A Transition from Heterogeneous to Homogeneous Nucleation in the Turbulent Mixing CNC

Abstract

A new method for changing the supersaturation in the Turbulent Mixing CNC has been developed and used to examine the transition from heterogeneous nucleation of test particles to homogenous nucleation of working uid: dibutylphthlate (DBP). Supersaturation was controlled by changing the DBP vapor pressure in the nozzle ow by saturating only a predetermined part of the ow, while the total ow and temperature remain constant. This approach allows for the changing of the initial DBP vapor pressure, while keeping the ow structure and temperature eld unchanged. The DBP concentration in the outlet of the vapor generator was measured experimentally for different ratios of saturated and bypass ows and found to be close to estimated values. Experimental results for transitions from heterogeneous nucleation to homogeneous nucleation are presented for NaCl and WO x particles at various DBP vapor pressures. With an increasing of the DBP vapor pressure, the concentration of enlarged particles increases until it reaches a plateau. At higher initial values of DBP pressure, homogeneous nucleation prevails, and the number concentration of particles follows a curve typical for homogeneous nucleation recorded in the absence of nuclei. Nuclei with different mobility diameters were activated at different values of vapor pressure. There are signi cant differences in the slopes of particle activation curves for NaCl and WO x particles. The reasons for such differences are a subject for continuing research.

Vapor phase nucleation on neutral and charged nanoparticles: Condensation of supersaturated trifluoroethanol on Mg nanoparticles

“…This is also a direct manifestation of the slow diffusion of the large Mg nanoparticles that act as nuclei for the condensation of TFE vapor at low supersaturations. These results are in good agreement with the results of Mavliev et al, 15 Chen et al, 17,18 and Rosenorn et al 26 where the critical supersaturation of the condensing vapor required for activating the nucleating particles was found to decrease with increasing the particle diameter. Similarly, the work of Seto et al 27 on the condensation of dibutyl phthalate vapor induced by seed ions generated by electrospray ionization showed a significant reduction in the critical supersaturation with increasing the size of the seed ions.…”

“…Although the importance of these parameters has been well-recognized, quantitative information on the heterogeneous nucleation of supersaturated vapors on charged nanoparticles under well defined supersaturation and temperatures are rarely available. [14][15][16][17][18] Most of the recent studies have focused on the application of the condensation nuclei counter ͑CNC͒ and the flow cloud chamber ͑FCC͒ to investigate the condensation of supersaturated vapors on neutral and charged particles. [15][16][17][18] Despite the practical advantages of the CNC and FCC devices, accurate determination of the degree of the vapor supersaturation at well-defined temperatures is not possible.…”

“…[14][15][16][17][18] Most of the recent studies have focused on the application of the condensation nuclei counter ͑CNC͒ and the flow cloud chamber ͑FCC͒ to investigate the condensation of supersaturated vapors on neutral and charged particles. [15][16][17][18] Despite the practical advantages of the CNC and FCC devices, accurate determination of the degree of the vapor supersaturation at well-defined temperatures is not possible. On the other hand, the thermal diffusion cloud chamber ͑DCC͒ allows accurate measurements of both temperature and supersaturation over a wide range of carrier gas pressures.…”

Comparison of Experimental and Theoretical Heterogeneous Nucleation on Ultrafine Carbon Particles

“…The basic components of the experimental system are a combustion chamber for carbon particle generation, a TMCNC for heterogeneous nucleation, and a differential mobility analyzer (DMA) and a conventional condensation nuclei counter (CNC) together for particle size distribution measurements. The TM-CNC employed is the same one used in the study of Hopke et al 18 and Mavliev et al 19 More detailed information is given in the following subsections.…”

Condensation Activation and Nucleation on Heterogeneous Aerosol Nanoparticles

“…Recently, Mavliev et al 3,4 developed a new method to improve a condensation nuclei counter (CNC) to measure the condensation of liquid compounds onto fine particles of various kinds. This research was oriented toward examining the relationship between the molecular properties of the working fluid and the particles.…”