An Equation of State for the Thermodynamic Properties of Dimethyl Ether

A thermodynamic property formulation for dimethyl ether has been developed based on a selection of experimental thermodynamic property data. The formulation includes a fundamental equation, a vapor-pressure equation, and saturated-density equations for liquid and vapor states. In determining the coefficients of the equation of state, multi-property fitting methods were used that included single-phase pressure-density-temperature (p rho T), heat capacity, vapor pressure, and saturated density data. Deviations between experimental and calculated data are generally within the experimental accuracy. The equation of state has been developed to conform to the Maxwell criterion for two-phase liquid-vapor equilibrium states, and is valid for temperatures from the triple-point temperature to 550 K, with pressures up to 50 MPa and densities up to 19 mol dm(-3). The uncertainties of the equation of state in density are 0.1% for the liquid phase and 0.3% for the vapor phase. In the extended critical region, the uncertainties in density are 0.5%, except for very near the critical point. The uncertainties in vapor pressure are 0.2% above 230 K, and increase as temperature decreases. The uncertainties in saturated liquid density are 0.05%, except for near the critical point. The uncertainties in heat capacity are 2.0%. Detailed comparisons between the experimental data and calculated values are given. (C) 2011 American Institute of Physics. [doi:10.1063/1.3582533]