Correlation and prediction of dense fluid transport coefficients. VI.n-alcohols

A previously described method, based on considerations of hard-sphere theory, is used for the simultaneous correlation of the coefficients of viscosity, self-diffusion, and thermal conductivity for then-alcohols, from methanol ton-decanol, in excellent agreement with experiment, over extended temperature and pressure ranges. Generalized correlations are given for the roughness factors and the characteristic volume. The overall average absolute deviations of the experimental viscosity, self-diffusion, and thermal conductivity measurements from those calculated by the correlation are 2.4, 2.6, and 2.0%, respectively. Since the proposed scheme is based on accurate density values, a Tait-type equation was also employed to correlate successfully the density of then-alcohols. The overall average absolute deviation of the experimental density measurements from those calculated by the correlation is ±0.05%.     

Thermal conductivity of liquid n-alkanes

The thermal conductivity of liquids has been shown in the past to be difficult to predict with a reasonable accuracy, due to the lack of accurate experimental data and reliable prediction schemes. However, data of a high accuracy, and covering wide density ranges, obtained recently in laboratories in Boulder, Lisbon, and London with the transient hot-wire technique, can be used to revise an existing correlation scheme and to develop a new universal predictive technique for the thermal conductivity of liquid normal alkanes. The proposed correlation scheme is constructed on a theoretically based treatment of the van der Waals model of a liquid, which permits the prediction of the density dependence and the thermal conductivity of liquid n-alkanes, methane to tridecane, for temperatures between 110 and 370 K and pressures up to 0.6 MPa, i.e., for 0.3T/T _c0.7 and 2.4P/P _c3.7, with an accuracy of ±1%, given a known value of the thermal conductivity of the fluid at the desired temperature. A generalization of the hard-core volumes obtained, as a function of the number of carbon atoms, showed that it was possible to predict the thermal conductivity of pentane to tetradecane±2%, without the necessity of available experimental measurements.     

The Tait equation: 100 years on

The Tait equation, which is now widely used to fit liquid density data over wide pressure ranges, is a modification of the original equation of Tait, published 100 years ago, to fit his results on the compressibility of fresh water and seawater at different pressures. The range of applicability of these different equations is discussed and it is concluded that their simplicity and accuracy in reproducing high pressure density data for dense gases, liquids, solids, and liquid mixtures will ensure their continued use.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal conductivity of n-tridecane at pressures up to 500 MPa in the temperature range 35–75°C

Thermal conductivity coefficients are reported for liquid n-tridecane along three isotherms, 35, 48, and 73°C, and for pressures from 20 to 500 MPa. The measurements have been made with a transient hot-wire instrument, and the results, when corrected for the effects of radiation absorption, have an estimated uncertainty of ±0.7%. The thermal conductivity as a function of density along isotherms can be represented by means of the same form of equation as that found suitable for other normal alkanes, and this is based upon a heuristic modification of the van der Waals theory of liquids.     

The PVT behavior of liquid 1,1,1- and 1,1,2-trichloroethane

The PVT behavior of liquid 1,1,1- and 1,1,2-C₂H₃Cl₃ has been determined at 298.15, 323.15, 348.15, 373.15, and 398.15 K and at different pressures to about 100 MPa. The experimental results are shown in tabulated form. Specific volumes at high pressures are represented by the Tait equation. These results are also compared with the results obtained by a generalized Tait equation and other correlation methods. The generalized Tait equation is found to be more suitable to explain this study than the other correlations tested.     

PVT and derived thermodynamic properties for the glycine-water system at temperatures from 298 to 323 K and pressures up to 300 MPa

The specific volumes for the glycine-water system have been measured in the temperature range 298–323 K and at pressures up to 300 MPa, using a glass piezometer. The uncertainties in the specific volume are estimated to be less than 0.03%. The PVT relations are correlated by the Tait equation. Good agreement was found with correlations by the Tait equation using a simple extension similar to that proposed by Dymond and Malhotra. The isothermal compressibility and apparent molar volume of glycine are calculated by the Tait equation. The apparent molar volume of glycine increases with increasing pressure.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Corresponding-States Modeling of the Speed of Sound of Long-Chain Hydrocarbons

Models based on the corresponding-states principle have been extensively used for several equilibrium and transport properties of different pure and mixed fluids. Some limitations, however, have been encountered with regard to its application to long chain or polar molecules. Following previous studies, where it was shown that the corresponding-states principle could be used to predict thermophysical properties such as vapor–liquid interfacial tension, vapor pressure, liquid density, viscosity, and thermal conductivity of long-chain alkanes, the application of the corresponding-states principle to the estimation of speeds of sound, with a special emphasis on the less studied heavier n-alkane members, is presented. Results are compared with more than four thousand experimental data points as a function of temperature and pressure for n-alkanes ranging from ethane up to n-hexatriacontane. Average deviations are less than 2%, demonstrating the reliability of the proposed model for the estimation of speeds of sound.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.     

Pressure dependence of the density of n-alkanes

Accurate density data for n-alkanes are essential for the measurement of interfacial tension of liquid-liquid systems as a function of pressure. The variation of density with pressure for three n-alkanes, n-hexane, n-heptane, and n-decane, was measured at 21.2°C and pressures ranging from 0.1 to 35 MPa with a digital density meter. The Tait equation of the form (– ₀)/=C log[(B+P)/ (B+P₀)] was used to represent the experimental data.     

Vapor pressure and liquid and gas densities of 2,2,2-trifluoroethanol

Forty-three vapor pressures were measured for temperatures from the normal boiling point to the critical point. These data were obtained with a phase-equilibrium cell designed for precise static measurements at pressures up to 20 MPa. The cell is located within an oil-operated thermostatic bath which provides a homogeneous temperature field with variations less than ±1 mK. The vapor pressure data were fitted to a Wagner-type equation. Sixty-two liquid densities were measured on seven isotherms between 20 and 140°C for pressures up to 16 MPa. These measurements were carried out with a precision density meter operating on a vibrational technique. Sixty-nine gas-PVT triples were determined from Burnett expansion series on five isotherms between 140 and 200°C for pressures up to the saturation line. In all experiments, temperature measurements were made with platinum resistance thermometers. Precise pressure measurements were performed using a mercury column of 6-m height and a standard deadweight gauge for the higher pressures.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Viscosity and density of liquid mixtures ofn-alkanes with squalane

Viscosity and density measurements are reported for binary liquid mixtures ofn-butane andn-hexane with squalane in the temperature range from 273 to 333 K. The viscosity measurements have been carried out by using a capillary viscometer calibrated with standard liquids. that is. JS5, JSIO, JS20, and water. The uncertainty in the viscosity data was estimated to be ± 1.7%. The density needed for the calculation of the viscosity has been measured by using a glass pycnometer within an accuracy of ±0.04%. In the prediction of the viscosity, the scheme of Assael et al. fails for mixtures of this type differing greatly in size.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994. Boulder, Colorado, U.S.A.     

Transport properties of nonelectrolyte liquid mixtures—VII. Viscosity coefficients for isooctane and for equimolar mixtures of isooctane + n-octane and isooctane + n-dodecane from 25 to 100°C at pressures up to 500 MPa or to the freezing pressure

Changes in the high-pressure self-centering falling-body viscometer system, and the new automated data logging system, are described. Viscosity coefficient measurements made with an estimated accuracy of ± 2 % are reported for isooctane and for equimolar mixtures of isooctane + n-octane and isooctane + n-dodecane at 25, 50, 75, and 100°C at pressures up to 500 MPa or to the freezing pressure. The pressure dependence of the results is found to be represented equally well by the recent equation of Makita and by a free-volume form of equation. The Grunberg and Nissan equation gives a good fit to the mixture viscosity coefficient data.     

Volumetric and thermodynamic properties of liquid 2-fluoroethanol

p-V T data for liquid 2-fluoroethanol (FE) have been obtained in the form of volume ratios at six temperatures (278.15, 288.15, 298.14, 313.14, 323.14, and 338.130 K) at pressures from atmospheric to 314 MPa or higher. Freezing pressures have also been measured in the temperature range from the normal freezing point to 288 K. Densities at atmospheric pressure in the same temperature range as that for thep V T data are also reported. Isothermal compressibilities, isobaric expansivities, changes in the isobaric heat capacity, and internal pressures have been calculated from the volumetric data. Representation of the volume ratios for FE, 2,2-difluoroethanol, 2,2,2-trifluoroethanol, and ethanol by a form of the modified Tait equation shows that the effect of the progressive substitution of fluorine into ethanol cannot be represented by a simple correlation.     

An absolute vibrating-wire viscometer for liquids at high pressures

The design and operation of a new vibrating-wire viscometer for the measurement of the viscosity of liquids at pressures up to 100 MPa are described. The design of the instrument is based on a complete theory so that it is possible to make absolute measurements with an associated error of only a few parts in one thousand. Absolute measurements of the viscosity of n-hexane are reported at 298.15 K at pressures up to 80 MPa. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%, an estimate confirmed by the comparison of values of viscosity of slightly inferior accuracy.     

Thermodynamic properties of 2,2,2-trifluoroethanol

(p, V, T) data for 2,2,2-trifiuoroethanol (TFE) have been obtained in the form of volume ratios for six temperatures in the range 278.15 to 338.15 K for pressures up to 280 MPa. Isothermal compressibilities, isobaric expansivities, and internal pressures have been evaluated from the volumetric data. The compressibilities and internal pressures indicate that the behavior of TFE is closer to that of methanol than of ethanol for most of the pressure range. The use of only the present volumetric results together with the requirement that the B coefficient of the Tait equation should become equal to the negative of the critical pressure at the critical temperature provides interpolations and extrapolations up to 413 K of comparable accuracy.     

The viscosity of five liquid hydrocarbons at pressures up to 250 MPa

This paper reports new measurements of the viscosity of toluene, n-pentane, n-hexane, n-octane, and n-decane at pressures up to 250 MPa in the temperature range 303 to 348 K. The measurements were performed with a vibrating-wire viscometer and with a relative method of evaluation. Calibration of the instrument was carried out with respect to reference values of the viscosity of the same liquids at their saturation vapour pressure. The viscosity measurements have a precision of ±0.1% but the accuracy is limited by that of the calibration data to be ±0.5%. The experimental data have been represented by polynomial functions of pressure for the purposes of interpolation. The data are also used as the most precise test yet applied to a representation of the viscosity of liquids based upon hard-sphere theory.     

An improved algorithm for connectivity analysis of distribution networks

In the present paper, an efficient algorithm for connectivity analysis of moderately sized distribution networks has been suggested. Algorithm is based on generation of all possible minimal system cutsets. The algorithm is efficient as it identifies only the necessary and sufficient conditions of system failure conditions in n-out-of-n type of distribution networks. The proposed algorithm is demonstrated with the help of saturated and unsaturated distribution networks. The computational efficiency of the algorithm is justified by comparing the computational efforts with the previously suggested appended spanning tree (AST) algorithm. The proposed technique has the added advantage as it can be utilized for generation of system inequalities which is useful in reliability estimation of capacitated networks.     

A vibrating-rod densimeter

Measurements are reported that confirm the applicability of the theory of a vibrating-rod densimeter to a practical instrument. It is demonstrated that with such a device, liquid density measurements evaluated on an absolute basis can be made with an accuracy of ±0.2% at pressures up to 100 MPa. When the density of the liquid is evaluated on a relative basis, a precision of ±0.1% can be achieved over the same range of pressure. Future developments of the instrument that would greatly enhance its sensitivity and that rely upon the availability of a proven theory are therefore now possible.     

Correlation of high-pressure diffusion and viscosity coefficients for n-alkanes

Self-diffusion coefficient and viscosity coefficient data for liquid n-alkanes over the whole pressure range at different temperatures are satisfactorily correlated simultaneously by a method which is just an extension of that previously used to apply the smooth hard-sphere theory of transport properties to individual transport coefficients. Universal curves are developed for reduced quantities D ^* and ^* as a function of reduced volume. A consistent set of values is derived for the characteristic volume V ₀ and for parameters R _D and R , introduced to account for effects of nonspherical molecular shape and molecular roughness. On this basis, accurate calculation can be made of self-diffusion and viscosity coefficients for other members of the n-alkane series, for which data are at present limited.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Measurements of the viscosity of n-heptane,n-nonane,and n-undecane at pressures up to 70 MPa

New absolute measurements of the viscosity of n-heptane, n-nonane, and n-undecane are presented. The measurements were performed with a vibrating-wire instrument at temperatures of 303.15 and 323.15 K and pressures up to 70 MPa. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%. A recently developed semiempirical scheme for the correlation and prediction of the thermal conductivity, viscosity, and self-diffusion coefficients of n-alkanes is applied to the prediction of the viscosity of n-heptane, n-nonane, and n-undecane. The comparison of these predicted values with the present high-pressure measurements demonstrates the predictive power of this scheme.