Hot air generating devices such as hot air blowers are used for many purposes, both industrial and domestic. For example, hairdryers provide a hot or warm air stream for drying hair. Certain hair curling or shaping devices also provide a warm or hot air output. In general, hair dryers provide a single warm air stream, which can be outputted through different shaped nozzles for providing one or more warm air streams of varying cross-section. In the case of hair curling and shaping devices, a tubular barrel may be provided around which the hair is wound, and the tubular barrel may be provided with radially extending members, such as, for example, comb-like teeth. A plurality of air outlet openings may be provided from the tubular barrel intermediate the radial teeth for delivering hot or warm air through hair wound around the tubular barrel. Industrial hot air generating devices and hot air blowers have many uses, for example, applying a stream of warm or hot air to heat shrinkable plastics tubes or sleeves, for example, of the type for providing insulation for wires, multi-core cables and the like, water carrying conduits, and also for moulding and shaping plastics materials and the like.

One such type of hot air generating device is electrically powered, and because of the power requirement must be connected to a mains electricity supply. In general, an electrically powered heating element is located in a tubular housing, and a fan located upstream of the heating element is powered by an electrically powered motor for passing air over and through the heating element for heating the air. The heated air is then delivered through a single air outlet or a plurality of air outlets as desired. In general, such electrically powered hot air generating devices, are suitable only for hair drying and hair treating purposes. The air handling capacity and the air temperature of the heated air of such electrically powered devices is generally inadequate for industrial application. Because such devices require main electricity for their powering, they are only suitable for using where a mains electricity supply is available, and thus, do not lend themselves to portability.

Gas or oil powered flame blow torches, in general, are required for Industrial Applications. However, such torches suffer from significant disadvantages, since the heated air stream exiting from the torch in many cases also includes the distal end of the flame. Thus, unless an operator is particularly careful in using such torches burning of the material on which the heated stream is being played can result in burning of the material. This is particularly so in cases where such blow torches are used for shrinking sleeves or tubes of plastics material.

U. S. Patent Specification No. 4, 726, 767 discloses a hot air generating device in which the hot air stream is heated by a gas catalytic combustion element which flamelessly converts gas to heat. The device of this U. S. Specification comprises a tubular housing within which at a downstream end the gas catalytic combustion element is located. A fan, which is driven by a battery powered electric motor is located in the tubular housing upstream of the gas catalytic combustion element and passes air around and through the gas catalytic combustion element for heating thereof. Heated air and exhaust gases are delivered through an outlet which may be put to various uses. In this device gas from a liquid gas reservoir in a handle of the device is delivered through a jet and then into a venturi mixer where the gas is mixed with air. The gas/air mixture is delivered through a burner and is initially ignited to burn with a flame for heating the catalytic element to its ignition temperature. A temperature sensor monitors the temperature of the bumer to ascertain when the catalytic element has reached its ignition temperature, at which stage the fan motor is activated for passing air through the tubular housing. A cowling is arrange around the venturi mixer for directing air from the fan into the venturi mixer, for in turn increasing the proportion of air in the gas/air mixture which extinguishes the flame. Flameless combustion of the gas/air mixture continues in the catalytic element.

The device of this U. S. Patent Specification No. 4, 726, 767 suffers from a number of disadvantages. In particular, the unit is relatively unstable, in that it is prone to failure as a result of extinguishing of the catalytic element due to chilling of all or part of the catalytic element as a result of the passage of the fan assisted air through the catalytic element. Fan assisted air is also passed over the outer peripheral surface of the catalytic element, and this can also lead to chilling, and thus extinguishing of

the catalytic element. Even should the catalytic element not extinguish, chilling of any part of the catalytic element results in unbumt fuel gas being exhausted from the device, with the consequent danger of subsequent unprotected flame combustion of the unbumt gas, and also inefficient conversion of fuel gas to heat in the catalytic element. Furthermore, there is little control over the gas/air mixture, since the ratio of air to gas is virtually entirely dependent on the fan, and should the outlet from the device be restricted, the proportion of air in the gas/air mixture being delivered to the catalytic element will vary. Furthermore, variation in the battery energy level, particularly, where the battery is beginning to wear or deteriorate also results in variation in the proportion of air in the gas/air mixture being delivered to the catalytic element. This is entirely undesirable, since it leads to inefficiencies in the conversion of the fuel gas to heat in the catalytic combustion element, and also leads to significant variations in the energy output and temperature of the heated stream from the device, as well as failure.

There is therefore a need for a hot air generating device which overcomes at least some of the problems of prior art devices, and which lends itself to being relatively portable.

The present invention is directed towards providing such a hot air generating device.

According to the invention there is provided a hot air generating device comprising a main housing which defines a hollow interior region, a main air inlet being provided to the hollow interior region, and a main air outlet being provided from the hollow interior region, a gas catalytic combustion element located for heating air passing from the main air inlet through the hollow interior region to the main air outlet, a fuel gas supply means for supplying fuel gas to the gas catalytic combustion element, and an air urging means for urging air from the main air inlet through the hollow interior region for heating thereof and outwardly from the main air outlet for providing a heated air output stream, wherein a heat exchange means is located in the hollow interior region between the main air inlet and the main air outlet and defines with the main housing a heat exchange passageway for accommodating and heating air passing from the main air inlet to the main air outlet, the gas catalytic combustion

element being located for heating the heat exchange means for in turn heating the air passing through the heating exchange passageway.

In one embodiment of the invention the gas catalytic combustion element is located so that exhaust gases from the gas catalytic combustion element are outputted through the main air outlet for mixing with the heated air output stream.

Preferably, the gas catalytic combustion element is located relative to the heat exchange means so that direct contact between the gas catalytic combustion element and the air being heated by the heat exchange means is minimised.

Advantageously, the gas catalytic combustion element is located relative to the heat exchange means so that direct contact between the gas catalytic combustion element and the air being heated by the heat exchange means is avoided for avoiding chilling of the gas catalytic combustion element.

Ideally, the heat exchange means acts as a shield for shielding the gas catalytic combustion element from air being urged by the air urging means through the hollow interior region.

In one embodiment of the invention the heat exchange means defines a combustion chamber within which the gas catalytic combustion element is located.

In one embodiment of the invention the heat exchange means defines an exhaust gas outlet from the combustion chamber for outputting exhaust gases from the combustion chamber into the heated air so that the heated air output stream comprises a mixture of heated air and exhaust gases. Preferably, a fuel gas inlet is provided in the heat exchange means to the combustion chamber for communicating with the gas supply means for receiving fuel gas therefrom.

Preferably, the gas supply means sealably engages the fuel gas inlet.

Advantageously, the main housing comprises a tubular portion which defines a main central axis.

In one embodiment of the invention the heat exchange means comprises an elongated tubular heat exchange housing located in the tubular portion of the main housing, the heat exchange housing defining a secondary central axis which extends parallel to the main central axis, and preferably, the main and secondary central axes defined respectively by the main housing and the heat exchange housing coincide with each other.

Advantageously, the heat exchange passageway extends parallel to the main central axis, and ideally, the heat exchange passageway is of annular shape.

In one embodiment of the invention a plurality of heat exchange fins extend radially from the heat exchange housing into the heat exchange passageway. Preferably, the heat exchange fins are spaced-apart circumferentially around the heat exchange housing. Advantageously, the heat exchange fins are elongated heat exchange fins, and extend parallel to the main central axis.

In one embodiment of the invention the fuel gas supply means comprises a mixing means for mixing air with the fuel gas, the mixing means being located so that the air urging means urging air through the hollow interior region has minimal effect on the air entering the mixing means for mixing with the fuel gas. Preferably, the mixing means is located in the hollow interior region upstream of the heat exchange means, and downstream of the air urging means. Advantageously, the mixing means is shielded from the effect of air being urged by the air urging means through the hollow interior region.

In one embodiment of the invention the mixing means comprises a venturi mixing means having at least one secondary air inlet thereto. Ideally, each secondary air inlet to the venturi mixing means is located within the hollow interior region of the main housing in a position substantially shielded from the air urging means.

In a further embodiment of the invention a communicating means communicating with the mixing means and the combustion chamber delivers the fuel gas/air mixture to the combustion chamber, the communicating means sealably engaging the mixing

means and the combustion chamber for preventing the passage of air being urged by the air urging means into the combustion chamber.

In another embodiment of the invention the air urging means is located upstream of the heat exchange means. Advantageously, the air urging means comprises an air blower. Preferably, the air blower comprises a fan. Ideally, the air blower comprises an axial fan, and preferably, the fan is driven by a motor located downstream of the fan.

In one embodiment of the invention the fan and motor are located co-axially relative to each other, and are located co-axially with the main central axis.

In a further embodiment of the invention a receiving means is provided in the main housing for receiving a portable power source for powering the air urging means.

Preferably, the portable power source is located in the receiving means.

Advantageously, the portable power source comprises at least one electric battery.

Altematively, the portable power source is a thermo-electric generator, adapted to be heated by the heat exchange means.

In one embodiment of the invention the fuel gas supply means comprises a fuel gas reservoir located in the main housing for storing a supply of fuel gas. Preferably, the fuel gas reservoir is rechargeable. Advantageously, the main housing defines a handle, and the fuel gas reservoir is located in the handle, and the handle defines the receiving means for receiving the portable power source.

In one embodiment of the invention a control means is provided for controlling the fuel gas supply means and power to the air urging means.

In another embodiment of the invention a safety cut-out means is provided for isolating the gas catalytic combustion element from the fuel gas supply means for preventing over heating of the device.

Ideally, the safety cut-out means is responsive to the temperature of the heat exchange means exceeding a predetermined temperature.

Additionally or altematively, the safety cut-out means is responsive to the temperature of the main housing exceeding a predetermined temperature, or additionally or alternatively the safety cut-out means is responsive to the air urging means ceasing to urge air, or additionally or alternatively the safety cut-out means is responsive to the temperature of the heated air output stream exceeding a predetermined temperature.

In another embodiment of the invention a temperature regulating means is provided for regulating the temperature of the heated air output stream, the temperature regulating means controlling the fuel gas supply means for controlling the supply of fuel gas to the gas catalytic combustion element.

Preferably, a temperature monitoring means is provided, the temperature regulating being responsive to the temperature monitoring means.

In one embodiment of the invention the temperature monitoring means is provided for monitoring the temperature of the heat exchange means. Additionally or altematively, the temperature monitoring means is provided for monitoring the temperature of the main housing. Additionally or altematively, the temperature monitoring means is provided for monitoring the temperature of the heated air output stream.

In one embodiment of the invention the safety cut-out means is responsive to the temperature monitoring means.

In one embodiment of the invention the temperature monitoring means is a thermo- magnetic monitoring means. Altematively, the temperature monitoring means is a bi- metal monitoring means. Altematively, the temperature monitoring means is a heat sensitive fuse. Altematively, the temperature monitoring means is a bead thermo- couple. Altematively, the temperature monitoring means is a thermistor.

In one embodiment of the invention the device is portable, and preferably, the device is of relatively small size suitable for being hand held.

In one embodiment of the invention the main housing is adapted for receiving a nozzle for communicating with the main air outlet for delivering a heated air output stream.

In another embodiment of the invention the nozzle defines a nozzle outlet shaped to deliver a heated air output stream of a desired transverse cross-section.

Additionally or altematively, the main housing is adapted for receiving a hair treatment attachment for receiving hair to be treated, the hair treatment attachment communicating with the main air outlet for receiving heated air therefrom, and at least one secondary outlet being provided from the hair treatment attachment for outputting heated air to the hair.

In one embodiment of the invention the hair treatment attachment comprises an elongated tubular barrel about which hair to be treated may be wound or engaged for curling or otherwise shaping the hair.

Preferably, a plurality of secondary air outlets are provided from the hair treatment attachment, the secondary air outlets communicating with the main air outlet for delivering a plurality of heated air output streams through the secondary air outlets, and in turn through hair wound onto or engaged on the hair treatment attachment.

Advantageously, the secondary air outlets are located in the tubular barrel at longitudinally and circumferentially spaced-apart intervals, and are arranged for directing the heated air output streams in generally radial directions from the hair treatment attachment.

In another embodiment of the invention the hair treatment attachment is adapted for securing to the main housing with the hair treatment attachment extending parallel to the main central axis of the main housing.

In a further embodiment of the invention the hair treatment attachment is adapted for securing to the main housing so that the hair treatment attachment extends co- axially with the main central axis.

In a still further embodiment of the invention the hair treatment attachment comprises a plurality of radially extending comb like teeth extending therefrom.

Altematively, the main housing terminates in the hair treatment attachment, and preferably, the heat exchange means is located in the hair treatment attachment.

In one embodiment of the invention the hot air generating device is adapted for delivering one or more heated air output streams at a temperature suitable for drying, setting, shaping, curling or otherwise treating hair.

In another embodiment of the invention the hot air generating device is adapted for delivering one or more heated air output streams at a temperature suitable for shrinking a heat shrinkable plastics sleeve, a conduit of plastics material, or for moulding or shaping mouldable plastics material.

In a further embodiment of the invention the hot air generating device is adapted for delivering one or more heated air output streams at a temperature suitable for paint stripping.

The advantages of the invention are many. The hot air generating device according to the invention provides a heated air output stream, which can be maintained at a relatively constant temperature. The hot air generating device operates relatively efficiently, and the gas/air ratio of the gas/air mixture is maintained relatively constant. There is virtually no danger of the gas catalytic combustion element being extinguished during use. By virtue of the fact that the heat exchange means forms the combustion chamber, and the gas catalytic combustion element is located within the combustion chamber, the heat exchange means acts as a shield for shielding the gas catalytic combustion element from the direct affect of air being urged through the heat exchange passageway by the air urging means. Because of this there is little or no danger of the gas catalytic combustion element being chilled by air being urged

through the hollow interior region by the air urging means, and thus, extinguishing of the gas catalytic combustion element as a result of chilling is avoided. Furthermore, by virtue of the fact that the secondary air inlets to the mixing means to which air is drawn into the mixing means for mixing with the fuel gas are also located to be out of the direct influence of the air urging means, the air urging means has little or no affect on the gas/air ratio of the gas/air mixture delivered from the mixing means to the combustion chamber. The gas/air ratio of the gas/air mixture is substantially determined by the rate of flow of fuel gas through the mixing means. Additionally, by virtue of the fact that the secondary air inlets to the mixing means are located to be out of the influence of the air being urged through the hollow interior region by the air urging means, the rate at which the air is being urged through the hollow interior region, and any changes in the rate at which the air is being urged through the hollow interior region by the air urging means has little or no affect on the gas/air ratio of the gas/air mixture. By sealably communicating the mixing means with the combustion chamber any direct affect of the air being urged through the hollow interior region by the air urging means has no affect on the gas catalytic combustion element, and accordingly, the rate at which air is being urged through the main hollow interior region may be varied without affecting flameless combustion of the fuel gas/air mixture in the gas catalytic combustion element.

Furthermore, by virtue of the fact that the combustion chamber is shielded from the air being urged through the hollow interior region by the air urging means any danger of the flame being extinguished when the fuel gas/air mixture is being initially bumed with flame combustion is avoided.

When the hot air generating device is adapted for use as a hair treatment device, a particularly effective and efficient hair treatment device is provided.

The invention will be more clearly understood from the following description of some preferred embodiments thereof which are given by way of example only with reference to the accompanying drawings, in which : Fig. 1 is a schematic cut away perspective view of a hot air generating device according to the invention,

Fig. 2 is a front end elevational view of the device of Fig. 1, Fig. 3 is a rear end elevational view of the device of Fig. 1, Fig. 4 is a partial transverse cross-sectional side elevational view of the device of Fig. 1 on the line IV-IV of Fig. 2, Fig. 5 is a transverse cross-sectional side elevational view of the device of Fig. 1 on the line IV - IV of Fig. 2, Fig. 6 is a perspective view of the hot air generating device of Fig. 1 with a hair treatment attachment mounted thereon, Fig. 7 is a cut away perspective view of the hot air generating device of Fig. 1 with the attachment of Fig. 6 mounted thereon, Fig. 8 is a perspective view of the hot air generating device of Fig. 1 with a different hair treatment attachment mounted thereon, Fig. 9 is a partly cut away perspective view of a hair treatment device according to another embodiment of the invention, and Fig. 10 is a perspective view of a portion of a hot air generating device according to another embodiment of the invention.

Referring to the drawings and initially to Figs. 1 to 5 thereof, there is illustrated a portable hand held gas powered hot air generating device according to the invention which is indicated generally by the reference numeral 1. The hot air generating device is particularly suitable for receiving hair treatment attachments 2a and 2b illustrated in Figs. 6 to 8 for adapting the hot air generating device 1 as a hair treatment device, as will be described below. The hot air generating device 1 comprises a main housing 3 of injection moulded plastics material, or indeed of any other suitable material. The main housing 3 in this embodiment of the invention is a

stepped tubular housing of circular transverse cross-section, which defines a longitudinally extending main central axis 7 which extends longitudinally centrally through the main housing 3. The main housing 3 comprises an upstream portion 5 of greatest diameter which forms a handle 6 of the device 1, a downstream portion 8, and an intermediate portion 9 which joins the upstream portion 5 and downstream portion 8. The main housing 3 defines a hollow interior region 10 of correspondingly stepped transverse circular cross-section. The upstream portion 5 of the main housing 3 terminates in a main air inlet 11 to the hollow interior region 10, and the downstream portion 8 terminates in a main air outlet 12 from which a heated air stream is delivered from the hollow interior region 10.

A heat exchange means, namely, a heat exchanger 15 for heating air for outputting through the main outlet 12 is co-axially located in a portion of the hollow interior region 10 defined by the downstream portion 8 of the main housing 3. The heat exchanger 15 defines with the downstream portion 8 of the main housing 3 an annular heat exchange passageway 17 through which air from the air inlet 11 is urged to the main air outlet 12 for heating thereof. An air urging means, namely, an axial flow fan 18 is located in the hollow interior region 10 formed by the intermediate portion 9 for drawing air through the main air inlet 11 for in turn urging the air through the heat exchange passageway 17, and thus through the main air outlet 12 for delivering a heated air output stream from the main air outlet 12. An electrically powered variable speed motor 19 also located in the hollow interior region 10 defined by the intermediate portion 9 powers the fan 18. The motor 19 and the fan 18 are axially aligned and define a common central axis which coincides with the main central axis 7. A power source for powering the motor 19 comprises four rechargeable electric batteries 20 which are located at equi-spaced-apart intervals circumferentially within the hollow interior region 10 defined by the upstream portion 5. The powering of the motor 19 by the batteries 20 is described below. A battery charging connection (not shown) and a battery charge control electrical circuit (also not shown) are provided in the handle 6 for facilitating connection to a mains electricity supply for recharging the batteries 20.

The heat exchanger 15 is formed by an elongated tubular member of aluminium material of circular transverse cross-section which defines a secondary central axis

21 which coincides with the main central axis 7. The heat exchanger 15 defines a co-axial elongated combustion chamber 25 of circular transverse cross-section having an upstream fuel gas inlet 26 and a downstream exhaust outlet 27 through which exhaust gases 27 are delivered to the main air outlet 12 for mixing with the heated air output stream issuing therefrom. A gas catalytic combustion element 29 for converting a fuel gas/air mixture to heat by flameless combustion is located in the combustion chamber 12 and is formed by an appropriate carrier appropriately coated with a precious metal. The carrier is formed into a tubular shape of circular transverse cross-section which is co-axial with the main central axis 7.

Longitudinally extending circumferentially equi-spaced-apart heat exchange fins 28 extend radially from the heat exchanger 15 into the heat exchange passageway 17 for enhancing heat exchange between the heat exchanger 15 and air passing through the passageway 17.

A fuel gas supply means for supplying fuel gas to the combustion chamber 25 comprises a fuel gas source, namely, a rechargeable fuel gas reservoir 30 located in the hollow interior region 10 formed by the upstream portion 5 of the main housing 3.

The reservoir 30 is co-axially located with the main central axis 7, and defines with the main housing 3 a receiving means, namely, an annular receiving area 31 for receiving the batteries 20. A charging valve 31 is located in the end of the reservoir 30 adjacent to the main air inlet 11 for re-charging the reservoir 30 with liquid fuel gas. A fuel gas supply pipe 33, a portion only of which is illustrated in Figs. 1, 4 and 5 supplies fuel gas from the reservoir 30 to a gas jet 34, which in turn delivers fuel gas in gaseous form into a mixing means, namely, a venturi mixer 35 where the fuel gas is mixed with air. Secondary air inlets, namely, four air inlet ports 36 are located equi-spaced circumferentially around the venturi mixer 35 for accommodating air into the venturi mixer 35. The fuel gas/air mixture is delivered from the venturi mixer 35 to a bumer unit 38 located in the fuel gas inlet 26 to the combustion chamber 25.

An ignition means, namely, a pair of electrodes 37 and 39 define a spark gap 40 for igniting the fuel gas/air mixture exiting from the bumer 38 to initially bum with a flame in the combustion chamber 25 adjacent the catalytic combustion element 29 for raising the temperature of the catalytic combustion element 29 to its ignition temperature. The bumer 38 and the catalytic combustion element 29 are located

relative to each other so that the flame plays on the upstream end of the catalytic combustion element 29 for raising the catalytic element to its ignition temperature.

The positional relationship between the catalytic combustion element 29 and the burner 38 is such that when the upstream end of the catalytic combustion element 29 reaches its ignition temperature it commences to convert the fuel gas/air mixture to heat by flameless combustion, thereby starving the flame of fuel gas for extinguishing the flame. As the upstream end of the gas catalytic combustion element 29 reaches its ignition temperature and commences to convert the fuel gas/air mixture to heat, the temperature of the remainder of the gas catalytic combustion element 29 rapidly reaches the ignition temperature, so that the entire catalytic combustion element 29 converts the fuel gas/air mixture to heat by flameless combustion. Alternative means for extinguishing the flame when the upstream end of the gas catalytic combustion element 29 has reached its ignition temperature may be provided. Such flame extinguishing means will be well known to those skilled in the art.

A piezo electric element (not shown) is located in the hollow interior region 10 formed by the upstream portion 5 of the housing 3 for providing a high voltage to the electrodes 37 and 39 for in turn generating a spark across the spark gap 40. One terminal of the piezo electric element (not shown) is electrically connected to the electrode 37, while the other terminal (also not shown) of the piezo electric element is electrically connected to the other electrode 39. Operation of the piezo electric element and the fuel gas supply from the reservoir 30 to the gas jet 34 will be described in more detail below.

A temperature monitoring means provided by a thermo-magnetic sensor and regulator valve 45 is associated with and in contact with the heat exchanger 15 for monitoring the temperature of the heat exchanger 15. Although not illustrated the fuel gas supply from the reservoir 30 through the fuel gas supply pipe 33 to the gas jet 34 is passed through the thermo-magnetic sensor 45 for controlling the flow of fuel gas to the gas jet 34, for in turn controlling the temperature of the heat exchanger 15, and in turn the temperature of the heated air output stream from the main air outlet 12. The thermo-magnetic sensor 45 is not described or illustrated in

detail, however, such a thermo-magnetic sensor and regulator valve is disclosed in PCT Published Application Specification No. WO-A-95/09712.

In this embodiment of the invention as well as controlling the flow of fuel gas for maintaining the heat exchanger 15 at a predetermined desired temperature, the thermo-magnetic sensor and regulator valve 45 also acts as an over temperature safety cut-out means. In other words, should the temperature of the heat exchanger 15 exceed a predetermined safe operating temperature the thermo-magnetic sensor and regulator valve 45 is arrange to isolate the gas jet 34 from the reservoir 30. It will of course be appreciated that the thermo-magnetic sensor and regulator valve 45 in certain cases may be provided to act only as an over temperature safety cut-out, and would have no temperature regulating function for regulating the temperature of the heat exchanger 15.

A thumb operated slider switch (not shown) is located in the handle 6 for operating a fuel gas supply valve (not shown) located in the fuel supply pipe 33 between the reservoir 30 and the gas jet 34. In this embodiment of the invention the fuel gas supply valve is located intermediate the reservoir 30 and the thermo-magnetic sensor and regulator valve 45. As well as operating the fuel gas supply valve (not shown) the thumb operated slider switch also operates the piezo electric element (not shown) for developing a spark across the spark gap 40. Such a thumb switch will be well known to those skilled in the art, and typically, is of the type disclosed in Published PCT Application Specification No. WO-A-97/38265. Briefly, the thumb switch operates the fuel gas supply valve (not shown) and the piezo electric element sequentially so that fuel gas/air mixture delivered to the bumer 38 is exiting from the burner 38 before the spark is developed across the spark gap 40 for ignition thereof.

Additionally, Published PCT Application Specification No. WO-A-97/38265 also illustrates and describes the arrangement of a gas catalytic combustion element relative to a burner for providing flame ignition for raising the temperature of the gas catalytic combustion element to its ignition temperature, and subsequently extinguishing the flame as a result of starvation of the flame of fuel gas/air mixture as the gas catalytic combustion element 29 reaches its ignition temperature.

The batteries 20 are electrically connected to the electric motor 19 of the fan 18 through an on/off switch (not shown) which is also operable by the thumb operated slider switch (not shown) in the handle 6. Accordingly, as the thumb switch is being urged for opening the fuel supply valve the electric on/off switch (not shown) is closed for supplying electric power to the motor 19. The motor 19 is operable at a plurality of selectable speeds for driving the fan 18 at different speeds. A speed selector knob (not shown) provided on the handle 6 controls the speed of the motor 19, and in tum, that of the fan 18.

In order to minimise contact between the catalytic element 29 and the air being urged through the hollow interior region 10 by the fan 18, the venturi mixer 35 is located just downstream of the motor 19, and is effectively shielded by the motor 19, and is thus in the lee of the motor 19. Thus, air which is mixed with fuel gas in the venturi mixer 35 is drawn into the venturi mixer 35 through the air inlet ports 36 almost solely by the venturi effect of the gas issuing from the gas jet 34 through the venturi mixer 35. The fan 18 plays virtually no part in urging air into the venturi mixer 35 through the air inlet ports 36. Thus, there is little or no forcing effect of air through the air inlet ports 36 by the action of the fan 18. In this way the fuel gas/air ratio of the fuel gas/air mixture is maintained substantially constant for all operating conditions of the device, and for all operating conditions and all operating speeds of the fan 18.

Furthermore, to further minimise contact between the catalytic element 29 and the air being urged through the hollow interior region 10 by the fan 18 the fuel gas/air mixture is delivered from the venturi mixer 35 to the bumer 38 through a tube 46 which sealably engages the venturi mixer 35 and the bumer 38. The bumer 38 sealably engages the fuel gas inlet 26 to the combustion chamber 35, thereby preventing the ingress of air into the combustion chamber 25 directly from the hollow interior region 10. Accordingly, the only air which enters the combustion chamber 25 and comes in contact with the gas catalytic combustion element 29 is that which is drawn into the venturi mixer 35 through the air inlet ports 36 by the action of the fuel gas issuing from the gas jet 34.

Thus, as discussed above the fuel gas/air ratio of the fuel gas/air mixture is maintained substantially constant for all operating conditions of the device 1 and for all operating conditions and speeds of the fan 18.

Since the heat exchanger 15 forms the combustion chamber 25 and the gas catalytic combustion element 29 is located within the combustion chamber, the heat exchanger 15 acts as a shield for shielding the gas catalytic combustion element 29 from air being urged by the fan 18 through the heat exchange passageway 17. This ensures that the air passing through the heat exchange passageway 17 is isolated from the gas catalytic combustion element 29, and has no affect on the fuel/gas ratio of the fuel/gas air mixture in the combustion chamber 25, or on the efficiency of flameless combustion of the fuel gas/air mixture by the gas catalytic combustion element 29. Furthermore, by acting as a shield for shielding the gas catalytic combustion element 29 from the air passing through the heat exchange passageway 17 this air can have no chilling effect on the gas catalytic combustion element, and thus, there is no danger of inadvertent extinguishing the gas catalytic combustion element 29 during flameless combustion. Additionally, there is no danger of the flame being extinguished when the fuel gas/air mixture is being combusted initially by flame combustion. Thus, the catalytic combustion element 29 operates at a substantially constant efficient conversion rate for converting the fuel gas/air mixture to heat.

Additionally, not only is the fuel gas/air ratio of the fuel gas/air mixture maintained substantially constant during flameless combustion in the gas catalytic combustion element 29, but the fuel gas/air ratio of the fuel gas/air mixture is also maintained substantially constant during flame combustion of the fuel gas/air mixture.

Furthermore, there is no danger of air which is being urged through the hollow interior region 10 by the fan 18 extinguishing the flame during flame combustion, and thus, the flame is only extinguished as a result of the gas catalytic combustion element 29 reaching its ignition temperature. This, thus, avoids faulty starting and ignition of the device. Additionally, the fan 18 can operate during flame combustion.

Referring now to Figs. 6 to 8 the hair treatment attachments 2a and 2b will now be described. The hair treatment attachment 2a of Figs. 6 and 7 is adapted for

releasably securing to the downstream portion 8 of the main housing 3 or may be integrally formed with the main housing 3, for adapting the device 1 as a hair treatment device. The attachment 2a is formed by an elongated barrel 51 of circular transverse cross-section which is closed by an end cap 52 at one end thereof. A plurality of longitudinally and circumferentially spaced-apart comb like teeth 53 extend from the barrel 51 for facilitating combing the hair and winding the hair onto the barrel 51 as the attachment 2a and device 1 is rotated by hand. An open end 55 of the barrel 51 communicates with the main air outlet 12 for receiving the heated air stream. A plurality of secondary air outlets 54 which are spaced-apart longitudinally and circumferentially along and around the barrel 51 output the heated air radially from the barrel 51 for treating the hair wound onto or engaged by the barrel 51 for curling, shaping or otherwise treating the hair. A releasable securing means (not shown) is provided on the downstream portion 8 of the main housing 3 for releasably securing the attachment 2a to the downstream portion 8 of the main housing 3 adjacent the main air outlet 12.

The attachment 2b illustrated in Fig. 8 is a hair curling attachment, and comprises a barrel 61 which is substantially similar to the barrel 51 of the attachment 2a. The barrel 61 is closed at one end by an end cap 62, and is open at the other end 63 for receiving the heated air stream from the main air outlet 12. The releasable securing means (not shown) on the main housing 3 secures the attachment 2b to the lower portion 8 of the main housing 3 adjacent the main outlet 12. A plurality of secondary air outlets 64 similar to the air outlets 54 of the attachment 2a are spaced apart longitudinally and circumferentially along and around the barrel 61 for delivering air through hair wrapped around the barrel 61. A clip 66 is pivotally connected at 67 to the barrel 61 for retaining hair wound around the barrel 61. A handle 68 extending from the clip 66 facilitates manual pivoting of the clip 66. The arrangement of such clips on hair curling barrels of hair treatment devices will be known to those skilled in the art.

In use, when the thumb operated slider switch (not shown) is operated for opening the fuel gas supply valve (not shown), closing the electric switch (not shown) for powering the motor 19 from the batteries 20 and for operating the piezo electric element (also not shown) for providing a spark across the spark gap 40, fuel gas/air

mixture is delivered from the bumer 38 which is ignited by the spark across the spark gap 40 to bum with a flame. The electric motor 19 is powered for rotating the fan 18.

As the gas catalytic combustion element 29 reaches its ignition temperature, the fuel gas/air mixture is converted to heat by flameless combustion, thus starving the flame of fuel gas/air mixture which rapidly extinguishes. Thereafter flameless combustion continues in the gas catalytic combustion element 29. The desired speed of the fan is selected by the speed control knob (also not shown).

Air is drawn by the fan 18 through the main air inlet 11 past the reservoir 30 and the batteries 20, and in turn is delivered through the heat exchange passageway 17, where it is heated by the heat exchanger 15. The heated air is then delivered through the main air outlet 12 into the attachment 2. As the heated air is passing through the main air outlet 12 hot exhaust gases from the exhaust outlet 27 are mixed with the heated air, thereby further raising the temperature of the heated air to a desired temperature. The mixture of heated air and exhaust gases is then passed through the secondary air outlets 54 in the barrel 51 for treating the hair as desired.

The device 1 may also be used as a hair dryer, in which case, it would be used typically without the attachments 2a and 2b. However, it is envisaged that various different shaped nozzles may be provided for providing air streams of different transverse cross-section which would be suitable for attaching to the main outlet 12 for directing the heated air stream at the hair.

The heat output of the heat exchanger 15 and the air handling capacity of the fan 18 are selected for providing a heated air output which includes the exhaust gases which is at a temperature suitable for treating or drying hair. This requires selecting the gas catalytic combustion element 29 to be of the appropriate size and selecting the fuel supply valve (not shown) to be of the appropriate size for delivering the appropriate amount of fuel gas to the gas jet 34.

Accordingly, when the gas catalytic combustion element 29, the fuel supply valve (not shown) and the fan capacity are appropriately selected, the thermo-magnetic sensor and regulator valve 45, in general, is only required to act as an over temperature safety cut-out for isolating the gas jet 34 from the reservoir 30 in the

event of an over temperature condition occurring. An over temperature condition of the device could arise, for example, as a result of insufficient power in the batteries 20 for driving the motor 19 for powering the fan 18, in which case, the air throughput past the heat exchanger 15 would rapidly drop off, thereby allowing the heat exchanger 15 to overheat.

Referring now to Fig. 9 there is illustrated a hot air generating device according to another embodiment of the invention, which in this case is indicated generally by the reference numeral 70, and which is also suitable for use as a hair treatment device.

The device 70 is substantially similar to the device 1, and similar components are identified by the same reference numerals. In the device 70 a barrel 71 forms the hair treatment part of the device 70 and is integrally formed with the main housing 3.

The heat exchanger 15 is located in the barrel 71, and thus, the barrel 71 effectively forms the downstream portion 8 of the housing 3. The barrel 71 is substantially similar to the barrel 51 of the hair treatment attachment 2a, and similar components are identified by the same reference numerals. In this embodiment of the invention air passing through the heat exchange passageway 17 is heated and in turn outputted through the secondary air outlets 54.

In this embodiment of the invention the gas catalytic combustion element 29 terminates at 73 in the combustion chamber 25. The electrodes 37 and 39 extend to a position just beyond the end 73 of the gas catalytic combustion element 29 for initially igniting the fuel gas/air mixture to bum in a flame between the end 73 of the gas catalytic combustion element 29 and the exhaust gas outlet 27 for initial flame combustion of the fuel gas/air mixture. A perforated end cap 74 of gauze material extends across the exhaust gas outlet 27 for retaining the flame within the combustion chamber 25 during initial flame combustion of the fuel gas/air mixture.

Additionally, the gas catalytic combustion element 29 is formed for causing the flame to bum in the combustion chamber between the end 73 of the gas catalytic combustion element 29 and the gauze end cap 74. For example, the gas catalytic combustion element 29 instead of being of cylindrical shape may be spiral wound.

Accordingly, on initial ignition of the fuel gas/air mixture to bum with flame combustion, the flame is retained in the combustion chamber 25 between the end 73 of the gas catalytic combustion element 29 and the gauze end cap 74. The root of

the flame heats the end 73 of the gas catalytic combustion element 29 to its ignition temperature, which commences to convert the fuel gas/air mixture to heat, and as the remainder of the gas catalytic combustion element 29 reaches the ignition temperature, thus converting the fuel gas/air mixture to heat, the flame is starved of fuel gas/air mixture and thus extinguished. Flameless combustion thus continues in the gas catalytic combustion element 29 converting the fuel gas/air mixture to heat.

The thenno-magneticsensor and regulator valve 45 instead of being mounted directly on the heat exchanger 15, in this embodiment of the invention extends from the housing of the gas jet 34 and extends upstream therefrom. The sensor and regulator valve 45 is located in line with the venturi mixer 35 and the fuel gas supply pipe 33, for controlling the supply of fuel gas from the reservoir 30 to the venturi mixer 35 in response to the temperature of the heat exchanger 15. The bumer 38, the communicating tube 46 and the venturi mixer 35, as well as the housing of the thermo-magnetic sensor and regulator valve 45 are of brass material and are in heat conductive engagement with the heat exchanger 15. Accordingly, the temperature being monitored by the thermo-magnetic sensor and regulator valve 45 is substantially similar to the temperature of the heat exchanger 15, and any slight temperature drop can be taken account of in the construction and setting of the thermo-magnetic sensor and regulator valve 45.

Otherwise, the hair treatment device 70 is substantially similar to the hot air generating device 1 when adapted with the hair treatment attachment to A.

Referring now to Fig. 10 there is illustrated an alternative construction of reservoir 30 for use with the hot air generating devices 1 and 70. In this embodiment of the invention four equi-spaced recesses 80 are formed in the reservoir 80 for forming a part of the receiving area for receiving the four batteries 20. By forming the recesses 80 in the reservoir the outer diameter of the handle 6 may be reduced. The reservoir 30 is located in the hollow interior region with its end 81 adjacent the main air inlet 11.

It is envisaged that the hot air generating device 1 as well as being provided as a hair treatment device may be provided for supplying a heated air output suitable for

shrinking, plastics sleeve of the type typically used for insulating and protecting wire joints and multi-core cable joints, and/or for shrinking conduit of plastics material, typically of the type which is used for water or other liquids or gases. The heated air stream could also be used for moulding a mouldable plastics material, or for heat welding plastics materials. In which case, the device 1 may be operated without any attachment, and the heated air output mixed with the exhaust gases delivered through the main air outlet 12 would be played directly on the plastics material to be shrunk, moulded or otherwise treated. In which case, in general, the temperature of the heated air output required would be significantly higher than that required for treating or drying hair, and accordingly, the catalytic combustion element 29 and the fuel gas supply valve (not shown) would be sized for providing a higher heat and temperature output from the main air outlet 12. Additionally, should a higher air flow be required, a fan 18 of the appropriate capacity would also be provided. In the event of the device 1 being provided as an industrial unit, it is envisaged that various attachments may be provided, for example, different shape nozzle attachments for attaching to the downstream portion 8 of the housing 5 adjacent to air outlet 12 for directing the heated air output stream and shaping and providing the heated air output stream with a desired transverse cross-section.

It is also envisaged that the hot air generating device according to the invention may be used for paint stripping, and indeed, for many other industrial purposes.

While the operation of the fuel gas supply valve, the piezo electric element and the fan motor have been described as being controlled by a single thumb operated slider switch, any other suitable switching arrangement may be provided, for example, a toggle switch, a rotary switch or the like. It is also envisaged that each of the functions, namely, the fuel gas supply, the piezo electric element and the fan motor may be independently operable by separate switches.

It is also envisaged that a pressure regulator may be located in the air supply pipe 33 for regulating the pressure of the fuel gas from the fuel gas reservoir 30. A suitable control knob would be provided on the handle for operating the pressure regulator.

It is also envisaged that a wire gauze or other device may be provided at the end of the exhaust gas outlet from the combustion chamber of the device of Figs. 1 to 8 for preventing reignition of unbumt gases due to any slippage in the catalytic element.

Further, it is envisaged that instead of the heat exchange means being longitudinally oriented in the main housing, the heat exchange means may be transversely oriented. Furthermore, it is envisaged that instead of a single bumer unit, two or more bumer units could be provided for supplying fuel gas/air mixture to the catalytic combustion element, and in which case, the gas from each bumer may be initially ignited to bum with the flame for raising the catalytic combustion element to its ignition temperature, and in some cases, the fuel gas/air mixture from only one or some of the bumers may be ignited to bum with a flame for raising the temperature of the catalytic combustion element to its ignition temperature. Furthermore, it is envisaged that a plurality of combustion chambers may be provided, each comprising a catalytic combustion element, and a burner for delivering fuel gas/air mixture to the catalytic combustion element. The heat exchange means would be appropriately arrange around each or all of the combustion chambers for heating the air driven by the fan or other such urging means. In other cases, it is envisaged that each combustion chamber may be defined by a separate heat exchange means.

While the heat generating devices according to the invention have been described as having a main air outlet located adjacent the exhaust gas outlet of the combustion chamber, it is envisaged that the main air outlet and the exhaust outlet need not be located close together. Indeed, it is envisaged that the exhaust outlet may be located to direct exhaust gases from the combustion chamber away from the heated air stream issuing through the main air outlet so that the exhaust gases would be separated and segregated from the air stream, and the heated air stream would issue without exhaust gases mixed therewith.