Note: Descriptions are shown in the official language in which they were submitted.
CA 02351297 2001-06-26
15-578
BURNER WITH VENTURI NOZZLE
Field of the Invention:
The present invention is directed to a burner and, in particular, to a burner
including a body formed by opposing plates and a venturi nozzle adjacent to
the
body.
Background of the Invention:
One type of residential, light commercial water heater burner is formed of
stamped sheet metal and includes two sheet metal plates or spreaders which
form a
chamber when the plates are fastened together. A plurality of ports extend
radially
outwardly from the chamber. The burner includes a central axis and the upper
and
lower plates include outer peripheries that are radially spaced from the
central axis.
The lower plate includes an inlet opening for air and fuel to enter the
chamber. A
gas conduit has an orifice that is spaced from the inlet opening of the
burner. Gas
from the orifice travels across the space and, along with primary air
entrained by it,
enters the inlet opening of the burner. This type of sheet metal burner does
not
employ a venturi as part of the burner. A bracket is fastened to the lower
plate for
securing the burner in place and for controlling the orifice distance from the
plates.
Another type of water heater burner having a higher input capacity (Btuh)
than a sheet metal burner is formed of cast iron. Such a burner is especially
adapted for use in commercial applications. Cast iron may be more difficult to
form
than sheet metal and is significantly more costly. The cast iron burner
includes
upper and lower horizontally extending cast iron plates or spreaders which
form a
chamber when the plates are fastened together. A plurality of ports extend
radially
outwardly from the chamber. The burner includes a central axis and the upper
and
lower plates include outer peripheries that are radially spaced from the
central axis.
The cast iron burner is different from the sheet metal burner in that it
employs a cast
CA 02351297 2001-06-26
iron, horizontally extending venturi. Also, downstream of the venturi is a
mixing tube
of increasing cross-sectional area in a direction of gas flow that extends
horizontally
and then bends upwardly and extends to the lower plate.
The sheet metal and cast iron burners have different input capacities,
performance and durabilities. The cast iron burner may be more expensive to
fabricate. The input capacity of a sheet metal burner is usually less than for
a cast
iron burner with the same port area and burner height. Using natural gas or
liquified
petroleum ("LP") gas, such as butane and propane, the cast iron burner has a
significantly higher input range than the sheet metal burner. At high input
rates, the
sheet metal burner has a tendency to undesirably candle on LP gas due to low
air
entrainment velocity and high specific gravity of the gas. That is when fuel
to the
burner is shut off, unburned fuel in the burner along with fuel in the gas
conduit
support a yellow flame at the orifice, which leads to carbon build up at the
orifice
and inside the burner. Therefore, for many years water heater manufacturers
have
used the more costly cast iron burners rather than the sheet metal burners for
higher input capacity applications.
Summary of the Invention:
In general, the present invention is directed to a burner that can receive
fuel
from a conduit and air, and can discharge a fuel/air mixture for combustion at
a
periphery of the burner. The burner includes first and second plates which are
constructed and arranged relative to one another so as to form a central
chamber.
A plurality of burner ports extend outwardly of the chamber. A venturi nozzle
includes a first inlet end portion which is disposed adjacent to the fuel
conduit and a
second end portion which is spaced apart from the first end portion and
disposed
near the second (e.g., lower) plate. In particular, the venturi nozzle may be
contiguous with the second plate. The venturi nozzle includes an internal
passageway of decreasing cross-sectional area between the first and second end
portions in a direction of flow. The venturi nozzle of the present invention,
in view of
its proximity to the second plate, advantageously causes fuel directed from
the
conduit to increase in velocity and decrease in pressure effective to entrain
air into
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the venturi nozzle, which is substantially mixed only in the chamber between
the
plates. This enables the burner to have a high input capacity and yet be
compact so
as to be ideally suited for use in a water heater.
In a preferred embodiment the burner comprises the first and second plates
constructed and arranged relative to one another so as to form the central
chamber.
The plurality of burner ports extend outwardly of the chamber. A venturi
nozzle
includes a first inlet end portion which is disposed adjacent to the fuel
conduit and a
second end portion which is spaced apart from the first end portion and
contiguous
with the second plate. The venturi nozzle includes an internal passageway of
decreasing cross-sectional area between the first and second end portions in
the
direction of flow, the cross-sectional area being at a minimum at the second
end
portion of the venturi nozzle.
Referring to more specific. aspects of the invention, an end portion of the
second plate forms an internal passageway having an increasing cross-sectional
area in the direction of flow and the second end portion of the venturi nozzle
is
contiguous with the end portion of the second plate. The internal passageway
of the
venturi nozzle may have any suitable shape and is preferably either tapered or
radiused. The burner may be formed of sheet metal, which enables it to be
fabricated much cheaper than cast iron burners, and yet exhibits high input
capacities typically effectively attained only by cast iron burners. In use,
the burner
is typically oriented such that the venturi nozzle extends generally
vertically and the
first and second plates extend generally horizontally.
In a preferred aspect relating to the compact size and surprising high input
capacity of the inventive burner, a ratio of burner diameter to venturi nozzle
height
ranges from about 5:1 to about ~ :1.
The venturi nozzle results in a venturi effect in the inventive burner. The
jet
of gas from the conduit or orifice achieves a high velocity in the "throat" of
the
nozzle with the resulting low pressure pulling in air around the gas jet. The
air
inspirited by the inventive burner is greater than in a conventional sheet
metal
burner. In the inventive burner the air and gas are better proportioned and
mixed
for improved combustion. The irnprovement in the air entrainment ability of
the
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burner results in increased burner capacity even using spreaders or plates
formed
of sheet metal. The higher velocity air entrainment also provides momentum
which
is some cases may eliminate candling on LP gas, especially at burner
extinction.
The venturi nozzle may be used without appreciably increasing the height of
a conventional sheet metal burner. Typical sheet metal burners employ the
mounting bracket below the lower plate which provides a space between the
burner
and the gas nozzle or orifice. The inventive venturi nozzle has a length which
approximately fits into this space. The venturi nozzle may be formed separate
from
or integral with the lower plate. Another advantage is that the burner may be
mounted in a water heater in a manner that is unchanged from current assembly
methods. The sheet metal burner input capacity may be increased using both
natural and LP gases. This enables the inventive burner to be used in higher
capacity water heaters installed in larger homes, multiple dwelling
apartments,
commercial applications and the like. The burner may be designed to operate
with
low CO and low NOx emissions. The burner advantageously may eliminate the
problem of candling of LP gas at the orifice on extinction which occurs when
conventional sheet metal burners are attempted to be used at high input
capacities.
Also, using sheet metal, the burner may be fabricated much cheaper than cast
iron
burners.
A method of operating a burner in accordance with the present invention
comprises directing fuel from the conduit into the internal passageway of the
venturi
nozzle. The velocity of the fuel is increased and its pressure decreased by
directing
the fuel through the venturi nozzle. Air is entrained into the venturi nozzle
as a
result of the decreased pressure of the fuel. The fuel and entrained air from
the
venturi nozzle enter the chamber where substantially all of the mixing occurs.
The
fuel/air mixture is discharged at the periphery of the burner and combusted.
In the
preferred method the fuel and entrained air flow from second, most constricted
end
portion of the venturi nozzle directly into the end portion of the second
plate.
Other embodiments of the invention are contemplated to provide particular
features and structural variants of the basic elements. The specific
embodiments
referred to as well as possible variations and the various features and
advantages
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of the invention will become better understood from the accompanying drawings
together with the detailed description that follows.
Brief Descri,~tion of the Drawina~:
Figure 1 is a perspective view of a water heater with a burner constructed in
accordance with the present invention;
Figure 2 is a partial, vertical cross-sectional view of the apparatus of Fig.
1;
Figure 3 is a bottom plan view of the burner of Fig. 1;
Figure 4 is a cross-sectional view of the burner as seen from the lines and
arrows designated 4-4 in Fig. 3;
Figure 5 is a side elevational view of a low NOx burner constructed in
accordance with the present invention having a venturi nozzle with a tapered
internal passageway; and
Figure 6 is a side elevational view of a low NOx burner constructed in
accordance with the present invention having a venturi nozzle with a radiused
internal passageway.
Detailed Description of Preferred Embodiments:
Referring now to the drawings, and to Figs. 1-4 in particular, a burner
constructed according to the present invention is shown generally by reference
numeral 10. The burner includes a body 12 formed by opposing plates 14, 16 and
a
venturi nozzle 18 disposed near the lower end of the body which enables the
burner
to improve its input capacity. The burner may be formed of any suitable
material, for
example, aluminized steel, cold rolled steel, stainless steel, ceramic or cast
iron,
and the plates and venturi nozzle may be formed of combinations of these
materials.
The burner is used in a water heater 20 which includes a tank 21 forming an
enclosure for containing water. The tank is connected to a cold water intake
22 and
to an outlet pipe 24 leading to a commercial or domestic water system. The
tank
includes an interior wall 26, exterior wall 28 and a central exhaust flue 30,
which is
vented in the conventional manner. The water heater includes commercially
available temperature control devices shown generally by reference numeral 32
CA 02351297 2001-06-26
including thermostats, thermocouples and switches. A pilot 34 produces flame
for
ignition of gas emitted from the periphery of the burner and is controlled in
a known
manner. A mounting bracket 36 is attached to the body of the burner and to a
gas
conduit 38 below the burner. The gas conduit includes a discharge nozzle 40
that is
generally axially aligned with the burner. The burner can receive primary air
and
gas, and discharge an gas/air mixture at its periphery for combustion.
The body of the burner has a central axis C and comprises the upper and
lower, generally circular plates 14, 16, which are constructed and arranged
relative
to one another so as to form a central chamber 42 (i.e., the internal region
of the
burner formed by the first and second plates). The upper and lower plates are
fastened together as by rivets or spot welding in the known manner as shown in
fig.
3. A plurality of burner ports 44 (only one of which is labeled for clarity)
extend
radially outwardly from the chamber (Fig. 3). Each of the upper and lower
plates
has an outer periphery P spaced radially from the central axis. Referring to
Fig. 4,
the upper and lower plates include a plurality of continuous, generally U-
shaped
walls 45. When the upper and lower plates are placed against each other
forming
the chamber, the walls 45 contact each other at abutment surfaces S and from
enclosures (i.e., the ports 44).
The lower plate includes a partially frustoconical end portion 46 which forms
an internal passageway 48. Ths~ internal passageway 48 has a minimum cross-
sectional area at its lowermost point 50 which continually increases in a
direction of
flow F. The lower end portion of the lower plate includes a central opening
52.
The venturi nozzle of the burner includes upper and lower end portions 54,
56, respectively. Formed by the venturi nozzle is an internal passageway 57
which
has a decreasing cross-sectional area between its lower end portion 56 and
upper
end portion 54 in the direction of flow. The internal passageway 57 of the
venturi
nozzle is aligned with the internal passageway 48 of the lower plate along the
central axis C. The upper end portion of the venturi nozzle is disposed near
the
lower plate. In the present invention the venturi nozzle is advantageously
positioned so that the component which increases in cross-sectional area
immediately downstream of the venturi nozzle is the body of the burner. In
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CA 02351297 2001-06-26
particular, the upper end portion 54 of the venturi nozzle is preferably
contiguous
with the lower end portion 46 of the lower plate.
The body of the burner interacts directly with gas and air from the venturi
nozzle such that mixing occurs primarily in the chamber 42 formed by the upper
and
lower plates. In preferred form, the burner is more compact, fabricated more
economically and is able to achieve the advantageous effects of the invention
without the use of a mixing tube of increasing cross-sectional area between
the
venturi nozzle and lower plate. ~fhe preferred inventive burner is quite
compact in
size and capable of operation at increased capacity, and is ideally suited for
use in
water heaters where space is limited. In this regard, a ratio of burner
diameter (i.e.,
largest plate diameter) to venturi nozzle height ranges from about 5:1 to
about 7:1.
It may be possible for a tube to be employed between the venturi nozzle and
second
plate so long as the tube does not increase in cross-sectional area in the
direction
of flow effective to function as a mixing tube and so long as the tube is not
of a
length which prevents the venturi effect from occurring substantially as a
result of
interaction between the venturi nozzle and body of the burner.
The cross-sectional area of the venturi nozzle's internal passageway 57 is
preferably at a minimum at its upper end portion 62. The upper end portion of
the
venturi nozzle is preferably contiguous with the lower end portion of the
lower plate.
The lower end portion of the lower plate includes a collar 64 forming the
opening 52. The upper end portion of the venturi nozzle is sized so as to
closely
approximate the size of the opening 52 in the lower plate. The upper end
portion of
the venturi nozzle is inserted into the collar and secured in place as by tack
welding
or mechanically expanding the diameter of the venturi nozzle to that of the
opening
52.
The bracket 36 is fastened as by rivets 37 to the lower plate. The bracket
includes two upright legs 66 extending from a lower base 68. Included in the
base
of the bracket is a central threaded opening 70 (Fig. 3) sized to engage
external
threads 72 formed on the gas nozzle. Alternatively, the bracket may be
fastened to
the gas nozzle by some other means such as an unthreaded opening in the base
of
the bracket for receiving the gas conduit and wherein the bracket is screwed
into
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place.
The venturi nozzle may have any shape of decreasing cross-sectional area.
For example, the venturi nozzle may employ a tapered internal passageway 74 as
show in fig. 5. An alternate design of the venturi nozzle may employ a
radiused
internal passageway 76 shown in Fig. 6. The venturi nozzle may be formed
separately from the lower plate. Alternatively, it may be possible to form the
venturi
nozzle integrally with the lower plate.
The burner may employ upper and lower plates which extend radially
oufinrardly from the central axis by the same or different distances as one
another.
It will be appreciated that the venturi nozzle of the burner shown in Figs. 1-
4, which
has upper and lower plates which extend substantially the same distance from
the
central axis, may include the tapered or radiused internal passageway shown in
Figs. 5 and 6. The burner may employ a lower plate that extends outwardly from
the
central axis by a greater distance than the upper plate as shown in Figs. 5
and 6 so
as to enable low NOx operation as disclosed in U.S. Patent Application Serial
No.
09/565,107, entitled "Low NOx Burner," which Was filed on May 5, 2000 and is
incorporated herein by reference in its entirety. The inventive burner may
also be
modified to include any other conventional low Nox burner features known to
those
skilled in the art.
The gas may be natural gas, LP gas or the like. The gas is supplied through
the conduit and travels through the nozzle or orifice. The gas increases in
velocity
as it passes through the venturi nozzle's internal passageway and is at a
highest
velocity at the smallest cross-sectional area portion 62. This increase in
velocity
results in a decrease in pressure which entrains primary combustion air into
the
venturi nozzle. The gas and entrained air travel from the upper end portion of
the
venturi nozzle directly into the lower opening 52 of the lower plate. The
partially
frustoconical portion of the burner that forms an increasing cross-sectional
area is
disposed immediately downstream of the venturi nozzle. Substantial mixing of
the
gas and entrained air takes place in the chamber 42 formed by the body of the
burner rather than in a mixing tube used in prior art designs. The upwardly
flowing
gas and entrained air travel inside the chamber of the burner and impinge upon
an
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inner surface of a central concave portion 72 of the upper plate (Fig. 1 ),
which mixes
the gas and air. The resulting air/gas mixture then flows uniformly radially
outwardly
in all directions through the plurality of ports.
Although the invention has been described in its preferred form with a certain
degree of particularity, it will be understood that the present disclosure of
preferred
embodiments has been made only by way of example and that various changes may
be resorted to without departing from the true spirit and scope of the
invention as
hereafter claimed.
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