A METHOD OF CREATING SMOKE, FOG OR HAZE, AND A SMOKE, FOG OR HAZE GENERATOR ASSEMBLY

DESCRIPTION The present invention relates to a method of creating smoke, fog or haze within a limited space, said method comprising providing a supply of nitrogen containing gas, mixing said gas with a smoke liquid, heating the mixture to vaporize it so as to form a gas mixture of smoke vapor and inert gas, and ejecting the hot gas mixture into surrounding air under essentially adiabatic cooling of the gas mixture to create a fine smoke, fog, or haze of essentially the temperature of the surrounding. The invention also relates to a smoke, fog or haze generator assembly for use within a limited space.

TECHNICAL FIELD

The present invention relates to a method of creating smoke, fog or haze within a limited space, said method comprising providing a supply of nitrogen containing gas, mixing said gas with a smoke liquid, heating the mixture to vaporize it so as to form a gas mixture of smoke vapor and inert gas, and ejecting the hot gas mixture into surrounding air under essentially adiabatic cooling of the gas mixture to create a fine smoke, fog, or haze of essentially the temperature of the surrounding.

The invention also relates to a smoke, fog or haze generator assembly for use within a limited space comprising a smoke, fog or haze generator having a supply of nitrogen containing gas, a combining unit with a first inlet for a smoke liquid, a second inlet for inert gas, and an outlet for a mixture of smoke liquid and inert gas, said smoke, fog or haze generator further having a heat exchanger for heating the mixture coming from the combining unit to vaporize the smoke liquid, and an outlet for and ejecting the hot gas mixture into surrounding air under essentially adiabatic cooling of the gas mixture to create a fine smoke, fog, or haze of essentially the temperature of the surrounding.

In the present context, the term "smoke" designates a thick, white smoke, and "haze" designates a fog that is so thin that it is almost invisible until it is illuminated. However, in the description below, the term "smoke" is used as a generic term that comprises also "fog" and "haze". The term "smoke liquid" designates a liquid, which after vaporization and subsequent condensation to micro droplets forms the smoke.

BACKGROUND ART

The use of artificial smoke on the stage is old and was originally based on pyrotechnics, e.g. by burning gunpowder and similar substances. Today, pyrotechnics most often is used for short effects outdoors. For creating entire milieus or continuous smoke covering of a stage, the smoke has to be odorless, inflammable and nontoxic and must not affect the equipment, and it must be possible to generate the smoke silently without disturbing noise.

Most smoke generators have a powerful heat exchanger, a pump and an electronic control unit. A smoke liquid is pumped into the heat exchanger, which operates at 250- 330 ⁰ C and vaporizes the liquid. Comparatively large amounts of smoke liquid are to be vaporized in a short time. The smoke discharged from the machine must not be damp or contain unvaporized liquid, because that may result in damages and toxic smoke may ensue. The desired result is a dry, white smoke without odor or other defects.

DE 35 02 231 Al discloses an apparatus and method of producing fog on theater stages. Water is used as smoke liquid and is fed from a source through a heater to a hot water container, where it vaporizes. Liquid nitrogen is sprayed onto the formed water vapor, making it condense to fog, which is blown out of the apparatus by of a fan. The resulting fog is nontoxic, but a dense smoke cannot be achieved.

Another apparatus and method of producing fog is disclosed in US 5,711,481 and has a mixing chamber. A steam nozzle in the mixing chamber injects high pressure steam into the chamber. The injected steam entrains ambient air, pulling it through an air opening into the mixing chamber. The steam and air mix to form humid air. Cryogenic fluid, preferably liquid nitrogen, is injected through a nozzle, which is positioned in the path of the humid air. The cryogenic fluid rapidly cools the warm, humid air which generates large quantities of fog. Also here, the resulting fog is nontoxic, but a dense smoke cannot be achieved.

Still another method and apparatus for of producing a breathable fog from water is disclosed in US 5,156,333. Here, air is passed through a drier to remove moisture, the dry air is cooled to a temperature below the freezing point, e.g. by passing it through a heat exchanger cooled by liquid nitrogen, and inducing water vapor into the dried and cooled air to produce a breathable fog. Like above, the resulting fog is nontoxic, but a dense smoke cannot be achieved.

US 4,732,085A discloses a method and apparatus for producing dense smoke clouds for camouflage purposes. The smoke liquid is of a type that decomposes to yield solid particles and is injected through an atomizing nozzle into a substantially inert carrier gas stream, which is a combustion product of a solid propellant fuel, whereupon the gas stream is passed into a reaction chamber. An electromagnet surrounds the reaction chamber for providing a magnetic field having flux lines parallel to the flow of the gas stream to permit growth of filaments of smoke particles. Then, the gas stream is passed through an ejector, where it is cooled by the introduction of a liquid cooling medium, such as liquid nitrogen, into the ejector. The smoke exiting the ejector preferably is further dispersed by a second stage air mover. This method and apparatus is unsuitable for indoor use.

Another smoke generator method and apparatus for using a high temperature liquid smoke agent is disclosed in US 5,870,524 and is especially suitable for firefighter trainees with a flame environment. The apparatus has an electrical resistance heating tube of large heat transfer area and low thermal mass, and a switch control circuit has a connection to a temperature sensor and controls the start-up and shut-down operation of the smoke generator by the activation of a pump, electrical resistance heating tube, and the turning on and off of a fluid injector circuit and an air blower for cooling the heater tube. The fluid injector circuit includes a source or container of fluid, such as compressed nitrogen gas, which is used during the start-up and cool-down periods while the electrical resistance heater tube is being heated up and cooled down. An optional mode of operation is to have a continuous gas injection from the gas injection circuit during all phases of operation. Smoke generation during steady-state without gas injection would depend on the superheated temperature and pressure to produce the desired smoke particle size and cloud characteristics. Injecting the gas at the outlet nozzle at selected temperatures produces a mechanical shearing effect on the hot reduced viscosity liquid to control the smoke particle size. Lower temperatures are thus possible as a trade off for more gas usage.

The use of oil as smoke liquid is widely known, vide US 7,302,170, for example. The disclosed smoke generator includes at least one heating rod and a vaporization tube. The vaporization tube includes a longitudinal passageway. The vaporization tube coils around the heating rod and includes an end connected to an outlet of a pump of a smoke generator. The oil vaporizes into smoke while passing through the passageway of the vaporization tube, and the smoke is ejected via the outlet end of the vaporization tube. Consequently, there is risk of the smoke being hot and reacting with oxygen in the air,

thus causing odor, and also of the smoke having a lower density than that of the surrounding air, thus causing the smoke to rise.

It is well known to use an inert gas for mixing with the oil based smoke liquid mentioned above. Thanks to the presence of this gas, the smoke liquid is more evenly vaporized and creates an even smoke with predetermined thickness and without droplets of unvaporized liquid. However, the gas used must not interact with the smoke liquid, since this would produce a lower quality smoke that could have defects such as odor or even be toxic. The gases preferred for this use are carbon dioxide (CO ₂ ) or nitrogen (N ₂ ). This means, however, that a supply of inert gas, often from a separate gas tube, is required for creating smoke of the desired quality. Such tubes are generally heavy and cumbersome and can limit the running time of a smoke generator considerably, since a change of tubes would cause a disruption in the smoke generating process. Gas tubes are also relatively expensive, and a number of different standardized connecting means are available for connecting said tubes to a smoke generator. When acquiring new tubes, great care must therefore be taken to find tubes which have the suitable connecting means to match the smoke generator used, a process which can be complicated when buying tubes in different regions or countries, such as when an entertainment production is on tour.

DISCLOSURE OF THE INVENTION

The object of the present invention is to address the problems discussed above. This is achieved by providing a method of creating smoke, fog or haze within a limited space, said method comprising providing a supply of nitrogen containing gas, mixing said gas with a smoke liquid, heating the mixture to vaporize it so as to form a gas mixture of smoke vapor and inert gas, and ejecting the hot gas mixture into surrounding air under essentially adiabatic cooling of the gas mixture to create a fine smoke, fog, or haze of essentially the temperature of the surrounding, whereby said nitrogen is supplied from compressed air and stored in a buffer tank for providing a steady supply of said air to a nitrogen separation unit where nitrogen is separated from other substances. Thereby, no supply tanks containing inert gas are needed, and the desired gas can easily be generated from the surrounding air in the amounts desired. This allows for a convenient method of generating smoke, fog or haze without being dependant on an external supply of inert gas and makes it possible to generate smoke continuously, without needing to stop for switching gas tubes or any such cumbersome maintenance procedures. Also, thanks to the buffer tank, compressed air can be stored in a convenient manner and led over to the filters for removing oxygen when this is required. The air compressor will not have to

be used continuously, but rather a larger amount of compressed air can be generated and used. The compressor can later be started again if there is a risk of running out of compressed air in the buffer tank. This way, maintaining the desired pressure inside the system is also simplified.

According to one aspect of the invention, the nitrogen is separated from said other substances by a membrane filter. Thereby, gases unsuitable for use in generating smoke, such as mainly oxygen, can be removed from the air in an easy and convenient manner and recycled into the surrounding air. Such a filter requires very little maintenance and can be used for a lengthy period of time before needing replacing.

According to another aspect of the invention, the method for generating smoke, fog or haze comprises the steps of compressing the air, cooling the compressed air, and removing possible oil and moisture from the compressed air before separating the nitrogen therefrom. Thereby, a gas of high quality and without contaminations in the form of oil from the compression process or moisture from the surrounding air can be created, and through a testing system it can be ascertained that the gas used with the fog generator has the desired properties without containing anything that could lower the quality of the generated fog.

According to yet another aspect of the invention, the air supply is compressed air from a compressor. Thereby, the fog generation method is truly independent of any external source of gas other than the surrounding air.

According to a further aspect of the invention, the limited space where the method is being applied is used for producing entertainment. Thereby, the fog generated can be used in venues such as theatres or stages for concerts, plays, operas, etc, or in spaces where movies are made. The limited space can also be outdoors, without clear physical boundaries, for instance when a certain scene in a movie or suchlike is recorded.

According to an aspect of the present invention, the smoke liquid used with the method is oil based, preferably a mineral oil. More preferably, said mineral oil is a food classified white oil. Thereby, a high quality smoke can be created and the nitrogen used as an inert gas in this creation process. Said food classified white oil is especially suited for use with the method according to the invention thanks to its excellent properties, among other its non-toxicity which allows for extensive use of this white oil without endangering the health of the persons involved in controlling the smoke generator or the

persons present in the location where the smoke is applied, such as on a theatre stage. The smoke created is also of a very high quality with respect to its visual appearance.

In a method of the kind referred to in the first paragraph above, the object of solving the problems mentioned in the description of the prior art is achieved in accordance with the present invention by producing said inert gas in a nitrogen generator by separating nitrogen from air by means of a membrane, and feeding the nitrogen to a smoke generator for mixing with said smoke liquid. Thereby, the method can be implemented in a simple yet efficient manner without the need for cumbersome gas tubes for supplying the inert gas required for smoke generation and the process of generating smoke will not have to be interrupted for exchanging gas tubes. The total running time of the smoke generator can be substantially longer than would be possible with the use of external tubes, and is limited mainly by the need for sometimes refilling a fog fluid tank containing the fog fluid used for creating the smoke.

According to a further aspect of the present invention, the compressor used for compressing the supplied air is an oilless piston compressor. Thereby, a good result can be achieved when compressing the supplied air and with the risk of contaminating the air being minimized.

According to a further aspect of the present invention, the nitrogen generator further comprises an electronic control module operatively connected to at least one of the following: the compressor, the combining unit, the heat exchanger, a nitrogen purity sensor provided in a line feeding the nitrogen to the combining unit, and an electronically controlled regulator provided in said line. Thereby, the operation of the smoke generator, as well as the nitrogen generator and the air compressor can be controlled and adapted to fit the requirements of each individual situation. Any factor endangering the quality of the produced smoke, such as oxygen or moisture present in the nitrogen supplied, can also be detected at an early stage and the smoke generation stopped until the problem can be solved, without risking the generation of a smoke which would have an undesired visual appearance or could endanger the health of the persons present in the vicinity.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings.

Fig. 1 shows a simplified view of a smoke generator according to the Prior Art.

Fig. 2 shows a simplified view of a preferred embodiment of a smoke generator according to the present invention, and

Fig. 3 shows a simplified view of a second embodiment of a smoke generator according to the present invention, and

Fig. 4 shows a detailed view of the preferred embodiment of Fig. 2.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a smoke generator according to the Prior Art. A smoke fluid, e.g. a mineral oil, from a smoke fluid supply 1 enters a combining unit 3 where it is mixed with an inert gas, often N ₂ or CO ₂ , from a gas supply 2. The mixture of smoke fluid and gas is transported to a heat exchanger 4 where the mixture is vaporized and ejected through an ejection nozzle 41. The combination and heating process is controlled by an Electronic Control Module 5, and the gas supply is regulated by a regulator 21 which is generally manually operated.

A common problem associated with this process is the need for a gas supply, often from a gas tube, which renders the apparatus heavy and transportation difficult. Since the gas used must not interact with the smoke fluid because of the risk of creating smoke with undesired defects such as odor or toxicity, ordinary pressurized air containing oxygen cannot be used.

A smoke generator according to a preferred embodiment of the invention is shown in Fig. 2. An oil based smoke fluid such as a mineral oil, preferably a food classified white oil, from a smoke fluid supply 1 is still mixed with a neutral gas (N ₂ ) in a combining unit 3 and transported to a heat exchanger 4 where the mixture is heated in order to vaporize said oil 1 and eject it into the surrounding area by way of a nozzle 41. This process is, as is described in connection with the Prior Art shown above, controlled by an Electronic Control Module 5, but in this preferred embodiment according to the present invention, said Electronic Control Module 5 also controls other aspects of the smoke generator.

The neutral gas (nitrogen N ₂ ) needed for mixing with the smoke fluid is here generated by compressing and filtering the surrounding air, thus eliminating the need for heavy

and impractical gas tubes. In this process, room tempered air is injected through an air inlet 61 into an air compressor 6 where the air is compressed. The compression causes a rise in temperature and therefore an air cooling unit 62 is provided for cooling the air before storing it in a buffer tank 71. From said buffer tank 71, the pressurized air is filtered in a pre-fϊlter 72 where any oil and/or moisture which might arise from the compressing and cooling process can be removed.

After the initial filtering process, the pressurized air is transported to a nitrogen separation unit comprising a main filter 73 where oxygen (O ₂ ) is removed by means of a membrane and let out through a waste outlet 731. In passing an N ₂ purity sensor 74, the remaining gas is tested to control its composition before arriving at an Electronic Controlled Regulator 22 where the flow of gas is controlled.

The previously mentioned Electronic Control Module 5 can be used to analyze and control several aspects of the neutral gas needed for the combining unit 3. Thanks to the direct influence over the air compressor 6, the amount of pressurized air generated can easily be adapted to match the needs for the vaporization in the heat exchanger 4, and the results from the N ₂ purity sensor 74 are beneficial in determining the efficiency of the pre-filter 72 and main filter 73 so that contamination in the form of oil or moisture, or indeed remaining oxygen or other gas content can be discovered before using the gas with the smoke generator.

Thanks to the buffer tank 71 provided, pressurized air can be stored to ensure high efficiency of the smoke generator even when the needed output of smoke is suddenly altered, thus ensuring the high quality of the smoke produced.

In Fig. 3, a second embodiment of the smoke generator according to the present invention is shown. In this embodiment, pressurized air from a supply is filtered and provided to the combining unit 3. Such supplies can be found for instance in theatres, and by simply plugging the supply of pressurized air into the machine an even more efficient and convenient smoke generator can be constructed.

Compressed air is thus connected to the smoke generator and guided into a buffer tank 71 via a passive pressure controlled valve 67. The air is filtered, as well in a pre-filter 72 for removing oil and moisture as in a main filter 73 where the air passes through a membrane in order to remove the oxygen via a waste outlet 731. After the filtering, the remaining gas is stored in a second buffer tank 75, namely a nitrogen buffer tank, before

reaching a purity sensor 74 where the quality of gas produced is continuously measured. This sensor, as well as the regulator 22 which controls the flow of gas into the combining unit 3, is controlled by the Electronic Control Module 5.

Fig. 4 shows a detailed view of a smoke generator according to the preferred embodiment of Fig. 2 previously described. The generator is shown in three sections, designated as A, B and C, for providing greater clarity in the description. These will now be described separately.

Section A comprises a source of compressed air, where room tempered air from the area surrounding the smoke generator is let in through an inlet 61 with an air filter for removing any larger objects such as dust or other particles. The air is transported into an air compressor 6 where it is compressed to a desired pressure. The compressed air from the compressor 6 now has a higher temperature, due to the compression process, and is therefore transported to an air cooler 62 where it is cooled to a desired temperature before being transferred to a buffer tank 71.

The air inlet 61, air compressor 6 and air cooler 62 can in an alternative embodiment, such as that described in Fig. 3 above, be replaced by another compressed air source 8, such as a conventional compressed air source which is often present in venues such as theatres. An inlet, such as the inlet 67 shown in Fig. 3, could then suffice, along with some type of control means for controlling the pressure of the incoming air, before the pressurized air is transported to the buffer tank 71.

The pressure inside the buffer tank is held at 6-8 bar, preferably at around 8 bar. This is controlled by a switch 66 and a pressure control valve 65. The power supply 64 for powering these control devices can be a conventional power net, a portable battery, or any other suitable power supplying means.

An air pressure controlled electric switch 63 is provided for controlling the air compressor 6. If the air pressure inside the buffer tank 71 drops to 6 bar, this switch 63 starts the compressor so that more air is inserted into the system, and conversely turns the air compressor 6 off if the pressure inside the buffer tank 71 reaches the highest allowed level of 8 bar.

After the air has thus been let into the system via inlet 61, compressed, cooled and stored inside buffer tank 71, it has a pressure of at least 6 bar and can be led into section

B, the N ₂ generator, where the oxygen is removed to create a substantially pure nitrogen gas.

The compressed air is now led through a series of filters 72, namely a cleaning filter 72a for removing any oil that might be present in the air, and a dryer filter 72b for removing any moisture from the air. The presence of moisture in the gas in the smoke generator could yield unwanted results with regards to the quality of the smoke generated. Oil or oil mist might be present in the air due to compression in an external compressor in a theatre or industry. After the filters, the air passes a flow control valve 76 and enters a nitrogen filter 73 in the form of a hollow membrane filter where oxygen molecules (O ₂ ) are separated from the air and removed from the system via a waste oxygen outlet 731. The resulting gas, which is let out via a nitrogen outlet 732, comprises mostly nitrogen molecules (N ₂ ) and small amounts of other gases, mainly noble gas such as helium (He). It will in the following be referred to as nitrogen.

The nitrogen is led into a buffer tank 75 where the pressure is held between 6 and 8 bar. When the nitrogen is required for the smoke generator, it is let out of the buffer tank 75 via a N ₂ purity output control valve 74, after first passing an oxygen sensor 77 which can detect any remaining oxygen present in the nitrogen gas. A small amount of oxygen would be present in most cases, since a perfect filtering process cannot always be achieved, but if too large a concentration of oxygen is left in the inert gas, this would have an undesired result on the smoke gas generation. If large concentrations of oxygen are therefore detected by the oxygen sensor 77, signals can be sent to shut the smoke gas generator down in any way that is convenient, e.g. by turning the compressor off, by closing the control valve 74 to prevent the damaged gas from entering section C, or by notifying an Electronic Control Module 5 which can stop or alter the operation of the smoke generator. The problem with high oxygen concentrations will likely arise when the nitrogen filter 73 needs to be cleaned or replaced.

If the nitrogen, however, is perceived as pure enough, it is allowed to pass when needed into section C containing the smoke generator. The pressure of this gas is still kept at at least 6 bar.

In section C, the nitrogen is first led through a pressure regulator 22 which can be controlled manually or electrically. An electronic control module 5 controls two valves, 51 and 52, which determine how much of the nitrogen is to be led into the fluid tank 1 and how much will go directly into the combining unit 3. The fluid tank 1 contains an

oil based smoke fluid and the nitrogen led there will act as a pump for said fluid, pushing it towards the combining unit 3 where it will mix with nitrogen led directly past valve 52. In combining unit 3 these substances are mixed in such a manner that the smoke fluid is contained in small droplets in the nitrogen gas. The mixture can now be led into the heat exchanger 4, controlled by the control module 5, where it is led through a vaporizer pipe coil 42 in the vicinity of an electric heater 43 that has a power in the range of 0,7-3 kW. Being thus subjected to the heat from electric heater 43, the oil based smoke fluid will vaporize and form a dry white smoke which is let out via outlet 41. The nitrogen in itself will not react with the smoke fluid during this stage.

Depending on the power chosen for the electric heater 43, how much smoke fluid is let into the heat exchanger 4, and certain other factors, the smoke created will differ in thickness and intensity, thus giving the opportunity for creating anything from a thick smoke or smoke to a thinner haze. Thanks to this, the smoke generator is suitable for use in a variety of different situations, as well inside buildings or on stages as outdoor when a smoke or haze is to be created in a landscape. A number of different distribution agents, such as hoses, nozzles and the like, can be attached to the smoke outlet 41 for spreading the created smoke in a desired manner.

EXAMPLE

The amount of nitrogen gas needed when using a smoke generator such as that described above is shown in the table provided below. The models #1-5 show different size and capacity, where #1 is the smallest, using 0,07 litres of smoke fluid per hour, and #5 is the largest, using 3,5 litres at maximum efficiency. The heat exchanger is adjusted depending on the desired capacity of the smoke generator and the type of smoke fluid used, and the working temperature is placed at 325°C but can vary slightly (about ± 10 ⁰ C) around this point.

Table 1. Consumption of nitrogen gas in the smoke generator.

As can be seen above, the amounts of nitrogen needed vary greatly and especially for the larger applications a considerable amount is used. If external gas tubes are used, the possible running time of a smoke generator before an interruption occurs is mainly limited by the need for changing these tubes. A method for generating nitrogen for use in a smoke generator according to the present invention can therefore be seen as very beneficial, especially for larger applications.

The invention is not to be seen as limited by the embodiments described above and can be varied within the scope of the appended claims. It can be realized by the person skilled in the art that the internal machinery of the smoke generator, air compressor and nitrogen generator can be constructed in a number of suitable manners and that the number of control valves, buffer tanks and placement of components can vary greatly. The pressure used can also be in different ranges, as long as the desired effect of creating the desired smoke is achieved, and the power and capacity of the heat exchanger can be varied. It would also be possible to use the smoke generator for a different number of purposes other than entertainment, such as for instance military applications or industrial applications.