AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Theoretical and Experimental Investigation of Particle Formation from Evaporating Microdroplets
Mohammed Boraey, Alberto Baldelli, REINHARD VEHRING, University of Alberta, Canada
Abstract Number: 301 Working Group: Aerosol Physics
Abstract Diffusion controlled particle formation from evaporating microdroplets was described using a numerical model which is based on a newly developed normalization of the diffusion equation in one-dimensional spherical coordinates. Radial concentration profiles as a function of time were calculated for isothermally evaporating multicomponent solution and suspension microdroplets. The model results were expressed in terms of non-dimensional process parameters such as Péclet number, normalized drying time, and normalized concentration. The numerical results were fitted with analytical expressions so that the results can be applied without programming. Final dry particle properties such as particle diameter, particle density, and aerodynamic diameter were predicted. For hollow particles, which are formed under conditions characterized by a high Péclet number, the shell thickness was approximated successfully. The model results were found to be in good agreement with published results, and were compared to experimental results generated using a novel monodisperse droplet chain setup. Monodisperse aqueous microdroplets were generated in a diameter range of 10 – 50 micro-meter, using a piezo-ceramic droplet-on-demand dispenser at frequencies < 100 Hz. The droplets were injected into a laminar gas flow with controlled temperature and relative humidity, creating an evaporating, widely spaced droplet chain. The droplet chain was illuminated by a pulsed diode laser and an argon ion laser to determine microdroplets diameter, spacing, and velocity. Dried microparticles were sampled from the flow onto membrane filters and subsequently analyzed by ultramicroscopy. The dry particles were found to be monodisperse, possessing nearly identical morphology. Geometric particle diameter and particle density as a function of process conditions were determined.