Fluorocarbon-based fire extinguishing agents are environmentally harmful since they cause depletion of the Earth's ozone layer. Fine Water Mist (FWM)-type systems have very favorable characteristics as replacements for existing Halon systems. Typically, these systems include nozzles for creating misting fluids using pressurized gas, and continue to show favor as a mechanism for fire prevention. In these systems, a liquid is typically directed into a central bore of the nozzle, which directs a flow of high-velocity gas. In some nozzles, the velocity and pressure of the gas are increased in a narrowed throat area of the bore, causing the atomization of the fluid into small droplets as the gas travels through the nozzle.
To aid atomization and provide an unobstructed flow path for the gas, the fluid is usually injected into the gas stream through an aperture in the bore wall so that the two different fluid streams impinge at approximately a 90-degree angle. Nozzles of this type require high-pressure spraying of the liquid and the gas, which is undesirable. Another problem with mixing nozzles of this type is the need for fine holes, e.g. holes of a small diameter. These small holes are easily clogged and worn, causing the mixture to exit the nozzle at a reduced level of efficiency and effectiveness.
The use of liquid-only, water-based systems for fire extinguishment is effective, and these systems create water droplets by deflecting the water flow just ahead of the spouting aperture. However, the droplet size is large, and the desirable fine water mist cannot be achieved.
A liquid atomizing nozzle was developed that produces extremely fine liquid atomization through low pressurization of the liquid and gas being delivered to the nozzle. The fluid and gas are delivered through relatively large apertures, thus effecting minimal wear and clogging of those apertures. The nozzle is a convergent/divergent nozzle (C-D); however, there is no apparatus for controlling/adjusting the output of the C-D nozzle, and it cannot be adapted to allow use of the C-D nozzle in particular environments.
There exists a need for replacement designs for existing Halon systems, especially for fire suppression and first responders, using the C-D nozzle for effective and efficient firefighting, and to quickly prevent fires from spreading. There is also a need for an apparatus for otherwise delivering the output of the CD nozzle in a manner that permits the operator to effectively control and tailor the output in a package that is portable and easy to handle by a single operator.
The nozzle described in this work is a high-efficiency nozzle that atomizes water with 80% less water pressure, and is adaptable to other applications where low liquid use is desirable. The nozzle sheers a water stream into droplets 100 microns in size. The droplets expand into a layer of fine mist that is carried to the target on a pressurized stream of air. The fine mist depletes the oxygen at the point of combustion, and extinguishes the fire with up to 90% less water.
The nozzle is fed by two hoses. The first is a water hose that can range in size from a garden hose to a fire hose; the second is a low-pressure air line fed either by a compressor or compressed air tanks. The low-pressure hose requires less physical strength to operate, and leads to lower exertion rates. The apparatus is fully adjustable for air/water ratio and the desired spray distance. Various prototypes have been built and tested. Improved efficacy compared to previous solutions has been demonstrated in field trials. The nozzle puts out fires faster than other solutions while using as few as 2 gallons of water per minute under 20 psi.
Developed as an alternative to Halon systems, the nozzle is applicable for water-constrained firefighting operations such as on boats, ships, aircraft, and for backcountry and remote firefighting with limited or unreliable water and power supplies.