Claims:
What is claimed
1. In a fuel burner in which the pressure energy of the fuel is accelerated at high velocity through and from an orifice, and into a coaxial burner tube, said burner tube comprising, sequentially a fuel-inspirated air entry and mixing section, a throat of diameter D, and an expansion section terminating in a burner tip, the movement in said expansion section comprising:
2. The burner as in claim 1 wherein said burner tip includes a support pipe fitting the outer surface of said second section and extending the length of said burner tube and terminating on the outer surface of said entry section.
3. The burner as in claim 2 in which said burner tip means is welded to said pipe means.
4. The burner as in claim 1 in which said burner tube is substantially a single monolithic cast structure.
5. The burner as in claim 1 a further improvement of which said entry section comprises a smooth, curved, section.
6. The burner as in claim 1 a further improvement of which said entry section comprises a conical tapered section.
7. A burner as in claim 1 wherein said entry section converges to said throat diameter for a length approximately 1.3D.
8. A burner as in claim 1 wherein said fuel orifice is mounted at a distance approximately a distance D/4 upstream of said entry section.
Description:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is in the field of fuel burners in which the pressure energy of the fuel is used for the purpose of inspirating combustion air into the burner tube.
More particularly, this invention is concerned with the design of burners of high efficiency, simple construction, and shorter length than prior art burners.
2. Description of the Prior Art
In the prior art, fuel burners, preferably gas burners, have been constructed of monolithic cast construction with an entry section, in which the combustion air is inspirated, leading to a throat section and followed by a long, outwardly expanding section leading to the burner tip. Since the burner tip is a replaceable part of the burner assembly, it is necessary to removably attach the tip to the burner tube. This has been done in the prior art by welding the tip to a threaded collar, and threading the outer surface of the end of the burner tube. This is a difficult and unsatisfactory method of attachment because of the difficulty of cutting threads into the cast material of which the burner tube is generally constructed. Also the long expansion section has made it difficult to design compact systems.
BRIEF SUMMARY OF THE INVENTION
These disadvantages of the prior art burners have been overcome in the present invention by designing the expansion section so as to provide the equivalent efficiency, with shorter length. Also, the burner tip is attached by welding to a cylindrical pipe which extends the length of the burner tube, snugly fitting the exterior contour at each end.
It is therefore an object of this invention to provide a fuel gas burner that is appreciably shorter than, and equally efficient to, the longer prior art burners. It is a further object of this invention to provide a simple, inexpensive, and convenient method of attaching the burner tip to the burner.
These and other objects of this invention will be clarified and a better understanding of the principles involved in this invention will be obtained from the following description, taken in relation to the appended drawings, in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a typical prior art pressurized fuel gas burner.
FIG. 2 is a cross-sectional view of the improved, shortened, pressurized fuel gas burner of this invention.
DESCRIPTION OF THE PRIOR ART BURNER
In order to appreciate the inventive concepts some detail description of the prior art burner design is necessary. Referring now to the drawings, FIG. 1 is a view of a prior art fuel gas burner. Typically such a burner 10 has an entry section 12 tapering in inner diameter, at a conical angle of from 20°-25°, down to a minimal throat diameter D in many instances of a short section 16, and then an enlargement, or expansion section 18 in which the diameter varies from the throat diameter D to an outlet diameter D 2 . In some prior art devices the long expansion section 18 is broken into two parts of different conical angle 20. Beyond the outlet end 21 is a burner tip 30, which is of a slightly expanding configuration, but can be of varied designs, e.g., that shown in the aforesaid pending application.
The input section is typically of an axial length about 1.3D. The short constant diameter section is generally of length about 0.8D and the long expanding section of length about 7.5D. The burner tip is typically of a length of about 2.4D. This makes the burner typically of an overall length about 12D. The outlet diameter D 2 is generally of a dimension equal to 2D.
In the prior art the burner tip 30 is generally attached to the burner by being welded 28 to an internally threaded collar 26 which is screwed onto the outer threaded surface 24 of the outlet end 21 of the burner tube.
At the input end, a coaxial pipe 32, which has an orifice 34, in its closed off end, supplies fuel gas at super-atmospheric pressure, typically twice atmospheric pressure. The orifice is typically positioned a distance about D/4 in front of the entry section 14.
OPERATION OF THE TYPICAL PRIOR ART BURNER
The operation of the typical prior art burner as shown in FIG. 1 is as follows: the high pressure fuel gas in the space 36 in pipe 32 flows through the orifice 34 into the entry section 12. The gas is accelerated by the expansion of the gas from pipe pressure to a lower pressure, generally below atmospheric pressure. This flow, shown by arrows 35 may, at times, reach as high a value as the velocity of sound in air. Because of this high velocity, by Bernoullis Theorem, as is well known in the art, the pressure in the throat is subatmospheric and air is drawn, or inspirated, into the entry section as shown by arrow 38 and is entrained and mixed with the fuel gas. Thus, at the throat, of minimum diameter D, the mixed gas has a maximum velocity, and as it flows down the burner toward the outlet, the gas flow decreases in velocity, while the pressure correspondingly increases. In other words the velocity head in the throat, which was necessary to inspirate the air, is converted back to pressure head in the long expansion section 18. Typically the flow velocity of the gas is inversely proportional to the square of the diameter. Thus, exit velocity at 21 will be D 2 /D 2 2 times the velocity at the throat, or approximately one quarter the velocity at the throat.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The prior art burners suffer from several serious disadvantages, which in this invention we have attempted to overcome. The principle difficulty is its length, which is unduly long and makes it difficult to design a compact furnace system. This great length is based upon the theory that to get efficient recovery of pressure in the expansion portion of the burner a long, slowly-expanding section is needed.
The invention, as shown in FIG. 2, reveals that a properly designed expansion section can be much shorter and still be substantially as efficient. The entry section 52 and throat section 54, respectively 1.3D and 0.8D are substantially the same length as the prior art burners. The expansion section is divided into two parts, a first section 56 and a second section 58. The first expansion section 56 has an internal conical angle 72 of 8°, and is about 1.5D long, while the second expansion section 58 has an internal conical angle 74 of about 16° leading to the outlet 60 (D 2 ). The length of the second expansion section is about 2D.
The burner tube 50 is generally made of cast iron because of the ease with which it can be cast to precise dimensions. In order to attach the burner tip 68 this invention provides a simple and effective method. The outer contour of the burner tube 50 includes, at each end, cylindrical seats 62 and 64, on which a standard size of steel pipe 66 will snugly fit. The pipe can be held to the burner tube by the snugness of the fit, or by means of screws, not shown, but well known in the art. The burner tip 68 is designed to be of the same diameter as the pipe and is welded 70 to the end of the pipe 66. The diameter of the outlet end 60 of the burner tube D 2 is approximately equal to 2D.
The inlet section 52 is smoothly curved from the inlet diameter at 80, to the throat diameter D. However, the conical contour of FIG. 1 can be applied to the burner of FIG. 2 without serious loss of efficiency. Also the placement of the fuel gas pipe 32 and the orifice 34 are substantially the same as in the prior art systems. The gas flow and air flow are shown respectively by arrows 76 and 78.
The burner length in FIG. 2 totals 5.6D exclusive of the tip, while the corresponding length of the prior art burner of FIG. 1 is approximately 9.6D. Including the burner tip the corresponding lengths are 8D and 12D respectively. Thus the length of the improved burner of this invention is approximately two thirds the length of the prior art design, while being of equal efficiency and simpler construction.
While we have described our invention with a certain degree of particularity, the scope is not to be limited by this description or by the drawings, but only by the scope of the appended claim or claims.