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Summary: Acoustic levitation was investigated as a model for spray processes. The influence of different parameters on the drying process of aqueous polyvinylpyrrolidone (PVP) solutions was studied and compared to the evaporation of water. The adequacy of acoustic levitation as model for spray processes was demonstrated. Experiments with water and aqueous PVP solutions indicated no dependency of the droplet size on the drying process for droplets with a diameter between 300 mm and 1.5 mm. Particles dried in an acoustic levitator displayed good accordance of morphology with those obtained in a spray tower. Surprisingly the addition of PVP to water resulted in faster evaporation of the solvent. Mathematical models of single droplets within a spray process typically refer to spherically symmetric droplet geometries. The simulation of other morphologies and their evolution throughout the process is still very challenging. A new drying model based on a fully threedimensional meshfree approach is under development and shows good agreement to basic established models regarding the drying of a single droplet.

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Simulation of Coalescence in Multiphase Systems Using a Mesh-Free Simulation MethodModeling coalescence effects within bubble collectives is a challenge with grid-based methods because of the extensive remeshing. Mesh-free simulation methods, such as the smoothed particle hydrodynamics (SPH) approach offer an alternative for systems with highly deformable free surfaces and complex geometries. This contribution investigates the suitability of the SPH method for the simulation of bubble collectives. The dynamics of a single bubble coalescing with a planar surface is studied. Moreover, the ability of the SPH approach to model bubble collectives is highlighted considering the coalescence of two bubbles of different sizes.