• Journal of Advanced Marine Engineering and Technology
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• v.29 no.1
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• pp.34-41
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• 2005

An experimental study of molecular motions on a liquid-vapor interface is limited due to micro-scale characteristics of a system with an angstrom or a nanometer size Therefore, in recent, many studies for micro-scale systems have been conducted by a computer simulation because it is free from experimental limitations. In this study, through the molecular dynamic (MD) method. molecular behavior was clarified on a liquid-vapor interface and a criterion to distinguish between liquid and vapor was suggested by a potential energy and the number of neighboring molecules. At an interface. the potential energy of a molecule was increased but the number of neighboring molecules was decreased when the molecule moved into a vapor region from a liquid region, and vice versa.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.167-170
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• 2012

A test-area molecular dynamics simulation method for the vapor-liquid interface of argon through a Lennard-Jones intermolecular potential is presented in this paper as a primary study of interfacial systems. We found that the calculated density profile along the z-direction normal to the interface is not changed with time after equilibration and that the values of surface tension computed from this test-area method are fully consistent with the experimental data. We compared the thermodynamic properties of vapor argon, liquid argon, and argon in the vapor-liquid interface. Comparisons are made with kinetic and potential energies, diffusion coefficient, and viscosity.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1086-1091
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• 2004

The boundary layer is a very important characteristic of a liquid-vapor interface since it governs the heat and mass transfer phenomena across an interface. However, the thickness of a boundary layer is generally micro- or nano-sized, which requires highly accurate measurement devices and, consequently, costs the related experiments very high and time-consuming. Due to these size dependent limitations, the experiments related with a nano-scaled size have suffered from the errors and the reliability of the obtained data. This study is performed to grasp the characteristics of a liquid-vapor interface, by using a molecular dynamics method. The simulation results were compared with other studies if possible. Although other studies reported that there existed a temperature discontinuity over an interface when the system was reduced to micro- or nano-sized, we confirmed that there was no such a temperature discontinuity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.102-111
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• 2000

A numerical model which simulates the simultaneous heat and mass transfer within a vertical tube GAX absorber was developed. The ammonia vapor and the solution liquid are in counter-current flow, and the hydronic fluid flows counter to the solution liquid. The film thickness and the velocity distribution of the liquid film were obtained by matching the shear stress at the liquid-vapor interface. Two-dimensional diffusion and energy equations were solved in the liquid film to give the temperature and concentration, and a modified Colburn-Drew analysis was used for the vapor phase to determine the heat and mass fluxes at the liquid-vapor interface. The model was applied to a GAX absorber to investigate the absorption rates, temperature and concentration profiles, and mass flow rates of liquid and vapor phases. It was shown that the mass flux of water was negligible compared with that of ammonia except the region near the liquid inlet. Ammonia absorption rate increases rapidly near the liquid inlet and decrease slowly. Both the absorption rate of ammonia vapor and the desorption rate of water near the liquid inlet increase as the vapor mass flow rate increases, but the mass fluxes of the ammonia and the water near the liquid outlet decrease as the mass flow rate of the vapor increases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.418-425
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• 2004

Characteristics of a liquid-vapor interface where a nonequilibrium condensation flow exists are considered based on molecular dynamics simulations, The condensation coefficient, the velocity distributions of the reflected and evaporated molecules and the number flux of the evaporated molecules are compared with those under the liquid-vapor equilibrium. The comparison shows that the condensation coefficient under the nonequilibrium condensation is slightly larger and the number flux of the evaporated molecules is considerably smaller than those under the liquid-vapor equilibrium. The net condensation flux under the nonequilibrium condensation is underestimated if it is evaluated from the condensation coefficient and the number flux of the evaporated molecules under the liquid-vapor equilibrium. However the underestimation is relatively small.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1558-1563
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• 2004

This work applies the nonequilibrium molecular dynamics simulation method to study a Lennard-Jones liquid thin film suspended in the vapor and calculates the thermal conductivity by linear response function. As a preliminary test, the thermal conductivity of pure argon fluid are calculated by nonequilibrium molecular dynamics simulation. It is found that the thermal conductivity decrease with decreasing the density. When both argon liquid and vapor phase are present, the effects of the system temperature on the thermal conductivity are investigated. It can be seen that the thermal conductivity of liquid-vapor interface is constant with increasing the temperature

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.159-168
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• 2005

In recent studies, it was reported that there existed the temperature discontinuity at a liquid-vapor interface in an equilibrium state. However, from the viewpoint of the classical thermodynamics, it is highly questionable result although considering that the experiments related with a boundary layer is very difficult due to the extremely thin thickness of it. To clarify whether the temperature discontinuity over a liquid-vapor interface really exists, the computer simulations were performed. From the simulation results, it could be concluded that the misconception in a temperature calculation might result in non-uniform temperature distributions over an interface under an equilibrium state.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.124-129
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• 2000

The flow of liquid and vapor is investigated in trapezoidal grooves. The effect of variable shear stress along the interface of the liquid and vapor is studied for both co-current and counter-current flows. Velocity contours and results fur the friction are obtained for both trapezoidal grooves. An approximate relation that was previously utilized for the friction for the liquid was modified to obtain accurate agreement with the results for trapezoidal grooves.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.17-24
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• 2003

A mathematical model of the hydrodynamic and heat transfer performances of two-phase flow (gas-liquid) in thin film region of micro channel is proposed. For the formulation of modeling, the flow of the vapor phase and the shear stress at the liquid-vapor interface are considered. In this work, disjoining pressure and capillary force which drive the liquid flow at the liquid-vapor interface in thin film region are adopted also. Using the model, the effects of the variations of channel height and heat flux on the flow and heat transfer characteristics are investigated. Results show that the influence of variation of vapor pressure on the liquid film flow is not negligible. The heat flux in thin-film region is the most important operation factor of micro cooler system.

• Journal of the Korean Chemical Society
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• v.15 no.3
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• pp.133-145
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• 1971

A method of theoretical calculation of the thermodynamic properties for liquid-vapor interface of binary solution is developed according to the transient state theory of significant liquid structure. The surface tensions, the adsorbed amounts at the liquid-vapor interface and the activity coefficients of the components for the solutions of $C_6H_{12}-C_6H_6$ $CCI_4-C_6H_6$, $CHCl_3-C_6H_6$, $CHCl_3-CCl_4$, $CCl_4-CS_2$ are calculated through the full ranges of the compositions.