Pneumatic spray nozzles mix a liquid and air by utilizing a high-velocity flow such as compressed air to atomizes the liquid, and have the following features as compared with hydraulic nozzles that spray using pumps only.
Excellent atomizing performance
Pneumatic spray nozzles are capable of achieving fine atomization with a mean droplet diameter of 10 μm or less, which is difficult with hydraulic spray nozzles.
Large turn-down ration
Pneumatic spray nozzles have large turn-down ratios of spray flow rate with little variation in droplet size and spray distribution, which makes them ideal for spray flow adjustable nozzles.
Large free passage diameter
Pneumatic spray nozzles have larger free passage diameters than hydraulic spray nozzles effectively reducing clogging problems.
Turn-down ratio means the ratio between the adjustable minimum and the maximum spray flow rate. Such the range is called a turn-down range.
The turn-down ratio of a hydraulic spray nozzle is small, because its spray flow rate is proportional to square root of a spray pressure and variation of the flow rate greatly depends on power of a pump. On the other hand, adjusting both compressed air pressure and liquid pressure enables a pneumatic spray nozzle to cover wide turn-down range.
Therefore, pneumatic spray nozzles are the most suitable for applications requiring small spray droplets and wide adjustable range of spray flow rate such as cooling of combustion gas.
Air-water ratio means a rate of air consumption divided by spray flow rate. This is expressed as either a volume ratio or a weight ratio. When a same nozzle is used, the spray droplet size becomes smaller as the air-water ratio becomes higher.
The air-water ratio here is based on the volume ratio.