Thermodynamic Behavior of Fluids Near the Critical Point

In this review we are concerned with the critical thermodynamic behavior of fluids, a field in which great activity and considerable progress has occurred in the past two decades. The field is considered mature, in the sense that the theoretical concepts have crystallized and that there appears to be consensus that theory and experiment are in agreement. Our purposes in this review are (a) to capture the present level of understanding and to pinpoint issues of substance that have not been resolved satisfactorily; (b) to sketch how much flesh has been put on the theoretical skeleton, that is, how far theory has led to practical formulations that can be used to describe real systems with accuracy and predictive power; and (c) to emphasize the most recent developments. Within the scope of a few dozen pages, it is impossible to be compre­ hensive. We have, on purpose, limited ourselves to ordinary critical points in gas-liquid systems. Both limitations are severe. Tricritical points have