Phase equilibria and interface properties of hydrocarbon propellant–oxygen mixtures in the transcritical regime

Abstract

Vapor-liquid equilibria and fluid interface properties of binary mixtures containing either methane or cyclohexane representing fuel and nitrogen or oxygen are reported. The mixtures are studied at different temperatures and pressures, which are chosen such that the temperature of the fuel component is subcritical, while that of the gaseous component is mainly supercritical. Data are obtained from molecular dynamics (MD) simulation, as well as density functional theory and density gradient theory in combination with the PC-SAFT equation of state (EOS). The studied interface properties include surface tension, interface thickness, enrichment and relative adsorption. Furthermore, bulk vapor-liquid equilibrium properties are computed with two distinct MD methods as well as the PC-SAFT EOS. All approaches are compared to data from highly accurate empirical EOS. Despite the fundamental differences between these methods, very good agreement between the results of MD, density functional theory as well as density gradient theory and EOS data is observed for the phase equilibria and interface properties, reinforcing the present predictions. It is found that the equivalence of nitrogen to oxygen is rather limited, in particular for the methane propellant. The disparities are primarily pronounced for low temperatures, where the compositions of the bulk phases differ significantly. As a result, enthalpy of vaporization as well as surface tension attain much higher values for mixtures containing oxygen.

Molecular modeling of interfacial properties of the hydrogen + water + decane mixture in three-phase equilibrium

“…Better agreements between MD and DGT have been reported in the literature with atomistic models. 25,114 Furthermore, reasonable agreement can be seen between MD and DGT for most of the other properties including the component density profiles (Fig. S8–S10, ESI†), enrichments (Fig.…”

Extension of the MolMod Database to Transferable Force Fields

“…Molecular simulations with force fields have become an important tool for predicting thermophysical properties – as well as for studying nanoscopic processes – in many scientific disciplines. The link of the simulations to the real world is established by the employed substance models, i.e., by the force fields.…”

Vapor–Liquid Interfacial Properties of the Systems (Toluene + CO2) and (Toluene + N2): Experiments, Molecular Simulation, and Density Gradient Theory

“…By simulations, either model systems ,,− or real systems ,,− can be studied to develop a better understanding of interfacial phenomena. Studies of model systems are suitable to investigate interfacial phenomena in a generic way and enable systematic variations of molecular parameters; they provide insights into the relation of molecular interactions and interfacial properties. ,,− In contrast, simulation studies of real systems (or, more precisely, studies of models of real systems) provide data that apply basically only for the considered system, but they can be compared directly to experimental data.…”