The basic function of pressure nozzles is to convert the pressure energy supplied by the high pressure pump into kinetic energy in form of a thin film, the stability of which is determined by the properties of the liquid such as viscosity, surface tension, density and quantity per unit of time, and by the medium into which the liquid is sprayed.
Most commercially available pressure nozzles, see Fig. 48 and 49, are designed with a swirl chamber giving the liquid a rotation, so that it will leave the orifice, the second main component of a pressure nozzle, as a hollow cone.
Fig. 48 High-pressure nozzle, "Delavan" Fig. 49 High-pressure nozzle, "Spraying System"
In addition to above characteristic design, the obtained spray pattern is a function of the operating pressure. Capacity (spraying water) can usually be assumed directly proportional to the square root of the pressure:
Capacity kg/h = K × √P (11)
As rule-of-thumb it can be established that higher viscosity, liquid density and surface tension and lower pressure will result in bigger particles.
Many proposed correlations have been reported, but the one below can be used with a certain degree of confidence:
(12)
Where:
ds = volume particle mean diameter of the spray (microns)
Ơ = surface tension of liquid (dynes/cm)
P = nozzle pressure (p.s.i.)
µ = viscosity of liquid (poises)
PL = liquid density gm/cc
Q = volumetric feed rate / unit of time
Kn = nozzle constant (depending on spray angle)
do = orifice diameter (inches)