22. Experimental Evaluation and Control of Interaction of Gas Environment and Rotary Atomized Spray for Production of Narrow Particle Size Distribution

The production of particles with a narrow particle size distribution by spray drying is a demanding challenge in industrial application. The laminar thread breakup is one option as employed by an innovative rotary spraying device (Schröder and Walzel, Chemical Engineering and Technology 21: 349–354, 1998; Erzeugung und Zerfall gedehnter Laminarstrahlen im Schwerefeld, Aachen, 2002; Designing thread forming rotary atomizers by similarity trials, 2012; Einfluss der Gasführung in Sprühtrocknern auf den Fadenzerfall an Rotationszerstäubern—Analyse und Optimierung, München, 2012). The feed enters the rotary wheel from the top and flows through the device as laminar open channel flow. It leaves the cup through bores and single laminar threads are obtained upon detachment. These threads ideally break up driven by surface tension. In spray experiments, a broader drop size distribution is observed than expected from theory. Within the presented work, the effect of a relative velocity between the thread the ambient gas on the laminar thread breakup is identified and addressed as mayor factor (Mescher et al., Chemical Engineering Science 69:181–192, 2012).

A similarity trial is used to quantify the influence of the cross-wind flow. The result influences the design of a gas distributor for small particles with a narrow size distribution. The gas distributor is designed by flow simulation (CFD) for noncommercial spray dryer (D = 2.7 m and H = 3.7 m) (Einfluss der Gasführung in Sprühtrocknern auf den Fadenzerfall an Rotationszerstäubern—Analyse und Optimierung, München, 2012). Spray drying experiments with aqueous PVP solution and Mannitol solution were performed to validate and to improve the gas distribution concept. Small particles with a narrow particle size distribution were obtained during experiments.