Thermodynamics Research Center / ThermoML | International Journal of Thermophysics

ABSTRACT

Two- and one-phase liquid and vapor isochoric heat capacities (CV-rho-T relationship) of diethyl ether (DEE) in the critical and supercritical regions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were carried out in the temperature range from 347 K to 575 K for 12 liquid and 5 vapor densities from 212.6kgm3 to 534.6kgm3. The expanded uncertainties (coverage factor k = 2, two-standard deviation estimate) for values of the heat capacity were 2 % to 3 % in the near-critical region, 1.0 % to 1.5 % for the liquid isochores, and 3 % to 4 % for the vapor isochores. The uncertainties of density and temperature measurements were 0.02 % and 15 mK, respectively. The values of the internal energy, U(T, V), and second temperature derivative of pressure were derived using the measured CV data near the critical point. The critical anomaly of the measured CV and derived values of U(T, V) and _2P/T 2_? in the critical and supercritical regions were interpreted in terms of the scaling theory of critical phenomena. The asymptotic critical amplitudes (A+ 0 and A? 0 ) of the scaling power laws along the critical isochore for one- and two-phase CV were calculated from the measured values of CV . Experimentally derived values of the critical amplitude ratio for CV _A+ 0 /A? 0 = 0.521_ are in good agreement with the values predicted by scaling theory. The measured CV data for DEE were analyzed to study the behavior of loci of isothermal and isochoric CV maxima and minima in the critical and supercritical regions.