Paper detail

A method to approximate cluster integrals and reproduce subcritical isotherms for model and real gases

A method is proposed to approximate the unlimited subcritical set of Mayer`s reducible cluster integrals (i.e., the power coefficients of the known virial expansions for pressure and density in powers of activity) on the basis of information about several irreducible integrals (virial coefficients) and the saturation activity. For the Lennard-Jones fluid, the first four irreducible integrals are actually sufficient to reproduce gas isotherms (including the flat phase-transition region) with high accuracy at temperatures between the triple and critical points. At low temperatures, even the usage of the first-order irreducible integral only (second virial coefficient) yields almost the same accuracy that, in turn, makes the method applicable to the real fluids with unknown interaction potential. In particular, the calculated water isotherms are in good agreement with experiments.