GB2045420A - Improved air heater for hot air balloon - Google Patents

Abstract

The invention relates to an improved air heater for a hot air balloon. The heater comprises a plurality of burners MC1 etc. of generally tubular cylindrical form each with division means 13, etc. within it to give a division of a combustible atmosphere formed at the burner during use generally with a mixture of propane and air and each having a gas jet J, etc. The heaters may produce 10<7> Btu/hr with a low noise level. Two constructions of burner are described, one an open tube having a foraminous wall and containing within its bore an obturator having at least two spaced apart foraminous members 13, Fig 2, and the other Fig. 7, an open tube supporting substantially concentrically two axially spaced apart members providing a partial constriction to its bore from which divided streams of gas and air emerge and when ignited form a stable flame. <IMAGE>

Description

SPECIFICATION Improved air heater for hot air balloon This invention relates to an improved air heater for a hot air balloon. Air heaters are essential to supply the lift to the balloon by reducing the weight of the air in the balloon due to its expansion. Today such air heaters are generally .supplied with a liquid petroleum gas which is usually propane (C3H8) having a boiling point of -450C and a calorific value of about 19,800 Btu/lb. In practical flight a high power is required which may be for example about 1 800 HP or more for a balloon having some 40,000 cu. ft. capacity and this power is generated by the air heater in sporadic bursts of flame with an attendant high noise level; which is objectionabie.

According to one aspect of the present invention there is provided an air heater for a hot air balloon able in use to provide a combustible atmosphere, said heater comprising a plurality of burners, each provided with a gas jet, each said burner and each said gas jet being spaced apart from one another; each said burner having a generally tubular cylindrical form with division means within it to give a division of the combustible atmosphere.

According to a further aspect of the present invention there is provided an air heater for a hot air balloon, said heater comprising a plurality of burners each provided with a gas jet and spaced apart therefrom, each burner comprising sn open tube having a foraminous wall over at least a part of it, said tube containing in its bore an obturator having at least two spaced apart foraminous members and a slight construction to its bore from which, in use, a gas/air mixture is provided with a divided flow that upon ignition produces a stable flame.

According to yet a further aspect of the present invention there is provided an air heater comprising a plurality of burners each provided with a gas jet, each burner comprising an open tube supporting substantially concentrically two axially spaced apart members providing a partial constriction to its bore from which, in use, a gas/air mixture is provided with a flow divided into at least four streams that upon ignition produces a flame above the uppermost of said two spaced apart members that is stabilized by a coronal flame.

Two air heaters of the invention will now be described by way of example only with reference to the figures of the accompanying drawings, in which: Figure 1 is a side elevation of a first air heater; Figure 2 is an exploded view in parallel perspective of a single burner of the heater of Figure 1; Figure 3 is a part cross sectional elevation of a flow valve taken on axial section station Ill-Ill of Figure 1, and Figure 4 is a detail of an alternative jet construction and Figures 5A, 5B respectively are a side elevation in part section and an exploded view of an alternative burner construction to that of Figure 2; Figure 6 is a side elevation of a second air heater; Figure 7 is an exploded view in parallel perspective of a single burner of the heater of Figure 6;; Figure 8 is a diagram (not to scale) of the flow of gas and air in one burner of Figure 6.

Referring now to Figures 1 to 5 of the accompanying drawing an air heater for a hot air balloon is seen to comprise one hundred and fourteen jets arranged in five concentric rings on a fuel pipe F1 the rings being identified by jets J 1, J2, J3, J4, J5. The jets are brass (size no. 140) and have an orifice diameter of 1.0 nim. An alternative jet arrangement is shown in Figure 4 the jet J 1 for example being supported by a stalk F2 from the fuel pipe F1.Each jet has a burner comprising a mixer and combustion open tube shown generally as MC1 MC2 etc. placed directly above it and spaced from it by a distance 11. The construction of any one mixer and combustion tube is identical for all of the one hundred and fourteen jets and one mixer-combustion tube MC 1 is shown in Figure 2, it has eight metal components, a skirt 10, a body 1 1, a collar 12 and a five element obturator comprising a sandwich of three foraminous members such as woven metal cloths 131 132, 133 separatec! by two helical spacers 14,, 142. The collar 1 2 is a flame retention collar having a foraminous wall and including an integral turned in top edge that provides a diameter d1 1 less than d1 and offers to the gas air stream a slight constriction in its through diameter d1.The body 11 is of sufficient length 12 to restrict outward dispersion of gas below the metal cloth 131 caused by it impinging thereupon as it leaves the jet J1 and of sufficient length 13 above the metal cloth 133 to give a directional formation of the combustible atmosphere emitted from the body. The skirt 10 also has a foraminous wall and possess a length 14 and diameter d2 that give a ratio, in relation inter alia to the jet orifice, that ensure an efficient gas/air mixture and at the same time restrains any tendency to a sideways dispersal of air that is entrained with the gas.

The three separate pieces of metal cloth 131, 132, 133 are made to have a suitable mesh size and a wire gauge that are correlated to give in combination the required turbulation and air induction within the burner. It is essential to have at least two cloths or similar foraminous members, but I prefer to use three. In the construction of the burner shown d1 is 22 m/m d2 is 22 m/m 11 is 3 m/m /2 is 18 m/m 13 is 12 m/m 14 is 60 m/m The mesh of each cloth is 1 mm and the gauge of stainless steel wire 24 S.W.G. The separation between each of the three cloths 131, 132, 133 is 4mm.

It is essential to produce a condition of turbulence and air induction by the proximity of the separate foraminous members of metal cloths such as 131 132, 1 33 to create a combustible atmosphere fractionally in time before ignition of the atmosphere occurs.

Referring now to Figures 5A, 5B the pilot lamp burner may have a similar construction to the burner of Figure 2 and comprise an open tube containing in its bore an obturator having three spaced apartforaminous members and a turned-in top edge producing a slight constriction to its bore from which in use a gas/air mixture ignites to produce a silent flame of about 105 Btu/Hr. above said obturator.

In construction the pilot lamp burner has six metal components the body 11 having a diameter d6 and an obturator comprising a sandwich of three foraminous members (such as woven metal cloths 113, 114, 1 15) separated by two helical spacers(118, 11,).

The body 11 has an integral turned-in top edge 111 that provides a diameter d61 less than the main diameter de of said body 11 and in consequence offers to the gas/air stream a slight constriction as it passes therethrough; immediately below said turned-in top edge is a single peripheral row of spaced apart holes 112 through which part of the gas/air mixture passes to produce a corona of flame to stabilise combustion of the bulk of the flow.

The obturator is positioned within the bore of body 11 to form a skirt section below and a collar section above the said obturator. The skirt section possesses a length 4 and diameter d6 to give a ratio, in relation inter alia to the jet orifice, that ensure an efficient gas/air mixture and at the same time restrains any sideway dispersal of air entrained with the gas. The collar section has a sufficient length i5 above the obturator to give directional formation of the combustible atmosphere emitted therefrom and act as a flame retention collar.

The three separate pieces of metal cloths 113, 114, 115 have a suitable mesh size and wire gauge that are correlated to give in combination the required turbulation and air induction within the burner. It is essential to produce a condition of turbulence and air induction by the proximity of the separate foraminous members of metal cloths (such as 113, 114, 1 15) two create a combustible atmosphere fractionally in time before ignition of the atmosphere occurs.

In one example of a burner such as Figure 2 that gives success; d is 25 mm; 4is 60 mm; /5 is 12 mm; the mesh of each cloth is 1 mm the wire gauge 24 swg; the separation between each of the three cloths 113,114,11 5is4mm;the diameter of the jet orifice, positioned 3 mm below the bottom edge of the body 11, is 1 mm.

The burners are provided with a pilot lamp 14 as described above and as shown at Figure 5A, 5B it is centrally mounted within the five concentric jet rings provided with a pilot lamp heater coil 14, the lamp being fed from a pilot lamp feed pipe 15 which is fitted to the pilot lamp feed pipe 16 via a union 15,. The pilot lamp feed pipe 16 and identical length cross pipe 16, (being the main constructional members) support a suspension ring 1 7 and also via strut 18, fuel pipes 20 and 20, a heater coil 19. Fuel pipes 20 and 20, (similar to strut 18) are at the ends of cross pipe 16, and extend upwardly to the heater coil 1 9.

Fuel pipe 20, carries gaseous fuel from the heater coil 19 downward to cross pipe 16, and thence to fuel pipe F1 etc. Fuel pipe 20 terminated at the top of the heater coil 19 by a fuel flow needle valve 21 which is shown in greater detail in Figure 3. At the lower part beneath the jets is a fuel flow control 22, two identical control valves 22, and a substantial support handle 23 for the use of the pilot and burner operator of the balloon. The fuel flow control valve 21 is fitted to the top of the heater coil 1 9 to prevent expansion freezing of the liquid propane gas and the malfunctioning of the valve.

A push rod 24 enables the actuation of the control 22 to be conveyed to the fuel flow needle valve 21. In Figure 3 the fuel flow needle valve is seen to comprise push rod 24; spring loaded against casing 25 by helical compression spring 26. The push rod 24 terminates in a needle 24, that co-operates with construction orifice 27.

The sequence of operations for lighting the gas burner is as follows: The pilot lamp 14 is lit and remains alight at all times in flight, its fuel is supplied from the main propane container (not shown) via by-pass pipes (not shown) from both control valves 22,. One of the valves 221 is then opened by its respective handle 222 and fuel from the said propane container controlled by the valve 21, from which it flows in the liquid state to the heater coil 19 which heats it and vaporises it before it passes via fuel pipe 20, down to the cross tube 16, and thence to jets J 1 , J2 etc.

where it flows with air to burners MC1, MC2 etc.

combustion occurring at a pressure, controlled by valve 21, of about 30 p.s.i. to give an operational but quiet flame above the obturator.

Referring now to Figures 5 to 8 of the accompanying drawing an air heater for a hot air balloon comprises ninety six jets arranged in eight separate circular jet assemblies (identified by JA1, JA2,JA3, JA4 etc. of which only four are shown).

Each jet assembly JA1, JA2 etc. has a burner comprising a mixer/combustion open tube shown generally at MC1, MC2 etc. placed directly above said jet assembly and which enclose it at the bottom of the open tube. The construction of any one burner mixer/combustion tube is identical for all eight jet assemblies and one mixer/combustion tube MC, is shown in Figure 7 it has three metal components, a body B 1 that supports in spaced axial relation of axis XX, a two element super structure comprising a frusto-conical skirted inner tube B2 and an open ended frusto-conical constrictor member B3.

The body Bl has an integral turned-in top edge B" that provides a diameter d11 less than the main diameter of said body dl and in consequence offers to the gas/air stream a slight constriction in its passage therethrough, immediately below said turned-in top edge is a single peripheral row of spaced apart holes B,2.

The body B, has a length /1 and a diameter dl giving a ratio to ensure an efficient gas/air mixture and at the same time restrains any tendency to a sideways dispersal of air that is entrained with the gas.

The skirted tube B2 has a diameter d2 and a length /2 with an integral frusto-conical shaped skirt B2, with a diameter dl centrally placed around which is a peripheral row of holes B22 spaced apart from one another. A further two peripheral rows of holes B23, B24 are positioned around the right cylindrical tube section above the skirt section. The skirted inner tube B2 has an integral turned-in top edge B25.

The constrictor member B3 is an open frustum of a cone having a length /3 a basal diameter d3 and a smaller upper diameter d4. The member is fixed concentrically, by sheet metal webs wedge onto the through flow, within the upper end of the inner tube B2 and positioned with but half its length 13 projecting.

The jet assembly JA, for example consists of a circular metal jet tube T with a mean diameter d5 mounted via a union 10 to fuel pipe F.1 and having supports to carry the mixer/combustion tube MC,. The jet tube T has twelve gas jet orifices 01, O2 etc. in its upper wall and they are spaced evenly around the mean circumference of the metal jet tube T to ensure greater air induction with better mixing and even dispersal of the gas and air thereby enabling a shorter length of the mixer/combustion tube than would be possible with a single larger gas jet orifice.

The cqnstriction member B3 performs a double function in use (1) the turbulation of the gas and the air entrained with it to produce a combustible atmosphere and (2) the sub-division of that atmosphere into four distinctive streams (F1, F2, F3, F4) (Figure 8) of different speeds.As the combining gas/air mixture passes up the mixer/combustion tube B, some part of it passes through the three peripheral rows of holes (B22, B23, B24) in the skirted inner tube B2 which holes meter and control its speed in passing it up the annuls A, (Figure 8) a portion of this stream F, is directed out of the holes B12 at the top edge B" of the body B, to produce a corona of flame to stabilise combustion, the remainder of the flow F2 continuing as a slow moving annular stream.The bulk of the combustible atmosphere passes up the inside of the inner tube B2 and is divided by the constrictor member B3 into two further streams one F3 passing the constriction component by the lower edge of the cone element and the wall of the inner tube to produce a relatively fast annular stream the other being funnelled through the cone element B3 (diameters d3 and d4) as a fast core stream F4. In combination this division of the combustible atmosphere produces a stable flame with low noise level whilst still retaining a high flame projection characteristic desirable in a hot air balloon application.In one example that gives success: dl is 75 mm; d2 is 65 mm; d3 is 60 mm; d4 is 30 mm; d5 is 50 mm; 11 is 115 mum; 12 is 63 mum; 13 is 30 mm; the jet 0,, 0, are one millimetre in diameter and the holes in rows B", B22, B23, B24 are each three millimetres in diameter.

The eight mixer combustion tubes MO1, MC2 etc. are provided with a pilot lamp 11 which may be as described above and shown at Figures 5A, 5B, it is centrally mounted and a pilot lamp heater coil 12 the lamp being fed from a pilot lamp feed pipee 1 3 which is fitted to the pilot lamp feed 14 via a union 1 5. Fuel pipes 18 and 18, (similar to struts 1 7 and 17, are at the ends of cross pipe 14, and extend upwardly to the heater coil 19. Fuel pipe 1 8 carries gaseous fuel from the heater coil 19 downward to cross pipe 14, and thence to fuel pipe F.1. etc. Fuel pipe 18, terminates at the top of the heater coil 1 9 by a fuel flow needle-valve 21 and is as described above and shown at Figure 3.

The sequence of operations for lighting the air heater is as follows:- The pilot lamp 11 is lit and remains alight at all times in flight, its fuel is supplied from a main propane container (not shown) via a by-pass pipe (not shown) from both control valves 22t through heater coil 12. One of the valves 221 is then opened by its respective handle 222 and fuel from the said propane container, controlled by the valve 21 , from which it flows in the liquid state to the heater coil 19 which heats it and vaporises it before it passes via fuel pipe 18 down to the cross tube 141 and thence to the jet assemblies JAl, JA2 etc. where it flows with air to mixer combustion tubes MC1, MC2, etc. combustion occurring at a pressure, controlled by valve 21, of about forty p.s.i. to give an operational but quiet flame above the superstructure.

The air heaters described above have an output of about 107 Btu/hr with a noise level at least half of that of a gas burner of equivalent heat output but of conventional arrangement and construction.

Claims (6)

1. An air heater for a hot air balloon able in use to provide a combustible atmosphere, said heater comprising a plurality of burners, each provided with a gas jet, each said burner and each said gas jet being spaced apart from one another; each said burner having a generally tubular cylindrical form with division means within it to give a division of the combustible atmosphere.

2. The air heater according to claim 1, wherein said heater comprises a plurality of burners each provided with a gas jet and spaced apart therefrom, each burner comprising an open tube having a foraminous wall over at least a part of it, said tube containing in its bore an obturator having at least two spaced apart foraminous members and a slight constriction to its bore from which, in use, a gas/air mixture is provided with a divided flow that upon ignition produces a stable flame.

3. The air heater according to claim 1 wherein said heater comprises a plurality of burners each provided with a gas jet, each burner comprising an open tube supporting substantially concentrically two axially spaced apart members providing a partial constriction to its bore from which, in use, a gas/air mixture is provided with a flow divided into at least four streams that upon ignition produces a flame above the uppermost of said two spaced apart members that is stabilized by a coronal flame.

4. An air heater constructed and arranged substantially as described herein and as shown in Figures 1 to 4 of the accompanying drawings.

5. An air heater constructed and arranged substantially as described herein and as shown in Figures 5 to 8 of the accompanying drawings.

6. An air heater according to claim 4 or claim 5 when modified to have a pilot lamp as shown in Figures 5A and 5B of the accompanying drawings.