On Free Moving Micron-Sized Droplet-Particle Collisions

TL;DR

This study investigates how droplet-particle collisions in mid-air depend on particle properties like density and wettability, proposing a modified Weber number to predict collision outcomes and unifying data across different conditions.

Contribution

It introduces a modified effective Weber number that accounts for particle density and wettability, providing a unified framework for collision outcome prediction.

Findings

Particle density influences whether particles are engulfed or remain at the droplet interface.

High wettability suppresses particle separation during collisions.

A unified regime map collapses data across different literature when size ratio and Ohnesorge number are fixed.

Abstract

Predictive modelling of agglomeration in spray drying and particle capture in aerosol scavenging requires a fundamental understanding of droplet-particle collisions. The study complements prior work by investigating mid-air collisions between free micron-sized spherical droplets and particles with a size ratio of three. Particle wettability and density are varied to elucidate the mechanisms governing collision outcomes and the role of collision offset. Results show that particle density determines whether a particle is engulfed by the droplet or remains at the droplet interface during capture, while high wettability suppresses particle separation even in glancing collisions. A modified effective Weber number incorporating particle density and wettability is proposed to map collision outcomes. To assess its robustness, the present data are combined with literature results in a unified regime map. The regime boundaries separating collision outcomes collapse when the size ratio and Ohnesorge number are held constant. However, at a given collision offset, variations in size ratio and Ohnesorge number alter the critical effective Weber number for particle separation through changes in collision geometry and viscous resistance.