Experimental Study of the Thermodynamic Properties of Diethyl Ether (DEE) at Saturation

Abstract

The isochoric heat capacities C V 1 , C V 1 , C V 2 , C V 2 , saturation densities (ρ S and ρ S ), vapor pressures (P S ), thermal-pressure coefficients γ V = (∂ P/∂ T ) V , and first temperature derivatives of the vapor pressure γ 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 piezocalorimeter. The measurements of (C V 1 , C V 1 , C V 2 , C V 2 ) 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, γ 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 − τ 123 560 Int J Thermophys (2011) 32:559-595 plot) and baro-gram (readings of the tensotransducer, P − τ plot) techniques were used to accurately measure the phase-transition parameters (P S , ρ S , T S ) and γ V . The total experimental uncertainty of density (ρ S ), pressure (P S ), temperature (T S ), isochoric heat capacities (C V 1 , C V 1 , C V 2 , C V 2 ), and thermal-pressure coefficient, γ 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 C V 1 , C V 1 , C V 2 , C V 2 and saturated thermal (P S , ρ S , T S ) properties were used to calculate other derived thermodynamic properties C P , C S , W, K T , P int , H vap , and (∂ V /∂ T ) P of DEE near the critical point. The second temperature derivatives of the vapor pressure, d 2 P S /dT 2 , and chemical potential, d 2 μ/dT 2 , were also calculated directly from the measured one-and two-phase liquid and vapor isochoric heat capacities (C V 1 , C V 1 , C V 2 , C V 2 ) near the critical point. The derived values of d 2 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 μ on the coexistence-curve diameter behavior near the critical point was studied. Extended scaling-type equations for the measured properties P S (T ), ρ S (T ), and (C V 1 , C V 1 , C V 2 , C V 2 ) as a function of temperature were developed.

Experimental Study of the Isochoric Heat Capacity of Diethyl Ether (DEE) in the Critical and Supercritical Regions

“…The experimental details (the physical basis and theory of the method, the apparatus, experimental procedures, and an uncertainty assessment) of the isochoric heat-capacity measurements have been described in our earlier publications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]42,43]. Only a brief review will be given here.…”

“…The uncertainty of temperature measurements was less than 15 mK. Based on a detailed analysis of all sources [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]42,43] of uncertainties likely to affect the determination of C V , the expanded uncertainty (coverage factor k = 2, two-standarddeviation estimate) of measuring the heat capacity was 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.…”

“…Isochoric heat capacity data are the most sensitive indicators of the occurrence of a phase transition, i.e., very sensitive instruments for accurate determination of the phase transition temperatures T S at fixed densities ρ near the critical point using the discontinuity behavior of C V [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15], especially for multicomponent complicated mixtures. Reliable experimental isochoric heat capacity data are necessary to establish an accurate equation of state (EOS), especially near the critical and phase transition points where the curvature of P-T isochores is essential.…”

“…For example, there are no previously reported C V V T data on DEE in the critical and supercritical regions. A detailed literature review of the available thermodynamic property data for DEE is provided in our previous publication [15]. The main objective of the present work is to provide accurate isochoric heat-capacity data for pure DEE in the critical and supercritical regions.…”

“…The main objective of the present work is to provide accurate isochoric heat-capacity data for pure DEE in the critical and supercritical regions. We recently reported [15] isochoric heat-capacity and density data for DEE at saturation in the temperature range from 416 K to 466.845 K (the critical point). In the present work we reported the measurements of the oneand two-phase isochoric heat capacities of DEE in the temperature range from 347 K to 575 K for 12 liquid and 5 vapor densities from 212.6 kg · m −3 to 534.6 kg · m −3 .…”