Patent Application
20110180276
This invention relates generally to fire suppression systems. More particularly, this invention relates to improved liquid distribution within the two-phase flow distribution network in an inerting fire suppression system.
Fire suppression systems are commonly used in commercial buildings for extinguishing fires. In one type of fire suppression system, a jet of liquid fire extinguishing agent, most commonly water from a water supply tank, is injected into a high velocity stream of pressurized inert gas from an inert gas storage tank as the inert gas passes through a supply pipe forming part of a network of distribution pipes communicating with a network of discharge nozzles mounted to the distal ends of the respective distribution pipes. Upon interaction of the high velocity stream of inert gas with the water jet, the water droplets in the water jet are atomized into a mist of very small or minute droplets, thereby forming a two-phase mixture of water mist droplets entrained in and carried by the inert gas stream. This two-phase mixture is distributed via the network of distribution pipes to the discharge nozzles that are operatively associated with the region to be protected. The discharge nozzles distribute the water mist droplets and inert gas over a desired area to flood that area with water mist droplets and inert gas to extinguish a fire in the protected region.
The inert gas commonly used in conventional inerting fire suppression systems is nitrogen, but argon, neon, helium, carbon dioxide or other chemically non-reactive gas, or mixtures of any two or more of these gases may be used. The inert gas suppresses fire within the protected region by diluting the oxygen content within the protected region and also increasing the heat capacity per mole of oxygen within the protected region thereby raising the overall heat capacity of the atmosphere within the protected volume. Due to the presence of the water droplets, the two-phase mixture of water mist droplets and inert gas has a higher overall local heat capacity than the inert gas alone. Consequently, the two-phase mixture of water mist droplets and inert gas will more effectively absorb heat from the flame to the point that the temperature of the gas within the vicinity of the flame sheath drops below a threshold temperature below which combustion can not be sustained. International Patent Application No. PCT/GB02/01495, published as International Publication WO02/078788, for example, discloses a fire and explosion suppression system of the type hereinbefore described.
In such two-phase fire suppression systems, non-homogenous distribution of water mist droplets within the two-phase mixture of water mist droplets and inert gas flowing through the fluid distribution network may occur. In long horizontally extending stretches of pipe within the fluid distribution network, the water mist droplets may not be evenly distributed in the gas flow. For example, the water mist droplets may have a tendency to concentrate in the lower half of the two-phase flow passing therethrough. When a pipe junction is reached whereat the two-phase is divided, it is desired that the water mist droplets be divided proportionally with the split of the inert gas flow as it passes from the inlet pipe to the junction into the two outlet pipes leading from the junction, thereby maintaining a constant mass flow ratio of liquid to gas. However, if the water mist droplets are not relatively uniformly distributed in the flow entering the junction, the water will not proportionally distribute between the respective inert flows discharging through the junction. Such a disproportionate distribution of water between the respective downstream streams could result in some spray nozzles being supplied with an excessive amount of water while other spray nozzles are under supplied.
A fire suppression system for extinguishing a fire in a protected space includes a plurality of fluid discharge devices disposed in operative association with the protected space, and a flow distribution network for directing a flow of the inert gaseous fluid and liquid fire extinguishing agent, such as water or other fire extinguishing liquid, to the plurality of fluid discharge devices. The flow distribution network includes a first pipe interconnected in fluid communication with a second pipe at a flow splitting tee having an inlet leg for receiving fluid flow from the first pipe, a first outlet leg for discharging a first portion of the received fluid flow to a first segment of the second pipe, and a second outlet leg for discharging a second portion of the received fluid flow to a second segment of the second pipe. The liquid fluid flow redistribution device is disposed in the first pipe upstream with respect to fluid flow of the flow splitting tee.
In an embodiment, the liquid fluid flow redistribution device comprises a swirler device for imparting rotation to the liquid fluid flow passing through the first pipe.
In an embodiment, the liquid fluid flow redistribution device comprises an annular ring member having a circumferential base having a plurality of flow openings extending therethrough and a cylindrical flange extending axially outwardly from a radially inward portion of the annular ring member. The annular ring is disposed coaxially in the first pipe with an outer circumferential rim of the base in contact with an inner wall of the first pipe and the inner cylindrical flange extending axially upstream with respect to fluid flow through the first pipe.
In an embodiment, the liquid fluid flow redistribution device comprises a ramp extending circumferentially about and outwardly from an inner wall of the first pipe, with the ramp extending at an inward inclination in a downstream direction with respect to fluid flow through the first pipe. In an embodiment, the liquid fluid flow redistribution device comprises a recessed cavity formed in and extending circumferentially about an inner wall of the first supply pipe.
In an embodiment, the liquid fluid flow redistribution device comprises a venturi scoop device disposed coaxially within the first pipe and including a central passage therethrough having a throat section and disposed coaxially within the first pipe in spaced relationship with an inner wall of the first pipe so as to form a cavity between the inner wall and the channel member. A plurality of fluid flow openings are provided in the throat of the venturi device that pass through the channel member to establish fluid flow communication between the cavity and the central passage through the channel member. The venturi scoop device may comprise a longitudinally elongated shell defining a throat, a converging section extending axially in an upstream direction from the throat and a divergent section extending axially in a downstream direction from the throat.
In an embodiment, the liquid fluid flow redistribution device comprises a first perforated circular disc is disposed in the first pipe immediately upstream with respect to fluid flow of the inlet to the flow splitting tee. In an embodiment, a second perforated disc is disposed in the second pipe immediately downstream of the first outlet of the flow splitting tee, and a third perforated disc is disposed in the second pipe immediately downstream of the second outlet of the flow splitting tee.
In an embodiment, a flow turbulence generating device may be disposed in each of the second pipes downstream with respect to fluid flow of the flow splitting tee. In an embodiment, the flow turbulence generating device may be at least one vortex generating device. In an embodiment, the flow turbulence generating device may be a venturi device inserted in the pipe.
In an embodiment, a tubular liner may be disposed within the first pipe upstream with respect to fluid flow of the first perforated plate at the inlet to the flow splitting tee. The tubular liner has an outside diameter smaller than the inside diameter of the first pipe, whereby a first annular flow passage is defined between the tubular liner and the first pipe and a second inner passage is defined within and extending axially through the tubular liner. The inert gas flows through both the first annular flow passage and the second inner flow passage, while the water, or other liquid fire extinguishing agent, is only admitted into the inert gas flowing through the inner passage. A plurality of openings are provided in the tubular liner to define a plurality of flow passages through which inert gas may pass from the first annular flow passage into the inner flow passage to penetrate into the two-phase flow of water and inert gas passing through the inner flow passage. The openings in the tubular liner may be arranged at axially spaced intervals along the tubular liner and at circumferentially spaced intervals about the tubular liner, as desired. The openings may also be arranged in discrete sets of openings as desired.
The following detailed description of the invention is to be read in connection with the accompanying drawing, where:
Referring now to
The inert gas storage vessels 20 are connected in parallel arrangement in flow communication with the spray nozzle assemblies 40 via an inert gas distribution network made of a supply pipe 15, an intermediate distribution pipe 17 and a plurality of circuit pipes 19. The inert gas supply pipe 15 at its terminus is in fluid flow communication with the intermediate distribution pipe 17. Each of the circuit pipes 19 branches off from and is in fluid flow communication with the intermediate distribution pipe 17 and has a terminus disposed within the space to be protected to which a respective one of the spray nozzles is mounted. As will be explained in further detail later, when a fire is detected within the space to be protected, inert gas under pressure within the inert gas vessels 20 passes therefrom through the supply pipe 15 to and through the intermediate distribution pipe 17 and thence to and through each of the circuit pipes 19 which feed the inert gas to a respective one of the spray nozzle assemblies 40.
Each of the inert gas storage vessels 20 has its gas outlet connected via a branch supply line 13 in flow communication with the supply pipe 15. A check valve 14 may be disposed in each branch supply line 13 for allowing the inert gas to flow from the respective inert gas storage vessel 20 associated therewith through branch supply line 13 into the inert gas supply pipe 15, but not to flow back into the inert gas storage vessel. Each of the inert gas storage vessels 20 may be equipped with an outlet valve 16 to regulate the gas discharge pressure. If desired, the outlet valve 16 may also be designed to control the rate of inert gas flow from the storage vessel associated therewith.
In the depicted embodiment, the supply pipe 15 and the intermediate distribution pipe 17 intersect in a T-shaped arrangement with the supply pipe 15 connected to the inlet leg 52 of the bull tee 50 and segments 17A and 17B of the intermediate distribution pipe 17 connected to the respective two outlet legs 54, 56 of the bull tee 50, as illustrated in
The two-phase fluid received from the inert gas supply pipe 15 through the inlet leg 52 of the bull tee 50 splits into two portions, one portion discharging through the first outlet leg 54 of the bull tee 50 into segment 17A of the intermediate distribution pipe 17 and the other portion discharging through the second outlet leg 56 of the bull tee 50 into segment 17B of the intermediate distribution pipe 17. The two-phase fluid received from the upstream segment 17A of the intermediate distribution pipe 17 through the inlet leg 62 of the side tee 60 splits into two portions, one portion discharging through the first outlet leg 64 of the side tee 60 into the circuit pipe 19A and the other portion discharging through the second outlet leg 66 of the side tee 60 into downstream segment 17C of the intermediate distribution pipe 17.
The water storage vessel 30 defines an interior volume 32 wherein a supply of water is stored. A gas inlet line 34 establishes flow communication between the inert gas supply pipe 15 and an upper region of the interior volume 32 of the water storage vessel 30. A water outlet line 36 establishes flow communication between a lower region of the interior volume of the water storage vessel 30 and the inert gas distribution network at a location downstream with respect to inert gas flow of the location at which the gas inlet line 34 taps into the inert gas supply line 15. Additionally, a flow restriction device 38 may be disposed in the inert gas distribution network at a location between the location upstream thereof at which the gas inlet line 34 taps into the supply line 15 and the location downstream thereof at which the water outlet line 36 opens into the inert gas distribution network. The flow restriction device 38, which may, for example, comprise a fixed orifice device interdisposed in the inert gas supply line 15, causes a pressure drop to occur as the inert gas traverses the flow restriction device 38, whereby a gas pressure differential is established between the upstream location at which the gas inlet line 34 taps into the inert gas supply pipe 15 and the downstream location at which the water outlet line 36 opens into the inert gas distribution network.
A spray nozzle 37 may be mounted to the outlet end of the water outlet line 36 to atomize or otherwise produce a mist of water droplets as the water from the supply tank 30 is introduced into the inert gas flow. In the embodiment of the fire suppression system 10 depicted in
The length of travel of the two-phase flow from the point of injection of the water into the inert gas through section 15C of the inert gas supply pipe 15 to its passing into the intermediate distribution pipe 17 for distribution amongst the various spray nozzles 40 via the respective circuit pipes 19 may be several meters, for example up to 20 or more meters depending upon the system design. In the course of traversing this path through section 15C of the inert gas supply pipe 15, the water droplets and inert gas may separate to varying degree. In some instances, the water droplets may coalesce and concentrate as a liquid film flowing along the inner wall defining the flow passage of section 15C of the gas supply pipe 15 forming a tunnel about a core flow of inert gas. In other instances, particularly in horizontal runs of pipe, the water droplets may concentrate primary along a lower arc portion of the wall with the inert gas flowing thereover. In still other instances, the water droplets may concentrate in a plug flow along the axis of supply pipe with the inert gas flowing circumferentially about the flow of water droplets.
At each of the pipe intersections within the fluid distribution network, the incoming two-phase fluid flow is split into two ongoing flows. For example, the two-phase fluid received through the inlet leg 52 of the bull tee 50 splits into two portions, one portion discharging through the first outlet leg 54 of the bull tee 50 into segment 17A of the intermediate distribution pipe 17 and the other portion discharging through the second outlet leg 56 of the bull tee 50 into segment 17B of the intermediate distribution pipe 17. In conventional two-phase flow inerting systems, because the distribution of the liquid film on the inner wall of the pipe is generally not uniform as the flow enters the flow splitting tee, the potential exists for an unequal distribution of the liquid phase to occur between the two-phase flows discharging from the flow splitting tee. Applicants have determined that the occurrence of such an unequal distribution of liquid phase between the two outgoing flows may be diminished by affecting a redistribution of the liquid phase of the two-phase flow upstream of the flow splitting tee.
To reduce, if not eliminate, the potential for unequal distribution of the liquid phase in the outgoing two-phase fluid flows leaving a flow splitting tee at a pipe intersection in the fluid distribution network of the system 10, a liquid fluid flow redistribution device 70 is disposed in the particular pipe feeding the two-phase flow to the inlet leg of the flow splitting tee at a location upstream of the intersection. For example, a liquid fluid flow redistribution device 70 may be disposed in the supply pipe 15 downstream with respect to fluid flow of the introduction of the liquid fluid flow into the flow of the inert gaseous fluid passing through the supply pipe 15 and upstream of the bull tee 50 to reduce the unequal distribution of the water between the outgoing two-phase fluid flows at the bull tee 50. In an embodiment, as illustrated in
Similarly, to reduce, if not eliminate, the potential for unequal distribution of the liquid phase between the outgoing two-phase fluid flows at the intersection of the intermediate distribution pipe 17 and one or more circuit pipes 19 in the fluid distribution network of the fire suppression system 10, a liquid fluid flow redistribution device 70 may be disposed in the intermediate distribution pipe 17. In an embodiment, as illustrated in
In an aspect of the invention, the liquid fluid flow redistribution device may be any device that when disposed in the two-phase flow passing through the inert gas distribution network redistributes water flowing along the inner wall of the pipe into a film distributed uniformly about the circumference of the inner wall of the pipe as the flow enters a flow spitting tee. For example, referring now to
In another embodiment, as depicted in
In another aspect of the invention, the liquid fluid flow redistribution device may be any device that when disposed in the two-phase flow passing through the inert gas distribution network redirects water flowing along the inner wall of the pipe into the core two-phase flowing of water droplets and inert gas flowing through the pipe. For example, referring now to
For example, the liquid fluid flow redistribution device may comprise an annular recessed cavity 370 extending in a band-like fashion about the circumference of the inner wall of the pipe 15, 17 as depicted in
In another embodiment, the liquid fluid flow redistribution device may comprise a ramp 470 extending in band-like fashion about the circumference of the inner wall of the pipe 15, 17 as depicted in
In yet another embodiment, the liquid fluid flow redistribution device may comprise a venturi scoop device 570 such as depicted in
When the water flowing along the inner wall of the pipe encounters the venturi scoop 570, the water collects in the cavity 573. As the core flow of two-phase fluid passes through the throat section 571, a low pressure zone is created at the throat of the venturi section. As a result of the pressure differential between the cavity 573 and the low pressure zone within the throat section 571, water collecting in the cavity 573 discharges therefrom through the plurality of openings 575 and is re-entrained in the core two-phase flow. Although shown as a plurality of circular holes disposed at uniformly spaced circumferential intervals about the throat of the throat section 571, it is to be understood that the openings 575 may be slots or of other shape, and that the number, size and spacing of the openings 575 may be varied as desired to optimize the effect of the venturi scoop device 570 in any particular application.
In an embodiment of the fire suppression system, perforated discs 80A, 80B, 80C are disposed in the two-phase flow streams entering and leaving the flow splitting tee 50 to promote a more uniform distribution of the two-phase flow 7 leaving the flow splitting tee 50. Referring now to
The perforated disc 80A disposed upstream of the flow splitting tee 50 promotes a more uniform distribution of the two-phase fluid and breaks up any relatively larger water droplets into relatively smaller droplets. Having passed through the upstream perforated disc 80A and entered the flow splitting tee 50, the two-phase flow impinges on the opposite wall of the tee and splits into two flows passing out of the tee 50 in opposite directions. Each of the perforated plates 80B and 80C disposed downstream of the flow splitting tee 50 promotes a more uniform distribution of the two-phase fluid following the impingement and flow splitting within the tee 50 and breaks up any relatively larger water droplets that may have formed as a result of coalescence of smaller water droplets due to inelastic collisions of smaller water droplets within the flow splitting tee 50.
In addition, vortex generating devices may be disposed in flow path of the two-phase flow passing through the supply pipe 15 at a location upstream of the inlet to the flow splitting tee 50. For example, in the exemplary embodiment depicted in
In the exemplary embodiment of the fire suppression system depicted in
Thus, both the annular flow passage 55 defined between the inner diameter segment 15C of the inert gas supply pipe 15 and the outer diameter of the tubular liner 60 and the inner passage 65 defined within the inner tubular liner 60 open to the upstream portion of the inert gas supply pipe 15 and receive inert gas flow from the upper stream portion of the inert gas supply pipe. A first portion of the inert gas flow passing through the inert gas supply pipe 15 enters into and traverses the inner flow passage 65 through segment 15C of the inert gas supply pipe 15 and a second portion of the inert gas passing through the inert gas supply pipe 15 enters into and traverses the annular flow passage 55 defined within segment 15C of the inert gas supply pipe. However, the discharge outlet of the water outlet line 36, or the atomizing nozzle 37 if mounted thereto, opens into the inner flow passage 65 at a location slightly downstream of the mouth 61 of the inner tubular liner 60 of the inert gas supply pipe 15. Thus, the droplets 5 in the mist of water, or other liquid fire extinguishing agent, introduced into the portion of the inert gas flow passing through the inner flow passage 65 mixes with the inert gas 3 to form a two-phase flow 7 of liquid mist droplets entrained in the inert gas flowing through the inner flow passage 65. Therefore, inert gas 3 only flows through the annular flow passage 55 bounded by the inner wall of segment 15C of the inert gas supply pipe 15 and the outer diameter of the inner tubular liner 60, while a two-phase flow 7 of liquid mist droplets entrained in inert gas flows through the fluid flow passage 65 extending axially within the inner tubular liner 60.
Additionally, a plurality of openings 67 are provided in the wall of the inner tubular liner 60. The openings 67 provide fluid flow communication between the annular flow passage 55 and the inner flow passage 65 defined within the inner tubular liner 60. The openings 60 are arranged at axially spaced intervals along the length of the tubular liner 60 and at circumferentially spaced intervals about the circumference of the tubular liner 60. In operation of the fire suppression system 10, a portion of the inert gas 3 flowing through the annular flow passage 55 passes through each of the openings 67 and into the inner flow passage 65 to discharge into and admix with the two-phase flow 7 of liquid and inert gas flowing through the inner flow passage 65. Thus, a series of jets of inert gas discharge into the two-phase flow at spaced intervals along the length of and about the circumference of the inner tubular liner 60. These jets of inert gas serve to break-up any water film that may be flowing along the inner wall of the inner tubular liner 60. Additionally, as the inert gas jets penetrate into the two-phase flow, the resulting turbulence in the two-phase flow serves to induce further intermixing of the liquid mist droplets and the inert gas to enhance uniformity in distribution of the liquid droplets in the inert gas flow.
The individual openings 67 or sets of openings 61 may be arranged in any configuration as desired. In the exemplary embodiment depicted in
To reduce, if not eliminate, the potential for unequal distribution of the liquid phase in the two-phase fluid flows in the distribution pipes 17A and 17B downstream of the respective outlets of the flow splitting tee 50 at the intersection of the inert gas supply pipe 15 and the distribution pipe 17, an additional flow turbulence generating device, such as for example a venturi device 90 or a vortex generating device 92, may be disposed in each of the particular pipes receiving the two-phase flow from the flow splitting. For example, in the exemplary embodiment illustrated in
As the two-phase flows passing from the flow splitting tee 50 traverses the venturi devices 90 or the vortex generating devices 92, unsteady flow vortices are generated in the two-phase flow which enhance mixing of the liquid phase and the gas phase to ensure a more uniform distribution of liquid mist droplets through out the inert gas passing to the spray nozzles 40. As noted previously, coalesced droplets of water, or other fire extinguishing fluid, that may have formed as a result of the inelastic collisions of finer mist droplets, are broken up as a result of the two-phase flow passing through the openings in the perforated circular discs 80A and 80B. Being positioned slightly downstream of these perforated circular discs, the flow turbulence generating devices 90, 92 facilitate the mixing and redistribution of the finer droplets resulting from the break-up of the coalesced droplets into the inert gas flow.
The inerting fire suppression system of the invention has been described with reference to water as the liquid fire extinguishing agent. It is to be understood that other liquid fire extinguishing agents may be used instead of water in the inerting fire suppression system of the invention. As those skilled in the art will recognize, the teachings of the invention may be applied to any two-phase fluid inerting fire suppression system wherein a maldistribution of liquid fire extinguishing agent amongst various branches or circuits of the system may potentially occur.
While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US08/59815 | 4/10/2008 | WO | 00 | 1/27/2011 |
