A VAPORISER

Abstract: In a vaporiser a flat horizontal heating element has 1 - 5 mm of fluid maintained above it to provide good vapour generation.

Description: A VAPORISER DESCRIPTION OF INVENTION THE PRESENT INVENTION relates to a vaporiser such as, for example, a vaporiser intended to generate artificial fog or mist for use in a theatre, nightclub or similar location. However, it is to be understood that the invention also relates to other forms of vaporiser such as vaporisers intended to generate a fog or mist used as a security device to hamper burglars or intruders and devices to generate a vapour or suspension of plant nutrients, or pesticides or the like for use in a greenhouse or other confined agricultural environment. Many vaporisers, especially "fog machines", as used in theatres and nightclubs, are difficult to make and are expensive to operate. A typical vaporiser in the form of a "fog machine" for use in a theatre or the like comprises an aluminium block which has a copper or stainless steel tube passing through it forming a channel or conduit for fluid that is to be vaporised to form the "fog". The tube is typically in the form of a coil extending through the block. The block is provided with a heater and an associated thermostat which is adapted to heat the block to a high temperature, which may typically be 290° centigrade. The block is thermally insulated with an outer insulation layer which is formed of rock wool or fibreglass. A pump is provided to pump the fluid to be vaporised through the conduit that passes through the block. In use of the "fog machine" the block is initially heated to the desired temperature, and subsequently, when "fog" is to be generated, the pump is utilised to pump an appropriate fluid through the conduit. The fluid is evaporated rapidly, since the block of aluminium comprises a thermal reservoir of heat which is available to vaporise the fluid. This typical "fog machine" exhibits various disadvantages. The machine is relatively bulky, since the aluminium block is of a substantial size. The machine typically has a steel framework and casing. The machine is thus bulky and heavy, which can lead to high transportation and handling costs. In manufacturing the machine it is necessary to apply the rock wool or fibreglass insulation to the aluminium block. This necessitates the use of masks and gloves by the workforce due to the nature of the rock wool or fibreglass. Even with the aluminium block insulated, electric power is consumed almost continually as the block is maintained, at its high temperature, under the control of a thermostat. Since the block is always hot, the device gives off a substantial amount of heat. This means that a substantial amount of electric power is used to operate the device, and also means that the temperature of the environment around the "fog machine" when it is in use, rises substantially. A further disadvantage, especially where the "fog machine" is being used in a theatre, is that the pump, when it is activated, makes a certain amount of noise which is undesirable. Also, when the fluid that is to be vaporised, which is relatively cool, passes through the copper or stainless steel tube, which is very hot, there is an extremely rapid initial vaporisation which can cause a relatively loud noise or "whoosh". It has been found that there is a tendency for the copper or stainless steel tube to become clogged with deposits from impurities in the chemicals or hardness in the water used to make the fluid to be vaporised. This cannot easily be removed. When the prior proposed machine is initially switched on it may take three minutes or more before the block is hot enough for fog to be generated. After the machine is switched off it may take several hours for the block to cool down. Thus, service engineers may have to wait several hours before carrying out maintenance or repair tasks if they are not going to risk being burnt. Should the thermostat fail, there is a risk that the block may be heated to a temperature at which the aluminium forming the block melts. This would represent a very substantial fire risk in addition to being extremely inconvenient. The present invention seeks to provide a vaporiser in which the disadvantages of the prior proposed "fog machine" as outlined above, are obviated or reduced. According to this invention there is provided a vaporiser, the vaporiser comprising a housing defining a chamber, the chamber being adapted to contain a liquid to be evaporated, the chamber containing a heater, the heater having an element defining an upper surface, means being provided for maintaining the relative positions of the said element and the surface of liquid within the chamber such that there is a predetermined depth of liquid above at least part of the said element, that depth of liquid being in the range of 1-5 millimetres, the heater being adapted to heat the said liquid above the said element. Preferably the said element is fixed in position, and means are provided always to maintain a predetermined level of liquid within the chamber, the level of liquid being such that said predetermined depth of liquid is established above the said element. In one embodiment the means to maintain the level of liquid within the chamber comprise means adapted to receive a reservoir containing fluid, the reservoir being provided with a release valve, and means provided on the housing adapted to actuate the release valve when the reservoir has been introduced to the housing through the aperture, the release valve being so positioned that liquid will flow from the reservoir until the level of liquid within the chamber reaches the level of the release valve, the level of liquid in the chamber above the heater then having the said depth. Alternatively the means to maintain the level of liquid within the chamber comprise a ball valve. In a further embodiment the said element is present on a floating structure, the floating structure being so configured that the said element is located at the predetermined depth beneath the surface of the liquid in which the floating structure is floating. Preferably the depth of liquid above the said element is in the range of 1-2 millimetres. Conveniently where in the upper surface of the said element is substantially planar. Alternatively the upper surface of the said element is arcuate in section. In one embodiment wherein the upper surface of the said element is provided with projections. Conveniently the said element is provided with means which heat the element, the heat thus being transferred to the liquid. Preferably the said element comprises a laminate consisting of a supporting substrate, an electrically conductive layer and an insulating over-layer. Conveniently the substrate comprises silica, the electrically conductive layer comprises an etched layer of metal and the insulating layer comprises a layer of glass. In an alternative embodiment the said element comprises a susceptor to microwave energy, means being provided to supply microwave energy to the heater. Alternatively, the said element is adapted to be inductively heated by an electro-magnetic field, means being provided to supply an electro-magnetic field to the said element. In a further alternative embodiment the element is associated with means which direct infra-red radiation on to the element to heat the element. The heater may incorporate means to direct infra¬ red radiation on to the liquid which is above the said element to heat the liquid. Also, the heater may incorporate means to direct micro-wave radiation on to the liquid which is above said element to heat the liquid. The vaporiser may be provided with fan means to discharge vapour from the housing. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a sectional view, with parts cut away, of one embodiment of the invention (the various parts are not shown to scale) , FIGURE 2 is a sectional view, with parts cut away, of another embodiment of the invention, FIGURE 3 is a sectional view of a component of a further embodiment of the invention, and FIGURE 4 is a sectional view illustrating a modification that may be effected to embodiments of the invention, and FIGURE 5 is a sectional view corresponding to Figure 1, of an alternate embodiment of the invention. Referring initially to Figure 1 of the accompanying drawings, a vaporiser 1 is illustrated in the form of a "fog machine" for generating fog. The fog machine comprises a housing 2 which may be injection moulded from a plastics material. The housing 2 comprises an upper cover 3 which has formed within it a circular aperture 4 surrounded by an upstanding flange 5. The aperture 4 provides access to a cavity 6 formed within the upper part of the housing. Beneath the aperture 4 the lower part of the cavity 6 is defined by a platform 7, the platform 7 having a small upwardly directed protrusion 8 formed at a position which is located on the axis of the aperture 4. The upper surface of the platform 7 is substantially horizontal, but at a position adjacent the periphery of the aperture 4, there is a downwardly directed ramp 9 which extends to a lower level or stage 10. Mounted in a position substantially co-planar with the stage 10 is the upper surface of a substantially planar element 11. The element 11 comprises a lower substrate 12 formed of silica or the like, on which is formed, by a plating and subsequent etching technique, a track 13 of metal, such as platinum, or an alloy such as nickel/chrome or nickel/chrome/copper, which has a predetermined electrical resistance. The track 13 is covered by a thin laminated layer 14 of electrically resistive material, such as glass, which is capable of transmitting heat. The element 11 has a planar upper surface. The element 11 is held in position with appropriate seals 15 and effectively forms the floor of a substantial part of the chamber 6. In one end wall 16 of the housing a slot 17 is formed providing communication from the interior of the chamber 6 to the atmosphere adjacent the "fog machine". The housing 2 defines a lower chamber 18 which is located beneath the upper chamber 6. Within the lower chamber 18 there is provided appropriate electric circuitry 19 adapted, when the "fog machine" is activated, to supply electric power to the resistive track 13, to cause the heater 11 to provide heat. It is to be appreciated that the aperture 4 is dimensioned to receive snugly a bottle 20 which contains a fluid that is to be vaporised. The bottle 20 is provided, at one end, with a screw cap 21 which is secured to a threaded neck provided on the bottle in a conventional manner. The cap 21 is provided with a spring biassed closure valve 22 which normally seals an aperture formed at a central position within the lid 21, with part of the valve projecting through the aperture. It is to be appreciated that the arrangement is such that when the bottle 20 is inverted, the cap may be lowered through the aperture 4 until the valve 22 engages the projection 8 formed on the upper surface of the platform 7. When the bottle is in this position, a substantial seal is created between the exterior of the bottle and the Upstanding flange 5. If appropriate, a sealing ring may be provided on the inner surface of the flange 5 or some other appropriate technique may be utilised to establish a substantial seal. Also, it is to be appreciated that when the bottle is in this position, the valve 22 will be moved inwardly against the spring bias applied to the valve, thus opening the aperture formed in the lid 21. Fluid from within the bottle will thus flow through the aperture formed in the lid 8 on to the upper surface of the platform 7 and will consequently flow down the ramp 9 on to the lower stage 10 and across the upper surface of the heater element 11. When the level of liquid within the upper chamber 6 is such that the upper surface of the fluid contacts the lower surface of the cap 21, no more fluid will flow into the chamber 6. Consequently, there is, when the "fog machine" is in this condition, a predetermined- depth of liquid always present above the heater element 11. The depth of liquid is determined by the vertical distance between the under- surface of the cap 21 and the upper surface of the heater element 11. This vertical distance may be selected to be of the order of 1 to 5 millimetres, but is preferably selected to be of the order of 1 to 2 millimetres. When the apparatus is in this condition, the apparatus is ready for use. When "fog" is to be generated, electrical current is supplied to the resistive track 13 on the heater element 11. The heater element 11 has a very low thermal capacity. In this regard it is to be noted that in the drawing, the thickness of both the silica substrate 12 and the upper glass layer 14 is significantly increased for the sake of clarity of illustration. Consequently, the heater element 11 rapidly reaches a temperature of 290° C or more. The heater element 11 presents a relatively large surface area which is covered by a very thin layer of liquid to be evaporated, that liquid typically having a thickness of 1 to 2 millimetres. The liquid is thus very rapidly evaporated to form a vapour. Because the heater element 11 is initially cool, there is no noise generated by a sudden vaporisation caused by a cool liquid impinging on a very hot surface. The cool liquid above the heater is heated as the heater becomes effective, and a vapour is created. The vapour forms the "fog" that is to be generated. Pressure within the upper chamber 6 rises and a stream of "fog" is thus ejected through the aperture 17. The dimension and velocity of the stream of "fog" may be selected to have desired parameters by appropriately designing the size and shape of the aperture 17. As the layer of liquid which was initially present over the heater element 11 is evaporated, the level of liquid within the chamber 6 begins to fall, permitting further liquid to flow from the inverted bottle 20. Thus, the level of liquid within the chamber is always maintained substantially constant, and thus a substantially predetermined depth of liquid is maintained above the heater element 11. It is to be appreciated that the described machine presents various advantages compared with the prior- proposed "fog machine" described previously. There is no aluminium block which is maintained at a high temperature, which requires the provision of fibreglass or rock wool insulation. There is no pump, and no fan, meaning that the machine can operate in a substantially silent manner. The machine may be made to be relatively small, and the outer part of the casing may be designed to have any appropriate appearance. The machine may be light and compact, leading to low transportation costs. The machine will only consume electric power when fog is being generated, leading to low power consumption. There is no aluminium block, meaning that there is no risk of melt-down, and the entire machine will return to a cool state, to enable service engineers to work safely on the machine, within a few minutes. Referring now to Figure 2 of the accompanying drawings, a modified embodiment of the invention is illustrated. In this embodiment of the invention, the housing 1 again defines an upper chamber 6, the lower part of which is defined by a heater 11 as in the embodiment of Figure 1. A bottle 20 of liquid to be vaporised is provided which is connected, by means of a conduit 30 to a ball valve 31 provided within the chamber 6. A length of pipe 32 may extend downwardly from the ball, valve 31 to a point adjacent the base of a "well" 33 formed at the end of the chamber 6, so that the ball valve can supply liquid in a silent manner. When the machine is to be used, the ball valve operates to establish a level of liquid within the chamber 6, that level of liquid being such that a predetermined thickness or depth of liquid is present above the heater element 11. The embodiment of Figure 2 possesses substantially the same advantages as the embodiment of Figure 1. In the embodiments of Figure 1 and 2, the design of the housing is such that a substantially predetermined depth of liquid or fluid is maintained over the heater element 11. In a modified embodiment of the invention, the heater is formed as part of a floating structure, the design of the floating structure being such that the heater is located a predetermined depth beneath the surface of the liquid in which the floating structure is actually floating. Figure 3 illustrates a floating structure of this type. The structure comprises a supporting component 35 formed of a thermally insulating material, having a heater element 11 located adjacent the upper surface. The supporting structure 35 is connected, by connecting arms 36 to two hollow floats 37. The floating structure is so designed that when floated on an appropriate liquid, the floating structure floats with the upper surface of the heater element 11 a predetermined distance beneath the surface of the liquid. When electric power is provided to the heater element 11, the heater element 11 heats the liquid immediately above the element, causing that liquid to evaporate, but further amounts of liquid will flow inwardly from the sides of the heater towards the centre of the heater element, to ensure that the heater element is always heating liquid and creating vapour. A floating structure, of Figure 3, would be utilised within a housing defining a chamber which contains the liquid, and which defines an outlet aperture, such as the aperture 17 of the embodiment of Figure 1, through which the "fog" created will emerge. Any appropriate technique may be utilised to maintain a quantity of liquid to be evaporated within the chamber. Whilst, in the embodiments described above, the heater element 11 has been described as being substantially planar, it is to be appreciated that the heater element 11 may not be planar, but may have a non-planar upper surface. Figure 4 illustrates a heater element 41 in cross- section, the upper surface of the heater element not being planar, but instead, being arcuate. The heater element is illustrated as being located beneath the surface 42 of a liquid to be evaporated. The support for the heater element 41 is not shown, since a heater of this type may be used in the embodiment of Figure 1, in the embodiment of Figure 2 or in the embodiment of Figure 3. It is envisaged that when electric current is supplied to the heater element 41, initially the liquid above the central part of the heater element 41, in the zone 43, which is located where the depth of liquid above the heater element is at a minimum, will become evaporated. In the outer zones, that is to say zones located to either side of the central zone 43, the depth of liquid above the heater element is greater, meaning, that the heat supplied to the liquid will not be sufficient to vaporise the liquid. Nevertheless, the temperature of the liquid will rise. When the liquid that was initially present in the central zone 43 has been evaporated, further liquid will flow inwardly to replace it, and that liquid will have been pre-heated by the parts of the heater element 41 located to either side of the central zone 43. Figure 5 illustrates a modified embodiment of the invention. Many of the structural parts of the embodiment of Figure 5 are identical with the embodiment of Figure 1 and like reference numerals have been used for those parts. These parts will not be re-described. In the embodiment of Figure 5, the heater element 11 which provides the upper surface that forms the lower part of the upper chamber 6 is not, itself, directly provided with means to heat the heater element 11. Instead, the heater element 11 is associated with other components adapted to supply the required heat. A radiation generator 50 is located beneath the heater element 11. The radiation generator 50 may generate infra-red radiation, in which case the heater element 11 may be made, for example, of glass or other transparent material. The radiation generator 50 may, alternatively, generate micro-wave radiation. In such a case, the heater element 11 would be made as a susceptor to micro-wave energy. Alternatively again, the radiation generator 50 may generate a high frequency electro-magnetic field, the heater element 11 being formed of an electrically conductive material, the arrangement being such that a current is induced in the heater element 11, the induced current causing the heater element to be heated. In the embodiment of Figure 5, a further radiation generator 51 is provided which is mounted within the chamber 6. The further radiation generator 51 is located at a position above the fluid which is located on top of the element 11. The radiation generator 51 may generate infra-red energy and/or micro-wave energy. This energy would be directed immediately on to the liquid which is lying on top of the element 11. It is to be appreciated that the radiation generator 51, located within the chamber 6 may be used in combination with, or instead of the radiation generator 50 which is located beneath the element 11. In the embodiment of Figure 5, the cover 3 for the housing 2 incorporates a projection 52 which contains a tangential fan 53. The upper part of the projection 52 is provided with a plurality of air inlet holes 54. When the fan is operational, air will be drawn, as indicated by the arrow 55, through the air inlet holes 54, across the upper surface of the element 11 and out through the aperture 17. The fan may be activated if it is desired to generate a rapidly flowing stream or "jet" of vapour or "fog". It is to be appreciated that whilst in the illustrated embodiment, the fan is shown as an integral part of the housing, the fan could alternatively be provided as a separate housing adapted to be releasably connected to the housing defining the chamber 6. Thus, the contemplated "fog machine" may generate a relatively gentle flowing stream of fog, in the manner described with reference to Figure l, or the fan may be mounted in position to provide a "jet" of fog. In the embodiment illustrated in Figure 5, the upper surface of the heater element 11 is not planar, but is provided with a plurality of small projections 51 which may assist in the vaporisation of the fluid. It is to be appreciated that the features described with reference to Figure 5 may be incorporated in the embodiments described above and consequently, the fan may be provided in connection with an embodiment using an electrically operated laminated heat element 11 as shown in Figure 1, and also in connection with a floating heater arrangement as shown in Figure 3. Also, the projections 56 illustrated in the embodiment of Figure 5 may be used, with benefit, in the remaining embodiments that have been described. Should, in any of the described embodiments of the invention, any deposits form on the heater element from impurities in the chemicals or hardness in the water used to make the fluid to be evaporated, such deposits may be easily removed from the heater element, since the operative surface of the heater will be relatively easily accessed. When a "fog machine" of the type described above is utilised, the fluid to be evaporated would comprise a mixture of glycol, such as tri-ethylene glycol or monopropylene glycol and water. Such fluid mixtures are well known in this art. Whilst it is envisaged that a "fog machine", as described above may use slightly more power than a conventional prior art machine incorporating an aluminium block when fog is actually being generated, it is believed that there will be an overall reduction in power consumption, since the described embodiments of the invention will only consume power when fog is being generated, and will not consume power when waiting to generate fog.

Claims: „„,„,„„„ O 97/25122 -17- CLAIMS : 1. A vaporiser, the vaporiser comprising a housing defining a chamber, the chamber being adapted to contain a liquid to be evaporated, the chamber containing a heater, the heater having an element defining an upper surface, means being provided for maintaining the relative positions of the said element and the surface of liquid within the chamber such that there is a predetermined depth of liquid above at least part of the said element, that depth of liquid being in the range of 1-5 millimetres, the heater being adapted to heat the said liquid above the said element. 2. A vaporiser according to Claim 1 wherein the said element is fixed in position, and means are provided to maintain a predetermined level of liquid within the chamber, the level of liquid being such that said predetermined depth of liquid is established above the said element. 3. A vaporiser according to Claim 2 wherein the means to maintain the level of liquid within the chamber comprise means adapted to receive a reservoir containing fluid, the reservoir being provided with a release valve, and means provided on the housing adapted to actuate the release valve when the reservoir has been introduced to the housing through the aperture, the release valve being so positioned that liquid will flow from the reservoir until the level of liquid within the chamber reaches the level of the release valve, the level of liquid in the chamber above the heater then having the said depth. 4. A vaporiser according to Claim l or 2 wherein the means to maintain the level of liquid within the chamber comprise a ball valve. 5. A vaporiser according to Claim 1 wherein the said element is present on a floating structure, the floating structure being so configured that the said element is located at the predetermined depth beneath the surface of the liquid in which the floating structure is floating. 6. A vaporiser according to any one of the preceding Claims wherein the depth of liquid above the said element is in the range of 1-2 millimetres. 7. A vaporiser according to any one of the preceding Claims where in the upper surface of the said element is substantially planar. 8. A vaporiser according to any one of Claims 1 to wherein the upper surface of the said element is arcuate in section. 9. A vaporiser according to any one of the preceding Claims wherein the upper surface of the said element is provided with projections. 10. A vaporiser according to any one of the preceding Claims wherein the said element is provided with means which heat the element, the heat thus being transferred to the liquid. 11. A vaporiser according to Claim 10 wherein the said element comprises a laminate consisting of a supporting substrate, an electrically conductive layer and an insulating over-layer. 12. A vaporiser according to Claim 11 wherein the substrate comprises silica, the electrically conductive layer comprises an etched layer of metal and the insulating layer comprises a layer of glass. 13. A vaporiser according to any one of Claims 1 to 9 wherein the said element comprises a susceptor to microwave energy, means being provided to supply microwave energy to the said element. 14. A vaporiser according to any one of Claims 1 to 9 wherein the said element is adapted to be inductively heated by an electro-magnetic field, means being provided to supply an electro-magnetic field to the said element. 15. A vaporiser according to any one of Claims 1 to 9 wherein the element is associated with means which direct infra-red radiation to the element to heat the element. 16. A vaporiser according to any one of the preceding Claims wherein the heater incorporates means to direct infra-red radiation on to the liquid which is above the said element to heat the liquid. 17. A vaporiser according to any one of the preceding Claims wherein the heater incorporates means to direct micro-wave radiation on to the liquid which is above said element to heat the liquid. 18. A vaporiser according to any one of the preceding Claims provided with fan means to discharge vapour from the housing.

Inventors: MORRIS NIGEL, MORRIS, NIGEL
Applicants: MORRIS NIGEL, MORRIS, NIGEL
Application year: 1996
Main classification: A63J5
IPC codes: A63J5, F22B1