Numerical simulation and experimental characterization of nanoparticle synthesis in flame spray processes

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Flame spray synthesis offers numerous possibilities for the production of custom-made nanoparticles. However, the interactions of spray, turbulence, phase transition, precursor decomposition, chemistry and particle formation are so complex that our understanding of the process is rather incomplete. During the first funding period, a reference burner and reference conditions and material systems were agreed upon. Experiments and models for the description of the complex processes were developed. In the second funding period, experiments and models shall be extended, and adapted for the optimised reference burner and new material systems. The new design of the reference burner now needs to be characterised using a variety of experimental techniques (Particle Image Velocimetry, Phase-Doppler Anemometry, Laser-induced Fluorescence, Elastic Light Scattering and Multiple-Angle-Light –Scattering). These methods alone are only partially useful in multi-phase systems. Hence, the advantages of combining imaging diagnostics and numerical simulations developed in funding period 1, will be applied for particle diagnostics. In order to achieve meaningful validation of models, despite the inherent ambiguities, we will compare synthetic signals, generated by the numerical simulations directly with experimental signals. The modelling is based on a stochastic method called Multiple Mapping Conditioning (MMC). This method allows for a detailed and efficient description of all processes involved including their interactions. Following the results of FP1 and the expected changes of the reference system, new challenges arise. New boundary conditions need to be defined and the new nozzle design including partial premixing of the dispersion gases may require an extension of the modelling that allows for the description of stratified flames. Furthermore, the description of the transport of nanoparticles shall be decoupled from transport for the gaseous phase to account for the different diffusive fluxes of the two phases.Finally, the – so far mostly ignored – microexplosions of the precursor-solvent mixtures will be investigated. Microexplosions were reported for the most standard material systems of the SPP in single droplet experiments and it can be assumed, that conventional evaporation models, based on phase equilibria – cannot describe the evaporative fluxes with sufficient accuracy. Hence, the occurrence of microexplosions in the SpraySyn configuration shall be verified experimentally for the first time and semi-empirical models for the description of this process shall be developed and implemented in the simulations.