Drop size refers to the size of the individual drops that comprise a nozzle’s spray pattern. Each spray pattern provides a range of liquid drop sizes. Many factors can affect drop size such as liquid properties, nozzle capacity, spray pressure and spray angle.
Air atomizing nozzles produce the smallest drop sizes(+-10 micron) followed by hydraulic fine spray, hollow cone, flat fan, and full cone nozzles.
For dust suppression, drops between 20 and 200 μm are typically required as airborne dust particles are usually in this size range. To produce this very small drop size, a higher degree of atomization is required. Atomization is achieved by pumping water through nozzles at high pressure or by using a combination of compressed air and water pumped at lower pressure to produce very small drops or fog.
If compressed air is available and economically feasible, air atomizing nozzles are generally a better choice. They produce smaller drops and have larger flow passages than hydraulic fine spray nozzles which helps to reduce clogging.
When dust is airborne and needs to be suppressed (also referred to as captured or knocked down), it is important to match liquid drop size to the particle size of the dust
Drops that are larger than the dust particle avoid collision with the dust. When drops are smaller than the dust particle, they may collide, but the drops evaporate too quickly and release the captured particles. The greatest chance for suppression occurs when the diameter of the drop size and dust particle are comparable. See Figure 2. Also keep in mind that dust suppression is most effective in areas where there is little air turbulence.
