Simulation of aerosol formation due to rapid cooling of multispecies vapors

An extended classical nucleation approach is put forward with which aerosol formation from rapidly
cooled, supersaturated multispecies vapor mixtures can be predicted. The basis for this extension lies in the treatment
of the critical cluster that forms as part of the nucleation burst—a multispecies treatment of the thermodynamically
consistent approach is proposed that can be solved efficiently with a Newton iteration. Quantitative agreement
with Becker–Döring theory was established in case the equilibrium concentration of the critical clusters is properly
normalized. The effects of nucleation, condensation, evaporation, and coalescence are consolidated in the numerical
framework consisting of the Navier–Stokes equations with Euler–Euler one-way coupled vapor and liquid phases.
We present a complete numerical framework concerning generation and transport of aerosols from oversaturated
vapors and focus on numerical results for the aerosol formation. In particular, using adaptive time-stepping to capture
the wide range of time scales that lie between the nucleation burst and the slower condensation and coalescence, the
aerosol formation of a system of up to five alcohols in a carrier gas is studied. The effects of the temperature levels,
the cooling rate, and the composition of the vapor mixture under a constant temperature drop, on the formation and
properties of the aerosol are investigated. A striking nonuniform dependence of the asymptotic number concentration
of aerosol droplets on temperature levels was found. A decrease of the rate of cooling was shown to reduce the number
concentration of aerosol droplets which asymptotically leads to significantly larger droplets. The simplification of
the vapor mixture by removing the higher alcohols from the system was found to yield an increase in the asymptotic
size of the droplets of about 15%, while the number density was reduced accordingly.