Molecular dynamics study on characteristics of reflection and condensation molecules at vapor–liquid equilibrium state

The kinetic boundary condition (KBC) represents the evaporation or condensation of molecules at the vapor–liquid interface for molecular gas dynamics (MGD). When constructing the KBC, it is necessary to classify molecular motions into evaporation, condensation, and reflection in molecular-scale simulation methods. Recently, a method that involves setting the vapor boundary and liquid boundary has been used for classifying molecules. The position of the vapor boundary is related to the position where the KBC is applied in MGD analyses, whereas that of the liquid boundary has not been uniquely determined. Therefore, in this study, we conducted molecular dynamics simulations to discuss the position of the liquid boundary for the construction of KBCs. We obtained some variables that characterize molecular motions such as the positions that the molecules reached and the time they stayed in the vicinity of the interface. Based on the characteristics of the molecules found from these variables, we investigated the valid position of the liquid boundary. We also conducted an investigation on the relationship between the condensation coefficient and the molecular incident velocity from the vapor phase to the liquid phase. The dependence of the condensation coefficient on the incident velocity of molecules was confirmed, and the value of the condensation coefficient becomes small in the low-incident-velocity range. Furthermore, we found that the condensation coefficient in the non-equilibrium state shows almost the same value as that in the equilibrium state, although the corresponding velocity distribution functions of the incident velocity significantly differ from each other.

Modeling snow isothermal metamorphism at the pore scale with the phase-field model Snow3D

<p><span>Representing snow isothermal metamorphism is key to model the evolution and properties of the snow cover. Recently, a new phase-field model allowing to describe 3D microstructure induced by curvature effects has been proposed (Bretin et al, Esiam: M2an, 2019). In the present work, this model is used to simulate isothermal metamorphism of snow at the pore scale, considering the only process of moving interfaces by sublimation-deposition driven by curvatures. This model runs on real 3D microtomographic images and gives a temporal series of 3D images simulating isothermal metamorphism. </span><span>To determine t</span><span>he condensation coefficient </span><span>to use</span><span> in </span><span>the</span><span> model, </span><span>which shows complex dependencies and is still poorly known,</span> <span>we </span><span>calibrated </span><span>it </span><span>by reproducing the time evolution of the specific surface area (SSA) measured during an isothermal experimental time-series at -2°C (Flin et al., Ann. Glaciol., 2004). This calibration has led to a value of the condensation coefficient </span><span>of </span><span>9.9 ± 0.</span><span>6</span><span> 10−4. </span><span>Using this calibration, we obtained a good agreement between simulations and an independent series of </span><span>isothermal metamorphism at -2°C (Hagenmuller et al., The </span><span>C</span><span>ryosphere, 2019). </span>Finally, 4 images representing different types of snow microstructure have been chosen as input to simulate isothermal metamorphism at -2°C during 75 days. <span>The obtained temporal series of 3D images were then used to calculate microstructural (porosity, SSA, covariance lengths) and physical transport properties (thermal conductivity, effective diffusion, permeability) evolution. </span><span>Comparing our numerical es</span><span>timations of physical properties </span><span>to </span><span>current parameterizations </span><span>gives overall good </span><span>agreement</span><span>. An interesting new result arising from the simulations is the conservation or enhancement of the structural anisotropy under isothermal conditions for </span><span>the samples that were initially strongly</span><span> anisotropic.</span></p><p> </p>

Selective deposition of silver and copper films by condensation coefficient modulation

Patterning evaporated silver and copper films without metal removal using extremely thin printed organofluorine films to modulate metal vapour condensation.

Molecular gas dynamics analysis on condensation coefficient of vapour during gas–vapour bubble collapse

This study investigates the influence of the condensation coefficient of vapour on the collapse of a bubble composed of condensable gas (vapour) and non-condensable gas (NC gas). We simulated vapour and NC gas flow inside a bubble based on the molecular gas dynamics analysis in order to replicate the phase change (viz., evaporation and condensation) precisely, by changing the initial number density ratio of the NC gas and vapour, the initial bubble radius and the value of the condensation coefficient. The results show that the motion of the bubble is unaffected by the value of the condensation coefficient when that value is larger than approximately 0.4. We also discuss NC gas drift at the bubble wall during the final stage of the bubble collapse and its influence on the condensation coefficient. We conclude that vapour molecules can behave as NC gas molecules when the bubble collapses, owing to the large concentration of NC gas molecules at the gas–liquid interface. That is, the condensation coefficient reaches almost zero when the bubble collapses violently.

The Effect of Menisci on Kinetic Analysis of Evaporation for Molten Alkali Metal Salts (CsNO3, CsCl, LiCl, and NaCl) in Small Cylindrical Containers

Using isothermal thermogravimetric data of alkali metal salts (CsNO3, CsCl, LiCl, and NaCl), we conducted kinetic analysis on atmospheric evaporation to investigate the effect of meniscus on determining the condensation coefficient. In the process of evaporation into an atmospheric gas, molten salt decomposed at the interface between molten salt and an atmospheric gas reacts with chemical compositions of the atmospheric gas to be an equilibrium state. In this atmospheric evaporation, the interface shape of molten salts is affected by the container diameter and the contact angle at the container wall. In the analysis results, the formed concave/convex meniscus led to underestimating the condensation coefficient of molten salts. However, whether the values of the condensation coefficient of molten salts were affected by menisci, the range of the predicted values was still low from 10−3 to 10−5. This result means that the presence of the foreign gas (air and Ar) is a dominant parameter in determining the condensation coefficient of atmospheric evaporation.