SPRAY STRUCTURE ANALYSIS IN ATOMIZATION PROCESSES IN ENCLOSURES FOR POWDER PRODUCTION

The production of powders and solids (in the micrometer to millimeter size range) with controlled morphology may be achieved in spray processes from solutions, melts, suspensions, or emulsions. The droplet-to-particle state change takes place in the dispersed spray situation by solidification or by drying and mass and heat transfer processes. The spray behavior is influenced by the interaction of the droplet spray flow and the gas flow in the surrounding vessel or chamber. The spray chamber design has a significant influence on the local flow structures as recirculation and re-entrainment of spray droplets. Flow structures induced by different spray chamber geometries also affect the local concentration of droplets. In this contribution, the influence of different spray chamber designs on unsteady flow structures in a spray is discussed. Since the powder and product properties of a spray process highly depend on the local mass and heat transfer within the spray, droplet trajectories as well as local droplet concentrations have to be assessed. Both phenomena are reviewed experimentally using particle imaging methods in planar light sheets of the spray. The effect of coherent flow structures on the local droplet concentration is the central point of this investigation.