James C. Rainwater

Transport properties of a moderately dense gas

The initial density dependences of both viscosity and thermal conductivity are calculated according to a microscopically based theory which includes effects due to collisional transfer (from only free two-body phase space), three-monomer collisions, and monomer—dimer collisions. A Lennard-Jones potential is used to model the interactions. Comparison of the calculated results with experiment (in reduced form) shows very good agreement for both viscosity and thermal conductivity over a wide temperature range.

Critical locus, (vapor + liquid) equilibria, and coexisting densities of (carbon dioxide + propane) at temperatures from 311 K to 361 K☆

Isothermal (vapor + liquid) equilibria and coexisting densities for (carbon dioxide + propane) have been measured at (311.05, 327.75, 344.43, and 361.15) K from the vapor pressure of propane to the critical pressure of the mixture, and the critical locus has thus been determined. Away from the critical locus, our measurements agree within combined experimental uncertainties with those of Reamer, Sage, and Lacey. The measurements confirm the observation of Roof and Baron that the critical pressures reported by Poettmann and Katz and by Reamer et al. are substantially in error. The critical pressures from this study are lower than those of Reamer et al. by as much as 0.785 MPa and of Roof and Baron by as much as 0.034 MPa. The dew- and bubble-points are correlated by three methods, the Soave-Redlich-Kwong (SRK) equation, the DDMIX program of Ely, and the Leung-Griffiths model as modified by Moldover and Rainwater. Except for poor predictions of liquid densities by the SRK equation, all three models provide good correlations of the measurements, but the modified Leung-Griffiths model is superior very near the critical locus.

Binary collision dynamics and numerical evaluation of dilute gas transport properties for potentials with multiple extrema

Prediction of gaseous transport properties requires calculation of Chapman–Enskog collision integrals which depend on all possible binary collision trajectories. The interparticle potential is required as input, and for a variety of applications involving monatomic gases the Hulburt–Hirschfelder potential is useful since it is determined entirely from spectroscopic information and can accomodate the long‐range maxima and minima found in many systems. Hulburt–Hirschfelder potentials are classified into five distinct types according to their qualitative binary collision dynamics, which in general can be quite complex and can exhibit ’’double orbiting’’, i.e., a pair of orbiting impact parameters for a single energy of collision. The collision integral program of O’Hara and Smith has been revised extensively to accomodate all physical cases of the Hulburt—Hirschfelder potential, and the required numerical methods are described and justified. The revised program substantially extends the range of potentials f...

Liquid structure under shear: comparison between computer simulations and colloidal suspensions

Simulated scattered light intensity plots are calculated for a soft sphere inverse‐12 system subjected to a shear and are compared to experimental plots for a colloidal suspension under approximately equivalent conditions. The simulated plots were obtained by a Fourier transform of the radial distribution function. The two sets show points of striking similarity: The Debye–Scherrer rings become elliptical when both systems are subjected to the shear, and the light intensity around the rings is a function of polar angle. An interesting feature is the degree to which the experimental plots display non‐Newtonian characteristics of the suspension. Overall, the work is a direct comparison of the results of a computer simulation with real experimental data. Suggestions for future work are given.

On the phase space subdivision of the second virial coefficient and its consequences for kinetic theory

Two new methods of partitioning the second virial coefficient B into free, bound, and metastable parts, which differ from the well known partitioning of Stogryn and Hirschfelder, are presented. It is shown that the proper partitioning to use depends on the specific physical problem of interest. In particular, in the kinetic theory of moderately dense gases due to Curtiss, Snider, and co‐workers, certain collision integrals reduce unambiguously to linear sums of B and its temperature derivatives for repulsive potentials, but it has not been clear to what such integrals reduce for realistic potentials. It is shown that such integrals reduce to the previously derived expressions with B replaced by one of our two new definitions of its free part. This contrasts with previous applications to real gases in which Curtiss and co‐workers have used the full B and Kuznetsov has used the free part of B as defined by Stogryn and Hirschfelder. Also, original numerical calculations for the collision integrals are presen...

CROSSOVER LEUNG-GRIFFITHS MODEL AND THE PHASE BEHAVIOR OF DILUTE AQUEOUS IONIC SOLUTIONS

A new parametric crossover model for the phase behavior of a binary mixture is presented that corresponds to the Leung–Griffiths model in the critical region and is transformed into the regular classical expansion far away from the critical point. The model is optimized to, and leads to excellent agreement with, isothermal vapor–liquid equilibrium data for dilute aqueous solutions of sodium chloride by Bischoff and co-workers. It then accurately predicts constant-composition phase equilibrium loci as measured by independent workers. This crossover model is therefore capable of representing the thermodynamic surface of ionic solutions in a large range of temperatures and densities around the critical points of vapor–liquid equilibrium.

Extended law of corresponding states and thermodynamic properties of binary mixtures in and beyond the critical region

Abstract A parametric crossover equation of state for pure fluids which incorporates the scaling laws asymptotically close to the critical point and is transformed into the regular classical expansion far away from the critical point is adapted to binary mixtures. An isomorphic generalization of the law of corresponding states is applied to the prediction of the thermodynamic properties and the phase behavior of binary mixtures over a wide region around the locus of vapor-liquid critical points. Methane-ethane and methane-propane are used as reference mixtures, and model parameters for other mixtures are determined completely from excess critical compressibility factors. A comparison is made with the experimental data for twelve binary mixtures. The crossover equation yields a satisfactory representation of the thermodynamic property data in a large range of temperatures and densities. Results for the ammonia-water mixture are consistent with an independent classical correlation.

Interfacial tension and vapor–liquid equilibria in the critical region of mixtures

In the critical region, the concept of two‐scale‐factor universality can be used to accurately predict the surface tension between near‐critical vapor and liquid phases from the singularity in the thermodynamic properties of the bulk fluid [M. R. Moldover, Phys. Rev. A 31, 1022 (1985)]. In the present work, this idea is generalized to binary mixtures and is illustrated using the data of Hsu, Nagarajan, and Robinson for CO2+n‐butane. We fit the pressure‐temperature‐composition‐density data for coexisting, near‐critical phases of the mixtures with a thermodynamic potential comprised of a sum of a singular term and nonsingular terms. The nonuniversal amplitudes characterizing the singular term for the mixtures are obtained from the amplitudes for the pure components by interpolation in a space of thermodynamic ‘‘field’’ variables. The interfacial tensions predicted for the mixtures from the singular term are within 10% of the data on three isotherms in the pressure range (Pc−P)/Pc<0.5. This difference is com...

Improved initial density dependence of the viscosity and a corresponding states function for high pressures

The initial density correction to gaseous viscosity using accurate realistic potentials of the noble gases is evaluated using the Rainwater–Friend theory. It is shown that this theory works satisfactorily for densities up to about 2moldm−3. Due to the superimposability of the noble gas potential functions, a universal function of the reduced second viscosity virial coefficient is obtained over the entire reduced temperature range. At densities beyond the range of the theory, a variant of the excess viscosity is developed, by which the viscosity of the different gases can be easily calculated above the critical temperature for pressures up to 900MPa. The accuracy of this method is within the experimental uncertainties.

Binary mixtures in and beyond the critical region: thermodynamic properties

Abstract An extended law of corresponding states, in combination with a parametric crossover equation of state, is applied to the prediction of thermodynamic properties and phase behavior of pure fluids and binary mixtures over a wide region around vapor–liquid critical points. For pure fluids, a generalized form of the model is given that requires only the acentric factor of the pure component. For mixtures, the critical locus is also required. A good representation of thermodynamic property data is achieved in the range of temperatures 0.8 Tc(x)≤T≤1.5 Tc(x) and densities 0.35 ρc(x)≤ρ≤1.65 ρc(x).