The Effect of Turbulence on Rates of Particle Formation by Homogeneous Nucleation

The elIect of turbulent mixing on the homogeneous nucleation rate was studied for a jet stream at 400 K injected into dry air at 298 K and I atm. To simplifY the calculations, it was assumed that the Lewis number was everywhere unity. Probability density functions for the temperature fluctuations in an axisymmetric shear layer were used to calculate the local particle formation rate, averaged over the fluctuations, and the resulting particle concentration profile. Taking turbulent fluc- tuations into account significantly reduces local maxima in the average nucleation rate and broadens the region of particle formation in the shear layer compared with calculations based on the mean saturation ratio profile. However, the overall rate of particle formation in the mixing layer, taking fluctuations into account, is of the same order of magnitude as the rates based on the mean concentration and temperature for the conditions of the calculation.