Experimental study on the path instability of a porous particle in a quiescent fluid

Abstract Understanding the motion of porous particles is essential for regulating multiphase flows and particle‐fluid interactions. To investigate path instability during settling, experiments using particle tracking velocimetry (PTV) and particle image velocimetry (PIV) were conducted. Based on two‐dimensional and three‐dimensional trajectory characteristics, four typical settling modes were identified: Oblique, S‐shaped, Zigzag, and Spiral. Under random release conditions of a single particle, the occurrence probabilities of these modes were approximately 13%, 51%, 18%, and 18%, respectively. Path instability decreased with increasing permeability, and at higher permeability, particles exhibited more stable settling trajectories. Porous particles showed higher terminal velocities than impermeable ones under the same driving force. Particle path instability correlates with wake asymmetry and is mainly controlled by permeability rather than Reynolds number, with higher permeability stabilizing the settling trajectory. These findings provide new insights into the motion behavior of porous particles such as catalysts and offer guidance for optimizing particle ‐ fluid interactions and enhancing mass and heat transfer efficiency in multiphase systems.