J. H. Dymond

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.

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

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%.

Correlation and prediction of dense fluid transport coefficients: II. Simple molecular fluids

Abstract A previously-described method is used for the simultaneous correlation of the coefficients of selfdiffusion, viscosity and thermal conductivity for acetonitrile, carbon disulphide, tetrachloromethane, cyclohexane, ethene and trichloromethane at densities above the critical density. The method, which has been developed from consideration of exact hard-sphere theory of transport properties, introduces just two molecular parameters; a characteristic volume v 0 and a roughness factor R, which take into account departure from spherical shape and molecular roughness. Values are given for these parameters. For a given compound, V 0 is temperature dependent but has the same value, at a given temperature, for the different properties. The R factor has a different value for each property, but these are independent of temperature and density.

Standard Reference Data for the Viscosity of Toluene

Viscosity is an important transport property for the optimum design of a chemical process plant and for the development of molecular theories of the liquid state. A large amount of experimental viscosity data has been produced for all types of liquids, from alternative refrigerants to molten salts and molten metals. The accuracy of these data is related to the operating conditions of the instrument and, for this purpose as well as for the calibration of relative instruments, standard reference data for viscosity are necessary over a wide range of temperatures. New experimental data on the viscosity of liquid toluene along the saturation line have been obtained recently, mostly at low temperatures. The quality of the data is such that recommended values can be proposed with uncertainties of 0.5% (95% confidence level) for 260 K⩽T⩽370 K and 2% for 210 K⩽T<260 K and 370 K<T⩽400 K. A discussion about the uncertainties in the measurements and about the purity of the samples is made. The proposed value for the ...

Viscosity of Selected Liquid n‐Alkanes

A critical assessment has been made of the available experimental viscosity data for liquid n‐hexane, n‐heptane, n‐octane, n‐decane, n‐dodecane, and n‐tetradecane, with the aim of establishing standard reference values along the saturation line. Recommended viscosities are given at 298.15 K with an uncertainty conservatively estimated to be ±0.3%, except for n‐hexane and n‐heptane where it is 0.4%. Selected data which cover most of the normal liquid range are satisfactorily correlated using a modified form of Arrhenius equation. The estimated uncertainty in this correlation is ±0.5% for viscosities above 0.25 mPa s and ±1% for lower viscosities.

Correlation and prediction of dense fluid transport coefficients. III. n-alkane mixtures

Viscosity and thermal conductivity coefficients for binary, ternary, and quaternary n-alkane mixtures are predicted over extended ranges of temperature and pressure, in excellent agreement with experiment, by extension of a method recently described for the correlation of n-alkane transport coefficients. The outstanding advantage of this approach is that there are no adjustable parameters. Furthermore, in contrast with other mixture viscosity equations, this scheme does not require experimental viscosity coefficient data for the pure components under the same conditions of temperature and pressure.

An improved representation forn-alkane liquid densities

New experimental density data have been used to improve a recently published correlation ofn-alkane densities, based on the Tait equation. The new correlation covers then-alkanes from methane ton-hexadecane in an extended pressure range of up to 500 MPa in some cases. The overall average deviation of the experimental measurements of the density from those calculated by the correlation is ±0.10%. A simple extension to n-alkane mixtures gives a satisfactory prediction of the density compared with experimental data.

Correlation and prediction of dense fluid transport coefficients. V. Aromatic hydrocarbons

A previously described method, based on consideration of hard-sphere theory, is used for the simultaneous correlation of the coefficients of self-diffusion, viscosity, and thermal conductivity for benzene, toluene, o-, m-, and p-xylene, mesitylene, and ethylbenzene in excellent agreement with experiment, over extended temperature and pressure ranges. Values are given for the roughness factors RD, Rη, and Rλ, and the characteristic volume, V0, is expressed as a function of both carbon number and temperature.

Densities of n-alkanes and their mixtures at elevated pressures

Accurate density data for n-alkanes over a wide range of temperature and pressure have been used to test existing correlation and prediction methods. It is found that the most successful representation at temperatures up to 0.66 times the critical temperature and pressures up to 150 MPa is given by the Tait equation in the form (ρ−ρ0)/ρ=C log [(B + P)/(B + P0)], where subscript 0 refers to 0.101 MPa, with C equal to 0.2000, and [B+(Cn−6)], where Cn is the number of carbon atoms in the alkane chain, is a smooth function of reduced temperature. A simple extension of this method to mixtures gives an excellent prediction of densities at pressures up to 150 MPa over the same reduced temperature range.

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 η* as a function of reduced volume. A consistent set of values is derived for the characteristic volume V0 and for parameters RD and Rη, 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.