Study on motion function adaptation and fluid-structure interaction characteristics of reciprocating agitation in liquid-solid multiphase flow

Abstract

Mechanical agitation is the most dominant engineering technique for achieving efficient solid-liquid multiphase mixing in stirred vessels, playing a core role in multiphase flow transport. Breaking the symmetrical flow field inherent in conventional agitation to enhance whole-tank mixing remains a persistent hotspot and challenge in process equipment. Aiming at the bottlenecks of traditional unidirectional rotating agitation – isolated mixing regions (IMR) and restricted local mass transfer – this study systematically investigates the solid-liquid mixing enhancement mechanism of reciprocating-rotating coupled stirring, based on a coupled computational fluid dynamics-discrete element method (CFD-DEM) framework integrated with the volume of fluid (VOF) multiphase model and overset dynamic mesh technology. This study quantitatively analyze the regulation laws of reciprocating motion functions (sine, trapezoidal, random, chaotic mapping) and stroke amplitudes on particle spatial distribution, and reveal the impeller force response and particle multi-state suspension characteristics via two-way fluid-structure interaction (FSI) analysis. Results show the sine motion function has the lowest spatiotemporal velocity correlation, with robust spatial ergodicity and optimal particle dispersion. When stroke amplitude is 2/3 of the tank diameter, the average particle nearest neighbor distance (NND) peaks, effectively mitigating severe local entrainment and bottom accumulation. FSI dynamic analysis reveals periodic alternating loads induce ∼5,000 Pa concentrated stress at the impeller disk and blade connections, accompanied by high-frequency wall shear stress, posing potential material fatigue and erosive wear risks. High-viscosity systems significantly inhibit particle settling via flu-id damping, achieving up to 85 % suspension rate by the second cycle, with broader property compatibility for diverse particles than low-viscosity systems. This study elucidates the dynamic evolution mechanism of reciprocating-rotating coupled stir-ring, providing explicit quantitative criteria for industrial design and scale-up of novel high-efficiency solid-liquid mixing equipment.