G. V. Stepanov

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.

Isochoric Heat Capacity Measurements for 0.5 H2O + 0.5 D2O Mixture in the Critical Region

The isochoric heat capacity CV of an equimolar H2O+D2O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kg⋅m−3. A high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter was used. The measurements were performed in the one- and two-phase regions including the coexistence curve. The uncertainty of the heat-capacity measurement is estimated to be ±2%. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from the experimental data for each measured isochore. The critical temperature and the critical density for the equimolar H2O+D2O mixture were obtained from isochoric heat capacity measurements using the method of quasi-static thermograms. The measurements were compared with a crossover equation of state for H2O+D2O mixtures. The near-critical isochoric heat capacity behavior for the 0.5 H2O+0.5 D2O mixture was studied using the principle of isomorphism of critical phenomena. The experimental isochoric heat capacity data for the 0.5 H2O+0.5 D2O mixture exhibit a weak singularity, like that of both pure components. The reliability of the experimental method was confirmed with measurements on pure light water, for which the isochoric heat capacity was measured on the critical isochore (321.96 kg⋅m−3) in both the one- and two-phase regions. The result for the phase-transition temperature (the critical temperature, TC, this work=647.104±0.003 K) agreed, within experimental uncertainty, with the critical temperature (TC, IAPWS=647.096 K) adopted by IAPWS.

The critical properties of binary mixtures containing carbon dioxide: Experimental data

Results are given of comprehensive analysis of the behavior of critical lines of binary mixtures which have CO2 as one of the components. Methods are considered of measuring the critical properties TC, PC, and ρC of pure substances and mixtures and the accuracy of these methods. Data from different sources on the critical properties of CO2 + soluble substance (SS) binary mixtures are compared for determining the quality and reliability of some or other results and their consistency, and recommendations are given for using these results for scientific and technological purposes. The effect is discussed of the shape of critical lines of CO2 + SS binary mixtures on the behavior of their phase diagrams. The classification of phase diagrams is given depending on the behavior of critical lines, and the effect of the properties of SS (shape, size of molecules, and specific interactions between CO2 and SS molecules) on the behavior of critical lines is investigated.

The experimental investigation of Cv,x, P, V, T properties and the equation of state of the n-hexane-water system

Abstract Experimental investigations of the Cv,x, P, V, T properties in the n-hexane-water system with the different compositions (x) 0.121, 0.200, 0.247, 0.256, 0.301, 0.345 and 0.615 molar fraction (m.f.) H2O were made with a high-temperature adiabatic calorimeter. The mixtures with 0.256 and 0.615 m.f. H2O were studied over the wide range of densities (ϱ) from 208.6 to 399.6 kg m−3 and from 191.4 to 416.7 kg m−3, respectively. For the description of some of the thermodynamic properties of the n-hexanewater binary system, the equation of state proposed by Jin et al. was used.

The Critical Properties of Binary Mixtures Containing Carbon Dioxide: Krichevskii Parameter and Related Thermodynamic Properties

The values of Krichevskii parameter are given, which are calculated using the data on critical lines for binary CO2 + solute mixtures (n-alkanes, alcohols, refrigerants, inert gases, water, diatomic gases, and other organic compounds), and detailed comparison is made with the results of other researchers obtained using different measuring techniques. In this review, special attention is given to the investigation of the thermodynamic (partial molar properties, Henry’s constant, distribution coefficient, solubility, and others) and structural (direct and total correlation integrals, size of clusters) properties of infinitely dilute solutions (IDS) of CO2 + solute in the vicinity of the critical point (CP) of pure solvent (CO2), for which purpose the values of Krichevskii parameter and the properties of pure solvent are used. The procedure is given of estimating the effect of small impurities on the accuracy of determination of the critical parameters of pure substances. The importance of critical lines (pattern and qualitative form) and of the Krichevskii parameter in the investigation of the scaling behavior (renormalization of the critical behavior) of thermodynamic functions of IDS in the vicinity of the CP of pure CO2 is discussed in detail. The boundaries are determined of regions in the T-x and Δρ-x planes, in which the renormalization is observed of the critical behavior of weakly divergent (isochoric heat capacity) and highly divergent (isobaric heat capacity and isothermal compressibility) properties in CO2 + solute mixtures.

Experimental study of the isochoric heat capacity and coexistence-curve singular diameter of sec-butanol near the critical point and Yang-Yang anomaly strength

One- and two-phase isochoric heat capacities ( ) and saturated liquid and vapour densities ( , and ) of sec-butanol near the critical point have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were made in the temperature range from 307 K to 551 K for 22 liquid and vapour isochores from 76.44 to 794.06 kg m−3. The isochoric heat capacity jump (quasi-static thermograms supplemented by the sensor of adiabatic control) technique have been used to accurately measure of the phase transition parameters ( ) near the critical point. The total experimental uncertainty of density ( ), temperature ( ) and isochoric heat capacity ( ) measurements were estimated to be 0.06%, 15  mK and 2–3%, respectively. The critical temperature (  = 535.95 ± 0.02 K) and the critical density (  = 276.40 ± 2 kg m−3) for sec-butanol were determined from the measured saturated properties ( ,  ) near the critical point. The measured and saturated density ( ) data near the critical point have been analysed and interpreted in terms of extended scaling theory for the selected thermodynamic paths (critical isochore and coexistence curve) to accurately calculate the values of the asymptotical critical amplitudes of heat capacity ( ) and coexistence curve ( ). The measured thermodynamic properties ( , ) of sec-butanol near the critical point were also interpreted in terms of the ‘complete scaling’ theory of critical phenomena and the theory of logarithmic singularity of . In particular, the contributions of the ‘incomplete’ ( ) and ‘complete’ ( ) scaling terms on the coexistence-curve singular diameter were estimated. We determined the values of the asymmetry parameters and of the ‘complete’ scaling theory of coexistence curve singular diameter. The strength of the Yang-Yang anomaly R μ for sec-butanol was estimated using asymmetry parameters and the contribution of the second temperature derivative of vapour-pressure and chemical potential in the singularity of two-phase isochoric heat capacity, , at the critical point.

A model approach to the thermodynamics of microemulsion systems: Estimation of adequacy of the two-phase model of microemulsions

An approach to the thermodynamics of microemulsions based on the use of the two-phase model was suggested. In this model, one phase is the dispersion medium, and the other, the sum of disperse phase nanodrops. Experimental estimation of the adequacy of this approach showed that the model can be used to quantitatively satisfactorily solve microemulsion thermodynamics problems. The degree of two-phase model inadequacy did not exceed 10%.

Critical properties of aqueous solutions. P. II

Results from a detailed study are presented in which we analyzed the shape of critical lines of binary aqueous solutions like H2O + common salt and H2O + hydrocarbon. We also present the results from a comparative analysis of data on the critical parameters of such solutions reported in the literature. The critical lines of the solutions are analyzed in different projections. Accuracy, reliability, and consistency of the data considered are estimated, and recommendations on using them for scientific and practical purposes are given.

Critical properties of aqueous solutions. Part 1: Experimental data

All data available in the literature on the critical properties of binary aqueous solutions like H2O + common salt, H2O + hydrocarbon, H2O + alcohol, H2O + gas, and others are gathered. Methods for determining them are presented together with errors and concentration measurement intervals for each source of data. The format in which the data are presented will allow the readers to quickly find the necessary information on the critical properties of aqueous solutions from the original sources and use them for solving scientific and engineering tasks. Certain general features of the critical lines and phase diagrams of aqueous solutions with volatile and nonvolatile components are discussed.