Direct insight into particle swarm dynamics and its effects in dense solid–liquid suspensions using inline image method

Concentrated suspensions of very high phase fractions (>10%) significantly complicate hydrodynamic characteristics in multiphase reactors. The inline image method proposed recently provides the possibility to peer into dense particle swarm dynamics, previously considered an impossible mission. In this work, the method was further developed to determine the particle-resolved flow field and comprehensive datasets of particles within a swarm. Transient swarm microstructure demonstrated two aggregation states, that is, doublets and multiplets, accompanied by frequent collisions and friction. Statistical analysis indicated the damping effect on slip velocity and net force induced by the particle swarm became significant as solid holdup reached 13.2%, which markedly enhanced particle suspension. Through correlation analysis of dynamic datasets and relevant mechanisms, the viscous effect and hindrance effect exerted by the particle swarm were quantitatively elucidated for the first time. Accordingly, a correlation was proposed to predict the swarm effect on axial slip velocity, and good agreement was demonstrated across wide concentration ranges.