Study on Mixing Behavior and Hydrodynamics of High-Solid-Holdup Liquid–Solid Systems in Multiphase Flow Reactor

Continuous-flow technology offers advantages in fine chemical and pharmaceutical processes; however, high-solid-holdup (solid mass fraction) liquid–solid systems are prone to clogging and mass transfer deterioration. Although multiphase flow reactors are widely applied, their performance remains insufficiently characterized. In this study, computational fluid dynamics (CFD) coupled with the Mixture model and kinetic theory of granular flow (KTGF) is combined with residence time distribution (RTD) experiments to establish and validate a numerical model. The effects of feed flow rate, rotational speed, and solid holdup on mixing and solid-phase RTD are systematically investigated. Simulation results reveal that the reactor exhibits satisfactory radial and axial mixing performance, alongside non-ideal flow characteristics including recirculation, wall enrichment, and weak back-mixing. Increasing feed flow rate enhances axial mixing and suppresses back-mixing. In the solid holdup range of 10–30%, rotational speed significantly influences axial mixing uniformity ζ and dimensionless variance σθ2; in the 30–50% range, ζ continuously increases while σθ2 first decreases and then increases. Based on CFD data within this range, an empirical correlation for the Péclet number Pe was established (with good fitting for Pe < 35); it serves only as an interpolation tool and does not possess predictive or general design capability. These findings provide a reference for applying multiphase flow reactors in high-solid-holdup liquid–solid mixing systems.