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BACKGROUND OF THE INVENTION
Space heaters having fuel-fired radiant burners have been used for drying
and for heating various enclosures; exemplary of such heaters are those
shown in my U.S. Pat. Nos. 3,315,656; 3,797,474 and 3,849,063. In the
devices of each of these patents I have employed a thin,
radiation-transmissive panel to act as a "window" for transmitting
infrared radiation into the space to be heated and also for sealing the
combustion chamber which houses the radiant from the space being heated.
In the devices of two of these patents, a stream of cooling air is
permitted to flow, by convection, downwardly over the generally tilted or
upright panels to cool the panels. In the last-named patent, a device is
described in which a coolant outside the combustion chamber serves to cool
the radiation-transmissive panel.
The devices in which cooling air is moved across a panel by convection must
be of fairly large size in order to prevent flue products from mixing with
external combustion air. In the device of the last-identified patent, the
ability of a coolant adjacent the outer, exposed surface of the
transparent panel is limited in its cooling effect by the thickness of the
panel, by its dependent location and by its generally poor heat
conductivity.
There is a definite need for a radiant heater employing a
radiation-transmissive panel which is in close proximity with the radiant
to reduce the heater size, and which is yet cooled continuously so as to
avoid overheating of the panel. There is also a need for such a radiant
heater which may assume somewhat different orientations in a space to be
heated without interfering with its operation.
SUMMARY OF THE INVENTION
The present invention relates to a fuel-fired, radiant heater which can be
manufactured in small sizes, and the orientation of which within an
enclosure to be heated may be adjusted as the occasion demands. The heater
comprises a fuel-fired radiant, a combustion chamber housing the radiant,
and a plenum adjacent the combustion chamber. The combustion chamber
includes a lower wall spaced from but confronting the radiant and
providing a generally outwardly open radiant port. The port is closed by a
thin panel which is highly transmissive of infrared radiation and which
has an inner surface confronting the radiant. The combustion chamber
includes an outlet port to permit combustion product gases to escape.
Means are provided for charging the plenum with air under a pressure
greater than that in the combustion chamber. The heater includes means
providing an air flow passage from the plenum to the combustion chamber
and which is configured to provide a constantly replenished pool of
cooling air against the radiation-transmissive panel to cool the same and
to prevent impingement on the panel of hot, combustion product gases from
the radiant. Means are also provided to convey air cocurrently from the
plenum to the radiant for use as as combustion air. The combustion product
gases and air from the constantly replenished pool of cooling air may be
combined for common discharge from the combustion chamber through the
outlet port. The heater may include an auxiliary heat exchanger adjacent
the combustion chamber for receiving combustion product gases from the
latter chamber and for transmitting the heat thereof into the space to be
heated or for other uses.
In a preferred embodiment, the combustion chamber and the plenum share a
common wall having a transverse slot-like opening adjacent the lower wall
of the combustion chamber and serving to direct air into a pool of cooling
air above the inner surface of the radiation-transmissive panel. A common
wall between the combustion chamber and the plenum may also mount the
radiant in such a manner that the radiant is provided with combustion air
from within the plenum. A blower or fan may be employed to provide air
under superatmospheric pressure to the plenum, or the blower may be
positioned to draw air and combustion product gases from the combustion
chamber. In either case, the pressure in the plenum is maintained above
the pressure in the combustion chamber to provide the cocurrent flow of
combustion air and cooling air.
The invention also provides a heat exchanger of unique construction. The
heat exchanger comprises a duct or channel having walls through which
extend a plurality of integral vanes. The vanes each protrude inwardly of
the duct in the path of a heat exchange fluid such as air, and also extend
outwardly of the duct. The inwardly protruding portions of the vanes may
define baffles to interrupt the flow of fluid through the duct, and the
outwardly extending vane portions provide an expanded heat exchange
surface, which may take the form of fins. The integral, unbroken nature of
the vanes provide minimum resistance to the conduction of heat by the
vanes. The heat exchanger may be fabricated simply by forcing the vanes
through the walls of a duct formed of malleable, easily penetrated
material such as aluminum sheeting, the holes thus made in the duct walls
snuggly sealing against the vanes.
DESCRIPTION OF THE DRAWING
FIG. 1 is an elevational view, in cross section, of a heater of the
invention;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1;
FIG. 4 is a cross-sectional view taken along line 4--4 of FIG. 1;
FIG. 5 is a broken away, cross-sectional view taken along line 5--5 of FIG.
1;
FIG. 6 is a side elevation, shown in cross section and partially broken
away, of a drying tunnel or oven employing heaters of the invention;
FIG. 7 is a broken away, cross-sectional view taken along line 7--7 of FIG.
6;
FIGS. 8 and 9 are broken-away side elevations, in partial cross section, of
modified forms of the invention;
FIG. 10 is a broken away perspective view, in partial cross section, of a
heat exchanger useful with the heater of the invention; and
FIG. 11 is an end view, in cross section, of the heat exchanger of FIG. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, the heater of the invention is designated
generally as 10, and is shown in an exemplary position as being secured to
the ceiling 12 of an enclosure to be heated. A generally
parallelepiped-shaped combustion chamber 14 is provided with generally
upright front and rear walls 14.1, 14.2, and side walls 14.3, 14.4. The
chamber includes a top wall 14.5 and a bottom wall 14.6 with a
radiation-transmissive port therein. Desirably, the port extends the full
distance between the side walls and the front and rear walls, although it
may be desirable in some instances to restrict the size of the port to a
smaller area. A radiation-transmissive panel 16 is positioned to close the
port, and may be fastened by clamps or rivets or the like (not shown) to
the periphery of the front, rear and side walls of the combustion chamber.
For convenience, the lower ends of the front and side walls may be turned
outwardly to form fastening flanges, which are designated generally as
14.7 in the drawing, and to which the thin, radiation-transmissive panel
16 may be affixed.
The radiation-transmissive panel 16 is desirably of a thin, flexible
plastic material which ordinarily softens or melts below about
1000.degree. F. Preferred materials for the panel include such
thermoplastics as polytetrafluoroethylene (Teflon "TFE", a trademarked
product of E. I. DuPont DeNemours and Company, Inc.) which has an infrared
transmissivity of approximately 0.88, poly
(tetrafluoroethylene-hexafluoropropylene) (Teflon "FEP", manufactured by
the DuPont Company), and polyester materials such as poly
(ethyleneterephthalate) a product sold under the name Mylar by the DuPont
Company and which has an infrared transmissivity of approximately 0.77.
Teflon TFE film having a thickness of approximately 0.002 inches is
preferred, since this material is flexible, is highly transmissive of
infrared radiation, and is more resistant to high temperatures than many
other polymeric materials.
Housed within the combustion chamber 14 is a radiant heater such as a gas
burner 18, which may be a Schwank-type burner having a downwardly facing
radiant face with small holes therein through which gas-air mixtures issue
and are burned, the small flames being shown as 18.1 in the drawing. The
rearward end of the burner includes a control box 18.3 having on-off,
safety and pressure controls and is received within the plenum and is
attached to the rear wall 14.2 of the combustion chamber. It will be
understood from FIGS. 1 and 2 that the width and length of the radiant are
at least half of the width and length of the interior of the combustion
chamber, and the radiant is spaced only a short distance above the
radiation-transmissive panel 16. The inner surface 16.1 of the latter
panel confronts the lower surface 18.2 of the radiant and transmits
infrared radiation from the radiant to the space to be heated. Desirably,
the radiant surface 18.2 of the burner, and the panel 16, lie in parallel
planes.
The combustion chamber is also provided with an exhaust port 14.8 which
desirably is located in the front wall 14.1 of the chamber, although the
exhaust port may be positioned elsewhere, such as in the top wall, as will
be explained. Desirably, the port is positioned near the top of the
combustion chamber.
A plenum 20 is provided adjacent, or contiguous the combustion chamber, and
the rear wall 14.2 of the combustion chamber is desirably shared with the
plenum as shown in FIG. 1. The plenum 20 is generally of a parallelepiped
shape, and has a bottom wall 20.1 which may be co-extensive with the
radiation-transmissive panel 16 of the combustion chamber. If desired, the
radiation-transmissive panel 16 may be continued rearwardly to form the
bottom wall 20.1 of the plenum. A blower, illustrated as fan 20.2, is
positioned to provide air under pressure to the plenum. The fan may be
housed in a blower housing designated generally as 22 in FIG. 1, the
housing 22 having an inlet port 22.1 for drawing fresh air into the
housing, and an exhaust port 22.2 for exhausting air under pressure into
the plenum 20. Although it is preferred to position the blower in the
system to provide superatmospheric air to the plenum, the blower may, if
desired, be positioned downstream of the exhaust duct 14.8 to draw air and
combustion product gases from the combustion chamber. In any event, it
will be recognized that the pressure in the plenum 20 is somewhat greater
than that in the combustion chamber 14.3. By "plenum" as used herein,
reference is made to a compartment continuously furnished with air under
pressure greater than that in the combustion chamber. Desirably, the
plenum is configured and sized so that the directionality of the air
furnished thereto has no substantial directional effect on the streams of
air exiting as combustion air and cooling air.
That portion 18.3 of the burner 18 which protrudes into the plenum 20 is
provided with openings 18.4 to receive air from the plenum, this air being
hereinafter referred to as combustion air which is mixed with fuel vapors.
The fuel-air mixture burns at the lower surface 18.2 of the radiant. The
protruding end 18.3 of the radiant is provided with a fuel conduit leading
to an external source of fuel under pressure.
The common wall 14.2 of the combustion chamber and the plenum is provided
adjacent its lower end with a transverse, slot-like opening 14.9, the
width of which approaches the full width of the combustion chamber 14. The
purpose of the opening 14.9 is to direct cooling air from the plenum into
the combustion chamber in the vicinity of the inner surface 16.1 of the
radiation-transmissive panel to form a constantly replenished pool of
cooling air above the panel to cool the same. If the top and bottom edges
of the opening are straight and parallel, as shown in FIG. 2, then the
edges may be separated one from the other by a distance of, for example,
1/8 inch. In another embodiment, the opening 14.9 may have one straight
edge and one serrated edge, with the points of the serrations approaching
or touching the straight edge. It will be understood that many different
configurations for the opening 14.9 may suggest themselves to one skilled
in the art; for example, the opening 14.9 may comprise a series of holes
aligned generally transversely of the wall 14.2, but the configuration for
the opening 14.9 should be chosen as to direct air from the plenum to the
vicinity of the inner surface of the radiation-transmissive panel so as to
provide and maintain a pool of cooling air above and in cooling
relationship to the panel.
As shown by the arrows 24 in FIG. 1, the pool of cooling air above the
panel 16 within the combustion chamber merges with the combustion product
gases from the radiant 18, and the combined gases are exhausted through
the port 14.8 of the combustion chamber. As thus described, the plenum 20
provides air both for combustion purposes and for cooling purposes. If the
fan 20.2 should fail for some reason, not only will the flow of cooling
air cease, but the flow of combustion air will also cease, thereby
extinguishing the radiant.
To further make use of the heat of the exhausted combustion product gases,
a heat exchanger, designated generally as 26 in FIG. 1, may be positioned
downstream from the exhaust port 14.8. As illustrated, the heat exchanger
may be generally parallelepiped in shape and may share a common wall, such
as front wall 14.1, with the combustion chamber. The heat exchanger has an
exhaust port 26.2 which may be provided with appropriate ducts 26.3 to
convey the combustion product gases and cooling air through an exterior
wall 12.2 and to release the gases to the atmosphere. Interiorly, the heat
exchanger 26 may be provided with a series of heat conductive baffles 26.1
which increase the flow path of exhaust gases through the heat exchanger
and which aid in the extraction of heat therefrom. The baffles extend
integrally through the walls of the heat exchanger to provide exterior
fins 26.5 for radiation of heat to the space to be heated. The exterior
fins formed by the baffles 26.1 may be separated from one another by a
space of approximately one inch. For efficient operation of the heater,
the heat exchanger 26 should offer minimum resistance to the passage
therethrough of combustion product gases and cooling air. For this reason,
the staggered openings 26.4 through the baffled interior of the heat
exchanger are fairly large.
In the embodiment depicted in FIG. 1 of the drawing, a bracket 28 extends
upwardly from the forward end of the heat exchanger for attachment to the
ceiling 12 of an enclosure to be heated, and thus supports the front end
of the heater of the invention. The blower housing 22 preferably is
positioned above the plenum 20 and is attached to and shares a common wall
20.3 with the plenum. The housing 22 is desirably parallelepiped in shape,
and has an upper wall which may be readily attached to the ceiling 12 of
the enclosure to be heated, as depicted in FIG. 1. Extending from the
outer wall 12.2 of the enclosure to the housing 22 is an intake air duct
22.3 which supplies fresh air from the exterior of the enclosure to the
housing 22. Arrangement of the blower housing 22, plenum 20, combustion
chamber 14, heat exchanger 26, in this manner permits the heater to be
easily and readily installed in an enclosure to be heated adjacent an
exterior wall, and causes the combustion chamber 14 to be spaced a safe
distance below the ceiling 12. It will also be understood that the ceiling
or walls of the enclosure which are adjacent the heater may be provided
with appropriate insulation to prevent them from becoming too hot.
Because of the constantly replenished pool of cooling air above the
radiation-transmissive panel 16 afforded by the opening 14.9, the size of
the heater may be quite small. In one embodiment, for example, the
combustion chamber may be on the order of 7 inches wide, 8 inches in
height, and 10 inches from front to rear (between the walls 14.1 and
14.2). The width and height of the contiguous plenum 20 may be the same as
the combustion chamber, and the plenum may have a length on the order of 6
inches. The blower housing 22 may have the same length and width as the
plenum, and may be on the order of 43/4 inches in height. The walls of the
housing 22, plenum 20, combustion chamber 24 and heat exchanger may be of
sheet aluminum appropriately bent and fastened as in the drawing. Because
the heater may be of fairly small size, as explained above, the various
parts thereof as depicted may be inexpensively manufactured from a
relatively few lengths of sheet metal. For example, the side and top wall
of the combustion chamber and the plenum may be provided by a single
length of sheet aluminum bent to form an inverted U-shaped trough, as
shown perhaps best in FIGS. 1 and 2. A single portion of sheet aluminum
may provide the common wall 14.2 between the combustion chamber and the
plenum and another length may provide the rearward walls of the plenum 20
and the blower housing 22. The heat exchanger 26, depicted as being
generally parallelepiped in shape with baffles 26.1 which pass through the
walls of the heat exchanger, will be recognized by those skilled in the
sheet metal art as being simple to fabricate.
A high temperature limit switch 32 (FIG. 1), appropriately shielded from
radiation, may be positioned within the combustion chamber adjacent the
radiation-transmissive panel 16 for the purpose of sensing the temperature
adjacent the panel and for shutting off the heater when the temperature
reaches or exceeds a given limit, which inevitably will occur if the
radiation-transmissive panel is broken. Limit switches of the type
described are well known in the art.
The heater of the invention may be vented to the exterior of a building or
the like in the manner shown in FIGS. 1 and 2 wherein the intake air duct
22.3 passes outwardly through the wall 12.2 of a building or the like, and
is made fast to the building exterior by means of a locking ring 22.4 or
the like with the duct 22.3 protruding outwardly from the outer surface of
the wall only a very short distance. A flue 30 is provided at the exterior
of the wall 12.2 and includes an outer wall 30.1 and side walls 30.2 to
form a generally U-shaped structure in cross section as shown in FIG. 5.
An upright dividing wall 30.3 divides the flue into inner and outer
passages, open at the top and bottom, as shown best in FIGS. 1 and 5,
which passages communicate with the atmosphere and serve to supply air to
the blower 20.2 and to exhaust combustion product gases, respectively. The
inlet air conduit 22.3 thus communicates with the flue passageway between
the divider wall 30.3 and the wall 12.2 of the enclosure. The exhaust duct
26.3 extends outwardly through the wall 12.2 and through the divider wall
30.3 to which it is held by means of a locking ring 30.4 so that
combustion product gases are exhausted into the flue passageway between
the outer wall 30.1 and the divider wall 30.3. When employing the flue 30
as depicted in the drawing, the air inlet and exhaust ducts 22.3 and 26.3
ordinarily will be vertically aligned, although they are shown out of
alignment for purpose of clarity in FIG. 5.
In use, fresh air is drawn through the duct 22.3, and is blown by the fan
22.2 into the plenum 20, the latter thus being under a pressure slightly
greater than atmospheric. The pressurized air within the plenum enters the
radiant through the rearwardly projecting portion of the radiant, and
mixes with fuel gas to form a combustible mixture which is burned at the
lower surface of the radiant. Concurrently, air under pressure from within
the pressure compartment 20 flows through the slot-like opening 14.9 in
the common wall 14.2, and forms and continuously replenishes a pool of
cooling air on the radiation-transmissive sheet 16. The pool cools the
panel, and provides a buffer layer of air which prevents combustion
product gases from the radiant from impinging on the panel. The cooling
air from the pool mixes with the combustion product gases, and exits
through the exhaust port 14.8 into the heat exchanger 26 from which heat
is further extracted by the baffles 26.1 and is radiated outwardly by the
exterior fins of the heat exchanger. The combustion product gases and
mixed cooling air then exit through the exhaust port 26.2 and pass through
the flue 30 to the atmosphere. The pressure within the plenum is
maintained slightly greater than the pressure within the combustion
chamber, and the latter pressure in turn is slightly greater than the
pressure in the heat exchanger so that air flow from the plenum to the
heat exchanger is maintained.
From FIG. 1, it will be evident that the flows of combustion air and
cooling air from the plenum are cocurrent; that is they flow
simultaneously from the same source (the plenum) and in generally the same
direction (into the combustion chamber). It has been found that although
only very small pressure differentials are employed between the plenum and
the combustion chamber 14, the constantly replenished pool of cooling air
provided above the radiation-transmissive panel 16 is distributed as a
layer across the entire panel. Smoke injected into the cooling air to
trace its movement has indicated moderate turbulence throughout the pool
or layer with marked, that is, increased, turbulence at the interface
between the pool and the hot gases driven downwardly from the radiant
burner. Combustion product gases from the radiant 18 which are propelled
downwardly toward the panel 16 are considerably hotter than the
continuously replenished pool of cooling air, and mix with the upper
portion of the latter and rise toward the exhaust port before impinging
upon and damaging the panel 16. The opening 14.9 through which cooling air
is admitted to the combustion chamber is configured to replenish the pool
of cooling air at a rate to maintain the pool at a significant pool depth
and thus prevent the combustion product gases from the radiant from
approaching too closely to the panel 16. In one embodiment, the overall
height of the combustion chamber may be on the order of 8 inches, and the
downwardly oriented surface 18.2 of the radiant may be spaced only about 5
inches from the panel 16. By judicious adjustment of the cooling air
opening 14.9, the combustion product gases issuing from the radiant may be
prevented from approaching the panel 16 more closely than, for example,
about 2 inches.
As will now be understood, "pool" as used herein refers to a layer of
cooling air maintained on the radiation-transmissive panel and which is
constantly replenished by the plenum and which is constantly depleted by
admixture with combustion product gases for exhaustion from the combustion
chamber. The pool of cooling air, in contrast to a rapidly moving air
stream, has only a relatively slow gross movement and is maintained at a
significant thickness to form a thick cushion or barrier preventing
strike-through of combustion product gases to the panel which would occur
in the absence of the pool. Since any substantial break in the panel would
permit escape of air from the pool of cooling air, thus decreasing its
thickness, a safety device (32 in FIG. 1) can be provided to indicate
breakage of the panel by sensing temperature changes at a level normally
in, or kept relatively cool by, the pool of cooling air when the panel is
intact.
Because of the positive flow of air within the combustion chamber which is
provided by the pressure compartment 20, the orientation of the heater may
be varied somewhat, e.g., by tilting forwardly or rearwardly or from side
to side, without undue interference with the operation of the heater. It
will be understood that in some instances it may be desired to provide the
combustion chamber with a reflective inner surface to reduce the amount of
heat absorbed by the combustion chamber walls, or to provide the heater
generally with insulated walls.
By supplying air under superatmospheric pressure to the plenum which houses
the controls for the radiant, leakage of gaseous fuel or combustion
product gases into the plenum is greatly reduced or eliminated. The
controls for the heater (which may control the air and gas flow rates, and
protective circuitry) may be provided in a control box designated
generally as 18.5 in the drawing; access to the controls may be had
through a suitable panel in the plenum.
Schematic representations of a bank or series of heaters of the invention
which may be employed in a drying tunnel or oven is shown in largely
schematic form in FIGS. 6 and 7, and reference numerals in FIGS. 1 - 5
identify similar parts in FIGS. 6 and 7. A web to be dried by the drying
oven is designated as 34 in FIG. 6, and is propelled in the direction
shown by arrows. Combustion chambers 14 (FIG. 7) are aligned side by side
across the width of the drying tunnel, and may share a common
radiation-transmissive panel 16. Cooling air inlet ducts 14.9 are shown
for each combustion chamber, although it will be understood that a common
opening may extend across the row of combustion chambers. Between every
two rows of combustion chambers is positioned a plenum 20 (FIG. 6) which
provides combustion air and cooling air in the manner described above to
the aligned combustion chambers. Admixed combustion product gases and
cooling air from the pool flow to a central upper exhaust duct 14.8 and
into a heat exchanger 26. A water jacket, designated 36, forms at least
the top wall of the combustion chambers, and preferably the side walls as
well, and serves to insulate the surrounding area from the heat eminated
from the combustion chambers, and also serves as a source of hot water for
auxiliary heating, if desired. The water within the water jacket is
circulated through exteriorly finned tubes 26.6 in the heat exchanger, the
fins extracting heat from the combustion product gases and transferring
the same to the water. If desired, the aligned combustion chambers may
together form a single combustion chamber, and reflective divider panels
15 (FIG. 7) may be employed between adjacent burners for the purpose of
evenly distributing the flow of radiant heat through the panels.
In the heater embodiment shown in FIG. 8, the lower wall 15 of the
combustion chamber 14 slants downwardly beneath the radiant 18 at an angle
of, e.g., 45.degree. to the horizontal, and is provided with an infrared
radiation-reflective inner surface 15.1. The radiation-transmissive panel
16 is positioned generally vertically and below the level of the radiant,
and faces the reflective surface 15.1. Cooling air from the plenum 20
enters the combustion chamber through the port 14.9 and forms a pool of
cooling air bounded at its bottom by the slanted wall 15 and at one end by
the panel 16. The cooling air flow rate is controlled so that the upper
end of the panel 16 remains immersed in the pool of cooling air. The
slanted inner reflective surface 15.1 of the wall 15 is also cooled by the
pool of cooling air, thereby avoiding gross changes in reflectivity which
might occur if the surface 15.1 were to become hot. As previously
described with reference to FIG. 1, the hot combustion product gases which
impinge from above onto the pool of cooling air are mixed with the cooling
air and exit through the exhaust duct 14.8.
In the heater embodiment of FIG. 9, the radiant 18 is mounted vertically in
the combustion chamber facing the generally vertically supported
radiation-transmissive panel 16. Cooling air from the plenum 20 flows
upwardly through duct 20.5 which turns inwardly of the combustion chamber
14 and has an open end 20.6 adjacent the upper end of the panel 16 to
supply cooling air thereto. The cooling air thus supplied forms a thick
cushion or barrier layer along the inner surface 16.1 of the panel which
prevents strike-through of hot combustion product gases onto the panel.
The latter gases, admixed with cooling air, exit through the exhaust port
14.8.
FIGS. 10 and 11 depict an embodiment of an easily fabricated heat exchanger
of general utility and useful with the heaters of the invention. The heat
exchanger is designated generally as 40 and includes a tube or duct 42 of
any convenient cross-sectional configuration and having piercable walls
42.1. A plurality of spaced, integral, heat conductive, metal vanes 44
extend through the walls of the duct. Each vane has a portion 44.1
protruding inwardly of the duct in the path of a heat transfer fluid to be
carried by the duct, and each vane has also a portion 44.2 extending
outwardly of the duct. As shown in FIGS. 10 and 11, the vanes 44 may pass
entirely through the duct so that both of its ends protrude outwardly
thereof, the vanes being thus fully and independently supported in
position by opposing duct walls.
The inwardly protruding vane portions 44.1 in the path of a heat transfer
fluid may act as baffles to increase the flow path of the fluid without
significantly reducing the fluid flow rate. The vanes may be elongated
bars of rectangular cross section, and may be twisted within the duct to
impart a rotary or cyclonic motion to fluid passing therethrough. Or, the
longest cross section dimension of the bars may be parallel to the axis of
the duct so that the inwardly protruding portions 44.1 merely expand the
interior surface of the duct available for heat transfer. The outwardly
extending portions 44.2 of the vanes increase the exterior area of the
duct available for heat transfer, and these portions may be generally
parallel and aligned to provide fins between which may pass, e.g., air to
be heated.
The vanes may be mounted to the duct simply and easily by piercing the duct
walls with the vanes and leaving the vanes in place. The duct may be made
of an easily pierced material such as thin aluminum sheeting, and the
edges of the pierced holes engage and substantially seal against the vanes
passing therethrough. The vanes may be of aluminum rod or bar stock
somewhat stiffer than the duct, and ends of the bars may be sharpened as
desired to facilitate piercing of the duct walls.
Of importance is the feature that the vanes are integral and unbroken as
they pass through the duct walls, thereby avoiding resistance to heat
conduction due to riveted interfaces.
Thus, manifestly, I have provided a fuel-fired radiant heater which can be
inexpensively manufactured and which can be of relatively small size for
use within small enclosures, such as in a drying tunnel. The orientation
of the heater with respect to the horizontal may be adjusted because of
the positive cocurrent flow of combustion and cooling air in the heater.
Moreover, air currents in the enclosure to be heated have little if any
effect upon the operation of the heater. My radiant heater makes use of a
constantly replenished pool of cooling air against a
radiation-transmissive panel confronting the radiant burners, the pool
forming a barrier-like layer to cool the panel and to prevent impingement
thereon of hot combustion product gases from the radiant.
While I have described a preferred embodiment of the present invention, it
should be understood that various changes, adaptations, and modifications
may be made therein without departing from the spirit of the invention and
the scope of the appended claims.
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