The available energy for atomization in two fluid atomizers is independent
of liquid flow and pressure. The necessary (kinetic) energy for atomization is
supplied by compressed air. The atomization is created due to high frictional
shearing forces between the liquid surface and the air having a high velocity
even at sonic velocities and sometimes rotated to obtain maximum atomization.
See Fig. 50.
Two fluid atomization is the only successful nozzle
method of producing very small particles, especially from highly viscous
liquids. The relation between drop size and operation conditions has been
sought and many scientists have tried to calculate the mean diameter. The best
known is:
Where:
ds = volume particle mean diameter (microns)
V = velocity
of the air relative to the liquid at the nozzle orifice (ft/sec.)
Ơ =
surface tension (dynes/cm)
PL = liquid density (lbs/ft3)
μ = viscosity
(centipoise)
J = air/liquid volume ratio at air and liquid orifices resp.