Numerical study of airborne particle dynamics in vortices subject to electric field

TL;DR

This study numerically investigates how aerodynamic, inertial, and dielectrophoretic forces collectively influence airborne particle behavior in vortical flows under electric fields, revealing mechanisms for particle trapping and separation.

Contribution

It introduces a comprehensive numerical analysis of combined forces on airborne particles in vortical flows with electric fields, highlighting new trapping and separation behaviors.

Findings

Inertial cut-off shifts to DEP capture at a critical force ratio.

Particles are spatially segregated based on size and density.

Vortex distortion leads to inverse inertial limit cycle trapping.

Abstract

Capture, selective collection and flight manipulation of airborne particulate are three important functional requirements in various actively growing aerosol technology applications. Aerodynamic drag, particle inertia and dielectrophoretic (DEP) force due to externally applied electrostatic forces influence the behavior of micron sized particles significantly, in such situations. In this work, we numerically study how a combination of these forces uniquely influences the behavior of uncharged or mildly charged airborne particles, distinct from that with their individual influences. Uncharged particle movements in a numerically fabricated well structured steady vortical flow between two curved electrode surfaces are analyzed. Vortical air circulation towards and away from the electrode tip enhances and deteriorates electrostatic particulate capture on the electrodes, termed as co and counter directions with respect to the electrostatic force on particles respectively. Particles in counter vortices under an electric field reveals a rich variety of unique behaviors due to the interplay of drag, inertia and DEP forces. Distortion of the vortex structure due to convexity of electrode surfaces results in an inverse inertial limit cycle trajectory trapping of particles; with the airborne particles spatially segregated, trapping larger particles further inside the vortex than the smaller particles.Value of a dimensionless number $\xi_v$, the ratio of DEP force and particle inertia, represents the combination of the operating flow and electric field strengths. Inertial cut-off of particle capture in this configuration abruptly shift to DEP capture at a critical value of $\xi_v\approx 0.2$, as its value increases. Selective deposition of particles within a closed range of size and density, emerges due to the interplay of vortex trapping, inertial expulsion and electrostatic capture.