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What is water mist?
Source: | Author:mistec | Publish time: 2017-02-24 | 751 Views | Share:
Key words: Water Mist Nozzles, Automatic Water Mist Nozzles, Nonautomatic Water Mist Nozzles

Water mist nozzles in Mistec refer to spray nozzles that produce small droplets and used for fire suppression. For other applications, such as humidifying, spray cooling, etc., the nozzles are usually called as misting nozzles, fogging nozzles. Some companies in the market call the general-purpose misting nozzles as water mist nozzles. It doesn’t matter.

 

In the following text, we define the water mist nozzle as a fire fighting terminology.

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.

Note: Dvf: A drop diameter such that the cumulative volume, from zero diameter to this respective diameter, is the fraction, f, of the corresponding sum of the total distribution. Take an example, for Dv0.99=100 microns, we can regard the 99% of the water mist droplets are less than 100 microns.

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.

 

Water Mist Nozzle: A special purpose device, containing one or more orifices,

designed to produce and deliver a water spray meeting either the definition of Water Mist or

meeting the specific requirements of an approved water mist fire test protocol.

 

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: A water mist system where the distribution system piping is exposed to pressures greater than 12.1 bar (175 psi) but less than 34.5 bar (500 psi).

Low Pressure System: A water mist system where the distribution piping is exposed to pressures of 12.1 bar (175 psi) or less.

 

Correspondingly, for high pressure water mist nozzles, the operating pressure larger than 34.5 bar (500 psi). for Intermediate pressure water mist nozzles, the operating pressures are from 12.1 bar (175 psi) to 34.5 bar (500 psi) while for Low pressure water mist nozzles, the operating pressures are lower than 12.1 bar (175 psi).

 

Automatic Water Mist Nozzles: Nozzles that operate independently of other nozzles by means of a detection/activation device built into the nozzle. In Mistec, 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 Mistec, it is the so-called Open Type Water Mist Nozzles.

 
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