Initial Stage Of Condensation Research Articles

Statistical Model for the Energy Exchange during Copper Vapor Condensation in an Inert Gas Atmosphere

Statistical analysis of the results of molecular dynamics (MD) calculation of gas-phase “self-assembling” of nanoclusters during metal vapor condensation revealed the laws of energy transfer between metallic clusters and inert gas atoms. A model is proposed to determine the parameters of heat exchange between clusters and the environment at the initial stage of condensation. This model is based on averaged MD data on the interaction between small clusters and argon atoms. The parameters that can be used to transfer information from MD to a macroscopic condensation model are numerically determined. The results obtained can be used to describe nucleation to predict a nanoparticle size distribution in the production of metallic powders.

Optical radiation accompanying metal nanoparticles coagulation in superfluid helium

The spectra of visible radiation from small clusters of tungsten and nickel self-heated under their mutual fusion in the bulk of superfluid helium (He II) have been investigated. The emissions were shown to be close to the black-body emission. At the initial stages of condensation, the nanoparticles are heated to temperatures significantly higher than the metal melting temperature (Tmelt), even for refractory tungsten. That would be so if the process of coagulation of clusters with similar sizes (not the deposition of atoms and small particles into a heavier center) to be the prevailing process. The condensation takes place only for particles trapped in the core of 1D quantized vortices existed in He II and it explains why the nanowires are the main product of metals condensation there. At further stages of condensation the color temperature of the thermal emission is almost constant and is close to the metal Tmelt. Along with exponential decay in the glow intensity with time, it fits scenario of nanowires growth by fusion of whiskers freely moving along the cores of vortices. The method just developed has good prospects for studying the radiative cooling of highly heated metallic and semiconductor nanoparticles.

Bicanonical ensemble Monte Carlo simulation of water condensation in the field of crystal lattice defects

The free energy, formation work and entropy dependences for water condensate formed from the vapor over the defect-free and containing surface defects basal face of β-AgI crystal at initial stage of condensation at temperatures of 260 K and 400 K are calculated using the bicanonical statistical ensemble method, with Ewald summation for long-range electrostatic and polarization interactions with the substrate. The effect of surface defects in form of rectangular “towers” as a part of regular structure on the stability of condensed phase embryos is investigated. In contrast to small-scale structures, relatively larger coarse-grained nanostructure of crystal surface demonstrates an unconditional advantage in the ability to stimulate condensation compared to defect-free surface. The formation of condensed phase embryos on the surface with multiple defects begins at vapor pressures 5–6 orders of magnitude lower than that on corresponding defect-free surface, and this effect is resistant to temperature variations. The condensate on the surface of the crystal is thermodynamically stable, both on defect-free and nanostructured surfaces, with the exception of short initial stage of the monomolecular film on the defect-free surface.

Modelling the Initial Stages of Condensation of As-S Atomic Clusters

Modelling the Initial Stages of Condensation of As-S Atomic Clusters

Numerical modeling of the initial fluctuation condensation stage with charge drops

This paper deals with a mathematical model of the phase transition of the first kind at the initial stage of forming drops in a liquid or in melted state in a volume of steam with a fixed charge on drops. The model of the process is represented by superposition of random diffusion and jump stochastic processes. The algorithms for solving stochastic differential equations (SDEs) of the model of processes, which form the cluster size, allow one to calculate a distribution function of drops according to their size. The kinetic approach makes possible evaluate the role of the Rayleigh capillary instability at the initial condensation stage and to employ the analysis of electrodispersion mechanisms in the production of metal and semiconductor powders.

Evolution of transient cluster/droplet size distribution in a heterogeneous nucleation process

The transient nucleation size distribution model was introduced into a water vapor condensation system to investigate the kinetics of the initial condensation stage. It was proven that the growth/decay of clusters was significantly affected by cluster size and contact angles of the condensation surface. As the cluster size increased, the cluster surface area exposed to vapor was also increased, and the attachment/detachment frequencies increased accordingly. As the contact angle decreased to a certain value, the attachment frequency became larger than the detachment frequency, which is beneficial for the growth of clusters. The evolution of cluster/droplet size distribution was also investigated. The results indicated that the transient cluster size distribution of the heterogeneous process translates from a monotonic decreasing to a unimodal distribution with time. Peak value of cluster/droplet population can be observed for a sufficiently long time, and the size distribution curve is found to be close to a lognormal distribution, which is distinctly different from the homogeneous equilibrium distribution. The peak value in the size distribution curve shifts to larger cluster sizes with time, and the absolute value decreases accordingly. It is very similar to the reported experimental results of micron scale droplets, revealing that the subsequent experimental phenomenon at macroscopic scale was the direct result of the further development of the initial cluster/droplet size distribution. The present study investigated the effect of contact angle on the growth/decay of clusters and analyzed the mechanism of the evolution of the cluster/droplet size distribution from the viewpoint of kinetics.

A multi-fluid model for non-equilibrium condensation in gaseous carrier flows

The inter-phase slip plays an important role in simulating the condensing flow, which is, however, generally neglected in most numerical studies. To address this, a generalized multi-fluid model is newly developed to predict the two-phase condensing flow in the presence of a carrier gas, where both the inter-phase velocity slip and the temperature difference are taken into account. The multi-fluid model is performed to simulate the condensing flow in two types of supersonic nozzles. Also, the traditional no-slip model is employed for comparing with the multi-fluid model. The simulated results obtained from the multi-fluid model are found to agree better with the experimental data. The effects of the inter-phase slip are revealed qualitatively by comparing the results obtained from these two models. The results show that the effects of inter-phase slip should not be neglected in the whole condensation process. At the initial stage of condensation, both the inter-phase velocity slip and temperature difference are noteworthy. When the condensation finishes and the gas–liquid equilibrium achieves, the inter-phase velocity slip and temperature difference become slight and can be neglected.

Multi-fluid Model for Non-equilibrium Condensing Flow

Spontaneous condensation flows are highly non-equilibrium processes, which has strong coupling with the gas flow field in the two-phase condensing flow. The development of accurate multi-phase numerical model is necessary to reveal the mechanism of the non-equilibrium condensation flow. The gas-liquid inter-phase slip not only has great influence on the gas flow and the motion trajectory of condensing droplet, but also would affect the condensation process. A multi-fluid condensing model is presented for the multi-component condensing system, of which the gas-liquid inter-phase velocity slip and the temperature difference is taken into account. The model is used for the numerical analysis of the wet steam condensing flow in supersonic nozzle. The simulation results showed that, the inter-phase velocity slip has significant effects in the two-phase wet steam flow, and the proposed multi-fluid model which takes the inter-phase slip into account can improve the simulation accuracy. In the wet steam flow, the inter-phase slip and temperature difference are very significant at the initial stages of condensation, and then the non-equilibrium properties almost disappear until the near equilibrium state is reached.

Dynamics of electron–hole liquid condensation in CVD diamond studied by femtosecond pump and probe spectroscopy

We report on the femtosecond pump and probe study of the condensation dynamics of electron–hole liquid in CVD IIa type diamond. The parameters of electron–hole liquid created after carrier excitation by one- and two-photon absorption were determined on the basis of the analysis of spectral shape of time-integrated photoluminescence. The dynamics of condensation of carriers into electron–hole liquid was probed by measuring the time evolution of changes in infrared light absorption. These changes were interpreted in terms of the density dependent carrier scattering time according to the Drude model of free-carrier absorption. Measured condensation times range from 50 to 500ps depending on the initial carrier density (3×1016cm−3–5×1018cm−3) and the sample temperature (13–130K). The measured dynamics was reproduced very well by a rate equation model of electron–hole droplet formation for low photoexcited carrier densities. A ~10ps delay in initial stage of condensation observed for high carier densities was interpreted in terms of density dependent carrier cooling rate.

Comparison of Decontamination Efficacy between the Rapid Hygrothermal Pasteurization and Sodium Hypochlorite Treatments

We developed a novel rapid hygrothermal pasteurization (RHP) method using saturated water vapor with a dew point of 100℃. The aim of this paper is to compare the effect of RHP treatment versus conventional sodium hypochlorite (NaClO) treatments on inactivation of natural mesophilic bacteria and quality attributes on fruits and vegetables. The RHP treatment was performed within a second by free-falling samples (cabbage, cucumber, carrot, bell pepper, pineapple and melon) through cylindrical processing chamber filled with steam. NaClO treatment was performed by washing samples with NaClO solution (100 mg/mL of free chlorine (pH 7), for 1 min). The RHP treatment showed a significantly higher inactivation effect than NaClO treatment on all tested samples. The RHP treatment had a slightly larger influence on color and vitamin C content than NaClO treatment in cabbage. Furthermore, the effects of treatment time and operated temperature were also determined using microbial model system. Elongation of treatment time did not significantly increase the microbial inactivation effect. Lowering of operated temperature by mixing air into steam tended to decrease the inactivation effect. From these results, RHP treatment could be used as an alternative method for decontaminating microorganisms on fruits and vegetables, except on leafy vegetable. In addition, it is suggested that microbial inactivation by RHP treatment was achieved through the initial condensation stage of water vapor on sample surface. By contrast, interfusion of air disturbed the effective condensation of water vapor.

Jet Plasma-Chemical Reactor for the Conversion of Methane: the Use of Clustering

The research results of processes proceeding in supersonic jets of light hydrocarbons, activated by an electron beam are presented. It is shown, that condensation suppressed at activation by electrons in the initial stage of condensation. The developed condensation conditions mode leads to increasing of a part of heavy corpuscles in activated stream and not only owing to stimulation of condensation but because of formation of heavy hydrocarbonic molecules.

Mono-component fuel droplet evaporation in the presence of background fuel vapor

A simplified set of equations is examined for the problem of droplet evaporation. The equations employ the Clausius–Clapeyron (CC) boundary condition for the surface fuel-vapor, which is responsible for mathematical behaviors that include an initial condensation stage of droplet swelling followed by an evaporation stage. Numerical methods of analysis are used in conjunction with an asymptotic analysis of each of the three stages: (I) condensation; (II) transition; and (III) evaporation. Droplet evaporation in partial condensation environments is discussed.

Chondrocyte Aggregation in Suspension Culture Is GFOGER-GPP- and β1 Integrin-dependent

Isolated chondrocytes form aggregates in suspension culture that maintain chondrocyte phenotype in a physiological pericellular environment. The molecular mechanisms involved in chondrocyte aggregation have not been previously identified. Using this novel suspension culture system, we performed mRNA and protein expression analysis along with immunohistochemistry for potential cell adhesion molecules and extracellular matrix integrin ligands. Inhibition of aggregation assays were performed using specific blocking agents. We found that: (i) direct cell-cell interactions were not involved in chondrocyte aggregation, (ii) chondrocytes in aggregates were surrounded by a matrix rich in collagen II and cartilage oligomeric protein (COMP), (iii) aggregation depends on a beta1-integrin, which binds a triple helical GFOGER sequence found in collagens, (iv) integrin alpha10-subunit is the most highly expressed alpha-subunit among those tested, including alpha5, in aggregating chondrocytes. Taken together, this body of evidence suggests that the main molecular interaction involved in aggregation of phenotypically stable chondrocytes is the alpha10beta1-collagen II interaction.

Effect of the Condensation on the Composition of Natural Gas Pulsed Supersonic Jets Activated bu an Electron Beam

The results of research of processes proceeding in supersonic jets of light hydrocarbons, activated by an electron beam are presented. It is shown, that activation by electrons at the initial stage of condensation suppressed condensation. The conditions of the developed condensation mode leads to increasing of a part of heavy corpuscles in activated stream and not only owing to stimulation of condensation but because of formation of heavy hydrocarbonic molecules.

Formation of cloud microstructure during hygroscopic seeding

The evolution of cloud microstructure initiated by hygroscopic seeding is studied on the basis of numerical simulation of cloud formation in the initial stage of condensation. The influence of both physicochemical properties of atmospheric aerosol and atmospheric conditions controlling the cloud type on the microstructure of a developing cloud (without hygroscopic seeding) is analyzed. It is shown that cloud seeding with additional particles whose sizes exceed the characteristic size of atmospheric condensation nuclei leads to a decrease in the concentration of cloud droplets and an increase in their sizes. This result of cloud seeding represents a positive effect for stimulation of precipitation from convective clouds. It is shown that this positive effect is achieved if there are some relationships between the parameters characterizing the hygroscopic particles and the atmospheric conditions. In particular, the maximum effect of action can be achieved at some optimal concentration of seeded particles. The decrease in the concentration of cloud droplets because of hygroscopic seeding is compared to the results of numerical simulations performed by other authors with allowance for coagulation processes in clouds. It is shown that this decrease can serve as an estimate for the effectiveness of hygroscopic seeding as a means for artificial intensification of precipitation from convective clouds.

Initial Stage of Condensation of C60 Films on Semiconducting Substrates of Different Chemical Nature

Conditions of growing C60 films deposited from the gas‐dynamic vapor flow on different substrates [layered GaSe substrates with inactive surface, AIIBVI (CdS, CdSe) crystals, silicon substrates of (1 1 1) orientations, porous Si substrate] are studied. The condensate structure and growth mechanisms for different substrate are compared. It is shown that the high‐quality epitaxial films of the fullerenes can be prepared by using GaSe layered crystals as substrates.

Capillary Condensation from Vapors of n-Hexane/Perfluoro-n-hexane Mixtures

We have used a modified surface force apparatus to study capillary condensation of near-saturated vapors of n-hexane/perfluoro-n-hexane mixtures in a model pore formed by the gap between two mica surfaces. The measured compositions and mean meniscus radii of curvature of the capillary condensates are in broad agreement with the predictions of the binary Kelvin equations. Our results also show that n-hexane is preferentially adsorbed at the mica/liquid interface of the condensed mixtures, with the extent of adsorption depending on the position in the liquid−liquid phase diagram of the mixture. In addition, liquid−liquid-phase separation was observed in condensates formed from vapors of bulk perfluoro-n-hexane-rich mixtures at, or very close to phase-coexistence. This results in the formation of novel two-phase or “double” condensates, consisting of an inner condensate of a n-hexane-rich phase within an outer condensate of perfluoro-n-hexane-rich phase. Capillary condensation from vapors coexisting with phase-separated bulk mixtures gives rise to condensates of the n-hexane-rich phase. Finally, we have observed that the composition of a mixed condensate can show a significant time-dependence in the initial stages of condensation.

Ion-cluster reactions initiated by an electron beam in mixtures of argon with methane and monosilane

The excitation of argon radiation in condensing supersonic jets of argon mixtures with methane, monosilane, and carbon dioxide upon electron-beam activation of the flow is investigated experimentally. It is found that, at certain condensation stages, the radiation intensity at some atomic argon lines increases anomalously. It is shown that the effect appears at the initial stages of condensation and is damped upon the formation of large mixed clusters.

Anomalous electron-beam-induced excitation of argon in pulsed supersonic streams of Ar+CH4, Ar+SiH4, and Ar+ CH4+SiH4 mixtures

The energy exchange in supersonic streams of argon mixtures with methane and monosilane activated by an electron beam was studied. In the initial condensation stage, the stream features a selective excitation of the atomic energy levels of argon. The threshold values of parameters were determined, for which the anomalous optical emission from the electron-beam-excited mixtures is observed.

The nucleation and growth of PdAu alloy particles on NaCl(100)

The early stages of thin film formation of PdAu alloys by simultaneous deposition of the components onto NaCl(100) cleavage surfaces had been investigated both experimentally and by a theoretical model in terms of rate equations, combined with an adatom diffusion model. Whereas the condensation coefficient of gold was initially very low, that of palladium was near unity even at an early stage. As a straightforward analytical solution of the rate equation approach is not feasible for such a complex case, we simulated the initial stages of condensation numerically by calculating the composition of the particles from atomic capture rates, taking into account the development in time of the adatom and particle number densities, and of the growth rates. Comparison of the results was also made with Monte Carlo calculations, which will presented in more detail elsewhere. A close fit of experimentally measured compositions and particle growth rates was obtained by an appropriately chosen difference of the adatom energies for adsorption and for surface diffusion of the components, which is ( E a- E d) Pd−( E a− E d) Au = 0.12±0.02 eV. However, the experimentally measured particle number densities varied much less with the deposition fluxes than was theoretically expected. We suspect that this is caused by dimer and cluster mobilities and/or defect decoration, which are not included in our simplified model. It is argued that this may affect the absolute values of the energy parameters, but is only of minor importance for the difference given above.