Coupled effects of particle morphology and confinement on irregular particle regime and drag coefficient

Abstract

The settling behavior of irregular particles in a confined space is critical to chemical engineering applications but remains incompletely understood due to the coupled effects of particle morphology and wall confinement. A two-dimensional coupled particle dynamics-lattice Boltzmann model for the gas–liquid–solid flow with an irregular particle represented by a multi-sphere algorithm is employed to simulate three-phase flows. Using a clover particle, we examine settling dynamics under different confinement widths, particle major axis and roundness, solid-to-liquid density ratios, and physical properties of the upper and lower fluids. Three distinct flow regimes are identified: stable rectilinear settling (Regime I), sustained lateral oscillation (Regime II), and wall collision settling (Regime III). A regime map clearly delineates the zones for the three regimes. The confinement width modulates the settling velocity more strongly than the particle major axis, and both effects are non-additive, their relative roles dictated by the change pathway. In Regime II, particle rotation is coupled with lateral oscillation, while increasing the density ratio drives the transition to Regime III. A new empirical drag coefficient correlation incorporating both particle roundness and confinement parameters is proposed. These findings offer a unified framework for predicting sedimentation behavior of irregular particles in a confined space.