US 3324845 A
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Description (OCR text may contain errors)
Jun is, 1967 G. A. HWE 3,3 45
FUEL BURNING APPARATUS Filed March 30, 1965 INVENTOR. GLEN A. WHITE.
United States Patent 3,324,845 FUEL BURNING APPARATUS Glen A. White, Westfield, Ind., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Mar. 30, 1965, Ser. No. 443,802 2 Claims. (Cl. 126-116) This invention relates to a fuel burning apparatus, and more particularly to gas-fired equipment, such as unit or duct heaters or warm air furnaces which are subject to the generation of an audible resonance effect.
In fuel burning apparatus, particularly of the type employing liquefied petroleum gas, such as propane, there frequently arises an objectionable phenomenon which is customarily referred to as resonance. This effect, when present in the audible range, gives rise to a screaming or howling noise emanating from the fuel burning apparatus, which is extremely objectionable to persons in its vicinity.
The physical explanation for the generation of an audible resonance effect is not definitely known. Some investigators of this subject believe that the resonance effect is due to the generation and shedding of gas vortices from the gas flame of the apparatus subject to this effect. Apparently, the rate or frequency of vortex shedding varies with the quantity of primary air supplied to the gas burner, the length of the heat exchange tubes in the apparatus, and the rate of flow of flue gas, as well as possible other factors. When this frequency falls within the natural frequency of the heat exchange tubes or one of its harmonic frequencies, the effect is apparently intensified so that the back pressure variations on the burner flame build up in amplitude resulting in the emission of a relatively high intensity audible sound.
Extensive investigation has been carried on in an attempt to prevent the generation of the resonance effect, but it appears that the geometrical design of the apparatus is only one factor in the generation of resonance. It has not been found feasible to completely eliminate resonance solely by altering the geometry of the heat exchanger, and in fact, resonance has occasionally been observed even when a burner is operating in free space.
It has been discovered that audible resonance can be prevented by adjusting the amount of primary air supplied to the gas burner. For propane gas burners of the atmospheric injection type, it has been found that decreasing the primary air below 45% of the total air or increasing it above 70% of the total air supplied to the apparatus will effectively prevent resonance. However, decreasing the primary air below 45% in a propane gas burner is not a satisfactory solution because of the tendency of the flame to burn with yellow tips, which represents ineflicient combustion and results in undesirable formation of soot. On the other hand, it is not generally possible to increase the supply of primary air above 70% in a burner because of the tendency of the flame to lift and become unstable.
Accordingly, it is a principal object of this invention to provide means in a gas burning apparatus to inhibit the generation of an audible resonance effect.
It is a further object of this invention to provide a gas burning apparatus wherein the quantity of primary air may be adjusted over a desired range without giving rise to the generation of an audible resonance effect.
In accordance with a preferred embodiment of this invention, a gas burning apparatus is provided with a burner for burning a mixture of gas and primary air in an atmosphere of secondary air, thereby generating hot combustion gas products. The hot combustion gas is passed through a heat exchanger in heat exchange relation with air to be heated. The combustion gas is discharged from the heat exchanger into a flue gas collector ice from which it passes to a suitable location. The flue gas collector is provided with a baflie having a wall facing the combustion gas passages in the heat exchanger. A blanket of glass fiber insulation is secured to the wall of the flue gas collector so as to effectively inhibit the generation of 'a resonance effect in the apparatus.
The precise reason for the effectiveness of the glass fiber material in the flue gas path is not definitely understood, but it has been observed that gas burning apparatus, which is normally subject to resonance when supplied with desired quantities of primary air, does not exhibit audible resonance when fibrous material is disposed in the flue gas path.
These and other objects of this invention will become apparent by reference to the following specification and attached drawing wherein:
FIGURE 1 is a perspective view of a unit heater employing the instant invention; and
FIGURE 2 is a cross sectional view through a heat exchanger of a warm air furnace embodying the present invention.
Referring particularly to the drawing, there is shown a unit heater 10 having a casing 11 provided with louvers 12 and a fan 13 in opposite walls of the casing. A heat exchanger 14 is disposed within the interior of casing 11. Heat exchanger 14 has air passages 19 through which pass room air to be heated.
A plurality of burners 15 are provided adjacent the lower portion of casing 11. Burners '15 are connected by a gas header 16 which is supplied with gas by gas valve 17 connected to a gas rnain 18. An aperture 20 is formed in casing 11 to admit air into the casing. An adjustable air shutter 21 is provided in each burner 15. Air shutter 21 is adjustable by rotating it with respect to the gas burner body to control the effective air opening for regulating the quantity of primary air induced into the interior of burner 15. It will be appreciated that additional air passes through aperture 20 and surrounds burner 15 to provide the secondary air in which the mixture of primary air and gas is burned as it passes through burner ports 22 formed in burner 15.
Heat exchanger 14 is also provided with elongated combustion gas passages 23 forming a combustion chamber having open ends for receiving and discharging combustion gas. Burners -15 are disposed adjacent one open end of passages 23 of heat exchanger 14. The other open end of passages 23 of heat exchanger 14 terminate in flue gas collector portion 30 of casing 11. A flue 31 communicates with flue gas collector 30 for discharging the combustion gases to a suitable location, such as the atmosphere.
In accordance with this invention, flue gas collector 31) has a baffle 36 having a wall 32 which extends partially over and faces the open discharge or outlet portion of passages 23 formed by heat exchanger 14. A blanket of porous, preferably fibrous, material 33, such as glass fiber or mineral. wool, is secured to wall 32 in the flue gas collector. The porous mate-rial may be suitably retained in position by covering its under surface with a wire screen 34 and securing the screen and porous material to baffle 36 with fastening means such as screws 35. The flue gas collector 30 may also include an opening 37 to prevent back drafts on burners 15.
It has been found that porous material 33 may suitably comprise glass fiber material having a density of about 2 pounds per cubic foot. Other densities of glass fiber and other fibrous materials which are porous in nature may be employed if desired. The quantity of material to be used is determined experimentally to be that quantity which effectively prevents the generation of an audible resonance effect in the gas burning apparatus over the desired range of adjustment of primary air that provides the desired gas flame burning characteristics for efficient combustion. It has been found that one or two inches of material may be sufficient to prevent resonance. Likewise, the degree of porosity of the material 33 suitable for use in this invention and its location in the apparatus is best determined by experiment in any particular application, but it must have sufficient porosity to prevent the development of audible resonance.
It has also been found that the addition of porous material in the flue gas passage of other gas burning apparatus, such as warm air furnaces which burn propane gas, effectively prevents the generation of audible resonance.
In FIGURE 2 there is shown a cross section through a heat exchanger 40 of a warm air furnace (not shown). A gas burner assembly 41 is disposed within heat exchanger 40 which forms a combustion chamber about the burner as shown in the drawing. Air to be heated by the furnace passes about the exterior of heat exchanger 40 and it will be appreciated that the warm air furnace may comprise a plurality of heat exchangers and burners disposed adjacent to each other as is well known in the art. A sheet metal baffle 42 is provided in the top por' tion of heat exchanger 40 in the path of the combustion gas generated by burner 41. A suitable flue (not shown) is connected to one end of the top portion of heat exchanger 40 to remove combustion gas and vent it to a suitable location. Baffle 42 is generally channel-shaped as is known in the art. In accordance with this invention, the interior of the baffle is filled with a layer of fibrous material such as glass fiber or rock wool, as other porous material.
It has been found that the addition of the fibrous material to the combustion or flue gas passage in the location shown in FIGURE 2 is highly effective in completely eliminating audible resonance in furnaces previously exhibiting this effect when burning propane gas fuel. A substantial advantage of the arrangement shown is that the glass fiber may be added to a presently installed furnace in this location without altering the construction of-the furnace to eliminate audible resonance.
The exact function of the porous material is not fully understood. This material may result in a reduction of the standing waves within the apparatus, or it may affect the vortex shedding characteristics of the burner flame, or it may provide sufiicient acoustic dampening so that the vibrations within the apparatus will not intensify sufliciently to react on the burner flame so as to result in oscillation. It may be necessary, however, to add an experimentally determinable minimum quantity of f1- brous material to produce any appreciable effect on the resonance. It should be noted that the audible resonance is not merely attenuated by the practice of this invention, but is completely eliminated by being prevented from developing. In any event, it has been found that the addition of porous materials in experimentally determinable quantities depending on porosity is highly effective to prevent the generation of an audible resonance effect in gas-fired apparatus over any desired range of primary air mixtures.
It will be appreciated that for purposes of illustration a preferred embodiment of this invention has been shown and described, but that it may be otherwise embodied within the scope of the following claims.
1. A fuel gas burning apparatus of a type which is normally subject to the generation therein of an undesirable aduible resonance eflect, said gas burning apparatus comprising:
(1) a gas burner assembly for burning a desired mixture of gas and air thereby producing hot combustion gas;
(2) a heat exchanger to pass a fluid to be heated in heat exchange relation with said hot combustion gas produced by the gas burner assembly;
(3) an upwardly open channel shaped baffle member disposed in the upper portion of said heat exchanger in the path of combustion gas generated by said gas burner assembly; and
(4) a quantity of porous material disposed in said channel shaped baffle member suflicient to prevent the generation of said audible resonance effect in said gas burning apparatus.
2. A fuel gas burning apparatus of a type which is 20 normally subject to the generation therein of an undesirable aduible resonance effect, said gas burning apparatus comprising:
(1) a burner assembly for burning a mixture of a gaseou's fuel and induced primary air in an atmosphere of secondary air;
(2) means to adjust the quantity of induced primary air over a desired range;
(3) a heat exchanger disposed to receive hot combustion gas products produced by said burner and to pass them in heat exchange relation with air to be heated, said heat exchanger including a plurality of elongated passages, said passages being open adjacent one of the ends thereof to receive said hot combustion gas products from said gas burner, and said passages being open adjacent the other ends thereof to discharge said combustion gas products from said heat exchanger;
(4) a flue gas collector disposed over said other open ends of said heat exchanger passages to receive combustion gas products therefrom and to discharge them to a suitable location, said flue gas collector including an internal baflie, said internal baflle having a wall thereof facing said other open ends of said heat exchanger passages, said wall of said internal bafl le extending partially across the top of each of said heat exchanger passages to admit flue gas from the uncovered portions of the ends of said heat exchanger passages into said flue gas collector; and
(5) a thickness of fibrous material secured to said wall of said baffle facing the said other open ends of said heat exchanger passages, said fibrous material being of sufficient thickness and density to effectively prevent the generation of said audible resonance effect in said fuel burning apparatus over a desired range of adjustment of primary air.
References Cited UNITED STATES PATENTS 7/1946 McCollum 126-116 7/1946 McCollum 1261 16 9/ 1949 McCollum 1261 16 10/ 1952 Flint. 10/1963 Lucas.