Orifice Diameter range starts from 0.3 mm to 2.00 mm.
Misting nozzles are designed to create a spray that angles out anywhere from 40° - 100°, depending on your system's water pressure. The wider the angle, the more area the spray will cover and the fewer nozzles will be needed. 18, 24 or 30 inch nozzle spacing is standard, but some suppliers will customize spacing to your needs. Nozzle spacing in plastic, nylon, and copper lines can be easily customized during installation, too.
How far in the air the spray "drifts" or spreads is determined by their height off the ground, the system's water pressure and the size of the nozzle, plus the temperature of the water and the outside air.
For maximum cooling effect, it makes sense that you would want a fairly dense curtain of mist. But there is a point at which the system simply cannot make you any cooler, no matter how closely the nozzles are spaced. The final determination of how closely to space the misting nozzles in your system will be based on, well, your system.