Experimental Studies of Heterogeneous Nucleation in the Turbulent Mixing Condensation Nuclei Counter

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.