US3857670A

US3857670A - Radiant burner

Info

Publication number: US3857670A
Application number: US00346071A
Authority: US
Inventors: A Karlovetz; E Placek
Original assignee: INT MAGNA CORP
Current assignee: INT MAGNA CORP
Priority date: 1973-03-29
Filing date: 1973-03-29
Publication date: 1974-12-31
Anticipated expiration: 1991-12-31
Also published as: AU7503774A; CA991980A

Abstract

A radiant burner that has a hollow body with a closed rear and a peripheral wall extending forwardly from the rear to define an open ended chamber. There is an outwardly extending, planar spacing flange on the front end of the peripheral wall. A perforated diffuser plate extends across the chamber in a plane located rearwardly from the end of the wall. The plate has a forwardly directed flange around its perimeter and an outwardly extending marginal edge which lies against the spacing flange. A primary screen consisting of a plurality of layers of fine bias cut mesh extends across the open end of the chamber with its edges overlying and adjacent to the front surface of the edge of the plate. A reverberator grid which has a planar body and a backwardly extending border flange is located in front of the primary screen with an outwardly extending edge of its flange adjacent the surface of the edge of the primary screen and its main body spaced forwardly from the primary screen by its flange. The layers of the primary screen and the reverberator grid are spot welded together at certain points. The central portion of the primary screen is dished forwardly toward the reverberator grid. Retaining lips on the spacing flange of the body are folded over inwardly against the front surface of the edge of the reverberator grid flange for retaining the diffuser plate and the primary screen and reverberator grid in place in the burner. There is an inlet for combustible gases into the chamber behind the diffuser plate.

Description

United States Patent [191 Karlovetz et al.

[ Dec. 31, 1974 RADIANT BURNER [75] Inventors: Arthur R. Karlovetz, Fremont; Eugene W. Placek, Middleburg Heights, both of Ohio Primary Examiner-Carroll B. Dority, Jr. Attorney, Agent, or Firml-lenry K. Leonard [57] ABSTRACT A radiant burner that has a hollow body with a closed rear and a peripheral wall extending forwardly from the rear to define an open ended chamber. There is an outwardly extending, planar spacing flange on the front end of the peripheral wall. A perforated diffuser plate extends across the chamber in a plane located rearwardly from the end of the wall. The plate has a forwardly directed flange around its perimeter and an outwardly extending marginal edge which lies against the spacing flange. A primary screen consisting of a plurality of layers of fine bias cut mesh extends across the open end of the chamber with its edges overlying and adjacent to the front surface of the edge of the plate. A reverberator grid which has a planar body and a backwardly extending border flange is located in front of the primary screen with an outwardly extending edge of its flange adjacent the surface of the edge of the primary screen and its main body spaced forwardly from the primary screen by its flange. The layers of the primary screen and the reverberator grid are spot welded together at certain points. The central portion of the primary screen is dished forwardly toward the reverberator grid. Retaining lips on the spacing flange of the body are folded over inwardly against the front surface of the edge of the reverberator grid flange for retaining the diffuser plate and the primary screen and reverberator grid in place in the burner. There is an inlet for combustible gases into the chamber behind the diffuser plate.

10 Claims, 9 Drawing Figures [L /6 I OI 27 /7 jt o l .4 ll] a as i i 2] F l I I G I 4 2: i I i 2/ 3| PATENTEDDEBIH I974 sum 2 of 2 3.857. 670

RADIANT BURNER BACKGROUND OF THE INVENTION Radiant heaters of the type which burn combustible gases to generate heat for raising their energy emitting elements to radiating temperature are well known and have been utilized in many industrial andcommercial installations as well as for portable heating units. The primary advantage of radiant burners of the infra-red type results from the substantially complete combustion of the air and gas mixture so that they can be utilized in enclosed spaces without generating noxious gases to a dangerous extent; In addition, the heat output per unit of combusted gas is very good.

Because industrial and commercial users require large numbers of individual units in order. to heat substantial areas of spaces, and because portable heaters such as those which might be used by campers or sportsmen or by householders for heating areas such as patios or chilled-rooms must be relatively inexpensive, considerable effort has-been devoted in the past to designing such burners toreduce their manufacturing costs by simplifying the operations, particularly the assembly operations which require manual labor.

Many efforts have also been made toward reducing the number of component parts of such a radiant burner thereby to reduce the raw cost of the basic materials which go into the construction and, again, to simplify the assembly and lower the cost of manufacture in that fashion. An efficient burner of this type must be so designed asito provide intimate admixture of the combustible gas and air, to-minimize heat losses and to endeavor to utilize as much'of the input energy for the production'of radiant heat energy as possible by reducing the temperature of the burner housing by utilizing the heat in part for raising the temperature of the incoming gases thereby improving the combustion process.

In addition to the problems of manufacture and assembly which have been inherent in many prior art gas fired infrared heaters, design faults have also existed. For example, many such heaters employ primary screens and reverberator grids which are rigidly attached at their edges to the housings, for example by welding or by machine screws set through mounting flanges. This introduces a problem in the operation of such heaters because the expansion rates of the screens or grids may not be uniform and no provision is made to allow varying expansion to take place without distortion;

From a safety standpoint many prior art infrared heaters of this general type which are assembled with machine screws permit the disassembly of the parts by a user and the consequent likelihood that reassembly will not place the parts in their proper relationship.

From an even more important safety angle, many such gas-fired infrared heaters, particularly the small portable types, are so designed as to result in flashbacks occurring with great frequency. In such'a situation, the gas which should burn at the'primary screen and heat the reverberator grid inorder that infrared energy may be emitted therefrom, do not contain the burning, but the rate of flow of the combustible mixture is inadequate to prevent the combustion of the gases from flashing back into the plenum in the interior of the burner housing. Some efforts have been made to employ diffuser plates interiorly of the housing of such a burner, but, to date, no success has been achieved in the design of a readily assembled diffuser plate which is so proportioned and designed as to substantially eliminate the likelihood of flashback.

It is therefore the principal object of the instant invention to provide a radiant burnerwith a very small number of parts so designed and arranged as to be of easy manufacture and assembly, the resulting structure being efficient and easily portable when desired.

It is yet another object of the instant invention to provide a radiant burner assembly comprising only two metal stampings, a shaped primary screen and a shaped grid, all so designed as to provide for ready assembly with the burner components in a proper relationship to each other for mixing the incoming combustible gases, for feeding them to the combustion zone and for controlling and utilizing the heat output in part to increase the efficiency of the burner.

It is yet another object of the instant invention to provide a radiant burner assembly wherein a gas diffuser plate, a primary screen, and a reverberator grid may readily be assembled by a simple operation and wherein the design of these component parts is such as to substantially eliminate the problem of flashback, to provide for uneven expansion of parts when raised to high temperatures and to substantially. eliminate combustion of the fuel at undesirable locations within the burner.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view in elevation of a radiant burner embodying the invention as mounted on the end of a supply pipe for the combustible gases;

FIG. 2 is a front view in elevation of the burner shown in FIG. 1 with parts broken away;

FIG. 3 is a vertical sectional view on an enlarged scale taken along the line 3-3 of FIG. 2;

FIG. 4 is a view in perspective of a body for a burner embodying the invention;

FIG. 5 is a view in perspective of a diffuser plate;

FIG. 6 is a similar view in perspective of a primary screen; I

FIG. 7 is a similar view of the welded assembly of the primary screen and a reverberator grid;

FIG. 8 is a greatly enlarged, fragmentary view in perspective of a corner of the assembled primary screen and reverberator grid shown separately in FIGS. 6 and 7; and

FIG. 9 is a fragmentary, detailed view taken along the line 9-9 of FIG. 3 and shown on a greatly enlarged scale to better illustrate the simplicity of assembly of the burner component parts.

DESCRIPTION OF PREFERRED EMBODIMENT A radiant burner embodying the invention is generally indicated by the reference number 10 and comprises a hollow body 11 (FIG. 4). In the illustrated embodiment the body 11 is square with a flat rear wall 12 and peripheral side walls 13 which extend forwardly generally perpendicular to the rear wall 12. In other embodiments, the rear wall 12 and side walls 13 may be blended into a substantially continuous curve. The rear wall 12 and side walls 13 define an open ended chamber 14. The burner 10 is shown as being mounted on a gas supply pipe 15 through which combustible gases are fed to the chamber 14. For example, in a portable heater, the gases may be supplied from a pressurized container of propane and delivered through a suitable venturi for the admixture of air with the propane prior to its entry into the chamber 14.

A perforated difi'user plate 16 (FIG. 5) extends across the chamber 14 with its main web 17 lying in a plane located inwardly from the forward end of the peripheral wall 13 and parallel to the rear wall 12. A primary screen l8 (FIG. 6) and a reverberator grid 19 (FIG. 7) extend across the open end of the burner 10, the grid 19 being spaced forwardly of the primary screen 18. The primary screen 18 is fabricated from two or more adjacent layers of fine mesh material, three being shown in this embodiment, and the reverberator grid 19 is fabricated from a much. coarser and heavier screen.

In the illustrated embodiment of the invention, the burner body 11 is shown as being. square in front elevation and the diffuser plate 16, primary screen 18, and

' reverberator grid 19- are also illustrated as being square. A rectangular front elevation and particularly a square shape, is advantageous from a cost standpoint by reducing the waste of material from which the primary screen 18 is fabricated. It will be appreciated, however, that a burner embodying the broader aspects of the invention may have a circular outline, an oval shape, an elongated or rectangular configuration, or any other shape providing a substantially planar face and enclosing a chamber defined by its peripheral walls regardless of their shape, and having a closed rear. In other embodiments, the vertical sectional configuration comparable to that shown in FIG. '3 may be a bullet shape so that the peripheral walls 13 would blend together at the rear of the body 11 for defining the chamber 14.

An outwardly extending planar spacing flange 20 is formed on the front end of the peripheral walls 13 to provide a flat surface against which the other component parts of the burner may be assembled and retained. The perforated'diffuser plate 16 has a forwardly directed flange 21 and an outwardly extending mar- 1 ginal edge 22. The dimensions of the flange 2l'and edge 22 are such that the entire diffuser plate 16 is recessed into the hollow body 11 so that its web 17 extends across the chamber 14 in a plane parallel to the spacing flange and, in the embodiment disclosed, parallel to the rear wall 12.

The utilization of a perforated gas diffuser plate, broadly similar to the perforated diffuser plate 16 of the instant invention has been suggested, as in Paulin US. Pat. No. 3,326,265. However, the perforated diffuser plate 16 of the invention has a unique design which renders it more efficient than those of theprior art and substantially if not entirely eliminates what is termed "flash back."

The perforated diffuser plate 16 of the invention has only sufficient open area so as to maintain a positive pressure on the gases in the plenum'chamber located behind the diffuser plate 16. This pressure is selected and maintained at a level such that the flame speed of the gases being burned is too low to permit burning to. move back behind the diffuser plate 16. In a four inch square burner embodying the invention as designed to burn propane gas, the open area in the diffuser plate 16 is optimum at 23 percent. In this burner, the plenum back of the diffuser plate 16 is one inch deep by four inches square.

It will also be appreciated that during operation, combustion of gases forwardly of the diffuser plate 16 creates a lower pressure in the zone in front of the diffuser plate 16 which contributes to the pressure drop through the diffuser plate.

The maintenance of a positive pressure in the plenum behind the diffuser plate 16 has an additional advantage. Because of this control, the incoming gases may be fed into the burner from any position behind the diffuser plate 16. In FIG. 1, the supply pipe 15 is shown in solid lines as being coupled to the burner by a coupling 27 located at the center of the rear wall 12. However, if desired, the supply pipe 15 may be coupled by a coupling 274, shown in dotted lines in FIG. 1, located in one of the peripheral walls 13 without affecting the burner operation.

The primary screen 18 comprises two or more layers of fine mesh screen cut on the bias. The screen has an unequal number. of wires in the warp and woof, for example, 30 wires per inch in the warp and 31 wires per inch in the woof. The three layers are then rotated relative to each other in order to increase the labyrinth effect through a multiplicity of primary screen layers. In addition, arrangement of the bias-cut screen with unequal numbers of wires in the two directions tends to equalize the screen expansion in all directions during its change in temperature.

In the illustrated embodiment there are shown three layers of the screen which are welded to each other at a number of points indicated by the

reference numbers

23 and 23a (FIG. 6). The central portion of the layers of mesh are welded to each other at the points indicated by the reference numbers 23 and, after welding, the central portions are coined convex. The convex shape of the central portion of the screen 18 preestablishes the direction of thermal expansion of the screen as its temperature increases thereby to eliminate any tendency for the screen layers to separate upon expansion or to move inwardly in the burner as they expand. If the layers of the screen 18 wereto separate from each other, the gases would be likely to burn in the space then existing between the layers, an undesirable and harmful result.

It has been found that the illustrated and described construction has the unexpected result of maintaining the inner of two layers or the innermost of three layers substantially cooler during operation. In a two layer primary screen l8 constructed according to the invention, the inner layer is at least 200F cooler than the front layer during operation. In a three layer screen 18, the inner most layer is at least 400F cooler than the front layer. As will later be explained, this adds to the temperature control of the burner 10 itself and the efficiency of operation.

The reverberator grid 19 (see FIGS. 7 and 8) is fabricated from a coarse mesh screen and shaped to have a planar body or web 24, a backwardly extending border flange 25, and an outwardly extending edge 26. In common with the diffuser plate 16 and primary screen 18,

. the outer dimensions of the edge 26 of the reverberator grid 19 are such that all of these'elements nest against each other in stacked relationship and against the spacing flange 20 of the burner body 11 within the confines of a lip 28 on the flange 20.

In forming a coarse mesh into a shape such as that of the reverberator grid 19 it is conventional to select a piece of the mesh larger than the final web 24 of the combined widths of the flange 25 and edge 26. Notches are then cut at the comers, and the mesh bent back wire ends at the corners, loose individual wires and I structural instability during the great temperature changes between quiescence and operation.

As can best be seen in FIG. 8, a reverberator grid 19 according to the invention is fabricated by drawing a flat piece of coarse mesh so as to eliminate cut wire ends at the corners and to substantially improve operating stability.

After the reverberator grid 19 is fabricated into the shape illustrated in FIG. 7, four welds 23a are made to join the layers of the primary screen 18 and the reverberator grid 19 to each other at the midpoints of their sides. This not only unitizes the screen 18 and grid 19 for simplification of subsequent assembly of the burner, but it also insures that all of the wire surfaces are in direct intimate physical contact to assure the rapid and equal heat of the wires up to the maximum operating temperature. The assembly thus formed by the nine welds provides a thermally unitized screen and grid assembly which expands and contracts in a direct ratio to the expansion and contraction of the burner itself.

When the body 11 is first shaped as, for example, by metal drawing steps, the lip 28 is left in its open position as illustrated in FIG. 4 and shown in dotted lines in FIG. 3 in which it extends forwardly at right angles to the spacing flange 20. In the embodiment of the invention illustrated in the drawings, because the body is square, the lip 28 is not continuous around the edge of the spacing flange 20, but is fabricated in four separate pieces. Lateral spacing between the elements of the lip 28 is such that all of the diffuser plate 16, primary screen 18 and reverberator grid 19 may be placed within the space defined by the lip 28 in succession and against each other as well as against the spacing flange 20.

After this simple assembly step, the lip 28 is folded over inwardly against the front surface of the edge 26 of the reverberator grid 19 as shown in FIGS. 1-3, to provide lip-like retainer 29 for holding these elements of the burner in place across the open front of the body 11. The retainers 29 are bent over to relatively tightly compress the edges of the diffuser plate 16, primary screen 18 and reverberator grid 19 against each other, but not tightly enough to prevent expansion of these elements when the burner is operating.

Because the edges of all three of the diffuser plate 16, primary screen'18and reverberator grid 19 lie outside the open end defined by the front ends of the peripheral walls 13, the open end of the burner is free from obstruction or elements which cause full flow diversion and distort the symmetry of the burning gases.

By the assembly just described wherein the layers of the primary screen 18 and the reverberator screen 19 are welded to each other and the intimate metal to metal contact achieved by the spacing flange and the retainers 29, high temperature gaskets frequently employed in superficially similar burners are eliminated. This also results in a considerable reduction in cost because high temperature gaskets are very expensive, difficult to maintain in condition and difficult to replace. Indeed, in a burner constructed substantially identically with the burner of the invention, and with gaskets inserted between the edges of the elements just discussed, the efficiency and functional performance of the burner suffered severe loss.

The incoming combustible mixture of air and gas enters the chamber 14 and is spread evenly over the inner surface of the diffuser plate 16 flowing through the perforated openings into the forward portion of the body 11 between the diffuser plate 16 and the primary screen 18. The diffused and admixed combustible gases burn at the primary screen 18 which rapidly becomes hot enough to sustain combustion and to generate infra-red radiant energy, but as explained above its innervthe output of infrared energy is very high. The engineered elimination of high temperature gaskets and the unitized engineered welding of the screen and grid package affords a path for much more rapid and efficient heat transfer and heat losses which greatly assist in achieving a constant operating temperature of highest efficiency.

A radiant burner designed according to the invention possesses a simplicity of design which results in inexpensive mariufacturing steps, few parts and rapidassembly.

The housing 11 may be manufactured by relatively simple metal drawing steps. The diffuser plate 16 is a simple stamping of perforated metal. The primary screen 18 is simply two or more layers of fine mesh screening spot welded to each other as described and then coined forwardly. The outwardly convex shape of the primary screen 18 eliminates inward bowing of the screen as it reaches temperature to thereby preclude the possibility that the primary screen 18 layers may separate or bulge inwardly as it heats and either contact the diffuser plate 16 or so reduce the space between the two as to interfere with proper operation. The welding of the screen 18 to the reverberator grid 19 not only achieves its heat transfer objects but also simplifies assembly.

Direct metal to metal contact between the spacing flange 20 of the body 11, the edge 22 of the diffuser plate 16, the edge of the primary screen 18, the edge 26 of the reverberator grid 19 and the folded over retainers 29, results in good heat transfer to the body 11. This heat flows to the flange of the body 11 and to the diffuser plate 16 where it preheats and expands the cool incoming gases.

Having described our invention, we claim:

1. A radiant burner. comprising a. a hollow cup-shaped body having a continuous peripheral wall extending forwardly and defining an open ended chamber,

b. an outwardly extending planar chamber flange on marginal edge on the front end of said spacing flange, and being spaced forwardly from the rear of said cup-shaped body, the surface of the edges of said diffuser lying in heat transfer contact against said chamber flange, d. a primary screen consisting of at least two contigu ous layers of substantially identical mesh material and e. an open mesh reverberator grid both extending across the open end of said chamber,

thelayers of said primary screen being welded together at the center thereof and at a plurality of spaced points around the edges thereof,

the edges of said grid and said screen overlying the marginal edges of said diffuser and said chamber flange in heat transferring stacked relationship,

f. a lip on the outer edge of said chamber flange that is folded over against the edge surface of said reverberator grid for retaining said diffuser, said screen and said grid in the open end of said body and g, a combustible gas inlet into said chamber behind said diffuser.

2. A radiant burner according to claim 1 in which the plurality of layers of the primary screen have forwardly coined convex central portions.

3. A radiant burner according to claim 1 having a substantially square body in front elevation.

4. A radiant burner according to claim 2 in which the layers of the primary screen are spot welded to each other at points on each edge midway between the corners thereof.

5. A radiant burner according to claim 1 in which the edges of the reverberator grid are also welded to the primary screen at the points where the edges of the layers of said primary screen are welded to each other.

6. A radiant burner according to claim 1 in which the reverberator grid has a planar web and a backwardly extending border flange having outwardly extending marginal edges overlying the edges of the primary screen for spacing the body of said reverberator grid forwardly of said primary screen.

7. A radiant burner according to claim 6 in which the wires of the mesh forming said reverberator grid are continuous through the web, the border flange and the marginal edges.

8. A burner according to claim 1 in which the lip of the chamber flange is folded over inwardly into heat transferring engagement with the edge of the reverberator grid for retaining the diffuser, the primary screen and the reverberator grid in place across the chamber while providing for movement of the edges thereof relative to the chamber flange resulting from thermal expansion and contraction.

9. A radiant burner according to claim 1 in which the perforated diffuser has an open area insufficient for the unrestricted flow of gases therethrough at a rate greater than the flame speed of the gases being fed into the chamber behind said plate.

10. A radiant burner according to claim 9 in which the forwardly extending spacing flange of the diffuser is inwardly spaced from the adjacent wall of the body .and is perforated in the same pattern as the planar web thereof.

Claims

1. A radiant burner comprising a. a hollow cup-shaped body having a continuous peripheral wall extending forwardly and defining an open ended chamber, b. an outwardly extending planar chamber flange on the forward end of said peripheral wall, c. a diffuser having a planar web with a regular pattern of uniform size perforations therein providing an open area substantially less than the area of said planar web, said web extending across said body in a plane parallel to said chamber flange, said diffuser having a peripheral forwardly extending spacing flange and an outwardly extending marginal edge on the front end of said spacing flange, and being spaced forwardly from the rear of said cup-shaped body, the surface of the edges of said diffuser lying in heat transfer contact against said chamber flange, d. a primary screen consisting of at least two contiguous layers of substantially identical mesh material and e. an open mesh reverberator grid both extending across the open end of said chamber, the layers of said primary screen being welded together at the center thereof and at a plurality of spaced points around the edges thereof, the edges of said grid and said screen overlying the marginal edges of said diffuser and said chamber flange in heat transferring stacked relationship, f. a lip on the outer edge of said chamber flange that is folded over against the edge surface of said reverberator grid for retaining said diffuser, said screen and said grid in the open end of said body and g. a combustible gas inlet into said chamber behind said diffuser.

10. A radiant burner according to claim 9 in which the forwardly extending spacing flange of the diffuser is inwardly spaced from the adjacent wall of the body and is perforated in the same pattern as the planar web thereof.