Chemical Engineering Department, Amirkabir University of Technology, P.O. Box 15875-4413 Tehran, I.R. IRAN
By considering the fact that the surface tension of a real fluid arises from a combination of both repulsive and attractive forces between molecules, a new expression for the interfacial tension has been derived from scaled particle theory (SPT) based on the work of cavity formation and the interaction energy between molecules. At the critical temperature, the interfacial tension between coexisting liquid and vapour phases vanishes and the intermolecular attractive forces must exactly counterbalance the repulsive forces associated with cavity formation. The effective Lennard-Jones energy parameter has been calculated by using a simple equation derived from SPT for a range of pure fluids including noble gases, diatomic and triatomic gases, short and medium length hydrocarbons, aromatic compounds, oxygen containing compounds. The evaluated Lennard-Jones energy parameters and Reiss's SPT theory were used to calculate the surface tension of pure compounds near critical temperature and were compared with the experimental data. The results indicated that the developed SPT in this work calculates the surface tensions much closer to the experimental data compared with those Reiss's SPT theory .