No abstract

A method for varying the supersaturation in a turbulent mixing CNC has been used to examine heterogeneous nucleation of different compounds (working fluid) on various nuclei's compositions. Supersaturation was controlled by changing the vapor pressure of working fluid in nozzle flow, which was accomplished by saturating only a predetermined fraction of the flow while the keeping the total flow and temperature constant. This approach allows the partial pressure of the working fluid to be varied while maintaining a constant flow structure and temperature field. Experimental results characterizing the initial stages of heterogeneous nucleation are presented for NaCl, KCl, AgCl, and Ag particles. Heterogeneous nucleation was examined at various pressures of dibutylphthalate, octadecane, octadecanol, and octadecanoic acid. For octadecanoic acid as the working fluid, the size distribution of the grown particles is unimodal with the size increasing with increasing pressure of the working fluid. For the other working fluids, the initial size distribution splits into a bimodal distribution with one mode approximately the same as the initial distribution and a larger sized mode that grows with increasing pressure of the condensing vapor. For NaCl and octadecane and octadecanol, the initial unimodal size distribution splits into a trimodal size distribution.

Using a modified turbulent mixing CNC, the heterogeneous nucleation of different compounds (working fluids) on nanometer sized carbon particles was examined. The working fluids were dibutyl phthalate, octadecane, octadecanol, and octadecanoic acid. Based on the particle size distributions measured with a scanning mobility particle sizer system, nucleation and consequent growth were examined with respect to different temperature and vapor pressure for each working fluid. Nucleation rates for all conditions were calculated from the fitted size distribution data by subtracting the residual nonactivated particle concentration for each condition. Experimental nucleation rates were compared to the calculated ones based on Fletcher's heterogeneous nucleation theory. This theory matches well with the experiments with octadecanol and octadecanoic acid, and at high supersaturation ratios for dibutyl phthalate. However, the theory shows discrepancies with the observed phenomena at low supersaturation for dibutyl phthalate, and especially for octadecane. Several possible hypotheses for the discrepancies and observed particle growth are discussed.