Showing papers by "Johann Fischer published in 1997"

Molecular dynamics simulation of the liquid–vapor interface: The Lennard-Jones fluid

Abstract: In this work we present new molecular dynamics simulation results for the liquid–vapor interface of the pure Lennard-Jones fluid. Our aims were further investigations on the simulation setup and the simulation parameters to obtain reliable data for the coexisting densities as well as for the surface tension. The influence of the cut-off distance to the interfacial properties is investigated and long-range corrections to both the dynamics and the surface tension are applied. It is found that the saturated liquid densities from the surface simulations agree with those from the NpT+test particle method within 1% for sufficiently large simulation boxes; the saturated vapor densities agree within 4%. In order to obtain reliable values for the surface tension, cut-off radii of at least 5 molecular diameters supplemented by a tail correction are required.

Vapor–liquid equilibria of the ternary mixture CH4 + C2H6 + CO2 from molecular simulation

Abstract: The NpT + test-particle method for the calculation of vapor–liquid equilibria by molecular simulations is extended to ternary mixtures. It is applied to the system methane + ethane + carbon dioxide, for which all binary molecular interaction models are available from previous work. Methane is described as one-center Lennard-Jones fluid, ethane as two-center Lennard-Jones fluid, and carbon dioxide as two-center Lennard-Jones plus point quadrupole fluid. The unlike interactions are treated in the same way as the binary mixtures, using two parameters for each binary interaction. No ternary parameters are introduced. Vapor–liquid phase equilibria are calculated for the ternary mixture at the following temperature–pressure pairs: 233.15 K - 2 MPa; 250.5 K - 2 MPa; and 250.5 K - 3.04 MPa. Comparison of the simulation data with experimental and equation-of-state results shows excellent agreement. Bubble and dew densities are also reported.

An equation of state for two-center Lennard-Jones fluids

Abstract: A new equation of state (EOS) is proposed for the Helmholzt energyF of two-center Lennard-Jones fluids. The EOS is written in the form of a generalized van der Waals equation,F=FH+FA, whereFH accounts for the hard-body interaction andFA for the attractive dispersion forces. The equation is constructed on the basis of previously published data sets and results from new extensive computer simulation studies. It correlates pressures and internal energies over a wide fluid range for two-center model fluids with elongations up to 0.67 in reduced units with a high accuracy and shows an excellent description of the vapor-liquid coexistence properties. Comparisons of results from the new EOS with other data sets and recently published VLE from the NpT plus test particle method show very good agreement.