AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Finite Element Analysis Simulations on the Photoacoustic Response of Aerosols with Water Coatings
JAMES RADNEY, Christopher Zangmeister, National Institute of Standards and Technology
Abstract Number: 546 Working Group: Aerosol Physics
Abstract The magnitude of absorption enhancement by an absorbing aerosol with a water coating is a topic that has received considerable attention. Mie theory predicts that the absorption cross-section should continuously increase with coating thickness and extinction minus scattering measurements have confirmed this response. However direct absorption-based measurements of this enhancement using a photoacoustic spectrometer have proved elusive at best. In some instances, rapid vaporization of water at the particle/water interface causes ultrasonic nano-explosions that are perceived as an apparent enhancement of the photoacoustic signal; as a result, measured absorption cross-sections are larger than physically explainable by Mie theory. In other instances, the evaporation of surface water reduces the photoacoustic signal by reducing the energy available for thermal relaxation. This array of observations arises because the thermal and acoustic response to light pulses by water-coated aerosol particles depends upon the intensity and duration of the pulse, the type of particle under investigation and the coating thickness. We will present finite element analysis simulation results on the photoacoustic effect in coated aerosols with an emphasis on the heat transfer, fluid flow and pressure (acoustic) wave propagation. Both spherical and aggregated aerosol particles with varying coating thicknesses will be examined in order to better understand the different responses.