Abstract
A burner module that can be used in combusting an air/fluid fuel flow is described. The burner module may be incorporated in an appliance. The burner module comprises a burner face comprising catalytic material for combusting the air/fluid fuel flow and a perforated screen having a plurality of micro-perforations where the perforated screen is positioned upline to the burner face to increase combustion; an integrated gas burner for connection to a pressurised fluid fuel flow where the integrated gas burner comprises a burner module and a gas train. The gas train comprises (a) an ejector for entraining air with the fluid fuel flow; and (b) a diffusor for converting the air/fluid fuel flow kinetic energy into pressure and for performing flow expansion.
Claims
1. A burner module for use in combusting an air/fluid fuel flow wherein the burner module comprises a burner face comprising catalytic material for combusting the air/fluid fuel flow and a perforated screen having a plurality of micro-perforations and the perforated screen is positioned upline to the burner face to increase combustion, wherein the perforated screen is formed from a material having a thermal conductivity adapted to reduce thermal bridging from the burner face and reflect incident heat radiation in a direction substantially perpendicular to the burner face.
2. A burner module as defined in claim 1 wherein the module is configured to cooperate with a gas train to deliver air/fluid fuel from at least one ejector.
3. A burner module as defined in claim 2 wherein the at least one ejector is closely coupled to the burner face via the gas train such that minimum axial space is required in use and positioned to provide a radial diffusion and mixture distribution to the burner face.
4. A burner module as defined in claim 3 wherein the burner is a radiant flameless burner configured to permit a minimal clearance between the burner face and a culinary vessel while ensuring maximum combustion of fuel during use.
5. A burner module as defined in claim 3 comprising a step positioned at an inlet to a radial diffuser configured to promote formation of a stable toroidal vortex to improve diffuser efficiency.
6. A burner module as defined in any one of the preceding claims which comprises at least two perforated screens upline of the burner face wherein the perforated screens comprise a throttling perforated screen and a homogenisation perforated screen wherein the perforations on the throttling perforated screen are selected to provide a predetermined degree of aeration of the air/fuel mixture; and the perforations on the throttling perforated screen are arranged to provide a flattened velocity profile of the air/fluid fuel flow perpendicular to the throttling perforated screen to provide uniform combustion.
7. A burner module as defined in claim 6 wherein the homogenisation perforated screen is positioned upline and adjacent to the burner face and the throttling perforated screen is positioned upline of the homogenisation perforated screen
8. A burner module as defined in claim 6 or claim 7 which is a radiant burner module comprising two perforated screens wherein the throttling perforated screen is configured to provide a fully-aerated air/fuel mixture.
9. A burner module as defined in any one of claims 6 to 8 wherein the degree of aeration of the air/fuel mixture provided by the throttling perforated screen is 12-24 parts of air entrained with each part of fuel gas by weight.
10. A burner module as defined in any one of the preceding claims wherein the plurality of perforations of the one or more perforated screens are shaped to increase spill resistance and/or noise attenuation.
11. A burner module as defined in claim 10 wherein the perforations comprise an area of at least 15% of the perforated screen surface area.
12. A burner module as defined in any one of the preceding claims wherein the perforations have a cusp.
13. A burner module as defined in any one of the preceding claims wherein the perforated screen comprises a foil material or a metallic foil.
14. A burner module as defined in any one of the preceding claims wherein the perforated screen is polished to reduce heat transfer to the gas train and consequent generation of temperatures at a surface confining the flow of air/fuel mixture which are high enough to initiate light-back.
15. A burner module as defined in any one of the preceding claims wherein the perforated screen is shaped to provide one or more supports for the burner face.
16. A burner module as defined in claim 15 wherein the one or more perforated screen supports have a pointed shape to minimise thermal bridging.
17. A burner module as defined in any one of the preceding claims wherein the perforated screen has one or more ribs to provide axial stiffness.
18. A burner module as defined in any one of the preceding claims which comprises a crimp ring for attaching the burner module to a gas train.
19. A burner module as defined in claim 18 wherein the crimp ring is dimensioned to provide a radial space to allow the burner module to thermally expand and contract freely in use.
20. A burner module as defined in claim 18 wherein the crimp ring comprises an axial spacer for providing axial separation between the burner face and perforated screen wherein the axial spacer has an axial length which is dimensioned to reduce risk of light back.
21. A burner module as hereinbefore described and/or illustrated with reference to the Figures of the accompanying drawings.
22. An integrated gas burner for connection to a pressurised fluid fuel flow wherein the integrated gas burner comprises a burner module as defined in any one of claims 1 to 21 and the gas train wherein the gas train comprises: a. an ejector for entraining air with the fluid fuel flow; and b. a diffusor for converting the air/fluid fuel flow kinetic energy into pressure and for performing flow expansion.
23. An integrated burner as defined in claim 20 wherein the integrated burner is a compact integrated burner having a folded gas train.
24. An integrated burner as defined in claim 23 wherein the gas train comprises a co-annular folded gas train.
25. An integrated burner as defined in claim 23 wherein the folded gas train has a reduced axial length.
26. An integrated burner as defined in any one of claims 22 to 25 which comprises an additional perforated screen having a plurality of micro-perforations; preferably the perforated screen is as defined in any one of claims 2 to 17.
27. An integrated burner substantially as hereinbefore described and/or illustrated with reference to one or more of the Figures of the accompanying drawings.
28. An appliance comprising an integrated burner as defined in any one of claims 22 to 27; preferably the appliance is: a) a chafing dish heater comprising two nesting metal vessels and one or more integrated burner; b) a space heater comprising a reflective surface, one or more integrated burners and a pressurised fuel source; preferably the space heater additionally comprises a support, an electrical igniter and/or a handle for positioning of the reflective surface; or c) a stove comprising an integrated burner, a pressurised fuel supply, a pot support, a pot and a burner shield; preferably the pot is shaped such that the other components can fit inside it for storage.
29. An appliance substantially as hereinbefore described and/or illustrated with reference to one or more of the Figures of the accompanying drawings.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] The invention will now be illustrated with reference to the following Figures shown in the accompanying drawings which are not intended to limit the scope of the invention claimed:
[0057] FIG. 1A shows a schematic plan view of a first embodiment of a perforated screen according to the invention; FIG. 1B shows a schematic plan view of a second embodiment of a perforated screen according to the invention; and FIG. 1C shows a schematic plan view of a third embodiment of a perforated screen according to the invention;
[0058] FIG. 2 shows a schematic partial cross-sectional view of a perforation of a perforated screen according to the first, second or third embodiment of a perforated screen according to the invention;
[0059] FIG. 3A shows a schematic cross sectional view of a first embodiment of an integrated burner according to the present invention; and FIG. 3B shows a schematic cross sectional view of a burner module according to the invention as part of the integrated burner of the first embodiment of the invention;
[0060] FIG. 4A shows a computational fluid dynamics visualisation of gas density in moles per cubic metre of the first embodiment of an integrated burner according to the invention in use; FIG. 4B shows a computational fluid dynamics visualisation of gas flow in metres per second of the first embodiment of an integrated burner according to the invention in use; FIG. 4C shows a computational fluid dynamics visualisation of gas temperature in degrees Centigrade in the first embodiment of an integrated burner according to the invention in use; and FIG. 4D shows a computational fluid dynamics visualisation showing dump diffuser diffusion effect;
[0061] FIG. 5 shows a schematic cross sectional view of a second embodiment of an integrated burner according to the present invention;
[0062] FIG. 6 shows a schematic cross sectional view of a third embodiment of an integrated burner according to the present invention;
[0063] FIG. 7A shows a computational fluid dynamics visualisation of gas concentration in moles per cubic metre through the third embodiment of an integrated burner according to the invention in use where a mixing shock is discernible close to the downline end of the radial transition duct after which air and fuel are no longer separate phases but are well mixed; and FIG. 7B shows a computational fluid dynamics visualisation of fluid velocity in metres per second of air and vaporous fuel streamlines of the third embodiment of an integrated burner according to the invention in use, indicating smooth air entrainment and compression through the ejector without flow separation followed by discharge into the annular plenum;
[0064] FIG. 8 shows a schematic cross sectional view of a fourth embodiment of an integrated burner according to the present invention, including two mixing ejectors arranged in parallel with common fuel and air inputs and a common discharge plenum;
[0065] FIG. 9 shows a schematic plan and partial cross-sectional view of the fourth embodiment of an integrated burner according to the present invention, but including three mixing ejectors arranged in parallel with common supply and delivery provisions;
[0066] FIG. 10 shows a graph depicting three alternate graded porosity distributions of the third embodiment of the perforated screen which may be used in the first, second or fourth embodiment of an integrated burner according to the invention;
[0067] FIG. 11 shows a schematic cross-sectional view of a first embodiment of an appliance according to the invention in the form of a chafing dish heater comprising a first embodiment of an integrated burner according to the invention;
[0068] FIG. 12 shows a schematic cross-sectional view of a second embodiment of an appliance according to the invention in the form of a patio heater according to the invention comprising a first embodiment of an integrated burner according to the invention; and
[0069] FIG. 13 shows a schematic partial cross-sectional and partial side view of a second embodiment of an appliance according to the invention in the form of a camping stove according to the invention comprising a first embodiment of an integrated burner according to the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0070] A first embodiment of a perforated screen according to the invention is generally indicated at 40 on FIG. 1A of the accompanying drawings. Perforated screen 40 is in the form of a metal disc 41 and has a plurality of perforations 48 in a perforated area marked 42, six radial ribs 45 to stiffen the perforated screen 40 and six circular shaped supports 44 for supporting a burner face (not shown). The perforated screen 40 is typically arranged in a gas train immediately upline of a burner module. The density and diameter of the perforations is homogenous across perforated area 42. Perforated screen 40 is a homogenisation perforated screen as its purpose includes homogenising air/gas flow and turbulating or energising any layer of stagnant gases which is coating a surface of the burner module. It has been found that by energising such a boundary layer adhering to surfaces of the burner module, the reactivity of the catalysts coating those surfaces is significantly increased.
[0071] A second embodiment of a perforated screen according to the invention is generally indicated at 30A on FIG. 1B of the accompanying drawings. Perforated screen 30A is in the form of a metal disc and has a plurality of perforations 38 in a plurality of perforated areas which are marked 32A,32B,32C,32D,34A,34B,34C,34D and four transverse ribs 35 to stiffen the perforated screen 30. The density of the perforations is different in each of the plurality of perforated areas 32A,32B,32C,32D,34A,34B,34C,34D and may vary across each perforated area 32A,32B,32C,32D,34A,34B,34C,34D. The purposes of the perforated screen 30A are, firstly, to tune aeration of the air/fuel mixture by controlling back pressure in the gas train and secondly to help flatten the velocity profile of flow across the aperture of the screen. Accordingly, perforated screen 30A is a throttling perforated screen 30A. In an alternative embodiment, the perforated areas 32A,32B,32C,32D,34A,34B,34C,34D may take an alternative shape such as a triangular, square, annular, polygonal, curved, sector and/or irregular shape as may be required in order to tune aeration of the air/fuel mixture and adjust the velocity profile of the flow across the aperture of the screen.
[0072] A third embodiment of a perforated screen according to the invention is generally indicated at 30B on FIG. 1C of the accompanying drawings. Perforated screen 30B is in the form of a metal disc 31B and has a plurality of perforations 38 in a plurality of perforated areas or zones which are marked 36A,36B,36C,36D,36E,36F,36G,36H. The density of the perforations is different in each of the plurality of perforated areas 36A,36B,36C,36D,36E,36F,36G,36H. Perforated areas 36A,36B,36C,36D,36E,36F,36G,36H cover an outer area of the metal disc 31A and have an annular shape. The purposes of the perforated screen 30B are, firstly, to tune aeration of the air/fuel mixture by controlling back pressure in the gas train and secondly to help flatten the velocity profile of flow across the aperture of the screen. Accordingly, perforated screen 30B is a throttling perforated screen 30B. In an alternative embodiment, the perforated areas 36A,36B,36C,36D,36E,36F,36G,36H may take an alternative shape such as a triangular, square, polygonal, curved, sector and/or irregular shape as may be required in order to homogenise the gas flow. In an alternative embodiment, the diameter of the perforations may vary across the plurality of perforated areas 36A,36B,36C,36D,36E,36F,36G,36H. In an alternative embodiment, the density and/or the diameter of the perforations may vary across each perforated area 36A,36B,36C,36D,36E,36F,36G,36H.
[0073] The perforations 38,48 in the perforated screens 30A,30B,40 have a cusp 39,49 which narrows the radius of the perforation 38,48 by an amount 37,47 as shown in partial cross-section in FIG. 2. Cusp 39,49 is believed to improve the performance of the perforated screen 30A,30B,40 as it allows perforation 38,48 to perform as a nozzle. Metal disc has a thickness 33,43 which is about 0.25 mm. The perforations 38,48 have a diameter of about 0.35 mm. In an alternative embodiment, the thickness 43 may be from 0.1 mm to 1 mm. Generally speaking, the diameter of perforations 38,48 may be greater than thickness 43 for ease of manufacture. In an alternative embodiment, the diameter of the perforations 48 may be from 0.1 to 0.5 mm. In an alternative embodiment, perforated screen 40 may have a different shape such as a square, rectangular, curved or three dimensional shape (such as a cylindrical, spherical or cuboid shape).
[0074] The perforated screens 30,40 have a hydraulic diameter which for each perforated screen 30,40 is the sum of the diameters of all of their perforations 38,48. The hydraulic diameter determines the back pressure of the throttling screen 30 and thereby the degree of aeration of an air/fluid fuel flow from the gas train may be selected by setting the hydraulic diameter by the appropriate choice of the number of the perforations 38,48 and their diameters.
[0075] Suitable perforated screens 30A,30B,40 are preferably made from a corrosion-resistant malleable, dimensionally-stable metal sheet material, capable of sustaining service temperatures in the range 300-600 C. for the intended life of the burner 100,200,300,400, and capable of being polished to efficiently reflect radiation in the wavelength range 0.5-7.5 m. Cold-reduced austenitic or martensitic stainless steel strip or FeCr alloy are suitable materials. The size of the required perforations depends in part upon the geometry of the burner 100,200,300,400, for example on the clearance between the perforated screen 30A,30B,40 and the upstream surfaces of a burner face 150,250,350,450. A perforated screen 30A,30B,40 having perforations 38,48 having a smaller diameter has improved noise attenuation and spill resistance as ingress by solid or liquid matter into the gas train or burner module is reduced.
[0076] The density of perforations 38,48 can either be fixed or can be varied across the surface of the screen to flatten the velocity profile of mixture entering the burner face 150,250,350,450. FIG. 1C shows an example of a perforated screen 30B for a flat circular burner. The surface has been divided into annular zones 36A,36B,36C,36D,36E,36F,36G,36H which all bear the same size of hole, but the hole density can easily be varied by increasing or decreasing the hole count monotonically in each zone to achieve a flat velocity profile across the area of the burner face, i.e.
[00002]
FIG. 10 depicts three alternate graded porosity distributions for the screen of FIG. 1C obtained in this way. Overall porosity is given by the ratio of total hole area to the burner entrance aperture, and can conveniently be used to adjust the mixture strength of the burner 100,200,300,400.
[0077] The perforated screens 30A,30B,40 may be manufactured by a number of methods, of which the more convenient include hot needle roller, laser-cutting, waterjet-cutting, CNC machining and chemical milling. For the first four methods, improved tolerances and reduced costs result where sheet material is laminated together during machining and clamped between thicker plates. On completion, screens may be electropolished to remove burrs. The preferred method of manufacture is chemical milling of the sheet material from both sides, with accurate mutual registration of a lithographic mask on each side. According to this process, the minimum hole size that is possible with high yield is given by the material thickness used. Referring to FIG. 2, the resulting profile of the etched perforation 38,48 will not have parallel walls but will have a reduced diameter cusp 39,49 approximately halfway down the bore. This can be advantageous in that it behaves as a sharp-edged orifice to fluid flow, producing consistent jet diameter with minimal frictional energy losses. Chemical milling can be conveniently coupled with electropolishing to remove sharp edges and improve the reflectivity of the burner-facing surface.
[0078] A first embodiment of an integrated burner according to the invention is indicated generally at 100 on FIGS. 3A and 3B of the accompanying drawings. Integrated burner 100 comprises a gas jet-driven air-aspirating ejector 110, a radial diffusor of elliptical wall profile 120, a disc shaped throttling screen 130 and a burner module indicated generally at 159 which comprises a homogenisation screen 140, a crimp ring 155 and a burner face 150. Ejector 110 has a co-axial primary nozzle 112, two radial air inlets 114 and an ejector secondary nozzle 116. The primary nozzle and two radial air inlets 114 provide inlets for the ejector secondary nozzle 116. Secondary nozzle 116 of ejector 110 discharges to a mixing tube 118 which discharges to a radial diffusor 120. Diffusor 120 has a cross-sectional area which broadens from narrow tube 118 to be substantially the same as that A.sub.B of the burner face 150. Diffusor 120 houses the throttling screen 130 and the burner module 159. Diffusor 120 has a lower lip 124 for supporting the throttling screen 130, an axial spacer 126 for supporting the burner module 159 and an upper lip 122 for securing the burner module 159.
[0079] Burner module 159 comprises the burner face 150, the homogenisation screen 140 and the crimp ring 155. Crimp ring 155 secures the homogenisation screen 140 to the burner face 150. Crimp ring 155 has a lower clip 158 for engagement with the homogenisation screen 140 and an upper clip 156 for securing burner face 150. Crimp ring 155 minimises the risk of air/fuel mixture bypassing the burner face 150.
[0080] The throttling screen 130 is supported by lower lip 124 of the diffusor 120. Axial spacer 126 is placed on top of throttling screen 130 to space it from the homogenisation screen 140 of the burner module 159. Burner module 159 is placed on axial spacer 126 and is secured by upper lip 122 of the diffusor 120. In an alternative embodiment, the burner module 159 may comprise the homogenisation screen 140. In a further alternative embodiment, the crimp ring 155 may comprise a clip for engaging with the diffusor 120.
[0081] Throttling screen 130 may be a perforated screen 30A according to the second embodiment of the invention as shown in FIG. 1B, having perforations 138. Homogenisation screen 140 may be a perforated screen 40 according to the first embodiment of the invention shown in FIG. 1A, having perforations 148. Homogenisation screen 140 is shaped to form three supports 144 for burner face 150 to prevent burner face 150 from sagging, to improve durability of the burner face 150 and to allow a wider burner aperture (A.sub.B). Support 144 has a pointed shaped to minimise thermal bridging between the homogenisation screen 140 and the burner face 150. Throttling screen 130 and homogenisation screen 140 are separated from each other by an annular spacer 153. Burner face 150 is formed from a metal mesh which is at least partially coated with a catalytic material to ensure substantially flameless combustion of a gas/air mixture. Upper clip 156 of the crimp ring 155 is shaped such that a radial space 152 is provided to allow for thermal expansion of the burner face 150 in use. Primary nozzle 112 has an adaptor (not shown) for connection to a pressurised fluid fuel source. Ejector 110 has an axial length which is indicated at L.sub.E. Diffusor 120 has an axial length which is indicated as the sum of L.sub.D and L.sub.P. Burner face 150 has an axial length L.sub.B. The integrated burner 100 has an overall axial length L.sub.Tax which is indicated as being the vector sum of L.sub.E, L.sub.D, L.sub.p and L.sub.B. In an alternative embodiment, there may be one or more air inlets 114 and/or one or more supports 144 for burner face 150
[0082] In the first embodiment of the invention, (L.sub.d+L.sub.p) is minimised by use of the radial diffuser 120 and substantial elimination of a plenum upline of the burner face 150. This is achieved by addition of the perforated screens 130,140 which are formed from a thin heat resistant material. The upline screen 130 acts as a semi-permeable boundary for the radial diffuser 120, ensuring high velocity mixture discharging the ejector 110 negotiates the axial to radial direction change with acceptable energy losses and without severe flow separation, while also enabling the flow to distribute across its aperture, permeate, and progress towards the burner face 150. The axial to radial direction change is required because the aperture of the burner face 150 is greater than that of the mixing tube 118. The downline screen 140 behind the burner face 150 acts to further homogenise the velocity distribution of the mixture flow and to reflect radiation emitted by the burner face 150 back out of the burner face 150. Flow passage through each screen 130,140 is accompanied by considerable microturbulence due to jet action through the perforations 138,148. In this way, the flow length of a conventional plenum can be greatly shortened, while the use of a radial diffuser 120 with semi-porous boundary wall formed by screens 130,140 enables flow expansion in a very short axial length. Quality of air/gas mixing over that delivered by the ejector mixing tube is improved due to the micromixing effects of jetting through the perforations 138,148. By fabricating the screens 130,140 from thin smooth material with high reflective efficiency to IR but relatively low heat conductivity, the gas train can be baffled from infrared radiation radiated from the rear of the burner face, limiting burner temperature rise, hence reducing risk of light-back and boosting radiant efficiency.
[0083] A further benefit of the use of thin perforated screens 130,140 in the burner 100 according to the first embodiment of the invention is relevant to cooking applications, where burners 100 are generally inverted and stationed below cooking vessels. The small diameter of the perforations 138,148typically of the same order as the thickness of the screen materialaffords some protection to the gas train from liquid and particulate ingress via the burner face 150.
[0084] A yet further benefit of the use of at least one thin perforated screen 130,140 stationed a few microjet diameters upstream of the rear of the burner face 150, is the ability to boost mass transport rate of reactant molecules to a catalytically-coated burner face 150 through the effects of jet impingement. The high levels of turbulence in jet impingement of a gas mixture onto catalytic surfaces thins and turbulates the boundary layer of reactants and products of combustion adhering to the surfaces. This decreases the catalytic area that would otherwise be required to combust a given massflow of mixture to a given standard of completeness.
[0085] Computational fluid dynamics (CFD) visualisations of the burner according to the first embodiment of the invention are shown in FIGS. 4A, 4B, 4C and 4D. FIG. 4A depicts a propane/butane gas jet at 280 kiloPascals gauge (dark grey at bottom LHS) mixing with ambient air (dark grey at left). Blended air/gas passes from the radial diffuser 120 through two perforated screens 130,140 and through the flat catalytic burner face 150 and is discharged to atmosphere. Combined screens and burner resistance of 50 Pascals was assumed. As the flow progresses down the mixing tube 118 and jet breakup occurs, momentum is transferred to the entrained air. Shortly after the entry to the axial-radial transition at the inlet to the radial diffuser 120, the streamlines and velocities in FIG. 4B clearly indicate a powerful toroidal vortex, which in FIG. 4A appears to homogenise a partially-mixed air/gas flow discharging from the ejector. Also clearly visible in FIG. 4B is the homogenising effect of the screens 130,140 on velocity profile across the burner face 150. Also visible is the jetting effect of the perforations 148 in the screen 140 closest the burner face 150 onto the catalytic surfaces. FIG. 4C indicates the effectiveness of the perforated screens 130,140 in baffling much of the rearward-emitted radiation from the burner face 150 from affecting upstream mixture temperature, reducing risk of lightback. FIG. 4D indicates the effectiveness of dump diffuser diffusion effect 119.
[0086] A second embodiment of an integrated burner according to the invention is indicated generally at 200 on FIG. 5 of the accompanying drawings. Integrated burner 200 comprises a gas jet-driven air-aspirating ejector 210, an annular diffusor 220, an annular plenum 225, a cylindrical homogenisation screen 240 and an outer cylindrical burner face 250. Ejector 210 has a co-axial primary nozzle 212, two radial air inlets 214 and an ejector secondary nozzle 216. The primary nozzle 212 and air inlets 214 provide inlets for the ejector secondary nozzle 216. Secondary nozzle 216 discharges to a mixing tube 218 which discharges into annular diffusor 220. Annular duct 219 turns fluid flow radially and then axially to enter annular diffusor 220. Fluid flow from the annular diffusor 220 is turned radially by one or more radial outlets 221 to enter plenum 225 and is directed towards the burner face 250 via cylindrical homogenisation screen 240. Homogenisation screen 240 may be a perforated screen 40 according to the first embodiment of the invention shown in FIG. 1A except that it has a cylindrical shape. Burner face 250 may be formed from a metal mesh which is at least partially coated with a catalytic material to ensure substantially flameless combustion of a gas/air mixture. Primary nozzle 212 has an adaptor (not shown) for connection to a pressurised fluid fuel source.
[0087] The integrated burner 200 according to the invention accordingly has a co-annular arrangement of ejector 210, diffuser 220 and plenum 225 which folds these three elements very efficiently via two flow reversals provided by radial tube 219 and radial outlet 221 from the diffusor 220. This minimises (L.sub.e+L.sub.d) and consequently L.sub.Tax. The folded gas train is used to feed a radially-firing cylindrical burner face 250. Flow from a conventional central jet ejector 210 is turned first radially then axially into an annular diffuser 220, before finally being turned radially again and discharged into an annular plenum 225. Flow entry into the plenum 225 can have tangential swirl imparted.
[0088] A single cylindrical perforated screen 240 is added in close proximity to the inlet surfaces of the burner face 250 to turbulate the catalytic surfaces (not shown) of the burner face 250 and acts as a radiation baffle. The co-annular ejector-diffuser 210,220 arrangement provides excellent mixing of air/gas as is clear from the CFD simulations of FIGS. 7A and 7B and a good degree of flow expansion. A second perforated screen for improving flow uniformity and mixing quality may be unnecessary.
[0089] A third embodiment of an integrated burner according to the invention is indicated generally at 300 on FIG. 6 of the accompanying drawings. Integrated burner 300 comprises a gas jet-driven air-aspirating ejector 310, an annular diffusor 320, an annular plenum 325, an annular homogenisation screen 340 and an annular burner face 350. Ejector 310 has a primary nozzle 312 for gas injection, two radial air inlets 314 and an ejector secondary nozzle 316. Primary nozzle 312 and air inlets 314 are provide inlets for ejector secondary nozzle 316. Secondary nozzle 316 of ejector 310 discharges into mixing tube 318 which discharges into diffusor 320. Annular duct 319 turns fluid flow radially and then axially to enter annular diffusor 320. Fluid flow from the annular diffusor 320 is turned radially by one or more radial outlets 321 to enter plenum 325 and is directed towards the burner face 350 via annular metering screen 330 and annular homogenisation screen 340. Homogenisation screen 340 may be a perforated screen 40 according to the first embodiment of the invention shown in FIG. 1A except that it has an annular shape. The integrated burner 300 according to a third embodiment of the invention provides a substantially flat burner face variant of the integrated burner 200 according to the second embodiment of the invention depicted in FIG. 5. Burner face 350 is formed from a metal mesh which is at least partially coated with a catalytic material to ensure substantially flameless combustion of a gas/air mixture. Primary nozzle 312 has an adaptor (not shown) for connection to a pressurised fluid fuel source.
[0090] Computational fluid dynamics (CFD) visualisations of the integrated burner 300 according to the third embodiment of the invention are shown in FIGS. 7A and 7B. FIG. 7A depicts gas concentration in moles per cubic metre of a propane/butane gas jet at 280 kiloPascals gauge (dark grey at top LHS) mixing with ambient air (dark grey at left). Blended air/gas discharges from the annular flat surface at the right hand end of the plenum 325 to an assumed perforated screen and burner face resistance of 50 Pascals. As the flow progresses down the ejector's mixing tube 318 and jet breakup occurs, momentum is transferred to the entrained air. Part-way around the flow-reversing axial-radial-axial duct 319 on the RHS, evidence of a mixing shock can be seen, before entry into the annular diffuser 320. Note that the flow leaving the mixing tube is subsonic and remains so throughout the annular duct 319. Therefore this rather sudden mixing does not involve a true shock wave phenomenon. It is believed that it is associated with fluid vorticity caused by the sharp direction change of the flow. By the time the mixture is discharged into the plenum 325, it has been thoroughly mixed (no visible stratification).
[0091] FIG. 7B depicts flow velocity in metres per second and streamlines. The effectiveness of the lengthy annular diffuser in decelerating the flow velocity is apparent, as is the good control of flow separation throughout the gas train which is often difficult to achieve in annular ducts. The mass ratio of entrained air to gas for this CFD case was 20.7:1, equivalent to approximately 25% excess air for a typical LPG-type fuel. This simulation indicates the outstandingly good combination of mixing effectiveness, high air entrainment and very compact dimensions possible using gas trains folded in this way.
[0092] A fourth embodiment of an integrated burner according to the invention is indicated generally at 400 on FIGS. 8 and 9 of the accompanying drawings. Integrated burner 400 comprises an axial gas inlet 405, three radially-arranged gas/air ejectors 410A,410B,410B, three axial diffusors 420A,420B,420C, an annular plenum 425, an annular homogenisation screen 440 and an annular burner face 450. The ejectors 410A,410B,410C each have a primary nozzle 412A,412B,412C for gas injection, an axial air inlet 414A,414B,414C and a secondary nozzle 416A,416B,416C. Primary nozzle 412A,412B,412C for gas injection and axial air inlet 414A,414B,414C provide inlets for the secondary nozzle 416A,416B,416C. Secondary nozzles 416A,416B,416C of ejectors 410 lead to radially-arranged mixing tubes 418A,418B,418C which discharge into diffusing bends 420A,420B,420C. Fluid flow discharging axially from the diffusing bend 420A,420B,420C exits into plenum 425 and is directed towards annular burner face 450 via homogenisation screen 440. Homogenisation screen 440 may be a perforated screen 40 according to the first embodiment of the invention shown in FIG. 1A except that it has an annular shape. Burner face 450 may be formed from a metal mesh which is at least partially coated with a catalytic material to ensure substantially flameless combustion of a gas/air mixture. Primary nozzles 412A,412B,412C have an adaptor (not shown) for connection to a pressurised fluid fuel source.
[0093] The fourth embodiment of the integrated burner according to the invention shown in FIGS. 9 and 10 illustrates the concept of segmentation of a single large ejector into multiple radially or axially-arranged smaller identical ejectors fed by a common gas supply, with single shared plenum and burner face. In an alternative embodiment, there may be more or less than three ejectors and diffusors, for example, the gas train may have two, four or five ejectors and diffusors.
[0094] In the integrated burner 400 according to the fourth embodiment of the invention, (L.sub.e+L.sub.d) is minimised. A diffusing duct 420A,420B,420C incorporating a 90 degree bend is provided at the discharge end of each ejector 410A,410B,410C. This gas train arrangement can be packaged efficiently with radial-firing or axial-firing burner faces 450, using at least one perforated screen 440 to homogenise flow distribution into the burner face 450 and to turbulate catalytic surfaces.
[0095] In an alternative embodiment, the burner face 150,250,350,450 may be a catalytic radiant burner head. In an alternative embodiment, the burner face 150,250,350,450 may comprise a porous ceramic monolith or open-cell metal foam treated with a combustion catalyst such as platinum (Pt), palladium (Pd), rhodium (Rh) and/or a rare earth compound. Burner face 150,250,350,450 has a sufficient area to fully combust the required fuel to generate the target power output. In practice, greater catalytic area may be required to assure complete combustion of fuel in the face of imperfections such as incomplete air/gas mixing, non-uniform mixture velocity across the burner face 150,250,350,450, or excessive conduction of heat away from the burner face 150,250,350,450 to its mounting means.
[0096] In some applications such as flat burner types, it is advantageous to prop the burner face at additional points on its aperture in addition to providing continuous edge support. This improves burner face durability in the face of rough handling of a portable gas appliance, for example. Malleable screen materials can easily have bumps formed into them through pressing, after perforation. By minimising the thickness of the screen material and favouring the use of materials of low conductivity, it is possible to provide support bumps at one or more points across the aperture which contact and stabilise the upstream side of the radiant burner face, while minimising thermal bridging to the burner support structure.
[0097] Radiant burner faces require mounting methods that minimise heat losses at the support points, minimise the degree of slip or bypassing of mixture around the burner perimeter, while enabling substantial thermal expansion and contraction of the burner face without restraint. High temperature gasketing materials of needled quartz fibre are suitable.
[0098] The compact gas train and radiant burner technology described here can be used in many portable and permanent combustion applications, including heating and combustible gas purification and flaring applications. Three specific examples of suitable appliances are provided in FIGS. 11, 12 and 13. FIG. 11 depicts a first embodiment of an appliance according to the invention which is indicated generally at 60. Appliance 60 is in the form of a well-known food warming or cooking device. A chafing dish 63,64 is provided, consisting of two nesting metal vessels 63,64, with substantially flat under-surfaces. The lower vessel 63 contains a shallow layer of water 62, used as a heat distribution and coupling agent. The upper dish contains solid or liquid foodstuffs 65 to be kept warm or cooked. Placed beneath the nested dishes are one or more integrated burners 100 each connected to a LPG-fuel container 107. As the integrated burner is radiant, the appliance 60 can be operated if necessary with minimal clearance between the burner face and the underside of the nested dishes, as, being a fully-aerated flameless technology there are negligible flame-quenching effects and carbon monoxide emission levels will comply with regulatory norms under all conditions of service.
[0099] FIG. 12 schematically depicts a second embodiment of an appliance according to the invention which is indicated generally at 70. Appliance 70 is in the form of space heating device for indoor or outdoor use, employing a radiant integrated burner 100 adapted to have a spherical burner face 150. In this case, the spherical burner face 150 is placed a short distance inside the focal point of a substantially parabolic reflector 72. Heat from the integrated burner 100 is reflected off parabolic reflector 72 as illustrated by beams 77. The integrated burner is both supported and fuelled via a tubular support 74 mounted coaxially with the reflector 72. A compact gas supply 107 is located behind, and is baffled by, the reflector 72 from direct radiation. Convenient burner power control can be provided via a projecting handle 76 which is rotatable about the reflector axis and incorporating a button control (not shown) to operate an electrical igniter (not shown). The handle 76 may additionally be used to adjust the pose of the reflector 72 in tip and tilt. Optionally, the intra-focal distance of the centre of curvature of the burner face 150 may be adjusted via the projecting handle 76 or by other means, enabling beam divergence to be adjusted. The reflector 72 and integrated burner 100 may be pole or wall-mounted and positioned for indoor or outdoor comfort heating, accelerated drying or curing of coatings or composites and other purposes.
[0100] There are many advantages of applying this technology in this application. A flameless radiant integrated burner has a better-defined object shape than a blue-flame burner, while a truncated spherical profile is optimal for projecting a uniform heat flux on the image plane. Radiant burners, being fully-aerated, are not susceptible to soot accumulation on the reflective optics over time. The low mass of the compact folded gas train embodiments disclosed here enable the suspended mass to be minimised to the benefit of safety and stability, while the mass of embodied materials and therefore the cost of the integrated burner is very low.
[0101] FIG. 13 depicts in half-section a third embodiment of an appliance according to the invention which is indicated generally at 80. Appliance 80 is in the form of a portable single-burner LPG-fuelled stove for camping and the like. Stove 80 comprises a pot 82, a pot support 86, a burner shield 84, an integrated burner 300 according to the third embodiment of the invention and fuel supply 307. The pot support 86, pot support 86, burner shield 84, integrated burner 300 and fuel supply 307 nest into the pot 82 for compact storage. The burner face 350, of outer diameter approximately 90 mm, combusts approximately 2 kW of gas, measured by heat input rate, equivalent to a heat flux of 320 kW/sq.Math.m approximately. Burner face temperature is approximately 820-900 C. depending on the reflectivity of the under surface of the pot 82. A stepped substantially-conical radiation reflector with air induction and exhaust holes doubles as a pot support 86 and as windproofing screen 84. Exhaust gases are discharged through perforations around the perimeter of the radiation reflector (not shown) while infrared radiation is concentrated within the cavity formed between perforated screen, underside of the pan, and the stepped radiation reflector.
[0102] The advantage of applying the technology in this application is the superior packaging efficiency, reduced weight, improved stability and lower cost of this stove when compared with state of the art stoves using other technology. This is achieved without sacrificing other contemporary performance features of modern LPG stove.
[0103] In the specification the terms comprise, comprises, comprised and comprising or any variation thereof and the terms include, includes, included and including or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.
[0104] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.
