A Study On Transport Properties And Phase Transition Of Fluids By Molecular Dynamical Simulation Method

The main purpose of the present dissertation is to perform systematically Molecular Dynamics (MD) simulation of the transport properties for fluids, which include simple fluids, complex fluids and mixture, in particular, nano-fluids. The MD technique has been widely used in various fields in the past years. In the study, the detailed simulation techniques are discussed in order to improve the precision of the calculation. In addition, according to the project in cooperation with Russia, the phase transition, transport properties and the micro-structure of the glasses are investigated by using the molecular dynamics simulation method. Some significant results were obtained.The knowledge of the transport coefficients for describing the macroscope transport properties is of considerable technological and academic importance, and it is also the most principal physical parameters for substances. However, the transport coefficients are very difficult to be precisely determined by experiments, so that the corresponding physical data are deficient. To search for a direct and accurate simulation method for determining the transport coefficients is an area of active research. The MD technique provides a promising and effective way to study the transport properties of fluids in different thermodynamical states.In the dissertation, firstly, molecular dynamics simulations based on the fractal theory are carried out to calculate the fractional dimensionality for the real fluid of Argon at the different temperatures. A hypothesis was proposed which suggested that the random motion of the molecules for real fluids can be described by the Fractional Brownian function. At the same time, the corresponding FB functions of displacement, velocity and speed are constructed. The results obtained by the functions were compared with the results obtained directly by molecular dynamics simulation. They agree pretty well, thus the reliability of the hypothesis is verified.Secondly, liquid Ar, water, and mixtures are chosen as the working substances to calculate their diffusion coefficients, shearing viscosities and thermal conductivities by MD methods. We analyzed mainly the shape of the curves of Auto-correlation function to reflect the transport properties in different thermodynamical states. For liquid water, different potential models were applied and compared. The results show that the potential model has strong influence on the transport coefficients. In the study, the calculation formula of thermal conductivity was deduced from that of the simple fluid.