US3771945A - Gas burner having a diffuser for mixing combustion air and gas - Google Patents

Abstract

Gas is mixed with air with the aid of a diffuser and is drawn into a hollow core of a radiant burner. The diffuser has a plurality of spring fingers around the top of a gas outlet orifice. The fingers carry a shallow cup having a concave surface which faces the orifice and deflects gas laterally and rearwardly in a mixing chamber surrounding the diffuser. Incoming air is thoroughly mixed with the gas in the mixing chamber prior to the induction of the mixture into the hollow core. Gas is burned on the surface of the radiant burner and the products of the combustion heat air for, for example, room heating.

Description

United States Patent [1 1 Teague, Jr.

1 Nov. 13, 1973 [22] Filed:

[ GAS BURNER HAVING A DIFFUSER FOR MIXING COMBUSTION AIR AND GAS [75] Inventor: Walter D. Teague, Jr., Nyack, NY.

[73 Assignee: Southern California Gas Co., Los

Aussie alif: 1.

Aug. 21, 1972 211 Appl. No.: 282,287

Related U.S. Application Data [62] Division of Ser. No. 65,374, Aug. 20, 1970, Pat. No.

[52] U.S. Cl. 431/328, 126/92 C, 431/354 [51] Int. Cl. F23d 13/12 [58] Field of Search 431/326, 329, 354; 239/432 [56] References Cited UNITED STATES PATENTS 3,208,247 9/1965 Weil et a1. 431/328 1,223,308 4/1917 Bone et al 431/328 2,533,104 12/1950 Golden et a1. 431/328 w 3,506,198 4/1970 Van Der Zwaal 431/354 FOREIGN PATENTS OR APPLICATIONS 11,041 0/1905 Great Britain 239/432 Primary ExaminerCarrol1 B. Dority, Jr. AttorneyRobert L. Parker et a1.

[57] ABSTRACT Gas is mixed with air with the aid of a diffuser and is drawn into a hollow core of a radiant burner. The diffuser has a plurality of spring fingers around the top of a gas outlet orifice. The fingers carry a shallow cup having a concave surface which faces the orifice and deflects gas laterally and rearwardly in a mixing chamber surrounding the diffuser. Incoming air is thoroughly mixed with the gas in the mixing chamber prior to the induction of the mixture into the hollow core. Gas is burned on the surface of the radiant burner and the products of the combustion heat air for, for example, room heating.

3 Claims, 7 Drawing Figures PATENTEDNUV 13 1975 SHEELQCF GAS BURNER HAVING A DIFFUSER FOR MIXING COMBUSTION AIR AND GAS CROSS REFERENCE TO RELATED APPLICATIONS The present application is a division of US. Pat. application Ser. No. 65,374 filed Aug. 20, 1970 and now US. Pat. No. 3,696,802.

BACKGROUND OF THE'INVENTION The present invention relates to gas burners in general, and in particular to an improved diffuser for mixing gas with combustion air in a short distance.-

In many situations it is desirable to heat a space without installing a central heating system. Thus, for example, in small apartments or the like, particularly in relatively warm parts of the country, it may be desirable to have separate heating systems for each unit. Similarly, in a mobile home one or more small heaters may be employed. Small heaters may also be used as auxiliary heating in spaces not adequately heated by a central system. In any of such systems for heating a limited space it is desirable to have complete safety for the occupants of the space, high fuel efficiency, low cost, as small a heater as possible, an attractive heater, and as little intrusion of the heater into the heated space as possible.

Individual room space heaters have in the past often involved a plurality of heated exhaust tubes arranged in a wall panel with much of the heating being due to natural convection and radiation. Forced air units for individual rooms have been bulky and relatively impractical for most applications. Most such forced air units have been mounted completely within a space to be heated and therefore draw combustion air from within the space.

One of the problems with gas heaters which adds to their bulk and overall size is that a great length must be provided for gas to adequately mix with combustion air.

It is therefore desirable to provide a small, low cost, efficient space heater for individual rooms or other limited areas. Such a unit should be attractive and preferably occupy only a small amount ,of wall space.

SUMMARY OF THE INVENTION The present invention provides for use ina gas heater or the like a diffuser which materially shortens the space required to effect adequate mixing of combustion air with gas. The diffuser is mounted immediately in front of the outlet of a gas orifice and has a concave surface facing the orifice. The concave surface is on a member supported, preferably, by a plurality of fingers extending from a fitting which defines the orifice. Combustion air is mixed with gas forced laterally and rearwardly of the concave member into a mixing chamber disposed concentrically about the diffuser and the orifice. The mixed combustion air and gas are drawn into burner where the gas is burned. The products of combustion from the gas and air can be used to heat air which is forced into a space to be heated. 1

These and other features, aspects and advantages of the present invention will become more apparent from the following description, appended claims and drawmgs.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 illustrates schematically the flow of gases within a space heater constructed according to principles of this invention;

FIG. 2 illustrates in longitudinal cross section a gas heater embodying principles of this invention;

FIG. Sis a transverse cross section of the heater of FIG. 2;

FIG. 4 is another transverse cross section of the heater of FIG. 2;

FIG. 5 is a detail of an igniter for the heater of FIG.

FIG. 6 is a longitudinal cross section of a portion of another embodiment of space heater; and

FIG. 7 is a transverse cross section of the heater of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT A better appreciation of the nature, effect and purpose of the gas burner of the present invention can be had by considering initially the preferred gas heater used with the burner.

FIG. 1 illustrates schematically the flow of exhaust gases and heated air in a gas fired space heater constructed according to principles of this invention. As illustrated in this schematic drawing, the flow of combustion products or exhaust gases is indicated by a series of arrows within conduits or passages of the heater. In general, the flow of exhaust is approximately parallel to the plane of the paper in FIG. 1. Likewise the flow of air in the space heater is indicated by tips and tails of arrows since the flow of air is, in general, substantially normal to the plane of the paper. Air flowing out of the plane of the paper is indicated by an arrow tip in the form of a circle and concentric dot. Air flow into the plane of the paper is indicated by the tail of an arrow in the form of a circle with a cross inscribed therein. The structural parts illustrated in this schematic of FIG. I are probably best understood by additional reference to FIGS. 2 and 4. 1

As illustrated in FIGS. 2, 3, and 4 the space heater tion 12 is preferably mounted on the exterior of a building. A mounting flange 13 is connected to the sheet metal housing 10 for attaching the heater to a building wall 14 or the like. Theflange I3 is preferably made adjustable in some conventional manner so that the heater can be mounted on walls of varying thickness, as may be required in a particular installation. With the heater mounted in such an arrangement the front 11 is within the building and the back portion 12 of the heater is in the exterior environment.

The sheet metal housing 10 and other sheet metal portions hereinafter set forth are illustrated in the cross sections of FIGS. 2-4 in the form of heavy lines representative of cross sections of the material. Edges of parts not in cross section are illustrated by lighter quality lines in these figures. The heavy lines are employed rather than attempting to illustrate the thin metal by conventional cross sections in order to improve the clarity of the drawings.

The housing 10 is lined with thermal insulation 16 for minimizing heat transfer between air within the housing I and the external environment. The insulation serves the additional important function of deadening sound and assuring quiet operation of the unit both inside and outside the region being heated. The housing serves as the exterior of a recirculation air conduit 18 running from the front 11 to the back 12 of the heater. Air from the space to be heated enters the recirculation conduit through louvered openings 17 in the housing.

The interior of the recirculation air conduit 18 is principally defined by a substantially cylindrical sheet of metal 19 which also forms the exterior wall of an exhaust conduit 21. The cylindrical exhaust conduit is approximately concentric with the rectangular recirculation conduit 18. The interior of the exhaust conduit 21 is defined by another substantially cylindrical sheet metal body 22, substantially concentric with the sheet metal body 19. The sheet metal body 22 continues forwardly of the cylindrical portion defining the inside wall of the exhaust conduit into a gooseneck or double elbow portion 23 leading to a heated air port 24, at the lower front of the heater, and within the space to be heated. Preferably the heated air port 24 is wider than it is high, in order to minimize flow restriction. Thus the sheet metal body 22 not only defines the interior wall of the exhaust conduit 21, but also forms the exterior wall of a heated air conduit 26, leading from the back 12 of the heater to the front 11.

Substantially concentric with the cylindrical portion of the body 22 is a cylindrical sheet metal member 27 with a closed forward end 28 defining a combustion chamber 29 therein. Mounted in and concentric with the combustion chambers 29 is a porous refractory radiant heater or burner 31, heating of which is described in greater detail hereinafter. Broadly speaking, the exterior of the radiant burner 31 is heated to incandescence by burning gas and emits combustion products from its entire exterior surface. Since the radiant burner 31 is at incandescence it serves to rapidly trans fer heat by radiation to the wall 27 of the combustion chamber 29.

An exhaust passage 32in the form of a rectangular opening relatively long parallel to the front to back axis of the heater and relatively short transverse thereto interconnects the interior of the combustion chamber 29 and the exhaust conduit 21 near the top portion of the heater. An exhaust port 33 at the lower portion of the heater in the form of a short passage relatively short in the direction parallel to the axis of the heater and relatively long transverse thereto, interconnects the interior of the cylindrical exhaust conduit 21 and the external environment outside the heater housing 10.

A conventional fan 34 at the back portion of the heater has its suction side in fluid communication with the recirculation conduit 18 and its pressure side in fluid communication with the heated air conduit 26.

Referring again to FIG. 1 combustion products emitted from the surface of the radiant burner 31 enter the combustion chamber 29 and, along with radiant heat from the radiant burner, heat the surrounding wall 27. The combustion products or exhaust, as indicated by the arrows, pass upwardly through the exhaust passage 32 and enters the cylindrical exhaust conduit 21 where the flow path divides. The combustion products then pass along a generally semi-cylindrical path down each side from the top of the heater through the exhaust conduit 21 to the exhaust port 33 where they are discharged from the heater. As the exhaust passes through the exhaust conduit 21 the walls 19 and 22 thereof are heated.

Air from the space to be heated enters the front of the recirculation conduit 18 through the openings 17 (FIG. 2) and passes to the back of the heater through the recirculation conduit. While so passing the relatively cool air is in thermal contact with the wall 19 which is heated by the exhaust, so that preheating of the air occurs. The air is then passed by the fan 34 (FIG. 2) into the heated air conduit 26 through which it flows forwardly in the heater ultimately to be discharged into the heated space through the heated air port 24. As the air passes forwardly through the heated air conduit it is in heat transfer relation with the wall 22 of the exhaust conduit and the wall 27 of the combustion chamber so as to be heated thereby.

It will be seen that the air flows substantially concentrically with the exhaust products from the radiant burner and also the flow of air and exhaust products are approximately counter-current for optimum efficiency. Thus the initially cooler air in the recirculation conduit 18 is in heat transfer related with the cooler exhaust in the exhaust conduit 21 and the relatively warmer air in the heated air conduit 26 is in thermal contact with the appreciably hotter exhaust and radiant heat from the combustion chamber 29. Such counter-current flow assures a minimum temperature in the exhaust emitted from the space heater and a maximum temperature in the air put into the room being heated. Both of these are indicative of optimum efficiency of operation of the space heater. Tests indicate an exhaust temperature in the range of 300 to 400 F and a thermal efficiency in the order of about percent.

In addition to the air recirculated from the heated space through the heater a selected fraction of makeup air is provided by a make-up air aperture 36 in the back portion of the housing 10 so as to be in fluid communication with the'exterior environment. This makeup air aperture is on the suction side of the fan 34 and a portion of the air passing through the heater is therefore drawn in through the aperture. By adjusting the size of the aperture 36 any desired fraction of make-up air can be provided in a heater. Typically 10 percent make-up air is provided through a 1 /4 inch diameter hole.

It may be noted that the exhaust port 33 and make-up air aperture 36 are both located on the lower side of the space heater. This arrangement is preferred so that these openings are inherently protected from the elements. It will be apparent of course that such openings can be provided one top, side, or back of the heater as may be desired with suitable baffles or shields to pre- ,vent rain and the like from entering the interior of the heater. Although both the exhaust port and the makeup air aperture are located on the bottom side of the heater, no problem has been found with short circuiting of exhaust products into the heater when these openings are located about 6 inches apart. If it is desired to locate these openings in some other position it will be apparent that suitable baffles can be provided to prevent short circuiting of combustion products.

The space heater is fueled with natural gas or the like which is supplied thereto through a pipe 37 which is preferably located in a wall 14 in which the heater is mounted. The gas line 37 leads to a conventional automatic control 38 typically in the form of an electrically controlled valve actuated by a conventional temperaa mixing chamber casting 42. The passage 41 termi-' nates in an orifice tip 43 having a central circular orifice (not shown) having a size commensurate with the required gas flow in the space heater. The orifice tip 43 is aligned with and pointed towards the radiant burner 31.

The radiant burner is a conventional commercially available element in the form of a hollow cylinder or porous refractory material, open at one end and closed at the opposite end. The porosity of the refractory material is selected so that during normal operation the flow rate of a combustible gas-air mixture through the pores is greater than the flame propagation rate. Prior to passing through the walls of the radiant burner 31 the combustion gas is mixed with combustion air and combustion occurs in a thin region adjacent the outside surface of the radiant burner. The combustion in this region heats the external surface of the radiant burner, which because of its rough porous surface has a high emissivity, to incandescent temperatures. The flow of gas air mixture from the interior of the radiant burner towards its outside surface maintains the interior relatively cool and substantially below the ignition temperature. Because the gas must pass through the porous refractory body of the radiant burner there is a pressure drop across the wall, and the interior of the radiant burner is pressurized somewhat relative to the exterior by an amount dependent on flow rate and porosity.

Combustion occurs over substantially the entire outside surface of the radiant burner (actually a very short distance below the surface) so that the entire surface is incandescent and radiates to the walls 27 and 28 of the combustion chamber 29. The pressure drop across the radiant burner assures that the exhaust products are emitted from the external surface of the radiant burner and enter the combustion chamber 29 for flowing through the exhaust system of the space heater as hereinabove described.

A problem that has been faced with previous radiant burners has been adequatemixing of the fuel gas with combustion air. Unless'the gas and air are thoroughly mixed prior to entering the elongated cylindrical radiant burner, composition gradients may occur, and-nonuniform heating with consequentinefficiency and even danger to the burner hasoccured. A variety of orifice designs have been explored in order to achieve adequate mixing, however, no acceptable arrangement has been provided. In general, it has been necessary to space the gas inlet orifice away from the open mouth forrnly mixed with incoming air prior to entering the mouth of the radiant burner 31.

The mixing chamber casting 42 not only includes a substantially cylindrical central mixing chamber 45 and a gas passage 41 leading thereto, it also includes a plurality of substantially radially extending fins 47. The fins 47 extend outwardly from a point approximately in line with the outside wall 27 of the combustion chamber to a point in line with the exterior wall 22 of the heated air conduit. The heated air conduit also includes a substantially conical portion 48 enlarging from the cylindrical wall 22 to approximately the effective diameter of the fan 34. The fins 47 are mounted within this cone 48. As seen in FIG. 3, the fins do not extend parallel to the axis of the heater, but generally follow a slightly helical path so that air impinging on the fins of the radiant burner by a distance of about five diameters. Such a distance is undesirable in a small space heater since it unduly lengthens the device and makes it less attractive.

A surprisingly-simple and efficacious solution to the gas-air mixing problem has been' discovered. In accordance with this discovery, a plurality of spring fingers 44 are provided around the orifice tip 43. The fingers 44 may be formed integral with the mixing chamber casting 42 or preferably are attached by the tip 43.

Clipped into the fingers 44 is a shallow cup 46 having its concave surface facing the gas orifice. The concave inside surface of the'cup 46 deflects the gas flow from the orifice and redirects it laterally and rearwardly in the mixing chamber wherein it 'is thoroughly and unifrom the fan 34 is straightened out so as to flow through the heated air conduit 26 parallel to the axis. This is done because the air coming out of the fan 34 is whirling to some extent due to the action of the fan blades and the slightly helical fins counteract this whirling to a large extent. If desired, radially extending fins can be provided on the exterior wall of the combustion chamber 29 in the heated air conduit to further assure axial flow of the air and also to conduct heat from the hot combustion chamber wall 27 to an increased area for thermal contact with the air. A particularly suitable arrangement is to provide the exterior wall 27 of the combustion chamber in the form of a corrugated cylinder with the greatest extent of the corrugations running parallel to the axis. This serves to direct the air to some extent and also substantially increases the heat transfer surface area without substantial cost increase.

In the embodiment illustrated herein an air duct 94 (FIGS. 2 and 3) extends from the pressure side of the fan 34 into the upper portion of the mixing chamber 45 for bringing combustion air in for mixing with the gas. The air duct 94 is like a curved scoop between a pair of the fins 47 leading forwardly and downwardly to the mixing chamber. A plate connected to the casting 42 blocks a portion of the inlet to the duct 94 and by selecting the size of plate, a desired pressure can be achieved in the mixing chamber and radiant burner for optimum'heater operation.

The arrangement illustrated herein comprises what is known as a nonsealed unit since combustion air is 'extracted from a portion of the air stream being heated. The exhaust side of the combustion chamber is of course sealed from the heated air. There is no problem with depletion of the air in the space being heated by such a non-sealed unit since the make-up air aperture 36 is sufficiently large to provide a greater quantity of make-up air than is required for combustion purposes. If desired a plurality of make-up air apertures can be provided in case of inadvertent blocking of one of the apertures.

A non-sealed unit as hereinabove described, has an overall length of about 20 inches and the portion extending outside the building is approximately 9 inches square. Within the building, the unit occupies a wall space of about 10 by 12 inches, or slightly less. A sealed unit as hereinafter described has the same dimensions, except it is about three inches longer to provide room for an additional fan.

In order tostart the gas heater in operation when an on signal comes from a thermostat power is first applied to a conventional glow igniter such as illustrated in FIGS. 4 and 5. The glow igniter comprises an insulating terminal block 51 mounted in an enlargement of the upper exterior wall 19 of the exhaust conduit 21. Clips 52 conduct current to a resistive element 53 that is rapidly heated to a temperature above the ignition temperature of a gas-air mixture. When the igniter 53 reaches temperature the fan 34 is turned on and a short time later the solenoid control valve 38 is opened to admit gas into the mixing chamber 45. The gas mixes with the air, flows through the porous radiant burner 31, quickly filling the small volume of the combustion chamber and the exhaust passage 32. This brings the gas-air mixture in contact with the hot igniter and the resultant flame quickly propagates back to the surface of the radiant burner. It is found that ignition occurs in less than 1/6 second in such a system and there is no noticeable popping upon ignition. It will be apparent to one skilled in the art that other ignition systems such as for example, pilot lights, spark igniters, or the like can be employed if desired. It is preferred that the igniter be located at the upper portion of the exhaust conduit so that the gas-air mixture reaches it in a minimum time.

FIGS. 6 and 7 illustrate in side cutaway and rear section, respectively, a gas-fired space heater constructed according to principles of this invention in the form of a sealed unit wherein the combustion air supply is completely independent of the air being heated. Only the rear portion of the space heater is illustrated for showing the air supply since the heating portion, exhaust ducts, radiant burner and the like are substantially identical to the non-sealed unit hereinabove described and illustrated.

The sealed unit comprises a sheet metal housing 56, the sides and rear end of which are slightly bulged for decorative purposes to avoid a boxy look on that portion of the unit exterior to the space being heated. Mounted witin the housing 56 is a heated air conduit 57 through which air is forced by a fan 58. Air enters the suction side of the fan 58 through a recirculation conduit 59 within the housing. Within the heated air conduit 57 is a combustion chamber 61 within which a radiant burner (not shown) is mounted. The combustion chamber, air flow conduits, and exhaust conduits (not shown) are substantially identical to those hereinabove described and illustrated in relation to FIGS. 1 through 4.

The fan 58 is driven by a conventional electric motor 62, the shaft 63 of which is connected to the fan 58 and also to a conventional centrifugal blower 64. The suction side of the blower 64 has a central aperture 65 open to a combustion air plenum 66 formed between a portion of the housing 56 and a sheet metal bracket plate 67, which also serves to mount the blower. The

combustion air plenum 66 is in fluid communication with the exterior environment surrounding the heater through a hole or holes 68, preferably located along the bottom edge of the heater for protection from the elements. A short tube 69 interconnects the blower 64 and motor 62, and provides a barrier to prevent air from the heated air system and the combustion air system from commingling, thereby providing a sealed unit wherein the exhaust products are isolated from the heated air and the combustion air is not drawn from the space to be heated.

The outlet of the centrifugal blower 64 is connected to an upwardly extending air flow tube 71 by a rubber sleeve 72. Air passing from the tube 71 flows through a rectangular combustion air conduit 73 running diagonally forward along the upper portion of the space heater. Air from the combustion air conduit then passes downwardly through a passage 74 into the combustion chamber 61 where it enters the radiant burner (not shown) as in the other embodiment.

Inserted through the side of the air tube 71 is a smaller diameter gas pipe 76 ending in an orifice tip 77 within the air tube. Combustion gas is added to the air through the orifice tip 77, and because of the long flow path between the tip and the combustion chamber, thorough mixing with the combustion air is obtained without use of the deflector cup hereinabove described and illustrated in relation to the embodiment of FIGS.

Although limited embodiments of space heaters constructed according to principles of this invention have been described and illustrated herein, many modifications and variations will be apparent to one skilled in the art. Thus, for example, although the heater has been illustrated with the exhaust flowing upwardly in the exhaust conduit and downwardly to the exhaust port, the flow can be from one side to the other, or from bottom to top, as may be desired. As another variation, the external housing forming the outer wall of the recirculation conduit can be cylindrical for a smaller apparent size and decorative effect. Many other modifications and variations will be apparent to one skilled in the art and it is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An improved burner combination comprising:

a. means defining a chamber for mixing air and gas;

b. means defining a gas inlet orifice into the mixing chamber; V c. a duct for introducing air into the mixing chamber; d. a radiant heat burner in the form of a porous cylinder having an open end, the open end facing the mixing chamber; and

e. a deflector in front of the gas inlet orifice means having a concave side facing the orifice.

2. The improved burner combination claimed in claim 1 wherein the deflector includes a segment of a hollow sphere having its'concave side facing the orifice.

3. The improved burner combination claimed in claim 2 including spring fingers mounted on the gas inlet orifice means and carrying the hollow spherical segment.

Claims (3)

1. An improved burner combination comprising: a. means defining a chamber for mixing air and gas; b. means defining a gas inlet orifice into the mixing chamber; c. a duct for introducing air into the mixing chamber; d. a radiant heat burner in the form of a porous cylinder having an open end, the open end facing the mixing chamber; and e. a deflector in front of the gas inlet orifice means having a concave side facing the orifice.

2. The improved burner combination claimed in claim 1 wherein the deflector includes a segment of a hollow sphere having its concave side facing the orifice.

3. The improved burner combination claimed in claim 2 including spring fingers mounted on the gas inlet orifice means and carrying the hollow spherical segment.

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