scholarly journals A formation and growth model of CO2 hydrate layer based on molecular dynamics

2020 ◽  
Author(s):  
Kota Honda ◽  
Rintaro Fujikawa ◽  
Xiao MA ◽  
Norifumi Yamamoto ◽  
Kota Fujiwara ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Mass Transfer ◽  
Layer Thickness ◽  
Diffusion Coefficients ◽  
The Self ◽  
Dynamics Simulation ◽  
Dissolution Behavior ◽  
Transfer Coefficients ◽  
Hydrate Layer ◽  
Self Diffusion

This study develops a model to predict the CO2 hydrate layer thickness. As to achieve this, we need the mass transfer coefficients at the interface between water phase and CO2 hydrate layer and the diffusion coefficients in CO2 hydrate. Firstly, we conducted the visualization experiment of CO2 hydrate layer dissolution behavior. From the experiment, we obtain the mass transfer coefficient on the CO2 hydrate layer. The experimental results show good agreement with the existing empirical equation. Secondly, we conducted the molecular dynamics simulation of CO2 hydrate to obtain the self-diffusion coefficients of CO2 and H2O molecules. As to calculate the self-diffusion coefficients, we identified inter-cage hopping and intra-cage movement of molecules based on each molecule travel distance. Finally, the results indicate that the kinetic model we proposed reproduce the layer thickness on the order.

A Molecular Dynamics Simulation of Molten (Li-Rb)Cl Implying the Chemla Effect of Mobilities

1980 ◽  
Vol 35 (5) ◽  
pp. 493-499 ◽  
Author(s):  
Isao Okada ◽  
Ryuzo Takagi ◽  
Kazutaka Kawamura
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Diffusion Coefficients ◽  
Strong Correlation ◽  
Pair Correlation ◽  
The Self ◽  
Dynamics Simulation ◽  
Self Diffusion ◽  
Pure Salt ◽  
Dynamics Simulations

Abstract A new transport property, the self-exchange velocity (SEV) of neighbouring unlike ions, has been evaluated from molecular dynamics simulations of molten LiCl, RbCl and LiRbCl2 at 1100 K and the mixture at 750 K. From the increase of the SEV's in the order Rb+ (pure salt) <Li+ (mixture) < Rb+ (mixture) < Li+ (pure salt), it is conjectured that there is a strong correlation between the SEV’s and the internal mobilities. An interpretation of the Chemla effect in its dependence on temperature is given. The pair correlation functions and the self-diffusion coefficients are also calculated and discussed.

scholarly journals Molecular-Dynamics Simulation of Self-Diffusion of Molecular Hydrogen in X-Type Zeolite

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Xiaoming Du
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Hydrogen Diffusion ◽  
Mean Free Path ◽  
The Self ◽  
Dynamics Simulation ◽  
Pulse Field ◽  
Self Diffusion ◽  
Hydrogen Molecules ◽  
Dynamics Simulations

The self-diffusion of hydrogen in NaX zeolite has been studied by molecular-dynamics simulations for various temperatures and pressures. The results indicate that in the temperature range of 77–293 K and the pressure range of 10–2700 kPa, the self-diffusion coefficients are found to range from 1.61 × 10−9 m2·s−1to 3.66 × 10−8 m2·s−1which are in good agreement with the experimental values from the quasielastic neutron scattering (QENS) and pulse field gradients nuclear magnetic resonance (PFG NMR) measurements. The self-diffusion coefficients decrease with increasing pressure due to packing of sorbate-sorbate molecules which causes frequent collusion among hydrogen molecules in pores and increase with increasing temperature because increasing the kinetic energy of the gas molecules enlarges the mean free path of gas molecule. The activated energy for hydrogen diffusion determined from the simulation is pressure-dependent.

Translational and rotational dynamics in supercritical methanol from molecular dynamics simulation

2004 ◽  
Vol 76 (1) ◽  
pp. 203-213 ◽  
Author(s):  
Michalis Chalaris ◽  
J. Samios
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Md Simulation ◽  
Time Correlation ◽  
The Self ◽  
Dynamics Simulation ◽  
Supercritical Methanol ◽  
Reorientational Motion ◽  
Self Diffusion ◽  
Theoretical Predictions

The purpose of this paper is to review our latest molecular dynamics (MD) simulation studies on the temperature and density dependence of the translational and reorientational motion in supercritical (SC) methanol. In the present treatment, Jorgensen's [W. L. Jorgensen. J. Phys. Chem. A102, 8641 (1998)] transferable potential model, tested in a recent MD study of hydrogen bonds in this fluid [M. Chalaris and J. Samios, J. Phys. Chem. B103, 1161 (1999)], was employed to simulate the dynamics of the system. The simulations were performed in the canonical (NVT) ensemble along the isotherms 523, 623, and 723 K and densities corresponding to the pressures from 10 to 30 MPa. Several dynamical properties of the fluid have been obtained and analyzed in terms of appropriate time-correlation functions (CFs). With respect to the translational dynamics, the self-diffusion coefficients obtained have been used to test the applicability of the well-known Chapman-Enskog kinetic theory. We have found that the theoretical predictions for the self-diffusion coefficients are only in qualitative agreement with the MD results over the whole temperature and density range studied. Finally, the inspection of the reorientational CFs and their corresponding correlation times lead to the conclusion that the reorientational motion of the SC methanol molecules in the sample is anisotropic.

scholarly journals Estimation of the Enrichment of Cs in Molten Chloride and Fluoride Systems by Molecular Dynamics Simulation

2001 ◽  
Vol 56 (3-4) ◽  
pp. 279-287 ◽  
Author(s):  
Masahiko Matsumiya ◽  
Ryuzo Takagi
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Diffusion Coefficients ◽  
The Self ◽  
Dynamics Simulation ◽  
Molten Chloride ◽  
Self Diffusion ◽  
Metallic Fuels ◽  
Relative Differences ◽  
Pyrochemical Reprocessing

Abstract For the pyrochemical reprocessing of spent metallic fuels in molten salt baths it is of importance to estimate the enrichment degree of Cs. A molecular dynamics simulation has been executed on molten (Li, Na, Cs)Cl at 900 K and (Li, Na, Cs)F at 925 K for various compositions in order to calculate the relative differences in the internal cation mobilities of Cs in molten LiCl-NaCl equimolar mixtures and the LiF-NaF eutectic. According to these results the self-exchange velocities of Li+, Na+ and Cs+ with respect to Cl- and F- have similar tendencies at each composition, and Cs can be enriched effectively up to xCs = 0.5 -0.6 in LiCl-NaCl melts. In addition, the sequence of the calculated self-diffusion coefficients for various compositions was in a fair agreement with that of the obtained self-exchange velocities.

Molecular Dynamics Study on the Adsorption Selectivity for Negative Elements in Aluminosilicates

2001 ◽  
Vol 56 (6-7) ◽  
pp. 459-465 ◽  
Author(s):  
Masahiko Matsumiya ◽  
Ryuzo Takagi
Keyword(s):  
Molecular Dynamics ◽  
Diffusion Coefficients ◽  
Ionic Radius ◽  
Fission Products ◽  
The Self ◽  
Dynamics Simulation ◽  
Monovalent Cations ◽  
Adsorption Selectivity ◽  
Self Diffusion ◽  
Metallic Nuclear Fuels

Abstract For the pyrochemical reprocessing of spent metallic nuclear fuels in molten salt baths it is important to investigate the adsorption selectivity of cations in aluminosilicates. A molecular dynamics simulation has been performed on sodalite and zeolite with exchangeable monovalent and multivalent cationic fission products at 673 K in order to calculate their self-diffusion coefficients in the aluminosilicate framework and estimate the selectivity of the exchangeable cations. The results enables us to conclude that the self-diffusion coefficients of monovalent cations decrease with increasing ionic radius. The order of the adsorption selectivity is Li < Na < K < Cs in zeolite. The self-diffusion coefficients of multivalent cations arealmost independent of the ionic radius, and these cations are in aluminosilicates more stable thanmonovalent cations. The results are consistent with the experimental results.

A Molecular Dynamics Simulation of the Molten Ternary System (Li, K, Cs)Cl

2000 ◽  
Vol 55 (11-12) ◽  
pp. 856-860 ◽  
Author(s):  
Masahiko Matsumiya ◽  
Ryuzo Takagi
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulation ◽  
Ternary System ◽  
Diffusion Coefficients ◽  
Pair Correlation ◽  
The Self ◽  
Dynamics Simulation ◽  
Eutectic System ◽  
Self Diffusion ◽  
Dynamics Simulations

The self-exchange velocity (SEV) of neighboring unlike ions, has been evaluated by molecular dynamics simulations of molten CsCl, (Li, K)C1 and (Li, K, Cs)Cl at 673 K. From the increase of the SEV's in the same order as the internal mobilities it is conjectured that there is a strong correlation between these two properties. The pair correlation functions, and the self-diffusion coefficients and the SEV's of Li+, K+, and Cs+ with reference to Cl- have also been calculated. The results allow to conclude that the self-exchange velocity of the cations become vCs < vK < vLi at xCs =0.1 and vLi < vK < vCs at xCs > 0.4. The sequence of the self-diffusion coefficients agrees with that of the SEV's. The results enable to conclude that it is possible to enrich Cs at up to xCs ~ 0.3 - 0.4 in the molten LiCl-KCl eutectic system.

Self-diffusion of lignite/water under different temperatures and pressure: A molecular dynamics study

2016 ◽  
Vol 30 (01) ◽  
pp. 1550253 ◽  
Author(s):  
Xinjian Liu ◽  
Yu Jin ◽  
Congliang Huang ◽  
Jingfeng He ◽  
Zhonghao Rao ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Water System ◽  
Simulation Method ◽  
The Self ◽  
Dynamics Simulation ◽  
Low Rank ◽  
Self Diffusion ◽  
Change Mechanism ◽  
Different Temperatures ◽  
Temperature And Pressure

Temperature and pressure have direct and remarkable implications for drying and dewatering effect of low rank coals such as lignite. To understand the microenergy change mechanism of lignite, the molecular dynamics simulation method was performed to study the self-diffusion of lignite/water under different temperatures and pressure. The results showed that high temperature and high pressure can promote the diffusion of lignite/water system, which facilitates the drying and dewatering of lignite. The volume and density of lignite/water system will increase and decrease with temperature increasing, respectively. Though the pressure within simulation range can make lignite density increase, the increasing pressure showed a weak impact on variation of density.

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