Revision of a multiparameter equation of state to improve the representation in the critical region: application to water

We have developed a crossover formalism for the thermodynamic surface of pu re fluids, which can be applied to any multiparameter equation of state. Th is procedure has been used to incorporate scaling law behavior into a repre sentation of the thermodynamic properties of water and steam developed by P russ and Wagner (PW EOS) and adopted recently by the International Associat ion for the Properties of Water and Steam. Our revision to this equation re tains most of the functional form and coefficients of the PW EOS, but repla ces two of the terms with a crossover representation of scaling law behavio r. In order to develop this model, we first developed a new crossover formu lation for steam in the critical region, and second, we have incorporated u niversal crossover functions into the original PW EOS. In the modified form , the PW equation of state reproduces the scaling laws down to dimensionles s temperatures tau=10(-7). Far from the critical point the equations practi cally coincide. (C) 1999 Elsevier Science B.V. All rights reserved.