Linear isotherms for dense fluids: a new regularity

Abstract

A general regularity has been found for dense fluids, both compressed liquids and dense supercritical fluids, namely, that (Z-1)v 2 varies linearly with respect to ρ 2 , where Z≡pv/RT is the compression factor and ρ=1/v is the molar density. The regularity is tested with experimental data for 13 fluids (Ar, N 2 , O 2 , CO, CH 4 , C 2 H 6 , C 3 H 8 , C 2 H 4 , C 2 H 2 , C 6 H 6 , CH 3 OH, NH 3 , H 2 ). It is shown to be compatible with equations of state based on statistical-mechanical theory, although the latter do not predict as great a range of linearity as is suggested by experiment. The regularity holds experimentally for densities greater than the Boyle density and for temperatures below about twice the Boyle temperature