# Special Issue on Multiphase Flows in Microfluidics: Fundamentals and Applications
###### Abstract
They showed that the penetration efficiency of particles decreased with increasing particle aspect ratio, Reynolds number, and pipe length-to-diameter ratio, and built a relationship between the penetration efficiency of particles and related synthetic parameters based on the numerical data. [PERSON] et al. [11] studied the contribution of an elliptical particle flowing between parallel plates to the effective viscosity, focusing on the particle-wall distance and particle rotational motion, and found that the contribution of particle shape to the effective viscosity was enhanced when the particle flowed near the wall; the spatial variation of the local relative viscosity was larger than the temporal variation regardless of the aspect ratio and particle-wall distance. [PERSON] et al. [12] numerically simulated the diffusion of non-spherical submicron particles in a converging-diverging micronozzle flow using the Euler-Lagrangian model, and showed how particle transportation with varying shape factors and densities resulted in different particle velocities, trajectories, and focusing; the particle with a larger shape factor or larger density exhibited a stronger aerodynamic focusing effect in a supersonic flow through the nozzle. [PERSON] et al. [13] simulated the motion of rod-like particles in the turbulent contraction flow and indicated that the rod particles aligned with the streamline in the central region as the particle concentration increased, but tended to maintain the original orientation distribution in the boundary layer. [PERSON] et al. [14] studied the rising characteristics of shaped bubbles in near-wall static water using the volume of fluid method, and found that the wall surface and the distance between the bubble and the wall influenced the rising of the bubble; the effect of interaction between the bubbles was significantly greater than the effect of the wall surface. There are also several papers on the motion of bi-disperse and self-driven particles, and the motion of particles in a non-Newtonian fluid. [PERSON] et al. [15] numerically simulated the motion and distribution of bi-disperse particles in Poiseuille flow and showed that the particle spacing would increase and could not remain stable when the smaller particle was downstream; the particle spacing first increased and then decreased, and finally tended to be stable when the larger particle was downstream. [PERSON] and [PERSON] [16] reviewed multiphase flow with self-driven particles and focused on the interactions between self-propelled/self-rotary particles and passive particles, the aggregation, phase separation,and sedimentation of squirmers, the effect of rheological properties on its motion, and the kinematic characteristics of axisymmetric squirmers. [PERSON] et al. [17] studied the trajectories and velocities of two side-by-side particles of different densities settling in a shear-thinning fluid with viscoelastic properties. They showed that the wake of the heavier particle could attract or rebound the light particle due to the shear-thinning or viscoelastic property of the fluid, and the sedimentation of the light particle could induce the distinguishable transverse migration of the heavy one. There are also papers on specific engineering applications in the Special Issue. [PERSON] et al. [18] proposed a three-phase foam (TPF) containing dispersed solid particles to improve foam stability under harsh reservoir conditions. They fabricated a novel TPF system, assessed the ability of the TPF to control steam channeling and enhance oil recovery, and observed a stronger foamability at a lower consolidation agent concentration. At the same time, there was a longer foam half-life period and solid particle settling time at a larger consolidation agent concentration. [PERSON] et al. [19] studied the effect of velocity on particle behavior in membrane filtration.