U.S. patent number 3,783,854 [Application Number 05/277,073] was granted by the patent office on 1974-01-08 for flow-through self-cleaning gas oven with heat exchanger.
This patent grant is currently assigned to General Electric Company. Invention is credited to Raymond L. Dills, Bohdan Hurko.
United States Patent |
3,783,854 |
Hurko , et al. |
January 8, 1974 |
FLOW-THROUGH SELF-CLEANING GAS OVEN WITH HEAT EXCHANGER
Abstract
A self-cleaning gas-fired oven having a power burner beneath the
oven cooking cavity so the flue gases pass up through the cooking
cavity and exit through an oven exhaust means at the top rear of
the oven. A counterflow heat exchanger rising from the oven exhaust
means, and an air collector means at the bottom of the heat
exchanger to convey the preheated cooling air to the power burner
by means of a motor-blower unit. The heat exchanger is of special
design with cylindrical flue gas tubes so the opposite wall plates
operate at relatively cool temperatures.
Inventors: |
Hurko; Bohdan (Louisville,
KY), Dills; Raymond L. (Louisville, KY) |
Assignee: |
General Electric Company
(N/A)
|
Family
ID: |
23059285 |
Appl.
No.: |
05/277,073 |
Filed: |
August 1, 1972 |
Current U.S.
Class: |
126/21R |
Current CPC
Class: |
F24C
14/025 (20130101) |
Current International
Class: |
F24C
14/00 (20060101); F24C 14/02 (20060101); A21b
001/28 () |
Field of
Search: |
;126/19,21,273 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Favors; Edward G.
Attorney, Agent or Firm: Richard L. Caslin et al.
Claims
What is claimed as new and is desired to be secured by Letters
Patent of the United States is:
1. A gas oven comprising a substantially box-like oven liner having
a front opening, and an oven door cooperating with the opening for
defining an oven cooking cavity, a fire box located beneath the
oven liner, gas burner means positioned in the fire box, flue gas
inlet openings in the bottom wall of the oven liner for passing the
flue gases into the cooking cavity, oven exhaust means positioned
adjacent the back of the oven liner near the top thereof, and a
counterflow heat exchanger at the back of the oven rising up from
the oven exhaust means, the heat exchanger having both flue gas
vent means and ambient air inlet means at the top of the heat
exchanger so that the ambient air extracts much of the heat from
the flue gases as they pass through the heat exchanger, and a
collector means attached to the bottom of the heat exchanger and
communicating with the burner means so that the ambient air flowing
down through the heat exchanger becomes heated and passes to the
gas burner means as preheated air to support combustion.
2. A gas oven as recited in claim 1 wherein the said counterflow
heat exchanger comprises a collapsed corrugated sheet metal panel
forming a generally flat closed wall plate with a plurality of
vertical spaced cylindrical flue gas tubes on the innermost side of
the wall plate, and a generally flat wall plate held across the
cylindrical tubes thereby forming alternate cooling air channels
between the gas tubes, whereby the flue gases are adapted to pass
by convection up the cylindrical tubes and the ambient air is
adapted to pass down through the cooling air channels, whereby the
outer wall plates operate at relatively cool temperatures during
the operation of the heat exchanger as compared with the
temperature of the flue gases.
3. A gas oven as recited in claim 2 wherein the said gas burner
means is furnished with a compressed air supply means for supplying
fresh combustion air to the burner means, said air supply means
being connected to the said air collector means beneath the heat
exchanger to draw the ambient air down through the heat exchanger
as preheated air before delivering it to the gas burner means.
4. A gas oven as recited in claim 3 wherein the said air supply
means is a centrifugal motor-blower unit located adjacent the gas
burner means beneath the oven liner.
5. A pyrolytic self-cleaning gas-fired oven comprising wall means
defining an oven cooking cavity, a bake burner at the bottom of the
oven cavity, an exhaust flue in the said wall means adjacent the
upper rear of the cavity for discharging flue gases from said oven
cavity, and a counterflow heat exchanger rising up from the exhaust
flue and located generally above the oven cooking cavity so as to
create a strong natural draft up through the heat exchanger and
avoid the necessity of a circulation fan, and an oven control panel
located in front of the heat exchanger, an air inlet means adjacent
the top of the heat exchanger, air collector means behind the oven
joined to the bottom portion of the heat exchanger and open to the
bake burner means to furnish preheated air to the burner to improve
the efficiency of combustion, the top of the heat exchanger having
flue gas vent means directed outwardly away from the back of the
oven with cooling means in conjunction with a warming shelf to
serve as a secondary heat exchanger.
6. A pyrolytic self-cleaning gas-fired oven as recited in claim 5
wherein the said bake burner means is a powered burner that is
furnished with a forced air supply means, the said air collector
means from the bottom of the heat exchanger being connected to the
forced air supply means, so that the air is both drawn down the
heat exchanger and compressed and then supplied to the burner
means.
7. A flow-through, self-cleaning gas-fired oven comprising an oven
cooking cavity formed by a box-like oven liner and a front opening
access door, a bake burner located beneath the bottom wall of the
oven liner, flue gas inlet openings in the said bottom wall for
passing the flue gases into the cooking cavity, oven exhaust means
adjacent the top rear of the oven liner, and a counterflow heat
exchanger with vertically arranged flue gas tubes and alternate
cooling air channels extending for substantially the width of the
oven liner, the flue gas tubes being connected at the bottom to the
said oven exhaust means and having flue gas vent means adjacent the
top of the heat exchanger that are directed away from the back of
the oven, the air channels having inlet means adjacent the top of
the heat exchanger, and an air collector means mounted on the
bottom portion of the heat exchanger and joined to the cooling air
channels and cooperating with the bake burner to supply preheated
air to support combustion.
8. A flow-through, self-cleaning gas-fired oven as recited in claim
7 wherein the said bake burner is a power burner that is furnished
with a motor-blower means interposed between the air collector
means and the power burner to both accelerate the velocity of the
air cooling means passing down through the heat exchanger and
compress this preheated air before delivering it to the power
burner so as to improve the efficiency of combustion and thereby
lower the amount of heat energy needed to cook as well as to
decompose the food soil lodged on the walls forming the oven
cooking cavity.
9. A flow-through, self-cleaning gas-fired oven as recited in claim
7 wherein the said counterflow heat exchanger comprises a collapsed
corrugated sheet metal panel forming a generally flat closed wall
plate with a plurality of spaced cylindrical flue gas tubes on the
innermost side of the wall plate, and a generally flat wall plate
held across the cylindrical tubes with a generally line contact
with each, thereby forming alternate cooling air channels between
the gas tubes, whereby the exterior walls of the heat exchanger
operate at relatively cool temperatures during the operation of the
heat exchanger as compared with the temperature of the flue
gases.
10. A flow-through, self-cleaning gas-fired oven as recited in
claim 9 wherein the said bake burner is a power burner that is
furnished with a motor-blower means interposed between the air
collector means and the power burner to both accelerate the
velocity of the air cooling means passing down through the heat
exchanger and compress this preheated air before delivering it to
the power burner so as to improve the efficiency of combustion and
thereby lower the amount of heat energy needed to cook as well as
to decompose the food soil lodged on the walls forming the oven
cooking cavity.
Description
BACKGROUND OF THE INVENTION
The present invention was developed while working toward improved
designs of pyrolytic or high temperature self-cleaning gas-fired
ovens wherein food soils and grease spatters lodged on the inner
walls defining an oven cooking cavity are degraded into gaseous
products that are completely oxidized before they are returned to
the kitchen atmosphere. In such a self-cleaning oven the oven wall
temperatures rise to somewhere between about 750.degree.F. and
about 950.degree.F. and are held for a sufficient time to complete
the transformation, on the order of 2 to 4 hours. In a gas-fired
oven only about one half of the heating value of the gas consumed
is used for heating the oven. The remainder is represented by both
the heat of exhaust and the heat losses radiating outwardly from
the walls of the oven body or cabinet. One difficult tehcnical
problem present in a gas self-cleaning oven that is not found in an
electric self-cleaning oven is the excessive amount of heat energy
that is exhausted into the kitchen atmosphere as a function of both
the high temperature and the large volume of flue gases.
Two earlier patents that are related to the present invention are
first U.S. Pat. No. 3,507,265 of the present inventors entitled
SELF-CLEANING GAS COOKING OVEN, and U.S. Pat. No. 3,659,646 also by
the present inventors entitled HEAT EXCHANGER CONSTRUCTION. Both of
these patents disclose so-called muffle ovens where the
self-cleaning oven cooking cavities are heated by passing
convection currents of flue gases over the outside of the oven
liner and then passing the gases up through a counterflow heat
exchanger located behind the oven liner.
The principle object of the present invention is to provide a
flow-through self-cleaning gas cooking oven with the most efficient
counterflow heat exchanger.
A further object of the present invention is to provide a
counterflow heat exchanger for a gas oven of the class described
where the heat exchanger has as its main component a collapsed
corrugated sheet metal panel that forms a generally flat closed
wall plate with a plurality of vertical spaced cylindrical flue gas
tubes, there being a second flat wall plate fastened across the
tubes to form alternate cooling air channels between the gas tubes
so that the outer surfaces of the heat exchanger operates at
relatively cool temperatures.
A further object of the present invention is to provide a gas
self-cleaning oven with a power burner means for improving the
efficiency of combustion as well as improving the down flow of
cooling air and the up flow of flue gases through the heat
exchanger.
SUMMARY OF THE INVENTION
The present invention, in accordance with one form thereof, relates
to a flow-through, self-cleaning gas-fired oven having an oven
cooking cavity with a bake burner located beneath the cavity so
that flue gases pass through the cavity and out through the oven
exhaust means adjacent the top rear of the oven cavity. A
counterflow heat exchanger rises from the oven exhaust means and it
has vertically arranged flue gas tubes and alternate cooling air
channels. An air collector means is mounted to the bottom of the
heat exchanger for joining the cooling air channels to the lower
bake burner to supply pre-heated air to support combustion. Further
improvements are made by the use of a heat exchanger construction
of collapsed corrugated sheet metal design with cylindrical flue
gas tubes so that the outer walls of the heat exchanger operate at
relatively cool temperatures thereby reducing the amount of thermal
insulation necessary to maintain relatively low exterior
temperatures on the oven body. Another important improvement was
realized in adopting a power burner in place of an atmospheric
burner.
BRIEF DESCRIPTION OF THE DRAWINGS
Our invention will be better understood from the following
description taken in conjunction with the accompanying drawings and
its scope will be pointed out in the appended Claims.
FIG. 1 is a side elevational view in cross section of a
free-standing gas range with a flow-through self-cleaning oven and
heat exchanger combination embodying the present invention.
FIG. 2 is a fragmentary, exploded perspective view on an enlarged
scale of the counterflow heat exchanger of FIG. 1 showing the
nature of the components and the method of assembling them.
FIG. 3 is a fragmentary perspective view of the tapered air
collector means attached at the top to the bottom portion of the
heat exchanger and tapering down to a small duct size adapted to be
joined to the intake of the motor-blower unit of the power bake
burner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to a consideration of the drawings and in particular to
FIG. 1, there is shown a free-standing domestic gas range 10
comprising a sheet metal outer cabinet or range body 11 supporting
a horizontal cooktop 13 at counter height and an underlying oven
cooking cavity 15. The cooktop 13 supports a plurality of surface
burners 17, but these are not illustrated in detail since the
present invention centers around the oven construction. The two
surface burners 17 that are shown are mounted on a single drip pan
19 having integral gas passageways which connect with individual
gas valves 21 arranged along the front edge of the cooktop 13 on a
common manifold that is in turn connected to a source of gas that
connects into the back of the range as is conventional in this art.
The surface burners are not illustrated in detail since they do not
form part of the present invention. Arranged along the back of the
cooktop 12 is a backsplash 23 which supports the oven controls 25
in the front control panel such as oven control valves, oven
timers, meat thermometer dials, automatic surface burner
temperature controls and electrical convenience outlets.
The oven cooking cavity 15 is formed by a box-like oven liner 27 in
combination with a front-opening access door 29. The oven liner 27
has a removable bottom wall or panel 31, opposite vertical side
walls 33, a rear wall 35, and a top wall 37. Normally the opposite
side walls 33 would be provided with some type of oven rack support
means such as embossed ledges (not shown) so that the racks may be
installed at varying heights within the oven. Such food supporting
racks are conventional and are not illustrated here for the sake of
simplicity. A thick layer of thermal insulation 39 surrounds the
vertical walls of the oven liner and also covers the top wall 37.
Moreover, the oven door 29 is well insulated by a fiber glass or
the like material 39. A fire box or combustion chamber 41 is
located beneath the oven liner and access may be gained to the fire
box either by removing the bottom plate 31 of the oven liner or by
opening a small dummy drawer front or panel 43 in the front of the
range beneath the oven door 29.
A bake burner 45 is supported within the fire box 41, and it is
shown as a power burner that is supplied with slightly compressed
air from a motor-blower unit 47 that is mounted adjacent the burner
within the fire box. It should be understood however that a
conventional atmospheric burner could be used in the present
invention, but that the use of a power burner 45 is the preferred
embodiment of the present invention since it results in improved
combustion efficiency and therefore less fuel being used and less
heat energy being expended as well as better overall operational
characteristics. The power burner 45 included a plenum or mixing
chamber 49 between the motor-blower unit 47 and the burner head 45.
The conventional oven gas manifold, gas lines, solenoid valves and
pilot burners or electric ignition means are not illustrated as
they do not form part of the present invention, but are
conventional components being used today in standard gas ranges. A
heat spreader plate 51 is carried beneath the removable bottom
panel 31 to protect this bottom panel from excessive heat which
might otherwise injure the porcelain enamel finish that covers the
interior walls forming the oven cooking cavity 15. Another layer 39
of thermal insulating material is arranged beneath the fire box 41
so as to protect from excessive temperatures the floor on which
this range is to be supported.
The removable bottom wall 31 of the oven liner is provided with
flue gas inlet openings 55, which are preferably larger at the
front of the oven than at the back so that more hot flue gases pass
near the oven door 29 so as to obtain generally uniform interior
wall temperatures for uniform cooking and cleaning results due to
the heat loss through and around the oven door 29. A high
temperature door sealing gasket 57 such as woven fiber glass is
furnished with the door to seal the door gap between the front
flange of the oven liner and the inner surface of the door to
restrict the amount of heat that leaks through the door gap as well
as to restrict the amount of ambient air that will be allowed to
enter the oven cooking cavity 15 during the high temperature
self-cleaning cycle. This oven door 29 is adapted to be latched and
maintained shut during the high temperature cycle by a door latch
mechanism 59 that is located in the front of the cooktop 13 just
above the free edge of the door 29. A satisfactory oven door latch
mechanism is described in the patent of Joseph S. Fox, Sr., U.S.
Pat. No. 3,367,697, which is assigned to the same assignee as is
the present invention.
An oven exhaust vent 65 is located adjacent the top of the oven
cavity 15 preferably in the back wall 35 of the oven liner so that
the hot flue gases that enter the cavity through the openings 55 in
the removable panel 31 may pass throughout the oven and finally be
exhausted through the vent 65. Rising upwardly from the oven vent
65 is a counterflow heat exchanger 67 which can best be seen in
FIG. 2. This heat exchanger is of light weight sheet aluminum
construction comprising a collapsed corrugated panel 69 and an
opposite, generally flat wall plate 71 having wraparound opposing
end walls 73. The corrugated panel 69 is collapsed in the plane
thereof so as to form a generally flat closed wall plate 70 with a
plurality of vertical, spaced cylindrical flue gas tubes 75. These
tubes are of generally oval configuration and each tube has a butt
joint 77 that is substantially closed due to pressure exerted from
each side of the corrugated panel tending to collapse the panel, as
is best seen in FIGS. 2 and 3. When the opposite wall plate 71 is
assembled around the collapsed corrugated panel 69, the end walls
73 encompass the corrugated panel 69 and restrain the corrugations
to the collapsed position as seen in FIG. 2. A metal tension strip
79 is wrapped around the assembly and clamped in place by a crimped
fastener 81 so that the heat exchanger is a self-sustaining
assembly. Thus it can be seen that the spaced flue gas tubes 75 are
separated by alternate cooling air channels 83 with an air channel
83 also arranged on each end of the heat exchanger.
The lower portion of the heat exchanger is fitted with an adaptor
or manifold 85 which extends the complete width of the heat
exchanger, and in the front it is fitted with the oven exhaust vent
65. The top wall of adaptor 85 is provided with holes 87 which are
aligned with the flue gas tubes 75 such that the flue gases pass
from the oven cavity 15 through the oven exhaust vent 65 and then
through the holes 87 up through the flue gas tubes 75. These flue
gases cannot enter the cooling air channels 83.
A horizontal adaptor 89 is fastened to the top of the heat
exchanger, and it has a bottom wall 91 that is provided with a
series of holes 93 which are also aligned with the flue gas tubes
75 for receiving the flue gases and passing them forwardly through
the adaptor to exhaust through an elongated slot or grillwork 95 in
the front of the adaptor. This top adaptor 89 has been fashioned
into a secondary heat exchanger by installing parallel fins 97 to
the underside of the top wall 99 of the adaptor. The purpose of
these fins 97 is to pick up some of the heat in the flue gases and
carry this heat through the top wall 99 thereby creating a warming
shelf for use during normal cooking operations so that food that
has been cooked may be kept warm by placing the food on the
secondary heat exchanger 89. Moreover, this warming shelf is useful
durng the self-cleaning cycle in reducing the heat energy in the
exhaust gases that are returned to the kitchen atmosphere by
conducting some of the heat to the warming shelf 99.
Notice that the heat exchanger 67 extends up behind the backsplash
23 of the range 10, and that no blanket of insulation is shown
between the heat exchanger and the backsplash. The reason that this
can be done is that the outer surfaces of the heat exchanger 67
operate at a relatively cool temperature as compared to the
temperature of the flue gases in the gas tubes 75. This is because
there is a generally line contact between each tube 75 and the rear
wall plate 71. Also the butt joint 77 of each tube 75 has only a
double metal thickness joining the front side of each tube with the
closed flat panel 70 of the collapsed corrugated plate 69. While I
have elected as my preferred embodiment a cylindrical flue gas tube
design 75 a generally oval transverse configuration, it will be
understood by those skilled in this art that other similar forms or
shapes can be used in the present invention, with the understanding
that there should be little or a minimum amount of a heat
conduction path between the tubes and the opposite panels 70 and
71. This of course is to maintain relatively cool temperatures on
the outer walls of the heat exchanger as compared with the
temperature of the flue gases. Looking at FIG. 1 a vertical layer
of thermal insulation 39 is shown beneath the backsplash 23 at the
rear edge of the cooktop 33. Moreover, there is another blanket of
insulation 39 behind the heat exchanger 67.
Looking at FIG. 2, the upper portion of the rear wall plate 71 of
the heat exchanger is provided with a horizontal series of holes
105 which communicate with the cooling air channels 83. An air
manifold 107, shown in FIG. 1, is assembled over these holes 105,
and this manifold is provided with a rear air inlet 109 so that
room air is drawn from the back of the range into the air manifold
107 and passes through the holes 105 into the alternate cooling air
channels 83 wherein the air passes down through the heat exchanger
and takes on some of the heat present in the walls of the flue gas
tubes 75 and thereby becoming heated at the same time lowering the
temperature of the flue gases which of course is the main purpose
of employing the heat exchanger 67.
The bottom portion of the rear wall plate 71 is also provided with
another series of holes 111 which also communicate with the cooling
air channels 83, and a second air manifold 113 extends the width of
the heat exchanger and fits over these holes for receiving the
heated air from the bottom of the heat exchanger.
An air collector means 117 is arranged behind the oven liner 27,
and it is adapted to connect through the air manifold 113 to the
bottom portion of the heat exchanger 67 and to carry this heated
air down to the fire box 41 where this heated air is delivered to
the motor-blower unit 47. The air collector means 117 is shown as
of downwardly tapered configuration, as is best seen in FIG. 3,
where it is drawn down into a small chamber 119 having a circular
opening 121 on its front side for receiving a cylindrical duct 123
that connects into the intake of the blower 47. Notice that a
blanket of insulation 39 is arranged behind the air collector means
117 as well as between the air collector means and the back wall 35
of the oven liner 27.
Modifications of this invention will occur to those skilled in this
art, therefore, it is to be understood that this invention is not
limited to the particular embodiments disclosed, but that it is
intended to cover all modifications and their equivalents which are
within the true spirit and scope of this invention as claimed.
* * * * *