Thermodynamics Research Center / ThermoML | International Journal of Thermophysics

ABSTRACT

The isochoric heat capacities (CV1CV1CV2CV2), saturation densities (S and (S)), vapor pressures (P S), thermal-pressure coefficients V=PTV , and first temperature derivatives of the vapor pressure ? S = (dP S/dT) of diethyl ether (DEE) on the liquid gas coexistence curve near the critical point have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic piezo-calorimeter. The measurements of (CV1CV1CV2CV2) were made in the liquid and vapor one- and two-phase regions along the coexistence curve. The calorimeter was additionally supplied with a calibrated extensometer to accurately and simultaneously measure the PVT, C V VT, and thermal-pressure coefficient, ? V , along the saturation curve. The measurements were carried out in the temperature range from 416 K to 466.845 K (the critical temperature) for 17 liquid and vapor densities from 212.6 kg * m-3 to 534.6 kg * m-3. The quasi-static thermo- (reading of PRT, T - t plot) and baro-gram (readings of the tensotransducer, P - t plot) techniques were used to accurately measure the phase-transition parameters (P S ,? S ,T S) and ? V . The total experimental uncertainty of density (? S), pressure (P S), temperature (T S), isochoric heat capacities (CV1CV1CV2CV2), and thermal-pressure coefficient, ? V , were estimated to be 0.02 % to 0.05 %, 0.05 %, 15 mK, 2 % to 3 %, and 0.12 % to 1.5 %, respectively. The measured values of saturated caloric (CV1CV1CV2CV2) and saturated thermal (P S, ? S, T S) properties were used to calculate other derived thermodynamic properties C P , C S, W, K T , P int, ?H vap, and VTP of DEE near the critical point. The second temperature derivatives of the vapor pressure, (d2 P S/dT 2), and chemical potential, (d2 micro/dT 2), were also calculated directly from the measured one- and two-phase liquid and vapor isochoric heat capacities (CV1CV1CV2CV2) near the critical point. The derived values of (d2 P S/dT 2) from calorimetric measurements were compared with values calculated from vapor pressure equations. The measured and derived thermodynamic properties of DEE near the critical point were interpreted in terms of the complete scaling theory of critical phenomena. In particular, the effect of a Yang Yang anomaly of strength R micro on the coexistence-curve diameter behavior near the critical point was studied. Extended scaling-type equations for the measured properties P S (T), ? S (T), and (CV1CV1CV2CV2) as a function of temperature were developed.