AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
The Structure of Nanoparticle Nucleation in Three-Dimensional Planar Jets
NATHAN MURFIELD, Sean Garrick, University of Minnesota
Abstract Number: 511 Working Group: Aerosol Physics
Abstract The effects of large-scale mixing and vapor concentration on homogeneous nucleation rates are investigated via direct numerical simulation (DNS) of dibutyl-phthalate (DBP) nucleation during cooling and mixing in three-dimensional planar jets. DNS is used as it contains no inherent assumptions about the cooling or mixing processes. In the simulated cases, a heated jet doped with DBP issues into a co-flow of room-temperature air. As the two streams mix, the DBP vapor becomes highly supersaturated and particles are formed by homogeneous nucleation. The simulation results provide a demonstration of how nucleation takes place in narrow regions where molecular mixing of the two streams occurs. Two distinct nucleation events are observed: initial shear layer nucleation, and later nucleation in coherent structures or eddies generated by the velocity difference between the jet and the co-flow. These observations agree with the trends seen in the experimental studies of DBP nucleation carried out by Lesniewski and Friedlander (Proc. R. Soc. Lond. A 454, 1998). A scatter plot diagram of observed dilution paths in temperature versus condensable vapor concentration space where nucleation rates are superimposed is shown to be a convenient tool for analyzing nucleation events. Convection by large-scale eddies gradually spreads the range of mixing paths in this space towards higher nucleation rates. The results also show that boundary conditions, including inlet concentration and velocity ratio, have both significant effects on particle nucleation. Both increased large-scale convective mixing and increased inlet DBP concentration are shown to increase nucleation rates. Additionally, heat release during nucleation is shown to affect the flow field in cases where the nucleation rate is very high.