AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Enhanced Growth Rates of Nanodroplets in the Free Molecular Regime
YENSIL PARK, Shinobu Tanimura, Barbara Wyslouzil, The Ohio State University
Abstract Number: 173 Working Group: Aerosol Physics
Abstract When Pathak et al. [Aerosol Sci. Technol., 2013, 47:1310-1324] studied the growth rates of nonane and D$_2O nanodroplets in the free molecular regime (Kn >10) using a supersonic nozzle, they found that neither the droplet temperature nor the growth rates matched the experimental values if they assumed the condensation coefficient (q$_c) and evaporation coefficient (q$_e) in the Hertz-Knudsen growth law were both equal to 1. Rather, to match the experiments they had to set q$_e < 1 with q$_c = 1. To confirm that this result was not due to uncertainties associated with the properties of supercooled water, we analyzed similar experiments for n-propanol under conditions where the alcohol is not supercooled with respect to the solid phase [Park et al., Aerosol Sci. Technol., 2016, accepted]. We again found that when q$_c = q$_e = 1, mass and energy balances yield theoretical temperatures and droplet growth rates that lie below the experimentally determined values. Much better agreement between theory and experiment is possible by setting (q$_c, q$_e) = (1, 0.6) or (q$_c, q$_e) = (1.3, 1). Retardation of evaporation is difficult to justify during rapid condensation, whereas a value of q$_c > 1 is consistent with the enhancement of the condensation rate by long-range attractive interactions. Since long range van der Waals interactions are known to enhance the coagulation of nanoparticles, it is reasonable to expect that they can also play a role in condensation.