| Pore burner and cooking appliance containing at least one pore burner -> Monitor Keywords |
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  Pore burner and cooking appliance containing at least one pore burnerUSPTO Application #: 20060035189Title: Pore burner and cooking appliance containing at least one pore burner Abstract: The disclosure relates to a pore burner, especially for cooking appliances, including a housing provided with at least one inlet for a gas/air mixture as a fuel and/or at least one inlet for air and/or at least one inlet for gas and/or at least one outlet for air and/or gas and/or waste gases. The housing includes at least one dimensionally stable, porous molded body formed of sintered metallic powder and/or pressed metallic wire mesh, on the surface of which and/or in the pore spaces of which are reaction zones for the flame development for forming a surface burner. The disclosure also relates to a pore burner including at least one distribution device for the targeted orientation of part of the gas and/or air flow and/or part of the gas/air mixture flow, said distribution device being at least partially arranged and/or molded in the hollow body in such a way that part of the air and/or gas flow or part of the gas/air mixture flow can be distributed such that the inner wall of the hollow body, especially in the region of the distribution device, has a non-homogeneous pressure distribution. (end of abstract) Agent: Marshall, Gerstein & Borun LLP - Chicago, IL, US Inventors: Karlheinz Berstecher, Franz Koch, Manfred Lichtenstern, Rainer Otminghaus, Stefan Rusche USPTO Applicaton #: 20060035189 - Class: 431329000 (USPTO) Related Patent Categories: Combustion, Porous, Capillary, Particulate Or Sievelike Flame Holder, E.g., Radiant Surface Burner, Etc., Means Supplying Fuel For Passage Through The Flame Holding Structure, E.g., Radiant Surface Burner, Woven Screen Holds Flame The Patent Description & Claims data below is from USPTO Patent Application 20060035189. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention concerns a pore burner, especially for cooking appliances, with a housing having at least one inlet for gas/air mixture as fuel and/or at least one inlet for air and/or at least one inlet for gas and/or at least one outlet for air and/or gas and/or exhaust, as well as a cooking appliance containing at least one pore burner. [0002] The invention also concerns a pore burner system, as well as the use of pore burners and pore burner systems for heat and/or steam generation in cooking appliances and heating appliances, as well as finally these cooking and heating appliances. [0003] Pore burners are adequately known to one skilled in the art. These generally involve a burner with a stipulated combustion chamber volume with spatially connected cavities, through which or in which a defined flame zone is formed. Variants of known pore burners are described, for example, in U.S. Pat. No. 5,522,723, WO 95/01532, DE 199 39 951 A1 and DE 199 04 921 C2. For example, by means of pore burners the size of industrial and household steam and hot water vessels can be reduced, since the heat energy is released both by radiation and by heat conduction so that the convective fraction of heat transfer is reduced. For example, a housing vessel is described in DE 199 04 921 C2 that includes a pore burner suitable for heating of liquids, in addition to a radiation heat exchanger and a convection heat exchanger. A large water space vessel for generation of steam and/or hot water equipped with a pore burner is found in DE 198 04 267 A1. [0004] Especially with a compressed design and high surrounding temperatures, according to DE 199 39 951 A1, a frequently occurring flashback or deficient flame stability under these conditions, for example, caused by pressure fluctuations and partial vacuum, is avoided by the fact that the pore size of the pore burner increases in the direction of flow. In this case a critical Peclet number must be maintained for the pore size in one zone of the porous material, above which flame development occurs and below which it is suppressed. In a pore burner as described in DE 199 39 951 A1, reaction of the fuel/oxidizing agent mixture occurs within the porous matrix. This porous matrix is preferably produced by packings made of temperature-resistant ceramic spheres or saddles. Filler packings according to DE 199 39 951 A1 accordingly have at least two zones of packing material with different pore size. WO 95/01532 also deals with the problem of generating a stable flame at low temperature and low pollutant emission. It can be gathered from this document that the porosity of the pore burner is changed along the combustion chamber so that the pore size increases in the flow direction of the gas/air mixture from the inlet to the outlet. The employed porous material of the pore burner is again obtained by a packing, for example, in the form of loosely layered grains that are solidified in a sintering process. Finally, basic variants for pore burner technology are described in EP 0 840 061 A1 and in DE-OS 2 211 297. [0005] In the pore burners known from the prior art just described, the reactions between the combustion gas and the oxidizing agent underlying flame formation generally occur mostly or fully within the porous matrix. The hot reaction products therefore emerge from the burner cavities without flame formation. This procedure means that flames are cooled by the burner material, which helps to prevent further flame propagation as well as flashback. However, if the burner masses and burner loads are chosen very small, flashback can occur. For example, this is regularly the case, if high temperatures are present in compact heating appliances because of high surrounding temperatures even in the combustion chamber itself. Flashback can often be reached merely because of sufficient flame cooling. However, a large mass with high heat capacity and good thermal conductivity is required for this. Another common feature of the described pore burner devices is that optimized gas homogenization and gas distribution over the burner surface, as well as sufficient flame stability as well as shape stability of the surface are regularly achieved only by using several components of different geometries and/or materials. [0006] Appropriate flat flame burners based on pore burners have thus far been known only in the form of sintered discs, for example, as flat flame burners according to the so-called "Kaskan type" (according to W. E. Kaskan, "The dependence of flame temperature on mass burning velocity", 6.sup.th Symposium (International) on Combustion, The Williams & Wilkins Company, Baltimore, 1956, pages 134 to 143). [0007] A high degree of flame stability, the prevention of flashback and ensuring a uniform and constant flame front in a flat flame burner can regularly be obtained only with a porous material of high homogeneity, since otherwise a nonuniform flow profile generally results. A porous matrix with sufficiently high homogeneity, however, for the most part can only be implemented up to a stipulated component size. For larger dimensioned burner units, trade-offs with respect to uniform flow profile and therefore the accompanying properties must therefore regularly be tolerated. [0008] Ordinary fully premixing burners, especially flat burners and flat flame burners have thus far generally been made from sheet metal provided with holes and/or slit patterns, for example, as known for burners in cylindrical combustion chambers. For roughly homogeneous distribution of the gas mixture, additional sheets are also required with a coarser perforation, which are situated beneath the aforementioned sheet. Only with these design stipulations is it possible to regularly adjust the flow rates so that the corresponding gas/air mixture can be fed to each site in the appropriate amount. Known flat burners can also consist of a flexible wire mesh, perforated ceramic or wire fabric fastened to a support structure. However, for gas homogenization and gas distribution as well as flame stability and shape stability of the surface, the combination of several components of different geometries and materials is always required. [0009] Thus far, conventional heating systems with electrical or gas-driven heating elements have been generally resorted to for cooking appliances. Improving the efficiency of such heating systems would contribute to a saving of natural energy resources and a reduction in pollutant emissions. [0010] It would therefore be desirable to be able to resort to cooking appliances that have a very energy-efficient and low-pollutant and therefore ecologically efficient heating system, regardless of their size. [0011] Pore burners now available are often also characterized by the fact that, when fully premixed gas/air mixtures are used, sharply differing compositions as well as very variable volume flows can be implemented at low surface load. Especially when a homogeneous gas mixture is used, very low exhaust emissions are obtained. However, it is also observed in these pore burners that, when the burner is in the so-called cold state and the employed gas mixture only has a very low energy content, for example, with a very high air ratio and/or low heating value of the combustion gas, ignition by spark ignition often fails. Even when spark ignition occurs under the conditions just outlined, the energy introduced by the sparks is often only sufficient for local ignition of the gas mixture because of the desired stabilization of the reaction zone in the vicinity of the porous material. Liberated heat of reaction is absorbed by the surrounding material so that energy is removed from the gas mixture in the ignition zone and the chain branching reactions required for flame formation are suppressed. [0012] The above drawbacks can be more or less avoided by using a strong ignition coil with high ignition energy, high ignition frequency and/or by the simultaneous use of several ignition electrodes, but these expedients require additional space and result in additional costs so that the original advantage of pore burners is qualified again. The same is true, if permanent ignition by means of an auto-igniter or ignition burner are provided instead of ignition coils or ignition electrodes. [0013] The task underlying the present invention was therefore to make pore burners available for cooking appliances in particular and to modify the generic pore burners so that they are no longer burdened with the drawbacks of the generic pore burners and, in particular, have a high degree of flame stability and homogeneity, especially when designed as flat burners or flat flame burners. Accordingly, another underlying task of the present invention was to modify a generic cooking appliance so that it can be heated with high energy efficiency constantly and efficiently from an ecological standpoint with the lowest possible operating costs. Finally, another task underlying the present invention was to furnish a pore burner that guarantees improved ignition regardless of the energy content of the fuel mixture or the condition of the pore burner and helps to avoid delayed ignition. [0014] This task is solved according to the invention by pore burners with a housing having sintered metal powder and/or especially pressed metal wire mesh in the form of at least one dimensionally stable, porous molded element, on whose surface and/or in whose pore spaces reaction zones for flame development are present to form a flat burner. Accordingly, the entire molded element surface can also represent the outlet of the pore burner according to the invention, because of the porous structure and optionally also without a defined, large-surface outlet, for example, on one end of the housing. The pore burner according to the invention regularly has at least one inlet for a gas/air mixture as fuel. In addition or as an alternative, the pore burner or housing of the pore burner can have at least one additional inlet for air and/or an additional inlet for gas. For example, separately supplied air can be used as secondary air or also for the cooling of components of the pore burner. So-called fully premixing burner systems are used preferably, especially in cooking appliances. [0015] The pore burner according to the invention can be used, for example, for heat and/or steam generation in cooking appliances, especially gas-heated cooking appliances and also in heating appliances, like heating vessels or gas heating appliances, for example, in the household, especially when using cylindrical combustion chambers. [0016] The pore burners according to the invention, used in cooking appliances, for example, can represent partially premixing and especially fully premixing pore burners. In this case the burners can be a cylindrical tube preferably closed on one end. The application of gas outlet openings distributed on the periphery of the tube has also been shown to work. [0017] It can be prescribed according to the invention that the molded element be an essentially hollow element, especially a hollow cylinder. Appropriate hollow elements can also have arbitrary geometric shapes, for example, an ellipse, triangle, square, rectangle or any polygon in cross section. Appropriate hollow elements can also fully dispense with a defined, large-surface outlet opening and be designed, for example, as an ellipse, sphere or cylinder with only at least one defined opening for inlet of the gas/air mixture. By using hollow elements it is possible in a simple manner to create the largest possible surface for a uniform flame front. [0018] It has turned out to be very advantageous that pore burners are accessible, in which the molded elements include at least one mounting and/or fastening element, especially a groove, a tongue, a flange and/or a thread. Mounting and fastening elements can be integrated with the pore burners according to the invention already in the dimensionally stable molded elements, for example, from pressed metal wire mesh, so that the production costs of the pore burner according to the invention can be reduced and production for large series can be implemented much more easily. Naturally, the dimensionally stable molded element can also be simply welded on for fastening, for example, on the tube to supply the fuel mixture. This can be achieved in particularly simple fashion, if both the tube and the dimensionally stable molded element have corresponding cross-sections and the molded element is configured cylindrical and the tube has a circular cross-section. [0019] Particular advantages with respect to handling and minimization of components are obtained by the fact that the mounting and fastening device is incorporated directly in the porous molded element material of the pore burner. For example, a thread can be made in the pore element. Consequently, no additional mounting or fastening devices and no joining technique for coupling to the pore burner are required. [0020] According to another aspect of the invention, pore burners containing at least two molded elements lying one against the other in form-fit fashion at least in sections are present, which are connected to each other in areas, preferably to form a groove. By combining dimensionally stable molded elements in form-fit fashion, large-dimensioned pore burners can also be made without having to tolerate drawbacks with respect to uniform gas passage or uniform flow profile. Two or more assembled molded elements can enter into a stable connection via a bevel or groove. It is particularly advantageous if the adjacent molded elements can be joined or inserted one in the other flush and firmly, for example, via a groove/tongue structure, without requiring additional fastening devices. However, it can be necessary to permanently fasten coupled molded elements by means of spot welding. The molded elements are then preferably only joined together at very few adjacent sites and secured against loosening. A constant material density therefore remains even in the region of joints so that a uniform flow profile is guaranteed. To the extent that in very large molded elements of the aforementioned type high homogeneity of the porous material and therefore the most uniform possible flow profile cannot always be maintained, with the variant just described pore burners of larger size become accessible, which have an extremely uniform flow profile over their entire burner surface. In a preferred variant, the dimensionally stable molded elements, especially hollow elements, are designed in their end regions or head surfaces so that they correspond to each other in shape so that the front region of one molded element is inserted to fit in the rear region of another molded element, especially one of identical design. Pore burners can therefore be obtained that can be arbitrarily extended in length without having to tolerate the drawbacks with respect to homogeneity. [0021] It has therefore turned out to be particularly advantageous that the pore burner according to the invention can be converted as such to a stable shape or be present in a stable shape configured so that two or more such pore burners can be connected to each other. For example, adjacent pore burner segments to be connected to each other can be configured on their sections being coupled so that they can be inserted one into the other without requiring additional fastening devices. According to one variant, for example, the open end section of one pore burner segment can be provided with at least one groove that can be connected to fit with an end section of an adjacent pore burner segment provided with at least one tongue. The shape stability of the employed pore burners is then already achieved during production by sintering of metal powder and pressing of metal wire mesh without requiring additional mechanical support elements. Naturally it is possible to couple not only two pore burners via groove/tongue elements corresponding to each other, but three or more pore burners or pore burner segments can be coupled to each other by means of the aforementioned joining technique to form a uniform pore burner. The end piece of this combined pore burner then preferably has a closure, for example, in the form of porous burner material so that the pore burner has no outlet opening. A one-piece pore burner, like a pore burner segment, can be configured both cylindrically and conically. The same applies to a pore burner formed from several pore burner segments. The pore burner then preferably tapers in the direction toward the end. [0022] It can be prescribed according to the invention that the material densities of at least two adjacent molded elements essentially correspond. [0023] It has also turned out in this context to be a preferred variant in which the material density in the region of the joining site of two joined molded elements corresponds especially to the material density of at least one of these molded elements. [0024] Another embodiment according to the invention is characterized by the fact that the surface of the molded element has at least one irregularity, especially at least one indentation and/or elevation that deviates from the base surface of the molded element. Continue reading... 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