| This dissertation developed an efficient and accurate engineering tool by combining discontinuous molecular dynamic simulation and thermodynamic perturbation theory (DMD/TPT). A useful database of reference fluid structure is created by running DMD simulation for purely repulsive fluid, and these data can be used for molecular modeling.; The simulation has been performed for united atom models of ethane, n-hexane, and n-octane. The interaction sites at eleven wells are recorded at certain time step. DMD/TPT has been used for Square-well chain molecules with variable well width. DMD simulation provides the information of reference fluid, while post-simulation analysis: TPT, recovers the full potential by adding the attractive force to the reference fluid. The study of vapor pressure and liquid density for these three systems at λ = 1.5, 1.8, and 2.0 shows this approach is accurate and efficient at βϵ > 0 and η > 0.28. The change of acentric factor shows that with the well-width increases, the acentric factor decreases. However, it is hard to find a universal potential model by using single well SW potential.; Since the single well potential cannot describe the thermodynamic properties correct, a more realistic potential model is needed. We proposed a multi-step potential model in this research, and DMD/TPT was applied to the multi-step potential model. Having the information of the pure repulsive fluid, with different combinations of well width and well depth, we can have different kinds of potential model. We studied ethane, n-hexane, and n-octane with multi-step potential model. By comparing the vapor pressure, liquid density, and acentric factor, we obtain a universal potential model, which give us the best estimate of these properties: 2580_862.; DMD/TPT approach was then applied to the mixture system. Comparing the attractive contribution of pure components and mixture, the quadratic mixing rule is suitable to use for attractive part. With this assumption, we can extend our new methodology based on the pure components properties. A novel equation of state based on DMD/TPT is proposed, and phase diagrams of four systems are studied in this work: ethane + methane, n-hexane + benzene, benzene + methanol, and methanol + water. By fitting the experimental data, we can adjust the binary interaction parameter, and this is similar to the conventional group contribution method, except DMD/TPT has a clear molecular origin.; DMD/TPT is an efficient and accurate method in predicting thermodynamic properties, and because its clear molecular origin, it provides an insight in the effect of intermolecular forces to the macroscopic properties. |
