Nozzles fire/explosion prevention systems

Engineering consideration 1 - low flow rate spraying

Both humidifying anti-sparking and moistening systems only require very moderate levels of spray.  Over- spraying can result in undesirable wetting and possibly water damage to sensitive equipment.  To avoid over-wetting, the water being put into the system needs to be in equilibrium with water being taken out of the system. In this way water can not build up.

The rate at which water will evaporate from any system depends upon heat, wind, surface area and ambient humidity.  As humidity increases the rate of evaporation also increases as there is more water held in the air for heat to act upon.  It is this fact that fire prevention systems exploit.  By increasing the level of moisture in the air one can increase the rate of removal and thus maintain a steady higher level of moisture through continual or regular spraying.  Of course, there is a limit to how 'loaded' with water air can be and once a certain level is reached condensation or precipitation will occur.

Fire prevention by moistening surfaces works in a similar way, with an equilibrium being established between the droplets injected into the system by the spray nozzle and natural evaporation from the surface.  An important difference is that droplet size is less important.  This is because the liquid is intended to hit the surface in question and so it is not important to ensure swift evaporation before reaching the surface, as is the case with humidifying anti-sparking systems.

When selecting nozzles for either system one needs to look at low flow rate variants.

For humidifying anti-sparking systems it is important to achieve very fine atomisation so that the natural evaporative forces can act swiftly on the spray.

Whilst droplet size is less important for wetting systems a relatively fine spray is still desirable as is a uniform coverage to avoid localised over wetting or pooling.