Nucleation of Ethylene Glycol Vapor and Growth of Sub-10-nm Particles in Nanoparticle Size Magnifier

We investigated the rates of heterogeneous and homogeneous nucleation of ethylene glycol vapor onto sub-10-nm particles in a newly developed condensation device called nanoparticle size magnifier (NanoPSM). The saturation ratio in the NanoPSM is precisely controlled by vapor-feeding system and mixing section, which are designed based on an earlier particle size magnifier (PSM) developed by Okuyama et al. (1984). Size-classified NaCl nanoparticles smaller than 10 nm in mobility diameter are used as heterogeneous nuclei for the condensation of ethylene glycol vapor. The activation efficiency and growth rate of the activated nuclei are determined by a pulse height analysis using an optical particle counter (OPC). A computer fluid dynamics (CFD) simulation is employed to calculate the profiles of the gas velocity, temperature, vapor concentration, and resulting supersaturation in the NanoPSM. Annular high-supersaturation region is generated around the mixing boundary between cold aerosol and hot vapor. The experimental activation efficiency is 50% for 4.5-nm and 0.8% for 2 nm NaCl particles, through the subsequent growth of droplets to 2 μm in diameter. The experimental data are in fairly good agreement with the predicted activation efficiencies based on the classical Kelvin-Thomson theory when the local profiles of supersaturation are taken into account.