Origin of Water Mist Systems
• Water Mist systems gained wide attention as the most valued substitute of Halon in 1980s ；
• The IMO (International Maritime Organization) required an enhanced fire protection for ships that help the development of WM technology in 1990s.
• NFPA Technical Committee on Water Mist Fire Suppression Systems was founded in 1993 and they start to write the specifications as NFPA standard.
• NFPA (The National Fire Protection Association) has officially issued the first edition of standard 750-Water Mist Fire Protection Systems as USA national Standard in 1996.
Origin of Water Mist Systems
• Water Mist systems gained wide attention as the most valued substitute of Halon in 1980s ；
• The IMO (International Maritime Organization) required an enhanced fire protection for ships that help the development of WM technology in 1990s.
• NFPA Technical Committee on Water Mist Fire Suppression Systems was founded in 1993 and they start to write the specifications as NFPA standard.
• NFPA (The National Fire Protection Association) has officially issued the first edition of standard 750-Water Mist Fire Protection Systems as USA national Standard in 1996.
What is Water Mist?
Definition in NFPA 750
Water Mist: A water spray for which the Dv0.99, for the flow-weighted cumulative volumetric distribution of water droplets is less than 1000 microns at the minimum design operating pressure of the water mist nozzles.
Definition in GA 1149-2014 (China National Standard)
Water Mist: A water spray produced by a water mist nozzle which sprays vertically at minimum design working pressure, the droplet size Dv0.99 of which at the cross section 1m from the nozzle tip is less than 400 microns while Dv0.50 less than 200 microns.
The performance of fire extinguishing using water mist systems is complicated which related with different targets of fire and the performance of water spray.
Droplet size is just one important factor of water spray that affect the ability of water mist to kill a fire. Other factors include the characteristic of fire, the closed space, the dynamics of the air stream, spray intensity, density and momentum of the water spray, etc.
High Pressure System: A water mist system where the distribution system piping is exposed to pressures of 34.5 bar (500 psi) or greater.
Intermediate Pressure System: 12.1 bar (175 psi) to 34.5 bar (500 psi).
Low Pressure System: 12.1 bar (175 psi) or less.
Automatic Water Mist Nozzles
Nozzles that operate independently of other nozzles by means of a detection/activation device built into the nozzle. In Watec, it is the so-called Close Type Water Mist Nozzles.
Nonautomatic Water Mist Nozzles (Open)
Nozzles that operate as an entire system or grouping of nozzles, containing open orifices and activating the water flow to the nozzles by an independent detection system. In Watec, it is the so-called Open Type Water Mist Nozzles.
Mechanism of water mist systems
The small water droplets allow the water mist to control, suppress or extinguish fires by:
cooling both the flame and surrounding gases by evaporation
displacing oxygen by evaporation
attenuating radiant heat by the small droplets themselves
I. Cooling both the flame and surrounding gases by evaporation
The smaller droplet size, the larger reaction surface, easier to evaporate. During the process of evaporation, the phase of water transfer from liquid to gas, large heat absorption occurs.
2260KJ/Kg energy by transition from liquid to gas!
| Droplet Diameter | Reaction Surface of 1 Liter Water | Vaporization time |
| 10.0mm | 0.6m2 | 620s |
| 1.0mm | 6m2 | 6.2s |
| 0.1mm | 60m2 | 0.062s |
| 0.01mm | 600m2 | 0.0062s |
II. Displacing oxygen by evaporation
when the water mist reaches the flame, they evaporate because of the very small droplets. Volume is enlarged rapidly up to 1650 times, hence the oxygen near the fire is expelled.
III. Attenuating radiant heat by the small droplets themselves
The droplets block or reduce re-radiation from flames and thereby lowers the heating rate and pyrolysis rate from surfaces.
Water Mist Systems Benefits
● Immediate activation
● High efficiency in the suppression of a wide variety of fires
● Minimized water damage
● Environmentally sound characteristics
● No toxic problems
Water Mist Systems
Applications of Water Mist Systems
Our Interest in Water Mist Systems
I. High performance Water Mist nozzles
1. Optimized design structure that require less energy to produce water mist meanwhile maintain a good performance of fire extinguishing.
2. product seriation: study and design different Water Mist nozzles- different flow rates at operating pressures with different droplets, coverage, intensity and momentum of water spray, according to different applications and test their ability to kill fire.
3. Life time, material, etc.
1. Optimized design structure that require less energy to produce water mist meanwhile maintain a good performance of fire extinguishing.
2. product seriation: study and design different Water Mist nozzles- different flow rates at operating pressures with different droplets, coverage, intensity and momentum of water spray, according to different applications and test their ability to kill fire.
3. Life time, material, etc.
II. Machining technique and quality control in mass production.
III. Real fire tests, data collection and analysis, CFD and persistent improvement.
Some Typical Water Mist Nozzles
Firefighting is a multidisciplinary science and the mechanism of fire suppression is very complicated. As a manufacturer of spray nozzles, Watec has a wide knowledge of different types of nozzles and we know how to produce mist. Operating pressure, flow rates, K factors, spray droplets, coverage, spray momentum, etc., as regarding the important factors to affect the performance of water mist nozzles and therefore affect the performance of whole system
Four types water mist nozzles would be introduced here:
I. Whirl Jet Type
II. Direct Jet Type
III. Impingement & Deflect Type
IV. Two Fluid Type
For any kind of query, contact us with the details below.
Contact: Mr zhang
15816801107
+86 (0769) 85119952
info@Mistec.cn
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