Radiant heaters

April 18, 1961

M. W. PATRICK ETAL

RADIANT HEATERS

2,980,104

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ATTORNEYS

April 18, 1961 m. w. Patrick etal 2,980,104

RADIANT HEATERS

Filed Jan. 22, 1958 4 Sheets-Sheet 2

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BY

INVENTORS hhiz//M? /At £&gt;/?r

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ATTORNEYS

April 18, 1961 m. w. Patrick etal 2,980,104

RADIANT HEATERS

Filed Jan. 22, 1958 4 Sheets-Sheet 3

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ATTORNEYS

April 18, 1961

M. W. PATRICK ETAL

RADIANT HEATERS

2,980,104

Filed Jan. 22, 1958

Sheets-Sheet 4

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ATTORNEYS

United States Patent Office _p. ..,²

Patented Apr. 18, 1961

2,980,104 RADIANT HEATERS Malcolm W. Patrick, Bedford Heights, Ohio, and William M. Day, Indianapolis, Ind., assignors to Hupp Corporation, Cleveland, Ohio, a corporation of Virginia

Filed Jan. 22, 1958, Ser. No. 710,528

Claims. (Cl. 126—271.2) the combustion being completed in a zone between the outer surface of the wall of a mixing chamber and the inner surface of a perforated mantle which is positioned with respect to the flame so as to receive a maximum amount of the heat of combustion. The mantle forms the direct source from which the heat is transmitted to the object to be heated.

The construction of the burner and the air and gas supply apparatus are such that combustion may be completed efficiently in an atmosphere of combustion products and secondary air is not required in significant amounts.

The wall of the mixing chamber is provided with flame ports described in detail below which are of unique configuration and which assure the maintenance of efficient combustion over a relatively wide range of operating conditions while minimizing the possibility of flash-back.

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

Figure 1 is a perspective view of a preferred form of radiant heater of this invention with parts broken away and shown in phantom lines for clarity;

Figure 2 is a fragmentary top plan view of a portion of the burner tube;

Figure 3 is a sectional view of the burner tube taken along the line 3—3 of Figure 2;

Figure 4 is a sectional view of the burner tube taken along the line 4—4 of Figure 2;

Figure 5 is a side elevation of a blower and a sectional view of a gas distributor head illustrating details of their mounting at the inlet end of the burner tube;

Figure 6 is a transverse sectional view taken along the line 6—6 of Figure 1;

Figure 7 is a fragmentary longitudinal sectional view ³⁵ of a modified form of the invention including an air control valve mounted on the upstream side of the gas distributor head; . .

Figure 8 is a perspective view of another embodiment of the invention illustrating a radiant heater mounted ⁴⁰ in a vertical position; and

Figure 9 is a' transverse sectional view taken along the line 9—-9 of Figure 8.

Referring now more specifically to the drawings, there is illustrated a radiant heater mounted on a chassis indi45 cated generally at 10 comprising a pair of elongated sides 12 and 14 diverging at an angle of substantially 90° to define a V-shaped channel or trough 16 which is closed at opposite ends by end plates 18 and 20, respectively. Drainage openings 22 are provided in the bottom 50 of trough 16 to prevent moisture from collecting therein.

Chassis 10 is. supported by feet 24 formed by the base of L-shaped brackets 26 having one leg welded at the corners of chassis 10 to sides 12 and 14 and end plates 18 and 20, respectively. Bracing spanners 28 are welded 55 between opposed brackets 26 to provide additional strength.

Bridging trough 16 is a plurality of arched mantles 30 supported by clips 32 welded to outer edges of sides 12 and 14. The mantles 30 are formed from a uniformly perforated sheet of stainless steel or equivalent material designed to withstand working temperatures of from 1600° to 1700° F. If desired, a mild steel coated with a suitable high temperature ceramic also may be used with good results. In the illustrated embodiment three mantle sections are employed and are loosely mounted to permit expansion.

. Mounted in trough 16 in equally spaced relation to sides 12 and 14 is an elongated cylindrical burner tube 34. One end of burner tube 34 is closed by a plate 36 welded therein which has a nut 38 welded to the inside surface thereof. A stud 40 threaded into the nut 38 is inserted into an opening 42 through plate 20 and serves

This invention relates to radiant heaters and more particularly to gas fired radiant heaters adapted to generate radiant energy in the. infra-red range.

Heaters of this general type have long been known in the art and their development has proceeded rapidly in recent years. However, prior to the present invention, the radiant heaters of this general class have been developed for a specific purpose such as for use in cooking ovens, indoor space heating or drying applications, and are not suitable for extended outdoor operation. They have a tendency to backfire or blow-out entirely when exposed to air currents and deteriorate rapidly if exposed to excessive moisture or frost.

The need has long existed for a heater of the type capable of efficient operation out of doors over extended periods of time. For example, the railroad industry has for years sought a heater which will efficiently thaw frozen bulk materials carried by railroad hopper cars which are often solidly frozen in the cars and cannot be removed by conventional methods. Various systems have been developed for thawing such materials either by direct impingement of the flame of a heater on the underside of the car or by convection. All presently known methods have proved to be slow and relatively expensive and have involved possible damage to the railroad cars.

With the foregoing considerations in mind, it is the primary purpose and object of the present invention to provide a versatile radiant heater which is not adversely affected by rain, snow, wind or air currents and which will function efficiently in various positions even when used outdoors under unfavorable weather conditions.

In accordance with the invention the burner element is provided with flame ports of unique construction which achieve a stable flame condition so that the flames neither tend to lift from the ports nor flash back to the interior of the elongated burner element even after long periods of operation.

It is another object of the invention to provide a rugged and efficient radiant heater of simple construction comprising an elongated burner tube having flame ports therein which direct flames toward an elongated mantle which, in operation, is heated sufficiently to emit radiant energy with high efficiency.

It is also an object of the present invention to provide improved radiant heaters which may be ignited readily even under unfavorable weather conditions.

It is a further object of the present invention to provide improved radiant heaters which are of general utility but which are particularly suited for use in thawing railroad cars and similar applications where durability and efficiency under inclement weather conditions are important. ।

It is an additional object of the present invention to provide improved radiant heaters in which the elements subject to deterioration in use are relatively inexpensive and may be replaced easily and quickly in the field.

; In general these and other objects are attained in the 70 present invention by the provision of burners in which combustion is effected with little or no secondary air,

2,980,104 ’ ' ’ ' 4 of the burner tube. Thus, flames of substantially equal size and intensity are projected from all the flame ports.

When it is desired to operate the burner, the blower 64 is started and the supply of gas is turned on. The gas 5 is normally supplied at a pressure of less than 20 inches W.C. which is considerably greater than the pressure at which the air enters the mixing chamber which is normally in the range of 1.0 W.C. or less. The gas enters the mixing tube in a plurality of radial jets in10 dined in the direction of the flow of the air. The position and shape of the openings 56 also promotes rapid and efficient mixing of the air and gas and the mixture is substantially homogeneous as it is delivered to the first of the flame ports.

The heater may be ignited manually by applying a lighted torch over any section of the mantle or by lifting one of the mantle sections applying a flame directly to one of the flame ports. However, the heater is preferably provided with a conventional pilot burner 100 20 which is mounted on the plate 18 adjacent the burner tube 34 as shown in Figure 5. The stability of the pilot burner 100 is maintained regardless of ambient weather conditions because of its protected location between the mantle and the tube 34. The pilot is preferably con25 nected with a source of fuel under pressure by a separate conduit 102.

It is known that the greater the amount of air which can be premixed with the gas without flashback, the greater the efficiency of the burner. This increased effi30 ciency results not only from the improved combustion process but also from the elimination of heat losses normally associated with secondary air combustion.

The flame ports are so positioned and spaced that each of the jets of gas issuing from the ports is ignited almost 35 instantaneously from the flame at the adjacent port. Nevertheless the jets are sufficiently far apart to prevent contamination of the individual flames. Both of the conditions will be satisfied if a clear space equal to twice the diameter of the port is allowed between the adjacent ⁴⁰ ports. It has been determined empirically that the distance from center to center of drill holes of average size, for instance up to Vs inch, should be Vi inch; that is, for holes up to Vs inch diameter, it is usual to drill three holes to the inch. For ports of larger size, two ports to 43 the inch will satisfy ordinary conditions. In the radiant tube burner herein disclosed, the mantle is sufficiently close to the flames so that it acts as a heat spreader to aid in effecting the smooth burning of the flames and to maintain the proper rate of flame propagation from the 50 ports. Further the mantle provides a means of obtaining a “back pressure” control that stabilizes the flame by providing the optimum ratio of gas velocity to rate of flame propagation. Further, the mantle provides a means of maintaining a stabilized flame front by providing a 55 heat source to maintain the flame propagation rate above the jet velocity rate outside of the burner port. It has also been found that the flames will not be extinguished even in strong winds as the perforations in the mantle diffuse and dissipate ambient air currents.

CO Because of its low mass the mantle 30 quickly reaches a temperature in the neighborhood of 1600° F. . At this temperature the outer surface of the mantle emits infrared radiant heat toward objects to be warmed. If desired the emissivity of the mantle may be increased by G5 the use of appropriate coatings.

Inasmuch as the combustion is effected in the subject burner with substantially no secondary air, the mixture within the burner tube 34 is combustible and accordingly flash-back must be effectively eliminated. The danger 70 of flash-back is prevented in the subject burner primarily by the utilization of flame port structures of unique size and configuration. The port dimensions given above are sufficiently large to avoid a tendency toward lifting or flame blow-out and yet small enough to prevent flash75 back, To assure these results along the length of the to slidably mount one end of the burner tube thereon so it may expand and contract during operation and shutdown, respectively, of the heater.

A collar 44 (Figure 5) welded to plate 18 surrounding an opening 46 therethrough serves to mount the inlet end of burner tube 34 which is rigidly secured to the collar 44 by a screw 48. An adaptor sleeve 50 inserted into the inlet end of burner tube 34 and held in position by screw 48 serves to connect a fuel and air supply subassembly thereto. Fuel is supplied to the inlet end of burner tube 34 through a gas distributor head indicated generally at 52 which comprises an annular collector ring 54 welded to a sleeve 57 in surrounding relation with a plurality of fuel gas passageways 56 formed in the sleeve, the passageways being inclined toward the inlet end of burner tube 34. The sleeve 57 is welded to the adaptor 50. A boss 58 formed on the collector ring 54 has connected thereto a gas line 60 leading from a fuel reservoir (not shown). The gas enters collector ring 54 through an orifice 62 therein which may be varied in size to suit the type of fuel being used. For example, a high heat content gas such as a liquid petroleum gas requires a small orifice while a low heat content gas such as manufactured gas requires a much larger orifice.

Air is supplied to the upstream end of the sleeve 57 by means of a conventional blower indicated at 64 which is connected to gas distributor head 52 by a blower adaptor sleeve 66 fitting closely in the outer end of sleeve 57. The air outlet end of blower 64 is secured in adaptor sleeve 66 by a screw 68. The blower 64 and gas distributor head 52 are enclosed by a suitable housing 70 secured to end plate 18 by brackets 71 (Figure 1).

The blower can be removed by removal of screw 68 or the entire distribution head assembly 52 can be removed by loosening screw 48 to permit quick servicing or replacement of these parts.

The top surface of burner tube 34 has a ported area indicated generally at 72 comprising a plurality of rows Of rivet type flame ports 74, 76 and 78 having central through passages 80, 82 and 84 respectively.

In a typical burner with a burner tube having an overall length of 71 inches made from a 16 gauge cylindrical tube of 2½ inch outside diameter, passages 80 have a length of Vi inch and a diameter of .1695 inch; passages 82 have a length of Vi inch and a diameter of .1540 inch and passages 84 have a length of % inch and a diameter of .1405 inch. Approximately one-third the length of ported area 72 adjacent the inlet end of burner tube 34 comprises four aligned rows of ports 74. The outermost rows of ports 74 are preferably spaced about 45° from the top center of burner tube 34 and the inner rows are spaced symmetrically from the top center thereof. The middle one-third of ported area 72 comprises four aligned rows of ports 76 which are aligned with the rows or ports 74. The end section of ported area 72 is preferably made up of five rows of ports 78, the outermost rows being in alignment with the rows of ports 74 and 76 and the center row being at the top center of burner tube 34. The elimination of the middle row of flame ports in the section of the ported area adjacent the inlet end and center section of burner tube 34 together with other factors discussed below substantially eliminate the possibility of back-firing.

The variations in length and size of the passages 80, 82 and 84 in the flame ports compensate for the differences in static pressures within the burner tube from the inlet end thereof toward the opposite or closed end. Adjacent the inlet end, the gas and air mixture is in motion, represented by both a velocity pressure and a static pressure. At the closed end of the burner tube, all of the velocity pressure has been converted into static pressure. The progressively increasing static pressures toward the closed end make it desirable in the preferred embodiment to use progressively smaller passageways in order to balance the outlet fluid velocities through all sections

8,980,104 :tube, the ports must be of different size as mentioned above.

The drilled rivets insure constant gas load at all temperatures. In addition the drilled rivets distributed throughout the tube assure the proper hole diameter and port thickness and permit the use of a thin walled pipe thus resulting in economy and convenience of manufacturing. Because of the fact that the depth of the port in the drilled rivets is relatively large, the rivets serve to act much like a gauze over a Bunsen burner by conducting away the heat at the base of the flame and thus preventing flash-back of the flame to the inner end of the rivet.

It has also been discovered that the shape of the rivet head exerts an important effect on the type of flame produced. The correct rivet shape such as shown in Figures 2, 3 and 4, produces a stable flame whereas a flat head rivet substantially increases the tendency toward flash-back or flame-lifting if the port loading and spacing of the ports is not optimum. The rivet lengths and port holes within the rivet have an effect not only on the establishment of correct port depth but the portion of the rivets within the metal tube also induce a turbulence which aids in mixing of the air and gas molecules to establish stable flame fronts. The rivets inserted in the top of the tube also tend to decrease the velocity of the top layer of the air gas mixture within the tube so that it more nearly matches the mixture velocity of the bottom of the tube thus providing more uniformity of air gas feeding to the ports.

An important factor in the burner of the present invention is the placement of the mantle sections 30 at the point where optimum radiation absorption from the flame and optimum absorption by convection occurs and in position to control the rate of flame propagation from the ports in the burner. If the mantle sections are not so located, the gas velocity may be greater than the rate of flame propagation and the flame will blow out. When the mantle is placed over the ports, a slight back pressure is exerted to control the rate of flame propagation so that it will balance the gas velocity and achieve an equilibrium condition. This is a unique feature of the burner of the present invention which contributes significantly to its improved operation. In a typical burner having a mixing tube 34 2½ inches in diameter the mantle will be spaced about an inch from the mixing tube.

Because of the construction and arrangement of the air and gas supply and mixing mechanisms, the ports and the position and arrangement of the mantle, the combustion surface is effectively localized and prevents both lifting and flash-back despite variations of mixture, pressure or flow rate over a wide although definite service range. The relation between the total port area and the positive pressure within the mixing tube is also important. If the port area is too large, the flames will decrease in height and finally a point will be reached when the velocity of the air and gas mixture through the ports will be so diminished by the reduction in the positive pressure that it is no longer in excess of the speed of the . flame propagation and back firing appears. As a general rule the proper relation between the port area and the positive pressure will be attained when the total port area is about 5 to 10% of the internal cross-sectional area of the mixing tube 34.

Figure 7 illustrates an embodiment in which air is supplied from a pressure tank (not shown). The adaptor sleeve 66 is replaced by an adaptor 86 connected to an air conduit 58. The volume of air is controlled by a damper 90 a portion 92 of which is mounted on a stud 94 welded to the sleeve 86. Up and down adjustment of damper 90 is made by lock nuts 96 and 98 threaded on stud 94.

Figure 8 illustrates another embodiment in which the . ......

heater is mounted in an inclined position on a cart indicated generally at 104.

The cart is preferably of generally conventional construction and includes a base plate 106 which supports 5 the blower end of the burner and an open framework 108 which supports the body of the burner. The framework 108 and the base 106 are suitably mounted on wheels 110 (one shown) so that the burner may be transported readily by tilting it rearwardly from its nor10 mal operating position shown in Figure 8. If desired the mantle sections may be hinged or rigidly secured to the trough members in this embodiment.

In order that the radiation from the heater may be concentrated and directed towards a desired area, sheet 15 metal reflectors 112 and 114 are secured to sides 12 and respectively as shown in Figure 9.

When the radiant heater of this invention has a pilot burner incorporated therein and is connected to a small gas tank 116 as shown in Figure 8, it may be desirable ²⁰ for reasons of fuel economy not to have the pilot burner ignited constantly, but only before placing the heater in operation. Thus the pilot burner may be ignited immediately before the burner tube is ignited, after which it may be turned off and not ignited again until ²⁵ it is desirable to re-ignite the burner tube.

From the foregoing it will be apparent that the abovestated objects of the invention have been obtained by the provision of improved radiant heaters which are of rugged durable construction and which are capable of ³⁰ giving efficient trouble-free service under a variety of environmental conditions including severe outdoor weather conditions.

The invention may be embodied in other specific forms without departing from the spirit or essential character⁵ istics 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 claims are therefore intended to be embraced therein.