US3405921A

US3405921A - Air-heating gas burner

Info

Publication number: US3405921A
Application number: US576363A
Authority: US
Inventors: Marvin K Rohrs
Original assignee: Aero Flow Dynamics Inc
Current assignee: Aero Flow Dynamics Inc
Priority date: 1966-08-31
Filing date: 1966-08-31
Publication date: 1968-10-15
Anticipated expiration: 1985-10-15

Description

Oct. 15, 1968 M. K. ROHRS AIR-HEATING GAS BURNER 2 Sheets-Sheet 1 Filed 31. 1966 m M 5 M 1 Oct. 15, 1968 M. K. ROHRS 3,405,921

AIRHEATING GAS BURNER Filed Aug. 31, 1966 2 Sheets-Sheet 2 Tl .7. 24 o 6 6" O O O O O O O O O O O O O O O I o o o o o o w o o o O O O 0 6 O 0 3:2 Q\ R o 0/ 7 1 N VEN TOR. MAM K fo 4 Z7 BY United States Patent 3,405,921 AIR-HEATING GAS BURNER Marvin K. Rohrs, Fanwood, N.J., assignor to Acre-Flow Dynamics, Inc. (L. J. Wing Mfg. Co. Division), Linden, N.J., a corporation of New York Filed Aug. 31, 1966, Ser. No. 576,363 21 Claims. (Cl. 26319) ABSTRACT OF THE DISCLGSURE Air-heating gas burner, of the type for mounting within a stream of air to be heated and which utilizes a portion of such air as combustion air, having curved, outwardly flaring, exposed mixing plates having particularly arranged and particularly sized air apertures therethrough for receiving combustion air through their exposed rearward surfaces from the impinging portion of the passing air stream; mixing plates include forward portions which project in a plane perpendicular to the forward direction of the burner. Modified forms include elongated and conical burners with particular configuration as described in the specification.

This invention relates to air-heating gas burners of the type intended to be mounted within a moving stream of the air to be heated, such as within an air duct or the like. Such burners utilize air from the passing stream to supply all or a part of the air required for combustion of the raw gas or gas-air mixture emanating as fuel from the burner, and dischar e the products of such combustion into the air stream itself.

Although the invention may have other uses, it was made in connection with attempts to improve upon the best of the known types of such burners when used as a high turn-down ratio, raw gas burner mounted centrally within a high velocity air duct such that only a portion of the passing air stream passes through the burner, the remainder of the air being permitted to flow past the burner. The invention will therefore be described in connection with such use.

The best know type of line burner, as these burners are sometimes called, is that described in Yeo et al. US. Patent 3,051,464, issued Aug. 28, 1962, now Re. 25,626, July 28, 1964, the disclosures of which are hereby incorporated by reference. In general, the basic burner of Yeo et al. provides either a raw gas of a gasair mixture supply manifold having an attached pair of mixing plates which extend outward and obliquely, in the downstream direction with respect to the passing air Stream, at the respective opposite sides of the manifold. Each mixing plate has substantially flat configuration, and the included angle between the pair is about 50. The combustion zone of the burner is the region formed at its downstream side by this angular disposition of the mixing plates, the gas ports of the supply manifold feeding fuel gas into this region. Air required for combustion is admitted from the upstream side of the burner, via a pattern of air apertures formed in each mixing plate, on which a portion of the total air stream impinges. The remainder of the air to be heated flows past and around the burner which is mounted centrally of an air duct or the like.

The underlying principle of operation of this type of 3,405,921 Patented Got. 15, 1968 'ice burner is that the high velocity air stream flowing past the burner creates reduced pressure within the combustion zone, this relative vacuum causing standing jets of incoming combustion air to form at each of the mixing plate apertures. The air jets themselves create a still higher vacuum region immediately adjacent the respective mixing plate surfaces within the combustion zone. Fuel gas flowing from the gas ports into the combustion zone is thus induced to flow outwardly along the mixing plate surface areas between the air jets, whereupon it becomes entrained with each air jet to form a combustible gas-air mixture which is intended to burn as a distinct, elongated jet of flame at each of the mixing plate apertures.

However, the high velocity flame jets emanating normal to the generally cofacing but angularly disposed mixing plate surfaces tend to intersect at the centerline plane of the combustion Zone so that, especially at high firing rates of the burner, the several-initially distinct flames actually merge and concentrate centrally to produce virtually a single large flame, up to eighteen inches long and somewhat triangular in cross-sectional shape, emerging from the downstream side of the burner. Such flame characteristic produces undesirable localized temperature concentration as well as temperature Stratification in the heated air stream.

In addition, the flame characteristics of the Yeo et a1. burner produce high surface temperature at each of its flat mixing plates, and large temperature gradient over their projecting lengths, resulting in a tendency of the plates to warp and buckle during and as a result of intermittent use at different firing rates. Such warpage or buckling, if it is permitted to occur, adversely affects burner performance because of resulting disturbance of the amount of vacuum as would otherwise be created at each of the combustion air jet locations throughout the respective areas of the mixing plate surfaces. Conventionally, such warpage and buckling is controlled, rather than prevented, by providing an initial bend or set of each mixing plate in a warp-compensating direction. However, such compensating change of the otherwise flat configuration of each mixing plate involves further compensating adjustments to the respective locations and sizes of the air jet apertures themselves, thereby complicating rather than simplifying the solution to the problem. Such compensating adjustments to account for warpage and buckling increases the complexity and cost of burner fabrication, even assuming that the same will fully compensate for the undesired effects.

Considering that the included angle between the mixing plates is about 50, the air velocity component in direction normal to each mixing plate surface, and by which each of the combustion air jets is formed, is of course considerably less than the velocity past the burner of the main air stream. In order to induce an increase of this normal velocity component so as to create higher vacuum at each air jet at the combustion sides of the respective mixing plate surfaces, the Yeo et al. burner provides appropriately located air deflecting tongues which project outwardly from the upstream sides of the mixing plates at each of the mixing plate apertures to direct a greater flow of air through each aperture than would otherwise occur. It has been found that the provision of such air deflecting tongues is relatively inefircient for the purpose, and impractical or at least undesirable from a manufacturing standpoint.

The present invention provides a line type air-heating gas burner having a fuel supply manifold and mixing plates having combustion air entry apertures, as do other burners of the type. However, the mixing plates are curved rather than flat, and have no projections, or formed flow nozzles, or reinforcing bars or initial set to control warpage, or complex arrangement of numerous sizes and types of air apertures. A modified form of the invention has a flat mixing plate arrangement as will be described, rather than curved mixing plates, by which the above enumerated advantages may be obtained although with some sacrifice of burner performance as compared with the preferred curved plate arrangement.

However, in any of its embodiments the present invention achieves improved burner efficiency and performance as compared with previously known line type gas burners, while also substantially reducing the cost of fabrication and maintenance of such burners.

The invention contemplates the provision of an improved gradient in the vacuum produced at the mixing plate walls within the combustion zone of such burners, thus creating better flow and mixture of combustion air and fuel gas within the burner so as to improve its efficiency. Further, the invention contemplates improved burner performance by even more distribution of the burner flame within the area of the combustion zone and consequent reduction in temperature stratification and temperature gradient within the air stream being heated by the burner.

An additional object of the present invention is to achieve flame stability and low-flame retention in such burners, and it is found that such is achieved Without necessity for inclusion of supplemental ignitor gas ports or specially formed W flame shielding walls for the purpose, by inducing an air velocity gradient through the burner which in the preferred embodiment ranges from zero (or substantially zero) adjacent the gas supply manifold to full (or substantially full) air stream velocity adjacent the outer ends of the mixing plates. Because their inclusion interferes with smooth air flow and establishment of the desired air velocity gradient through the burner, and because they create manufacturing difficulties as previously mentioned, it is further intended that air deflecting means at the combustion air apertures of the mixing plates, such as the air deflecting tongues of the Yeo et a1. burner, may be eliminated.

Shorter flame length in the burner is a further advantage achieved by the more complete combustion of the air and gas mixture resulting from the construction to be described. As required under various codes, the burner achieves virtual elimination of odor-causing aldehydes, and carbon monoxide, as products of combustion.

It is believed that the advantages of the invention will also be obtainable in so-called point-type burners wherein an annular shaped mixing plate surrounds a gas supply head.

Briefly and generally describing the invention in its preferred embodiment, it provides a raw gas burner having a pair of mixing plates defining a combustion zone of outwardly flared shape in the forward or downstream direction of an elongated type gas supply manifold, each mixing plate having curved configuration which is convex in the downstream direction and such that the outermost end of each mixing plate is disposed at substantially right angles to the direction of flow of the passing air stream whereas the innermost end of the mixing plate, which is attached to the gas supply manifold, has no substantial inclination with respect to the passing air stream. The preferred embodiment contemplates that the curvature of each mixing plate will be circular, although parabolic or other curved shape might afford substantially the same results.

Each mixing plate is provided with a considerable numher of combustion air apertures formed merely by drilling or punching holes therethrough, the air apertures being arranged in a grid-like pattern of aligned rows and columns thereof extending outwardly from the gas supply manifold throughout the surface of the mixing plate. In this connection, it will be noted that the upstream side of each mixing plate has plainly smooth surface, no projecting air deflector tongues being provided. The sizes of the air apertures, which produce the upstanding combustion air jets at the downstream or combustion side of the mixing plate, vary from smaller sizes adjacent the gas manifold to larger sizes adjacent the outer end of the plate. Each of the aligned columns of air apertures, as the same extend outwardly from the location of the gas manifold, is laterally offset with respect to the location of any gas port of the gas supply manifold, rather than in alignment therewith. That is, the columns of mixing plate air apertures are respectively located midway of the spacings between the gas supply ports of the manifold. The respective side areas of the burner, as defined by the spaced apart relation of the pair of mixing plates, are closed by respective end plates which extend outwardly from the gas manifold in the downstream direction.

In a so-called point-type raw gas burner as distinguished from the elongated type, a series of narrow and tapering but similarly curved mixing plate portions are welded together at their side edges in an annular pattern to form a generally conical, outwardly flaring curved mixing plate which is attached at its narrow end to a gas supply head in surrounding relation to the latter. The combustion air apertures, which vary in size, are arranged in columns extending adjacent the joined edges of these mixing plate portions, as will be seen. The gas supply head is provided by the end of a gas supply pipe which is closed by a flat plate having a plurality of gas port openings therethrough which are disposed in an annular pattern adjacent the plate periphery. Thus, the gas emanates in the downstream or forward direction of the burner, intermediate the columns of combustion air apertures, from the base of the combustion zone formed by the mixing plate.

Another modified form of the invention achieves some, though not all of its benefits. Such modified form provides a pair of substantially flat-type mixing plates each extending from 3" to 5 in opposite, oblique disposition from the respective sides of an elongated gas supply manifold, the included angle being from to 90. Where a 3" straight length, relative disposition is used, the outer ends of the mixing plates are curved on a 2 /2" radius over of arc length so that their ends project at right angles with respect to the air stream. A perhaps less advantageous alternative provides elimination of these curved outer end portions and substitution of a flat face plate projecting outwardly at right angles into the passing air stream, in which case the lengths of the diverging straight length portions are somewhat longer. As do the curved outer end portions, these flat projecting plates have combustion air apertures therethrough in alignment with the columns of air apertures in the main portions of the mixing plates, the columns being at locations intermediate of the gas ports.

Such modified forms of the invention can be incorporated in point-type burners. That is, the narrow end of a conical shaped mixing plate, whose central angle is 45 to is attached to a gas supply head in surrounding relation, the columns of combustion air apertures of the conical mixing plate being aligned intermediately of the gas port apertures of the gas head. Either a curved end portion, or a flat, disc-shaped end portion is attached to the wide end of the conical mixing plate to project outwardly of the burner combustion zone, at right angles to the passing air stream, leaving open the front end of the combustion zone. The end portion has combustion air apertures disposed in radially outward direction in alignment with the columns of air apertures formed in the main portion of the mixing plate.

It should be noted that all of the burner forms which incorporate the invention are mounted centrally of a high velocity air stream such that a portion of the air by-passes the burner. That is, the extreme outer end portions of the mixing plates, which project transversely of the air stream, are spaced away from the adjacent walls of the air duct or the like in which the burner is situated.

These and other of its objects, features and advantages will become apparent from the following detailed description of the invention, when taken together with the accompanying drawings in which:

FIGURE 1 is a longitudinal cross-sectional showing of a high velocity air duct having the preferred form of burner in accordance with the invention properly mounted therein;

FIGURE 2 is a transverse sectional showing of the duct of FIGURE 1, the view being taken at lines 22 of FIGURE 1;

FIGURE 3 is a perspective showing of a gas burner unit in accordance with the present invention;

FIGURE 4 is an enlarged cross-sectional showing of a modified form of burner unit in accordance with the invention; FIGURE 4a diagrammatically shows a variation, to smaller scale;

FIGURE 5 is a fragmented cross-sectional showing, to still further enlarged scale, of a burner unit incorporating another modification;

FIGURE 6 is a fragmented cross-sectional showing, to the scale of FIGURE 5, of a portion of the burner unit which is included in FIGURE 1 to show certain details;

FIGURE 7 is a fragmented plan view, approximately to the scale of FIGURES 5 and 6, to illustrate the development of the location and respective sizes of the combustion air apertures which are provided in each of the mixing plates of burner units in accordance with the invention, the view also including a portion of the adjacent gas supply manifold for purposes of understanding;

FIGURE 8 is a perspective showing of a point-type burner unit in accordance with the invention;

FIGURE 9 is a fragmented showing in perspective of a modified form of elongated gas burner unit; and

FIGURE 10 is a perspective showing of a point-type burner unit incorporating the features of the burner of FIGURE 9.

Referring first to FIGURES l and 2, an air heating gas burner 11 in accordance with the invention is shown mounted in a high velocity, low pressure air duct 12. By way of example, the air duct 12, which is made of sheet metal or the like, is 20" x 20" square in transverse section as shown in FIGURE 2. A profile plate 13 is attached to depend from its upper Wall 12a a distance of three inches downwardly into the air stream at the front face location of the burner 11. The height of the profile plate 13 may be varied as, for example, by the substitution of a two-inch profile plate in the arrangement shown. The profile plate 13 extends the full width of the duct 12 as seen in FIG- URE 2, thereby providing a duct opening of nominal dimensions 17" x 20" at the face of the burner 11. The burner 11 is secured in the position shown, as by the rigidity of its gas supply manifold 14. For such air duct, the burner 11 is of the elongated type having front face dimensions 9" x 12", and is mounted centrally of the reduced opening of the air duct 12 at the location of the profile plate 13.

Air to be heated flows in the direction of arrow A, its velocity being varying or constant within a range of from about 2,000 to 3,500 f.p.m. (feet per minute), preferably from 2,500 to 3,000 f.p.m. For example, assuming a rate of flow of 4,615 c.f.m. (cubic feet per minute), the air velocity at the profile plate 13 is 2,860 f.p.m. where a three-inch profile plate is provided, or 2,640 f.p.m. where a two-inch profile plate is used. The burner 11 is intended to heat the passing air A which, for example, may be make-up air either drawn or blown into the duct from an outside or atmospheric source, as by a fan (not shown) within the duct 12 in conventional manner. The heated air is discharged from the downstream end of the duct 12 into a room or equipment area (not shown), such as that of a factory or the like, and it is therefore apparent that the burner 11 must be highly efficient to avoid undesirable products of combustion being deposited within the room. Further, it-must perform in such manner as to uniformly heat all of the passing air stream A so as to avoid temperature stratification or unacceptable gradient of temperature within the heated air as it is discharged into the area to be heated. Moreover, and because the temperature of the outside source of air may vary widely between summer and winter seasons, the burner 11 should be capable of so-called high turndown, i.e., a turn-down ratio on the order of more than 20:1, to provide a wide range of its rate of operation. That is, in relatively warm season, only a relatively small quantity of heat need be added by the burner 11 to adequately warm the incoming air to a desired room temperature whereas, in cooler seasons, high combustion rates of the burner 11 will be required to heat much cooler air to the same desired room temperature.

In any of its preferred forms as shown in FIGURES 16, the burner unit is a raw gas burner having a maximum combustion rate furnishing 450,000 B.t.u.s per hour per linear foot of burner length, and a minimum combustion rate of 20,000 B.t.u.s per hour per linear foot of burner length. Thus, its turn down ratio is about 22 /2 :1. Its details of construction are illustrated in FIG- URES 3 to 7, the several variations thereof being designated by

reference numerals

11, 11a, 11b and 110.

The burner in any of its variations has a gas supply manifold 14 formed by a straight length of conventional gas pipe, its diameter being from about A" to about 1%, a 1" diameter pipe being preferred. Referring briefly to FIGURE 2 which in this respect is illustrative of any of the burners, the manifold 14 receives raw gas G from a gas supply line 15 which includes a regulator and valve as generally indicated by numeral 16. The terminal end 14a of the elongated manifold 14 is capped in a conventional manner. Although it might have a double row of gas ports, in the embodiment shown the manifold 14 has a single row of plainly drilled gas supply ports 17 in spaced apart relation along its length on the side thereof which faces into the combustion zone 18 of the burner unit, the gas ports 17 extending through the length of /s" x A" bar stock 20 which is attached, as by welding 21, with its narrower face extending along the downstream side of the manifold 14 as will perhaps be more clearly understood from FIGURES 46 which are sectional views taken at any typical gas port 17. As shown in connection with any embodiment, the combustion zone 13 of the burner faces the downstream direction A when the burner is mounted within a duct 12. Where the length of the elongated type burner in any of its embodiments is 12", twenty gas ports 17, are provided along the length of the burner, the eighteen innermost gas ports being each in diameter and spaced from each other, and the two outermost gas ports 17a (FIGURES 2, 3 and 9) being 7%4" in diameter and respectively spaced from its

adjacent gas port

17 and 35 inwardly 0f the burner end plates 19. Gas ports having A3" diameter have also been successfully used. It has been found that performance is improved where the endmost ports 17a, adjacent the end plates 19, have smaller diameter than the other ports 17, and are spaced closer to their adjacent ports 17 and to end plates 19.

The inclusion of the manifold front face bar 20 facilitates attachment of a pair of mixing plates of the burner. In FIGURES 1-6 wherein several variations in the configuration of the respective pairs of mixing plates are illustrated, each mixing plate in the pair is respectively referenced by

numerals

22, 22a, 22b, and 220, corresponding to the modified forms of

elongated burner units

11, 11a, 11b or 11c with which the mixing plate pair is associated.

In all of the illustrated embodiments of the invention, the respective mixing plates are formed of 20 gauge sheet metal, either hot rolled steel or cold rolled steel, suitably bent to shape.

In each of the burners 11, 1112-110, each member of the respective pairs of mixing plates has curved configuration, the convex direction of its curvature facing in the forward direction of the burner, i.e., the direction in which gas is emitted from the gas ports 17, as shown. The respective mixing plates in the pair are attached, as by spot or other conventional welding at their respective rearward or inner end straight portions 23, 23a-23c, to the manifold bar 20 at opposite sides thereof as shown, so that the line of gas ports 17 is situated at the narrow end of the outwardly flared burner combustion zone 18 which is formed by the pair of mixing plates. In all embodiments of the burner, the combustion zone 18 is completely open at the wide forward end thereof, as will be understood from FIGURE 3 for example. The curvature of each mixing

plate

22, 22a-22c, is such as to provide forward end portions respectively 24, 24a, 24b, 24c thereof which project outwardly of the burner combustion zone 18 at right angles, or nearly at right angles, to the forward direction of the burner.

In FIGURE which illustrates a modified form of burner unit 110, the curvature of each mixing plate 220 is circular over 90 of are extending from tangential relationship with its associated horizontal surface of the manifold bar 20 immediately adjacent the front face of the latter, to its forward end portion (not seen) which is disposed at 90 with respect to the horizontal centerline plane of the burner passing through the centrally located row of gas ports 17. Thus, the outer or forward ends of the mixing plates 226 of the burner 110 are disposed at right angles with respect to the passing air stream A, in the same manner as indicated by forward end portion 24 in FIGURE 1.

The respective mixing plates 22b of the burner unit 11b shown in FIGURE 4 also have circular curvature over an arc length of 90 as indicated by the angle a, but each plate includes a straight length portion 25b at its inner end, disposed and extending in the forward direction at an angle of 5 to the horizontal centerline plane of the burner, to which the curved portion a is tangent, as shown. Thus, the extreme outer or forward end portion 24b of each mixing plate is disposed at 5 with respect to, but towards the rearward side of the vertical. However, each plate has a forward end edging strip 26b which projects rearwardly and parallel to the horizontal centerline plane of the burner, in alignment with the air stream A when the burner is mounted within a duct as shown in FIGURE 1.

It will be noted in FIGURE 4 that the straight length portions 25b of the two mixing plates provide an included angle 0 of at the inner or rearward end of the com bustion zone 18 in the burner 11b. In the preferred form of burner 11 as illustrated by FIGURE 6, the straight length portions 25 at the inner ends of its circularly curved mixing plates 22, and which are also long, extend forward in parallel relation with the horizontal centerline plane of the burner.

A variation of this embodiment is shown diagrammatically in FIGURE 4a. The mixing plate straight length portions 25b are extended to a length of 3", and disposed at an included angle 0 of 50. The outer end portions 24b are circularly curved on 2 /2" radius over an angle a of 65 from tangential relation with the respective portions 25b so that their respective outer edges are disposed at 90 to the centerline plane. Further, the bar 20 has been omitted so that the gas ports 17 only pass through the manifold 14. Welded attachment of each mixing plate 22b to manifold 14 is made using Mr" x A" bar stock 30.

Referring to all of the figures of the drawings, and now particularly to FIGURE 7, it will be understood that the mixing plates in all embodiments have a plurality of plainly drilled air apertures, generally designated by reference numeral 27, for admitting a portion of the passing air stream A into the burner combustion zone 18 to admix with raw gas emanating from the

manifold gas ports

17, 17a. These combustion air apertures are arranged in columns thereof extending outwardly from the region of the manifold in the forward direction of the burner. In all of the illustrated embodiments of the invention, and as shown more particularly in FIGURE 7, each air aperture column C is out of alignment with any

gas port

17, 17a. With respect to the lateral spacings between adjacent ports, the respective aperture columns C are located midway thereof and are therefore laterally spaced apart the same distance. That is, in the previously referred to specific example, where twenty

gas ports

17, 17a are spaced as mentioned along the length of manifold 14, there will be in each mixing plate nineteen spaced apart air aperture columns C extending from respective locations midway of the ports, the respective columns at the ends of the burner being located A inside of their associated outside ports 1711.

It will also be noted that the air apertures of adjacent columns C are also aligned in respective rows R (FIG- URE 7) which extend in the horizonal direction.

The apertures 27 in each of the air aperture columns C are respectively sized in accordance with their distances outward from the gas emitting ends of the

manifold gas ports

17, 17a. Generally, the diameters of the apertures closest to the manifold are smaller than those of the apertures located nearer the forward end portion 24 of the mixing plate. FIGURE 7 shows the arrangement and respective sizes of apertures 27 as they appear in a typical mixing plate 22 when the latter is in fiat condition prior to bending to curved form, and properly positioned as it will ultimately be attached to the manifold bar 20. In the latter regard, the straight length manifold attachment portion 23 of the mixing plate is not shown since it is considered as being already in attachment with the bar 20, extending along the line of interface 28 between the bar and the plate 22. The aperture arrangement and sizing shown is appropriate for any other referred to mixing

plate

22a, 22b, or 22c. Considering that the outward projecting length of the mixing plate 22 is 6 /2" from the line of interface 28, it is seen that each aperture column C is formed by eighteen combustion air apertures 27 of varying size as will now be described. It has been found that excellent results are afforded where, starting adjacent the line of interface 28, the first row of apertures is located 4" outwardly of the manifold bar 20, as will also be understood from FIGURES 4, 5 and 6-. The diameter of each aperture 27 in the first and second row R is A and the second row R is spaced 4" outwardly from the first row. The apertures in the third and fourth rows, which are spaced A" from the second row and from each other, are each 4 in diameter. The next five rows of apertures (rows 5-9) are also spaced A" from each other and from row four, all of the apertures having 732" diameter. The six rows following (rows 10-15) are spaced from the ninth row and from each other, the apertures in the tenth and eleventh rows each being /s" diameter, and the apertures in rows twelve through fifteen each being diameter. The apertures in rows sixteen through eighteen are each diameter, these rows being spaced /2" from row fifteen and from each other. It will be noted that the outermost row is centered /2" away from the extreme outer edge of the flat plate, which will be bent rearward along the illustrated dotted line to form the edging 26 of the plate as previously referred to. The aperture sizes and locations are the same in both mixing plates of the pair in any elongated type burner.

When both of the pair of apertured mixing plates are bent to shape and attached to the gas supply manifold,

the open front face of the typical burner being described is nominally 9" high x 12 wide. Each of the flat end plates 19, also of gauge steel, is attached as by welding to the respective side edges of the mixing plates 22, a rearwardly facing side edging 29 (FIGURES 4, 5 and 6, for example) appearing along the edges of the mixing plates as shown.

Referring again to FIGURES 16, it will be understood that a portion of the air stream A to be heated impinges upon the rearwardly facing mixing plate surfaces of the burner, the remainder of the air A flowing past the top, bottom and sides of the burner when mounted as shown in FIGURES 1 and 2 within a duct 12. The impinging air enters the burner combustion zone 19 via the apertures 27, and emerges therein in distinct high velocity jets, each jet projecting normally with respect to the mixing plate surface at the location of the aperture 27 by which it entered the combustion zone. The circular curvature of each mixing plate establishes a gradient of air jet velocities along any air aperture column C as it extends across the curvature. Typical upstanding air jets are indicated by dotted lines I in FIGURE 4. The jet velocity gradient G in each of the FIGURES 1-6 embodiments (except FIGURE 40:) varies uniformly from zero, or substantially zero adjacent the gas supply manifold 14 to full or substantially full air stream velocity adjacent the outermost regions of the combustion zone 19. In FIGURE 4a the angle 0 may be from about 45 to 90. Accordingly, the velocity gradient will vary from a component velocity commensurate with such angle to full air stream velocity at the outermost ends of the mixing plates.

When installed in an air duct as shown by FIGURES 1 and 2, the gas valve 16 is appropriately adjusted to the desired fuel rate, and the burner is ignited by any conventional raw gas burner igniter system (not shown), as for example an electrically actuated igniter rod attached within the combustion zone 19 adjacent the front face of the manifold bar 20.

The gas G emitted from the manifold gas ports 17 is caused to flow outwardly along, and to evenly distribute between the interior surfaces of the mixing plates within the zone 19, the flow being between the air aperture columns C as will be understood from FIGURE 7, by reason of the vacuum conditions within the zone 19 which are created by the burner by-passing portion of the air stream A and the presence of the distinct combustion air jets I. As the gas tends to flow along the mixing plate surfaces between the aperture columns C, it becomes entrained with each of the air jets 1 within the rows thereof extending outwardly of the manifold, the air jets each entraining suificient gas to establish a combustible air-gas mixture thereat which, when the burner is ignited, burns in the same distinct jet pattern excepting in the region of the first two aperture rows R, approximately /2" forward of the front face of the manifold, where a wall of flame is actually produced, rather than distinct flame jets as appear outwardly thereof. The number of rows of air jets which are ignited depends upon the rate of fuel fed to the burner. That is, a minimum rate of gas flow produces flame jets at only the one or two innermost rows of air apertures, or a wall of flame immediately adjacent the front face of the burner as aforesaid, whereas a maximum gas flow produces distinct flame jets at substantially all of the mixing plate apertures 27. At intermediate rates of operation, an intermediate number of rows of air jets will ignite and burn steadily, the ignited rows extending outwardly from manifold 14.

The low flame operating characteristics of the burner may be varied for particular applications by inclusion or not of the straight length portions b (FIGURE 4) or 25 (FIGURE 6) of the respective mixing plates. It is believed that the burner will operate satisfactorily, albeit without capability of low-flame operation and therefore with a more limited turndown range, where the rearward edges of the respective mixing plates are spaced :1 short distance forward of the manifold, as by cutting away all or a portion of the straight length portions 25b or 25c. Of course, the mixing plates would still be attached to the gas manifold, as by spaced apart strips snapping the cut out area. It will also become apparent that the overall operating characteristics of the burner may be varied by changing the curvilinear shape of the mixing plates, as for example to parabolic curvature, so as to correspondingly alter the air stream velocity components entering the respective plate apertures 27, and thereby the velocity gradient G, and consequently the heights of the flame jets established thereat.

Referring now to the point-type burner 31 illustrated in FIGURE 8, the raw gas line 32 (which has a suitable valve, not shown) feeds gas G through a gas port plate 33 at its forwardly facing end. The gas ports 34 are plainly drilled holes, as aforesaid, and extend in spaced apart annular pattern adjacent the plate periphery. The mixing plate, generally indicated by numeral 35, is formed by a plurality of curved mixing plate portions 35a, 35b, etc. which are welded together at their respective side edges to form the illustrated shape. As in the elongated-type burner embodiments, the curvature of each plate portion 35a, 35b, etc. is preferably circular along an arc of 90, and provides an outer end portion 36 which will be disposed at right angles to the passing air stream when the burner 31 is mounted within a high velocity air duct in a manner similar to that shown in FIGURE 1. Mixing plate air apertures 37, having the same size gradient as previously described as they extend from the gas port plate 33 towards the outer or forward end portions 36, are aligned in columns thereof adjacent the respective side edges of the joined plate portions 35a, 35b, etc., as shown. Each column of air apertures 37 is aligned midway of the spacing between two gas ports 34, as in the previously described elongated-type burners. A conventional type of raw gas igniter system (not shown) is attached within the combustion zone 38 which is formed by the mixing plate 35, as will be understood. The mixing plate portions may further include straight length portions at their inner ends similar to the

portions

25, 25b of the FIGURES 4 and 6 embodiments, if desired. Of course, the mixing plate 35 is attached as by welding to the gas supply line 32 in surrounding relation with the gas port plate 33, as shown.

The burner 31 operates in the same manner, and provides essentially the same operating characteristics as does any of the previously described elongated types of burners. However, it is particularly useful in circular or small sized ducts, as will be apparent.

Referring now to the burner unit embodiments shown in FIGURES 9 and 10 by which some though not all of the advantages of the invention may be obtained, FIG- URE 9 shows an elongated type burner unit 40 having a gas supply manifold 14 which has gas ports 17 as in the previously described elongated burners, although a manifold 'bar, such as the bar 20 of FIGURE 4, has 'been omitted. The pair of mixing plates, generally indicated by numeral 41, have direct welded attachment to the manifold 14 at respective opposite sides thereof, as shown. Each mixing plate 41 has an inner end straight length portion 42 extending about /8" forwardly of the line of the gas ports 17, a divergent portion 43 of flat configuration, and a flat outer end portion 44, the latter being disposed at a right angle with respect to the horizontal centerline plane of the burner passing through the gas ports 17. The outer end portion 44 includes a rearwardly turned edge portion 44a which is disposed parallel to the centerline plane. A pair of end plates 45 (only one of which is shown) close the respective sides of the burner combustion zone 46 which is formed by the divergent relation of the respective

mixing plate portions

42 and 43. The included angle between the respective mixing plate divergent portions 43 is from about 45 to preferably 50. The columns C of combustion air apertures 27 are located midway of the spacings between the respective gas ports 17, and extend outwardly from adjacent the manifold 14 across all of the mixing

plate portions

42, 43 and 44, as shown. The gradient of sizes of apertures 27 within the rows of apertures extending forwardly of the manifold is substantially that as described in connection with FIGURE 7, except that the air apertures 27:: in the mixing plate forward end portions 44 may be of uniform, relatively large size.

In FIGURE 10, these features are shown as incorporated in a concial shaped burner 50 whose mixing plate 51 is formed by a truncated cone-shaped inner portion 52 and a flat, disc-shaped outer portion 53. The cone-shaped inner portion 52 is attached at its narrow end to a gas supply head 54 in surrounding relation with respect to the annular pattern of gas ports 34 which are adjacent the periphery of the gas port plate 33, as shown. The gas supply head is at the end of a raw gas supply pipe 55. The conical-shaped inner portion 52, which has an included angle of from about 45 to 90 (preferably 50), forms a flared-shaped combustion zone 56 which, as in all embodiments, has a wide open forward end. The flat, annular shaped outer end portion 53 is disposed perpendicularly with respect to the central axis of the burner so that it is, of course, perpendicular to the passing air stream when the burner 50 is mounted within a duct in the manner indicated by FIGURES 1 and 2. The mixing plate inner portion 52 and outer end portion 53 have combustion air apertures 27, 27:: which extend in columns C outwardly from adjacent the gas supply head 54, the gradient of aperture sizes being as indicated in connection with the FIGURE 9 embodiment. As in all other embodiments, the columns of air apertures are disposed to extend outwardly from respective locations midway between the gas ports 34. The peripheral outer edge of the outer end portion 53 has a rearwar-dly turned port-ion 53a which will be in alignment with the air stream, as in other embodiments, when the burner is operating within a duct.

As are the other burner units which have been described, the

burners

40 and 50 are intended to be mounted centrally of an air duct or the like, the duct being larger than the burner so that a portion of the air stream flows around and by-passes the burner whereas only a portion of the air stream impinges upon the rearward surfaces of the burner mixing plates. Further, and although not illustrated, it will be understood that the

burners

40 and 50 will have conventional raw gas ignitor means as described in connection with the other embodiments.

When either of the

burners

40 or 50 is mounted and operated within an air stream, the flow of raw gas to the burner is regulated by a gas valve (not shown) within the gas feed system, as will be understood. Gas emanating from the gas ports 17 (FIGURE 9) or 34 (FIGURE 10) flows outwardly along the interior surfaces of the mixing plates and between the air aperture columns C to be successively entrained with the upstanding distinct air jets within the combustion zone, as described in connection with the other embodiments. At higher rates of operation, the gas reaches the forward surface of the fiat-plate type forward end portion of the mixing plate where it continues to be successively entrained with the forwardly projecting distinct air jets formed at the air apertures 27a. Although a constantly increasing air jet velocity gradient is not achieved in the burners of FIGURES 9 and 10, these burners afford good high rate operation by avoidance of jet flame merger. Further the flat type

forward end plate

44 or 53 aid in the establishment of more desirable vacuum conditions within the respective combustion zones and along the front facing combustion face of either burner. In addi- 12 tion, these burners afford the simplified burner construction achieved by the invention.

It will be understood that, in air ducts of larger or different cross section than has been described, either a burner unit of different size or more than one burner unit may be mounted therein. The elongated burner units as have been described may be made in any length, and may be made in the form of elbows and TS to be attached to straight sections for assembling complex and interconnected burner arrangements in the manner shown in the referred to patent to Yeo et al.

Thus, several embodiments of the invention have been described which achieve all of its objects.

What is claimed is:

1. An air-heating gas burner of the type for mounting within a stream of air to be heated and which utilizes a portion of such air as combustion air in the burner, said burner comprising gas supply means including gas port means for emitting gas in a forward direction of the burner, and fully exposed, flared-shape mixing plate means projecting forwardly and outwardly from a rearward end thereof adjacent said gas port means to a wide forward end thereof thereby defining an open-faced burner combustion zone forward of said gas port means, said mixing plate means at its said forward end having portions which project outwardly in opposte directions with respect to said burner combustion zone substantially within a plane which is perpendicular to said forward direction of the burner, said mixing plate means including its said forward end portions presenting exposed surfaces in the rearward direction to be impinged by said portion of the air stream to be heated, and means defining a uniformly distributed plurality of combustion air apertures through said mixing plate means including its said forward end portions.

2. An air-heating gas burner according to claim 1 wherein said flared-shape mixing plate means includes length portions having curved configuration which is convex in said forward direction of the burner.

3. An air-heating gas burner according to claim 2 wherein said curved configuration is circular.

4. An air-heating gas burner according to claim 2 wherein said mixing plate means further includes straight length portions extending substantially from its said rearward end a distance towards its said forward end, said curved length portions extending from said straight length portions to said forward end of the mixing plate means including said forward end portions thereof.

5. An air-heating gas burner according to claim 1 wherein said mixing plate means forward end portions have flat configuration within said perpendicular plane.

6. An air-heating gas burner according to claim 5 wherein said mixing plate means comprises straight length portions extending substantially from its said rearward end to its said forward end portions.

7. An air-heating gas burner according to claim 1 wherein said gas supply means comprises an elongated gas manifold extending transversely with respect to said forward direction of the burner, said gas port means comprises means defining a plurality of spaced apart gas ports along said manifold at the side thereof which faces said forward direction, and said flared-shape mixing plate means comprises a pair of elongated mixing plates having respective forward and rearward ends which are determinative of said forward and rearward ends of said mixing plate means, said pair of mixing plates being attached substantially along the respective opposite sides of said manifold which are laterally adjacent said gas port means, said forward end portions of said mixing plate means comprises a forward end portion of each of said pair of mixing plates which projects outwardly in opposite direction with respect to the forward end portion of the other, each said mixing plate having curved configuration which is convex in said forward direction of the burner along at least a portion of its length in the direction towards its said forward end, said plurality of combustion air apertures being arranged in a plurality of transversely spaced apart columns of aligned apertures on both of said mixing plates, each said column of combustion air apertures extending in said forward direction of the burner at a transverse location which is out of alignment with any of said gas ports.

8. An air-heating burner according to claim 7 wherein said curved configuration of each said mixing plate is circular and extends substantially the length of said mixing plate to its said forward end from adjacent its said rearward end.

9. An air-heating gas burner according to claim 8 wherein said length of each said mixing plate is determined by the arc of curvature of said curved configuration, said are being equal to substantially ninety (90) degrees, and each said column of combustion air apertures in each said mixing plate extends from substantially adjacent said rearward end of the mixing plate.

10. An air-heating gas burner according to claim 9 wherein said plurality of combustion air apertures in each said column thereof are substantially uniformly graduated in size as they extend in said direction of the colman, the aperture adjacent said rearward end of the mixing plate having diameter which is less than the diameter of one of said gas ports, and the aperture adjacent said forward end of the mixing plate having diameter which is substantially equal to from about two (2) to about three (3) times the diameter of said aperture adjacent said rearward end of the mixing plate, the spacing between adjacent apertures in the column being substantially equal to from about three (3) to about four (4) times the diameter of the aperture which is situated at the rearward end of the spacing.

11. An air-heating gas burner according to claim 7 wherein each said mixing plate includes a portion having fiat configuration and which extends from substantially adjacent its said rearward end a distance along its length in the direction of its said forward end, said curved configuration portion of each said mixing plate being circular and extending from said flat configuration portion to said forward end of the mixing plate, and each said colmm of combustion air apertures in each said mixing plate extends from substantially adjacent said rearward end of the mixing plate.

12. An air-heating gas burner according to claim 11 wherein each said flat configuration portion of each said mixing plate extends parallel to the fiat configuration portion of the other, and said distance of its extension is short with respect to said length of the mixing plate of which it forms a part.

13. An air-heating gas burner according to claim 11 wherein said flat configuration portions of said pair of mixing plates are disposed at a forwardly widening included angle with respect to each other, said included angle being within the range of from slightly greater than zero degrees to about ninety (90) degrees.

14. An air-heating gas burner according to claim 11 wherein said flat configuration portions of said pair of mixing plates are disposed at a forwardly widening included angle of substantially twenty (20) degrees with respect to each other, said distance of extension of each said flat configuration portion is short with respect to said length of the mixing plate of which it forms a part, and each said curved configuration portion has length in said direction as determined by an arc equal to substantially ninety (90) degrees.

15. An air-heating gas burner according to claim 1 wherein said gas supply means comprises a disc-shaped plate, said gas port means comprises an annularly disposed plurality of spaced apart gas ports substantially adjacent the periphery of said disc-shaped plate, said flared-shape mixing plate means has generally conical shape, and said plurality of combustion air apertures comprises a plurality of annularly spaced apart columns of 14 aligned apertures, each column of apertures extending along the length of said mixing plate means in said forward direction of the burner at an annular location which is substantially midway of the spacing between two of said gas ports.

16. An air-heating gas burner according to claim 15 wherein said mixing plate means comprises an annularly disposed attached plurality of tapered mixing plate portions, said mixing plate portions having respective forward and rearward ends which are determinative of said forward and rearward ends of said mixing plate means, and each said mixing plate portion having curved configuration which is convex in said forward direction of the burner along at least a portion of its length in the direction towards its said forward end.

17. An air-heating gas burner according to claim 16 wherein said curved configuration of each said mixing plate portion is circular and extends substantially the length of said mixing plate to its said forward end from adjacent its said rearward end.

18. An air-heating gas burner according to claim 17 wherein each said mixing plate portion has two of said columns of combustion air apertures, said two columns of air apertures being respectively substantially aligned with and disposed substantially adjacent the respective locations of attachment of the mixing plate portion with its two adjacent mixing plate portions.

19. An air-heating gas burner according to claim 15 wherein said mixing plate means comprises a forwardly widening conical portion extending substantially from said rearward end of the mixing plate means to a forward end terminus and having a central angle of substantially fifty (50) degrees, said forward end portions of the mixing plate means comprising an annular flat plate attached to said forward end terminus of said conical portion in surrounding and outwardly projecting relation with respect to said burner combustion zone, said annular flat plate being disposed within said perpendicular plane.

20. An air-heating gas burner of the type for mounting within a stream of air to be heated and which utilizes a portion of such air as combustion air in the burner, said burner comprising gas supply means including gas port means for emitting gas in a forward direction of the burner, and fully exposed, flared-shape mixing plate means projecting forwardly and outwardly from a rear- Ward end thereof adjacent said gas port means to a wide forward end thereof thereby defining an open-faced burner combustion zone forward of said gas port means, said mixing plate means having curved configuration which is convex in said forward direction of the burner along at least a portion of its length between its said rearward and forward ends, said mixing plate means presenting exposed surfaces in the rearward direction to be impinged by said portion of the air stream to be heated, and means defining a uniformly distributed plurality of combustion air apertures through said mixing plate means.

21. An air-heating gas burner according to claim 20, wherein said gas supply means comprises elongated gas pipe means, said gas port means comprises means defining at least four aligned and longitudinally spaced apart gas port openings along the length of said gas pipe means, those of said gas port openings between and including both penultimate openings in the line thereof each having equal diameter and being spaced an equal distance from each other, and the respective endmost of said gas port openings in said line thereof each having equal diameter which is smaller than said diameter of the other of said openings and being respectively spaced from said penultimate gas port openings an equal distance which is less than said equal spacing distance between said other openings, said plurality of combustion air apertures being arranged in respective columns of aligned apertures extending outwardly along said mixing plate means at respective locations substantially midway between the respective of said gas port openings, said gas burner further having respective end plate means projecting outwardly from said gas pipe means and closing the respective side areas of the burner between said mixing plate means, and said endmost gas port openings being respectively spaced from the adjacent of said respective end plate means an equal distance which is substantially equal to one-half /2) said spacing distance between said endrnost gas port opening and its adjacent penultimate gas port opening.

References Cited UNITED STATES PATENTS JOHN J. CAMBY, Acting Primary Examiner.