US3225815A

US3225815A - Gas burners

Info

Publication number: US3225815A
Application number: US202729A
Authority: US
Inventors: Konrad E Bauer; Harry R Carlson
Original assignee: Hupp Corp
Current assignee: SCHWANK Inc; Hupp Corp
Priority date: 1962-06-15
Filing date: 1962-06-15
Publication date: 1965-12-28
Anticipated expiration: 1982-12-28
Also published as: GB963186A

Description

Dec. 28, 1965 K. E. BAUER ETAL 3,225,815

GAS BURNERS Filed June 15, 1962 4 Sheets-Sheet 1 Konrad E. "Bauer Harry R.Corlson AOR Dec. 28, 1965 K. E. BAUER ETAL GAS BURNERS 4 Sheets-Sheet 2 Filed June 15, 1962 #9 Om; mi

wN Om ATTORNEYJ' GAS BURNERS Filed June 15, 1962 4 Sheets-Sheet 5 INVENTORS Konrad E. Bauer Harry R. Carlson ATTO 1 1965 K. E. BAUER ETAL GAS BURNERS 4 Sheets-Sheet 4 Filed June 15, 1962 INVENTORS Konrad E. Bauer ATTORNEYS Harry R. Carlson yw United States l atent @fifice 3 ,225,815 Patented Dec. 28, 1965 3,225,815 GAS BURNERS Konrad E. Bauer, Mentor, and Harry R. Carlson, Cleveland, Ohio, assignors to Hupp Corporation, Cleveland, Ohio, a corporation of Virginia Filed June 15, 1962, Ser. No. 202,729 1 Claim. (Cl. 15899) This invention relates to gas burning devices and more 1 el and air is burned on or adjacent the surface of a rner element to heat the surface to incandescence to thereby emit energy in the infra-red spectrum.

Efiicient and dependable burners of this type are disclosed and claimed in United States Patent No. 2,775,294 granted December 25, 1956. These burners have met with wide-spread acceptance in the United States and in foreign countries. Essentially, these burners comprise a cast housing containing an integrally cast venturi through which a mixture of gas and air is fed. One wall of the housing is formed by a refractory plate or plates having a large number of perforations through which the combustible gas-air mixture is fed for combustion adjacent the outer face thereof, the outer face of the refractory element being raised to a temperature in excess of 1500 F. to emit energy in the infra-red spectrum.

However, the output of these burners and competitive burners is limited because of their relatively small physical dimensions. For example, in their commercial form these burners have an output in the neighborhood of 12,500 B.t.u./hr. Problems have been encountered in previous attempts to provide burners with substantially greater output i.e. 30,000 to 50,000 B.t.u./hr. which are required for many industrial and domestic applications. Prior to the present invention, the most effective method of achieving this greater output was by mounting a suitable number of the smaller units in side-by-side relation in a special frame or housing. While the performance of these multiple unit burners has been satisfactory, they nevertheless are inherently relatively costly and heavy since they incorporate three to five separate case housings, each housing including an interior venturi and baffles, and each requiring a separate fuel-air-inlet.

With these considerations in mind, it is the principal purpose and object of the present invention to provide improved high output radiant gas burning devices comprising a single housing of relatively simplified lightweight construction.

It is a further object of the present invention to provide improved high output radiant gas burners in which the principal components, other than the burner elements, are constructed of relatively light-weight sheet metal of simple configuration.

It is also an object of the present invention to provide improved radiant gas burners having a simplified chamber for distributing a combustible fuel-air mixture, perforated burner elements which form a wall of the chamber and a sheet metal venturi positioned externally of said chamber for supplying a combustible mixture of fuel and air to said chamber.

It is also an object of the present invention to provide improved radiant gas burners having a distributing chamber of novel configuration which effectively uniformly distributes a combustible mixture of fuel and air to the garticularly to such devices in which a mixture of gaseous inner surface of the radiant burner elements with minimum interference with its free flow.

It is an additional object of the present invention to provide improved high output radiant gas burners which occupy considerably less space and have considerably less Weigtht than prior burners having comparable performance characteristics.

It is also an object of the present invention to provied improved high output radiant gas burners in which the radiant face of the burner is flat and uninterupted thus providing increased radiant surface area within given overall dimensions and facilitating ignition by the elimination of discontinuities on the radiant surface associated with former comparable burners.

It is also an object of the present invention to provide improved reflector assemblies for radiant gas burners.

Since the quantity of radiant energy emitted by a surface varies geometrically with the temperature of the surface, many attempts have been made toincrease this temperature without a corresponding increase in the fuel input. For example, it has been proposed to position a relatively coarse metal screen over the radiant burner face. While it has been found that such a screen raises the temperature of the radiant face; it also tends to prevent perfect combustion and to cause production of carbon monoxide in amounts which cannot be tolerated when the burners are used indoors. In prior burners such screens could be used reliably only in conjunction with a blower for increasing the flow of air into the burner, and the incorporation of such blower in the system increased the initial cost, weight and complexity of the unit, thus offsetting the advantages of the screen to a certain extent.

It is a further object of the present invention to provide a solution to this problem in the art and to provide improved radiant gas burners in which a full screen may be positioned opposite the radiant face of the burner without the necessity of employing a separate blower to induce a flow of the required amount of primary air to maintain clean eflicient combustion.

It is desirable that burners of the type involved in this invention be usable with all of the kinds of gases commercially supplied, such as manufactured gas, natural gas, propane and butane. The pressures under which these gases are supplied varies greatly, so that the burners must burn perfectly at a considerable range of pressures as well as with gases having variations in composition.

The amount of air required for perfect combustion depends on the carbon-hydrogen ratios of the hydrocarbon gases (so that butane, for instance requires more air per B.t.u. input than natural gas, which may be principally methane) while the amount of air induced by the flow of the gas flhrough a venturi depends on both the quality of the gas and its pressure at the orifice. It can thus be seen that to induce suflicient air for perfect combustion using any of the commercial gases at any available line pressure with no change in the burner other than to provide an orifice suitable to the gas supplied, makes the problem especially difficult. It has been this problem which has heretofore prevented the use of a single burner without a blower where outputs from 30,000 to- 50,000 B.t.u. per hour were required.

It is therefore a further object of this invention to provide a single aspirating burner which 'will meet the combustion requirements of approval authorities, such as the American Gas Association Laboratories at outputs up to 50,000

B.t.u. per hour for use with all of the usual commercial gases at the required ranges of pressures, with no change in the apparatus other than the insertion of a suitable oriflce.

This is accomplished in the burner of the present invention by provision of a novel venturi and housing and a new relationship between the venturi and housing which effectively increases the air flow for a given gas input.

The venturi comprises a gas orifice, a surrounding uniquely-shaped air entrance bell coaxial with the gas orifice, a coaxial throat through which the gas and air flow, a coaxial tapered tube in which the gas and air are mixed and the mixture expanded, and an elbow of special configuration for directing the mixture into the distribution chamber.

The entrance bell has a cylindrical air entrance, the cross-sectional area of the cylinder being preferably nine times the area of the throat (which in a burner of 50,000 Btu. per hour capacity has a diameter of two inches). The entrance cylinder is connected to the throat by a smooth contraction wall having a reverse curve (or ogive) contour.

The gas orifice is located on the axis of the venturi well within the bell near the plane of juncture of the cylinder and the contraction wall.

The tapered expansion tube has an included angle of not over five degrees and its large end has an area approximately 2 /2 times the area of the throat.

The axis of the entire venturi is inclined upward from the entrance at an angle preferably not less than five degrees.

The elbow connects the large end of the tapered tube with an opening in the mixing chamber. This opening has an area greater than the large end of the tapered tube so that the mixture continues to expand as it passes through the elbow into the mixing chamber.

The venturi is positioned externally of the housing and lies alongside of the mixing chamber so that a large venturi may be used without unduly increasing the size of the heater.

By maintaining the configuration and the proportions given, the maxi-mum induction effect is secured, with no increase in length or height of the heater and only a very slight increase in width over prior designs using conventional venturis. The proportions can be changed to some extent, with, in some cases, only a small reduction in air induction. For example, if the air inlet cylinder were made with an area six times the area of the throat, the induction of air would be less than if it had an area nine times that of the throat, but greater than if a conventional venturi were used.

As in conventional venturi designs, the gradual increase in area from the throat to the mixing chamber converts the velocity head at the throat to static pressure in the mixing chamber. The very gradual increase in area combined with the reduction of friction brought about by the proportions and smooth interior surface incorporated in the venturi of the present invention eliminates losses ordinarily encountered.

Flow and induction of air are further increased by the upward slops of the axis of the venturi, the mixture, at the temperature it attains in the warm venturi being lighter than the cool outer air, thus providing a thermal head to aid the fiow.

It is therefore a further object of this invention to provide a burner having a venturi which will aspirate all the air required for complete combustion of gases commercially available at ratings up to 50,000 Btu. per hour within the confines of a compact heater casing.

Another object of the invention is to provide in an overhead radiant heater means to illuminate as well as to heat the space below.

Other objects of the invention are to provide an infrared gas space heater which is economical to manufacture by quantity production methods; one which presents an attractive appearance after it is installed; and one which is very durable under corrosive atmospheric conditions, the burner parts being made of vitreous enamelled steel and the reflector of aluminum, and a surrounding shroud suitably coated against heat and corrosion.

Additional advantages and objects of the present invention will become apparent as the description proceeds in connection with the accompanying drawings, in which:

FIG. 1 is a perspective view of an overhead radiant heater embodying the present invention;

FIG. 2 is a top view of the heater shown in FIG. 1;

FIG. 3 is a side view of the same heater with parts broken away to show interior construction;

FIG. 4 is a view of the underside of the same heater;

FIG. 5 is an end view of the heater with the outer shroud partly broken away;

FIG. 6 is a transverse sectional view of the burner, taken on line 6-6 of FIG. 2;

FIG. 7 is a longitudinal sectional view of the burner taken on line 77 of FIG. 6; and

FIG. 8 is an end view similar to FIG. 5 of a modification of the heater, incorporating apparatus for illumination as well as that for heating;

Referring to FIGURES 1 to 7 inclusive, the principal components of the heater of the present invention are the sheet metal distributing chamber, indicated generally at 20, the sheet metal ventun' assembly, indicated generally at 22, an intermediate frame assembly, indicated generally at 24, a reflector assembly, indicated generally at 26, the radiant burner element, indicated generally at 28, and a shroud indicated generally at 30.

v The distributing chamber 20 is preferably formed of a slngle piece of relatively thin sheet steel with an essentially flat inclined base wall 32, flat

parallel side walls

34 and 36 and end

walls

38 and 40. Adjacent their lower edges, the side and end walls are formed outwardly to provide a peripheral recess as at 42. Formed integrally with the housing 20 at the base of the recess 42 is a flat marginal flange 44. It will be noted that while the housing 20 is of substantially uniform width along its entire length, it is of uniformly decreasing depth. The open side of the housing is tied with bracer strips 46 of channel section which prevent distortion during the subsequent vitreous enamelling operation.

Adjacent to end wall 38, side wall 36 has a flanged-in oval hole 48 (FIG. 6), which in a burner having at capacity of 50,000 Btu. per hour is six inches long and about 2% wide at its widest part. The axis of the oval is inclined at an angle of five degrees with flange 44, sloping downward from wall 38 and tapering down in the same direction. The large end of the opening 48 is formed on an arc of 1% inch radius and the small end is formed on an arc of 1% inch radius, straight .top and bottom flanges connecting the arcs as best shown in FIG. 3.

Within chamber 20 adjacent end 38 is a plate 50 extending diagonally across the end of the chamber (FIGS. 6 and 7), the low end of plate 50 being located below hole 48, the plate being a little longer than the hole. Attached to plate 50 is a U-shaped screen 52 of wire or expanded metal, the legs of the U extending to points near the plane of the offset forming recess 42, both legs substantially filling the area below plate 50 and above this plane. One leg is located close to the edge of plate 50 remote from wall 38 while the other leg is near the middle of the plate.

On the, axis of venturi 22 is a gas nozzle 54 having an orifice 56 and supplied with gas from a supply pipe 53. The flow of gas may be manually or automatically controlled by a valve (not shown) of any of the well-known types.

The venturi is formed of three sheet metal parts welded together at

external flanges

60 and 62 and at 64 to form a unitary member comprised of an entrance bell 66, a throat 68, expansion tube 70 and an elbow 72.

Entrance bell 66 is cylindrical and has a flared opening 76 at its inlet end and a converging wall connecting it to the throat 68. The cylinder has a cross-sectional area nine times the area of the throat, which for a capacity of 50,000 B.t.u. per hour is two inches in diameter. The converging wall is composed of a spherical portion 80 connected to cylindrical bell portion, the spherical portion merging into a reversely-curved connection which merges into the expansion tube 70 at the throat.

The throat is located at a distance from the opening 76 (measured on the axis of the venturi) approximately equal to the diameter of the opening 76. Expansion tube 70 has an included angle of taper equal to five degrees.

Elbow 72 connects the large end of tube 70 with opening 48 in chamber 20, fitting snugly within the flange around the hole. Edge 82 of the outlet end of the elbow is welded to the flange surrounding hole 48. The elbow makes a smooth transition from the end of tube 70 to the chamber 20, and provides the necessary outlet area for minimum disturbance of the gas flow without making necessary any increase in the height of chamber 20 which would be necessary if the outlet were round.

The axis of the venturi is not only inclined downward at an angle of about five degrees but is also inclined outwardly as shown in FIG. 2 so that the bell 66 will clear the heater frame 24, the plane of the outlet of elbow 72 making an angle of about seven degrees with the axis of the venturi.

After the venturi is welded to the chamber, the assembly is coated with vitreous enamel to protect it from corrosion in service and to aid in reducing frictional resistance to flow of the gas air mixture.

Nozzle 54 is supported on the axis of hell 66 with its orifice 56 within the bell about on the plane through the junction of the cylindrical and spherical bell portions by a spider having three thin legs 84 (one shown) to assure a rigid mounting of the nozzle with minimum flow restriction.

The intermediate frame assembly 24 com-

prises side pieces

86 and 88 and

end pieces

90 and 92, spotwelded together. It will be noted that the side piece 88 is wider than the side piece 86. Accordingly, when the bottom edge of the frame assembly is disposed in a horizontal plane as shown in FIGURES 6 and 7, the housing 20 is tilted at an angle of about 5 degrees. The side piece 88 has a plurality of exhaust openings 94 leading to two exhaust stacks 96 mounted on the piece 88. At its upper edge frame assembly 24 is provided with an integral flange of essentially the same dimensions as the flange 44 of the housing. The

flanges

44 and 100 are secured together by screws 108. At its lower edge the intermediate frame assembly 24 is formed with a peripheral flange 110 which extends outwardly at right angles to the planes of the side and end pieces forming the intermediate frame assembly.

Stacks 96 are rectangular in section and are provided with a plurality of transverse baifles 112 to prevent flame flashing out of the stack when the burner is ignited. Between the two stacks is a circular hole 114 for ignition of the burner from a pilot 116 mounted outside of the frame assembly 24. This pilot may be of any desired type (either constantly burning or electrically ignited) and may be provided with a safety valve to prevent gas flow if the pilot goes out. The design of the pilot forms no part of the present invention.

The reflector assembly 26 is made up from sheet

aluminum side pieces

118 and 120 and end

pieces

122 and 124. Each of the end pieces is provided with a flange wrapped around and spotwelded to the adjacent side piece. At its upper edge the reflector assembly 26 is provided with a peripheral flange 128 which matches the flange 110, the two flanges being secured together by a plurality of screws 129 which may be readily installed 6 because of the disposition of the flanges and 128 The parts are so dimensioned that the reflector assembly 26 forms a continuation of the intermediate frame assembly 24, the elements together providing a pyramidal assembly for concentrating and directing the radiant energy produced by the burner as desired.

The lower edge of the reflector assembly 26 terminates in a flat peripheral horizontal flange 130.

The buner elements 28 are preferably of the type disclosed and claimed in the aforesaid United States Patent #2,775,294. These elements comprise refractory plates about thick which are provided with a large number of very small though cylindrical perforations. Since they are exposed to rapid heating and cooling and to thermal and mechanical shock and because of practical manufacturing reasons, it is not feasible to make them in sizes large enough to produce an output in the range of 30,000 B.t.u. per hour to 50,000 B.t.u. per hour. At pres ent, commercially available burner elements are in a form having a capacity of about 6,000 B.t.u. per hour each under normal operating conditions. Accordingly, in the burner of the present invention, eight of these elements are used in side-by-side relation to produce a total gross output in the neighborhood of 50,000 B.t.u per hour.

As best shown in FIG. 6, the burner elements 28 are received in the recess 42 of the burner housing but are separated from the housing by a strip of insulating material 134 which is preferably a compressed mat of ceramic fibers of the type sold under the trade name Fiberfrax. The individual burner blocks are held in place by U-shaped retainer strips 136 which have a portion projecting slightly over the face of the blocks 28, a U-shaped portion extending into the recess 42 to compress the insulating strip 134, the remainder of the retainers extending between the

flanges

44 and 100 on the housing and the intermediate frame assembly, respectively. The retainers 136 extend substantially along the full length and width of the housing. However, suitable discontinuities are provided to accommodate the effects of thermal expanison and contraction. Because of the resilient nature of the insulating strip and the retainers, it is not necessary to employ cement or other holding means between the adjacent edges of the burner elements. Also this method of mounting and positioning the burner elements permits quick and easy replacement of a single one of the elements should it become damaged in use.

As indicated above, a screen is positioned in spaced parallel relation with the front face of the burner blocks 28 to increase the temperature of this radiant face. This screen 138 is made of relatively coarse mesh heat resistant wire such as Nichrome. It is held in position by angle clips 140. There are eight of these clips, one located at each of the bolts 108. One leg of each clip is clamped between the

flanges

44 and 100, with bolt 108 passing through an opening in the leg. The other leg is slotted. A few of the screen cross wires extend through the slot in each of the clips, thus supporting the screen but leaving it free to expand when it is heated.

Shroud 30 is made of two

trapezoidal side pieces

142 and 144 and two

trapezoidal end pieces

146 and 148, each having a top flange 150 and a bottom flange 152 and being provided with ventilation holes 154 near the bottom. Side 142 is spot-welded to end 148 at their joining corner. Similarly, side 144 is spot-welded to end 146. The other two corners are not welded together so that half of the shroud may be taken off to service the burner (for example, to change the orifice to suit the gas supply).

As shown in FIG. 2, side 144 has a right angle flange 156 on the edge adjacent to end 148. This flange fits between end 148 and an offset strip 158 spotwelded thereto. End 146 has a similar flange 160 which fits between side 142 and an offset strip 162 spotwelded to side 142.

As shown in FIG. 1, an angle clip 163 is welded to shroud side 144. This clip lies beneath top flange 150 on end 148, and the two parts are bolted together. A similar construction is used at the diagonally opposite top corner of the shroud.

At the other two top corners of the shroud where the

sides

142 and 144 are welded to ends 148 and 146 respectively, reinforcing gussets 164 are spotwelded to flanges 150 of the two parts attached to each other.

As shown in FIGS. 4, and 6, bottom flanges 152 on side 144 and ends 146 and 148 are bolted to overlapping flanges 130' on the corresponding reflector pieces by means of bolts 165. Since the shroudbottom is deeper from front to back than the reflector bottom to provide room for the venturi, there is an opening between flange 130 and flange 152 on the venturi side. This opening provides additional air for cooling any valves or automatic controls which may be located within the shroud. For appearance the opening is provided with a grill 166, which is made of crossed longitudinal and transverse vertical strips interlocked in eggcrate fashion. The grill is held in place by bolts 168.

Welded to intermediate frame 24 at opposite ends are two supports 170 the entire frame being vitreous enameled after the supports are welded. Bolted to these supports are angles 172 provided with holes by which the heater may be attached to any desired supporting structure above.

In use, the heater is normally mounted as shown in the drawings to direct the radiant heat downward, in which position housing 20 and burner 28 will be tilted five degrees upward toward exhaust openings 94.

The burner may be placed in operation by turning on gas to the pilot 116 by means of a valve (not shown), lighting the gas at the pilot by any suitable means, then turning on gas to the main burner uspply line 58 by means of a suitable valve (not shown).

As the gas flows into the open end of the venturi, it entrains slightly more than the amount of air required for complete clean combustion. The aspiration of the sufiicient amount of air without an auxiliary blower and particularly with large size burners having a single inlet, is solved for the first time by the present invention. One of the factors responsible for the successful operation of the burner in this respect is the inclination of the venturi. As a result of this inclination, all thermal and gravity factors work to promote the flow of primary air. This advantage is increased as the venturi is warmed and the burner has been in operation for some time.

The length of the venturi is selected to slow the gas sufliciently to establish the proper pressure at the region opposite the inner face of the burner element adjacent the relatively enlarged end of the housing 20. The desired pressure at the succeeding burner elements is determined by the shape of the housing which is of uniformly decreasing cross-section as a function of the distance from the venturi. This construction eliminates the need for internal baffling invariably associated with prior burners of this type, except for baffle 50 and screen '52 which prevent an excessive flow of mixture to the part of the burner directly opposite to opening 48.

The side mounting of the venturi not only conserves space but also contributes significantly to the achievement of proper pressures within the housing without the usual internal baffling. Because of the inclination, disposition of the venturi, the configuration of the housing and the smooth interior surfaces, sufficient air flow is assured under all operating conditions despite the use of the full screen. The relatively reduced mass of the components increases the rate at which heat is dissipated thus maintaining the supply of air at the rear face of the tile relatively cool, minimizing the tendency toward flashback.

Because of the inclination of the housing 20 and the corresponding inclination of the radiant face of the burner elements 28, the combustion products flow smoothly toward the outlet passages 94 and thence to the exhaust stacks 96. Since the exhaust stacks are located at the side of the burner opposite the venturi, there is no possibility of contamination of the incoming fresh air by the combustion products.

When less than 50,000 B.t.u./hr. output is desired, for example an output of 30,000 B.t.u./hr. which can be achieved by the use of five burner elements instead of the eight shown, the side pieces of the intermediate frame assembly 24, the reflector assembly 26 and the shroud 30 will be shortened appropriately. The housing 20 will also be shortened without any other change in its configuration, thus permitting the use of the same major dies for the formation of housings of different size. Larger capacity burners can be provided by suitable increases in dimensions.

The form of the invention shown in FIGURE 8 comprises the same heating arrangement and parts with the addition of means to illuminate as well as to heat the area below the heater. Shroud end members are longer than the corresponding member of the form shown in FIG- URES l to 7 inclusive, to provide space for two grills 174, one grill being on each side of the reflector.

Suitably attached to each of the shroud side pieces are two spaced apart facing fluorescent lamp sockets 176 of the usual commercial type. Each pair of sockets supports a standard fluorescent light tube 178 above the center of one of the grills. Also attached to the shroud sides are brackets 180 welded to and supporting reflectors 182 above tubes 178 to reflect light from the tubes out through the openings in the grills. The lights have the usual ballasts, starters control switches and wiring (not shown) which may be located at any desired points.

A single lamp of the same construction can be installed in the form of the heater shown in FIGS. 1 to 7, without change in the heater other than provision of mounting holes for the parts added for illumination. However, the two grills and tubes provide better illumination and a more balanced and pleasing appearance.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claim are therefore intended to be embraced therein.

For example, other types of radiant burner elements may be substituted for the ceramic blocks with many small round holes, such as ceramics with slots instead of round holes or single or multiple fine screens instead of ceramics; or instead of the flat plates used to form the reflector, curved plates may be used to secure a different pattern of radiation downward from the heater.

What is claimed and desired to be secured by United States Letters Patent is:

A radiant heater comprising a dish shaped distributing chamber having a base wall and side walls, said chamber being elongated and being of progressively decreasing cross-sectional area from one end to the other, essentially planar burner means comprising a plurality of perforated refractory blocks mounted to form a wall in said distributing chamber opposite said base wall, a screen co-extensive with the aggregate area of said blocks, a plurality of clips, each clip having a mounting portion attached to said distributing chamber and a slotted portion, said screen being supported in said slotted portion of said clips in parallel spaced relation with said outer surface of said blocks, a venturi assembly mounted externally of said distributing chamber and extending along one of said side walls and having its outlet end in communication with the interior of said chamber through said one side wall adjacent said one end thereof, the axis of said venturi being inclined to dispose the inlet end thereof below the outlet end thereof, a fuel nozzle carried by said venturi adjacent its inlet end to supply gaseous fuel to said venturi, the flow of gaseous fuel entering said venturi, entraining combustion air, the gaseous fuel and air being mixed in said venturi and delivered to said one end of said distributing chamber for passage through said perforated burner means and combustion on the outer surface thereof.

References Cited by the Examiner UNITED STATES PATENTS 164,652 6/1875 Mason. 1,424,760 8/ 1922 Grayson. 1,653,285 12/1927 Houlis 158116 X 1,800,616 4/1931 Forster 158118 X 10 Kirby. Lindemann et al. 158114 X Hollman 158-104 Kelley 15 8-71 Lutenbacher 158118 X Parker. Cartter.

Formiti 126-92 Honger 158114 Lambert.

Koltun 126-41 Great Britain.

FREDERICK L. MATTESON, JR., Primary Examiner.

JAMES W. WESTHAVER, Examiner.