DROPLET SIZE MEASUREMENT .1. EFFECT OF 3 INDEPENDENT VARIABLES ON DROPLET SIZE DISTRIBUTION AND SPRAY ANGLE FROM A PNEUMATIC NOZZLE

The effect of three independent variables (atomizing air pressure, flo w rate of binder solution and polyvinylpyrrolidone concentration) on t he droplet size distribution from a pneumatic nozzle was studied using a normal 3(3) factorial design. The droplet sizes and size distributi ons were determined by laser diffractometry. The effect of the same va riables on the spray angle and cross-sectional area of spray cone (des cribes the area of wetted bed in a fluidized bed granulator) was also evaluated. The dependence of these latter response variables on the in dependent variables was studied by a multilinear stepwise regression a nalysis. It was noted that increasing the amount of polyvinylpyrrolido ne in binder solution decreased the number of bimodal distributions an d increased the width of the distributions. A high pressure with water as a binder solution resulted in a pronounced bimodality and a narrow width of distribution, Increasing the flow rate had no clear; effect on the shape of distributions (uni- or bimodal), but the width of dist ributions increased. The atomizing air pressure was the most significa nt factor affecting the spray angle and the cross-sectional area of th e spray cone. Increasing the pressure led to a decline in the spray an gle and to a decreased area. The effect of PVP concentration was oppos ite to that of pressure. The effect of flow rate was controversial bec ause, according to the regression analyses, it affected inversely the spray angle and the area.