A review of experimental studies on the influence of particle properties on sedimentation and settling dynamics

Sedimentation is a fundamental particle–fluid interaction process that governs transport and separation phenomena across environmental, industrial, and biological systems. At its core, the process is controlled by the balance between gravitational forcing, viscous resistance, and inertial effects, which together define the flow regime and resulting particle dynamics. The settling behavior of particles emerges from a coupled interplay between particle size, shape, and density, together with the rheological response of the surrounding fluid. While theoretical and numerical models have provided important mechanistic insight, experimental studies remain essential for resolving wake structures, orientation dynamics, confinement effects, and collective interactions under realistic flow conditions. This review synthesizes experimental investigations that elucidate how particle size, shape, and density individually and jointly influence sedimentation and settling dynamics in Newtonian and non-Newtonian fluids. Unlike existing reviews that primarily compile observations, the present work emphasizes a physics-informed interpretation of experimental results by linking observed behaviors to underlying flow regimes and particle–fluid interaction mechanisms. Emphasis is placed on laboratory measurements that reveal geometry-induced settling modes, size-dependent hindrance, density-controlled interactions, and wall- and confinement-modified hydrodynamics. Where possible, these observations are interpreted in terms of Reynolds-number-dependent transitions, wake evolution, and deviations from classical drag laws. The review also highlights advances in experimental diagnostics, including high-speed imaging, refractive-index-matched techniques, and volumetric particle image velocimetry, that have transformed the ability to resolve particle-fluid coupling at the microscale. A dedicated section on new experimental directions and suggestions outlines how these emerging tools can be strategically integrated to overcome current experimental limitations, including unresolved size-shape-density coupling, collective effects in polydisperse suspensions, and sedimentation in complex rheological environments. Particular attention is given to the need for regime-based experimental design and data-driven approaches capable of capturing multiscale interactions. Collectively, the insights presented in this review provide a coherent experimental framework linking particle-scale dynamics to macroscopic transport behavior, and point toward the development of unified, predictive descriptions of sedimentation across a wide range of flow conditions with relevance to fundamental fluid mechanics, soft-matter physics, and multiphase flow research.