Combustion – Mixer and flame holder
Reexamination Certificate
2000-03-02
2002-04-02
Lazarus, Ira S. (Department: 3743)
Combustion
Mixer and flame holder
C431S286000, C431S350000
Reexamination Certificate
active
06364657
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to gas burners, and more particularly to a stamped sheet metal gas burner and method of making the burner.
BACKGROUND ART
Gas-fired refrigerators, which may also be referred to as absorption-type refrigerators, require a gas burner or other source of heat for heating a generator containing an ammonia-water solution. The heat provided by the gas burner vaporizes ammonia from the solution which, in turn, flows to a rectifier. The rectifier separates the water from the ammonia and returns the water to the generator. The high-pressure ammonia vapor flows to the condenser where it condenses and then continues its path throughout the rest of the refrigeration circuit.
Portable gas-fired refrigerators, such as those designed for installation in recreational vehicles, require a gas burner with a relatively low output, typically less than 2000 Btu/hr., and a physical size that is compatible with other elements of the refrigerator, such as the generator, condenser, evaporator and absorber. This type of gas burner usually includes a gas input passage, an air supply hole and one or more burner ports. Air and gas are mixed in the body of the burner and then burned as the mixture is discharged from the burner port or ports. To maximize efficiency, the gas burner should provide clean combustion, a stable flame (for example not easily blown out by wind), and have a resistance to flashback.
Flashback occurs when the flame from the burner burns backwards into the burner port. The flame may travel into the combustion chamber itself and eventually damage the burner. The conventional approach to inhibiting burner flashback is to make the burner ports with multiple holes or narrow slots. An increase in the depth of the burner port or slot will also reduce the potential for flashback. To achieve this, some prior art designs use thick cast iron from which an appropriately sized burner port is machined. The thick cast iron, however, may impede heat transfer from the material and is costly.
Burners made of thin materials, for example tubular or sheet metal burners, use a plurality of burner ports to achieve the required port area for the burner. The holes or slots are sized such that the flame is maintained within the cross-sectional area of the combustion chamber opening. However, as the size of the refrigerator increases and the corresponding output requirements of the burner increase, it becomes increasingly difficult to arrange the burner ports in a manner sufficient to fire into a relatively smaller area combustion chamber opening.
SUMMARY OF THE INVENTION
The present invention provides an improved gas burner and method of making the burner. The gas burner includes a burner body comprised of a pair of adjoining metal stampings. The metal stampings form an integral and serially connected gas supply passage, venturi region, and plenum chamber. The gas supply passage defines at least one air supply opening for introducing air into the gas supply passage. Each metal stamping includes an integrally formed recess such that when joined the stampings form a burner port in fluid communication with the plenum chamber. The burner port is oriented about 90 degrees with respect to the central axis of the burner.
In accordance with a preferred embodiment of the invention, the adjoining metal stampings are mirror images of each other. This facilitates cost-effective fabrication since the dies used to fabricate each metal stamping are likewise mirror images of each other. The stampings are joined together to form a seal at the joint of the stampings.
The present invention also provides a method of making the gas burner. A pair of sheet metal pieces are selected taking into consideration the final height and length of the burner as well as the desired length of the plenum chamber, venturi region, and gas supply passage. In the illustrated embodiment, air supply openings are provided in the sheet metal piece, most preferably at 180 degrees to each other. Each sheet metal piece is stamped on a die to form half sections of the gas burner. The stamped half sections are joined together using methods including, but not limited to, metal upsetting, mechanical closure, fusing or welding, to form a burner port and a serially connected gas supply passage, venturi region, and plenum chamber. A seal is formed between the adjoining stamped half sections.
According to the invention, the burner port is formed in a flange region of the burner by an offset portion formed in at least one of the burner halves. This construction results in a burner in which the burner port is raised above the combustion chamber, the spacing or distance between the burner port opening and the combustion chamber being determined by the height of the flanged region. The width of the flange in effect determines the “quenching depth” of the burner port. As is known, the greater the depth, the less chance of flashback. In addition, by providing a raised port opening, cooling of the overall burner is promoted since the flame itself is spaced from the combustion chamber and other portions of the burner.
According to another embodiment of the invention, the burner port is tapered in the direction of a longitudinal axis of the plenum chamber. In the illustrated embodiment, the width of the port nearest the inlet to the burner is narrower than the opposite end of the burner port. In the preferred embodiment, the width of the burner port increases uniformly from a minimum width to the maximum width. This tapering or decreasing width has been found to provide a more uniform flame height because it compensates for the variation in fuel mixture velocity that occurs in the burner.
According to another feature of this embodiment, a divider plate is disposed within the burner port and divides the port opening into two equal, symmetrical openings. In accordance with this feature, the burner halves are formed with transitions or formed sections which define a recess for the divider plate when the two halves of the burner are joined. In a more preferred embodiment, the ends of the plate have beveled ends which abut an abutment formed by the burner halves when they are joined which inhibits the divider plate from falling into the plenum chamber during assembly.
The alternative embodiment preferably includes a hexagonal-shaped insert having a centrally positioned threaded bore for receiving a gas orifice or other gas fitting. The burner halves are formed with hexagonal shaped portions which define a hexagonal recess adapted to receive the insert when the two burner halves are joined.
From the above it is seen that one object of the present invention is to provide a gas burner made of sheet metal and a method of making such a gas burner. This and other objects, advantages and features of the invention will be described in conjunction with a detailed description of a best mode for practicing the invention.
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Beckett Gas, Inc.
Cocks Josiah C.
Lazarus Ira S.
Watts Hoffmann Fisher & Heinke
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