Ilmutdin M. Abdulagatov

P-V-T-x measurements of aqueous mixtures at supercritical conditions

We report P-V-T-x measurements for five binary systems: water+methane, water+n-hexane, water+n-octane, water+benzene, and water+nitrogen at supercritical conditions for several compositions. The experimental data were obtained along isotherms with a phase-equilibrium cell designed for accurate measurements at pressures up to 100 MPa. The uncertainties in temperature, pressure, density, and concentration are ±0.01 K, ±0.2%, ±0.2%, and ±0.002 mole fractions, respectively. The behavior of the second virial coefficient, the excess volume, and the excess Gibbs free energy is also discussed.

ThermoData Engine (TDE): software implementation of the dynamic data evaluation concept. 3. Binary mixtures.

ThermoData Engine (TDE) is the first full-scale software implementation of the dynamic data evaluation concept, as reported in this journal. The present paper describes the first application of this concept to the evaluation of thermophysical properties for ternary chemical systems. The method involves construction of Redlich-Kister type equations for individual properties (excess volume, thermal conductivity, viscosity, surface tension, and excess enthalpy) and activity coefficient models for phase equilibrium properties (vapor-liquid and liquid-liquid equilibrium). Constructed ternary models are based on those for the three pure component and three binary subsystems evaluated on demand through the TDE software algorithms. All models are described in detail, and extensions to the class structure of the program are provided. Reliable evaluation of properties for the binary subsystems is essential for successful property evaluations for ternary systems, and algorithms are described to aid appropriate parameter selection and fitting for the implemented activity coefficient models (NRTL, Wilson, Van Laar, Redlich-Kister, and UNIQUAC). Two activity coefficient models based on group contributions (original UNIFAC and NIST-KT-UNIFAC) are also implemented. Novel features of the user interface are shown, and directions for future enhancements are outlined.

Isochoric Heat Capacity Measurements for Heavy Water Near the Critical Point

Isochoric heat capacity measurements of D2O are presented as a function of temperature at fixed densities of 319.60, 398.90, 431.09, and 506.95 kg·m−3. The measurements cover a range of temperatures from 551 to 671 K and pressures up to 32 MPa. The coverage includes one- and two-phase states and the coexistence curve near the critical point of D2O. A high-temperature, high-pressure, adiabatic, and nearly constant-volume calorimeter was used for the measurements. Uncertainties of the heat capacity measurements are estimated to be 2 to 3%. Temperatures at saturation TS(ρ) were measured isochorically using a quasi-static thermogram method. The uncertainty of the phase transition temperature measurements is about ±0.02 K. The measured CV data for D2O were compared with values predicted from a parametric crossover equation of state and six-term Landau expansion crossover model. The critical behavior of second temperature derivatives of the vapor pressure and chemical potential were studied using measured two-phase isochoric heat capacities. From measured isochoric heat capacities and saturated densities for heavy water, the values of asymptotic critical amplitudes were estimated. It is shown that the critical parameters (critical temperature and critical density) adopted by IAPWS are consistent with the TS–ρS measurements for D2O near the critical point.

Isochoric Heat Capacity Measurements for Light and Heavy Water Near the Critical Point

The isochoric heat capacity was measured for D2O at a fixed density of 356.075 kg·m−3 and for H2O at 309.905 kg·m−3. The measurements cover the range of temperatures from 623 to 661 K. The measurements were made with a high-temperature, high-pressure, adiabatic calorimeter with a nearly constant inner volume. The uncertainty of the temperature is 10 mK, while the uncertainty of the heat capacity is estimated to be 2 to 3%. Measurements were made in both the two-phase and the one-phase regions. The calorimeter instrumentation also enables measurements of PVT and the temperature derivative (∂P/∂T)V along each measured isochore. A detailed discussion is presented on the experimental temperature behavior of CV in the one- and two-phase regions, including the coexistence curve near the critical point. A quasi-static thermogram method was applied to determine values of temperature at saturation TS(ρ) on measured isochores. The uncertainty of the phase-transition temperature measurements is about ±0.02 K. The measured CV data for D2O and H2O are compared with values predicted from a recent developed parametric crossover equation of state and IAPWS-95 formulation.

Densities and Apparent Molar Volumes of Aqueous NaNO3 Solutions at Temperatures from 292 to 573 K and at Pressures Up to 30 MPa

Densities of four aqueous NaNO3 solutions (0.100, 0.303, 0.580, 0.892 mol-kg−1 H2O) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made at ten isotherms between 292 and 573 K. The range of pressure was 0.1–30 MPa. The total uncertainty of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 10 mK, and 0.014%, respectively. Values of saturated densities were determined by extrapolating experimental P-ρ data to the vapor pressure at fixed temperature and composition. Apparent molar volumes were derived using measured values of density for the solutions and for pure water. The apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes at infinite dilution. The temperature, pressure, and concentration dependence of partial and apparent molar volumes were studied. The measured values of density and apparent and partial molar volume were compared with data reported in the literature.

PVTx measurements for dilute water+n-hexane mixtures in the near-critical and supercritical regions

Abstract The PVTx relationship of four binary dilute (water+ n -hexane) mixtures (0.0021, 0.0050, 0.0850 and 0.0138 mole fraction of n -hexane) were measured with a constant-volume method. Measurements were made at five near-critical and supercritical temperatures of pure water: 643.05, 645.05, 647.05, 649.05 and 651.05 K. The range of pressures was from 8 to 35 MPa. The total uncertainty of density, pressure, concentration, and temperature measurements were estimated to be less than ±0.2%, ±5 kPa, 0.001 mole fraction, and 10 mK, respectively. The derived PVTx data have been differentiated to yield infinite dilution partial molar volumes V 2 ∞ . Asymptotic properties for V 2 ∞ along the critical isotherm–isobar of the pure solvent (water) are experimentally studied. We show that PVTx measurements for the dilute water+ n -hexane mixture confirm the non-classical power-law behavior of V 2 ∞ along the experimental path of constant T C – P C with a critical exponent of 0.79. The values of the Krichevskii parameter of 96.4 MPa for the dilute water+ n -hexane mixture was estimated from PVTx measurements and compared with values calculated from the initial slopes of the T C – x and P C – x critical lines and the slope of the vapor-pressure P S – T S curve at the pure solvent critical point. The excess molar volumes of the mixture near the critical point of pure water are calculated using measured PVTx properties for mixtures and pure components.

Crossover SAFT Equation of State and Thermodynamic Properties of Propan-1-ol

In this work we have developed a new equation of state (EOS) for propan-1-ol on the basis of the crossover modification (CR) of the statistical-associating-fluid-theory (SAFT) EOS recently developed and applied to n-alkanes. The CR SAFT EOS reproduces the nonanalytical scaling laws in the asymptotic critical region and reduces to the analytical-classical SAFT EOS far away from the critical point. Unlike the previous crossover EOS, the new CR SAFT EOS is based on the parametric sine model for the universal crossover function and is able to represent analytically connected van der Waals loops in the metastable fluid region. The CR SAFT EOS contains 10 system-dependent parameters and allows an accurate representation of the thermodynamic properties of propan-1-ol over a wide range thermodynamic states including the asymptotic singular behavior in the nearest vicinity of the critical point. The EOS was tested against experimental isochoric and isobaric specific heats, speed of sound, PVT, and VLE data in and beyond the critical region. In the one-phase region, the CR SAFT equation represents the experimental values of pressure with an average absolute deviation (AAD) of less than 1% in the critical and supercritical regions and the liquid densities with an AAD of about 1%. A corresponding states principle is used for the extension of the new CR SAFT EOS for propan-1-ol to higher n-alkanols.

Isochoric heat capacity of heavy water at subcritical and supercritical conditions

The heat capacity of heavy water was measured in the temperature range from 294 to 746 K and at densities between 52 and 1105 kg·m−3 using a high-temperature, high-pressure adiabatic calorimeter. The measurements were performed at 14 liquid and 9 vapor densities between 52 and 1105 kg·m−3. Uncertainties of the measurements are estimated to be within 3% for vapor isochores and 1.5% for the liquid isochores. In the region of the immediate vicinity of the critical point (0.97≤T/Tc≤1.03 and 0.75≤ρ/ρc≤1.25), the uncertainty is 4.5%. The original CV data were corrected and converted to the new ITS-90 temperature scale. A parametric crossover equation of state was used to represent the isochoric heat capacity measurements of heavy water in the extended critical region, 0.8≤T/Tc≤1.5 and 0.35≤ρ/ρc≤1.65. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and saturation densities were extracted from experimental data for each measured isochore. Most of the experimental data are compared with the Hill equation of state, and the overall statistics of deviations between experimental data and the equation of state are given.

The two-phase specific heat at constant volume of propane in the critical region

Abstract This paper contains the results of a new experimental study of two-phase specific heat at constant volume, Cv, and liquid-gas coexistence of propane near the critical point. The measurements cover the temperature range from 298 K to Tc and at densities from 61.88 to 480.8 kg m−3. The measurements were made in a high-temperature and high-pressure adiabatic constant-volume calorimeter. Uncertainties of the specific heats measurements are estimated to be less than ± 2%. The results are compared with earlier measurements. An analysis is presented of the experimental data on Cv and coexisting vapor-liquid densities in the critical region of propane. The model used is that of extended scaling, as given by the modern theory of critical phenomena. The results of Cv measurements have been used to calculate other thermodynamic properties on the coexistence curve.

Reference Correlation of the Thermal Conductivity of Sulfur Hexafluoride from the Triple Point to 1000 K and up to 150 MPa

This paper contains new, representative reference equations for the thermal conductivity of SF6. The equations are based in part upon a body of experimental data that has been critically assessed for internal consistency and for agreement with theory whenever possible. Although there are a sufficiently large number of data at intermediate temperatures, data at very low or very high temperatures as well as near the critical region are scarce. In the case of the dilute-gas thermal conductivity, a theoretically based correlation was adopted in order to extend the temperature range of the experimental data. Moreover, in the critical region, the experimentally observed enhancement of the thermal conductivity is well represented by theoretically based equations containing just one adjustable parameter. The correlations are applicable for the temperature range from the triple point to 1000 K and pressures up to 150 MPa. The overall uncertainty (considered to be estimates of a combined expanded uncertainty with a...