Equation Of State For Fluids Based On Hard Sphere Repulsion

The structures and thermodynamic properties of fluids are determined by the complex interactions among particles, i.e., the repulsive interaction and the attractive interaction. The simplest equation of state model maybe the one of hard sphere. It well describes the repulsion.Worthwhile, both the classical van der Waals equation and the Carnahan-Starling(CS) equation are not the accurate solutions to hard sphere systems. Followed by the rapid promotion of the accuracy of hard sphere equation of state in the past dozens of years, one question rises as whether more accurate hard sphere repulsion with a special attraction derives better prediction to the structures and properties of real fluids.In Chapter one, we introduce the background and significance of the equation of state of fluids. In Chapter two, the theoretical basis and some basic concepts of equation of state of fluids are presented. In Chapter three, we use two repulsions with different precision and some attractions to construct a series of equations of state for real fluids. We numerically calculate the saturated properties of fluids at liquid-vapor equilibrium by using the constructed equations of state, and compare the obtained results with the experimental data. We are trying to solve the following problem: when an attraction is fixed, whether a more accurate repulsion means a better numerical prediction or not?Our results show that a more accurate repulsion does not absolutely mean a better numerically prediction. There is no completely positive or negative answer. The final results depend on both the repulsions and the attractions. Although the repulsive intermolecular interaction plays the central role in the complex interaction of substances, attractive interactions cannot be ignored. Following this work, we plan to do researches on improving the accuracy of attractions.