AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Impact of Crystallization Kinetics on Spray Dried Microparticles Properties
ALBERTO BALDELLI, Reinhard Vehring, University of Alberta, Canada
Abstract Number: 10 Working Group: Aerosol Physics
Abstract The influence of the crystallization process on spray dried microparticles was investigated theoretically and validated experimentally. A piezoceramic dispenser was used to generate a chain of monodisperse droplets with an initial diameter in the range of 60 to 80 µm. Sodium nitrate (NaNO3) was chosen as solute for its crystallinity and strong presence in atmospheric aerosol. A broad range of solutions of NaNO3 with deionized water were prepared in a concentration range from 5 mg/ml to 5 × 10-5 mg/ml. The solution droplets were ejected into a laminar flow with temperatures of 25, 50, 75, 100, 125 and 150 °C, varying the evaporation rate and droplet temperature, accordingly. Dried particles with particle diameters between 0.3 to 18 µm were collected. A time dependent theoretical model was developed to determine saturation and crystallization time. The theoretical model introduced a dependence of the diffusion coefficient of NaNO3 in water to the droplet viscosity. The viscosity trend was experimentally determined with respect to the increase of NaNO3 mass fraction during the evaporation process. The theoretical model also considered the influence of the change of NaNO3 mass fraction on evaporation rate. The combination of theoretical derivations and experimental results showed that a higher amount of time available for crystallization lead to a larger crystal size and higher degree of crystallinity in the final microparticles.