Experimental and Computational Investigation of Fluid Dynamics and Solid Transport in Split-and-Recombine Oscillatory Flow Reactors Using Water as Medium

In processing of chemical reactions involving solid phases, the physical properties of reagent suspensions is of critical importance. Therefore, we present herein a comprehensive analysis of fluid dynamics and solid transport in split-and-recombine oscillatory flow reactors. The research aims to improve the understanding of the mechanisms behind the resuspension capacity of solids in flow driven by the proven efficacy of such reactors in processing of reactions involving multiple phases. On the basis of its importance as a sustainable reaction medium, water was utilized as liquid phase during our comprehensive analysis. Experiments in a commercially available flow reactor (HANU 2X 5) verified a six-fold reduction of particle deposition in case of oscillatory flow compared to constant flow conditions using SiO2 slurries. Further investigations with a full factorial Design of Experiment approach revealed that the tuning of oscillation parameters enables the system to reach an optimal homogeneous suspension instead of incipient clogging. The net slurry flow rate was also found to significantly influence solids suspension capabilities. Under optimized conditions, quantitative transport of up to 10 wt% SiO2 slurries was achieved. A computational fluid dynamics model was developed to give insight into the multiphase fluid flow within the reactor geometry. It was found that oscillatory flow creates large recirculation regions and remarkable positive vertical velocities near the static mixers within the reactor plate that generate upward forces facilitating particle resuspension. By employing oscillations, suspension capabilities improved up to 5 times compared to stationary flow conditions. It was also observed that strategic asymmetries within the reactor could enhance resuspension, while the cross flow section aspect ratio exhibited only minimal influence. By utilizing a novel calculation method for Lagrangian particle tracing simulations, computational times for acquiring particle positions under oscillatory flow conditions were reduced by 82%. The simulation validated the benefits of oscillations in sustaining particle suspension. Oscillatory flow demonstrated a significant reduction in particle deposition at the reactor bottom compared to constant flow. The combination of experimental and computational approaches provides valuable insights for optimizing oscillatory flow reactor design, further advancing their utilization in chemical reaction technology and also potentially in manufacturing.