Particle Formation via Droplet Drying: Observing Morphological Evolution and Measuring Aerodynamic Diameter

DANIEL HARDY, Jim Walker, Pascal Lemaitre, Jonathan P. Reid, University of Bristol

     Abstract Number: 111
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
The coupled motion and evaporation of droplets and resulting dry particle formation are pivotal in a range of applications. These include powder production in the food and pharmaceutical industries, understanding airborne disease transmission and the quantification and mitigation of risk from aerosolised material in the nuclear industry.

Measuring the evaporation and morphological evolution of individual droplets presents significant technical challenges but is critical for understanding the microphysical processes that determine final particle properties.

This work presents a Falling Droplet Column (FDC) capable of analysing in detail the entire evaporative lifetime of droplets, with a sub-microsecond temporal resolution. The instrument operates by establishing a chain of uniform falling droplets within a temperature and humidity-controlled environment. Multiple exposure stroboscopic imaging enables direct measurement of geometric and aerodynamic diameter of individual particles. Dry particles are deposited at the bottom of the FDC and imaged using SEM.

In this talk we will present evaporative profiles and resulting morphologies over a range of conditions and inorganic salt solutions, detailed images of phase and morphological change and variations in aerodynamic diameter. We will make comparisons with simulations to probe the microphysical parameters governing droplet drying and transport.