Binary Diffusion Coefficients of Acetone in Carbon Dioxide at 308.2 and 313.2 K in the Pressure Range from 7.9 to 40 MPa

Binary diffusion coefficients of acetone in carbon dioxide were measured by the Taylor dispersion method at 308.2 K and 7.9 to 40 MPa and at 313.2 K and 8.0 to 37 MPa. The D ₁₂ values obtained from the response curves by the method of fitting in the time domain were more accurate than those obtained by the moment method. At pressures lower than about 8.3 MPa at 308.2 K or 9.1 MPa at 313.2 K, the accuracy in the D ₁₂ values was found to decrease significantly with decreasing pressure by examining (peak area)×u _{a, cal}, the values of S ₁₀, the fitting error , and u _{a, cal}/u _{a, exp} as a function of pressure. The D ₁₂ values at pressures higher than 8.3 MPa at 308.2 K or 9.1 MPa at 313.2 K were well represented with the Schmidt number correlation. The D ₁₂ data with larger fitting errors (>0.01) showed larger deviations from the values predicted by this correlation.     

Infinite-Dilution Binary Diffusion Coefficients of 2-Propanone, 2-Butanone, 2-Pentanone, and 3-Pentanone in CO2 by the Taylor Dispersion Technique from 308.15 to 328.15 K in the Pressure Range from 8 to 35 MPa

Infinite-dilution binary diffusion coefficients of 2-propanone, 2-butanone, 2-pentanone, and 3-pentanone in carbon dioxide were measured by the Taylor dispersion method at temperatures from 308.15 to 328.15 K and pressures from 7.60 to 34.57 MPa. The D ₁₂ values were obtained from the response curves by the method of fitting in the time domain. The accuracy in the fitting error was examined for each measurement. The measured D ₁₂ data were found to be well correlated by the Schmidt number correlation, with AAD%=3.74% for all solutes.     

Infinite Dilution Binary Diffusion Coefficients of Benzene in Carbon Dioxide by the Taylor Dispersion Technique at Temperatures from 308.15 to 328.15 K and Pressures from 6 to 30 MPa

Infinite dilution binary diffusion coefficients, D ₁₂, of benzene in carbon dioxide were measured by the Taylor dispersion technique at temperatures from 308.15 to 328.15 K and pressures from 6 to 30 MPa. The diffusion coefficients were obtained by the method of fitting in the time domain from the response curves measured with a UV–vis multidetector by scanning from 220 to 280 nm at increments of 1 or 4 nm. The wavelength dependences on the binary diffusion coefficient and the uncertainty were examined. The detector linearity, in terms of the relationship between the absorbance intensity and the product of the peak area of the response curve and CO₂ velocity, was found to fail at some characteristic absorption wavelengths such as 243, 248, 253, and 259 nm, even when the maximum absorbance intensities of the response curves were less than 0.5 and the fits were good. Although the D ₁₂ values obtained from the response curves measured at 253 nm were almost consistent with some literature data, the D ₁₂ values measured at wavelengths showing the detector linearity to be satisfactory, i.e., at 239 nm, were higher than those at 253 nm. The present D ₁₂ data at 239 nm were well represented by the Schmidt number correlation, except for those showing the anomalous decrease in a plot of D ₁₂ vs density in the density range from 250 to 500 kg·m^–3.     

Transport Properties of Nonelectrolyte Liquid Mixtures. XI. Mutual Diffusion Coefficients for Toluene+n-Hexane and Toluene+Acetonitrile at Temperatures from 273 to 348 K and at Pressures up to 25 MPa

Mutual diffusion coefficients,D ₁₂, have been measured at pressures up to 25 MPa using the chromatographic peak broadening technique (Taylor dispersion method) forxtoluene+(1–x)n-hexane in the temperature range 298 to 348 K and forxtoluene+(1–x) acetonitrile in the temperature range 273 to 348 K. The estimated uncertainty is ±4%. Both systems show negative deviations from straight-line behavior. The fractional decrease inD ₁₂is about 0.8% per MPa. Hard-sphere theory is applied under limiting conditions where one of the components is present in a trace amount. It is shown that the diffusion coefficients can be estimated by the Dullien method from a knowledge of the viscosity and density under the same conditions.     

Measurements of the virial coefficients and equation of state of the carbon dioxide+ethane system in the supercritical region

Gas-phase densities of the system carbon dioxide+ethane were measured with a Burnett apparatus at 320 K and at pressures up to approximately 10 MPa. Measurements were made on systems having carbon dioxide mole fractions of 0, 0.25166, 0.49245, 0.73978, and 1. Second and third virial coefficients were determined for each composition, and the cross virial coefficients were calculated. Comparisons were made with other recent high-quality measurements on this system. For each mixture compositionPT measurements were made on five isochores having densities within ±30% of the critical density. Temperatures varied from 288 to 320 K. The two-phase boundary was determined and estimates are given forT _c andP _c for each composition.     

Correlation and prediction of dense fluid transport coefficients. I. n-alkanes

Recent accurate measurements of the self-diffusion coefficient for n-hexadecane and n-octane and of the viscosity coefficient for n-heptane, n-nonane, and n-undecane over wide pressure ranges have been used to provide a critical test of a previously described method, based on consideration of hard-sphere theory, for the correlation of transport coefficient data. It is found that changes are required to the universal curve for the reduced viscosity coefficient as a function of reduced volume and, also, to the parameters R _D, R , and R which were introduced to account for effects of nonspherical molecular shape. The scheme now accounts most satisfactorily for the self-diffusion, viscosity, and thermal conductivity coefficient data for all n-alkanes from methane to hexadecane at densities greater than the critical density.     

Hyperbaric reservoir fluids: High-pressure phase behavior of asymmetric methane +n-alkane systems

In this paper, experimental three-phase equilibrium (solidn-alkane + liquid + vapor) data for binary methane +n-alkane systems are presented. For the binary system methane + tetracosane, the three-phase curve was determined based on two phase equilibrium measurements in a composition range fromx _c24 = 0.0027 tox _c24 = 1.0. The second critical endpoint of this system was found atp = (1114.7 ± 0.5) M Pa.T = (322.6 ± 0.25) K, and a mole fraction of tetracosane in the critical fluidphase ofx _c24 = 0.0415 ± 0.0015. The second critical endpoint occurs where solid tetracosane is in equilibrium with a critical fluid phase (S _c24 +L =V). For the binary systems of methane with then-alkanes tetradecane, triacontane, tetracontane, and pentacontane, only the coordinates of the second critical endpoints were measured. The second critical endpoint temperature is found close to the atmospheric melting point temperature of then-alkane. The pressures at the second critical endpoints do not exceed 200 MPa. Based on these experimental data and data from the literature, correlations for the pressure. temperature, and fluid phase composition at the second critical endpoint of binary methane +n-alkane systems withn-alkanes between octane and pentacontane were developed.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Zr-Hf interdiffusion in polycrystalline Y2O3-(Zr+Hf)O2

Lattice and grain-boundary interdiffusion coefficients were calculated from the concentration distributions determined for Zr-Hf interdiffusion in polycrystalline 16Y₂O₃·84(Zr_1–x Hf _x )O₂ withx=0.020 and 0.100. The lattice interdiffusion coefficients were described byD=0.031 exp [–391 (kJ mol^–1)/RT] cm² sec^–1 and the grain-boundary diffusion parameters byD=1.5×10^–6exp [–309(kJ mol^–1)/RT] cm³ sec^–1 in the temperature range 1584–2116° C. Comparison of the results with those for the systems CaO-(Zr+Hf)O₂ and MgO-(Zr+Hf)O₂ indicated that the Zr self-diffusion coefficient was insensitive to the dopants in the fluorite-cubic ZrO₂ solid solutions.     

A new apparatus for the measurement of the isobaric heat capacity of liquid refrigerants

A new automated adiabatic flow calorimeter was developed which enables one to measure the isobaric heat capacity, C _p, of pure fluids and their mixtures in the liquid phase. The calorimeter has been carefully designed to keep the heat loss from the sample fluid as small as possible being regarded as negligible. The experimental apparatus constitutes a closed circuit of the sample circulation using a combination of two mounted metallic bellows and a metering pump. The present apparatus is designed to measure C _p at temperatures to 500 K and pressures to 15 MPa and is also applicable to measurements in the critical region as well as the region near the saturated liquid state because of its excellent mass flow rate control stability and the high adiabatic efficiency of the calorimeter. The C _p of liquid refrigerant 114 (R114) has been measured at temperatures from 275 to 415 K and pressures up to 3.2 MPa including the critical region with experimental uncertainty of less than ±0.4%. The heat capacity of saturated liquid R114 has also been derived from the data measured in the single phase.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity and viscosity of 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123)

The thermal conductivity and the viscosity data of CFC alternative refrigerant HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane: CHCI₂-CF₃) were critically evaluated and correlated on the basis of a comprehensive literature survey. Using the residual transport-property concept, we have developed the three-dimensional surfaces of the thermal conductivity-temperature-density and the viscosity-temperature-density. A dilute-gas function and an excess function of simple form were established for each property. The critical enhancement contribution was taken no account because reliable crossover equations of state and the thermal conductivity data are still missing in the critical region. The correlation for the thermal conductivity is valid at temperatures from 253 to 373 K, pressures up to 30 MPa, and densities up to 1633 kg m^–3. The correlation for the viscosity is valid at temperatures from 253 to 423 K, pressures up to 20 MPa. and densities up to 1608 kg·m^–3. The uncertainties of the present correlations are estimated to be 50% for both properties, since the experimental data are still scarce and somewhat contradictory in the vapor phase at present.     

Special Equations of State for Methane,Argon, and Nitrogen for the Temperature Range from 270 to 350 K at Pressures up to 30 MPa

In order to describe the thermodynamic behavior of methane, argon, and nitrogen in the so-called “natural-gas region,” namely, from 270 to 350 K at pressures up to 30 MPa as accurate as possible with equations of a very simple form, new equations of state for these three substances have been developed. These equations are in the form of a fundamental equation in the dimensionless Helmholtz energy; for calculating the pressure or the density, the corresponding equations explicit in pressure are also given. The residual parts of the Helmholtz function representing the behavior of the real gas contain 12 fitted coefficients for methane, 8 for argon, and 7 for nitrogen. The thermodynamic relations between the Helmholtz energy and the most important thermodynamic properties and the needed derivatives of the equations are explicitly given; to assist the user there is also a table with values for computer-program verification. The uncertainties when calculating the density ρ, the speed of sound w, the isobaric specific heat capacity c _p, and the isochoric specific heat capacity c _v are estimated as follows. For all three substances it is Δρ/ρ≤±0.02 % for p≤ 12 MPa and Δρ/ρ ≤ ±0.05% for higher pressures. For methane it is Δw/w≤±0.02% for p≤10 MPa and Δw/w≤+-0.1% for higher pressures; for argon it is Δw/w?-0.1 % for p≤ 7 MPa, Δw/w≤±0.3 % for 7 <p≤30 MPa; and for nitrogen it is Δw/w≤±0.1% for p≤1.5 MPa and Δw/w±0.5% for higher pressures. For all three substances it is Δc _p/c _p≤±1 % and ΔC _v/C _v≤±1 % in the entire range.     

Equations for the viscosity and thermal conductivity coefficients of methane

An equation is proposed to calculate the viscosity and thermal conductivity coefficients of methane from the dilute gas to the dense liquid. The range of validity of the equation is approximately 95–400 K for pressures up to 50 MPa (～500 atm). The reliabilities of the coefficients calculated are estimated at approximately 2% and 5% for the viscosity and thermal conductivity coefficients, respectively. The equation includes a contribution for the thermal conductivity enhancement in the critical region.     

Measurement of Diffusion in Ternary Liquid Mixtures by Light Scattering Technique and Comparison with Taylor Dispersion Data

Results of diffusion coefficient measurements by dynamic light scattering (DLS) in the ternary liquid systems, glycerol–acetone–water (GAW), and cyclohexane–methanol–toluene (CMT), are reported. Data for the GAW system are compared with Taylor dispersion (TD) measurements in overlapping concentration regions close to the critical solution point at 298.15 K. A fit of the intensity autocorrelation function (ACF) could be used to predict values and explain the physical character of the corresponding diffusion coefficients. In the vicinity of the critical solution point, the DLS measurements reveal two and more hydrodynamic relaxation modes with well separated characteristic relaxation times. From the ACF, at least two effective diffusivities, D ₁ and D ₂, can be experimentally determined. Theoretical predictions reveal that they may result from pure mass diffusion and pure thermal diffusion transport processes. A possible physical meaning of the modes D ₁ and D ₂ in the ternary liquid mixtures is discussed. When we compare the transport modes from DLS with the Taylor dispersion results, only the slowest mode represents mass diffusion, and this mode agrees very well with one of the eigenvalues of Fick’s diffusion matrix. There is no relation between the mass diffusion mode from DLS and any one of the four diffusion coefficients obtained by TD.     

A Generalized Model for the Thermodynamic Properties of Mixtures

A mixture model explicit in Helmholtz energy has been developed which is capable of predicting thermodynamic properties of mixtures containing nitrogen, argon, oxygen, carbon dioxide, methane, ethane, propane, n-butane, i-butane, R-32, R-125, R-134a, and R-152a within the estimated accuracy of available experimental data. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real gas) contribution, and the contribution from mixing. The contribution from mixing is given by a single generalized equation which is applied to all mixtures studied in this work. The independent variables are the density, temperature, and composition. The model may be used to calculate the thermodynamic properties of mixtures at various compositions including dew and bubble point properties and critical points. It incorporates accurate published equations of state for each pure fluid. The estimated accuracy of calculated properties is ±0.2% in density, ±0.1 % in the speed of sound at pressures below 10 MPa, ±0.5% in the speed of sound for pressures above 10 MPa, and ±1% in heat capacities. In the region from 250 to 350 K at pressures up to 30 MPa, calculated densities are within ±0.1 % for most gaseous phase mixtures. For binary mixtures where the critical point temperatures of the pure fluid constituents are within 100 K of each other, calculated bubble point pressures are generally accurate to within ±1 to 2%. For mixtures with critical points further apart, calculated bubble point pressures are generally accurate to within ±5 to 10%.     

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 T _S () were measured isochorically using a quasi-static thermogram method. The uncertainty of the phase transition temperature measurements is about ±0.02 K. The measured C _V 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 T _S – _S measurements for D₂O near the critical point.     

A kinetic study of the silver-mercury contact reaction

The solid-liquid diffusion couple technique was employed to determine the interdiffusion coefficient of the gamma phase in the Ag-Hg contact reaction. Diffusion coefficients were calculated with the aid of an equation given by Wagner. The composition range of the gamma phase was determined to be between 55.3 and 57.5 at% by electron microprobe analysis, and values for the average interdiffusion coefficient of the gamma phase were found to beD _av(cm²sec^–1)=3.181×10^–5exp (–32539 (J mol^–1)/RT) in the temperature range 40 to 115° C. The amalgamation reaction between silver and liquid mercury proceeded with the formation of gamma phase and a solid solution of Ag-Hg. The growth of gamma phase followed a parabolic rate law. The penetration of liquid mercury into grain boundary of the gamma phase caused the gamma to be crumbled off. The possibility of short-circuit diffusion is discussed.     

Study of interdiffusion and growth of topologically closed packed phases in the Co–Nb system

Interdiffusion study of the Co–Nb system is conducted to determine the diffusion parameters in different phases. The integrated diffusion coefficients at different temperatures are calculated for the Nb₂Co₇ phase, which has very narrow composition range. The interdiffusion coefficients at different compositions in the NbCo₂ Laves phase are determined. The interdiffusion coefficient in this phase decreases with increasing Nb content to the stoichiometric composition. Further, the average interdiffusion coefficient in the N₆Co₇-μ phase is determined. The activation energies for diffusion in different phases are calculated, providing valuable information regarding the diffusion mechanism. In addition, an experiment using Kirkendall markers is conducted to calculate the relative mobilities of the species.     

Vacancy Assisted Motion of Charges in Quantum Crystals

From comparison of results of measurements of diffusion coefficients D(T) of the positively and negatively charged complexes (charges), created under irradiation in perfect crystals, grown from pure helium or hydrogen at small pressures, with diffusion coefficients of the isotopic impurities or the self-diffusion coefficients known from NMR studies one can conclude that motion of the more mobile charges through these crystals (of positive charges in HCP ⁴ He, ³ He and D ₂ samples and of negative charges in BCC ⁴ He and ³ He and also in HCP crystals, grown from pure p–H ₂ ) is vacancy assisted. Thus strong departures of the temperature dependencies of diffusion coefficients of the positive charges D ₊(T) in HCP ⁴ He samples and of the negative charges D _–(T) in p–H ₂ samples from the simple Arrhenius type of behavior D= D ₀ exp[–G/T] at low temperatures can be attributed to the change of the mechanism of diffusion of thermal vacancies: from classical thermally activated hopping of the localized vacancies near T _melt to the band motion of delocalized vacancions at T< T _melt/2. To explain the nature of the maxima on the D ₊(T) curves observed in perfect ⁴ He crystals, it may be assumed that the flow conditions of the vacancion gas around a positive charge (a probe particle with an effective radius of a few lattice constants) can change significantly with lowering the temperature: from a hydrodynamic flow of the viscous gas round the probe at the transition temperatures to a kinetic flow of the rarefied vacancion gas at low temperatures. In this case the bandwidth of the vacancions in studied ⁴ He samples is near Q _V 10^–4 K.     

Thermodynamic and transport properties of 1, 2-dichloroethane

(p, V, T) data for dichloroethane (DCE) have been obtained at 278.15, 288.15, 298.15, 313.15, 323.15, and 338.15 K for pressures either slightly below the freezing pressure or up to a maximum of 280 M Pa, together with densities at 0.1 MPa. A high-pressure self-centering falling-body viscometer method has been used to measure shear viscosities at 278.15, 288.15, 298.15, 313.15, and 323.15 K for pressures either slightly below the freezing pressure or up to a maximum of 330 MPa. Self-diffusion coefficients for DCE are reported at 278.15, 288.15, 298.15, and 313.15 K for maximum pressures up to 300 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The shear viscosities and self-diffusion coefficients have been interpreted in terms of a modified rough hard-spheres theory. The anomalous behavior observed for p-V-T, shear viscosities, and self diffusion at higher temperatures and pressures is suspected to be the result of temperature and pressure altering the population ratio of the two molecular conformers, trans and gauche.     

n-hexane as a model for compressed simple liquids

Isobaric thermal expansivities, _p, ofn-hexane have been measured by pressure-controlled scanning calorimetry from just above the saturation vapor pressure to 40 MPa at temperatures from 303 to 453 K and to 300 MPa at 503 K. These new data are combined with literature data to obtain a correlation equation for _p valid from 240 to 503 K at pressures up to 700 MPa. Correlation equations are developed for the saturated vapor pressure, specific volume, and isobaric heat capacity of liquid n-hexane from 240 to 503 K. Calculated volumes, isobaric and isochoric specific heat capacities. isothermal compressibilities, and thermal coefficients of pressure are presented for the entire range of pressure and temperature. The pressure-temperature behavior of these quantities is discussed as a model behavior for simple liquids without strong intermolecular interactions.