Morphological patterns and interface instability during withdrawal of liquid-particle mixtures

HYPOTHESIS

The stability of fluid-fluid interface is key to control the displacement efficiency in multiphase flow. The existence of particles can alter the interfacial dynamics and induce various morphological patterns. Moreover, the particle aggregations are expected to have a significant impact on the interface stability and patterns.

EXPERIMENTS

Monodisperse polyethylene particles of different sizes are uniformly mixed in silicone oil to form the granular mixtures, which are injected into a transparent radial Hele-Shaw cell through different strategies to obtain the homogeneous and inhomogeneous (with particle aggregations) initial states. Subsequently, a systematic study of morphology and interface stability during the withdrawal of granular mixtures is performed.

FINDINGS

For homogeneous mixtures, we observe earlier onset of fingering, more fingers and lower gas saturation at breakthrough than for pure fluid with equivalent viscosity. This effect can be attributed to the particle-induced perturbations. For inhomogeneous mixtures, particle clusters and bands significantly enhance the interface instability. Furthermore, we find that particle deposition due to liquid film entrainment occurs above a critical local flow velocity, and we elucidate the responsible mechanism through force balance analysis and the thin film theory. This work could be of practical significance in geoenergy and industrial applications.

Distinct recovery of copper and aluminum from waste electric wires using a roll-type electrostatic separator

Electrostatic separators are commonly employed for the sorting of insulating and conducting fractions of granular mixtures. However, separation of the various metals that compose the conductive fraction still represents a major challenge for the recycling industry. The aim of this paper is to identify the conditions in which a roll-type electrostatic separator could be used for distinctly recover the copper and aluminum from waste electric wires. A numerical model of particle trajectories was employed to predefine these conditions and guide the experimental study. The electrostatic separation experiments were carried out using a reverse-S-type-plate high-voltage electrode. The visualization of particle trajectories using a high-speed camera paved the way to an original design. Thus, a metallic trap was attached to the high-voltage electrode, to facilitate the collection of the aluminum flake-like particles from a mixture that also contains copper strands. With a plastic trap replacing the metallic one, to avoid electric field modification, 68.6% of the copper was recovered with a purity attaining 99%.