Aspects of homogeneous nucleation

Citation

Wyslouzil, Barbara Ellen (1992) Aspects of homogeneous nucleation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5M1F-WC03. https://resolver.caltech.edu/CaltechETD:etd-08172007-132240

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Experimental investigations of vapor phase binary nucleation were carried out for both the methanesulfonic acid-water and the sulfuric acid-water systems. A rapid mixing device produced acid-water aerosols under isothermal conditions and at relative acidities (Ra), 0.04 < Ra < 0.65, relative humidities (Rh), 0.01 < Rh < 0.65, and temperatures, T = 20, 25 and 30°C. The number concentration of the aerosol at the exit of the nucleation and growth tube is extremely sensitive to the binary nucleation rate. Thus at low particle concentrations, when condensation did not significantly change the saturation levels the binary nucleation rates were estimated from the number concentration data as a function of Ra, Rh and temperature. Particle size distributions were also measured and found to vary with the amount of acid and water present. An integral model considering both nucleation and growth simulated the experimental system and predicted the total number of particles, the total mass in the aerosol phase, and the mass average diameter at the exit of the nucleation and growth tube. The simulations reproduced the experimental results quite well for the methansulfonic acid-water binary, if the nucleation rate was adjusted by a temperature dependent correction factor which ranged from [...] to [...]. Further analysis showed that the ratio of experimental to theoretical nucleation rates for both acid-water systems was a strong function of the predicted number of acid molecules in the critical nucleus. Classical homogeneous nucleation theory was extended to nonisothermal conditions by simultaneously solving cluster mass and energy balances. In vapor phase nucleation, the steady state nucleation rate was lower than the corresponding isothermal rate and this discrepancy increased as the pressure of the background gas decreased. After the initial temperature transients decayed, subcritical clusters were found to have temperatures elevated with respect to that of the background gas.

Thesis Files