Thin Film Pressure Estimation of Argon and Water using LAMMPS (original) (raw)
Related papers
2018
The applicability of the S-model kinetic equation for simulation of evaporation and condensation phenomena is investigated by comparing its results for Argon with those of Molecular Dynamics(MD). The steady-state evaporation and condensation between two liquid Argon layers, kept at different but constant temperatures, is simulated. The temperature ratio between the hot/cold Argon layers is fixed at and the rarefaction parameter is equal to , which corresponds to the beginning of transitional flow regime. The macroscopic profiles of temperature and heat flux in vapor between the liquid layers are depicted. Both methods predict an inverted temperature profile. The agreement between the methods depends on the evaporation/condensation coefficients and the temperature at the liquid boundaries. Therefore, it is important to obtain the evaporation/condensation coefficients and the positions of the liquid boundaries accurately.
Micro & Nano Letters, 2018
In the present study, non-equilibrium molecular dynamics (MD) simulations have been performed to reveal the effect of solid-liquid interfacial wettability on the evaporation characteristics of thin liquid argon film placed over the flat solid surface. The atomistic model considered herein comprises of a three-phase simulation domain having a solid wall over which liquid argon and argon vapour co-exist. Initially, the system is thermally equilibrated at 90 K for a while after which rapid increase in the solid wall temperature induces a phase change process, i.e. evaporation. Both hydrophilic and hydrophobic wetting conditions of the solid surface have been considered at an evaporation temperature of 130 K for three different surface materials such as platinum, silver, and aluminium. The simulation results show that both the surface wettability and surface material have a significant role in phase transition phenomena of thin liquid film, particularly the surface wettability for the present system configuration. The thermal transport phenomena between the wall and liquid thin film have been studied thoroughly and discussed in terms of wall heat flux, evaporative mass flux, upper bound of maximum possible heat flux etc. The results obtained in the present MD simulation study are compared with the macroscopic predictions based on classical thermodynamics. Interestingly, a very good agreement has been found indicating that macroscopic thermodynamics approach can predict the characteristic of phase change phenomena of nanoscale thin liquid film.
Molecular simulation of water vapor–liquid phase interfaces using TIP4P/2005 model
EPJ Web of Conferences, 2015
Molecular dynamics simulations for water were run using the TIP4P/2005 model for temperatures ranging from 250 K to 600 K. The density profile, the surface tension and the thickness of the phase interface were calculated as preliminary results. The surface tension values matched nicely with the IAPWS correlation over wide range of temperatures. As a partial result, DL POLY Classis was successfully used for tests of the new computing cluster in our institute.
Molecular gas dynamics approaches to interfacial phenomena accompanied with condensation
Experimental Thermal and Fluid Science, 2006
This paper deals with the condensation coefficient of methanol, which is evaluated from a condensation rate at the vapor-liquid interface. Film condensation is induced on the endwall of a vapor-filled shock tube, when a shock wave is reflected at the endwall and the vapor becomes supersaturated there. The liquid film grows with the lapse of time. The evolution in time of the liquid film thickness is measured by an optical interferometer with a high accuracy, and thereby the net condensation mass flux at the interface is obtained. The mass flux is incorporated into the kinetic boundary condition (KBC) at the interface for the Gaussian-BGK Boltzmann equation. Such a treatment of the boundary condition makes it possible to formally eliminate the evaporation and condensation coefficients in KBC and to obtain the unique numerical solution of the vapor-liquid system. In this way, the instantaneous condensation coefficient is accurately evaluated from the conformity with experiment and numerical solution. It is found that the values of condensation coefficient are, near vapor-liquid equilibrium states, close to those evaluated by molecular dynamics simulations.
The gas-liquid surface tension of argon: A reconciliation between experiment and simulation
The Journal of Chemical Physics, 2014
We present a simulation of the liquid-vapor interface of argon with explicit inclusion of the threebody interactions. The three-body contributions to the surface tension are calculated using the Kirkwood-Buff approach. Monte Carlo calculations of the long-range corrections to the three-body contribution are calculated from the radial distribution function g (2) (z 1 , cos θ 12 , r 12). Whereas the effective two-body potentials overestimate the surface tension by more than 15%, the inclusion of the three-body potential provides an excellent agreement with the experimental results for temperatures up to 15 K below the critical temperature. We conclude that the three-body interactions must be explicitly included in accurately modelling the surface tension of argon.
Investigation of Molecular level phase change phenomena are becoming important in heat and mass transfer research at a very high rate, driven both by the need to understand certain fundamental phenomena as well as by a plethora of new and forthcoming applications in the areas of micro- and nanotechnologies. Molecular dynamics simulation has been carried out to go through the evaporation and condensation characteristics of thin liquid argon film in Nano-scale confinement. In the present study, a cuboid system is modeled for understanding the Nano-scale physics of simultaneous evaporation and condensation. The cuboid system consists of hot and cold parallel platinum plates at the bottom and top ends. The fluid comprised of liquid argon film at the bottom plate and vapor argon in between liquid argon and upper plate of the domain. Three different simulation domains have been created here: (i) Both platinum plates are considered flat, (ii) Upper plate consisting of transverse slots of low height and (iii) Upper plate consisting of transverse slots of bigger height. Considering hydrophilic nature of top and bottom plates, two different high temperatures of the hot wall was set and an observation was made on normal and explosive vaporizations and their impacts on thermal transport. For all the structures, equilibrium molecular dynamics (EMD) was performed to reach equilibrium state at 90 K. Then the lower wall is set to two different temperatures like 110 K and 250 K for all three models to perform non-equilibrium molecular dynamics (NEMD). For vaporization, higher temperature of the hot wall led to faster transport of the liquid argon as a cluster moving from hot wall to cold wall. But excessive temperature causes explosive boiling which seems not good for heat transportation because of less phase change. In case of condensation, an observation was made which indicates that the nanostructured transverse slots facilitate condensation. Two factors affect the rate of condensation when nanostructures are there: (i) increased surface area and (ii) the nanostructure height. The variation of temperature and evaporation number with respect to time was monitored for all cases. An estimation of heat fluxes normal to top and bottom walls also was made to focus the effectiveness of heat transfer in hydrophilic confinement.
Molecular Modeling of Macroscopic Phase Changes 2: Vapor Pressure Parameters
ForsChem Research Reports, 2022
Evaporation takes place when the kinetic energy of a molecule reaching the interface is large enough to overcome a cohesive energy barrier caused by intermolecular forces at the interface. As the temperature of the system increases, both the fraction of molecules overcoming the barrier and the frequency of molecules reaching the surface increase, resulting in a larger flux of molecules leaving the liquid. Such flux exerts an equivalent pressure known as vapor pressure. Thus, the effect of temperature on vapor pressure of liquid is highly nonlinear. Different parametric models have been used to describe such effect. In this work, a large experimental database is used to fit three different evaporation models (Antoine equation, mechanistic energy barrier and empirical energy barrier). Cohesive temperatures and energy barriers of over 1400 pure compounds are obtained from the mechanistic model.
International Journal of Heat and Mass Transfer, 2014
Molecular dynamics simulations have been conducted to understand the mechanism for bubble formation on a platinum substrate with particular emphasis on the surface texture. Liquid Argon, that follows the model of Lennard-Jones fluids, is the fluid of interest. The nano-sized bubbles are formed under different degree of superheat and surface conditions. The bubble nucleation and vapor film formation show dependence on the degree of superheat and solid-liquid interfacial wettability. A bubble does not form easily on a non-wetting surface. It is easy to nucleate a bubble on a smooth surface for higher degree of superheats. The hydrophilic surfaces provide favorable conditions for bubble nucleation and formation of vapor films.
AIP Conference Proceedings
Molecular dynamics simulations of vapor-liquid equilibrium states and those of evaporation from liquid phase into a virtual vacuum are performed for water. In spite of the formation of molecular clusters in the vapor phase and the presence of the preferential orientation of molecules at the interface due to uneven sharing of the bonding electron pair, essentially the same results as in our previous study for argon are obtained. That is, when the bulk liquid temperature is relatively low, the distribution function of evaporation can be expressed as the product of the equilibrium distribution of saturated vapor at the temperature in the bulk liquid phase and a well-defined evaporation coefficient, which is determined as a decreasing function of the liquid temperature, and is found to approach unity with the decrease of the temperature. α e = J evap J out eq , (3) where the brackets denote the ensemble average (see Fig. 2).
EPJ Web of Conferences, 2016
In our previous study [Planková et al., EPJ Web. Conf. 92, 02071 (2015)], several molecular simulations of vapor-liquid phase interfaces for pure water were performed using the DL POLY Classic software. The TIP4P/2005 molecular model was successfully used for the modeling of the density profile and the thickness of phase interfaces together with the temperature dependence of the surface tension. In the current study, the extended simple point charge (SPC/E) model for water was employed for the investigation of vapor-liquid phase interfaces over a wide temperature range from 250 K to 600 K. The TIP4P/2005 model was also used with the temperature step of 25 K to obtain more consistent data compared to our previous study. Results of the new simulations are in a good agreement with most of the literature data. TIP4P/2005 provides better results for the saturated liquid density with its maximum close to 275 K, while SPC/E predicts slightly better saturated vapor density. Both models give qualitatively correct representation for the surface tension of water. The maximum absolute deviation from the IAPWS standard for the surface tension of ordinary water is 10.4 mN • m −1 and 4.1 mN • m −1 over the temperature range from 275 K to 600 K in case of SPC/E and TIP4P/2005, respectively.