Study On Fluid Viscosity Density Functional Theory Under Restricted Condition

Fluid viscosity is one of the primary physicochemical data and technical specifications, which plays a central role in many industrial and scientific research fields. Therefore, extensive attentions have been devoted to the determination of viscosity by more and more researchers. In contrast to the investigation of behavior in the bulk phase, the characteristics of fluid flow under confined conditions differ from that of the bulk fluid under identical thermodynamic conditions. Accordingly, fluids exhibit different structures and properties as a result of solid-fluid interactions, which make it more difficult to investigate the structural properties and behaviors. At present, the theoretical research concerning fluid viscosity under confined conditions is still very scarce and in it’s infancy. In this thesis, on the basis of the interactions between molecules, density functional theory(DFT) was constructed by integrating other statistical mechanics approaches as well as corresponding viscosity models. The microcosmic structures and viscosity properties under distinct geometrical confinements(i.e., solid surface and slit pore) were systematically investigated. The main contents are given as follows:(1) The accurate description was achieved based on a modified fundamental measure theory(MFMT) for the hard-core repulsion. Besides, a new weighted density approximation(WDA) was proposed for attraction combined with modified Benedict-Webb-Rubin(MBWR) equation of state. On the basis of the aforementioned DFT, the vapor-liquid phase equilibrium of methane was calculated. Besides, the bulk viscosity distribution was further obtained by employing the viscosity model in the bulk phase. It was found that the prediction was consistent with the experimental data from the national institute of standards and technology(NIST) far away from the critical region.(2) Combining the aforementioned DFT with a Chapman-Enskog viscosity model confined in different conditions, the density and viscosity distributions of methane were investigated under different confined conditions(e.g. solid surface/slit-like pore). On this basis, the influences of temperatures / pore widths / interactions between fluid-solid on the microscopic structures and viscosities were further analyzed. Furthermore, the correlations between them were determined.(3) A full DFT model was constructed in order to describe the properties of the real chainlike fluids by taking further consideration of the interactions between chains. And the global phase equilibrium of n-decane was predicted accurately by combining with the renormalization group theory(RGT). It was apparent that the RGT had a significant influence on the critical phase behavior and the result coincided well with the experimental data. Meanwhile, the viscosity of n-decane was well studied in the bulk phase by integrating with the friction theory. Thus, the aforementioned DFT was verified and feasible, which would provide an excellent foundation for the viscosity study.