrical potential" but to any means whereby closure 154 is
actuated/deactuated as a result of detection of heat
energy.
Main bumer 14 and combustion chamber 15 can have different constructions such
as those described in U.S.
patents 4,924,816; 5,240,411; 4.355,841, for example..
Duct 270 may be made from a number of heat and corrosion resistant materials,
may be shaped and sized in
different configurations, and can have flame trap 229 placed in any number of
relative position. including
horizontal. venical and at various angles.
Finally, it is possible that container 306 shown in Figure 22 may be located
in alternative positions within
combustion chamber 215 or even exteriorly of the water heater so long as
fusible material 310 and nozzles 312 are
located adjacent flame trap 229, either above or below it.
Moving now to the description of figures 24 to 85
Conventional water heaters typically have their source(sl of ignition at a low
level. They also have their combustion
air inlets at of near'floor level. In the course of attempting to develop
appliance combustion chambers capable of
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27
confining flame inside appliances, we discovered that a type of air inlet
constructed by forming holes in sheet metal
in a particular way has particular advantages in damage resistance when
iocated at the bottom of a heavy appliance
such as a water heater which stands on a floor. We further discovered that
providing holes having well defined and
controlled geometry assists reliability of the air intake and flame confining
functions in a wide variety of
circumstances.
A thin sheet metallic plate having many ports of closely specified size
formed, cut, punched, perforated, etched,
punctured and/or deformed through it at a specific spacing provides an
excellent balance of performance. reliability
and ease of accurate manufacture. In addition, the plate provides damage
resistance prior to sale and delivery of a
fuel burning appliance such as a water heater having such an air intake and
during any subsequent installation of
the appliance in a user's premises.
On the other hand, both ceranuc plaque tiles (such as SCHWANK tiles) and
certain less robust types of woven
metal mesh have the disadvantage of being easily damaged. Moreover, ceramic
plaque tiles are typically 20 to 25
times thicker than thin metallic plates or metal mesh and, therefore, have the
disadvantage of creates a greater flow
resistance per unit of area of air intake.
In the disclosure relating to figures 1 to 23 above we addressed the question
of reliability by disclosing certain
arrangements applicable to water heaters whereby an incidence of combustion of
flammable fumes (arising from a
nearby spill) confined safely to the side of the air intake facing the inside
of the combustion chamber, can be
quickly extinguished by several arrangements which result in the air and
flammable fume entry to the combustion
chamber of a water heater being blocked by a variety of means triggered by one
or more effects of combustion,
such as temperature rise. This blocking was directed to a desire to extinguish
all flame sources within the
combustion chamber within a matter of minutes, or less, of such a combustion
incident contmencing. While this
structure will be successful in seeking to ensure maximum reliability, we
subjected that structure to exhaustive
testing in the absence of provision of an entry blocking means involving
prolonged combustion of one US gallon
(3.79 litres) of gasoline which, in 30 or 40 US gallon domestic sized water
heaters tested of nominal 30,000 or
45,000 BTU/hour heating capacity requires more than one hour to completely
combust.
In experiments conducted with air intakes in general having a variety of port
shapes and patterns formed through a
thin metal plate. it was observed that some variants were more effective than
others in flame confinement function.
We noted that certain ones enabled a flame to bum in close contact with the
inside surface of air inlet plate, thereby
leading to substantial temperature rise of the plate on its outside surface,
by heat conduction. In some instances, this
was observed to involve a pulsating combustion phenomenon which enhanced heat
release in the combustion
chamber.
An excessive rising temperature of the perforated plate in contact with the
flame can transfer heat by conduction
through the relatively thin metal plate to the extent that it can reach a
sufficiently high temperature (of the order of
1250"F or 675 C) such that a failure might possibly occur under some
conditions caused by hot surface ignition of
the spilled fumes on the outside of the combustion chamber.
During experimentation, which was designed to create potential ignition
conditions not likely to occur under
normal operating conditions and, with a video camera filming the inside of the
combustion chamber, a potential
mode of failure was observed in some instances to involve flame retention more
closely to the periphery of the inlet
plate than in the centre. Where the flames are closely retained the inlet
plate becomes visibly hotter such as by
becoming red, which indicates a temperature in excess of 1250 F and which was
confirmed by thermocouple based
temperature measurement.
The embodiments attempt to address ways of meeting extreme conditions and
keeping the overall temperature of
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23
the inlet plate to a level that will not encourage external ignition by
excessive heating of any portion of the inlet
plate. The invention also addresses ways of avoiding detonation wave type
ignition that we discovered propagates
from the inside to the outside of the combustion chamber through the inlet
plate under certain circumstances, by
minimising the amount of flammable fumes which may enter the combustion
chamber before initial ignition inside
the combustion chamber occurs; and, also, during prolonged combustion
incidents, in controlling thermally
induced resonance within the combustion chamber.
Working from the basis that a burner designed to heat the contents of a water
heater of a given capacity in a
satisfactorily short time requires a particular air flow rate for proper
combustion of the gaseous fuel, the inventors
found that the shape and the pattem of the ports in an air intake plate having
the required air flow rate can be
surprisingly significant in preventing detonation ignition and delaying or
preventing temperature rise of the plate
during prolonged combustion testing resulting from a spill. Furthermore, the
inter-port spacing in the plate can be
specified to minimise flash-through ignition, all other parameters being in a
satisfactory range.
Turning now to the drawings in general and Figure 24 and Figure 25 in
particular, there is illustrated a storage type
gas water heater 462 including jacket 464 which surrounds a water tank 466 and
a main bumer 474 in an enclosed
chamber 475. Water tank 466 is preferably capable of holding heated water at
mains pressure and is insulated
preferably by foam insulation 468. Alternative insulation may include
fibreglass or other types of fibrous insulation
and the like. Fibreglass insulation surrounds chamber 475 at the lowermost
portion of water tank 466. It is possible
that heat resistant foam insulation can be used if desired. A foam dam 465
separates foam insulation 468 and the
fibreglass insulation.
Located underneath water tank 466 is a pilot bumer 473 and main burner 474
which preferably use natural gas as
their fuel or other gases such as LPG, for example. Other suitable fuels may
be substituted. Bumers 473 and 474
combust gas admixed with air and the hot products of combustion resulting rise
up through flue 470 possibly with
heated air creating a suction that draws ambient air into the combustion
chamber 475, as will be further described
below. Water tank 466 is lined with a glass coating for corrosion resistance.
The thickness of the coating on the
exterior surface of water tank 466 is about one half of the thickness of the
interior facing surface to n nimise "fish
scaling". Also, the lower portion of flue 470 is coated inside to prevent
eventual formation of scale that could
detach as flakes of rust due to prolonged effects of acidic condensate. Such
flakes could fall into chamber 475
possibly blocking off or reducing air flow by lodging on the air inlet plate
490.
The fuel gas is supplied to both burners (473,474) through a gas valve 469.
Flue 470 in this instance, contains a
series of baffles 472 to better transfer heat generated by main burner 474 to
water within tank 466. Near pilot
burner 473 is a flame detecting thermocouple 480 which is a known safety
measure to ensure that in the absence of
a flame at pilot burner 473 the gas control valve 469 shuts off the gas
supply. The water temperature sensor 467,
preferably located inside the tank 466, co-operates also with the gas control
valve 469 to supply gas to the main
burrter 474 on demand.
The products of combustion pass by natural convection upwardly and out the top
of jacket 464 via flue outlet 476
after heat has been transferred from the products of combustion. Flue outlet
476 discharges conventionally into a
draught diverter 477 which in turn connects to an exhaust duct 478 leading
outdoors.
Water heater 462 is mounted preferably on legs 484 to raise the base 486 of
the combustion chamber 475 off the
floor. In base 486 is an aperture 487 which is closed gas tightly by an air
inlet plate 490 which admits all required
air for the combustion of the fuel gas combusted through the main burner 474
and pilot burner 473. regardless of
the relative proportions of primary and secondary combustion air used by each
bumer.
Air inlet plate 490 is preferably made from a thin metallic perforated sheet
of stainless steel. Copper or brass sheet
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24
metal can be used to take advantage of its superior heat conducting
properties. Stainless steel when used mav be
surface treated by dipping in rnolten sodium and/or potassium dichromate, to
blacken it and raise its emissivity.
Preferably the metal plate has a thickness of about 0.4mm to 1 mm
Altematively, a ported ceramic tile of the
SCHWANK type (registered trade mark) can be utilised although the robustness
of thin perforated metaf when
compared to its good flow capacity commends its use. The cerantic tile type
functions adequately as long as the
porosity is suitable and it does not become damaged during assembly, transit,
installation or use.
Where base 486 meets the vertical combustion chamber walls 479, adjoining
surfaces can be either one piece or
altematively sealed thoroughly to prevent ingress of air or flammable
extraneous fumes. Gas, water, electrical,
control or other connections, fittings or plumbing, wherever they pass through
combustion chamber wall 479 are
sealed.
The combustion chamber 475 is air/gas tight except for means to supply
combustion air and to exhaust combustion
products through flue 470. Some altemative structure of the combustion chamber
is shown schematically in Figure
56 to Figure 58, which is discussed later.
Pilot flame establishment can be achieved by a piezoelectric igniter. A pilot
flame observation window can be
provided which is sealed. Cold water is introduced at a low level of the tank
466 and withdrawn from a high level
in any manner as already well known.
During normal operation, water heater 462 operates in substantially the same
fashion as conventional water heaters
except that all air for combustion enters through air inlet plate 490.
However, if spilled fuel or other flanurtable
fluid is in the vicinity of water heater 462 then some extraneous fumes from
the spilled substance may be drawn
through plate 490 by virtue of the natural draught characteristic of such
water heaters. Air inlet 490 allows the
combustible extraneous fumes and air to enter but confines combustion inside
the combustion chamber 475.
The spilled substance is bumed within combustion chamber 475 and exhausted
through flue 470 via outlet 476 and
duct 479. Because flame is confined by the air inlet plate 490 within the
combustion chamber, flammable substance
external to water heater 462 will not be ignited.
We define the "quenching distance" of a port in an inlet plate in a combustion
chamber of a water heater or similar
appliance to account for a wide variety of suitable shape of port. The
quenching distance in this context is that
distance measured in the plane of the port area below which a flame formed by
a combustible mixture of a fume
species and air passing or having passed through the port in a forward
direction will not propagate through the port
in a reverse direction, whether as a result of detonation or deflagration type
initiation of combustion or as a result of
prolonged steady combustion at the inlet plate within the combustion chamber.
For shapes of ports such as may be categorised as geometrically regular such
as circular holes or straight slots or
irregular, such as curved or wavy slots, we define the quenching distance of
such a port by first defining an axis of
the open area of that port as the longer or longest line, which may be
straight or curved, which divides that open
area in half exactly or approximately. The quenching distance of that port, is
then the length of the longest straight
line which passes perpendicularly through the defined axis to meet the
boundary of the open area. Thus the
quenching distance according to this definition for a straight slot is its
width and, for a circle, its diameter.
For both geometrically regular and irregular shapes of port, complex patterns
may be formed by superimposing
shapes where axes may cross or intersect, in many ways, one example being wavy
slots intersecting
perpendicularfy.
Preferably, the blocking plate 492 if used is the same or slightly larger size
and shape as the inlet plate and has the
purpose of stopping condensate or scaly particulate matter falling from above
and occluding the openings of the air
inlet plate 490.
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As best seen in Figure 25. the inlet plate has mounted on or adjacent its
upward facing surface a thermally sensitive
fuse 494 in series in an electrical circuit with pilot flame proving
thermocouple 480 and a solenoid coil in gas valve
469.
With reference to Fig 1, the size of air inlet plate 90 is dependent upon the
air consumption requirement for proper
5 combustion to meet mandated specifications to ensure low pollution burning
of the gas fuel. Merely by way of
general indication, the air inlet plate of Fig I should be conveniently about
3700 square mm in perforated area
when fitted to a water heater having between 35,000 and 50.000 BTU/hr
(approximate) energy consumption rating
to meet US requirements for overload combustion.
Figure 26 shows schematically an air inlet 490 to a sealed combustion chamber
including an aperture 487 in a
10 portion of the lower wall 486 of the combustion chamber and, overlapping
the aperture 487, a thin sheet metal air
inlet plate 490 having a perforated area 500 and an unperforated border 501.
Holes in the perforated area 500 of plate 490 can be circular or other shape
although slotted holes have certain
advantages as will be explained, the following description generally referring
to slots.
Figure 27 to Figure 41 show in each case an air inlet plate 490 of various
configurations as will be described to
15 admit air to the combustion chamber 475. The air inlet plate 490 is a thin
sheet metal plate having many small slots
504 passing through it. The metal may be stainless steel having a nominal
thickness of about 0.5 mm although other
metals such as copper, brass, niild steel and aluminium and a thickness in the
range about 0.3 mm to about I mm as
an indication, are suitable. Depending on the metal and its mechanical
properties, the thickness can be adjusted
within the suggested range. Grade 409, 430 and 316 stainless steel, having a
thickness of 0.45 mm to 0.55 mm are
20 preferred.
Figure 27 is a plan view of an air inlet plate 490 having a series of ports in
the shape of slots 504 aligned in rows.
All such slots 504 have their longitudinal axes parallel. The ports are
arranged in a rectangular pattern formed by
the aligned rows. The plate is about 0.5 millimetres thick. This provides
inlet plate 490 with adequate damage
resistance and, in all other respects, operates effectively. The total cross-
sectional area of the slots 504 is selected
25 on the basis of the flow rate of air required to pass through the inlet
plate 490 during normal combustion. For
example, a gas fired water heater rated at 50,000 BTU/hour requires at least
3.500 to 4,000 square millimetres of
port space in plates of nominal thickness of approximately 0.5 mm.
Figure 4 to Figure 41, and Figure 45, Figure 47, Figure 48 and Figure 49 show
numerous variations in the pattern
of slots 504 in the perforated area 500, each variation representing one of
many pattems which is suitable in the
practice of this invention. In each illustration of a plate 490, a pattem of
slots 504 and the size and shape of them
constitutes an important consideration for optimum function in the event that
extraneous flammable fumes
accidentally enter with the air entering the combustion chamber 475, thereby
creating a risk of accidental and
dangerous ignition of a substantial or significant quantity of such spilled
flammable volatile substance, such as
gasoline. external to the combustion chamber.
Figure 33 shows one particularly suitable pattern with longitudinal axes of
the edge slots 507 at right angles to
those of the ports 504 in the remaining perforated area 505.
The slots 504 are provided to allow sufficient combustion air through the
inlet plate 490 and there is no exact
restriction on the total number of slots 504 or total area of the plate, both
of which are determined by the capacity
of a chosen gas (or fuel) bumer to generate heat by combustion of a suitable
quantity of gas with the required
quantity of air to ensure complete combustion in the combustion chamber and
the size and spacing of the slots 504.
The air for combustion passes through the slots 504 and not through any larger
inlet air passage or passages to the
combustion chamber, no such larger inlet or air inlet being provided.
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26
While Figure 27 to Figure 45 and Figure 54 illustrate ports which are
elongated in shape, the present invention is
applicable to inlet plates formed with circular shaped ports as is illustrated
in Figure 53. or alternatively the slot
ports of the other figures can be replaced by circular ports preferably no
bigger than 0.5 mm or 0.6 mm.
To form the slots 504 or other form of port 502 one of several manufacturing
operations are appropriate. Such
operations include laser cutting, etching, photochemical machining, stamping,
punching, blanking or piercing. A
process of piercing and bending, sometimes referred to as lancing, can be used
to produce a slot formed as shown
in cross section in Figure 45. In the process a tool punctures a line in a
plate and a portion of the plate to one side
of the line is then displaced laterally to create a slot of desired length and
width W as shown.
We find the pattern of Fig 34 to have an advantage of good rigidity, favoured
by the off-set arrangement of adjacent
rows of slots 1 to 4.
Figure 42 shows a single slot 504 having a length L, width W and curved ends.
To confine any incident of the
abovementioned accidental dangerous ignition inside the combustion chamber
475, the slots 504 are formed having
at least about three times the length L as the width W and are preferably at
least about twelve times as wide. Length
to width (UW) ratios outside these limits are also effective. We found that
slots are more effective in controlling
accidental detonation wave ignition than circular holes although beneficial
effect can be observed with IJW ratios
in slots as low as about 3. Above UW ratios of about 15 there can be a
disadvantage in that in a plate 490 of thin
flexible metal possible distortion of one or more slots 504 may be possible as
would tend to allow opening at the
centre of the slots creating a loss of dimensional control of the width W.
However, if temperature and distortion can
be controlled then longer slots can be useful; reinforcement of a thin inlet
plate by some form of stiffening, such as
cross-breaking, can assist adoption of greater L!W ratios. L/W ratios greater
than about 15 are otherwise usefui to
maximise air flow rates and use of a thicker plate material than about 0.5 mm
or a more highly tempered grade of
steel, stainless steel or other chosen metal, can be expected to favour a
choice of a ratio of about 20 to 30. Also the
slot pattem shown in Figure 34 favours a choice of a relatively high UW ratio.
To perform their ignition confinement function, it is important that the slots
504 perform in respect of any species
of extraneous flammable fumes which may reasonably be expected to be involved
in a possible spillage external to
the combustion chamber 475 of which the air inlet plate 490 of the invention
forms an integral part or an
appendage.
In combustion science and engineering literature quenching diameters for
circular tubes for various gas species at a
pressure of one atmosphere and a temperature of 20 C in a mixture with air
have been determined and are tabulated
below: (Reference: Jones, H.R.N. "The Application of Combustion Principles to
Domestic Gas Burner Design",
British Gas plc, 1989, p57, quoting Harris, J. A. & South, R, Gas Engineering
Management 18, 153 (1978))
Gas Quenchin~ Diameter, mm
Methane 3.5
Ethylene 1.8
Ethane 2.5
Propane 2.9
Butane 3.0
Natural Gas 2.7
(For butane, an altemative source, quotes 0.12 inches or 3.0 mm which is
consistent but also lists an absolute
minimum quenching distance of 1.78 mm which is not consistent with other data
in Jones indicating that for
methane, another hydrocarbon in the same family as butane, the minimum
quenching distance is experienced with
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27
mixtures close to the stoichiometric ratio. See "Basic considerations in the
combustion of hydrocarbon fuels with
air" Bamett. H. C. & Hibbard, Robert R., eds.. Report 1300 of The National
Advisory Committee for Aeronautics,
by Propulsion Chemistry Division, Lewis Flight Propulsion Laboratory, 1957.)
We find that a quenching distance for either holes or slots in a thick metal
plate is not more than about 0.6 mm. We
have discovered the following factors account for the quenching distance that
we prefer is reduced substantially in
relation to the above tabulated values by reason of several variables.
Increase in temperature of a plate 490 and its immediate surroundings preheats
the unbumed gas/air mixture, which
increases its burning velocity and reduces the quenching distance. Also it has
been discovered by other workers that
preheating widens the flarnmability limits of a given gas species mixed with
air. For example, in methane/air
mixtures, at 200 C a primary aeration as low as 55% is flammable but at 20' C
mixtures below 65% are not
flammable.. Other flammable substance/air mixtures show the same phenomenon as
methane..
The quenching distance adopted for the slots 504 or other port 502 needs to be
modified downwards to allow for
preheating of the unburnt extraneous fume/air mixture which inevitably
obtains, although its intensity is variable
depending on specific water heater design parameters and other variables
associated with particular incidents. We
recognise that flame speed increases with preheat of the unbumt nuxture and
have read that for a mixture of butane
( as a convenient example of an extraneous fume species) with air that the
maximum flame temperature achievable
occurs with a slightly lean mix (about 103% air) and is about1900 C. In our
tests we measured typical air inlet
plate temperatures at 675 C maximum. Computer modelling of unburnt gas passing
through our highly preferred
0.5mm by 6mm long slots indicated a temperature of the unburnt gases reaching
375 C.. Our belief is that
preheating causes the flame temperature (1900 C) to be increased by about the
same amount as the preheat
temperature, i.e., to about 2275 C. Using relationships familiar to those
skilled in combustion engineering
principles it would be estimated that for paraffins such as propane or butane
a reduction in quenching distance of
about 30% is expected as a result of this amount of preheat. This must be
emphasised as an estimate only and
assumes for example that the temperature of the wall of the slot is the same
as the temperature of the unburnt
fume/air mixture passing through. However, we found this not to be true due to
natural draft "pulling" the mixture
through the plate 490 a heat transfer effect occurs but not to the extent that
it reaches anywhere near the red heat
observable on the combustion chamber side of the plate 490. Such temperatures
would be well in excess of the hot
surface ignition temperature of the extraneous fume species/ air mixture.
Since combustion has been reliably
observed to be confined within the combustion chamber the hot surface ignition
temperature is not attained in
practise. A further assumption made in estimating the 30% reduction in
quenching distance is that the fume/air
mixture is at the stoichiometric ratio. In the situations addressed by the
present invention there is no way of
controlling the air/extraneous fume ratio over a prolonged period of
combustion given the random nature of
accidental spillage situations wherein many different species of combustible
extraneous fumes and arrival of
potentially significant quantities of any or each at the inlet 490 to a fuel
burning appliance desired to be rendered
more safe, are random and unpredictable quantities spread over wide liniits.
Givert the random nature of variations
in these species and events and the possibility of pre-heat effects, we
determined that literature based estimates of a
quenching distance to adopt were insufficient to give the improved safety of
the water heaters of the invention and
we determined that a quenching distance not more than about 0.6mm in a thin
metal plate of about 0.5 mm
thickness is preferred and these we have a further preference for slots with
an L/W ratio of at least 3 but more
preferably about 12 but can in appropriate pattems be as high as about 20.
We found published literature ultimately gave little practical guidance. A
quenching distance can best be
determined with the assistance of some experimental observations for a given
design of air inlet plate 490 in a water
heater 462 having a combustion chamber 475. Our defined quenching distance is
affected by one or more of the
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28
following factors: the incoming air and extraneous fume temperature. as
affected by preheating: the ratio between
extraneous fumes and air; the nature of the extraneous fumes in relation to
its flame speed and flammability limits
in combination with air as an oxidant; appliance design related variables,
including flue length and therefore the
velocity of input air and extraneous fume mixtures and pressure difference
across the air inlet plate 490: the depth
and shape of the chosen air inlet ports 502: intemal construction of
combustion chamber 475 relative to the main
burner 474 positioning and the air inlet plate 490 positioning including
effects of back radiation from the burner to
the air inlet plate4 90 and any other internal or external restrictions to air
flow through the air inlet plate 490; the
material of the flame trap including its thermal conductivity, the emissivity
of its surface and the effect of any
catalytic substance having combustion influence applied to its surface; and
the effect of any combustion driven
oscillation of the system as a whole; this can be a factor depending on the
natural frequency of the structure as
constructed by comparison with the natural frequency and amplitude of any
combustion process occurring inside
the combustion chamber 475.
Figure 42 to Figure 44 show slot and inter-port spacing dimensions adopted in
the embodiments depicted in Figure
27 to Figure 41 generally, Figure 43 and Figure 44 particularly referring to
Figure 33 and Figure 34. The
dimensions of the ports are equal and have a length L of 6 mm and a width W of
0.5 mm. The ends of each slot are
semicircular but more squarely ended slots are suitable. The chosen
manufacturing process can influence the actual
plan view shape of the slot. However, metal blanking such large numbers of
holes can be difficult as regards
maintaining good condition of such small punches if the corner radii are not
rounded. The photochemical
machining process of manufacture of plates 490 with slots 504 is adapted to
also produce radiused comered slots.
The discussion has so far assumed ports 502 that are either circular 503 or
slot shaped 504. There is no reason that
the invention be restricted to such shapes. Slots 504 may in fact, be formed
as lines which can be curved or wavy.
The quenching distance of such non straight lines fits our definition and thus
is independent of length L so long as
L>3W. For squares, pentagons, hexagons or other polygons, the quenching
distance as we define it also applies.
The interport spacing illustrated in Figure 43 and Figure 44 performs the
required confinement function in the
previously described situation. The dimensions indicated in the Figure 43 and
Figure 44 were as follows:
C. 4.5 mm; E. 3.7 mm; J, 1.85 mm; K, 1.6 mm; M, 1.4 mm and P, 3.7 mm.
As one example, the inlet plate 490 having the dimensions and spacing of slots
504 as indicated above and the
pattem shown in Fig 33, during one testing procedure, allowed passage of fumes
of spilled gasoline through the
inlet plate 490 where they ignited inside the combustion chamber 475 and bumed
until 1 U.S. gallon was
consumed. This was done without the outside surface temperature of the inlet
plate 490 increasing at any point such
as to ignite fumes which had not yet passed through the inlet plate, the test
concluding when no more gasoline
remained to be consumed after more than one hour of continuous burning on the
plate 490.
We found by conducting experiments that interport spacing differences of 1.1
mm, 1.6 mm and 2.6 mm each gave
satisfactory results. Our experiments led us to believe that interport
spacings greater than 6 mm would be equally
successful. However, close interport distances are preferred because the
perforated area expressed as a percentage
of the total area of an air inlet plate 490 is greater for closer interport
distances, for example, with the slot
dimensions already given of 0.5 mm wide by 6 mm long perforated area
percentages are as follows:
Interport Distance mm 1 2 3 4
Perforated Area % 29 15.5 9.8 6.9
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We found interport spacings of 0.5 mm having slot dimensions 0.5 mm x 6 mm to
the Fig 4 pattem in 0.5 mm
thickness plates 90 not to be as versatile to all possible situations.
Figure 46 depicts schematically an outline of a lower portion of a water
heater 462 having an air inlet leading to a
combustion chamber 475 including a plate 490 of the type or similar to those
depicted in Figure 27 to Figure 41.
Because of the small size of the ports 502 in plate 490 they could, in certain
circumstances, be prone to block up or
become clogged with lint or other foreign materials. Furthermore, being at a
relatively inaccessible part of a water
heater 462, an accumulation of lint may not be noticed since water heaters in
general are usually not serviced
regularly.
Accordingly, it can be desirable to provide an accessible, more noticeable
lint filter 512 as now described. The inlet
plate 490 is connected to an air entry duct 510 which tums at right angles and
extends substantially horizontally to
the front of a water heater 462 whereupon it again turns at right angles to
extend upwardly to terminate any
convenient distance above the floor level, about 60 cm to 100 cm or higher
being suitable. Higher levels are
preferred because generally airborne lint levels decrease with increasing
height above floor level. The air entry duct
510 is nominally gas-tight (this term is amplified below) where it is
terminated by the inlet plate 490 at one end
portion and by a non-removable lint filter 512 facing the front of the heater
462 at an accessible height above floor
level.
The lint filter 512 has many accessible small holes which can be circular,
slotted or other shape, with no hole
individually substantially larger in dimensions than the lintiting distance as
above defined of the ports (502,504)
chosen in the particular air inlet plate 490 adopted. The total open area must
at least exceed the total open area of
the air inlet plate 490 so as not to add greater restriction to air flow than
the inlet plate 490 itself. To this end, it is
better if the lint filtering holes have in total a very much greater area for
air flow than the ports (502, 504) in the air
inlet plate 490 so that the total resistance to flow is minimised and,
furthermore, the available area for lint
interception is maximised. Most of the lint filtering holes are positioned
ideally as far above the floor as possible to
face the front of the heater so as to be accessible for cleaning routinely,
ideally with a vacuum cleaner. A safety
maintenance notice to occupiers of premises in which such water heaters or
other gas consuming appliances
benefiting from equivalent protection are installed, is ideally fixed adjacent
to the face of the lint filter 512 to
remind of the need for regular intervention to remove any apparent lint build-
up.
The duct 110 was above described as nominally gas tight - it is not required
to be fully gas tightly sealed, so long as
its connection to the combustion chamber wall 86 meets the criterion of having
no gap or crack exceeding the
defined quenching distance for any feasible extraneous fume species (entering
the air inlet) which is desired to be
confined if ignited, within the combustion chamber 75.
Fig 29 shows in schematic cross-section one suitable connection between an air
inlet plate 90 and lower wall 86 of
a combustion chamber 75. We observed that prolonged combustion of a relatively
large quantity of extraneous
fumes on the inside surface of the plate 90 (e.g. such as would vaporise from
the spill of one US gallon of
gasoline), leads to intermittent heating to incandescence at various points
around the inside surfaces various plates
90 tested. We observed as expected that heating to maximum incandescence of
the plates 90 particularly correlates
to extraneous fumes to air ratios close to the stoichiometric value for the
particular extraneous fumes. The air inlet
plate 90 in such circumstances acts like some types of perforated metal gas
burners which function at red heat such
as for broiling or grilling but, unlike any such burner of that type, the air
inlet plate in this invention must be able to
provide reliable confinement operation despite an uncontrollable and
uncontrolled spectrum of flow rates of
flammable fumes relative concentration in a mixture of air and the flammable
fumes. With our air inlet plate 90,
any pre-mixing of the air and extraneous fumes is incidental and random,
unlike the uniform pre-mixing of air and
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fuel in a normally designed gas bumer.
The form of construction shown in Figure 47 and Figure 48 shows two variants
in which separated from its
assembled position, an inlet plate 490 which has an unperforated bord'er 501
which is assembled downwardly (as
indicated by the dashed lines) in highly thermally conductive contact with a
combustion chamber opening 487
5 formed, such as by piercing and extruding, a flanged border 514 defining an
inwardly opening hole 487 into the
combustion chamber 475. The compressive contact, can be achieved by metal to
metal frictional contact involving
mating flanges 514 and 501 or may include some form of gasket between the
contacting faces of those flanges.
Figure 47 shows a circular plate 490 which fits tightly inside the flanged
border 514 around the extruded hole 487
in the combustion chamber wall 486. Figure 48 shows a rectangular plate 490
which fits tightly on the outside of
10 the flanged border 514 around the mating hole 487 in the combustion
chainber wall 486. It is optional whether
either the circular or the four-sided variant mates inside or outside the
flanged border.
While Figure 47 and Figure 48 show one method of affixing the air inlet plate
490 to the combustion chamber wall
486, a second method is illustrated in Figure 83, Figure 84 and Figure 85
which show another arrangement to
suitably 6x or seal the two components. It is intended that the air inlet 490
be substantially sealed against
15 combustion chamber wall 486 to prevent air and or extraneous fumes passing
between the surfaces of air inlet 490
and combustion chamber wall 486. Air inlet plate 490 has an outer flange 601
that extends beyond the edge of the
opening in combustion chamber wall 486. periodically, along flange 601,
mechanical crimps 602 are pressed into
flange 601 and corresponding portion of combustion chamber wall 486. Such
crimps 603 are well known in the
sheet metal art as TOG-L-LOC being a particular preferred example. Other
means of securing or fixing air inlet
20 plate 490 to combustion chamber wall 486 are possible, spot welding being
one of them.
Figure 49 to Figure 52 illustrate a rectangular inlet plate 490 including a
perforated central portion 505 bounded by
a non-perforated portion 501 which is formed to include a peripheral channel
516. The peripheral channel 516 is
shaped to enable the inlet plate 490 tightly engage, or otherwise to snap into
a mating connection 518 (Figure 52)
formed around an opening 487 in the base 486 of the combustion chamber 475.
The combustion chamber 475 with
25 inlet plate 490 fitted is enclosed at the top by a mating connection to or
adjacent the outside periphery of the curved
base of the tank 466 of a water heater 462 and so forms a closed combustion
chamber 475. Those potential sources
of ignition of extraneous fumes forming part of a water heater bumers 473 and
474 are enclosed by location in the
combustion chamber 475. The combustion chamber walls 479 support the mass of a
water tank 466. The peripheral
channel 516 in the inlet plate 490 and the mating peripheral groove 518
surrounding the opening 487 in the base of
30 the combustion chamber 475 frictionally engage to nominally sealed standard
as explained above. The groove 518
can function as a dam to exclude condensed moisture accumulating on the base
486 of the combustion chamber
475 from spreading across the perforated areas 505 of the plate 490.
Figure 53 to Figure 55 schematically show alternative forms of profiled ports
on a portion of air inlet plate. The
ports (slots in Figure 54) can provide a more streamlined flow profile through
them and can provide a convenient
"valley" matrix in which to position viscous form(s) of intumescent swellable
coating 536. The application of
intumescent swellable coating 536 to this invention will be described
subsequently in relation to Figure 62 to
Figure 64.
In relation to all the forms of inlet plate 490 so far illustrated. it is of
concern that an initial ignition of flammable
extraneous fumes inside the combustion chamber 475 as a sudden energetic
detonation be minimised. Otherwise,
there might theoretically be a risk of blowing a flame front back through the
ports 502, 504 of the inlet plate 490.
Forms of water heater 462 showri schematically in Figure 56 to Figure 58
particularly address this concern.
In Figure 56, the entire base 486 of the combustion chamber is positioned at
the top of a drawn wall 525 of the
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31
combustion chamber 475, the lowest perimeter of the combustion chamber
providing a support which rests on a
support pan 528 which in turn is supported above floor level on feet 484. The
base 486 of the combustion chamber
475 and the inlet plate 490 are co-planar or approximately so and, by virtue
of the described structure position the
inlet plate 490 as close as possible to the bumers 473, 474.
In Figure 57, the main burner 474 is conventionally positioned but the pilot
burner 473 is positioned immediately
above the inlet plate 490 upper surface. This provides opportunity for a more
immediate ignition of extraneous
fumes entering the combustion chamber 475 through the inlet plate ports 502,
504 and, thereby, substantially
increases the probability that only a very small quantity of extraneous fumes
would be in the combustion chamber
475 when ignition first occurs. Such a small volume of extraneous fumes, if
ignited, is likely to bum with a
relatively low energy of initial ignition prior to establishment of a
continuous flame upon the upper surface of the
inlet plate 490. In order to ensure reliable ignition of the main bumer 474 of
a water heater during normal
operation, when the pilot bumer is positioned particularly closely adjacent to
the inlet plate as shown in Figure 58,
a flash tube 530 is provided leading from the pilot bumer 473 up to the level
of emission of the gaseous fuel from
the main burner 474 to facilitate the frequent re-ignition of the main burrter
474 from the pilot burner 473 during
normal use of a water heater 462.
In order to avoid the development of high sound pressures various
predeterminable design parameters can be
chosen or operating conditions influenced to minimise undesirable effects. If
a design is prone to excessive sound
level generation, then changes to that design to lessen the tendency include
the reduction of temperature of the plate
490, changes to the length of the flue pipe 470, the spacing of ports 502 and
the thickness of the air inlet plate 490,
embossments to stiffen the air inlet plate 490 and gasket placement between
the plate 90 and combustion chamber
lower wall 486, as will be described.
Figure 59 to Figure 61 show arrangements to terminate prolonged combustion on
a plate 490 for use in those
instances in which it is desirable to extinguish that combustion quickly
rather than allow it to draw remaining
spilled extraneous fumes to consume them by combustion. Figure 59 depicts a
portion of air inlet plate 490 covered
by a thin layer 532 of solder which has matching ports 533 to those in the
plate 490. When this layer 532 is heated
by extraneous fumes burning on the inside of the combustion chamber 475, the
heated solder layer 532 liquefies
and spreads to block or tend to block the adjacent slot or slots 504. The
plate 490 may be also formed with surfaces
converging toward each slot 504, allowing the liquefied solder to more readily
block each slot.
Because of the small dimensions of the slots 504 the solder bridges them by
capillary action by virtue of its surface
tension,. so occluding them fully or, at least partially. Partial occlusion is
desirable even if full occlusion is not
achieved since any reduction of port cross-section area under the
circumstances tends to destabilise the flames,
thereby increasing the probability of extinguishing them quickly. To further
assist the flow of solder 532 the surface
of the plate 490 can be pre-treated with a fluxing agent such as widely known
in soldering techniques.
At times when the inlet plate 490 admits a near stoichiometric mixture of air
and extraneous fumes, particularly
over a prolonged period, then the temperature of the inlet plate 490 caused by
combustion of that mixture
inevitably increases. We discovered that upon a sufficient increase in the
temperature of the inlet, a harmonic
resonant sound may be generated by various complex thermal effects including
that known as the Rijke tube effect.
In certain embodiments of the invention, we discovered that these effects
cause energetic sound waves to be
produced in the combustion chamber 475, most noticeable when combusting at
around 100% aeration. This can
build to sound at a high level at a frequency or frequencies, usually in a
frequency range about 80-250 Hz during
operation, continuing until such time as the gas to air mixture changes
sufficiently away from the stoichiometric
value or buming conditions otherwise change
CA 02338078 2006-11-03
32
With reference to Figure 62 to Figure 64 a portion of inlet plate 490 is shown
in cross-section having a solid matrix
separated by ports 102. Closely positioned above the upper surface of the
inlet plate 490 is a sensor 494 applicable
to all variants of the present invention, being adapted to shut off the gas
supply to the main bumer 474 and pilot
burner 473 if a flame becomes established on the upper surface of the inlet
plate 490. In the inlet plate 490 shown
in Figure to Figure 64 an intumescent ablative coating 536 has been applied to
cover the solid matrix of the inlet
plate, leaving (in Figure 62) the ports 502 unobstructed. As shown in Figure
63, if extraneous fumes enter through
the ports 490, and form a combustible mixture in the combustion chamber 475,
the main bumer 474 or pilot bumer
473 (as shown in Figure 24, positioned typically 5 - 10 cm above the inlet
plate) would establish ignition of the
extraneous fumes as flames 537 on the upper surface of the inlet plate 490.
The sensor 494 then reacts quickly to
cause shut-off of gas to the main and pilot burners (474, 473).
Combustion on the plate 490 most likely continues and the flames 537 cause the
temperature of the inlet plate 490
as a whole to rise and at a temperature appropriate to the intumescent coating
selected, the coating 536 softens and
reacts, to swell to numerous times its original volume (Figure 64), thereby
occluding the ports 502 of the inlet plate
490. Such occlusion has the effect of excluding the extraneous fumes and air
so combustion on the inlet plate 300
quickly ceases. No further possibility then exists of igniting extraneous
fumes inside or outside the combustion
chamber 475 without replacing the plate 490. Suitable intumescent/ablative
coatings include "FIRETEX"TM
"M70/71" (basecoat/top seal intumescent fire retat'dant coating, manufactured
by Fyreguard); and "FIREDAM TM
2000" intumescent coating supplied by 3M. A coating thickness of about 200pm
on a SCHWANK tile or plate of
the types shown in Figure 55, Figure 54 and Figure 55, is suitable and a
lesser thickness about 100 m, is more
appropriate for a flat or substantially flat perforated metal sheet type inlet
plate 490 as illustratld in Figure 62 to
Figure 64.
Figure 65 to Figure 70 show a series of devices in which a prolonged
combustion incident inside a combustion
chamber 475 can be more quickly extinguished. Mounted to the inlet plate 540
is a sliding plate 541 which has
ports 502 of corresponding size, pattems and orientation to the ports 502 in
the fixed inlet plate 540. Figure 66
shows alignment of the ports 502 to provide a through passage for air and
extraneous fumes to pass. The sliding
plate 541 is biased to the position shown in Figure 66 by one or more
spring(s) 543, which as depicted in Figure 65
can be tension spring(s) 543. The sliding plate 541 is locked into one
location by a solder or thermoplastics pin
544. tension being applied to the spring 543. The sliding plate 541 can move
by sliding relative to the fixed plate
540. guided in a restricted path by sealed rivets 542 which are secured leak
tightly to the fixed plate 540 and which
are a sliding fit into a pair of guide slots in the sliding plate 541.
In the event that extraneous fumes pass through the fixed inlet plate 540 and
sliding plate 541, the extraneous
fumes with an appropriate air mixture would be ignited by either the pilot 473
or main burner 474 of the water
heater 462. Following a short period of buming, the sliding plate 541 would
heat to a temperature sufficient to melt
the solder or thermoplastics pin 544 whereupon the force applied by the spring
543 would move the sliding plate
541 in the direction of the arrow. The guide slot(s) can only be long enough
to allow unperforated parts of sliding
plate 541 to align with the ports 502 in fixed plate 540 or, as an altemative.
the slots 502 can be longer but two
stops 146 can be provided to limit the travel of the sliding plate 541 over
the fixed plate 540 and, either way, as
shown in Figure 67, result in the closure of all the ports 502 thus
extinguishing any further combustion.
To reopen the combustion chamber 475 after an episode of ignition of
extraneous fumes, the sliding plate 541 is
held against the bias provided by the spring 543 while placing a replacement
solder or thermoplastics pin 544 into
the aligned holes provided for the purpose through the plates 540, 541. The
air inlet 490 would then be functional
again to allow nprmal cqmbustion air flow but to cut off air and extraneous
fumes if needed.
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ln a suggested variation of the inlet cut-off of Figure 65 to Figure 67. the
solder or thermoplastics pin can be
replaced by a thin layer of solder between the plates. This layer of solder
creates a laminate of the two metal plates
sandwiching the solder, being also provided with ports aligned initially
through all three layers of the laminate.
Connection of the sliding plate to a spring could be provided as shown in
Figure 65 or equivalent. This variation
has advantages including that the solder facilitates relative sliding between
the plates once the solder liquefies due
to heat input. Moreover, its ability to exclude extraneous fumes from finding
a leakage access between the plates is
an advantage. The sliding plates shown in Figure 65 to Figure 67 could be
susceptible to seizure in their open
position in the likely event of only extremely rarely being activated and, to
move, any friction between them must
be overcome. This suggested variation having a laminate of solder between
slidable plates will not seize and once
the solder liquefies, will slide freely.
Figure 68 to Figure 70 show a similar occluding mechanism to those of Figure
65 to Figure 67, although in this
case the cut-off of air entry is by relative rotation between the plates
rather than linear movement.
Figure 68 shows a circular inlet plate like that illustrated in Figure 25.
Overlying the fixed plate 540 is a rotary
plate 541 with ports 545 aligning with ports 502 in fixed plate during normal
use, as shown in the cross section of
Figure 69. Secured to the fixed plate 540 is one end of a spindle 149, which
carries, at its other end, one end of a
bimetallic torsion spring 548 which in tum, at its other end, is attached to
the rotary plate, by a pin 550. Upon
heating of the bimetallic torsion spring 548 by the buming of extraneous fumes
at the ports 545 the bimetallic
torsion spring 548 rotates the rotating plate 541 relative to the fixed.plate
540. Appropriate stops between the two
plates 540, 541, are provided to enable the respective ports 502 and 547 to
remain out of mutual alignment, as
shown in Figure 70.
Upon cooling of the bimetallic torsion spring 548, the rotating plate 541
retuarns to its original position bringing the
ports 502, 545 in both plates into alignment again, ready to allow air to pass
through to enable combustion and to
allow extraneous fumes if present, to pass through.
Figure 68 to Figure 70 features can be combined, such as the bimetallic
torsion spring 548 being replaced by a coil
spring or other spring, and the plates 540, 541 being held in register (to
allow air to pass) by a solder or
thermoplastics plug 544 or a layer of solder between them, in each case
relying on heat to melt the solder or
thermoplastics, so allowing the spring force to rotate the rotating plate 541
relative to the fixed plate 540 to shut off
combustion of extraneous fumes in the combustion chamber 475.
Inlet plates of the invention which have ports solely in the shape of slots
504 allow flames burning extraneous
fumes inside the combustion chamber 475 to lift further off the air inlet
plate 490 and thereby reduce the operating
temperature of the air inlet plate 490 as compared to a plate of the same
material and thickness having circular
holes 503. Therefore, a plate 490 with slots 504 can consume more spilled
substance over a longer combustion
period, than can a plate 490 with holes 503 having an equivalent Quenching
distance. Also, slots 104 enable lint
passage more readily than holes of equivalent quenching distance.
Figure 71 shows two additional provisions possible to incorporate, so
enhancing the likelihood of a safe outcome
following a flammable substance spillage incident near a gas water heater
having an air inlet 490 according to the
invention. Either provision may be included separately or together.
The first provision is an audible alarm 558 which operates in the event of a
flame becoming established in the
combustion chamber 475 at or adjacent the inside surface of the air inlet
plate 490. The alarm 558 can be actuated
by a number of energy sources, one being an enclosed metallic bulb 555
containing a volatile substance which
expands when heated, the bulb 555 being connected to the alarm by a small bore
tube. The tube is sealed by a
frangible diaphragm that bursts to vent the volatile substance through a
whistle or similar audible device included
CA 02338078 2001-01-18
WO 00/06947 PCT/AU98/00585
34
in the alarm 558.
The second provision is a cooling device including a spray nozzle 556
positioned and aligned capable of directing a
fine spray of water 557 at the perforated area of the air inlet plate 490. The
water 557 is sourced from the mains
pressurised cold water supplied to the tank through a pipe 551, diverted
therefrom by a branch pipe 552 through a
valve 553, the outlet of which is connected to the spray nozzle 556. The valve
553 is biased in a normally closed
position and is opened to allow passage of water through the valve by lateral
admission of a pressurised fluid via a
small bore tube 154. The pressurised fluid is in tum sourced from the
temperature sensitive element 555 on any
such occasion that it is heated by flame arising from combustion of extraneous
fumes on the inside surface of the
air inlet plate 490. Other flame extinguishing substances such as compressed
carbon dioxide may be suitable and
can be released using generated heat to similarly open an appropriate escape
path.
Figure 73 to Figure 75 shows the possibility of forming the ports 502 in
plates 490 of the invention having not only
a parallel sided cross-section, as shown in Figure 72, which can be readily
formed by any of the processes
previously mentioned. Ports 502 can be used, which in cross-section have both
convergent and divergent shapes.
The photochemical machining process lends itself to forming holes with
convergent or divergent shapes as
illustrated in Figure 473, Figure 74 and Figure 75.
Figure 73 shows a hole 563 or slot 565 which converges from a larger dimension
at the upstream face (i.e. the
lower side, as illustrated) of the air inlet plate 490. Air and, if present,
extraneous fumes, passes through the
tapering hole 563 or tapering slot 565 in a downstream direction indicated by
the two vertical arrows into the
combustion chamber 475. The hole 563 or slot 565 as illustrated in Figure 73
converges in an upstream direction
firstly but then ternunates with substantially parallel sides
Figure 74 shows a tapered hole 567 or tapered slot 569 which converges to a
throat of nanimum cross-sectional
area between the upstream and downstream faces of the air inlet plate 490
which tends to provide minimum drag
for a given limiting dimensiori of the port 567, 569. By this technique the
air inlet plate 490 can provide an
optimised combination of maintaining restriction to air flow within workable
bounds with ability to confine
combustion inside the combustion chamber 475 for as long a time as necessary.
Figure 75 shows a tapering hole 571 or tapering slot 573 in which air for
combustion passing through the air inlet
plate 490 in the direction of the vertical arrows into the combustion chamber
475 first passes through a divergent
portion which then converges such that the intersection of the port 571, 573
intersects with the inside (upper)
surface of the plate 490 at an angle somewhat less than 490 . The very sharp
edged orifice so formed at the inside
surface of the air inlet plate 490 may function as a flame lift promoter so
that combustion of extraneous fumes
occurring near the inside surface of the plate 490 is encouraged to lift
flames away from that surface, with the effect
of causing the plate to remain cooler during prolonged buming or, even more
preferably, to cause the flame to lift-
off entirely and extinguish. The tapered ports of Figure 73, Figure 74 or
Figure 75 can be formed by applying
higher concentration of etchant solution to one side of the metal sheet from
which the air inlet plate 490 is
constructed, until the ports are perforated to the required shape.
With reference to Figure 77, the air inlet plate 490 with perforations 504 is
provided with diagonal cross-breaking
lines 580 which can provide the plate 490 with additional stiffness in order
to change the natural frequency of the
combination of the combustion chamber 475 and connected air inlet plate 490 to
move that natural frequency away
from a frequency of combustion process which may occur if extraneous fumes
entering the air inlet chamber
become ignited inside the combustion chamber 475. Depending on the frequency
of combustion encountered for a
particular design of water heater, the stiffened structure shown in Figure 77
may be even more efficient than a
corresponding flat air inlet plate 490 as illustrated in Figure 58.
CA 02338078 2001-01-18
WO 00/06947 PCT/AU98/00585
In Figure 81 an air inlet plate 490 having slots 504 is shown having
stiffening members extending at 90" to each
edge of the plate 490. In the case of Figure 51, the central perforated area
as shown in Fig 35 is altered by deleting
a suitable number of rows of slots followed by the forming of one or more
rounded channels 582 extending in one
or more directions across the unperforated portions of the perforated area 500
of the plate 490. The stiffening of the
5 plate 490 and the dividing of it into a number of smaller separated
perforated areas by the rounded channels 582
causes both a change in the natural frequency of mechanical vibration of the
structure of the combustion chamber
in a particular water heater 462 with the air inlet plate 490 fitted and also
changes the acoustic frequency of any
combustion process that occurs at the air inlet plate 490 as a result of
extraneous fumes entering the combustion
chamber 475 and igniting. Thus the incorporation of a perforated plate 490 as
illustrated in Fig 81 can be beneficial
10 in providing an increased level of safety for a water heater of this
invention. Any troublesome resonance during
combustion can be reduced or prevented by stressing the base 486 of the
combustion chamber 475 to change the
natural frequency of the stntcture as a whole. One approach to make the
structure effectively immune to
troublesome acoustic related problems is as shown in Fig 82, in which the air
inlet plate 490 mounted to the base
486 of the combustion chamber is separated from the support pan 528 by
compressing a batt 584 of fibrous heat
15 insulation such as, KAOWOOL (registered trade mark) and, adjacent the
perimeter of the air inlet plate 490, a loop
or, alternatively, for a rectangular shaped air inlet plate 490, two to four
lengths, of fibreglass rope 586 under
additional compression. This is one alterna/ive form of rigidising and
muffling which particularly effectively
enables damping of combustion induced oscillation from exciting vibration of
the water heater structure, further
enhancing effectiveness.
20 It is to be understood that the invention disclosed and defined herein
extends to all altemative combinations of two
or more of the individual features mentioned or evident from the text or
drawings. All of these different
combinations constitute various alternative aspects of the invention.
The foregoing describes embodiments of the present invention and
modifications, obvious to those skilled in the
art, can be made to them without departing from the scope of the present
invention.
