WO2011074979A1

WO2011074979A1 - Fire extinguishing assembly for transforming a liquid to a liquid mist

Info

Publication number: WO2011074979A1
Application number: PCT/NO2010/000457
Authority: WO
Inventors: Bjørn Rafael HANSEN
Original assignee: Prevent System As
Priority date: 2009-12-14
Filing date: 2010-12-14
Publication date: 2011-06-23
Also published as: US20120279730A1; US9573006B2; CA2784230C; NO333988B1; EP2512607B1; CA2784230A1; NO20093514A1; PL2512607T3; EP2512607A1; DK2512607T3; AU2010330955A1; AU2010330955B2; EP2512607A4

Abstract

The present invention relates to a fire extinguishing assembly for transforming a liquid into a liquid mist. The assembly includes an adapter section (3a, 14a) having at least one liquid inlet (3b, 14b) and a nipple section (6a, 9a) that connects to the adapter section. The nipple section includes a plurality of bores (6c, 9c) extending between an internal duct (12g) that connects to the liquid inlet (3b, 14b), and outlets on an outside of the nipple section (6a, 9a). The bores (6c, 9c) are located around the nipple section (6a, 9a). A deflecting surface (3d, 12d) for guiding the liquid is positioned around the outlets of the bores (6c, 9c). The deflecting surface (3d, 12d) includes recesses extending in a direction substantially from the nipple section (6a, 9a) to a circumference of the deflecting surface (3d, 12d). The bores (6c, 9c) and deflecting surface (3d, 12d) have a mutual positioning so that straight liquid jets flowing through the bores (6c, 9c) will hit the deflecting surface (3d, 12d) with at least a bevel angle α.

Description

Fire extinguishing assembly for transforming a liquid to a liquid mist

The present invention relates to a fire extinguishing assembly for putting out fire in installations and for transforming a liquid into a liquid mist.

In many installations it is common to have more or less permanent piping with nozzles ejecting water or water mist. Examples of such installations include buildings, ships, offshore installations, tunnels, mines, or generally any facility or location at which it is desired to be able to put out or prevent fire. Sprinkler systems have been used in such installations for a long time.

In many situations, the use of water mist is preferable to sprinkler systems from which water is discharged in the form of larger drops, because water mist often provides for a more efficient fire-extinguishing, requires less water, causes less water damages, may be used in connection with fire in liquids and gases, and has a lesser negative impact on electric installations. Water mist systems may be used anywhere as a replacement for sprinkler systems. In connection with permanently installed fire extinguishing systems it is common for the fire- extinguishing assemblies to be under a certain water pressure. These

characteristics are common for prior art sprinkler systems and fire extinguishing assemblies. Heat-sensitive glass bulbs are commonly used in permanently installed fire extinguishing systems.

However, water-based fire extinguishing assemblies suffer from certain associated disadvantages. Such assemblies are often manufactured with small nozzle openings which easily become clogged by contaminations in the water, and therefore normally a screening or water filtering system is required. Also, such assemblies typically have been relatively weighty, which is undesirable especially on vessels and floating structures as a large number of assemblies are required which combines to increase the overall weight significantly. Moreover, many of these assemblies also require a high inlet pressure in order to function properly, which increases the complexity, the necessary rating of the piping, the costs, as well as reduces the reliability particularly in case of fire. In addition, another problem is related to seals of known assemblies, and poor seals may result in leaks disrupting the mist pattern. Many assemblies also produce a relatively poor spreading of the mist, and a single generator, therefore, may only be used in rooms of a relatively limited size. From NO 314835 an arrangement is disclosed for providing small water droplets, for use in particular for water-based fire-extinguishment. The

arrangement is adapted for pivoting around its own axis, and is constituted by a hollow shaft. At least two circular water distribution disks are attached to the one end of the shaft by way of bolts. The water distribution disks are arranged in a spaced relation by means of spacers on the bolts. Each water distribution disk has an open center section, an inner horizontal annular surface, a steeply descending section, a less steeply descending section, as well as a narrow outer horizontal surface. A water supply conduit is provided in the hollow shaft. The conduit connects to a water supply at a one end and is closed and protrudes to the lowermost water distribution disk at the other end. The conduit comprises at least a water outlet at the levels in between two by two water distribution disks.

The present invention relates to a fire extinguishing assembly having relatively large flow-though openings, hence being less sensitive to water contaminations. The invention also relates to an assembly which is able to operate within a wide range of pressures, and the large flow-through openings allows the assembly to operate even at relatively low pressure levels.

The entire pressure drop of the assembly occurs across entirely fixed holes, and consequently no dynamic seals are required, which could potentially cause leaks. The assembly may also be made very small and light, and may be adapted for dispersing the mist in different angles. Moreover, testing has shown that an assembly according to the invention will be able to protect a larger volume than the assemblies which are commonly used today.

Hence, the present invention relates to a fire extinguishing assembly for putting out fire in installations and for transforming a liquid into a liquid mist. A liquid, in this context, will in most cases be water, with or without additives.

The assembly includes an adapter section having a substantially circular cross-section and at least one liquid inlet which connects to an internal duct.

Typically, the adapter section is provided with ordinary threads for being

connected to a piping system for the supply of extinguishant, usually water, and will typically be made of materials commonly used for fittings, such as brass or stainless steel, for example. The adapter section has an internal duct or bore extending into a duct or bore of a nipple section. The nipple section includes a plurality of openings or bores extending through the nipple section from this duct and having outlets located substantially along a ring pattern in one or two planes around the nipple section. Typically, the bores/openings are circular, but could naturally be implemented with another shape. These bores form nozzles for discharging the liquid. The number of bores and the sizes thereof must be adapted for the desired flow-through rate, for the pressure range within which the assembly is intended to operate, etc. An assembly of this kind typically will operate with a discharge rate of 25 l/min and will cover an area in the order of 25m² or more, for example.

A first, circular deflecting surface having an outer circumference for guiding the liquid is located in a position around the outlets of the bores.

The bores extend between the internal duct connected to the liquid inlet and outlets at an outside of the nipple section. The bores are positioned around the nipple section. The deflecting surface for guiding the liquid is positioned around the outlets of the bores.

The deflecting surface includes recesses running in a direction substantially from the nipple section to a circumference of the deflecting surface. The bores and deflecting surface have a mutual positioning so that straight liquid jets flowing through the bores will hit the deflecting surface with at least a bevel angle. The bores may be directed in different angles so that different bevel angles between the jet and deflecting surface may be formed on the very same assembly.

The deflecting surface may be annular and is constituted by a part of the adapter section. In one embodiment, the nipple section may be threaded into the adapter section in a center hole of the deflecting surface. In an embodiment in which the deflecting surface is a loose ring, this ring may be fastened to the adapter section with the nipple section. Typically, the deflecting surface will have the shape of an internally truncated cone opening towards the area to be exposed for the liquid mist, in a direction away from the adapter section and nipple section.

The distance between the outlets of the bores and the deflecting surface is typically between 3-15mm.

The recesses of the deflecting surface may be designed so as to provide a component of movement in a tangential direction. The recesses then will typically have a tangential component so that these don't extend in a plane in a purely radial direction relative to a nipple having a circular cross-section. The recesses may also be curved.

The nipple section may have a circular cross-section, and jets of liquid flowing through the bores may pass in a plane in a radial direction out of the bores relative to the circular cross-section of the nipple section.

The nipple section may have a longitudinal axis and the bores may run in a bevel angle to the longitudinal axis of the nipple section.

The nipple section may include an internal guiding body in order to increase the velocity of the liquid towards the bores.

The assembly may include a valve having a valve body. The valve body may include a valve spindle contacting a heat sensitive actuator element, and the valve body may assume a first position in which the inlet is sealed off, and a second position in which the inlet is in fluid communication with the bores. The heat sensitive actuator element may be an ordinary frangible element commonly used in connection with sprinkler systems, or may be based on electronic sensing, electrical actuators, remote control, etc. This is well-known technology within this field.

The bores may be provided in at least one ring around the nipple section, and the outlets on the outside of the nipple section may be adjusted so that every second liquid jet hit a point at a first distance from the deflecting surface and the remaining liquid jets hit a point at a second distance from the deflecting surface, with the first distance being different from the second distance.

The first and second distances may be adjusted by varying an angle of discharge.

The first and second distances may be adjusted in that every second outlet is positioned along a first ring around the nipple and the remaining outlets are positioned along a second ring around the nipple, with the first and second rings being located at a distance from each other.

The deflecting surface may be designed with two different angles so that every second liquid jet hit the surface at the first angle and the remaining liquid jets hit the surface at the second angle in order to provide a liquid mist screen having a larger volume. Brief description of the accompanying drawings:

Fig. 1 shows a side view of an assembled fire extinguishing assembly having thermal release according to the invention;

Figs. 2-7 show the individual components of which the fire extinguishing assembly of fig. 1 is comprised;

Fig. 2 shows a screen;

Fig. 3 shows an adapter;

Fig. 4 shows a valve body;

Fig. 5 shows a glass bulb;

Fig. 6 shows a nipple having a glass bulb fastening clamp; - Fig. 7 shows a plastic cover;

Fig. 8 shows a side view of an assembled fire extinguishing assembly not having thermal release according to the invention;

Fig. 9 shows a nipple a nipple not including a glass bulb fastening clamp;

Fig. 10 shows a cut-through side view of an assembled fire extinguishing assembly having thermal release according to the invention as shown in fig 1 , in which the components of the assembly can be seen;

Fig. 10(i) corresponds to fig. 10, but shows more clearly an angle between a nozzle and a deflecting body;

Fig. 10(ii) exhibits features similar to fig. 10, but shows an alternative embodiment not having thermal release;

Fig. 10(iii) exhibits features similar to fig. 10, but shows an alternative embodiment having an angled deflecting surface;

Fig. 11 shows a nipple as shown in fig. 9 in more detail;

Fig. 12 shows an assembled fire extinguishing assembly not having thermal release according to the invention, as seen in a front view;

Fig. 12(i) shows a detail of fig. 12 illustrating serrations or grooves;

Fig. 13 shows a screen similar to the one shown in fig. 2;

Fig. 14 shows an adapter similar to the one shown in fig. 3;

Fig. 15 shows a plastic cover similar to the one shown in fig. 7.

The present invention will now be described in more detail with reference to the accompanying drawings. Referring to Fig. 1 , a fire extinguishing assembly in the form of an

assembled fire extinguishing assembly having thermal release according to the invention is illustrated. The fire extinguishing assembly is made up of the components shown in figs. 2-7 in the order shown in the drawings. Hence, the fire extinguishing assembly is made up of a screen 2a positioned into an adapter 3a in an inlet 3b of the adapter 3a. Further, the assembly is shown having a fastening clamp 6d for a glass bulb 5a. The glass bulb contacts a section 4c constituting part of a valve body. A plastic cover 7a is positioned around the adapter 3a.

A tightening screw (not shown) presses a valve element against a valve seat via the bulb. When the heat-sensing bulb 5a is broken, the valve element inside the fire extinguishing assembly is allowed to move between a closed and an open position. The cover 7a is extorted from and falls off the assembly when the extinguishant is activated after the bulb has been broken and water flows through the assembly.

In Fig. 2, the screen 2a is shown in more detail. The screen 2a includes a lower edge 2b retaining the screen within the adapter after installation. The screen 2a prevents impurities from clogging nozzle openings of the assembly.

In Fig. 3, adapter 3a is shown. Adapter 3a includes an inlet 3b that typically includes an internal thread for connecting the assembly to a piping system.

Fig. 4 shows a moveable valve body 4a having sealing surfaces for sealing against valve seats of the assembly 3a. A first sealing surface 4e provides for sealing against a valve seat of the adapter 3a so that no water flows out of the assembly when the assembly is not in operation. A second sealing surface 4b seals against the valve seat of the adapter 6a, making sure no extinguishant leaks out of the assembly so that all the liquid flows out the nozzles, bores or openings 6c of nipple 6a. The first sealing surface 4e is tapered and also serves to guide the liquid towards the nozzles when the valve is in an open position. The first sealing surface 4e hence serves two purposes. The valve body 4a further includes a valve mandrel or valve spindle 4d having an engagement section 4c for engaging the glass bulb (5a of fig. 1 ).

A plastic cover 7a is mounted on top of the assembly to improve the appearance of the assembly, as well as to help preventing the assembly from being affected by any dirt or other undesired substances which could influence the function of the assembly.

Fig. 5 shows a heat-sensitive glass bulb 5a commonly used in sprinkler systems and other installations that is supposed to break at a given temperature. The glass bulb 5a is located between section 4c for engaging a glass bulb on valve spindle 4d and the fastening clamp 6d of nipple 6a.

Fig. 6 shows the nipple 6a with the glass bulb fastening clamp 6d. Nipple 6a includes a threaded section 6b which may be screwed into threads of the adapter 3a. The nozzle openings or holes 6c are positioned in a ring around the nipple 6a. In operation, extinguishant flows in through nipple inlet 6e and out through nozzle openings 6c. The clamp 6d keeps the glass bulb 5a in place between this and the valve 4a having engagement section 4c (fig. 1).

A plastic cover 7a is provided on top of the assembly for making the appearance more appealing. In addition, the cover may also prevent fouling of the assembly and of a deflecting surface. A hole (not shown) for the clamp 6d for the heat-sensitive bulb may be formed in the cover 7a. Typically, the cover is made of plastic.

An embodiment of a fire extinguishing assembly in the form of a fully assembled assembly without thermal release according to the invention is shown in Fig. 8. In this embodiment, a nipple 9a (shown in fig. 9) is used which does not include any glass bulb clamp. Also, in this embodiment, it is not necessary to have a valve body inside the assembly. Nipple 9a hence has a somewhat simpler construction than the nipple of the solution with thermal release, as the valve, glass bulb and clamp are not eliminated. Also in this embodiment a screen 13a (fig. 13) is shown. For example, in this embodiment, the water supply may be controlled centrally and be released in an otherwise known manner. If it is known for sure that the water is sufficiently free of impurities, then also screen 13a may be eliminated. Alternatively, larger central filtering units may be used. This solution also includes a protective cover 15a (fig. 15) which is extorted when pressure is applied to the assembly.

Fig. 13 shows a detailed view of the screen 13ba. The screen 13a includes a lower edge 13b. The screen may have the same design and function as the screen shown in fig. 2. Fig. 14 shows the adapter 14a. The adapter 14a includes an inlet 14b. The adapter may have the same design and function as the adapter shown in fig. 3.

In Fig. 9 can be seen a nipple 9a having no glass bulb fastening clamp. Nipple 9a includes a threaded section 9b which may be screwed into mating threads of the adapter 9a. Nozzle openings or holes 9c are positioned in a ring around the nipple 9a. In operation, extinguishant flows in through an opening 9e and is discharged through nozzle openings 9c. In this embodiment, the assembly has a lesser outward extent, it is easier to manufacture an assembly having a plastic cover covering the assembly, and it is easier to conceal the assembly.

To give the assembly a more appealing appearance, a plastic cover 15a has been placed on top of the assembly. The cover may also prevent fouling of the assembly as well as of a deflecting surface.

Figs. 10 and 10i show the assembly of fig. 1 in a cut-through side view so that the internal configuration of the assembly and the various elements therein can be seen.

Fig. 10 hence shows the adapter 3a with the extinguishant inlet 3b. Nipple 6a has been screwed into the adapter 3a. The internal valve is shown in a closed position. The adapter 3a is also shown to include a valve seat 3c, against which the valve body 4a is pressed by the glass bulb 5a. The glass bulb is kept in place by fastening clamp 6d. In Fig. 10, the assembly is shown with the valve in a closed position and with the glass bulb 5a in place so as to maintain the valve body 4a engaged with the valve seat 3c. If the glass bulb 5a is heated to the point of rupture, the valve body 4a is forced downwards and will abut against a valve seat 6f of the nipple, so that the valve seat forms a seal against the second sealing surface 4b of the valve body to prevent leakage so that all the extinguishant is discharged through the nozzle opening 6c. The lower position of the valve seat has been indicated with a dotted line down into fastening clamp 6d. In operation, the liquid will be sprayed out of the nozzle opening 6c and will be deflected by the deflecting surface 3d of the adapter 3a. The valve spindle descends towards the clamp for the heat-sensing bulb when the valve is in the open position 14.

Fig. 10(i) corresponds to fig. 10, but shows more clearly an angle a between a liquid jet flowing out of nozzle 6c. A dotted line 6g runs through the nozzle 6c to indicate a direction of the liquid jet. A second dotted line 10e is shown along the deflecting surface 3d (in a radial direction). Thus, the angle a between these lines corresponds to the angle between the liquid jet discharged through the nozzles and the deflecting surface, and hence also the angle with which the jet hits the deflecting surface 3d. The angle a is between 10° and 45°.

The angle may vary between 20° and 35°.

The angle a may be varied in order to vary the dispersion and distribution of the liquid. The angle also has an impact on the atomization of the liquid.

Fig. 10(ii) exhibits features similar to fig. 10, but shows an alternative embodiment not having thermal release. Fig. 10(ii) has been included in order to show an internal guiding body 9d for increasing the velocity of the liquid towards the nozzles 6c. In the solution including a valve, such as the one shown in fig. 10, for example, the valve body will serve as an internal guiding body. In the solutions not including a valve, and as shown in fig. 10(ii), this body may be integrated into the nipple 9a. The guiding body 9d may also be constituted by a loose part introduced into the assembly. In the embodiment shown, the body is shaped as a taper or cone. However, the guiding body 9d may assume other shapes, in that the taper has a rounded top, for example. The body 9d may also have the shape of a trumpet or funnel having a downward facing opening. Other shapes

contributing to guide the water from the inlet and out of the nozzles may also be used.

Fig. 10(iii) shows an alternative embodiment having an angled deflecting surface 3d for which a liquid jet from outlet 6c directed along a first ring around the nipple hits a first section of the deflecting surface with an angle a1 and a liquid jet from outlet 6c2 directed along a second ring around the nipple hits a second section of the deflecting surface with an angle a2. In the embodiment shown, the first angle a1 is larger than the second angle a2. In order to simplify the illustration, outlets 6c and 6c2 are shown positioned directly above each other. However, in the normal case, such outlets will be radially offset relative to each other and will run along separate rings around the adapter, with every second outlet running along an upper and lower ring, respectively, in a staggered pattern.

In Fig. 11 , a nipple having an external thread 11c and an inlet 11 d is illustrated. Fig. 11 also shows that the holes 11 A and 11 B of the nipple are offset relative to each other. The advantage of having holes in an offset configuration is that the points of impingement of the liquid jets on the deflecting surface may then be varied so that the area of the deflecting surface are more fully exploited. The reason for this is that tests have shown that each jet of liquid needs a certain area on the deflecting surface in order to be transformed into a mist with no too large liquid drops being formed. Large liquid drops are typically formed when liquids from two jets / liquid screens collide, and this is undesirable when the intention is to create a mist. When the angle of the nozzle is increased, the axial velocity of the water also increases. Nozzles with a zero angle maximize the velocity of the water in a radial direction.

This variation in the point of impingement between the jets and deflecting surface may also be achieved by creating different angled nozzles.

Fig. 12 shows a front view of an assembly according to the invention wherein the nipple has been partially cut-through in order to illustrate a nozzle opening 12c. A duct 12g extends in the center of the assembly. Liquid flowing from the duct 12g and out nozzle 12c forms a liquid jet 12e. The liquid jet hits recesses provided in a deflecting surface 12d to become deflected and atomized so that preferably a liquid mist is formed. For example, the recesses may be shaped as grooves, ripples, or serrations. The recesses may be curved grooves 12A or straight grooves 12B. Typically, the recesses will be slightly curved or angled in order to help guiding, dispersing, and atomizing the liquid. The purpose of the recesses is to tear up the liquid so that this liquid is atomized to form a liquid mist. The assembly may be designed with en external edge 12f for being engaged by a tool, typically a hexagonal edge.

Fig. 12(i) shows a detail of the recesses. For example, these recesses may be shaped as teeth in a cog wheel, be saw-toothed or serrated.

I the embodiments illustrated, the adapter is shown threaded into the nipple. Alternatively, these two elements could have been made in one piece. The deflecting surface may also be constituted by a separate part that may be replaced, and each assembly may be adapted, for example, for deflecting surfaces having different angles or surface structure. Typically, the deflecting surface may be produced as a separate serrated ring. The embodiments shown have been found to be easily producible as well as cost efficient, while at the same time being flexible and possible to deliver with or without thermal release. Normally, the deflecting surface is substantially circular. In this connection, substantially circular also includes oblong or oval, for example, and such shapes may be relevant for use in oblong rooms, for example, as the water throwing length may vary in different directions. Normally, the deflecting surface runs around the entire nipple.

In normal operation of the arrangement, extinguishant flows through the liquid inlet of the adapter section, through the internal duct that connects to the liquid inlet, and out through openings provided around the nipple section. From these openings, the jet of extinguishant flows freely to the deflecting surface, which it hits with the angle a and is atomized to a water mist in the form of small droplets. The angle is dictated by the angle of the openings determining the angle of the jet relative to the angle of the deflecting surface, as explained above. The serrations or grooves may have deep to shallow grooves with varying directional angles for the grooves as shown in fig. 12(i).

In the above description the fire extinguishing assembly has been described in connection with a permanent installation. Of course, however, an assembly according to the invention may be used for portable equipment, and is very well adapted for such use as the invention is light and compact. For example, the fire extinguishing assembly may be used in small vehicles or lances being entered into a fire zone or on a spear which is run through walls/roofs/floors of a rom being in fire.

The present fire extinguishing assembly has been described in connection with the extinguishment of fire. Of course, however, the assembly may also be used in places at which a need exists for a water mist or dispersion of water, such as in connection with moistening of air, for different purposes in green houses, storage of timber to be kept in a moist condition, etc.

Claims

C L A I M S

1. A fire extinguishing assembly for transforming a liquid into a liquid mist, the assembly comprising an adapter section (3a, 14a) having at least one liquid inlet (3b, 14b) and a nipple section (6a, 9a) in connection with the adapter section, the nipple section comprising multiple bores (6c, 9c) extending between an internal duct (12g) that connects to the liquid inlet (3b, 14b) and outlets on an outside of the nipple section (6a, 9a), with the bores (6c, 9c) being positioned around the nipple section (6a, 9a)

c h a r a c t e r i z e d i n that:

a deflecting surface (3d, 12d) for guiding the liquid is positioned around the outlets (6c, 9c) of the bores;

the deflecting surface (3d, 12d) includes recesses running in a direction substantially from the nipple section (6a, 9a) to a circumference of the deflecting surface (3d, 12d); and

the bores (6c, 9c) and deflecting surface (3d, 12d) have a mutual positioning so that straight liquid jets flowing through the bores (6c, 9c) will hit the deflecting surface (3d, 12d) in a point of impingement having at least a bevel angle a.

2. The fire extinguishing assembly of claim 1 , wherein the recesses of the deflecting surface are shaped in order to provide a component of movement in a tangential direction.

3. The fire extinguishing assembly of claim 2, wherein the nipple section has a circular cross-section, and liquid jets flowing through the bores (6c, 9c) passes in a plane extending in a radial direction out of the bores (6c, 9c) relative to the circular cross-section of the nipple section.

4. The fire extinguishing assembly of claim 3, wherein the recesses extend with a component tangential to the circumference of the nipple.

5. The fire extinguishing assembly of claim 3, wherein the nipple section has a longitudinal axis and the bores (6c, 9c) have a bevel angle relative to the longitudinal axis of the nipple section.

6. The fire extinguishing assembly of claim 1 , wherein the nipple section comprises an internal guiding body (9d) in order to increase the velocity of the liquid towards the bores (6c, 9c).

7. The fire extinguishing assembly of claim 1 , further comprising a valve having a valve body (4a), the valve body (4a) comprising a valve spindle (4d) contacting a heat-sensitive element (5a), and the valve body (4a) being able to assume a first position in which the inlet (3b) is sealed off and a second position in which the inlet (3b) is in fluid communication with the bores (6c).

8. The fire extinguishing assembly of claim 1 , wherein the angle a ranges from 10° to 45°.

9. The fire extinguishing assembly of claim 1 , the bores (6c, 9c) being positioned in at least one ring around the nipple section (6a, 9a), and wherein the outlets on the outside of the nipple section (6a, 9a) are adjusted so that every second liquid jet hit a point at a first distance from the deflecting surface (3d, 12d) and the remaining the liquid jets hit a point at a second distance from the deflecting surface (3d, 12d), with the first distance being different from the second distance.

10. The fire extinguishing assembly of claim 9, wherein the first and second distances are adjusted by varying an outlet angle.

11. The fire extinguishing assembly of claim 9, wherein the first and second distances are adjusted in that every second outlet are positioned along a first ring around the nipple and the remaining outlets are positioned along a second ring around the nipple, with the first and second ring being located in a spaced relation from each other.

12. The fire extinguishing assembly of claim 9, wherein the deflecting surface is designed with two different angles (a1 , a2) so that every second liquid jet hit the surface at the first angle (crt) and the remaining liquid jets hit the surface at the other angle (a2) in order to provide a larger volume liquid mist screen.