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3D turbulence has been the main framework for the development of micromixing models for chemical reactors design, and thus these models rely on the description of 3D turbulent mixing: large vortices stretch into smaller vortices that reduce the mixing scales and dissipate. Highly viscous fluid mixing and micro mixers are yet far from this description and are better fitted by laminar mixing models, which are generally not particularly suited for the practical design of chemical reactors due to the number of unknown parameters or to the computational effort to compute such parameters as the fully resolved shear rate field. These laminar reactors operate generally with a large confinement of one of the flow dimensions, which prevents the turbulence dissipation by vortex stretching, because the normal direction to the flow is confined by reactor walls. The flows in these reactors are well described by 2D turbulence theories, that differ from 3D by the fact that energy is injected from a small scale, for example the width of the inlet injector in an opposed jets reactor, and grows to the scale of large vortices that is determined from the reactor geometry – inverse energy cascade. In 2D turbulence the dissipation of vorticity is slower than in 3D turbulence and the mixing mechanisms are those described from laminar mixing models that relate the scales of mixing to the field of shear rates applied to the original inlet laminae thickness. A unified framework for laminar mixing models and 2D turbulence would enable to introduce micromixing models for the design of 2D chemical reactors based on turbulent quantities derived from the 2D turbulence power spectra from where the injection scales, the large scales and the energy transfer between scales are obtained.
Some reactors that are strongly affected by dimensionality and are thus well described by 2D models, were studied and developed at FEUP during the last decade: NETmix and T-jets. Rotor/stators are also reactors where dimensionality confinement plays a major role. This project will use these three reactor types for the analysis of mixing and chemical reaction in 2D turbulent flows. The flow study will heavily rely on Computational Fluid Dynamics (CFD) simulations of the fully resolved time and space domains without subgrid models. The CFD simulations will relate 2D modelling with the simulation of the actual 3D geometry where the dimensionality is constrained but the third dimension actually exists. CFD simulations will relate the 2D turbulence with mixing and chemical reaction, providing full data for the unification of 2D turbulence and laminar mixing theories for the design of 2D chemical reactors using micromixing models.
The flows in the reactors are going to be thoroughly characterized with laser velocimetry methods to obtain the fully resolved time and space flow dynamics. This will provide data for the characterization of the bidimensionality of turbulence in the reactors and will enable to validate the CFD results. Mixing and reaction will also be studied experimentally with laser visualization methods and from the selectivity of a complex chemical reaction. For this end, the 2Dmix project introduces new micromixing test reactions that are particularly suitable for reactions with large viscosity ratios and for laser visualization via induced fluorescence of one of the reaction products.
T-jets, NETmix and rotor/stators are proven in the processing of nanomaterials, reactive polymers that are of particular application to composites and nanocomposites, slurries and processing of large viscosity ratios and flow rate ratios. And thus, this research topic is inline with EU priorities for Factories of the Future. These topics also have been singled out to us by some major chemical industries and within the framework of SPIRE technology platform. Thus the project team intends with this fundamental research to lay the foundations that enable in a short period to have this project findings being applied in chemical industries research grants or in H2020 industry-academia research.