04 Fakultät Energie-, Verfahrens- und Biotechnik

Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/5

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Author: search.filters.author.Nieken, UlrichSubject: search.filters.subject.670

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    Electrically heated oxide ceramic tubes for high temperature reactions
    (2023) Matthies, Jörn; Schall, Thomas; Pritzkow, Walter; Tuttlies, Ute; Nieken, Ulrich
    Endothermic high temperature reactions are usually carried out in metal tubes heated by gas burners. Electrical heating allows substantial reduction of CO2 emissions. We propose the usage of a composite tube, where a thin metallic layer is embedded between an inner and outer ceramic layer. While monolithic ceramics suffer from brittleness and low tolerance to thermal stress, only the inner layer is made from monolithic ceramics, while the outer layer is made of fiber reinforced oxide ceramics. In first tests the hybrid ceramic tube was electrically heated to 1250 °C with a maximum heat release of 85 kW m-2.
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    Modeling of the branching point distribution during the polymerization of N‐vinylpyrrolidone
    (2022) Welzel, Stefan; Zander, Christian; Hungenberg, Klaus‐Dieter; Nieken, Ulrich
    To gain insights into the microstructure of polyvinylpyrrolidone (PVP), a detailed reaction mechanism is developed, which characterizes the polymer along the property coordinate chain length, terminal double bonds (TDB), and branching points. For practical purposes, calculations with three property coordinates are unfeasible, and model reduction is needed. Here, a reduced model with only one single property coordinate without significant loss of accuracy is derived. In the first step, the coordinate TDBs are reduced by a linear relationship between TDBs and chain length. As the parameters of this relation are state dependent, they are dynamically adjusted from a parallel calculated 0D model. In a second step, the pseudodistribution approach is used to reduce the 2D distribution to chain length as the only property coordinate and calculate moments of branching points as a function of chain length. A 2D class model is set up for validation. To demonstrate the benefits of the model, the chain length distribution and moments of branching points are calculated for different average residence times and monomer concentrations in a stirred tank reactor. In a future publication, the model will be validated by experimental data in terms of chain length distribution and branching points.