A study of the detachment of droplets from a clean surface

Abstract

The detachment of an aerosol from a solid surface is an important phenomenon. The detachment of a particle is a process during which a solid particle or liquid droplet on a surface leaves its’ original position. They can slide or roll on the surface or even be re-suspended to become airborne again. Detachment of aerosols from solid surfaces is a concern in many different industrial and environmental processes. It is undesirable in many scenarios, e.g. contamination in the manufacturing of microelectronics and semiconductors, spraying of pesticide and paint, resuspension of filtered particles, and disease transmission. Sometimes it is also desirable, e.g., surface decontamination, filtration, oil recovery. Understanding the detachment behaviour can help in improving the numerous engineering operations and protecting human health. One droplet type and two substrate materials were studied. The resuspension behaviours for solid aerosols and liquid aerosols are not necessarily the same. Unlike solid particles, liquid may deform under an applied force and a portion of the droplet may detach even if the removal force is not high enough to detach the whole droplet. Three experiments were conducted to investigate the detachment of a droplet from a substrate, they were a centrifuge experiment, wind tunnel experiment and air jet impingement experiment. In the centrifuge experiment, a constant removal force field was provided by a centrifuge and the detachment behaviour was investigated. Larger droplets split into smaller portions during detachment; some portions were detached and the remains formed smaller droplets on the substrate. The wind tunnel experimental investigated the deformation and detachment of liquid droplets on two different solid surfaces in a fully developed turbulent channel flow. The air jet impingement experiment studied the detachment of droplets on a plastic substrate. Droplets of two different size ranges were impinged by an air jet with different impinging angles.

Date of Award	2016
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology