Infrared energy generator with orifice plate

An infrared energy generator, which is capable of effective operation when provided with fuel from a relatively low pressure supply, such as from a relatively mobile liquid propane tank, to radiate infrared energy over a relatively large output area, has an orifice plate in the plenum to impede fuel flow to the fuel output where combustion occurs. The orifice plate has openings therethrough to conduct fuel from one portion of the plenum, which is coupled to the fuel supply at a fuel input orifice, to another portion of the plenum, which leads to the fuel output, and the sum total of the cross-sectional areas of the openings in the orifice plate is smaller than the cross-sectional area of the fuel input orifice so that a back pressure is created in the one plenum portion to assure fuel flow at a suitable velocity in a positive direction toward the other plenum portion and subsequently to the fuel output, thereby to reduce or to eliminate the possibility of encountering a blow out or a backfire during operation.

BACKGROUND OF THE INVENTION 
The present invention is directed, as indicated, to an infrared energy 
generator or heater with an orifice plate that impedes fuel flow through 
the generator plenum to cause a back pressure therein, and, more 
particularly, is directed to a mobile infrared energy generator capable of 
operation with a relatively low pressure fuel supply, such as liquid 
propane, while providing an infrared energy output over a relatively large 
area. 
A conventional infrared generator or heater, which generates and radiates 
an infrared energy output in response to combustion of a fuel input, may 
include a housing, a plenum chamber or the like within the housing, a fuel 
input to the plenum, a fuel output from the plenum, and a radiating screen 
exposed to the products of the fuel combustion occuring normally between 
the fuel output and the screen and responsive to the thermal energy of 
such combustion to radiate infrared energy as an output of the infrared 
heater. The radiated infrared energy may be used for a variety of 
purposes, including, for example, indoor heating, paint drying, melting of 
ice outdoors, etc. Most infrared generators or heaters, especially those 
that are relatively large and provide their infrared energy output over a 
relatively large area, say forty or more square inches at the heater 
output, typically are supplied with a natural gas fuel input, which 
usually is at a relatively high pressure, say on the order of eleven 
inches of water, from the utility company. The relatively high pressure of 
the fuel allows such infrared generators to operate usually without a blow 
out of the flame or a backfire at the fuel input orifice to the plenum, 
which might be caused by a wind or other ambient atmospheric pressure or 
the like variation. 
The fuel pressure available to an infrared generator from a mobile fuel 
supply, such as a liquid propane tank, is much less than the fuel pressure 
from a natural gas supply, often being four inches of water or less. The 
loweroperating pressure, then, of liquid propane supplied infrared 
generators would then tend to cause such infrared generators to be much 
more responsive to wind, drafts, pressure, or other ambient atmospheric 
conditions and changes, whereby blow outs or backfires would be more 
likely to occur. Therefore, to avoid reducing or diluting the effective 
fuel pressure and the sensitivity to the ambient environmental conditions, 
prior art mobile infrared generators supplied, for example, with vaporized 
or gaseous propane from a relatively mobile liquid propane fuel tank have 
been limited to relatively small sizes, for example, of several, usually 
less than four, square inches of radiating output surfaces. 
SUMMARY OF THE INVENTION 
In the present invention a fuel flow impediment is located in the infrared 
generator between the fuel input to the plenum and the fuel output 
therefrom to increase the fuel pressure or, in other words, to provide a 
back pressure, in the plenum between the fuel input and the flow 
impediment. That back pressure created by the flow impediment helps to 
maintain fuel flow in a positive direction, that is, in a direction from 
the input orifice of the plenum toward the fuel output of the plenum for 
subsequent fuel combustion. The maintained positive fuel flow, even when 
the fuel supply is a relatively low pressure pre-mixture of vaporized 
liquid propane and air, allows the infrared generator to be mobile, 
supplied by a mobile liquid propane tank fuel supply, while still being 
able to radiate an infrared energy output over a relatively large area, 
for example, larger than four square inches and usually larger even than 
40 square inches. 
Due to its mobility and relative insensitivity to wind and atmospheric 
pressure, the infrared generator of the present invention is especially 
suited for use outdoors. In one such use, the infrared heater of the 
invention is employed to expedite drying of an earth road bed to condition 
the latter for subsequent preparation preliminarily to the pouring of a 
concrete highway or the like. By directing the infrared energy toward a 
relatively large area of moist earth, for example, evaporation of the 
moisture is increased so that the road bed is efficiently dried and 
readied for subsequent preparation, etc. Moreover, the flow impediment 
created back pressure also allows several infrared generators to operate 
successfully while supplied from a common liquid propane tank or other 
mobile fuel supply, whereby when mounted on a vehicle, the infrared 
generators can heat simultaneously several adjacent areas to cover the 
entire width of the road bed. 
In one embodiment of the invention the flow impediment comprises an orifice 
plate located in a housing within which the plenum is formed. The orifice 
plate is secured about its periphery in fluid tight engagement with the 
housing, for example, by welding or the like, and a plurality of holes 
through the orifice plate are distributed over the surface area thereof to 
effect a relatively uniform delivery of fuel to the fuel output of the 
plenum. In order to maintain the back pressure in the plenum chamber 
behind the orifice plate, the sum total of the area of the holes through 
the orifice plate is preferably smaller than the area of the fuel input 
orifice to the plenum. For example, the total cross-sectional area of the 
holes may be on the order of from about 15% to about 40% less than the 
total cross-sectional area of the fuel input orifice and preferably is 
approximately in the range of from 20% to about 30% less. 
With the foregoing in mind it is a primary object of the invention to 
provide an infrared energy generator improved in the noted respects, and 
especially an infrared generator operable to provide an infrared energy 
output over a relatively large area while being supplied with fuel from a 
relatively low pressure fuel supply. 
Another object is to provide a mobile infrared generator, and especially 
one capable of radiating an infrared energy output over a relatively large 
area. 
An additional object is to reduce and/or to eliminate the possibility of 
occurrence of a blow out in an infrared generator. 
A further object is to reduce and/or to eliminate the possibility of 
occurrence of a flashback or backfire in an infrared generator. 
Still another object is to provide a back pressure in the plenum of an 
infrared generator that is of a magnitude greater than the ambient 
pressure. 
Still an additional object is to expedite the drying of a road bed or the 
like, especially by using the infrared energy radiated by an infrared 
generator. 
These and other objects and advantages of the present invention will become 
more apparent as the following description proceeds. 
To the accomplishment of the foregoing and related ends, the invention, 
then, comprises the features hereinafter fully described and particularly 
pointed out in the claims, the following description and the annexed 
drawings setting forth in detail a certain illustrative embodiment of the 
invention, this being indicative, however, of but one of the various ways 
in which the principles of the invention may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now more particularly to the drawings, wherein like reference 
numerals designate like parts in the several figures, an infrared energy 
generator in accordance with the invention is generally indicated at 1 in 
FIGS. 1 and 2. The fundamental elements of the infrared generator 1 
include a hollow housing 2 within which a plenum 3 is formed, a fuel input 
orifice 4 to the plenum and a fuel output 5 from the plenum, seen most 
clearly in FIG. 3, a fuel flow impeding orifice plate 6 located in the 
plenum and dividing the same into upper and lower plenum chambers 3a, 3b, 
and a radiating screen 7 secured to the housing over its open face 8. 
The housing 2 may comprise a stamped sheet metal body 9, which has a top 
wall 10 and opposite sidewalls 11, 12, and a pair of sheet metal end 
plates 13, 14 welded to the body 9 to form an integral fluid-tight 
structure preferably open only at the input orifice 4 and at its open face 
8 leading to the hollow interior 16 of the housing. A plurality of hangers 
17, such as angle irons, are welded to the top wall 10 of the housing to 
facilitate mounting the infrared heater 1, for example, on a boom 
extending from a vehicle in position over a raod bed to expedite drying of 
the same. 
As is shown most clearly in FIGS. 1, 2 and 3, the input orifice 4 includes 
an opening 19 in the top wall 10 of the housing 2 and a fuel entry fitting 
20, such as a typical pipe fitting, which is welded or otherwise secured 
to the top of the wall so that the hollow interior tubular volume of the 
fitting is generally aligned within the opening 19 in the top wall and 
provides a fluid-tight path from a fuel supply pipe, not shown, to the 
plenum 3. The fuel supply pipe preferably brings a pre-mixed fuel supply, 
including a combustible gas, such as vaporized propane, and air mixture, 
from a source, not shown, to the infrared heater 1. Such a fuel source, 
which may comprise a mobile liquid propane tank, will usually provide fuel 
to the infrared heater at a relatively low pressure, say on the order of 
about four inches on a water column. Reference to fuel herein, then, means 
a pre-mixed combination of air and combustible gas or vapor, such as 
propane. A primary fuel diffuser 21, shown in FIGS. 1 through 4, may be a 
screen or formed sheet metal with a plurality of holes drilled 
therethrough and is attached to the interior side of the housing top wall 
10 over the input orifice 4 to effect distribution of the fuel received 
from the input orifice 4 relatively evenly throughout the upper plenum 
chamber 3a, as is depicted by the arrows 22. 
The orifice plate 6 is approximately the same length and width dimension as 
the interior rectangular length and width dimensions of the housing 2, for 
example, say from about three to five inches wide and from about ten to 
forty inches long, and the orifice plate, which is preferably of a metal 
similar to that of which the housing 2 is formed, is welded at 23 about 
its perimeter to the housing side and end walls for mechanical support of 
the orifice plate in the housing and preferably to avoid fuel flow at the 
interface of the orifice plate and the housing walls. A plurality of holes 
24 in the orifice plate 6 are distributed relatively evenly over the 
orifice plate to provide flow paths from the upper plenum chamber 3a to 
the lower plenum chamber 3b, which can be seen most clearly in FIGS. 2 and 
3. 
It is the function of the orifice plate 6 to impede the flow of fuel from 
the upper plenum chamber 3a to the lower plenum chamber 3b and thereby to 
create a back pressure in the upper plenum chamber or, in other words, a 
pressure in the upper plenum chamber that is larger than the pressure in 
the lower plenum chamber, which in effect is at atmospheric pressure, or 
just slightly greater than atmospheric pressure to assure continued fuel 
flow for combustion, due to the large opening or exposure provided at the 
plenum fuel output 5. The back pressure assures fuel flow in the positive 
direction and at a suitable velocity to avoid blow out and backfires. 
Therefore, the sum total of the effective cross-sectional areas of the 
holes 24 perpendicular to the major flow direction therethrough is smaller 
than the effective cross-sectional area of the input orifice 4 
perpendicular to the major flow direction through the latter. The total 
area of the holes 24 is on the order of from about fifteen percent (15%) 
to about forty percent (40%) less than the cross-sectional area of the 
input orifice, with the preferred range being on the order of from about 
twenty percent (20%) to about thirty percent (30%) less. For convenience, 
the cross-sectional area of the input orifice may be considered to be the 
hollow interior cross-sectional area of the fuel input fitting 20, which 
has approximately the same cross-sectional area of the fuel pipe, not 
shown, and the opening 19. 
Moreover, in one successfully tested embodiment of the invention, the 
orifice plate 6 included 2 rows of 38 1/8 inch diameter holes 
substantially evenly distributed over the approximately 40 inch length of 
the orifice plate, and the input orifice was a 11/4 inch pipe fitting. 
Although the actual inner diameter of such a pipe fitting is slightly 
larger than 11/4 inch, the total area of the holes 24 in the described 
tested embodiment was at least approximately twenty-six (26) percent less 
than the cross-sectional area of the input fitting The pre-mixed fuel 
supplied to such tested infrared generator was a mixture of vaporized 
propane derived from a relatively mobile liquid propane tank and air, and 
the relative back pressure or fluid pressure in the upper plenum chamber 
3a was approximately 11/2 inches on a water column, while the pressure in 
the larger plenum chamber was approximately equal or just slightly larger 
than atmospheric pressure, as described above. 
While the magnitude of the back pressure in the upper plenum chamber 3a 
relative to atmospheric pressure may vary in accordance with the ratio of 
the total area of the holes 24 and the effective area of the input orifice 
4 and with the pressure of the fuel supplied from the fuel source, during 
normal operation of the infrared generator 1 it is desired that the back 
pressure in the upper plenum chamber 3a be greater in magnitude than that 
of the atmospheric pressure at or near which the lower plenum chamber 3b 
is usually maintained in order to assure fuel flow in a positive 
direction, i.e. from the input orifice 4 through the holes 24 in the 
orifice plate 6 and then through the fuel output 5. Moreover, although a 
single hole or slot or a plurality of holes or slots, which are larger in 
size but smaller in number than the illustrated holes 24 and which present 
a cross-sectional area approximately equal to the total area of the holes 
24, may be substituted in their place in the orifice plate 6 to provide an 
equivalent function of impeding flow through the orifice plate and 
increasing the back pressure in the upper plenum chamber 3a, the plurality 
of holes illustrated are preferred in order to obtain a relatively even 
distribution of fuel to the lower plenum chamber 3b and to the fuel output 
5 for subsequent substantially even distribution of the combustion process 
in the infrared generator. Also, although the orifice plate 6 is 
preferably welded about its perimeter of the housing walls, other 
equivalent means may be employed to mount the orifice plate in the housing 
and to preclude fuel flow at the interface of the orifice plate perimeter 
and the confronting housing walls. Alternatively, the controlled fuel flow 
through the orifice plate 6 actually may be equivalently provided in a 
relatively accurately determined space between the perimeter of the 
orifice plate and the confronting housing walls. 
A plurality of screw nuts 25 are welded to the bottom surface of the 
orifice plate 6 to provide for attachment of screws 26 that secure a 
baffle plate 27 to the sub-assembly of the housing 2, orifice plate 6, and 
primary diffuser 21. The screw nuts 25 provide a spacer function to space 
the baffle plate 27 away from the orifice plate 6, thereby to create or to 
define the lower plenum chamber 3b of which the baffle plate establishes a 
lower boundary. Although the length dimension of the baffle plate 27 is 
preferably the same as the orifice plate 6 and the interior length 
dimension of the housing 2, the width dimension of the baffle plate is 
somewhat smaller than the width dimension of both the orifice plate and 
the housing interior so that the two edges 28, 29 of the baffle plate 
effectively cooperate with the housing sidewalls 11, 12 to define the 
output passageways 30, 31 of the fuel output 5 from the plenum 3, as can 
be seen most clearly in FIG. 3. The total area of the output passageways 
30, 31 is sufficiently large to provide substantially unimpeded flow of 
fuel generally in the direction of the arrows 32 and to allow the pressure 
in the lower plenum chamber 3b to approach that of the ambient atmospheric 
environment externally of the infrared generator 1. 
A peripheral flange 33 circumscribes the housing 2 at the open face 8 
thereof, and the radiating screen 7 is secured to the flange 33. More 
specifically, flanged portion 34 of the screen 7 is sandwiched between 
gaskets 35 and 36, which, respectively, may be of a single part or 
multiple parts to facilitate expansion and preferably are of heat 
resistant material, such as asbestos-like material or the like. A metal 
ring holder 37, which may be comprised of a plurality of metal strips to 
permit thermal expansion thereof, secures the screen flange 34 and the 
gaskets 35, 36 to the housing flange 33 by a plurality of screw, washer 
and nut combinations 40a, 40b, 40c. The gaskets 35 and 36 permit thermal 
expansion and contraction of the radiating screen 7 without detriment to 
the latter, isolate the screen heat from the housing flange 33 and ring 
holder 37, and assure that the combustion products of the combusted fuel 
pass through the main radiating portion 41 of the screen 7. The radiating 
screen 7 may be, for example, material comprised of inconel, which is able 
to withstand the relatively high temperatures to which the radiating 
screen is brought during operation of the infrared generator 1 and which 
has desirable infrared radiating characteristics; such an inconel infrared 
energy radiating screen is sold by the Cleveland Wire Cloth Company of 
Cleveland, Ohio. 
In using the infrared generator 1, a pre-mixed gaseous fuel supply of 
propane and air, for example, is provided to the fuel entry fitting 20 of 
the input orifice 4. The fuel is diffused or dispersed relatively evenly 
in the upper plenum chamber 3a by the primary diffuser 21. The orifice 
plate 6 assures that the back pressure in the upper plenum chamber 3a is 
larger than the pressure in the lower plenum chamber 3b, as fuel flows in 
a positive direction through the holes 24. Fuel exits the lower plenum 
chamber 3b at the fuel output 5 into the volume 43 bounded by the baffle 
plate 27 and the screen 7 and from that volume the fuel may flow through 
the screen to the ambient environment. 
By holding a flame adjacent the radiating screen 7, the fuel in the volume 
43 may be ignited, and as long as fuel is delivered from the fuel output 5 
to that volume fuel combustion normally will continue to occur at the fuel 
output and/or in the volume 43. Some combustion also may take place in the 
lower plenum chamber 3b, but due to the back pressure in the upper plenum 
chamber 3a and the maintained fuel flow through the holes 24 in the 
positive direction from the upper to the lower plenum chambers, there 
normally will not be any combustion in the upper plenum chamber. The 
screen 7, of course, is exposed to the products of the fuel combustion, 
and heat generated by such combustion elevates the temperature of the 
radiating screen 7 to a temperature level such that the screen radiates 
infrared energy, for example, toward the earth for drying the same. 
Since the back pressure in the upper plenum chamber 3a is relatively higher 
than atmospheric pressure, fuel flow through the holes 24 of the orifice 
plate 6 is assured. Therefore, a draft or a wind blowing toward the 
radiating screen 7 tending to push the fuel back into the upper plenum 
chamber and ambient atmospheric pressure increases usually will not be 
able to blow out the continuing combustion process in the infrared 
generator 1 and especially usually will not be able to blow the combustion 
back into the upper plenum chamber 3a to cause a backfire at the input 
orifice 4. Moreover, since the back pressure in the upper plenum chamber 
3a and fuel flow therethrough in a positive direction are assured, the 
overall area of the open end face 8 of the housing and the radiating area 
41 of the screen 7 may be relatively large, for example, on the order of 
about 40 inches long and about 3 to 5 inches wide so as to provide the 
radiated infrared energy over a relatively large output area. Further, due 
to the back pressure and assured positive fuel flow, several infrared 
generators may be supplied in parallel from a common fuel source and may 
be physically positioned to supply infrared energy to a combined even 
larger overall output area. 
Due to its relative insensitivity to wind and changing atmospheric pressure 
and, therefore, its ability to operate from a relatively low pressure fuel 
source, the infrared generator 1 of the present invention may be 
effectively used outdoors for drying earth. During such usage, a plurality 
of such infrared generators may be supported by their hangers from a 
vehicle or the like, which may be driven along the proposed road bed, in 
positional relationship to effect drying of a relatively wide strip of 
earth of the road bed over which concrete may later be poured during 
highway construction. This is, of course, but one of the many purposes for 
which infrared generators in accordance with the invention may be 
employed. Moreover, it will be appreciated that although the flow 
impediment and back pressure obtained by the orifice plate of the 
invention make the infrared energy generator especially useful with low 
pressure fuels, such as pre-mixed propane and air, the principles of the 
invention also may be employed with infrared energy generators that use 
other types of low or higher pressure fuels.