A new form of the equation of state for pure substances and its application to oxygen

Schmidt, R. and Wagner, W., 1985. A new form of the equation of state for pure substances and its application to oxygen. Fluid Phase Equilibria, 19: 175–200.A new wide range equation of state is presented and expressed analytically in the form of the free energy as a function of density and temperature. This fundamental equation contains, in addition to pure polynomial and “BWR”-terms, new exponential functions especially convenient for the critical region. To guarantee an effective structure, the combination of the terms of the equation was found by using an optimization method recently developed. As a result, the optimized function for the free energy is capable of representing the thermodynamic surface of oxygen in the range 54 ≤ T ≤ 300 K, 0 < p ≤ 818 bar and 0 < ρ ≤ 41 mol dm^?3 within the experimental uncertainty of the data available. With the exception of very few items of data, this statement is also valid for the whole coexistence curve and the critical region. Extrapolations of this new equation beyond the range of data yield physically meaningful results.