WO2008142444A2

WO2008142444A2 - Gas fire ember element

Info

Publication number: WO2008142444A2
Application number: PCT/GB2008/050356
Authority: WO
Inventors: Robert Smith
Original assignee: Keramos Technology Limited
Priority date: 2007-05-18
Filing date: 2008-05-16
Publication date: 2008-11-27
Also published as: GB2446667A; EP2156099A2; GB0709572D0; WO2008142444A3; GB2446667B; US20100151398A1

Abstract

A gas fire ember element comprises a bundle of wire of a heat and oxidation resistant metal (Fecralloy® or Nichrome®, for example). The density of wire in the bundle is so loose (between 0.01 and 0.1% by total volume of the bundle) that burning gas percolates through it. The wire has a filament cross section of between 500 μm2 and 8,000 μm2. so that it quickly glows and stops glowing as it is heated or not heated by flickering gas flame. The bundle can be hollow, said wire being confined to a surface region of the bundle having a thickness between 50 μm and 5,000 μm. Either the density of wire in the surface region is between 0.01% and 0.1% by total volume of the surface region, or a projection of the wire in the surface region occupies between 0.01% and 0.1% by total area of said projection. The wire in the surface region may be a mesh.

Description

Gas fire ember element

This invention relates to domestic gas fires, typically using natural gas, liquid propane gas (LPG) or alcohol based gel (gel fires), and biofuels as their fuel source. Many of these fires are constructed with one or more burners on the lower face of a chamber having a window through which the fire can be viewed. These burners may be surface combustion burners or burners which have loose material piled on top of them to create a porous media bed which acts to distribute the gas more evenly before it is combusted.

In many of these fires, natural-looking fuel components, such as pebbles, logs, driftwood, coal, fir cones, etc are situated on top of the burner to create the impression of a real fire.

BACKGROUND

In some gas fires ie Decorative Gas fires (DGF), it is common practice to burn the gas in between a ceramic under bed and ceramic shapes placed on top. This process causes the temperature of the ceramics to rise until they start to radiate heat into the room. The products of combustion pass on into a flue for venting to atmosphere. It is possible to shape the ceramics so that they have the appearance of logs or coals, and when they glow red-hot, this is an effective appearance. In this type of fire it is both easy and common to create a glowing fire which imitates a "real fire".

In other fires which are more landscape in nature and can be either open or closed fronted, it can be more difficult to create a glowing effect. In this type of fire, the emphasis is more on creating large yellow flames, more associated with a wood burning fire than on creating glow. Generally, there is no ceramic under bed and therefore the amount of glow created is significantly reduced. In addition the time taken to achieve any glow depends on the construction of the fire and can take 10-30 minutes. In order to improve the glow of these fires various lightweight low thermal mass materials have been used, which are scattered on top of the burner/porous media. The intention is that, due to their small thermal mass, they will start to glow when the gas flames hit them, creating a glowing ember effect. These embers are typically made from rock wool, vermiculite, pumice, ceramic fibres and glass fibres. US-A-68051 15 suggests a synthetic ember in the form of a ceramic wool coated with an oxidation catalyst such as platinum. Sales literature relevant to the system claims the following list of advantages:

• Brighter glowing effect • More complete combustion of fuel

• Reduced soot formation

• Greater heat output

• No refractory ceramic fibre

• No deterioration when burned

The "catalytic ember" comprises a saffil ceramic fibre structure which is coated in a catalyst in order to promote clean combustion. These embers are situated in the burning gas flame and glow when the flame hits them.

Schott AG produce a silicon carbide fibre burner which is commercially available under the trade name Ceramat®. The silicone carbide fibres used in the product have also been used as embers for use on gas fires.

All the embers mentioned above are based on ceramic materials, many of them on fibres of one sort or another. Ceramic fibres are generally quite short in length from a few mm up to 20mm. Generally, because it is a brittle ceramic, as the fibre gets bigger it will tend to break under deformation to form a shorter fibre. In addition the fibres can be regarded as being straight fibres and cannot be shaped or bent. All embers formed using ceramic fibres tend to form clumps of fibres. These clumps, although lightweight, are effectively solid to the gas flame which travels around the outside of the clump and heats the fibres on the outer surface of the clump.

In US-A-6095794 there is disclosed the use of metallic or ceramic filaments which are either cast into or wrapped around gas fire logs. When the gas flame hits these filaments they are intended to glow (incandesce) creating a glowing effect. More specifically these filaments are chosen from:

• stainless steel

• steel wool

• platinum wire • rock wool, and

• spun glass

Furthermore the fibre has a diameter in the range 0.0002 inches (5 microns) to 0.020 inches (500 microns). The present invention seeks to provide an alternative form of glowing ember for a gas fire. The present invention exploits the properties of a number of metals that have appropriate characteristics as described further below.

One such metal is Fecralloy®, whose nominal composition is as follows:

Cr !22%

Al ^5 3%

Ϋ!^'.^"'.^".^'.^".^'.^".^'.^".^'.^".^"'.^"'.7. lAddition

Zr i Addition

Fe Balance

Fecralloy® is a ferritic, stainless steel with aluminium and other additives. It is available as wire, bar and strip. It is used mainly for electrical heating elements in both industrial and domestic applications. Industrial applications vary from small laboratory kilns to heavy-duty heat-treatment furnaces under all types of atmospheres. Fecralloy® is a versatile alloy and is suitable for use over a wide range of temperatures up to about 1300⁰C. The yttrium/zirconium additive is key to its longer high temperature life, having greater oxidation resistance and form stability over other resistance alloys. A similar alternative is Alchrome® 875.

Another such metal is Nichrome®, or Tophet A/30®, which are non-magnetic alloys of nickel and chromium, generally used as resistance wire. A common alloy is 80% nickel and 20% chromium, but there are many others to accommodate various applications or lower cost. The alloy is corrosion resistant, and has a high melting point of about 1400⁰C. Due to its relatively high resistivity and resistance to oxidation at high temperatures, it is widely used in heating elements, such as in hair dryers, electric ovens and toasters.

These metals have the characteristics set out in Table 1 below:

Table 1 (Source: http://www. goodfellow.com/csp/active/gfhome. csp?Language=E)

Thus both alloys have somewhat similar characteristics. The present invention is not restricted to Fecralloy® or Nichrome®, however, or any particular alloy, but only to metals of a similar characteristic in terms of heat and oxidation resistance, and such similar metals are hereinafter termed as "heat and oxidation resistant" metals. A metal that is "heat and oxidation resistant" is therefore defined herein as a metal which does not melt below 1200⁰C and, when in wire form of about 50 microns diameter, oxidises no more than 20% more quickly in a methane burning environment than the average of corresponding wire forms of typical Fecralloy® and Nichrome® alloys.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with the present invention there is provided an ember element for use in domestic gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the density of wire in the bundle being between 0.005% and 0.75% by total volume of the bundle and the wire having a filament cross section of between 500 μm² and 10,000 μm². When said cross-section is round, said cross section is preferably between 1000 μm² and 8000 μm² that is to say, between about 35 μm and 100 μm in diameter. However, larger cross sectional areas may be accommodated while still achieving a low thermal mass where a thin, ribbon-type cross section is employed, for example with dimensions in the region 50 μm by 200 μm, or 40 μm by 250 μm, for example. When inserted on a gas fire, for example between artificial logs, the burning gas mixture passes between the fibres of the bundle as well as swirling around the bundle. The fibres in the burning zone, because they are of low thermal capacity, instantly incandesce. However, as the flame position of the fire constantly changes, the fibres isolated momentarily from the flame cool and cease incandescing. The bundle gives the overall effect of being solid because most of the fibres of the bundle are heated and glow. The overall effect is to give a natural and cheerful appearance to the fire, particularly if the bundles are supplemented by artificial logs or coals, with the bundles of the invention flickering incandescence in a natural way similar to natural wood embers of a wood fire.

Preferably, said metal is an alloy of iron, chromium, aluminium and yttrium and/or zirconium. Preferably, said components are in the proportions:

Cr 115-25

AΪ.^".^'.^".^'.^".^'.^".^"'.^"'.^"'.^"'.^".^'.^' 13-10

Y !θ.1 to 1

Zr io to 1

Fe Balance

Alternatively, said metal may be an alloy of nickel and chromium. Preferably, there is between 55% and 85% nickel and 15% and 45% chromium.

Preferably, said wire has a cross-section of between 2000 μm² and 5000 μm². It may have a cross section of between 3500 μm² and 4000 μm². Said cross section may be round rectangular, square or any other shape.

Said density is preferably between 0.01 % to 0.4% by volume. It may be between 0.03% and 0.3% by volume. Said wire may be a single wire tangled into a ball. Preferably, said bundle is a plurality of wires of length between 30 mm and 300 mm.

The looseness of the bundle is significant in allowing the gases of the fire to pass through and burn inside the bundle, whereby more of the wires incandesce giving a solid appearance of the bundle. Preferably, said bundle has a volume between 0.5 cm³ and 8000 cm³. A bundle as large 8000 cm³ would be used alone as the bed of a fire, sat on a burner. The bundle may be between 1 cm³ and 500 cm³ or even between 5 cm³ and 50 cm³.

Indeed, it should be made clear that in defining the invention as comprising a "bundle of wire" this necessarily implies that the wire has the requisite ductility to be formed into a bundle by, for example, crushing and folding the wire in and around itself multiple times in order to create a bundle. Brittle material cannot, by definition, be formed into such a bundle since the wire of such material will break during such a forming process and not form self supporting, loosely bound "bundle".

In another aspect of the present invention, there is provided an ember element for use in gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the wire having a filament cross section of between 500 μm² and 10,000 μm², wherein said bundle is hollow, at least 70% of said wire being confined to a surface region of the bundle having a thickness between 50 μm and 5,000 μm wherein the density of wire in the surface region is between 0.005% and 0.75% by total volume of the surface region. Where a single filament of wire is employed, approximately 100% of the wire may be within said surface region, but where multi-filaments are employed, many ends of the filaments may extend out of said surface region.

Put another way, this aspect of the present invention also provides an ember element for use in gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the wire having a filament cross section of between 500 μm² and 10,000 μm², wherein said bundle is hollow, at least 70% of said wire being confined to a surface region of the bundle having a thickness between 50 μm and 5,000 μm, wherein a projection of the wire in the surface region occupies between 0.005% and 0.75% by total area of said projection. Both ways of considering the bundle of this aspect may apply.

Whichever way this aspect is represented, (and it depends on the thickness of the surface region which way is simplest to measure), the surface region is sufficiently porous to permit burning gases in the fire to penetrate the bundle and burn within it, as well as to pass through it. The surface region may be a self-supporting mesh or felt. Said bundle may comprise only said wire. However, it may also be formed on a frame that gives rigidity to the bundle. The frame may be constructed from a mesh or similar structure which can be used to support the bundle.

Preferably, said bundle is given a geometric shape, which may be tetrahedral, for example.

The focus of the present invention is the use of special metal fibres to create extremely open structures to act as glowing embers and glowing objects for use on gas fires. Using the ductility and longer fibre length that can be achieved with metal fibres of the appropriate constituency, very open structures of any size can be constructed by manipulating the fibres using, for example, one's fingers. When gas passes through these structures an aesthetically pleasing glowing/shimmering effect can be achieved which resembles glowing embers. The appearance is very different to that which can be achieved with ceramic fibre embers.

In a further aspect of the present invention, the fibres are preferably coated with an oxidation catalyst material, such as platinum. The benefits are two fold, the first is that a continuous coating of platinum or other oxidation metal could extend the life of the metal fibres and second, the fibres could assist in the combustion process on a fire so that the risk of harmful gases, such as CO escaping the fire is minimised. This could be useful on all gas fires but particularly on fires which are called flue-less. Flue-less fires vent their products of combustion into a room rather than a chimney. It is therefore imperative that the products of combustion from these fires are "clean". This concept would also apply to bio ethanol, gel and bio fuel fires, as well as gas fires.

An embodiment of the invention is further described hereinafter, with reference to the following non-limiting Examples.

Example 1

Strip wire was employed having an alloy composition: Al 5.0%, C 0.02%, Cr 22.0%, Mn 0.2%, Si 0.3%, Y 0.1 %, Zr 0.1 %, Fe Balance. The wire was of square cross section and had dimensions of 50 μm x 50 μm, giving a cross-sectional area of about 2500 μm². The strip was supplied as loose tow of average fibre length 50 mm, and was formed into bundles having a volume of about 100 cm³ of irregular shape. The weight of each bundle was about 0.4 g so that the percentage by volume (density of alloy is 7.22 g cm³) of wire in the bundle was about 0.05% and mixed with artificial logs. These were placed on a Ceramat® ceramic fibre mat burner sold by Schott AG of dimensions 440 mm x 100 mm and the burner was supplied with 7 kw of natural gas. The gas was ignited and flames passed through and around the bundles heating up individual filaments erratically so that they oscillated between incandescence and not glowing, the effect being pleasing and natural.

After over 400 hours of burning, the majority of the fibres where still present, indicating very little loss of structure and effectiveness. Some oxidation had taken place which is to be expected. The fibres where still glowing effectively and creating the desired effect. During the first 20-3Oh hours of cycling, the fibres started to create an oxide layer on the surface of the fibre causing it to lose its metallic sheen. In addition, the structure began to tighten up (shrink in volume) as the fibres started to curl at their ends. After the initial curling of the ends, however, this phenomenon ceased. On some of these ends, after a few hundred hours, some larger scale oxidation could be seen for a mm or so. This deteriorated no further with time.

Example 2

A Fecralloy® continuous wire of diameter 50μm and cross sectional area of 1966μm² was wound into a structure of approx 150 cm³ of irregular shape. The weight of the bundle was 0.32g, so that the percentage by volume (density of alloy is 7.22 g cm^'3) of wire in the bundle was about 0.03% and mixed with artificial logs. Again this was tested on the same burner as described in Example 1 for over 400 hours. After 20 hrs to 30 hrs the material again formed an oxide coating causing it to lose its metallic sheen. Very little further noticeable oxidation occurred beyond the first 20 hrs to 30 hrs, although it should be expected that further oxidation did occur. After 400 hours the structure was still radiating and flickering as the gas flames hit it. As in Example 1 the structure had tightened (shrunk) a little from its original size as the ends of the fibre tended to curl up.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1 . An ember element for use in domestic gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the density of wire in the bundle being between 0.005% and 0.5% by total volume of the bundle and the wire having a filament cross section of between 500 μm² and 10,000 μm². .

2. An ember element for use in domestic gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the wire having a filament cross section of between 500 μm² and 10,000 μm², wherein said bundle is hollow, at least 70% of said wire being confined to a surface region of the bundle having a thickness between 50 μm and 5,000 μm wherein the density of wire in the surface region is between 0.005% and 0.75% by total volume of the surface region.

3. An ember element for use in domestic gas fires comprising a bundle of wire of a heat and oxidation resistant metal, the wire having a filament cross section of between 500 μm² and 10,000 μm², wherein said bundle is hollow, at least 70% of said wire being confined to a surface region of the bundle having a thickness between 50 μm and 5,000 μm, wherein a projection of the wire in the surface region occupies between 0.005% and 0.75% by total area of said projection.

4. An ember element as claimed in claim 1 , claim 2 or claim 3, in which said bundle comprises only said wire.

5. An ember element as claimed in claim 1 , claim 2 or claim 3, in which said bundle is formed on a frame that gives rigidity to the bundle.

6. An ember element as claimed in claim 5, in which said frame is constructed from a mesh to support the bundle.

7. An ember element as claimed in any preceding claim, in which said metal is an alloy of iron, chromium, aluminium and yttrium and/or zirconium.

8. An ember element as claimed in claim 7, in which the components of said alloy are in the proportions: Cr 115-25

Al 13-10

Y !0 1 to 1

Zr Io to 1

Fe Balance

9. An ember element as claimed in any claim between and including claim 1 and claim 6, in which said metal is an alloy of nickel and chromium.

10. An ember element as claimed in claim 9, in which said alloy has between

55% and 85% of nickel and 15% and 45% of chromium.

1 1 . An ember element as claimed in any preceding claim, in which said wire has a cross-section of between 2000 μm² and 5000 μm².

12. An ember element as claimed in claim 1 1 , in which said wire has a cross section of between 3500 μm² and 4000 μm².

13. An ember element as claimed in any preceding claim, in which said wire has a round cross section and a diameter between 50 μm and 80 μm.

14. An ember element as claimed in any preceding claim, in which said density is between 0.01 % to 0.4% and preferably 0.03% and 0.3% by volume.

15. An ember element as claimed in any preceding claim, in which said wire is a single wire filament tangled into a ball.

16. An ember element as claimed in any claim between and including claim 1 and claim 14, in which said bundle is a plurality of wire filaments of lengths between 30 mm and 300 mm.

17. An ember element as claimed in any preceding claim, in which said bundle has a volume between 0.5 cm³ and 8000 cm³, preferably between 1 cm³ and 500 cm³ or even between 5 cm³ and 50 cm³.

18. An ember element as claimed in any preceding claim, in which said bundle is given a regular geometric shape.

19. An ember element as claimed in claim 18, in which said shape is tetrahedral.

20. An ember element as claimed in any preceding claim, in which the wire has an oxidation catalyst coating.

21 . An ember element as claimed in claim 20, in which the catalyst is platinum.

22. An ember element for a gas fire, substantially as hereinbefore described in the Examples.