Calculation of thermodynamic properties and transport coefficients for SF6-N2 mixtures in the temperature range 1,000–30,000 K

We have computed the equilibrium composition, the transport coefficients (viscosity, electrical and thermal conductivities), the thermodynamic properties (Gibbs and Helmholtz potentials, entropy, enthalpy, specific heats), and the derived quantities (mass density, sound velocity) for SF₆-N₂ mixtures in conditions relevant to circuit-breaker arcs: temperatures between 1000 and 30,000 K, pressures in the range 1–10 atm. The validity of our computation has been checked by a detailed comparison of our results with those available in the literature concerning pure SF₆ and pure N₂. In SF₆-N₂ mixtures the chemical reactions (dissociation, ionization) have a strong influence on thermal conduction and heat capacities. The effect of SF₆ on the properties of such mixtures is elucidated: in a mixture containing 40% SF₆, the amplitude of the thermal conduction peak appearing around 7500 K is reduced by a factor of 4 relative to that of pure N₂. The influence of pressure on the properties of the plasma between 1 and 10 atm is relatively low.     

Calculation of thermodynamic and transport properties of a typical arc furnace plasma

Using a previously developed computer program, thermodynamic and transport properties of a typical arc furnace plasma are calculated in order to single out those species and / or reactions which exert a dominating influence on the properties of such complex mixtures. The results indicate that dissociation of molecular species in the arc furnace atmosphere has a strong effect on the specific heat and on the thermal conductivity of the mixture. The electrical conductivity is strongly affected by metallic vapors from the molten metal pool and the slag cover.     

Transport coefficients of air,argon-air,nitrogen-air,and oxygen-air plasmas

Calculated values of the viscosity, thermal conductivity and electrical conductivity of air and mixtures of air and argon, air and nitrogen, and air and oxygen at high temperatures are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. The calculations, which assione local thermodynamic equilibrium, are performed for atmospheric pressure plasmas in the temperature range from 300 to 30,000 K. The results for air plasmas are compared with those of published theoretical and experimental studies. Significant discrepancies are found with the other theoretical studies; these are attributed to differences in the collision integrals used in calculating the transport coefficients. A number of the collision integrals used here are significantly more accurate than values used previously, resulting in more reliable values of the transport coefficients.     

A parametric study of electron energy distribution functions and rate and transport coefficients in nonequilibrium helium plasmas

Electron energy distribution functions in helium plasmas have been calculated by solving the Boltzmann equation at given values of reduced electric field, in the presence of superelastic and electron-electron collisions. Analytical expressions have been found connecting macroscopic coefficients to reduced electric field E/N, relative metastable concentration [He(2³S)]/N, and degree of ionization n_e/N.     

Critical analysis of viscosity data of thermal argon plasmas at atmospheric pressure

Reliable values of the viscosity in thermal argon plasmas are most important for our understanding of the momentum transfer and for realistic modeling of various plasma applications. Despite numerous attempts to determine reliable viscosity values over the last three decades, discrepancies still exist among the data reported by different authors. In this paper, a critical analysis is undertaken of calculated and experimental data of the argon viscosity based on recent publications. Our recalculation of viscosities in thermal argon plasmas are performed by using Lennard-Jones, Morse, Aziz, and exponential repulsive potentials for Ar-Ar atom interactions in different temperature ranges from 300 to 20,000 K. The contributions of elastic collisions of e-Ar, e-Ar⁺, and Ar⁺-Ar, as well as charge exchange of Ar⁺-Ar, to the viscosity become important with increasing temperature and degree of ionization in argon plasmas. Based on a critical analysis and recalculations, improved values of the argon viscosity are recommended, covering temperatures from 300 to 20,000 K. Polynomial expressions have been developed for calculating argon viscosities, which will be useful for numerical work and other applications of thermal argon plasmas at atmospheric pressure.     

Model calculations for Setchenow coefficients

The calculations of Setchenow coefficients reported earlier [H. L. Friedman, C. V. Krishnan, and C. Jolicoeur,Ann. N.Y. Acad. Sci. 204, 79 (1973)] have been extended to aqueous solutions of various nonelectrolytes mixed with alkali or alkylammonium halides. A few data for Setchenow coefficients in methanol have also been treated. The GurneyA _ij parameters for nonelectrolyte-ion interactions in models which fit the data are mostly negative, and more so the larger the solute molecules. A value ofA _ij near-100 cal-mole^–1 seems to characterize hydrophobic bonding. In several systems these is evidence that some nonsolvation contribution to theu _ij pair potential which is not explicitly accounted for in the models is important in the real systems. Quite possibly this contribution is due to dispersion forces or to the chargepolarizability interaction. On the whole, theA _ij parameters do not seem to depend upon the charges on solute particlesi andj; this is evidence that the model is fairly realistic.     

Transport coefficients of argon,nitrogen, oxygen,argon-nitrogen,and argon-oxygen plasmas

Calculated values of the viscosity, thermal conductivity, and electrical conductivity of argon, nitrogen, and oxygen plasmas, and mixtures of argon anti nitrogen and of argon anti oxygen, are presented. In addition, combined ordinary, pressure, and thermal diffusion coefficients are given for the gas mixtures. These three combined diffusion coefficients fully describe di fusion of the two gases, irrespective of their degree of dissociation or ionizati on. The calculations, which assume local thermodynamic equilibrium, are performed! for atmospheric-pressure plasmas in the temperature range /torn 300 to 30,000 K. A number of the collision integrals used in calculating the transport coefficients are significantly more accurate than values used in previous theoretical studies, resulting in more reliable values of the transport coefficients. The results are compared with those of published theoretical and experimental studies.     

A compact formulation for multi-component transport coefficients in gas mixtures

A linearly independent set of generalized cross-sections and their ratios is identified to describe all the elements of the system matrices needed to evaluate transport coefficients in dilute, field-free, gas mixtures with an arbitrary number of polyatomic species. The cross-section ratios are also defined in terms of more customary collision integrals and are related to a number of macroscopic observables. The practical advantages of the proposed formulation when performing calculations of transport coefficients for computationally demanding flow simulations are discussed.     

Ion channel gating and proton transport

A model of ion channel gating has been proposed (J. Biomol. Struct. Dyn. 19 (2002) 725). It includes the following. (1) There is a bacterial channel for which an X-ray structure is known (KcsA) that opens (‘gates’) with a drop in pH. In the proposal, a proton gates this channel by adding a charge to the glutamate residues that form the center of the gating region. It is postulated that two water molecules form a strong short hydrogen bond when the glutamates plus the water have a −2 charge. Adding a proton leads to a normal, weak, hydrogen bond, and the groups can separate, opening the channel. 98 calculations support this part of the proposal (J. Phys. Chem. B 105 (2001) 5298). (2) Voltage gated channels contain six transmembrane (TM) segments in each of four domains. We suggest that the additional four TM segments (KcsA has two) act as a voltage-to-proton current transducer. In the model, the first step in gating is proton tunneling (J. Phys. Chem. A 102 (1998) 7181), followed by a proton cascade. Calculations supporting the latter step are presented here. One of the eukaryotic TM segments, S4, is known to be involved in gating. This segment has arginines (occasionally lysine) at every third amino acid. The arginines appear capable of transmitting a proton, or possibly a proton cascade (three per S4 would produce the observed charge movement (‘gating current’) that precedes gating). We have carried out density functional calculations, using 98, on a system that includes: one pair of guanidinium groups, the side chains of arginines responsible for carrying the proton current; a mobile proton; one, two or three water molecules. Several guanidinium spacings have been tried, all in the range of carbon–carbon distances 4–6 Å. The potential energy surface was computed for each, and a minimum path found for the proton, at B3LYP/6-311G** level. It was found that the proton, under some conditions, could follow a path between guanidiniums that had no barriers greater than a few kT (thermal energy), thereby supporting the proposal that protons could move along the chain of guanidiniums.     

On the accuracy of non-equilibrium transport coefficients calculation

The algorithms of non-equilibrium transport coefficients calculation in reacting gas mixtures are discussed. The influence of the molecular interaction potential on the transport properties is estimated in the various temperature ranges.     

Prediction of thermodynamic, transport and vapor-liquid equilibrium properties of binary mixtures of ethylene glycol and water

Equilibrium and non-equilibrium molecular dynamics and Monte Carlo simulation techniques were applied to predict various thermodynamic, transport and vapor-liquid equilibrium properties of binary mixtures of ethylene glycol and water (EG-W) based on OPLS-AA and SPC/E force fields. The properties predicted include density, vaporization enthalpy, enthalpy of mixing, heat capacities, diffusion coefficients, shear viscosities, thermal conductivities, vapor-liquid coexistence isotherms and isobaric curves, and saturation vapor pressures. Good agreements with experimental data were obtained for most of these properties. Errors are mostly related to inaccuracy found in predictions of pure fluids; a correction to prediction of pure substance can systematically improve prediction for the mixture. This work suggests that OPLS-AA and SPC/E force fields using the common combining rules are transferable for predicting multiple physical properties of EG-W mixtures.     

Electron energy distribution functions and rate and transport coefficients of H2/H/CH4 reactive plasmas for diamond film deposition

Electron energy distribution functions (eedf) and rate and transport coefficients for H₂/H/CH₄ mixtures have been calculated by solving a stationary Boltzmann equation as a function of reduced electric field E/N, of molar fraction, and of different concentrations of electronically excited states. Superelastic electronic collisions superimpose structures to eedf especially for E/N values < 40 Td.     

Experimental and theoretical studies on vibrational spectra of 4-(2-furanylmethyleneamino)antipyrine, 4-benzylideneaminoantipyrine and 4-cinnamilideneaminoantipyrine

This work deals with the IR and Raman spectroscopy of 4-(2-furanylmethyleneamino) antipyrine (FAP), 4-benzylideneaminoantipyrine (BAP) and 4-cinnamilideneaminoantipyrine (CAP) by means of experimental and quantum chemical calculations. The equilibrium geometries, harmonic frequencies, infrared intensities and Raman scattering activities were calculated by density functional B3LYP method with the 6-31G(d) basis set. The comparisons between the calculated and experimental results covering molecular structures, assignments of fundamental vibrational modes and thermodynamic properties were investigated. The optimized molecular geometries have been compared with the experimental data obtained from XRD data, which indicates that the theoretical results agree well with the corresponding experimental values. For the three compounds, comparisons and assignments of the vibrational frequencies indicate that the calculated frequencies are close to the experimental data, and the IR spectra are comparable with some slight differences, whereas the Raman spectra are different clearly and the strongest Raman scattering actives are relative tightly to the molecular conjugative moieties linked through their Schiff base imines. The thermodynamic properties (heat capacities, entropies and enthalpy changes) and their correlations with temperatures were also obtained from the harmonic frequencies of the optimized strucutres.     

Determination of concentration-dependent transport coefficients in nanofiltration: Experimental evaluation of coefficients

To characterize solute transport in nanofiltration (NF) the Spiegler–Kedem equation requires that two coefficients be determined for two-component solutions (a solute in water), solute permeability ω and reflection coefficient σ. For salts both coefficients strongly and in a complex way depend on concentration, which greatly complicates their evaluation from experiments. For this reason, the parameters are usually assumed constant for a given feed and the concentration dependence is assessed from flux–rejection curves for several feeds. This procedure however ignores the fact that the solute concentration and hence the coefficients significantly vary across the membrane. One way to overcome this inconsistency and address concentration dependence is to use physical models explicitly introducing exclusion mechanism(s) and fitting relevant membrane-specific parameters, such as fixed charge or dielectric properties. This procedure often fails to produce unique values of parameters for a given membrane and different salts. In the present study a new phenomenological approach is proposed and critically analyzed, based on the assumption of a similar concentration dependence of ω and 1 − σ, previously shown to be valid under fairly general conditions, thereby the Peclét coefficient A = (1 − σ)/ω may be assumed to be independent of concentration. The coefficients and their concentration dependence for a given solute may be directly and consistently evaluated by fitting flux–rejection data for several feeds and fluxes to numeric solution of the modified transport equations without the need to invoke specific physical models. The values of transport parameters deduced in this way for representative membranes and salts allow important conclusions regarding the transport mechanism. In particular, the roles of different mechanisms in overall salt exclusion could be addressed directly from the variation of ω or 1 − σ with concentration. On the other hand, the value of the Peclét coefficient, free of the effect of salt partitioning, may be analyzed in terms of hindered transport. Using the proposed method, this value was found to be very small for studied thin-film composite membranes, which may significantly simplify the transport equations.     

Gas sorption and transport properties of bisphenol-I-polycarbonate

Gas sorption and transport characterization of a new polymer in the polycarbonate family, based on the bisphenol of 3,3,5-trimethylcyclohexane-1-one (BPI) is reported at 35°C. By comparison with properties of other known polycarbonates, the effects of inhibition of both packing and segmental motion due to the introduction of the bulky substituent in the backbone are elucidated. The T_g of the material was measured with differential scanning calorimeter (DSC) and was found to be unusually high for a polycarbonate (233°C). This indicates a successful inhibition of the large-scale segmental mobility of the polymer. Variable ¹³C NMR analysis indicated that rotation of one phenylene ring has an unusually high (ca. 10 kcal) energy barrier, whereas the other phenylene ring has a more typical rotation profile (barrier < 3 kcal). The density was measured and found to be low (1.107 g/cm³), indicating a high fractional free volume (FFV) for the polymer. Consistent with expectations, the introduction of the bulky-substituted cyclohexane group gave high permeabilities for the various gases tested (N₂, O₂, He, CH₄, CO₂) compared to most standard polycarbonates. On the other hand, the permselectivities were typical for standard polycarbonates. The solubility coefficients of all gases were rather high, as expected for a polymer with such an open structure. © 1994 John Wiley & Sons, Inc.     

Rationalizing the meaning of coefficients in Flory-Huggins approach to polymer-solvent interactions

The Flory-Huggins interaction parameter for a polymer solution can be represented as the product of two functions, which separately take into account the effects of the polymer volume fraction and temperature. The latter factor contains three constants, usually viewed as best-fit coefficients. They are expressed in terms of two thermodynamic quantities, namely, the excess partial molar heat capacity of the solution and a reference temperature, thus allowing to guess their physical meaning. The formulae so obtained were tested with satisfactory results for two solutions of polystyrene in acetone and for two polymer blends (PC/PMMA and PS/PVME.) Furthermore, an attempt was made to calculate the above-mentioned reference temperature from data referring to the phases in solution.     

Charge transport in stacking metal and metal‐free phthalocyanine iodides. Effects of packing,dopants, external electric field,central metals,core modification,and substitutions

The charge‐transport properties of the one‐dimensional stacking metal phthalocyanine iodides (M(Pc)I, M = Fe, Co, Ni, Cu) and metal‐free phthalocyanine iodide (H₂(Pc)I) have been theoretically investigated. On the basis of the tight‐binding approximation and two‐state theory, both the site‐energy corrected energy splitting in dimer and Fock‐matrix‐based methods are used to calculate the transfer integral. The intermolecular motions, including interplanar translation, rotation, slip, and tilt, exert remarkable impacts on the transfer integral. The order/disorder of the dopant stack and the long‐range electrostatic interactions are also demonstrated to be crucial factors for modulation of charge‐transport properties. The transfer integral undergoes slight changes under an applied electric field along the stacking direction in the range of 10⁶ ? 10⁷ V cm^?1. The change of central metals in MPc has little effect on the transfer integrals, but significantly affects the reorganization energies. The extension of the π‐conjugation in macrocyclic ligand brings about considerable influence on the transfer integrals. Peripheral substitutions by animo, hydroxyl, and methyl lead to deviations from planarity of macromolecular rings, and hence affect the valence bands significantly. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Higher order hydrodynamic interactions in the calculation of polymer transport properties

Higher order hydrodynamics interactions are short-range modifications to the Oseen tensor T _ij and its self-interaction counterpart T _ii. They differ from the Oseen tensor in having terms of higher order than the first in a/R, a being a bead radius and R being a bead-bead distance. Effects of higher order hydrodynamic interactions on whole chain–whole chain hydrodynamic interactions are here computed. Higher order hydrodynamic interactions are shown to lead to a concentration dependence of the diffusion and friction coefficients of a free monomer. However, while higher order interactions make contributions of the same nature to the drag coefficients of a monomer and of a whole chain, the contributions are not simply multiplicative, removing a justification for the common practice of correcting polymer solution transport data for “monomer friction effects” via a normalization with data on friction coefficients of free monomers. © 1993 John Wiley & Sons, Inc.     

Thermoelectric properties of two-dimensional ternary transition metal nitrides HfNF

The exceptional electron transfer properties and low thermal conductivity of two-dimensional layered materials render them a promising choice for thermoelectric applications. In this study, we explore the stability, electronic properties, and thermoelectric characteristics of materials composed of two-dimensionally layered transition metal nitride HfNF. Our research findings show that the structure of HfNF is stable and exhibits the properties of a direct bandgap semiconductor. Furthermore, we employ the Boltzmann transport theory and Slack model to investigate the thermoelectric properties of HfNF within the temperature range of 300 to 900 K. The HfNF materials exhibit relatively large thermoelectric dominance values ( $$ values), with the $$-type HfNF demonstrating a maximum $$ value of 1.46. Furthermore, utilizing the quasi-harmonic Debye model, thermodynamic properties such as heat capacity, coefficient of thermal expansion, and bulk modulus within the 6 GPa and 600 K range are estimated. Based on these calculations, it is predicted that two-dimensional HfNF materials will serve as promising new materials for thermoelectric applications spanning from 300 to 900 K.