Homogeneous Nucleation In Supersaturated Vapor Research Articles

Homogeneous nucleation rate measurements in supersaturated water vapor

The rate of homogeneous nucleation in supersaturated vapors of water was studied experimentally using a thermal diffusion cloud chamber. Helium was used as a carrier gas. Our study covers a range of nucleation rates from 3x10(-1) to 3x10(2) cm(-3) s(-1) at four isotherms: 290, 300, 310, and 320 K. The molecular content of critical clusters was estimated from the slopes of experimental data. The measured isothermal dependencies of nucleation rate of water on saturation ratio were compared with the prediction of the classical theory of homogeneous nucleation, the empirical prediction of Wolk et al. [J. Chem. Phys. 117, 10 (2002)], the scaled model of Hale [Phys. Rev. A 33, 4156 (1986)], and the former nucleation onset data.

Accounting for fluctuations in cluster parameters upon the description of nucleation in supersaturated vapor

A theory is proposed for stationary homogeneous nucleation in supersaturated vapor in which a modified expression for the rate of cluster evaporation was used to calculate the equilibrium distribution over the nucleus sizes and the rates of their formation. This rate was determined by the extrapolation to the region of small sizes of the corresponding expression for the macroscopic droplet derived according to thermodynamic notions that take fluctuations into account. Modified dependences of the size of critical nucleus and the rate of nucleation on the supersaturation and the temperature are determined and compared with the data of the classical theory of nucleation and experimental results.

Homogeneous nucleation in supersaturated vapors of methane, ethane, and carbon dioxide predicted by brute force molecular dynamics

Molecular dynamics (MD) simulation is applied to the condensation process of supersaturated vapors of methane, ethane, and carbon dioxide. Simulations of systems with up to a 10(6) particles were conducted with a massively parallel MD program. This leads to reliable statistics and makes nucleation rates down to the order of 10(30) m(-3) s(-1) accessible to the direct simulation approach. Simulation results are compared to the classical nucleation theory (CNT) as well as the modification of Laaksonen, Ford, and Kulmala (LFK) which introduces a size dependence of the specific surface energy. CNT describes the nucleation of ethane and carbon dioxide excellently over the entire studied temperature range, whereas LFK provides a better approach to methane at low temperatures.

Homogeneous nucleation rate measurements of 1-propanol in helium: The effect of carrier gas pressure

Kinetics of homogeneous nucleation in supersaturated vapor of 1-propanol was studied using an upward thermal diffusion cloud chamber. Helium was used as a noncondensable carrier gas and the influence of its pressure on observed nucleation rates was investigated. The isothermal nucleation rates were determined by a photographic method that is independent on any nucleation theory. In this method, the trajectories of growing droplets are recorded using a charge coupled device camera and the distribution of local nucleation rates is determined by image analysis. The nucleation rate measurements of 1-propanol were carried out at four isotherms 260, 270, 280, and 290 K. In addition, the pressure dependence was investigated on the isotherms 290 K (50, 120, and 180 kPa) and 280 K (50 and 120 kPa). The isotherm 270 K was measured at 25 kPa and the isotherm 260 K at 20 kPa. The experiments confirm the earlier observations from several thermal diffusion chamber investigations that the homogeneous nucleation rate of 1-propanol tends to increase with decreasing total pressure in the chamber. In order to reduce the possibility that the observed phenomenon is an experimental artifact, connected with the generally used one-dimensional description of transfer processes in the chamber, a recently developed two-dimensional model of coupled heat, mass, and momentum transfer inside the chamber was used and results of both models were compared. It can be concluded that the implementation of the two-dimensional model does not explain the observed effect. Furthermore the obtained results were compared both to the predictions of the classical theory and to the results of other investigators using different experimental devices. Plotting the experimental data on the so-called Hale plot shows that our data seem to be consistent both internally and also with the data of others. Using the nucleation theorem the critical cluster sizes were obtained from the slopes of the individual isotherms and compared with the Kelvin prediction. The influence of total pressure on the observed isothermal nucleation rate was studied in another experiment, where not only temperature but also supersaturation was kept constant as the total pressure was changed. It was shown that the dependence of the nucleation rate on pressure gets stronger as pressure decreases.

Homogeneous nucleation rate measurements in 1-pentanol vapor with helium as a buffer gas

The rate of homogeneous nucleation in supersaturated vapors of n-pentanol was studied experimentally using an upward static diffusion chamber. Helium was used as a buffer gas, holding the total pressure in the chamber at P t=25 kPa. A recently improved photographic technique was used to determine the nucleation rate as a function of supersaturation at temperature T=260 K. This dependence was compared with predictions made by the classical theory of homogeneous nucleation. Furthermore, the influence of gaseous ions on nucleation rate was studied, and a minimum voltage across the chamber, necessary to avoid nucleation on ions, was determined. The effect of the wall heating power on nucleation was found to be negligible in the range studied.

Homogeneous Nucleation in Supersaturated Vapors of n-Nonane

The upward thermal diffusion cloud chamber was used to measure the supersaturations of n-nonane vapors required to cause an observed rate of homogeneous nucleation of 1 droplet/cm3 s. New temperature-dependent correlations for the surface tension and the density of n-nonane have been applied in theoretical prediction of the corresponding supersaturation. The measurements are found to be in reasonable agreement with the predictions of the classical (Becker-Doering) theory whereas both the Dillmann-Meier and the Girshick-Chiu theories lead to a significant underestimation of supersaturation in the whole range of temperatures measured.

Homogeneous nucleation in supersaturated vapors of polar molecules: Acetonitrile, benzonitrile, nitromethane, and nitrobenzene

The critical supersaturations (Sc) required for the homogeneous nucleation of acetonitrile, benzonitrile, nitromethane, and nitrobenzene vapors have been measured over wide temperature ranges using a thermal diffusion cloud chamber. At Tr=0.44, the experimental results are higher than the predictions of the classical nucleation theory by 20% (CH3NO2), 50% (CH3CN), 57% (C6H5NO2), and 112% (C6H5CN). This trend correlates well with the dipole moments and to a lesser extent with the polarizabilities of these substances. Corresponding states of simple fluids and scaled nucleation law show that CH3CN and CH3NO2 have similar nucleation behavior which is different from that of C6H5CN and C6H5NO2. Correlations with other less polar substances are examined. The scaled law, with Ω (the excess surface entropy per molecule) determined from the temperature dependence of the bulk surface tension, gives a better description of the experimental results than the classical theory with the exception of nitromethane. The results suggest that the classical theory does not take proper account of the dipole–dipole interaction in calculating the free energy of the embryonic droplets.

Homogeneous Nucleation of Supersaturated Vapors. A Comparison of Experimental Results with Theory

Some theories of homogeneous nucleation based on liquid droplet model were tested by comparing with experimental supersaturations of naphthalene, phthalic anhydride, stearic acid, bis(2-ethylhexyl) phthalate, and bis(2-ethylhexyl) sebacate required to bring about the rate of homogeneous nucleation of about 5 drops/cm3 s-1. It was found that except for highly polar substance phthalic anhydride, the classical (Becker-Doring) theory of homogeneous nucleation, if suitably scaled, yielded fairly good predictions of the nucleation behaviour.

Homogeneous nucleation of supersaturated vapors

A theory of homogeneous nucleation from the vapor phase is presented. The classical Becker-Döring-Zel'dovich theory is contained as a limiting case. The theory is based on a semiphenomenological droplet model for the Gibbs free energy of formation of the cluster. Since this droplet model also allows the construction of a thermal equation of state for real gases below the critical point, all free parameters of the model can be determined from well-known macroscopic quantities. A new formulation of the surface free energy for small droplets is crucial. The theory gives a much better prediction of observed nucleation rates than the classical theory.

Homogeneous nucleation in supersaturated vapor containing foreign seed aerosol

The formation of aerosol particles by homogeneous nucleation in a supersaturated vapor containing seed aerosol has been studied experimentally and theoretically. In the laboratory, a room-temperature gas optionally containing zinc chloride particles is continuously mixed with a high-temperature gas saturated with dibutyl phthalate (DBP) vapor in a previously discussed device for the study of aerosol nucleation known as a particle size magnifier (PSM). A highly supersaturated vapor is rapidly formed in the mixing zone of the PSM, and gas-to-particle conversion ensues. The vapor may be converted to the aerosol phase by condensation onto the preexisting particles or by homogeneous nucleation to form new particles which then serve as condensation sites themselves. The split between these alternate pathways for gas-to-particle conversion may be deduced from measurements of the resulting aerosol concentrations for different initial supersaturations, seed aerosol concentrations, and seed aerosol sizes. The measured final aerosol concentrations are compared with those predicted by a dynamic model that combines expressions for classical nucleation theory and for steady-state particle growth, and agreement is found to within experimental uncertainties. Suppression of homogeneous nucleation by seed aerosol is not predicted to be strong unless seed aerosol number concentrations are larger than the number concentrations which would result from homogeneous nucleation alone.

Homogeneous nucleation in supersaturated vapors

Homogeneous nucleation in supersaturated vapors

Experimental results of homogeneous nucleation of supersaturated vapors

An r0 structure is determined for dimethylamine from earlier microwave data. With the constraint δr0(CH–CD)=δr0(NH–ND), CH bond lengths of 1.0958, 1.0981, 1.1060 A≡ are obtained, in excellent agreement with earlier predictions from ‘‘isolated’’ CH stretching frequencies. The new value of r0NH of 1.011 A≡ is significantly shorter than the earlier rs value of 1.022. The angular asymmetry of the methyl group is greater than previously supposed.

Dynamics of Cluster Growth During Homogeneous Nucleation of Supersaturated Vapors

An analysis of cluster growth and dynamics leading to phase transformation through homogeneous nucleation is developed to account for thermal nonaccommodation within the period of one vibration of the newly formed cluster. The approach, which is an extension of studies by Volmer and Feder et al., considers the following different mechanisms of interaction between clusters: (1) condensation of single molecules, (2) evaporation of molecules from clusters, and (3) coagulation between clusters. This approach is evaluated by comparing computer simulations of the population balance equations with classical nucleation theory and with experimental results reported in the literature. The interaction of the impinging molecule with the surface of the condensed phase is central to the development. The probability that such an impinging molecule will condense, be thermally equilibrated, and be incorporated into the cluster is included in the thermal nonaccommodation term in the basic population balance equations. Simu...

Energy of cluster formation for homogeneous nucleation in supersaturated vapors

Energy of cluster formation for homogeneous nucleation in supersaturated vapors