Modeling of particle distribution and dispersion in spray and spray drying processes

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Spray drying processes aim to produce particles with prescribed properties including the particle structure, geometric properties, bulk density and chemical structure. First, a spray is generated, which in the course of the process evaporates and dries – the process is influenced, for instance, by droplet interaction as well as drag and gravity force and particle formation.The scope of the present project is the modeling and simulation of spray and spray drying processes where special attention is given to the characteristics of both the spray and spray drying, and their effect on the characteristics of the resulting powder. In particular, spray inhomogeneity associated with the atomization process and its transport in the convective medium is not well understood. Moreover, detailed information about the particle formation and its influence on the properties of the resulting powder is required.In the present project, the complete process ranging from atomized spray to powder is studied by means of numerical simulation where the distribution of the spray is modeled using direct quadrature method of moments (DQMOM), which is a powerful method to include all physical processes of interest. DQMOM must be coupled to the evaporating and drying environment.The first period concerned the setup and verification of the one-dimensional mathematical model using experimental data from BASF, where a water spray was injected into nitrogen at room temperature. In the second period, two-dimensional axi-symmetric systems of water and Polyvinylpyrrolidone (PVP)/water solutions sprayed in to still air are studied. For PVP/water sprays, in order to treat the bi-component evaporation and drying of droplets, a new evaporation and drying model is developed, analyzed and implemented in DQMOM. The bi-component droplet evaporation and drying model was also evaluated for Mannitol/water droplets. The final period concerns the drying of PVP/water sprays into powder where the effect of drying conditions such as gas temperature and velocity as well as droplet size on particle formation and characteristics will be investigated for both PVP and Mannitol.