Mean drop sizes from pressure-swirl nozzles

A study of the factors governing the atomization process in pressure-swirl nozzles is presented. Extensive measurements of mean drop size are conducted on six simplex nozzles of different sizes and spray-cone angles. The liquids employed are water, diesel oil, and several blends of diesel oil with polybutene. These liquids provide a range of viscosity from 3 to 18 X 10~6 m2/s (3-18 cs), and a range of surface tension from 0.027 to 0.0734 kg/s2 (27-73.4 dyne/cm). The results are used to substantiate an equation for mean drop size derived from basic considerations of the hydrodynamic and aerodynamic processes that govern the atomization processes in pressureswirl nozzles. A very satisfactory correlation is demonstrated between predictions based on this equation and the actual measured values of mean drop size. Nomenclature A,B = constants, Eq. (16) Aa = air core area, m2 A0 = discharge orifice area, m2 Ap = swirl chamber port area, m2 Ds = swirl chamber diameter, m d0 = liquid orifice diameter, m m =mass flow rate, kg/s P = pressure, Pa AP = pressure differential, Pa Re = Reynolds number SMD = Sauter mean diameter, m t - film thickness in final orifice, m ts = liquid sheet thickness after exit from nozzle, m U = velocity, m/s We = Weber number X =Aa/A0 6 = spray cone half-angle, deg fj. = dynamic viscosity, kg/ms v = kinematic viscosity, m2/s p = density, kg/m3 a - surface tension, kg/s2 Subscripts A =air F = fuel L = liquid R = air relative to liquid