PARTICULATE TRANSPORT IN THE LOW-REYNOLDS-NUMBER FLUID CONFINED IN A SPHERICAL CAVITY

Particulate transport in low-Reynolds-number fluids in confined environments play key roles in applications related to biology, medicine, chemical engineering, and energy, to name a few. Recently, much attention has been paid on particle dynamics in low-Reynolds-number fluids under spherical confinement, owing to its importance in life processes in living cells and technologies related to microfluidic encapsulation and droplet-based microreactors. To understand fundamental principles and microscopic mechanisms behind the particulate transport processes, scholars and researchers around the world have undertaken extensive and comprehensive investigations from theoretical, numerical, and experimental approaches. These efforts have led to the significant advancements in our understanding of particle transport in confined low-Reynolds-number fluids. Despite these efforts, a review article describing the current state of research progress in this area remains absent. In this article, we will summarize relevant progress and achievements obtained by using theoretical, numerical, and experimental methods. In theoretical studies, scholars mainly investigated confined particle dynamics in the spherical cavity with no-slip and slip conditions on particle and cavity boundaries, and particle motion in a spherical cavity with a deformable elastic wall. In numerical studies, simulations have been conducted to investigate the behavior of particles with different shapes in both stationary and rotating spherical cavities. In experimental endeavors, researchers have employed advanced optical microscopy techniques to trace and analyze three-dimensional trajectories of colloidal particles within spherical water globules, and the particle’s diffusional behaviors were quantitatively analyzed. Besides, the Brownian motion and diffusivities of particles in a spherical cavity have been used to probe the confined environment’s properties. By reviewing the above work related to particulate transport in low-Reynolds-number fluids under spherical confinement from three different aspects, namely theoretical models, numerical simulations, and experimental investigations, this work could provide a reference for experts and scholars working in areas such as microfluidics, nanofluidics, and particulate transport.