Metal burner membrane
The invention relates to a gas burner comprising a metal burner membrane having a base section (201), a dosing section (203) and a transition region in between (202). The shape of the membrane is such that the smallest radius of curvature of the transition zone is smaller than the smallest radius of curvature of the base section. Furthermore the burner membrane uninterruptedly flows over from the base section through the transition region into the closing section. The advantages of such a gas bunner am amongst others a large dynamic power range, an improvadflame front and a low production cost.
The present invention relates to a gas burner comprising a metal burner membrane.
BACKGROUND OF THE INVENTIONPrior art gas burners with different shapes and different burner membranes have been described e.g. in WO 02/44618 A1 and WO 01/79756 A1.
The first drawback of these burners is that for a given dimension, they do not allow for a large range in output power at low power, i.e. if the gasflow is low, there is a risk for flame extinguishment, and at high powers, i.e. if the gasflow is high, there is a risk that the flame blows off. This results in the need of a range of burners that differ only slightly in dimensions (e.g. in their height) adapted to specific power ratings: a second drawback.
A third drawback of these burners is that different parts have to be punched, formed and welded together which leads to expensive burners. The welding seams themselves are weak points in the burner, because they are most susceptible to failure in the heating and cooling cycles that occur during the use of a gas burner. Hence, the weldings reduce the lifetime of the product, which constitutes a fourth drawback.
SUMMARY OF THE INVENTIONIt is a general object of the present invention to eliminate the drawbacks of the prior art burners. It is a first object of the present invention to provide a burner with an increased range in output power. It is a second object of the present invention to provide a burner with an increased lifetime. It is a third object of the present invention to provide a burner with a reduced production cost. It is a fourth object of the present invention to provide a burner with an improved flame distribution.
A gas burner according the present invention comprises a metal burner membrane. Geometrically this burner membrane comprises a base section end a closing section. The base section has a smallest radius of curvature Rbase. What is meant with “smallest radius of curvature” will be explained further on. The base section is connected uninterruptedly to the dosing section through a transition region: the transition region burner membrane comprises the same elements as the base and closing section. The transition region has a smallest radius of curvature rtransition being larger than zero and being smaller or equal to Rbase.: 0<rtransition≦Rbase. The case in which the base section is a plane, hence Rbase is infinitely large, is not excluded. More preferred is: 0.02×Rbase≦rtransition≦0.7×Rbase. Even more preferred is: 0.02×Rbase≦rtransition≦0.35×Rbase There is no limitation on the smallest radius of curvature of the closing section.
The notion of “smallest radius of curvature of a section” will now be explained:
Geometrically, at each point of the burner membrane, many radii of curvature can be defined: each of them is associated with a particular cut according a plane containing the normal fine at the point under consideration. The intersection of this plane with the burner membrane results in a trajectory. The radius of curvature is the radius of the circle in the intersecting plane, which osculates to second order the trajectory at the point under consideration. Out of all these possible planes, containing the normal line through the point under consideration, with associated trajectories and radii of curvature, the smallest radius is selected. As each point of a section has a smallest radius, the smallest of all smallest radii of the section can be defined to be the smallest radius of curvature of this section. As the radius of curvature is always a positive number, the smallest radius of curvature that may be found is zero. The same definition applies mutatis mutandis to each of the three parts of the burner membrane: the base section, the transition region and the closing section. For each of them a smallest radius of curvature can thus be found. For example: for a base section having a tubular shape with a rounded polygonal cross section this smallest radius of curvature is equal to the radius of the rounding in the edges. Likewise for a cylinder the smallest radius of curvature is equal to half its diameter.
As this geometrical construction must be reduced to practice, it should be clear that the invention relates to the embodiment of this geometrical construction, which of course is subject to engineering tolerances. Hence, it should be clear that the invention is not delimited to the abstract geometrical shape as such but to the shape of the actual burner membrane. This shape can be easily measured by means of an appropriate computerised 3-D measuring bench that allows for immediate determination of the geometrical features in general and the radii of curvature in particular.
The shape of the burner membrane influences the functioning of the burner in the following way: those regions of the burner membrane that have a smaller radius of curvature yield a lower gas speed outside the membrane compared to the regions with a higher radius of curvature. A lower gas speed leads to a lower flame front. So the speed of the gas outside the membrane, and subsequently the flame front, can be advantageously modulated over the surface by changing the radius of curvature.
This yields, amongst others, the following advantages:
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- Due to the area of reduced gas speed, the flame is less prone to blow-off.
- Due to the different gas speeds over the burner membrane, a large variation in gas flow rate can be accommodated with the same burner, thus eliminating the need to have different types of burners on stock.
- The area with a smaller radius of curvature, due to the slower gas flow, lends itself advantageously for the ignition of the gas.
According to the present invention the transition from base section to closing section is realised without interruption. With uninterrupted is meant that the membrane forming the different sections (base, transition and dosing) are not connected by any means that would lead to a seam of the membrane with a blocked gas flow at the burner surface as a result. I.e. the three sections: base, transition and dosing must be gas permeable. The fact that the burner membrane is free of interruption ensures a dosed flame front throughout the whole burner membrane. The three sections (base, transition and dosing) can be realised uninterruptedly in one of the following ways:
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- by using a fabric of braided or knitted or woven stainless steel fibres. Such fabric can be woven or braided or knitted in such a way that it fulfils the geometrical requirements of the invention;
- by deep drawing or stamping a plate into a shape which fulfils the geometrical requirements of the invention. Small holes must be drilled into the plate in the three sections (base, transition and dosing) in order to achieve the desired gas flow;
- by deep drawing or stamping of an already foraminated plate thus eliminating the need for drilling holes into the plate afterwards;
- by deep drawing or stamping a wire mesh where the wires have a suitable thickness and formability
Combinations of the above methods are possible, e.g.
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- a fabric of braided or knitted or woven stainless steel fibres which is stretched over a deep drawn or stamped plate in which holes are drilled;
- a fabric of braided or knitted or woven stainless steel fibres which is stretched over a deep drawn or stamped foraminated plate;
- a fabric of braided or knitted or woven stainless steel fibres that is supported by a deep drawn or stamped wire mesh. The wire mesh can also be integrated into the stainless steel fibre fabric i.e. it can be interbraided or interknitted or interwoven with the stainless steel fibres.
It is clear that the above enumeration is non-exhaustive and even different possibilities according the claims of this invention are possible.
By realising the burner membrane in this way, one or more of the following advantages, amongst others, can be achieved:
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- a reduction in production cost is obtained by elimination of the welding seams and the assembly of the different parts of the prior art burners, by the use of a deep drawn or stamped plate or foraminated plate;
- an improved lifetime of the gas burner is obtained due to the elimination of the welding seams;
- the use of stainless steel fibres on top of the foraminated plate isolates the flame from the plate and results in a lower thermal stress on the foraminated plate and hence an improved lifetime;
- the use of stainless steel fibre results in a further random scattering of the gas flow upon exit of the feed through holes which leads to an improved flame distribution.
- The uninterrupted burner membrane ensures a flame front in every section of the burner and in particular in the transition region. This improves greatly the stability of the flame.
The invention will now be described into more detail with reference to the accompanying drawings wherein
FIGS. 4(b) and 4(c) show the section through planes MA and BB of
The basic geometrical features of the invention are illustrated in
It will be clear from this embodiment that the crossover from base section to transition region need not be smooth (with ‘smooth’ is meant continuous first order derivatives) but must be uninterrupted (zero order continuity).
Knitted metal fibre fabric allows for a high elongation thus leading to a continuous transition from the base section to the dosing section. The arrows 307, 308 and 309 indicate the velocity of the gas as it flows out of the membrane. The lower gas velocity in the transition region 202 is represented with a shorter vector 308, while the gas velocity at the base section 201 and the dosing section 203 is higher which is represented by a longer vector 309 resp. 307. Also the lower flame front 310—where the gas ignites—and the outer flame front 313—where the top of the flame is—is indicated for each of the sections.
With this preferred embodiment, it was possible to achieve a maximum heating power of 40 kW/dm2. A minimum heating power of 1 kW/dm2 was necessary in order to got a stable flame. This yields an overall dynamic range of 1:40.
In
Note that in this embodiment, the dosing section has vanished into a single line 408.
In a third preferred embodiment illustrated in
An alternative to the third embodiment is depicted in
In a fourth preferred embodiment illustrated in
An alternative to the fourth embodiment is depicted in
Claims
1. A gas burner, said burner comprising a metal burner membrane, said membrane comprising a base section having a smallest radius of curvature being Rbase and a closing section, characterised in that said membrane being uninterrupted comprises a transition region for connecting said base section to said closing section, said transition region having a smallest radius of curvature rtransition being larger than zero and being smaller or equal to said Rbase.
2. A gas burner as in claim 1, wherein said membrane comprises a fabric comprising stainless steel fibres.
3. A gas burner as in claim 2, wherein said stainless steel fibres are arranged essentially parallel into bundles.
4. A gas burner as in claim 3, wherein said bundles are knitted or braided or woven.
5. A gas burner as in claim 1, wherein said membrane comprises a foraminated plate or sheet.
6. A gas burner as in claim 1, wherein said burner membrane comprises a foraminated plate, said transition region is at the outside disposed with stainless steel fibres.
7. A gas burner as in claim 6, wherein said base section and said closing section are at least partially disposed with stainless steel fibres.
8. A gas burner as in claim 6, wherein said stainless steel fibres are arranged essentially parallel into bundles.
9. A gas burner as in claim 8, wherein said bundles are knitted or braided or woven.
10. A gas burner as in claim 1, wherein said base section has a frustoconical shape.
11. A gas burner as in claim 1, wherein said base section has a cylindrical shape.
12. A gas burner as in claim 10 wherein said transition region is part of a torus surface delimited by two planes perpendicular to the axis of symmetry of said torus.
13. A gas burner as in claim 1, wherein said base section has a polygonal cross section, the corners of said cross section being rounded.
14. A gas burner as in claim 1, wherein said base section has a rectangular cross section, the corners of said cross section being rounded.
15. A gas burner as in claim 1, wherein said base section is a truncated pyramid, said pyramid having rounded edges
Type: Application
Filed: Feb 25, 2004
Publication Date: Nov 9, 2006
Inventors: Dinand Lamberts (Assen), Alfred Van Goor (Assen), Geert Folkers (Bruchterveld)
Application Number: 10/553,405
International Classification: F23D 14/46 (20060101);