Orthobaric Liquid Research Articles

Chemical potentials and phase equilibria of Lennard-Jones chain fluids

Computer simulations (molecular dynamics) were performed for ensembles of flexible tangent Lennard-Jones chains consisting of n sites (n = 1, 2, 4, 8, and 16). From these simulations, the orthobaric liquid and vapour densities were calculated not only with the traditional method of simulating a liquid film in coexistence with vapour, but also using the rigorous thermodynamic condition of satisfying the chemical potential equality between the phases in equilibrium. The agreement with literature data, as far as such exist, is excellent.

Molecular dynamics simulation of potassium along the liquid-vapor coexistence curve

The applicability of pair potential functions to liquid alkali metals is questionable. On the one hand, some recent reports in the literature suggest the validity of two-parameter pair-wise additive Lennard-Jones (LJ) potentials for liquid alkali metals. On the other hand, there are some reports suggesting the inaccuracy of pair potential functions for liquid metals. In this work, we have performed extensive molecular dynamics simulations of vapor-liquid phase equilibria in potassium to check the validity of the proposed LJ potentials and to improve their accuracy by changing the LJ exponents and taking into account the temperaturedependencies of the potential parameters. We have calculated the orthobaric liquid and vapor densities of potassium using LJ (12–6), LJ (8.5–4) and LJ (5–4), effective pair potential energy functions. The results show that using an LJ (8.5–4) potential energy function with temperature-independent parameters, e and σ, is inadequate to account for the vapor-liquid coexistence properties of potassium. Taking into account the temperature-dependencies of the LJ parameters, e(T) and σ(T), we obtained the densities of coexisting liquid and vapor potassium in a much better agreement with experimental data. Changing the magnitude of repulsive and attractive contributions to the potential energy function shows that a two-parameter LJ (5–4) potential can well reproduce the densities of liquid and vapor potassium. The results show that LJ (5–4) potential with temperature-dependent parameters produces the densities of liquid and vapor potassium more accurately, compared to the results obtained using LJ (12–6) and LJ (8.5–4) potential energy functions.

Coexistence Densities of Methane and Propane by Canonical Molecular Dynamics and Gibbs Ensemble Monte Carlo Simulations

We present preliminary canonical molecular dynamics (MD) and Gibbs ensemble Monte Carlo (GEMC) results for the vapour-liquid orthobaric densities of methane and propane. Computational advantages and drawbacks of both simulation methods are discussed and future work is outlined on the application of these techniques to the calculation of transport and interfacial properties. n -Alkanes are described through the TraPPE-UA force field. We study the effect of the truncation of interactions in the Lennard-Jones potential on the accuracy of the orthobaric liquid densities for these inhomogeneous systems along the phase diagram. We observed that a cut-off of at least 5.5 times the Lennard-Jones diameter is needed to obtain accurate results for saturated liquid densities.

Corresponding-states correlation for the saturated liquid density of metals and metal mixtures

A corresponding-states correlation for the prediction of the orthobaric liquid density of molten metals has been developed. The correlation is the extension of the recently developed correlation by Iglesias-Silva and Hall, which needs the values of the critical and triple point constants as well as an adjustable parameter. The critical constants are scarce for almost all metals. Our corresponding-states correlation uses the normal boiling and melting point constants plus an adjustable parameter. While the present correlation is simpler in form than the correlation by Iglesias-Silva and Hall, all of its input data are more readily available for almost all metals. In this work, we have applied the present correlation to molten alkali metals, mercury, bismuth, tin, and lead. From about 150 data points for pure liquid metals the average absolute deviation and the maximum deviation are 0.29 and 1.06%, respectively. Also, we have extended the correlation to mixtures of any number of components. The predicted results for the liquid densities of K–Cs and K–Na mixtures over the whole range of concentrations and that of a ternary molten eutectic of K–Na–Cs at temperatures ranging from melting point up to several hundred degrees above the normal boiling point are in excellent agreement with experimental data. From 247 data points examined for molten alloys, the average absolute deviation and the maximum deviation are 0.59 and 1.91%, respectively.

Dimerization and thermodynamic properties of nitric oxide

Measurements are presented of p-v-T properties of saturated and compressed liquid nitric oxide which complete an earlier report. It can be shown that literature values on the critical properties are in error. The new estimations are T c = 177 K, p c = 5.834 MPa, and v c = 70.62 cm 3mol −4, with an uncertainty (due to extrapolation) of 0.5 % in T c and 3 % in p c and v c (the four digits in p c and v c are given because of use in subsequent calculations). The anomalies of the temperature dependencies of orthobaric liquid volume, vapour pressure, and isothermal compressibility are characterized and explained by the varying degree of dimerization. The amount of dimers could be quantitatively estimated by a novel form of the theory of corresponding states for mixtures.

Excess properties and phase equilibria calculated from a generalized van der Waals equation of state for the example of the mixture methane + ethane

A generalized van der Waals equation of state, formulated recently for pure non-polar substances, is now adapted for the treatment of mixture. The main contribution to the van der Waals attractive term, the critical temperature T c, is now considered as a mixture parameter for the equivalent substance (the one-fluid mixture model). It is determined from the orthobaric liquid density of the mixture, i.e. from the excess volume. All other parameters are supposed to be additive in mole fraction. With these mixing rules, the equation gives good agreement for the excess Gibbs energy of methane + ethane over a larger temperature range. The phase equilibria are calculated according to the algorithm of Deiters (1985) and cover the whole range of temperatures and composition up to the critical curve. Apart from the immediate neighborhood of the critical points of the mixtures, the agreement is very satisfactory. The densities in the homogeneous region and the interaction second virial coefficients are also well reproduced.

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric densities of tetramethylsilane and 2,2-dimethylpropane have been measured by means of a hydrostatic density balance. For tetramethylsilane the liquid density has been determined from 289.73 K to the critical point 448.60 K and the vapor density from 353.55 K to the critical point, while for 2,2-dimethylpropane the liquid density has been measured from 290.88 K to the critical point 433.71 K and the vapor density from 349.01 K to the critical point. The results are represented well by the extended-scaling equation of Wegner with three correction terms and the critical indices α, β, and Δ1, obtained from renormalization-group theory. The fit is not improved by a term expressing an anomaly in the diameter using either of the exponents (1−α) or 2β. The critical density for tetramethylsilane is estimated as (0.2436±0.0001) g·cm−3 and that for 2,2-dimethylpropane as (0.2318±0.0001) g·cm−3.

Neutron-diffraction study of liquid hydrogen iodide.

Neutron-diffraction experiments on liquid DI, HI, and on an equimolar mixture of HI and DI are presented. All these three samples were in the same thermodynamic state corresponding to the orthobaric liquid at T=253 K. The three partial structure factors ${\mathit{S}}_{\mathrm{II}}$(Q), ${\mathit{S}}_{\mathrm{HI}}$(Q), ${\mathit{S}}_{\mathrm{HH}}$(Q) are derived exploiting the standard isotopic substitution procedure. The corresponding pair correlation functions ${\mathit{g}}_{\mathrm{II}}$(r), ${\mathit{g}}_{\mathrm{HI}}$(r), and ${\mathit{g}}_{\mathrm{HH}}$(r) are evaluated and compared with those given by a model that neglects all orientational correlations. Our data indicate that ${\mathit{g}}_{\mathrm{II}}$(r) (which is essentially the center-center correlation function) is well reproduced by the pair distribution function of a monatomic Lennard-Jones fluid and that ${\mathit{g}}_{\mathrm{HI}}$(r) (which should be sensitive to the correlations between molecular and intermolecular axes) is very similar to the one derived neglecting orientational correlations. On the contrary, orientational correlations between the molecular axes are clearly present in the ${\mathit{g}}_{\mathrm{HH}}$(r), which deviates significantly from the uncorrelated model results. These facts are consistent with the idea that H bonding is not present in liquid HI and indicate also that the only relevant terms of the anisotropic intermolecular potential are those due to the electric multipolar interactions.

Structure of the He-Xe mixture near the 30-MPa demixing curve at T=294 K.

We report measurements of the neutron-scattering differential cross section for the He-Xe mixture in the two coexisting states at T=294 K on the 30-MPa isobaric section of the demixing surface corresponding to Xe molar concentration of 0.78 and 0.48, respectively, and for pure orthobaric liquid Xe having the same number density as in the 0.78 mixture. From these data, the total structure factors have been extracted. For the same thermodynamic states we also performed molecular-dynamics simulations using different interatomic potentials. Analyzing the partial pair-correlation functions, we find that, as already found at lower pressure, in this case, where the He concentration is noticeably higher, the partial structure factor of Xe is also essentially unaffected by the presence of He. This supports a simple picture of the He-Xe gas-gas demixing transition in terms of the liquid-gas transition of pure Xe. Analyzing the He-Xe correlations in the mixture, we also discuss the role played by He in the gas-gas immiscibility transition.

Statistical-mechanical theory of a new analytical equation of state

We present an analytical equation of state based on statistical-mechanical perturbation theory for hard spheres, using the Weeks–Chandler–Andersen decomposition of the potential and the Carnahan–Starling formula for the pair distribution function at contact, g(d+), but with a different algorithm for calculating the effective hard-sphere diameter. The second virial coefficient is calculated exactly. Two temperature-dependent quantities in addition to the second virial coefficient arise, an effective hard-sphere diameter or van der Waals covolume, and a scaling factor for g(d+). Both can be calculated by simple quadrature from the intermolecular potential. If the potential is not known, they can be determined from the experimental second virial coefficient because they are insensitive to the shape of the potential. Two scaling constants suffice for this purpose, the Boyle temperature and the Boyle volume. These could also be determined from analysis of a number of properties other than the second virial coefficient. Thus the second virial coefficient serves to predict the entire equation of state in terms of two scaling parameters, and hence a number of other thermodynamic properties including the Helmholtz free energy, the internal energy, the vapor pressure curve and the orthobaric liquid and vapor densities, and the Joule–Thomson inversion curve, among others. Since it is effectively a two-parameter equation, the equation of state implies a principle of corresponding states. Agreement with computer-simulated results for a Lennard-Jones (12,6) fluid, and with experimental p–v–T data on the noble gases (except He) is quite good, extending up to the limit of available data, which is ten times the critical density for the (12,6) fluid and about three times the critical density for the noble gases. As expected for a mean-field theory, the prediction of the critical constants is only fair, and of the critical exponents is incorrect. Limited testing on the polyatomic gases CH4, N2, and CO2 suggests that the results for spherical molecules (CH4) may be as good as for the noble gases, nearly as good for slightly nonspherical molecules (N2), but poor at high densities for nonspherical molecules (CO2). In all cases, however, the results are accurate up to the critical density. Except for the eight-parameter empirical Benedict–Webb–Rubin equation, this appears to be the most accurate analytical equation of state proposed to date.

ChemInform Abstract: Orthobaric Liquid Densities of Trichlorofluoromethane, Dichlorodifluoromethane, Chlorodifluoromethane, 1,1,2‐Trichlorotrifluoroethane, 1,2‐Dichlorotetrafluoroethane, and of the Azeotropic Mixture of (Chlorodifluoromethane + Chloropentafluoroethane) Between 203 and 463 K.

Chemischer InformationsdienstVolume 17, Issue 39 Article ChemInform Abstract: Orthobaric Liquid Densities of Trichlorofluoromethane, Dichlorodifluoromethane, Chlorodifluoromethane, 1,1,2-Trichlorotrifluoroethane, 1,2-Dichlorotetrafluoroethane, and of the Azeotropic Mixture of (Chlorodifluoromethane + Chloropentafluoroethane) Between 203 and 463 K. M. OKADA, M. OKADASearch for more papers by this authorM. UEMATSU, M. UEMATSUSearch for more papers by this authorK. WATANABE, K. WATANABESearch for more papers by this author M. OKADA, M. OKADASearch for more papers by this authorM. UEMATSU, M. UEMATSUSearch for more papers by this authorK. WATANABE, K. WATANABESearch for more papers by this author First published: September 30, 1986 https://doi.org/10.1002/chin.198639085AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue39September 30, 1986 RelatedInformation

Orthobaric liquid densities of trichlorofluoromethane, dichlorodifluoromethane, chlorodifluoromethane, 1,1,2-trichlorotrifluoroethane, 1,2-dichlorotetrafluoroethane, and of the azeotropic mixture of (chlorodifluoromethane + chloropentafluoroethane) between 203 and 463 K

The orthobaric liquid densities of six halogenated hydrocarbons: trichlorofluoromethane (CCl 3F), dichlorodifluoromethane (CCl 2F 2), chlorodifluoromethane (CHClF 2), 1,1,2-trichlorotrifluoroethane (CCl 2FCClF 2), 1,2-dichlorotetrafluoroethane (CClF 2CClF 2), and of (0.6321CHClF 2 + 0.3679CClF 2CF 3), an azeotropic mixture, have been measured. Measurements were carried out with a magnetic densimeter for temperatures from 203 K up to a temperature close to the critical. An accuracy of ±0.1 per cent except for the results at temperatures above 423 K was confirmed by examining the present measurements for orthobaric (liquid + gaseous) water. The temperature dependence of the orthobaric liquid density has been correlated analytically on the basis of the present results and the more reliable of the reported measurements critically evaluated by the present authors.

Description of polyatomic real substances by two-center Lennard-Jones model fluids

Bohn, M., Lustig, R. and Fischer, J., 1986. Description of polyatomic real substances by two-center Lennard-Jones model fluids. Fluid Phase Equilibria, 25: 251–262. For O 2, CO, CS 2, C 2H 4, Cl 2 and Br 2 orthobaric properties were calculated by perturbation theory on the basis of two-center Lennard-Jones (2CLJ) model molecules. The LJ-parameters σ and ε were determined by fitting the vapour pressure and the bubble density at one temperature about halfway between the triple point and 0.8 T c. The elongation L in the model was fixed to give the correct temperature variation of the vapour pressure. The temperature variation of the orthobaric liquid density turned out to be less dependent on L, and could be satisfactorily reproduced. With the parameters determined from the orthobaric properties of the liquid, second virial coefficients were calculated. This was also done for Ar, Kr, Xe, CH 4, N 2, F 2 and C 2H 6 for which the parameters have been determined previously in a similar way. The agreement between the predicted and the experimental second virial coefficients is excellent for C 2H 4 and C 2H 6. For O 2, N 2, CO and F 2 it is still better than for the spherical molecules. The agreement for Cl 2 and CS 2 is less satisfactory.

Orthobaric liquid densities and dielectric constants of ethylene

Measurements of the orthobaric liquid densities and dielectric constants of ethylene have been obtained at temperatures from 200 to 270 K. Simultaneous measurements of these properties were carried out using a magnetic suspension densimeter and a concentric cylinder capacitor. Comprehensive comparisons of the present results with the data of other investigators are presented. Also reported are computed values of the Clausius-Mossotti function.

A Generalized van der Waals Equation of State IV. Corrections for Medium and Low Densities for the Example of Methane

AbstractAn equation of state, recently developed for high densities, is extended to the whole density range and is compared to tabulated values of the thermodynamic data of methane. The agreement is very satisfactory. At subcritical temperatures, the parameters can be derived from second virial coefficient, vapour pressure, orthobaric liquid volume, and isothermal compressibility. At supercritical temperatures, the number of necessary p‐ν‐T measurements can be considerably reduced in comparison to conventional equations of state.

ChemInform Abstract: ORTHOBARIC LIQUID DENSITIES AND DIELECTRIC CONSTANTS OF (METHANE + 2‐METHYLPROPANE) AND (METHANE + N‐BUTANE) AT LOW TEMPERATURES

Chemischer InformationsdienstVolume 15, Issue 2 Article ChemInform Abstract: ORTHOBARIC LIQUID DENSITIES AND DIELECTRIC CONSTANTS OF (METHANE + 2-METHYLPROPANE) AND (METHANE + N-BUTANE) AT LOW TEMPERATURES W. M. HAYNES, W. M. HAYNESSearch for more papers by this author W. M. HAYNES, W. M. HAYNESSearch for more papers by this author First published: January 10, 1984 https://doi.org/10.1002/chin.198402072Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue2January 10, 1984 RelatedInformation

Orthobaric liquid densities and dielectric constants of (methane+2-methyl-propane) and (methane+ n-butane) at low temperatures

Measurements of the orthobaric liquid densities and dielectric constants of methane-rich (methane+2-methylpropane) and (methane+ n-butane) have been obtained at temperatures between 110 and 140 K. Densities were determined with a magnetic-suspension densimeter, while a concentric-cylinder capacitor was used for simultaneous measurements of dielectric constant. These measurements were part of an experimental program that has provided a consistent and comprehensive set of densities for the major components of liquefied natural gas (LNG) and their mixtures, which was used to develop mathematical models for the calculation or prediction of LNG densities. Along with the (methane+2-methylpropane) and (methane+ n-butane) experimental densities and dielectric constants, are presented experimental vapor pressures, as well as excess volumes, Clausius-Mossotti functions, and excess Clausius-Mossotti functions, derived from the densities and dielectric constants. Comparisons are shown between the excess volumes of the present work and those from independent measurement using an extended corresponding-states model that had been optimized to the results from this work. The total uncertainty of a single density measurement is approximately 0.1 per cent with a precision of a few parts in 10 4. Dielectric constants are estimated to be accurate to approximately 0.05 per cent. A brief description of the apparatus, experimental method, and procedures is also presented.

Prediction of liquefied natural gas (LNG) densities from new experimental dielectric constant data

A concentric cylinder capacitor has been used to measure the orthobaric liquid dielectric constants of multicomponent mixtures of the major components of liquefied natural gas (LNG) to an accuracy of approximately ± 0.05% at temperatures from 110 to 130 K. These mixtures ranged from a ternary mixture containing nitrogen, methane, and normal butane to four to eight component methane rich (74 to 90 mol %) mixtures containing up to 5 mol % of nitrogen, 16 mol % of ethane, 7 mol % of propane, 5 mol % of the butanes, and 0.44 mol % of the pentanes. Some of these mixtures were prepared to simulate commercial LNG compositions. Experimental densities previously reported for these mixtures have been combined with the mixture dielectric constant data to calculate values of the Clausius-Mossotti (CM) function and the excess CM function. Pure component experimental CM functions for LNG components except for propane and isobutane have been combined with the mixture data in the development of a simple calculational technique for the prediction of LNG densities to an uncertainty of approximately ± 0.15% based on a knowledge of the composition and dielectric constant of the liquid mixtures. In fitting the data, pseudo values of the CM function are derived for the slightly polar components, propane and isobutane, while constraining the mixture excess CM function to be zero.

On the dynamical properties of liquid hydrogen chloride: a light scattering experiment

Depolarized rotovibrational Raman spectra of orthobaric liquid HCl are studied to obtain information on the molecular reorientational motion. Second order spectral moments are obtained and the presence of collision induced scattering is discussed, while fourth spectral moments are used to obtain values of mean square intermolecular torques. Orientational correlation functions and correlation times are studied and a comparison with other experimental data is made. The liquid is dominated by strong anisotropic forces at low temperature and is collision limited on approaching the critical point. A comparison is made with the quasi-lattice random jump model and with generalized hydrodynamics and it is found that a fair rotational coherence is necessary to explain the viscosity dependence of the correlation times below 250 K.