IT202300008538A1 - MIXING DEVICE AND METHOD FOR CAFS SYSTEMS - Google Patents

Description

DESCRIPTION

Attached to a patent application for an INDUSTRIAL INVENTION having as its title

?MIXING DEVICE AND METHOD FOR CAFS SYSTEMS?

The present invention relates to a mixing device and method for CAFS systems.

The present invention therefore refers to a device and a method for mixing a solution of water and foam with pressurized air for the generation of compressed air foam (Compressed Air Foam System) capable of extinguishing fires.

As is well known, the necessary elements that fuel combustion, often referred to as the "fire triangle", are fuel, oxygen and heat. Compressed air foam (CAFS) is more effective at extinguishing a fire than plain water or even a mixture of water and concentrated foam because it addresses all three elements of the fire triangle.

In fact, the CAFS system is highly effective because:

- coats the fuel, cooling it below combustion temperature;

- coats the fuel, separating it from the oxygen needed to keep it burning, which also prevents the outgassing of the fuel gases;

- cools an overheated environment by creating steam with the application of water-based foam.

Another advantage that the CAFS system has over water is that water damage and runoff is dramatically reduced.

In fact, the CAFS system is a foamy solution that, depending on its consistency, flows at different speeds, generally lower than the speed of delivery of water alone.

Lower speeds, and consequently lower flow rates, are related to a smaller quantity of mixture used and therefore less damage to the surrounding environment.

It follows that reduced speeds, compared to the pressure of water alone, result in greater protection with regard to possible damage to objects and/or people.

Additionally, depending on the response needs, a very dry CAFS system will remain in place like a blanket for hours, while a very wet CAFS system may drain away in minutes.

The distinction between wet CAFS and dry CAFS is linked to the ratio between the air flow rate and the mixture flow rate (foam water).

The dry CAFS system has a very long drainage time due to the bubbles that burst less easily and consequently do not lose their water quickly.

In this way, the extinguishing action of the foam is prolonged for a longer time and until the burnt parts have cooled optimally.

In other words, the CAFS system is able to provide a range of useful consistencies, from very dry to very wet, by controlling the air/water ratio and foam concentrate.

The very wet CAFS system is often used in the initial phase of firefighting to immediately cool the fuel and atmosphere.

The dry CAFS system, on the other hand, has a very long drainage time: the bubbles do not burst and quickly lose their water, which is effective if used in a later stage of firefighting, as a blanket to separate the fuel from the oxygen, to protect exposed fuel from the advance of the fire and to prevent the outgassing of overheated materials.

Additionally, CAFS systems can be especially valuable to firefighters because the use of foam reduces the amount of water needed to extinguish a fire in areas where water sources may be limited or nonexistent.

Less water required also dramatically reduces the weight and size of the CAFS system, allowing for reduced manpower and rapid threat clearance prior to the arrival of additional equipment and/or personnel.

Current methods and devices for mixing compressed air and foam solution feed the compressed air into a single injection port located on the outer periphery of a hydraulic component which may be for example a valve body, a fitting or a tube through which the foam solution flows.

With such single-point injection, the compressed air is not uniformly distributed within the foam solution and the resulting structure of the bubbles contained in the mixture is inhomogeneous.

Furthermore, the compressed air injection section is typically large in size, resulting in the production of bubbles with a diameter of higher order than 10<0 >mm.

For example, CAFS systems are known that use static mixers or scrubbers consisting of a series of perforated plates, disks or other irregular shapes, arranged within the mixture delivery duct and downstream of the air injection location to interrupt the flow path and cause turbulence to further mix the compressed air and foam solution.

While this interruption in flow improves mixing and foam formation, friction across the device increases, resulting in a reduction in the pressure of the flow delivered. Consequently, the CAFS systems described above have the significant disadvantage of limiting the flow rate exiting a fire hose or nozzle directed at the fire being extinguished.

Furthermore, while the prior art systems and methods described above (and other systems and methods currently in use for foam generation) may result in foam generation adequate for some specific purposes, these systems and methods nevertheless fail to generate foam in a manner and quality suitable for widespread and effective use and are improvable in several respects.

Therefore, there remains a need for foam generation devices that are capable of producing high volumes of foam with homogeneous bubbles that can be efficiently dispensed when and where needed.

In this context, to improve the effectiveness of CAFS systems it is necessary to obtain a flow with bubbles of the smallest possible size and homogeneous both in spatial distribution and in average dimensional dispersion.

All other things being equal, a smaller average bubble diameter and a more homogeneous distribution provide several advantages:

- given the same volume of air, smaller bubbles maximize the heat exchange surface and therefore directly influence the heat extracted from the target combustion;

- a homogeneous injection of air with small bubbles maximizes the expansion process of the bubbles in the mixture (water - foam - air) once the ambient pressure is reached, resulting in the production of foam with better extinguishing properties;

- a homogeneous injection of air with small bubbles also maximizes the adhesion power of the foam thus generated on the surfaces, allowing for greater protection potential of the fire-fighting foam layer on vertical and/or very inclined walls;

- the greater extinguishing power allows for the use of less water, resulting in greater autonomy of the fire-fighting vehicle with the same tank size.

Advantageously, the lower use and consumption of water leads to further benefits in terms of the size of the devices for dispensing and transporting the mixture, as the water-foam tanks are smaller.

Furthermore, lower water consumption also brings economic and environmental benefits.

The technical task of the present invention is therefore to provide a mixing device and method for CAFS systems that is able to overcome the drawbacks that have emerged from the prior art.

The aim of the present invention is therefore to provide a device and a mixing method for CAFS systems capable of minimising the average diameter of the air bubbles by implicitly maximising their quantity for the same volume injected per unit of time.

A further aim of the present solution is therefore to provide a device and a mixing method for CAFS systems capable of making the flow of air injected into the volume of the foam fluid (water and foaming agent) as homogeneous as possible in order to maximise the physical reaction of bubble generation and consequently increase the density of the compressed air foam.

Finally, a further aim of the present invention is to provide a mixing device and method for CAFS systems capable of minimizing the dimensional dispersion of the diameter of the air bubbles.

The specified technical task and the specified purposes are substantially achieved by a mixing device and method for CAFS systems comprising the technical characteristics set out in one or more of the accompanying claims.

According to one aspect of the present invention, a mixing device for CAFS systems is provided.

The mixing device comprises a mixture source consisting of at least one water component and one fire-fighting foam component.

The mixing device also includes a source of pressurized air.

The mixing device comprises a first duct and a second duct, respectively connected to the mixture source and to the pressurized air source.

The first duct features a channel that extends from an inlet to an outlet.

The inlet is in fluid communication with the mixture source.

The outlet is configured to release compressed air foam.

The second duct, for the injection of compressed air, extends from a first end in fluid communication with the source of pressurized air and a second end inside the first duct.

The second duct comprises at least a first tubular portion and at least a second tubular portion inserted concentrically within the first duct.

The second tubular portion also includes at least one compressed air passage section.

This feature allows to maximize the physical reaction of bubble generation and consequently increase the density of the compressed air foam.

The specified technical task and the specified purposes are further achieved by a mixing method for CAFS systems.

The method comprises the step of injecting mixture into a first duct, internally defining a channel, connected to a source of mixture towards an outlet, of the first duct, configured to release compressed air foam.

The method further comprises the step of injecting compressed air transversely to the direction of mixture injection into the channel of the first duct.

This feature allows the mixture of pressurized air and foam to be as homogeneous as possible.

Further features and advantages of the present invention will become clearer from the indicative, and therefore non-limiting, description of a device and a mixing method for CAFS systems.

This description will be set out below with reference to the attached drawings provided for indicative purposes only and therefore not limiting, in which:

- Figure 1 shows a side elevation and longitudinal section view of a mixing device for CAFS systems according to the present invention;

- Figure 2 is a side elevation view of the device of Figure 1; and - Figure 3 is a perspective and front view of the device of Figure 1.

With reference to the attached figures, 1 generally indicates a mixing device for CAFS systems which, for simplicity of description, will be referred to below as mixing device 1.

The mixing device 1 comprises a mixture source ?A?, a pressurized air source ?B?, a first duct 2 in fluid communication with the mixture source ?A? and a second duct 6 for the injection of compressed air.

The mixture source "A" is made up of at least one water component and one fire-fighting foam component.

The first conduit 2 has a channel 3 that extends from an input 4 to an output 5.

Preferably, the channel 3 of the first duct 2 comprises at least one expansion 12 of the section.

Inlet 4 is in fluid communication with the mixture source ?A?, while outlet 5 is configured to release compressed air foam ?C? towards a fire to be extinguished.

The second duct 6, for the injection of compressed air, extends from a first end 7 in fluid communication with the pressurized air source ?B? and a second end 8 inside the first duct 2.

Preferably, the second end 8 of the second duct 6 is occluded. In other words, the second duct 6 has an inlet, i.e. the first end 7 in fluid communication with the pressurized air source “B”, but at the second end 8 there is no opening or outlet for the passage of compressed air.

The second duct 6 comprises at least a first tubular portion 9 and at least a second tubular portion 10 inserted concentrically inside the first duct 2.

In other words, the second tubular portion 10 is arranged with its respective longitudinal development axis coinciding with the longitudinal development axis of the first duct 2. This positioning is obtained by means of respective fins 14 (visible in figures 1 and 3) which engage the second tubular portion 10 in position with respect to the internal surface of the first duct 2.

In particular, four fins 14 are provided, equidistant from each other and arranged around the peripheral development of the second tubular portion 10. Each fin 14 engages the external surface of the second tubular portion 10, close to the first portion 9, with the internal surface of the duct 2. In this way the fins 14 have the function of centering the second portion 10, keeping it at the center and inside the duct 2.

Advantageously, from a structural point of view, the fins 14 allow the avoidance of risky vibration phenomena.

Furthermore, each fin 10 is arranged edgewise, i.e. with a flat surface parallel to the direction of advancement of the mixture, so as not to deviate or interfere with such feeding.

Preferably, the first tubular portion 9 is transverse to the second tubular portion 10 and the first tubular portion 9 is arranged perpendicular to the longitudinal development of the first duct 2.

According to a possible embodiment, at least one expansion 12 of the section of the channel 3 of the first duct 2 is placed in proximity to the first tubular portion 9 of the second duct 6.

Specifically, the at least one expansion 12 of the channel section 3 can be placed between the inlet 4 of the first duct 2 and the first tubular portion 9 of the second duct 6.

In other words, the geometry of the first duct 2 has an expansion 12 of the channel 3 in proximity to the insertion of the second duct 6.

Advantageously, the expansion 12 of the channel 3 is arranged upstream of the second duct 6.

The resulting recovery of local static pressure, resulting from the geometric positioning of the at least one expansion 12 of the section, allows the containment of the local volume of bubbles that are created by the mixing of the mixture and pressurized air.

In other words, it is essential that the bubbles that form the compressed air foam are correctly formed and distributed, thanks to which it is possible to derive, depending on their physical and chemical properties, all the technical characteristics that facilitate the extinguishing of fires.

The second tubular portion 10 further comprises at least one passage section 11 for compressed air.

The injection takes place coaxially in the centre of channel 3 in such a way as to make the mixture of air and foam as homogeneous as possible.

More specifically, the injection occurs from the center of channel 3 and towards the periphery, in a radial direction with respect to the cross-section of channel 3 itself.

Advantageously, the coaxial injection allows the compressed air to follow the channel 3 of the first duct 2, where the mixture is injected, without creating a high pressure drop inside the mixing device 1.

Furthermore, advantageously, the coaxial injection, unlike a 90? inlet, prevents the fluid section from being blocked by the incoming air, always leaving a passage section for the mixture.

The proposed geometries maximize the shear stresses generated by the mixture around the coaxial injector since high tangential stresses allow to minimize the size of the bubbles generated by the mixture source "A".

Advantageously, the proposed geometries for the mixing device 1 maximize local turbulence with a significant contribution to the maintenance of bubbles with a relatively small diameter. Preferably, at least one passage section 11 has a diameter of 1 mm.

More preferably, the passage sections have the same size.

According to one possible embodiment, the passage section 11 comprises multiple perforations.

The multiple perforations arranged along the second tubular portion 10 are shaped to deliver compressed air transversely to the direction of injection of the mixture along the channel 3.

Preferably, none of the multiple perforations delivers compressed air into channel 3 of the first duct 2 in the same direction as the injection direction of the mixture.

For this purpose, as specified above, the terminal end 8 is occluded to prevent the delivery of air in a direction parallel to the direction of delivery of the mixture.

The multiple perforations develop along a longitudinal section of the second tubular portion 10 of the second duct 6.

Preferably, the multiple perforations are evenly distributed along the second tubular portion 10 of the second duct 6.

Therefore, as can be seen from figure 1, the holes are made on the cylindrical external surface of the second tubular portion 10.

According to a possible embodiment, the second tubular portion 10 may comprise a surface layer.

In a first case, the second tubular portion 10 comprises a metal mesh surrounding the portion itself.

Alternatively, the second tubular portion 10 may comprise a surface layer of sintered material.

In figure 1, the possible presence of a metal mesh or sintered material around the second tubular portion 10 is schematized with a hatched line, surrounding the portion itself, and indicated in both cases with the number 13.

Preferably, the surface layer 13 made of sintered material has a porosity in the range between 50 μm and 100 μm.

The dependence on the pore size (as defined in terms of the grade of the medium) and on the volume of compressed air injected shows that lower grades and lower flow rates correspond to smaller bubble sizes and less dispersed dimensions.

Advantageously, the use of porous injectors is the preferred methodology for producing a larger bubble population per unit time.

Preferably, the sintered material 13 has a hydrophilic substrate. Advantageously, the hydrophilic substrate promotes the formation of bubbles with smaller dimensions compared to a hydrophobic substrate.

In other words, the injection of compressed air can occur through the second tubular portion 10 comprising multiple small-sized holes which can in turn be covered by a metal mesh and/or a surface layer 13 in sintered material.

Advantageously, the diameter of the at least one passage section 11 obtained on the second tubular portion 10, from the multiple solutions proposed, is proportional to the size of the bubbles in the mixture.

Thanks to the proposed solutions, the bubbles of the compressed air foam "C" delivered to the outlet 5 of the first duct 2 can reach dimensions of the order of 10-10<2 >?m.

Advantageously, the smaller diameter of the bubbles, all other things being equal, statistically reduces the probability of coalescence of the bubbles themselves during their feeding inside the channel 3 up to the outlet 5 of the latter.

The small passage sections 11 and/or the porosity of the sintered material of the second tubular portion 10 achieve a high total compressed air injection area resulting in a low inlet velocity of compressed air into the channel 3.

It follows that, for the same volume of compressed air foam "C" per unit of time delivered, low compressed air inlet speeds correlate with a smaller average diameter of bubbles generated.

Advantageously, the generation of bubbles with a low average diameter allows to increase their number in channel 3 at the same flow rate of compressed air foam "C" per unit of time.

The present invention also provides a mixing method for CAFS systems.

The mixing method includes the steps of injecting mixture and compressed air into a common channel 3.

The phase of injecting the mixture occurs in a first duct 2, defining the channel 3, starting from an inlet 4 of the channel 3, connected to a source of mixture ?A?, towards an outlet 5 of the channel 3 configured to release compressed air foam ?C? towards a fire to be extinguished. The phase of injecting compressed air instead occurs transversely to the direction of injection of the mixture inside the channel 3.

Preferably, the compressed air injection phase occurs through a second duct 6 from a central portion towards the outside of the channel 3.

The second duct 6 is placed internally and concentrically to the first duct 2.

More preferably, the compressed air injection phase does not occur in the same direction as the mixture injection direction.

According to a possible embodiment of the method, the compressed air injection phase occurs downstream of a section expansion 12 of the channel 3 of the first duct 2.

Advantageously, the present invention provides a device 1 and a mixing method for CAFS systems capable of overcoming the drawbacks emerging from the prior art.

It should be noted that the present invention allows to minimize the average diameter of the air bubbles by implicitly maximizing their quantity for the same volume injected per unit of time. This advantage is derived from the presence of the passage section 11 in the form of holes or pores of the sintered material. Furthermore, the network 13 further allows to minimize the section of the bubbles.

Advantageously, the present invention is also able to make the flow of air injected into the volume of the fluid mixture (water and foaming agent) as homogeneous as possible in order to maximize the physical reaction of bubble generation and consequently increase the density of the compressed air foam "C". This advantage derives from the direction of injection of the compressed air, always transversal to the direction of the foaming agent flow and concentric at the point of maximum fluid speed.

Furthermore, this condition also allows to minimize the dimensional dispersion of the diameter of the air bubbles, and consequently increase the fire-fighting properties of the compressed air foam.

Advantageously, the present invention allows for the possible production of lighter hoses, which can help personnel to be more efficient during an emergency, as there is limited use of water and a consequent decrease in the density of the compressed air foam delivered by the device.

Advantageously, a reduced use of foaming agent allows to increase the autonomy of the mixing device 1, as well as to save money.

Advantageously, the present invention provides an environmental benefit by reducing the dispersion of toxic gases.

Claims (15)

1. Mixing device (1) for CAFS systems, comprising: - a mixture source (A), where said mixture is formed by at least one water component and one fire-fighting foam component; - a source of pressurized air (B); - a first duct (2) having a channel (3) extending from an inlet (4) to an outlet (5), said inlet (4) being in fluid communication with the mixture source (A) and said outlet (5) being configured to release compressed air foam (C); and - a second duct (6) for the injection of compressed air, which extends from a first end (7) in fluid communication with the source of pressurized air (B) and a second end (8) inside the first duct (2); characterised in that said second duct (6) comprises at least a first tubular portion (9) and at least a second tubular portion (10) inserted concentrically within said first duct (2), said second tubular portion (10) comprising at least one passage section (11) for the compressed air. 2. Mixing device (1) according to the previous claim, wherein said at least one passage section (11) comprises multiple perforations, said multiple perforations developing along a longitudinal section of the second tubular portion (10) of said second duct (6). 3. Mixing device (1) according to claim 2, wherein said multiple perforations are homogeneously distributed along said second tubular portion (10) of said second duct (6). 4. Mixing device (1) according to one or more of the preceding claims, wherein said second tubular portion (10) comprises a metal mesh (13) surrounding the portion itself. 5. Mixing device (1) according to one or more of the preceding claims, wherein said at least one passage section (11) has a diameter of 1mm. 6. Mixing device (1) according to one or more of the preceding claims, wherein said second tubular portion (10) comprises a surface layer (13) of sintered material surrounding the portion itself. 7. Mixing device (1) according to claim 6, wherein said surface layer (13) in sintered material has a porosity within a range between 50 μm and 100 μm. 8. Mixing device (1) according to one or more of the preceding claims, wherein said first tubular portion (9) is transversal to said second tubular portion (10) and wherein said first tubular portion (9) is arranged perpendicularly to the longitudinal development of the first duct (2). 9. Mixing device (1) according to one or more of the preceding claims, wherein said channel (3) of said first duct (2) comprises at least one expansion (12) of the section. 10. Mixing device (1) according to claim 9, wherein said at least one expansion (12) of the section of said channel (3) of said first duct (2) is placed in proximity to said first tubular portion (9) of said second duct (6). 11. Mixing device (1) according to claim 9 or 10, wherein said at least one expansion (12) is placed between said inlet (4) of said first duct (2) and said first tubular portion (9) of said second duct (6). 12. Mixing method for CAFS systems, including the steps of: - injecting mixture into a first duct (2), defining a channel (3), starting from an inlet (4) of said channel (3), connected to a mixture source (A), towards an outlet (5) of said channel (3) configured to release compressed air foam (C); and - inject compressed air transversely to the direction of mixture injection into said channel (3). 13. Mixing method for CAFS systems according to the previous claim, wherein said compressed air injection phase occurs from a central portion towards the outside of a second duct (6), said second duct (6) being internal and concentric to said first duct (2). 14. Mixing method for CAFS systems according to claim 12 or 13, wherein said compressed air injection phase occurs in proximity to a section expansion (12) of the channel (3) of said first duct (2). 15. Mixing method for CAFS systems according to one or more of the preceding claims 12 to 14, wherein said compressed air injection phase does not occur in the same direction as the mixture injection direction.