HK1044300A1 - Method for attenuating a heat flow and device for realising the same - Google Patents

Abstract

The invention relates to fire-prevention equipment and may be applied for the protection of the equipment and people during fighting a fire, for dividing the area of buildings, ground and underground structures and apparatus into fire-checking section, preventing the fall of ceilings and intermediate floors, and stopping the spread of large fires destroying the environment. The objective of the present invention is to provide a higher efficiency method of attenuating energy flow in the form of light, heat and convective gas flows and designing of an apparatus attachable to the fire monitor for the forming of a protecting screen against thermal radiation, safe, convenient and reliable; and allowing to protect from light spectre radiation and convective gas flows. The method envisages the creation of curtain from a cooling liquid that is sprayed into the space between the surfaces. When more than one curtain is formed, a combined supply of cooling liquid is used. One of the curtains is made by spraying the liquid, whereas the others by supplying foam. The apparatus consists of a frame, a sprinkling assembly and nets attached at interval to the both sides of the frame. In the openings of the frame is equipped by sprayers. <IMAGE>

Description

The present invention relates to a method and apparatus for attenuating a heat flow. The innovation may be used for screening heat flows of fires to protect equipment and people against fire attacks and to stop spread of fires on exposed areas as well as in buildings and structures.

Patent GB-A-1 492 003 discloses a flame and smoke containment system which isolates a fire starting area from neighbouring areas by means of a fire curtain and which is designed for use in a room having a floor and ceiling. The curtain is created by a method comprising the steps of installing two protective surfaces from a non-inflammable material (two nets or cloths) and of supplying a cooling fluid, which is a foam or a mixture of water with a foaming agent, in a space between the surfaces. The cooling fluid runs out from a device, which arranged above the fire curtain and outside of it. By gravity, the cooling liquid freely falls down between the nets or the clots as well as flows over the nets or the clots and fills the space between ones.

The method disclosed in the said patent has disadvantage consisting in that foams decompose under exposure to large heat flows. For example, on exposure to the heat flow of 20 kW/m², foam bubbles coalesce over several seconds and the curtain loses its fire-protective property. Therefore the curtain created using the said method does not apply as fire-protective means even at a fire with the heat flow of 20 kW/m², whereas at fires heat flows may ranges up to 250 kW/m² (The heat flow of the order of 250 kW/m² can take place at large fires on timber warehouses).

Inventor's Certificate of the USSR "Avtorskoe svidetel'stvo SSSR No. 1666129" discloses an apparatus attached to a monitor to protect from heat radiation. The apparatus contains a sprinkling assembly, which consists of a V-shaped water stream splitter, two parallel plates, a mechanism for changing the angle between the plates of the V-shaped splitter. Water supplied under pressure through the monitor casing enters the sprinkling assembly. There it changes its direction and spreads over the plates forming two thin water films separated by the layer of air.

The disadvantage of this apparatus is that it requires a fixed pressure of water in order to maintain the aforementioned water films in a stable state. However this condition is difficult to ensure since water pressure is not stable and difficult to control. Furthermore, the monitor cannot change its position, which is a disadvantage too.

The apparatus disclosed in patent GB-A-1 492 003 is a fire protection curtain (screen) being formed from two protective surfaces placed some distance apart. These protective surfaces are two nets or cloths. In another embodiment of the invention, the curtain is formed from one vertically installed net (or coarse cloth). The cooling fluid (a foam or a mixture of water with a foaming agent) is supplied in a space between the protective surfaces from the device (foaming means with a diffusion chamber and foam producers), which arranged above the fire protection screen and outside of it. The apparatus is intended for use in a room having a floor and a ceiling. The device is mounted on the ceiling. If this system is applied for prevention in a wide room, a plurality of the curtains can be arranged in a checking pattern to divide the room into several sections.

The use of the apparatus disclosed in patent GB-A-1 492 003 is restricted to applications in buildings and structures. The apparatus include complex equipment with device for forming and supplying a cooling fluid, and the equipment requires a ceiling in order to be mounted. The apparatus cannot be used on exposed areas, and also cannot be used in cases when the fire protection screen is to be movable (for example, to use it for protection of a fireman who fights a fire). A monitor cannot be fitted to the apparatus. As mentioned above, the apparatus cannot be used as a fire protection means even at heat flow of 20 kW/m².

An object of the present invention is to provide a method and apparatus for attenuating a heat flow to protect equipment and people against attack of a fire with a heat flow of as large as 20 kW/m² and over and to stop spread of such fire on exposed areas as well as in buildings and structures.

In accordance with the present invention, there is provided a method for attenuating a heat flow, comprising the step of creating a fire protection screen by installing two protective surfaces and by supplying a cooling fluid in a space between the surfaces, characterized in that water is used as a cooling fluid, said water is supplied by means of controlled sprinkling or controlled spraying in the space between the protective surfaces at least one of which is a net, said sprinkling or spraying is performed controlling the quantity (mass) of the supplied water and the distance between said protective surfaces and creating a vapour-drop-air medium between said surfaces and water films on said surfaces.

Further, in accordance with the present invention, there is provided an apparatus for attenuating a heat flow, the apparatus comprising a fire protective screen being formed from two protective surfaces placed some distance apart and a device for supplying a cooling fluid in a space between the protective surfaces, characterized in that said device is a sprinkling assembly comprising a frame and sprayers for fine dispersion of cooling fluid, said sprinkling assembly is mounted between said surfaces at least one of which is a net, said frame is made in form of communicating tubes being placed vertically and horizontally and having openings for supplying water as cooling fluid, said sprayers are mounted in said openings of tubes so that a vapour-drop-air medium is formed in space between said surfaces at least one of which is a net and so that water films are formed on said surfaces at least one of which is a net, and in central part of the protective screen there is an aperture for monitor nozzle projecting through said aperture.

The nets are wattled and/or perforated and/or punched.

The nets are made of powder metallurgy products.

The nets are made of fireproof plastic.

The nets are made of copper.

The nets are made of a material coated by a metal film.

The nets are made of a galvanized steel.

The size of a net cell is 0.1×0.1- 8.0×8.0 mm.

An interval between the frame and protective surface is 1-200 mm.

The characteristics of the external net (the diameter of a wire, the material, the size of a cell, the type: wattled, perforated, punched) are identical with those of the internal net.

The characteristics of the external net (the diameter of a wire, the material, the size of a cell, the type: wattled, perforated, punched) are different from those of the internal net.

The protective screen can be arranged in front of the monitor and on its sides.

The protective screen can be arranged along the perimeter around the monitor, and, if need be, it can be arranged overhead and below of the monitor.

The object of the present invention is accomplished owing to the fact that water is controlled sprinkled/sprayed by sprayers in a space between two protective surfaces, at least one of which is a net, forming a vapour-drop-air medium in a space between said surfaces and water films on said surfaces, and owing to the fact that the degree of attenuation of a heat flow depends heavily on conditions of interaction of water drops and vapour particles in said medium and of said films with each other and with the protective surfaces. The change of the quantity (mass) of the supplied water and of the distance between the surfaces leads to change of the density of water drops in the space between the surfaces and thus to change of the conditions of said interaction. By controlling the quantity of water and the distance between the surfaces, the different degree of attenuation of a heat flow can be obtained, including the degree of attenuation which is suffice to attenuate a heat flow as large as 250 kW/m² up to safe values (less than 3-4 kW/m² which is safe for firemen equipped with ordinary protection means, or up to 1.5 kW/m² which is safe for man not equipped any protection means).

The average diameter of drops decreases with an increase of the fluid pressure at the sprayer.

The fire pumps supply water under a pressure of 1.2 MPa; in so doing the average diameter of sprayed fluid drops is equal 400-500 micron. When devices of high pressure are used the differential in pressure inside sprayers may reach 15 MPa; in this case the diameter of drops may be reduces to 5-10 micron. Absorbing the heat radiation, the drops of sprayed fluid are starting to evaporate when they approach the protective surfaces as well as come in contact with these surfaces; it is enhanced by the fact that the drops of liquid with high kinetic energy are reflected repetitively from protective surfaces in space between them. The type and material of the protective surfaces, e.g. in the form of nets, their characteristics, the size of the nets cell, diameter and the material of the wire, etc. are chosen so that a cooling fluid film is being formed as a result of surface tension. The consistency of the film is maintained by dynamic equilibrium between the process of its evaporation, while heat energy is absorbed, and the process of constant supply the fluid into the film, when the sprayed fluid drops bump against the film.

Thus, there is a medium formed of vapour, cooling fluid drops and air (a vapour-drop-air medium) in the space between the surfaces. The flows of heat and visible spectrum radiation, as well as convection gas flows is partly reflected from these surfaces (e.g. from the nets), from the cooling fluid films and the vapour-drop-air medium. In addition the heat energy is partly absorbed by these films and medium and "channelled" perpendicularly to the direction of the attacked heat flow movement.

It is obvious that the symbiosis of the above-mentioned processes of reflection and absorption determines one unique feature of the apparatus under consideration: the efficiency of the screening effect against the attacking heat flow increases along with growth of the intensity of this heat flow.

The spraying of the cooling fluid into fine dispersion state by means of a high pressure devices, so that diameters of drops are comparable with the wavelengths of heat radiation (1.5-7 micron), also adds to the increase in the heat flow screening efficiency by the apparatus under consideration. In accordance with the laws of geometrical optics, the scattering of the heat radiation increases several times if dispersity of the fluid drops is optimal.

The necessity of controlling the quantity M of cooling fluid supplied into the space between protective surfaces (they may be made of metal fabric, glass fabric, metal plates or other materials) is caused by considerable variation of the value of heat flows W which take place at fires (from 0 to 200-250 kW/m²). A special protection is required for fire-fighters if W≅3-4 kW/m².

Let us assume that the heat flow W ₀ falls perpendicularly on the surface of the fire protection screen: ${\text{W}}_{\text{0}}\text{=}{\text{W}}_{\text{1}}\text{+}{\text{W}}_{\text{2}}\text{+}{\text{W}}_{\text{3}}$    where W ₁ is the part of heat flow reflected from the screen, W ₂ is the part of heat flow penetrated through the screen, W ₃ is the part of heat flow absorbed by the cooling fluid of the screen. Obviously, with the changing of M, W ₃ is changed mostly.

Let us consider a hypothetical case where the heat flow W ₀ is totally absorbed by the cooling agent (by the water in particular).

Let us assume that 100 gm. of water is sprayed into the 1 m² space between the screen nets. Let us estimate the W ₀ assuming that the heating up to 100°C as well as vaporisation run during 1 second.

In this case ${\text{Q}}_{\text{0}}\text{=}{\text{Q}}_{\text{h}}\text{+}{\text{Q}}_{\text{s}}$ where

• Q0 is the total quantity of heat,
• Qh=CM(t2-t1) is the quantity of heat required for the heating from temperature t1=0°C to temperature t2 = 100°C of 100 gm. of water with specific heat C=4.2 kj kg.-1 deg-1 ,
• Qs = λM is the vaporisation heat,
• λ=22.6·102 kj/kg. is the specific evaporation heat of water.Q0 = 4.2·104 j + 22.6 ·104 j.

Notice that Q _s is more than Q _h by the factor of 5.

For the case under consideration such value of Q ₀ corresponds to W ₀ = 268 kW/m².

Heat flows with such volume of W ₀ are seen at large fires on timber warehouses. When a gas gusher is in flame, the heat flow may be as much as 30-40 kW/m². Largest attenuation of W ₀ by vapour-drop-air medium can be obtained if the average diameter of water drops is comparable to the wavelength of the heat radiation (5-10 micron).

In this case a 5-7 times attenuation was achieved experimentally. Since speed of water drops was 10-100 m/sec, the process of steam generation is of little significance for the absorption of heat.

The attenuation of W ₀ by the factor 4-5 was obtained using a curtain of only one net cooled by water.

In the case where a curtain with two nets placed at some interval is employed, the water drops are reflected repeatedly from surfaces of the nets in the space between of them. This phenomenon is accompanied by following processes: slowing of the speed of drops, splitting of drops into more fine ones, adhering of some drops on the nets. As a result of the aforementioned process there appears a water film on the surface of the net wire, besides, a water film is formed the net cells if the size of the net cells allows it. Owing to these processes, the absorption of the attacking heat flow increases since it goes on heating and evaporation the drops and films of water. Besides, the two protecting surfaces increase the process of dissipation and reflection of heat flows and convective gas flows - W ₁. This dissipation and reflection is effected both by the nets and the water film, formed on the net surface, as well as by a vapour-drop-air medium formed in the space between the nets.

It is important to note that during the experiments it was possible to observe the interaction between the flows of the infrared and visible spectrum radiation visible and convective gas flows with the vapour-drop-air medium formed immediately in front of the protecting screen on the side of the heat flow falling.

When the water drops collide with the protecting nets, drops split into even finer ones; several of those go out of the space between the net surfaces. Fine-dispersed water splashes, passed through the forward net (it is arranged on the side of the falling of the heat flow) and evaporating water steam form a visually observable layer consisting of a vapour-drop-air medium and adjacent to the external surface of the frontal net, facing towards the fire.

The interaction between the convection flows of hot gases, falling on the frontal net surface facing towards the fire and reflected from them with this external layer of vapour-drop-air medium causes the visually observable unstable pulsation of this medium and "running" down of heat energy along the frontal net surface in direction that is perpendicular to the direction of the vector of the heat flow (W ₀) expansion.

Thus, the proposed method for attenuating a heat flow differs essentially from the known ones. It qualitatively changes the situation in cases when the process of absorption and evaporation begin to play a considerable role in attenuation of heat flows. As was shown by the above calculations, theoretically these processes are capable to solve the problem of protecting from heat attack even at largest fires. It should be noted that in this method W ₁ and W ₂ increase with increasing W ₀, i.e. during the functioning of the screen there is a self-regulating attenuation of the falling heat flow. At the same time, the present invention makes for the regulation of this process by artificial means, since the degree of attenuation of the falling heat flow essentially depends on the processes of absorption and evaporation. This regulation may be performed either automatically (by means of computer program, receiving data from the heat sensor) or manually. Experimentally, the regulation was performed by closing and opening of some of the sprayers, supplying water into the space between the nets, or by changing the pressure of water or any other cooling agent. The artificial regulation of attenuation of the falling heat flows makes possible obtaining the desired attenuation of W ₀ with economical consumption of water, with is used for forming and maintaining the vapour-drop-air medium.

The addition of colour agents to the supplied liquid, increases the efficiency of the heat screening by the present device, since in this case the absorptivity of falling energy by the vapour-drop-air medium will increase.

When the sprinkling assembly is made as a system of sprayers arranged by special way on the frame, it allows to ensure a homogeneous distribution of drops of the liquid in the space between the surfaces, or the nets, that fixed on both side of the frame at some interval from each other.

If the protecting screen is made in the form of a semicircle, it allows the protection of monitor operator against hazardous factors of fire at the front and the sides. In order to put out a fire on especially dangerous objects, the screen may be arranged along the perimeter of the monitor as well as on top of it. In this case the monitor operator will be screened from the front, the sides, the rear and from above.

If all the construction is placed on the wheeled flat-car, it will make it easily movable. If it is equipped with a drive, it will make the construction mobile.

The present invention will now be further described with reference to the accompanying drawings; in doing so an embodiment of the invention, which is an apparatus for protecting of monitor operator, will be described by way of example. The accompanying drawings are: Figure 1 shows the general view of the stationary version of apparatus for protecting a monitor operator; Figure 2 shows a top view of the apparatus; Figure 3 shows a fragment of the sprinkling assembly with sprayers (View A of Figure 1); Figure 4 shows a side view of the apparatus in the direction B of Figure 1; Figure 5 shows a top view of the apparatus with a screen located round the monitor; Figure 6 shows the apparatus equipped with wheels and a drive.

The apparatus for protecting a monitor operator has a support 2, a fire protective screen 3, and a sprinkling assembly. The support analogous with that of the monitor or the frame of the sprinkling assembly can be used in capacity of the latter. The sprinkling assembly is made in the form of a frame 4 of communicating tubes placed both horizontally and vertically. The tubes are equipped with sprayers 5. In central part of the frame there is an aperture 6 for vertical movement of the monitor nozzle 1. The frame 4 equipped by two metal nets 7 and 8, which are fixed on both side of the frame at some intervals and forms the fire protective screen 3 (in Figures 2 and 4 these nets are shown by special hatching; in Figures 5 and 6 some fragments are shown by the same hatching; in Figure 1 it is shown by perpendicular lines 9, which graphically represent the net cells without regard to the scale). The support 2 has an arched guide 11 of radius R, and the frame 4 has rollers 10 placed at its bottom. Thanks to these rollers the frame can be moved along the support. The monitor 1 has a handle 12.

The vertical axis of rotation O ₁ of the monitor is shifted away from the vertical axis of rotation O ₂ of the fire protection screen towards the screen 3. Owing to the shift, a monitor operator is closer to the screen 3 and consequently more protected.

The support 2 connected with the monitor is placed on the platform 13, which equipped with wheels 14 and motor 15. The fire protection screen 3 may be arranged so that a monitor operator will be protected from the front and the sides (Figure 2), or it may be arranged along the perimeter protecting a monitor operator from the front, the sides, the rear and from above (Figure 5 and 6). The nets 7 and 8 of the fire protection screens 3 may be wattled or perforated. In the former case, the diameter of the wire may vary in the range from 0.1*0.1 mm to 8.0*8.0 mm. The wire in diameters under 0.1 mm is not capable to resist mechanical tensions, whereas the use of wire in diameters over 3.0 mm leads to the increasing of weight of the screen, with the result that the apparatus loses its manoeuvrability. The size of the wattled net cells may vary in the range from 0.1*0.1 mm to 8.0*8.0 mm depending on the diameters of the wire. The net, that is exterior with regard to the monitor operator, may be made from thicker wire and with larger cell size.

The nets may be made of wire with the same diameters, and their cells may be uniform in size. The nets may be made using any wires, e.g. manufactured of metals (copper, brass or any other), ceramics or products of the powder metallurgy. The net may be made of fire proof plastic. The nets may be perforated or punched.

The fire protection screen, which includes two protective surfaces in the form of nets (the net 7, that is internal surface, and the net 8, that is external surface), can be made as a combination of surfaces in various types. For example, the external surface may be made as net (wattled, perforated or punched), whereas the internal surface may be made of metal sheet, transparent fireproof polymer, which may be reinforced by metal net, or it may be made as compound one (e. g., it is a net on the level of the operator's eyes internal surface 7 is made in the form of a net, whereas the rest of it is the metal sheet).

The apparatus works as follows: at the fire, water through the communicating tubes (not shown on the figures) is supplied to the monitor and through the system of tubes 4 is further supplied to the sprayers 5. A powerful jet of water is supplied to the fire-core by means of the monitor, and simultaneously water is sprayed by means of the sprayers 5 in the space between the nets 7 and 8. Water, sprayed by the sprayers, and vapour, generating as a result of interaction of the heat flow and sprayed water drops, create in the space between the nets a vapour-drop-air medium, which effectively reflects and absorbs the heat flows and therefore, ensures the safe working condition for the monitor operator. Additionally, a silhouette visibility of the situation at the fire-site is ensured.

Apart from self-controlling increase in attenuating a heat flow, a regulated attenuation by means of existing methods (computer systems of automatic regulation or manual methods of regulations) can be used.

This kind of regulation can be achieved by placing the heat sensors with spectral diapason including a visible and infrared spectrum of radiation in front of the protecting screen.

During the fire computers systems constantly receives information the sensors, and introduces necessary corrections in the number of sprayers, water pressure and the quantity of water supplied into the space between the nets.

This regulation of the protecting properties of the screen may be effected by the monitor operator themselves by the existing methods.

When the protecting screen 3 is placed on rollers, it makes it possible to turn it around vertical axis O₂ and to fix it in the desired direction by means of a handle 12.

The same handle allows the vertical movement of the monitor in accordance with the desired angle with regards to the horizon to supply the cooling fluid to the desired distance.

A combined curtain is used to safeguard the life of people at the places with the concentration of large number of people, e.g. specific anti-fire curtain at theatres. In this case, the curtain, the first on the side of the stage is formed by the two surfaces and water sprayed between them; the second curtain is formed by supplying foam into the space between the second and third surfaces. In this case, a step-by-step attenuation of the powerful heat and gas flows at strong fire on the stage. The vapour-drop-air curtain, next to fire, is the first to reduce the heat flows and protect the next foam curtain against destructive impact of heat. All aforementioned allows to increase the efficiency and longevity of this combined curtain at extreme situations, e.g. in the moment prior to the evacuation of people from the theatre hall; it also allows to stop the penetration of toxic gases into the theatre hall.

Claims (11)

1. A method for attenuating a heat flow, comprising the step of creating a fire protection screen by installing two protective surfaces and by supplying a cooling fluid in a space between the surfaces, characterized in that water is used as a cooling fluid, said water is supplied by means of controlled sprinkling or controlled spraying in the space between the protective surfaces at least one of which is a net, said sprinkling or spraying is performed controlling the quantity (mass) of the supplied water and the distance between said protective surfaces and creating a vapour-drop-air medium between said surfaces and water films on said surfaces.
2. An apparatus for attenuating a heat flow, comprising a fire protective screen (3) being formed from two protective surfaces (7, 8) placed some distance apart and a device for supplying a cooling fluid in a space between the protective surfaces, characterized in that said device is a sprinkling assembly comprising a frame (4) and sprayers (5) for fine dispersion of cooling fluid, said sprinkling assembly is mounted between said surfaces (7, 8) at least one of which is a net, said frame (4) is made in form of communicating tubes being placed vertically and horizontally and having openings for supplying water as cooling fluid, said sprayers (5) are mounted in said openings of tubes so that a vapour-drop-air medium is formed in space between said surfaces and so that water films are formed on said surfaces, and in central part of the protective screen (3) there is an aperture (6) for monitor nozzle (1) projecting through said aperture.
3. An apparatus as claimed in claim 2, characterized in that the protective surfaces are wattled and/or perforated and/or punched nets (7, 8).
4. An apparatus as claimed in claim 2 and 3, characterized in that the nets (7, 8) are made of powder metallurgy products.
5. An apparatus as claimed in claim 2 and 3, characterized in that the nets (7, 8) are made of fireproof plastic.
6. An apparatus claimed in claim 2 and 3, characterized in that the nets (7, 8) are made of copper.
7. An apparatus as claimed in claim 2 and 3, characterized in that the nets (7, 8) are made of a material coated by a metal film.
8. An apparatus as claimed in claim 2 and 3, characterized in that the nets (7, 8) are made of galvanized steel.
9. An apparatus as claimed in claim 2, characterized in that the interval between the frame (4) and the protective surfaces (7, 8) is 1-200 mm.
10. An apparatus as claimed in claim 2, characterized in that the protective screen is arranged in front of the monitor and on its sides.
11. An apparatus as claimed in claim 2, characterized in that the protective screen is arranged along the perimeter around the monitor, and, if need be, overhead and below of the monitor.