Boundary and concentration effects on the creeping motions of core-shell particles

• Published in: Chemical engineering science 2019-08, Vol.203, p.122-137
• Main Authors: Chen, Shih Hsin, Li, Xin-Fang
• Format: Article
• Language: English
• Subjects: Boundary effect; Cell model; Concentration effect; Core-shell particle; Emulsion
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2019.03.065

[Display omitted] •Three situations: single core-shell particle free motion, a core-shell particle moving in a concentric cavity, and core-shell particles in a monodispersed emulsion.•The results are in analytical forms, which are formulated and applied to the most general situations for the emulsion system of core-shell (or encapsulated) particles.•Shell viscosity and shell-to-core radius ratio, as well as boundary effects and particle interactions, are important factors influencing the particle motions.•In the limiting situations, our general results for two-phase particles could be simplified to the cases of solid particles, liquid droplets and gas bubbles in the literature, all of which are single-phase. In this study, the creeping motions of core-shell particles at low-Reynolds numbers were analyzed and discussed in three cases: (i) a freely translating particle; (ii) a particle in a concentric hole; (iii) particles in a monodisperse suspension. The core and shell were assumed concentric and consist of immiscible liquids. The results revealed the particle motions were significantly influenced by the radius (or volume fraction) and viscosity of the shell and core, especially the shell viscosity. In the limiting situations, our general results for two-phase particles could be simplified to the studies of single-phase particles (solid, liquid or gas bubble) in literature. For the case of a freely suspending particle with the same volume fraction of shell and core, the modified coefficient was reduced by more than 30% as the dimensionless shell viscosity reduced from 100 to 0.01 at ηc∗=1; however, the coefficient was only slightly reduced by less than 1.5% as the dimensionless core viscosity reduced from 100 to 0.01 at ηs∗=1. For the translation of a particle in a concentric hole, the boundary effect of the cavity wall performed to significantly hinder the particle motion. When the volume fraction of the particle in the hole was 0.01 and 0.1, in the case of a21 = 1.25, ηc∗=1 and ηs∗=0.01, the boundary effect retarded the particle velocity to 2/3 and 1/3 of the free particle velocity, respectively. In a monodisperse system, the mean translational velocity of particles was hindered by the hydrodynamic interaction between the particles, and the hindrance effect increased as the particle concentration increased. Particle concentration and shell viscosity were the main properties affecting the fluid dynamics of the suspension.