Abstract
ABSTRACTThe vapour–liquid equilibrium of the Mie potential, where the dispersive exponent is constant (m = 6) while the repulsive exponent n is varied between 9 and 48, is systematically investigated by molecular simulation. For systems with planar vapour–liquid interfaces, long-range correction expressions are derived, so that interfacial and bulk properties can be computed accurately. The present simulation results are found to be consistent with the available body of literature on the Mie fluid which is substantially extended. On the basis of correlations for the considered thermodynamic properties, a multi-criteria optimisation becomes viable. Thereby, users can adjust the three parameters of the Mie potential to the properties of real fluids, weighting different thermodynamic properties according to their importance for a particular application scenario. In the present work, this is demonstrated for carbon dioxide for which different competing objective functions are studied which describe the accuracy of the model for representing the saturated liquid density, the vapour pressure and the surface tension. It is shown that models can be found which describe simultaneously the saturated liquid density and vapour pressure with good accuracy, and it is discussed to what extent this accuracy can be upheld as the model accuracy for the surface tension is further improved.
Highlights
In process engineering, knowledge of the vapor-liquid equilibrium is crucial for process design
This is demonstrated for carbon dioxide for which different competing objective functions are studied which describe the accuracy of the model for representing the saturated liquid density, the vapor pressure and the surface tension
It is shown that models can be found which describe simultaneously the saturated liquid density and vapor pressure with good accuracy, and it is discussed to what extent this accuracy can be upheld as the model accuracy for the surface tension is further improved
Summary
Knowledge of the vapor-liquid equilibrium is crucial for process design. The single-site three-parameter Mie potential with m = 6 and 9 ≤ n ≤ 48 is studied systematically: the saturated liquid density, the saturated vapor density, the vapor pressure, the enthalpy of vaporization and the surface tension are determined by molecular dynamics simulation of systems that contain a vapor phase and a liquid phase (and the interface between them) and correlated as a function of the model parameters. For this purpose, a long-range correction of the Mie potential is developed for inhomogeneous simulation volumes with planar symmetry. The work presented here for the Mie potential extends previous work of our group on other molecular model classes, namely the 2CLJQ [4, 6, 37,38,39,40,41,42,43] and the 2CLJD [3, 44,45,46] potential
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