DROPLET SIZE MEASUREMENT .2. EFFECT OF 3 INDEPENDENT VARIABLES ON PARAMETERS DESCRIBING THE DROPLET SIZE DISTRIBUTION FROM A PNEUMATIC NOZZLE STUDIED BY MULTILINEAR STEPWISE REGRESSION-ANALYSIS

The influence of three independent variables (atomizing air pressure, flow rate of binder solution and polyvinylpyrrolidone concentration) o n the parameters describing the droplet size distribution from a pneum atic nozzle (volume of droplets under 18.9 mu m, median and 90% fracti le of droplet size) was studied using a normal 3(3) factorial design. The droplet size measurement was carried out by laser diffractometry. The dependence of the response variables on the independent variables was studied by a multilinear stepwise regression analysis. On the basi s of this study, it was concluded that a high atomizing air pressure l ed to an increased volume of small droplets. Thereafter, the polyvinyl pyrrolidone concentration and the binder flow rate affected this respo nse variable inversely. Increasing the atomizing air pressure resulted in a fall in the droplet size. A larger droplet size was obtained wit h increased binder now rate and polyvinylpyrrolidone concentration. In addition to main and quadratic effects, the regression analyses revea led some interactions between independent variables. For example, the atomizing air pressure had a stronger effect on the median of droplet size when the polyvinylpyrrolidone concentration was lower. This was s upposed to be due to changes in viscosity.