Thermodynamic Properties of Ethylene from the Freezing Line to 450 K at Pressures to 260 MPa

Abstract

A new fundamental equation explicit in Helmholtz energy for thermodynamic properties of ethylene from the freezing line to 450 K at pressures to 260 MPa is presented. Independent equations for the vapor pressure for the saturated liquid and vapor densities as functions of temperature, and for the ideal gas heat capacity are also included. The fundamental equation was selected from a comprehensive function of 100 terms on the basis of a statistical analysis of the quality of the fit. The coefficients of the fundamental equation were determined by a weighted least-squares fit to selected P-ρ-T data, saturated liquid, and saturated vapor density data to define the phase equilibrium criteria for coexistence, Cv data, velocity of sound data, and second virial coefficient data. The fundamental equation and the derivative functions for calculating internal energy, enthalpy, entropy, isochoric heat capacity (Cv), isobaric heat capacity (Cp), and velocity of sound are included. Tables of thermodynamic properties of ethylene are given for liquid and vapor states within the range of validity of the fundamental equation. The fundamental equation reported here may generally be used to calculate pressures and densities with an uncertainty of ±0.1%, heat capacities within ±3%, and velocity of sound values within ±1%. Comparisons of calculated properties to experimental data are included to verify the accuracy of the formulation.