Patent Application
20150184848
1. Technical Field
The present invention relates to a tubular burner which is provided with a mixing tube having a rear-end inlet port into which a fuel gas and primary air flow. A flame hole member is fitted into a front end region of the mixing tube. The flame hole member has a plurality of flame holes such that a mixture of the fuel gas and primary air (hereinafter called gas/air mixture) is ejected from these flame holes for combustion.
2. Background Art
As this kind of burner, there is known an arrangement as described in JP-A-2012-37110. In this known burner, the front end face of the flame hole member is arranged to be flush with the front end face of the mixing tube. In addition, the outer periphery of the flame hole member has formed therein a portion which gives rise to an annular clearance between the outer periphery and an inner circumference at the front end region of the mixing tube. This portion has formed therein a plurality of flame holding holes (or flame retention holes) which are disposed at a circumferential distance between respective flame holding holes and which are directed toward the inner circumference at the front end region of the mixing tube. By employing the above-mentioned arrangement, the gas/air mixture ejected from each of the flame holding holes is caused to strike the inner circumference at the front end region of the mixing tube so as to get diffused. In this manner, the velocity of ejection of the gas/air mixture ejected forward through the annular clearance is lowered. Therefore, the flame to be formed by the combustion of the gas/air mixture ejected from the flame holding holes gets hardly lifted off, thereby securing flame holding characteristics.
Since the flame holding holes are small in dimension, it is difficult to mechanically form them at a high accuracy. Further, in this known burner the flame hole member is caused to be press-fit into the front end region of the mixing tube to thereby prevent the flame hole member from getting pulled out of position. Therefore, there is a possibility that the flame holding holes get deformed at the time of press-fitting the flame hole member. Once the flame holding holes get deformed, the amount of ejection of the gas/air mixture from the flame holding holes decreases, resulting in a failure to obtain sufficient flame holding characteristics.
In view of the above points, this invention has a problem of providing a tubular burner in which the flame hole member can be prevented, without applying an excessive (radial) force thereto, from getting pulled out of position and in which the flame holding characteristics can be secured.
In order to solve the above-mentioned problem, this invention is a tubular burner comprising a mixing tube inclusive of a rear-end inlet port into which a fuel gas and primary air flow, and a flame hole member having a plurality of flame holes and being fitted into a front end region of the mixing tube, such that a mixture of the fuel gas and primary air is ejected from these flame holes to perform combustion. A cylindrical elongated section which is elongated beyond a front face of the flame hole member is disposed at a front end of the mixing tube. The cylindrical elongated section has a convex portion which protrudes diametrically inward of the cylindrical elongated section such that the flame hole member is prevented from getting pulled out of position in a forward direction.
According to this invention, the neighborhood of the inner circumference of the cylindrical elongated section of the mixing tube serves the function of a recirculation zone of the gas/air mixture ejected from the flame holes, whereby a flame that is hardly lifted off is formed in this recirculation zone. Therefore, the flame holding characteristics can be secured without providing the flame holding holes. As a result, there is no need of forming flame holding holes on the outer periphery of the flame hole member. There will be no such disadvantage as deterioration in flame holding characteristics due to deformation of the flame holding holes. In addition, the flame hole member can be prevented from getting pulled out of position due to the convex portion that is formed at the cylindrical elongated section. Therefore, such an undue force as will tighten the flame hole member from the diametrically outside will not be operated on the flame hole member. Disadvantage such as the deformation of the flame holes to be formed in the flame hole member will neither happen.
In addition, according to this invention, preferably the mixing tube has a second convex portion which is formed adjacent to the portion into which the flame hole member gets fitted. The second convex portion is arranged such that a rear-end outer periphery of the flame hole member comes into contact with the second convex portion from the front side rearward. According to this arrangement, the flame hole member can be accurately set in position.
In
The tubular burner 1 is made up of a mixing tube 2, and a flame hole member 3 which is fitted into a front end region of the mixing tube 2. Also with reference to
In this embodiment two tubular burners 1 are disposed in parallel with each other. The two mixing tubes 2, 2 of the two tubular burners 1, 1 are constituted by joining two sheet materials 4, 4 together. The two sheet materials 4, 4 are made up of an upper plate material 4 and a lower plate material 4, each having formed therein laterally disposed two half-divided parts 41, 41 of mixing tubes 2 at a lateral space therebetween. At such a front end region of each of the plate members 4, 4 as is located at a position in which the two mixing tubes 2, 2 are respectively located, there is formed a dented portion 42 which is dented in a direction in which both the plate members 4, 4 are away from each other. Due to the clearance to be generated by the dented portion 42 between the two plate members 4, 4, there is formed a carryover flame hole 43 which causes flames to be carried over between the two tubular burners 1, 1.
The flame hole member 3 is made up of a front plate 31, and a rear plate 32 which is disc shaped and is located rearward of the front plate 31. The front plate 31 has a cylindrical member 31a which is elongated rearward from the outer periphery of the disc-shaped front face portion so as to be fit into the inner periphery at the front end portion of the mixing tube 2. Further, the front plate 31 has formed therein a first flame hole 31b in the central portion of the front face, and a plurality of slit-shaped second flame holes 31c which are located around the first flame hole 31b.
The rear plate 32 has formed therein a first ventilation hole 32a in the central portion thereof, and a plurality of second ventilation holes 32b which are smaller in diameter than, and are located around, the first ventilation hole 32a. The rear plate 32 has further formed therein a tubular member 32c which protrudes from the hole edge of the first ventilation hole 32a forward toward the first flame hole 31b. It is thus so arranged that the gas/air mixture that has flown into the first ventilation hole 32a is introduced into the first flame hole 31b through the tubular member 32c.
According to the arrangement of the tubular burner 1 of this embodiment, the flow of the gas/air mixture that is introduced into the first flame hole 31b in the front plate 31 is rectified by the tubular member 32c of the rear plate 32, and the gas/air mixture is forcefully ejected forward from the first flame holes 31b. On the other hand, the flow velocity of the gas/air mixture ejected from the second flame holes 31c in the front plate 31 through the second ventilation holes 32b in the rear plate 32 is restricted to a relatively low speed. As a result, by Bernoulli's law, the gas/air mixture ejected from the second flame holes 31c is attracted or drawn toward the flow of the gas/air mixture ejected from the first flame hole 31b at a high speed. As a consequence, the flame that is formed by the gas/air mixture ejected from the second flame holes 31c gets integrated with the flame that is formed by the combustion of gas/air mixture ejected from the first flame hole 31b. A united flame Fa that is thinly elongated forward as shown in
The front end region of the mixing tube 2 is formed into a cylindrical shape which is elongated forward from the rounded enlarged-diameter section (flared section) 23a at the front end of the tapered tube section 23. The flame hole member 3 is fitted into this cylindrical section. At the front end of the mixing tube 2 there is provided a cylindrical elongated section (i.e., an elongated section of cylindrical shape) 24 which protrudes forward beyond the front face of the flame hole member 3. According to this arrangement, the neighborhood of the inner peripheral face of the cylindrical elongated section 24 becomes negative in pressure. The gas/air mixture ejected from the diametrically outer ends of the second flame holes 31c will be recirculated in a manner to form swirls in the neighborhood of the inner circumference of the cylindrical elongated section 24. In other words, the neighborhood of the inner circumference of the cylindrical elongated section 24 of the mixing tube 2 serves as a recirculating zone of the gas/air mixture, and the flame holding characteristics can be secured by those flames Fb which are formed in the recirculation zone and which are hard to be lifted off. Therefore, it is not necessary to form flame holding holes in the outer periphery of the flame hole member 3. There will neither be such a disadvantage as the deterioration in flame holding characteristics due to deformation of the flame holding holes.
By the way, if the length of elongation of the cylindrical elongated section 24 beyond the front face of the flame hole member 3 is too small, there will be secured no recirculation zone, resulting in deterioration in the flame holding characteristics. If the length of elongation is too large, the cylindrical elongated section 24 will be subject to overheating. Therefore, the length of elongation shall preferably be set to a range of 3% to 10% of the diameter of the flame hole member 3.
Further, the cylindrical elongated section 24 has formed therein convex portions 24a which protrude diametrically inward so as to prevent the flame hole member 3 from getting pulled out of position in the forward direction. In this embodiment, four convex portions 24a are formed at a predetermined circumferential distance from one another. According to this arrangement, unlike the case in which the flame hole member 3 is prevented from getting pulled out of position in a state of being press-fit into the front end region of the mixing tube 2, there will be applied no undue force to the flame hole member 3 such as for tightening it from the diametrically outside. Therefore, there will be no disadvantage of deformation of the first flame hole 31b, the second flame holes 31c, the first ventilation hole 32a, and the second ventilation holes 32b that are formed in the flame hole member 3.
It is also necessary to hold the flame hole member 3 in position so that the flame hole member 3 does not positionally deviate rearward. In this case, it is considered to positionally fix the flame hole member 3 by bringing the rear end circumference of the flame hole member 3 into contact with the front end of the rounded enlarged-diameter section 23a. However, there is a possibility that the rounded enlarged-diameter section 23a may vary much in the dimensional deviations due, for example, to wear or aged deterioration of the molds to be used for pressing the rounded enlarged-diameter section 23, resulting in rattling of the flame hole member 3.
As a solution, according to this embodiment, the mixing tube 2 has a second convex portion 25 which is formed adjacent to the portion in which the flame hole member 3 is fitted, the second convex portion 25 being so configured as to come into contact with the outer periphery of the rear end of the flame hole member 3, i.e., into contact with the outer periphery of the rear plate 32 of the flame hole member 3 from the front side. According to this arrangement, the flame hole member 3 can be accurately fixed in position. It is to be noted that the second convex portion 25 is formed in such a degree that the flow of the gas/air mixture inside the mixing tube 2 is not affected.
Further, in this embodiment the second convex portion 25 is formed in a shape of a circumferentially continuous bead. It may alternatively be so arranged that a plurality of convex portions are formed at a circumferential space therebetween. Still furthermore, dents or projections elongated in the back and forth direction may be formed in part of the circumferential direction of the second convex portion 25 so that dents or projections formed in the outer circumference of the flame hole member 3 get engaged with the above-mentioned dents or projections, thereby obtaining the function of locking or preventing the flame hole member 3 from rotating.
Although descriptions have so far been made of embodiments with reference to the figures, this invention is not limited thereto. For example, in the above-described embodiments, the flame hole member 3 is constituted by the front plate 31 and the rear plate 32. However, the first flame hole 31b of the front plate 31 is formed into a cylindrical shape that is configured to protrude from the front face, whereby the rear plate 32 may be eliminated. Furthermore, the flame hole member 3 may be fabricated of a thick plate in order to form a plurality of flame holes which open forward. Still furthermore, in the above-described embodiments, this invention has been applied to a tubular burner for use in a residential heating appliance. Needless to say, this invention is applicable to a tubular burner that is used in a combustion apparatus other than residential heating appliance.
