New equation of state for ethylene covering the fluid region for temperatures from the melting line to 450 K at pressures up to 300 MPa

This work reviews the available data on thermodynamic properties of ethylen e and presents a new equation of state in the form of a fundamental equatio n explicit in the Helmholtz energy. The functional form of the residual par t of the Helmholtz energy was developed by using state-of-the-art linear op timization strategies. The new equation of state contains 35 coefficients w hich were fitted to selected data of the following properties: (a) thermal properties of the single phase (ppT) and (b) of the liquid-vapor saturation curve (p(s),p ' ,p ") including the Maxwell criterion, (c) speed of sound w of the single-phase region and the saturated vapor and liquid, (d) isocho ric heat capacity c(v), (e) specific isobaric heat capacity c(p) of the sin gle-phase region and of the saturated liquid, and (f) second and third ther mal virial coefficients B and C. For the density, the estimated uncertainty of the new equation of state is less than +/-0.02% for pressures up to 12 MPa and temperatures up to 340 K with the exception of the critical region. Outside the range mentioned above, the estimated uncertainty is less than +/-0.03% for pressures up to 30 MPa and temperatures between 235 and 350 K. The new formulation shows reasonable extrapolation behavior up to very hig h pressures and temperatures. Independent equations for the vapor pressure, for the pressure on the sublimation and melting curve, and for the saturat ed-liquid and saturated-vapor densities are also included. Tables for the t hermodynamic properties of ethylene from 104 to 450 K for pressures up to 3 00 MPa are given in the appendix. (C) 2001 American Institute of Physics.