Impact of turbulence on the product, modelling and simulation

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Previous work has shown that turbulence, which occurs in all large nano-particle production reactors, has a massive influence on product properties: for example, the size growth of aggregates can be limited by rapid cooling, which can only be achieved by rapid and thus turbulent mixing of cold, inert gas. At the same time, however, product properties can be made more uniform if these products undergo a - largely - random temperature and concentration history. Unfortunately, the prediction and simulation of the turbulence effects on the particles is not trivial, since turbulent mixing causes inhomogeneity of the particle concentration fields on very small scales, which cannot be sufficiently resolved even with massive computing power. One therefore uses time-averaged simulations (RANS) or, in recent work, spatially filtered simulations (LES), which allow acceptable computational time. Unfortunately, averaging or filtering implies an irretrievable loss of information that leads to erroneous predictions unless the lost information is estimated with sufficient accuracy (using appropriate models). Therefore, in the third phase of the „Forschergruppe", experiments will be performed to investigate the effect of turbulence on product properties on the one hand, and to determine the smallest spatial scales (in a small spatial domain) with very high resolution on the other hand. The present project will recalculate the performed experiments using state-of-the-art LES methods and models. In this way, the experiments can be interpreted and phenomena that occur can be analyzed. At the same time, the relevant, available and developed turbulence models will be tested, improved, and, if possible, validated in the simulation based on the new, detailed measured experiments. The results of these validated simulations will then show the influence of turbulence on product properties such as particle size distribution or degree of agglomeration, and moreover, explain them.