A New Theory of Fluids: The 'Tunnel' Model

A new method for calculating the thermodynamic properties of liquids and compressed gases is proposed, based on a model in which lines of molecules move almost one-dimensionally in " tunnels ", the walls of the tunnels being formed by neighbouring lines of molecules. This picture is related to the " cell " model, but it is a disordered picture, as is appropriate in a model for fluids, and the problem of the " communal entropy " which besets the cell model, does not arise. The method is applied to the hard-sphere fluid and the calculated pressure/volume isotherm is in very much better agreement with the expected isotherm than either the cell theory or the superposition theory, and also in rather better agreement than the virial expansion truncated after five terms.