Field of invention The present invention relates to an apparatus for production of very small water droplets which apparatus is particularly suited for the use in extinguishing fire in rooms an tunnels.

Background art The interest for the use of water mist for fire extinguishing is strongly increasing. In contrast to the use of CO2-gas, water mist systems are environmental friendly and non-toxic and have further the advantage the water will cool the surroundings which are not already on fire. The use of water mist has further the advantage that that the amount of water necessary for extinguishing a fire is only about 10 % of the amount of water necessary for use in conventional sprinkler systems. The water damages are therefore much smaller when using water mist systems than when using conventional sprinkler systems.

The efficiency of water mist systems are closely related to the water droplet size. The amount of water that vaporise is strongly dependent on the droplet size. When water is supplied in the form of very small droplets as a water mist, the surface area of a given amount of water is much higher than the surface area of water supplied through conventional sprinkler systems.

The smaller the droplets, the less water is needed to extinguish a fire. Thus small droplets have a greater ability to absorb heat from the fire and thereby vaporise faster. If a sufficient amount of water vaporises before or when the water vapour reaches the flame zone, the fire will be extinguished due to lack of oxygen. Efficient fire extinguishing by use of water mist is usually a combination of cooling and creation of an atmosphere which does not contain oxygen.

The known systems for producing water mist are based on high pressure dies having a plurality of very small openings. These systems are dependent on that the water supplied is very clean in order to avoid clogging of the openings. Such systems therefore have to be equipped with water purification devices. Water purification devices are, however, costly and do not give complete avoidance of clogging of the water openings. The known systems for producing

water mist further has the disadvantage that the produced water droplets have a relative large size distribution. For water mist systems it is of advantage that the size of the water droplets varies as little as possible.

Disclosure of invention By the present invention one has arrived at an apparatus for the production of water droplets or water mist that makes it possible to produce water droplets having a very small size and where clogging of small water openings is avoided such that there is no need for water purification devices. The apparatus according to the invention is very flexible as to the amount of water that can be supplied and to the production of water droplets having a predetermined size.

The present invention thus relates to an apparatus for production of small water droplets, which apparatus comprises a hollow axle which is intended to be rotated about its longitudinal axis, at least two circular-shaped water distribution disks affixed to the lower end of the hollow axle, which water distribution disks are at a distance form each other by means of spacers, the disks having a central opening, an inner horizontal, ring-shaped part, a strongly downward sloping part, a less downward sloping part and a small outer horizontal part, a stationary water supply pipe arranged in the hollow axle, which water supply pipe in one end is connected to a water supply source and where the other end is closed and extends into the central openings of the water distribution disks, and which water supply pipe has at least one opening for water between each two water distribution disks.

According to a preferred embodiment the water distribution disks have grooves on the outer horizontal part of the disks. The grooves have a depth of at least 0.5 mm and a distance between the centres of two adjacent grooves of at least 0.5 mm. The depth of the grooves is preferably at least 1 mm and the distance between adjacent grooves is preferably at least 1 mm The grooves are preferably V-shaped, but U-shaped grooves can also be used.

According to a further embodiment the radial grooves extends inwardly onto the less downward sloping part of the water distribution disks.

The water outlet openings in the stationary water supply pipe preferably have a diameter of at least 2.5 mm and more preferably at least 3 mm. These relatively large openings secure that any particles in the water will not clog the openings. The number of openings at each level in the water supply pipe is preferably three and the openings are preferably arranged at an equal circumferential distance.

The distance between the water distribution disks are at least equal to the openings in the water supply pipe. It is thereby avoided that particles which pass through the openings in the water supply pipe are caught between two water distribution disks.

The number of water distribution disks can vary according to the amount of water one wishes to supply. In principle there is no restriction on the number of water distribution disks, but for practical reasons the number of water distribution disks are preferably less than 20.

The axle can be rotated by conventional means, but it is preferred to use a turbine run by water or air. The rotation means must, however, be able to rotate the axle with the water distribution disks at a speed of rotation between 1000 and 100,000 rotations per minute.

The apparatus according to the present invention works in the following way: The axle with the water distribution disks is rotated at a predetermined speed of rotation and water is supplied to the stationary water supply pipe arranged centrally in the hollow axle. Water will thus flow into the space between two and two of the water distribution disks. The flow of water will hit the horizontal inner part of the water distribution disks and will be directed against the strongly downward sloping part of the above water distribution disk. The water will, due to the rotation of the water distribution disks, form a thin film on this part of the water distribution disk and flow outwards on the less downward sloping part, over the outer horizontal part of the water distribution disk and will leave the water distribution disk in the

form of very small water droplets. By using water distribution disks having radial grooves as explained above, splitting of the water film into substantially equally sized droplets is ensured.

Test have shown that there is a correlation between the droplet size, speed of rotation, diameter of the water distribution disks and the amount of water supplied. It has been found that for a constant diameter of the water distribution disks and a constant supply of water, the droplet size is reduced about 35 % at a 100 % increase in speed of rotation. A reduction of 50 % in the amount of water supplied gives a reduction of about 35 % in the droplet size. Finally, a 100 % increase in the diameter of the water distribution disks gives a reduction in droplet size of about 35 %. By the apparatus according to the present invention a predetermined droplet size can be obtained by regulating the amount of water and the speed of rotation.

By use of the apparatus according to the present invention it can thus be obtained a water mist consisting of substantially equally sized water droplets, where the size of the water droplets can be regulated by choosing a suitable combination of speed of rotation, amount of water and diameter of the water distribution disks. By use of the apparatus according to the invention the droplet size can be regulated to between 10 and 200 micrometer. The apparatus according to the invention is thus very flexible. Due to the rather large openings in the water supply pipe the risk of clogging is small. The water supply pipe can thus be directly connected to a normal water supply source.

Since the openings in the water supply pipe have a rather large diameter it is not necessary to use filters to remove small particles from the water that is supplied to the water supply pipe. in order to avoid clogging of the openings in the water supply pipe, particles having a larger diameter than the openings in the water supply pipe are preferably removed.

The apparatus according to the present invention is particularly suited for fire extinguishing in closed room, in tunnels and other places. The distribution of water droplets in the space about the apparatus can easily be calculated in order to determine the number of apparatuses needed to cover a room or a tunnel.

Short description of the drawings Figure 1 is a vertical cut through the apparatus according to the invention, Figure 2 show a water distribution disk from below, and Figure 3 is an enlarged cut along line A-A in Figure 1.

Detailed description of the invention In Figure 1 there is shown an apparatus according to the present invention for producing small water droplets. The apparatus comprises a hollow axle 1 intended to be rotated at a high speed of rotation by a rotation means (not shown) such as an air or water driven turbine. The axle 1 is rotatably suspended in bearings 2. The lower end of the axle 1 has an outward extending flange 3. To the flange 3 a plurality of water distribution disks 5 are connected by means of bolts 4. The water distribution disks 5 are affixed at a vertical distance from each other by means of spacers 6 arranged about the bolts 4. When the axle 1 is being rotated the water distribution disks 5 will thus also be rotated.

A stationary water supply pipe 7 is arranged in the hollow axle 1. The lower end of the water supply pipe 7 is closed and extends downwards to the lowest water distribution disk 5. At levels between each of the water distribution disks 5 the water supply pipe 7 has at least one opening 8 that allows water to flow from the water supply pipe 7 and into the space between two and two water distribution disks 5. The water supply pipe 7 has preferably at least three openings 8 at each level and the openings 8 at each level are preferably arranged at an equal circumferential distance. The openings 8 preferably have a diameter of at least 2.5 mm in order to avoid clogging of the openings 8 by particles contained in the water. The distance between two adjacent water distribution disks 5 is preferably at least equal to the diameter of the openings 8 in the water supply pipe 7 in order to prevent particles in the water to be caught between the water distribution disks 5.

On Figure 2 one of the water distribution disks 5 is shown seen from below. The disk 5 has as shown in Figure 1 an inner horizontal part 9, an outwardly extending strongly downward sloping part 10, a less downward sloping part 11 and an outer horizontal part 12. When water passes through the stationary water supply pipe 7 and the axle 1 together with the water distribution disks 5 is rotated, water passes trough the openings 8 in the water supply pipe 7 and hits against the inner horizontal part 9 on each of the water distribution disks 5. From here the water will flow radial outwards and hit the strongly downward sloping part 10 on the water distribution disks 5 and will, due to the rotation of the water distribution disks 5, be distributed over the whole surface of the strongly downward sloping part 10. The water will thereafter be distributed as a water film on the less downward sloping part 11 and will leave the water distribution disks 5 along the periphery of the outer horizontal part 12 in the form of small water droplets. Even if the apparatus shown in Figure 1 has five water distribution disks 5, the apparatus according to the invention has at least two water distribution disks 5.

In order to ensure best possible droplet formation, the water distribution disks 5 have radial grooves 13 at the outer end of the horizontal part 12 as shown in Figures 2 and 3. The grooves 13 preferably have a V-shaped cross-section and a depth of at least 0.5 mm, preferably more than 1 mm, and the distance between the centres of two adjacent grooves 13 is at least 0.5 mm, preferably more than lmm. The grooves 13 may alternatively have an U-shaped cross-section or a cross-section between V-shape and U-shape. The grooves 13 will ensure that the water film is very efficiently broken into equally sized water droplets.

In order to further ensure that the water film is being broken into small equally sized water droplets, the inner edge of the horizontal part 12 of the water distribution disks 5 also have radial grooves 14. The grooves 14 have the same shape and size as the grooves 13.

When using the apparatus according to the present invention the water distribution disks 5 are rotated by rotating the axle 1 at a speed which can be adjusted within a large range, for instance between 5000 and 100,000 rotations per minute. Tests have shown that by the use of the apparatus according to the present invention very small water droplets having a substantial equal size can be produced.

Tests have also shown that there is a correlation between the droplet size, the speed of rotation, the amount of water supplied and the diameter of the water distribution disks. It has thus been found that at a constant diameter of the water distribution disks and at a constant supply of water, the droplet size is reduced by about 35 % when the speed of ration is increased by 100 %. If the supply of water is reduced by 50 % the droplet size is reduced by about 35 %. Finally, a 100 % increase in the diameter of the water distribution disks reduces the droplet size by about 35 %. By the apparatus according to the invention the droplet size can therefore be adjusted to a size between 10 and 200 micrometer by adjusting the amount of water supplied and by regulating the speed of rotation for an apparatus having a constant diameter of the water distribution disks.