Basic Studies of Nucleation
Nucleation Initial experiments were conducted using the original turbulent
mixing CNC system (Mavliev and Wang, 2000; Mavliev et al., 2001). Supersaturation
was controlled by means of changing the DBP vapor pressure in nozzle flow by
saturating only a predetermined part of the flow while the total flow and
temperature remain constant. This approach allows changing the initial DBP
vapor pressure while keeping the flow structure and temperature field
unchanged. The DBP concentration in the outlet of the vapor generator was
measured experimentally for different ratios of saturated and bypass flows
and found to be close to estimated values. Experimental results for
transitions from heterogeneous nucleation to homogeneous nucleation are
presented for NaCl and WOx
particles at various DBP vapor pressures. With 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 significant differences in the slopes of particle
activation curves for NaCl and WOx
particles. The reasons for such differences are a subject for the continuing
research of this project and studies continue at this time. These results
have been presented and published by Mavliev et al.
(2001). This work largely completes the work on the nucleation of dibutylphthalate on various substrates. A new and
improved turbulent mixing CNC has been designed, constructed, and studied. We
made side-by-side tests of two identical units to ensure that the parallel
measurements made at IIT and Clarkson would be comparable. We made a series of
measurements of nucleation of additional vapor compounds on a series of
different composition nuclei at both schools. Nucleation for all of the
vapors have been measured for NaCl, silver, and
carbon particle particles. These results have prompted some limited
additional studies on related solid substrates such as KCl
and AgCl. We have experimentally measured the
contact angle for most of the combinations of the vapor compounds on the
various substrates. These data were then used in interpreting the results of
the nucleation measurements.
KC1 and AgC1
At IIT, heterogeneous
nucleation of working fluids' vapor on NaCl, Ag, KCl, and AgCl was examined.
Three different patterns of nucleation and growth were observed. In the case
of octadecanoic acid, all of the nuclei were
activated and could then grow as they accumulated vapor. The activation of
these nuclei did not appear to be dependent on the composition of the
nucleus. For octadecane, octadecanol,
and DBP, a bimodal pattern was observed for all of the nuclei except the case
of octadecanol on NaCl.
In this case, some nuclei activate and grow while the remaining particles
keep their initial size distribution. In the case of octadecanol
with NaCl, a second mode only slightly larger than
the initial size distribution forms in the presence of even small amounts of
vapor. When the partial pressure of octadecanol
reaches a sufficiently high value, some of the nuclei activate into a grown
mode. It appears nucleation occurs on both of the smaller modes in equal
proportion as the relative intensity of the two smaller modes remains
unchanged as the vapor concentration is increased. These results were
submitted to the Journal of Chemical Physics. In order to more fully
interpret these results, a theoretical model was developed. They outline of
this model was developed by Vladimir Smorodin and
this work is being prepared for publication. At Clarkson, experimental
heterogeneous nucleation of the working fluids' vapor on carbon particles was
measured. Experimental nucleation rates from these results were calculated
and, then, compared to the estimated nucleation rates based on Fletcher's
heterogeneous nucleation theory. This theory matches well with the
experiments with octadecanol and octadecanoic acid, and at high supersaturation
ratio for DBP. However, the theory shows discrepancy with the observed
phenomena at low supersaturation for dibutyl phthalate, and, especially, for octadecane. Hydrophilicity of
functional groups of working fluids was considered as an important factor.
Several other possible hypotheses related to physico-chemical
properties of carbon particles and working fluids' vapor for the
discrepancies in heterogeneous nucleation and observed particle growth are
discussed in Lee et al., 2003).
We are also examining the influence of pressure on homogeneous nucleation of
vapors. Prior work has suggested that there are effects of both the
composition and pressure of the support gas on the rate of homogeneous vapor
nucleation. However, there is no theoretical basis for the observed effects.
Thus, additional experimental work is needed to better understand the nature
of this effect.
The List of Recent
Publications is as follows:-
of a Turbulent Mixing CNC to Study the Influence of Composition and
Vapor Properties on Heterogeneous Nucleation, P.K. Hopke, D.W.Lee, Rashid Mavliev,
and Hwa-Chi Wang, In: Nucleation and Atmospheric Aerosols,
B. Hale, and M. Kulmala, eds., American
Institute of Physics, AIP Conference Proceedings 534, pp.139-142 (2000).
of the Homogeneous Nucleation Rate Measurements in a Static Diffusion
Chamber with Use of a CCD Camera, V. Zdímal,
J. Smolík, P.K. Hopke, and J. Matas, In: Nucleation and Atmospheric Aerosols,
B. Hale, and M. Kulmala, eds., American
Institute of Physics, AIP Conference Proceedings 534, pp. 311-314
- n-Pentanol-Helium Homogeneous Nucleation Rates, M.P. Anisimov, P.K. Hopke, S.D. Shandakov
and I.I. Shvets, J. Chem. Phys.
Transition from Heterogeneous to Homogeneous Nucleation in the Turbulent
Mixing CNC, R. Mavliev, P.K. Hopke, H.-C. Wang, and D.-W. Lee, Aerosol Sci. Technol. 35:
Channel Vapor Nucleation in the Vicinity of the Triple Point, L. Anisimova, P.K. Hopke, and J. Terry, J. Chem.
Phys. 114:9852-9855 (2001).
N-Octanol - Sulfur Hexafluoride
Nucleation, M P. Anisimov, P. K. Hopke, I.N. Shaimordanov, S. D. Shandakov,
and L.-E. Magnusson, J. Chem. Phys. 115: 810-816 (2001).
Rate Surface Topologies for Binary Systems, M.P. Anisimov
and P.K. Hopke, J. Phys. Chem. B; 105:11817-11822 (2001).
Recommendations For Vapor Nucleation Rate Experiments, M.P. Anisimov,
P.K. Hopke, and Z.N. Esina, Aerosol
Sci. Technol. 37:183-186
of Experimental and Theoretical Heterogeneous Nucleation on Ultrafine
Carbon Particles, D.-W. Lee, P.K. Hopke, D.H. Rasmussen, H.-C. Wang, R. Mavliev, J. Phys. Chem. B 107:
of Nucleation and Growth Events of Ultrafine Particles Measured in Rochester, NY,
C.-H. Jeong, P.K. Hopke, D. Chalupa, M. Utell, Environ.
Sci. Technol. 38: 1933 - 1940 (2004).
Studies of Heterogeneous Nucleation in the Turbulent Mixing Condensation
Nuclei Counter, R. Mavliev, P.K. Hopke, H-C
Wang, D.-W. Lee, J. Phys. Chem. B 108:
Activation and Nucleation on Heterogeneous Aerosol Nanoparticles,
V.Y. Smorodin and P.K. Hopke, J. Phys. Chem.
B 108: 9147-9157 (2004).
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