This invention relates to a device for generating a fog.

The object of the invention is to provide a device, allowing to gasify a relatively small quantity of liquid extremely quickly, in order to fill a closed space entirely or almost entirely.

The invention intends in particular to provide a device, by means of which a quantity of non- transparent vapour can be generated in a space starting from a signal emitted by an alarm device so that in case of burglary the burglar is in a room where any visual observation or orientation has become impossible.

The use of a fog, filling one or more spaces, as means for preventing burglaries is suggested by German patent No. DE-A-21 61 378. This document gives no indication of the way wherein large quantities of fog can be generated quickly. This is indeed an absolute requirement to apply this method with success. French patent 2 501 960 describes a method and a device for generating an artificial fog, wherein water has to be preheated for transferring thermal energy to the liquid or frozen C0 ₂ in order to vaporize this C0 ₂ into the vapour phase. This transfer occurs in a subsequent mixing room or mixing and storage room.

The thermal energy used here is therefore not used to exert a sufficient pressure for permitting the artifi¬ cial fog to be emitted quickly.

An essential object of the invention is thus to generate large quantities of fog and to dis-

tribute it by using the pressure, which can be continu¬ ously generated by a small quantity of liquid during a known and determined period.

To allow this according to the invention, the device according to the invention comprises : a) a first closed vessel kept at temperature and filled with a mixture consisting of mono- or polyvalent alcohols and a liquid and/or a gas or a mixture of liquids or gasses having such a vapour pressure curve that pressure can be generated by varying the temperature of the mixture; b) a second closed vessel with a heat exchanger kept at a temperature higher than the temperature of the liquids and/or gasses in the first vessel; c) a pipe connecting the liquid or the liquid mixture from the first vessel to the inside of the second vessel, said pipe comprising a valve mounted thereon between the first and the second vessel and opening the connection between the first and the second vessel upon activation by a signal emitted by an alarm device; d) an outlet in the wall of the second vessel for dis¬ tributing the fog generated in this latter vessel into the environment, optionally by using a pipe mounted on this outlet.

Still according to the invention said first and second vessels are kept at the required temperature by thermostatically controlled heating resistances and said heat exchanger mentioned under b) is formed by a mass kept at the required temperature, onto which mass the liquid, liquid mixture or liquid/gas mixture coming from the first vessel can be evaporated and/or overheated.

In a preferably applied embodiment said mass consists of metal particles (die-waste) .

Other details and advantages of the invention will become apparent from the following description of a device for generating a fog, according to the invention. This description is only given by way of example and does not limit the invention. The reference numerals relate to the figures annexed hereto.

Figure 1 is, according to a longitudinal cross section, a schematic view of the device according to the invention in a first embodiment. Figure 2 is a similar view of a device according to a possible variant.

Figure 3 is a similar view of the second vessel from a device according to a second variant.

The device represented by these three figures, consists of the combination or juxtaposition of two vessels called hereinafter the first vessel 1 and the second vessel 2, respectively 2' and 2". Preference is given to a cylindrical embodiment, but it is clear that one of the vessels 1 and 2 or both vessels may show any cross section.

In the embodiments according to figures 1 and 2 the first vessel 1 is partially filled with a glycol mixture and water indicated with reference 3.

For the same purpose use can be made of a mixture of several mono- or polyvalent alcohols and a liquid and/or a gas (or a mixture of liquids and/or gasses) having such a vapour pressure curve that the pressure in the space 4 above the liquid can be gener¬ ated by varying the temperature of the mixture. Preferably, use is made of a mixture consisting of about 48 % propylene glycol, about 32 % triethylene glycol and about 20 % water.

Certain alcohols apparently permit to generate a "fog" by heating upto above their respective boiling points. This property was especially observed in case of bivalent alcohols, the so-called glycols or

diols. The best known representatives of this group are : propylene glycol, ethylene glycol, diethylene glycol and triethylene glycol. Diols with a relatively high molecular weight, such as triethylene glycol, have a relatively high boiling point and generate a rather "heavy fog" clinging at a low level.

Diols with a relatively low molecular weight, such as propylene glycol, have a relatively low boiling point and generate a rather "light fog" having the tendency to rise.

By mutually combining the different types of diols, the structure of the formed fog can be influ¬ enced as to space filling properties.

Other mono-, bi-, tri- or polyvalent alcohols or mixtures of these alcohols could cause the same effect.

In the vessel 1 (according to both embodi¬ ments) a heating resistance 5 is mounted surrounded by a distribution bar 6 for example of aluminium. The whole forms thus a cylindrical part situated in the middle of the vessel 1. The temperature in this vessel is in the order of magnitude of 125 / 150°C.

In the mixture of said liquids and/or gasses, a pipe 7 is placed, comprising a valve 8 mounted thereon. The valve 8 is activated by a signal, emitted by an alarm device reacting in case of burglary. This alarm device is not represented in the figures.

The pipe 7 runs out of the vessel 1 down¬ wards and penetrates into the vessel 2. From now on, there are thus at least three possible embodiments, which will be described hereinafter with reference to the figures 1, 2 and 3.

In the embodiment according to figure 1, the pipe 7 enters thus at the top in the middle of the cover 9 and extends down to about the middle of the grit mass 10 enclosed in the vessel 2. The grit mass 10 does

not touch the outer wall 11 of the vessel 2 but is enclosed in an inner pipe 12.

Instead of a grit mass use can be made of metal particles 10* as shown by figure 3. The grit mass 10 (figure 1) or the metal particles 10' (figure 3) are brought at a high tempera¬ ture by the electrical resistance 13 caught in the bottom plate 14. This temperature is in the order of magnitude of 320°C. The bottom plate 14 consists of a material having a high heat storage capacity. The temperature of the bottom plate 14 is kept at a constant level thanks to the thermostat 15 which is in contact with this bottom plate or which is mounted therein.

The role of the bottom plate 14 with heating resistance 15 in the embodiments described herein can be taken over by elements provided to perform the same function. It is for example possible to design the vessel 2 in such a way that at least a part thereof is made of a material and/or has a mass with a high heat storage capacity. The heating resistance could then be mounted in the wall or on another place in the mass.

The vapours generated in the vessel 2 respectively 2" leave these vessels through an outlet 16, respectively 16'. If necessary, a pipe which is not shown in the figures can be mounted on these outlets 16, 16'. This allows to mount or to incorporate the device at a place which is not necessarily the space which is to be protected.

Referring now to the embodiment according to figure 2, it will be noticed that the first vessel, 1, shows the same structure.

The pipe 7, penetrating into the vessel 2 ' , is wound spirally around a distribution bar 17 bathed in a thermo-oil. This distribution bar which may consists for example of aluminium comprises a heating resistance 18. The spiral windings of the pipe 7 around

the distribution bar 17 are indicated with reference 7 ' . At the bottom of the distribution bar 17, the last spiral winding of the pipe 7' is converted in a pipe 7" through which the generated fog escapes. With respect to the embodiment according to figure 3, it will be noticed that the inner pipe 12 ' is connected at the top to the part which can be considered as the cover 9 of the second vessel. At the bottom, a passage 17 is maintained between the edge of the inner pipe 12 ' and the bottom plate 14 ' .

Thanks to this structure a better and stronger distribution of the fog is ensured.

It will be noticed that the mixture leaving the pipe 7, in the vessel 2", is spread out over the metal particles 10' by a distribution plate 18. This further increases the power with which the mixture is forced out of the vessel 2 through the outlet 16'.

The device according to the invention offers thus a number of advantages which are set forth hereinafter, such as i.a. :

- Exceptional compact construction ;

No moving parts at all. The device comprises only one valve ;

- The required mixture, usually a glycol mixture, is filled up via an ordinary filling stopper - further actions are not required ;

- Because of the cylindrical construction the device can be easily insulated and has a very advantageous volume/surface ratio ; - In case of a power failure (220 Volt) the inner temperature and the heat capacity remain many hours at a high level, depending on the reliability of the insulation, and anyway high enough to guaranty nevertheless the operation of the device upon application of the 12 V control signal to the valve ;

- ' Very simple construction with a high operational reliability ;

The glycol or the glycol mixture is brought auto¬ matically under pressure without using pumps and/or pressure storage reservoirs ;

- The pressure on the glycol mixture (or similar mix¬ ture) is rather constant. This results in a con¬ stant evaporation independent of the glycol volume ;

- A relatively small heat exchanger may be sufficient because the liquid is already preheated when sup¬ plied to this heat exchanger.

It is clear that the invention is not limited to the embodiments described hereinabove and that a lot of modifications could be brought thereto without leaving the scope of the patent application.