This project focuses on the optimization of transport processes in between (nano-)structured reactive surfaces and the bulk liquid phase on micro- to millimetre scales by considering time dependent concentration fields and Lagrangian Coherent Structures.
Today, one of the major problems of multiphase reactors is the hardly predictable transport of momentum, as well as heat- and mass, in between boundary layers and the heterogeneous turbulent liquid bulk phase. This concerns catalytic active surfaces on reactor walls or porous structures as well as dispersed gaseous, liquid or solid particles.
Barriers inhibiting transport can appear in stable vortices in dead zones or wakes behind obstacles, e.g. behind rods in structured reactors or gas bubbles. Flow structures of this type dominate the local mixing and residence time distribution and can have a tremendous impact on the performance of a biochemical or chemical reaction. For an optimal yield of a conversion process, the most critical flow condition that diminishes transport needs to be identified and eliminated. Recently, new analysis tools have been developed for the detection of transport limitations in process engineering: trajectories and velocity fields of the fluid flow and dispersed particles can be captured in 2D and 3D and evaluated to get detailed information about Lagrangian Coherent Structures (LCS), for instance, by analyzing Finite-Time Lyapunov Exponents (FTLE).
In this project recent optical micro-measurement techniques to study the fluid dynamics in SMART reactors, like time-resolved micro-Particle Image Velocimetry (m-PIV), Stereo Particle Tracking Velocimetry (S-PTV) or Astigmatism Particle Tracking are applied. From the trajectory and velocity data of flows close to micro-structured surfaces Lagrangian measures like LCS are derived. In this way transport barriers on the microscale due to, e.g. engulfment flow, stretching, folding and/or back mixing within and above CNT-carrier structures, porous materials or carbon foams are identified. Together with micro-concentration field measurements using Confocal Laserscanning Microscopy (CLSM) and Light Sheet Fluorescence Microscopy (LSFM) the transient mass transport is recorded. This enables the evaluation of the concentration changes along fluid parcel trajectories.
In this way, the history of the mass transport can be incorporated in the Lagrangian mixing statistics. With these new methods the micro- and mesostructures of, e.g. catalytic active surfaces, will be optimized concerning the relevant transport and reaction conditions. Especially the effect of switchable states of nanostructured surfaces altering wettability or geometrical configurations will be analyzed in detail with regard to mass transport and mixing performance. The aim of this project is the experimental determination, phenomenological modelling, and optimization of transport processes at and within the structured reactor components developed in project area A of the SFB 1615 and the optimal integration of such components into SMART reactors in Area C of the SFB 1615. Therefore, this project is a link in between the two project areas and serves for knowledge transfer. More specifically, we intend to answer the following research questions:
- How do nanostructured components for in situ detection and self-adjustment influence transport processes from micro- to millimetre scales?
- How can the influence of adapted components on transport processes be modelled phenomenologically and translated to suitable correlations?
- How must nanostructured components be integrated into reactors to achieve maximum functionality?
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