Transfer properties of mixtures of rarefied neutral gases. Hydrogen–argon system

A method is proposed for generalization of the transport properties of mixtures of rarefied gases on the basis of their particle-interaction potentials and relations of the molecular-kinetic theory. A simultaneous processing of data on the viscosity of a binary Ar–H₂ mixture and its components as well as data on the concentrationdiffusion and thermal-diffusion coefficients of this mixture has been carried out by the weight method. The parameters of three functions of the Lennard-Jones (m–6) potential of interaction between the Ar atoms and H₂ molecules in the indicated mixture were determined. Tables of reference data on the transport properties of the Ar–H₂ mixture at a temperature of 200–2000 K and a concentration x(Ar) varying from 0 to 1 were calculated.     

Modeling of capillary pressure hysteresis and of hysteresis of relative phase permeabilities in porous materials on the basis of the pore ensemble concept

We propose a class of models of porous media based on the pore ensemble concept with a certain distribution of the main geometric parameters (e.g., pore size). The case of the saturation of the pore space with a two-phase liquid mixture has been considered. The transfer laws are deduced from the free energy dissipation condition. The hydrodynamic connection of pores is described by two kinds of kernels: one kernel describes the connection of pores in the space, and the other kernel describes the connection of pores in an elementary macrovolume. A simple model of capillary pressure hysteresis associated with the monotonicity of the function of the area-to-volume ratio of the pore is proposed. The results of numerical calculations of the capillary pressure hysteresis and relative phase permeabilities are presented. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 6, pp. 1086–1093, November–December, 2008.     

Quantum-chemical calculation of the adhesion energy of contacting dissimilar metals in a medium

We have constructed a model of the contact interaction of dissimilar metals Al–Fe, Al–Cr, Cu–Al, and Cu–Fe in the presence of particles of a corrosive medium. We have used here the quantum-chemical method of density functionals with the exchange-correlation functional of generalized gradient approximation and LANL2DZ basic set in the cluster approximation. The adhesion energy for clusters of dissimilar metals has been calculated, and its dependence on the composition of corrosive medium has been evaluated. We have established that the adhesion energy of dissimilar metals is determined by the summary contribution of the surface energies of both contacting metals. It has a “quasichemical character,” i.e., its values are intermediate between the chemisorption energy and the energy of forces of physical nature. We have established a substantial change in the distribution of surface charges and spin electron densities of contacting metals in the course of their interaction with water molecules, chlorine ions, and glycerol molecules.     

Influence of the coefficient of vaporization on the parameters of the gas near the surface

The dependence of the coefficient of concentration jump on the coefficient of vaporization for a diluted binary mixture, when the concentrations of the components are significantly different, has been investigated. The analytical expression of the concentration jump for the case where the frequency of collisions of molecules is in proportion to their velocity has been obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 2, pp. 121–126, March–April, 2007.     

An Extended Equation of State Modeling Method II. Mixtures

This work is the extension of previous work dedicated to pure fluids. The same method is extended to the representation of thermodynamic properties of a mixture through a fundamental equation of state in terms of the Helmholtz energy. The proposed technique exploits the extended corresponding-states concept of distorting the independent variables of a dedicated equation of state for a reference fluid using suitable scale factor functions to adapt the equation to experimental data of a target system. An existing equation of state for the target mixture is used instead of an equation for the reference fluid, completely avoiding the need for a reference fluid. In particular, a Soave–Redlich–Kwong cubic equation with van der Waals mixing rules is chosen. The scale factors, which are functions of temperature, density, and mole fraction of the target mixture, are expressed in the form of a multilayer feedforward neural network, whose coefficients are regressed by minimizing a suitable objective function involving different kinds of mixture thermodynamic data. As a preliminary test, the model is applied to five binary and two ternary haloalkane mixtures, using data generated from existing dedicated equations of state for the selected mixtures. The results show that the method is robust and straightforward for the effective development of a mixture- specific equation of state directly from experimental data.     

Shock adiabat of a one-velocity heterogeneous medium

An expression for the shock adiabat of a multicomponent mixture has been obtained. It agrees with the equations of the one-velocity model of a heterogeneous medium. The predictions are compared with the generally used shock adiabat equation based on the assumption on additive shock compression of mixture components. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 46–52, September–October, 2006.     

Modification of polypropylene surface by CH<Subscript>4</Subscript>–O<Subscript>2</Subscript> low-pressure plasma to improve wettability

The aim of this work is to study the effect of surface treatment of a polypropylene film with low-pressure plasma using CH₄–O₂ mixture gas in an 80:20 ratio. The effect of the variation of the plasma treatment conditions has been studied to optimize the plasma effects. The film wettability has been analyzed by the study of the variation of free surface energy and its polar and dispersive components. The surface functionalization of the PP film was also analyzed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (FTIR-ATR) analysis. The surface topography was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The CH₄–O₂ plasma treatment induces the ablation inherent of a traditional plasma treatment and polymerization mechanisms to take place simultaneously at the treated surface. The PP film treated with CH₄–O₂ plasma shows a remarkable improvement on the surface free energy mainly caused by surface functionalization as XPS reveals. Slight changes in surface topography are observed, but they do not contribute in a significant way to improve wettability.     

Theoretical study of hydrodynamics and heat transfer by free convection of non-Newtonian fluids near a cooled surface with regard for variable viscosity

We have made a theoretical study of the hydrodynamics and heat transfer of non-Newtonian fluids near a cooled isothermal surface by laminar free convection with regard for the change in the fluid viscosity with temperature. A power rheological model has been used. The solutions to the systems of differential equations for the boundary layer have been obtained numerically. It has been shown that the strongest influence in the considered kinds of convection is produced by the relative viscosity. Moreover, of great importance is the nonlinearity index of the medium. With increasing rheological parameter the influence of variable viscosity decreases. Criteria equations for calculating the local and mean Nusselt numbers and friction coefficients have been obtained. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 49–56, November–December, 2006.     

Surface energy controlled α–γ–α transformation texture and microstructure character study in ULC steels alloyed with Mn and Al

In this article, an ultralow-carbon steel grade alloyed with Mn and Al has been investigated during α–γ–α transformation annealing in vacuum. Typical texture and microstructure has evolved as a monolayer of grains on the outer surface of transformation-annealed sheets. This monolayer consists of <100>//ND and <110>//ND fibre, which is very different from the bulk texture components. The selective driving force is believed to reside in the anisotropy of surface energy at the metal–vapour interface. The grain morphology is very different from the bulk grains. Moreover, 30–40% of the grain boundary interfaces observed in the RD–TD surface sections are tilt incoherent <110> 70.5° boundaries, which are known to exhibit reduced interface energy. Hence, the conclusion can be drawn that the orientation selection of surface grains is strongly controlled by minimization of the interface energy; both metal/vapour and metal/metal interfaces play a roll in this.     

Thermophysical Properties of Nitrogen from a New Potential Energy Surface Using the Mason–Monchick Approximation

A recent N₂–N₂ potential has been used to calculate the second virial, viscosity, and diffusion coefficients. Calculations have been done up to the first quantum correction for virial coefficients and the second-order kinetic theory approximation for transport coefficients. The Mason–Monchick approximation (MMA) has been used for the calculation of collision integrals and, via a numerical analysis, a common intersection point has been found for reduced cross sections and collision integrals of different orientations. This regularity has been interpreted with the aim of the orientation dependence of the potential energy and different types of collisions between molecules. The overall agreement of the calculated second virial coefficient with experiment is reasonable but suggests that a slight re-scaling of the potential would be beneficial. In the case of transport properties, calculated and experimental results show an average deviation of about 1.6% and 0.7% for viscosity and relative diffusion coefficients, respectively.     

Characteristics and plasma parameters of a short-wavelength low-pressure discharge lamp

We have studied the working optical characteristics and electron kinetic coefficients of a short-wavelength, electric discharge exciplex-halogen UV-VUV lamp employing a mixture of argon and chlorine with a total pressure of P = 0.5–10 kPa. The lamp operates on a system of broadened electron-vibrational bands of ArCl (175 nm) and chlorine (200, 258 nm) molecules, which overlap to form a continuum in the spectral range of 160–260 nm. It is established that the optimum mixtures are those with p(Ar) − p(Cl₂) = (2–4)−(0.15–0.30) kPa. The average output power of the short-wavelength radiation is 1–2 W at an efficiency of ∼5%. The electron energy distribution functions (EDFs) and the discharge plasma parameters have been calculated by solving the Boltzmann equation for a gas mixture with the experimentally determined optimum composition in the range of E/P values from 1 to 200 V/(cm Torr), where E is the electric field strength and P is the total gas pressure. Using the obtained EDFs, the electron transport characteristics, specific discharge power losses for the main elementary processes, and rate constants of electron processes are determined.     

Surface Tension Prediction Using Characteristics of the Density Profile Through the Interfacial Region

A simple surface tension estimation technique is described that is based solely upon the characteristics of the density profile in the interfacial region and the physical properties of the molecules in the fluid. This method, denoted free energy integration (FEI), links interfacial tension to known interfacial region density profile characteristics obtained via experiment or simulation. The general FEI methodology is provided here, and specific relations are derived for a methodology that incorporates the Redlich–Kwong fluid model. The Redlich–Kwong based FEI method was used to predict interfacial tension using the density profile characteristics of molecular dynamics (MD) simulations of argon using the Lennard–Jones potential, diatomic nitrogen using the two-center Lennard–Jones potential, and water using the extended simple point-charge (SPC/E) model. These results for argon compare favorably to values calculated by the traditional virial approach, known values from the literature using the finite-size scaling technique, and ASHRAE recommended values. In addition, the FEI predictions agree well with ASHRAE values and predictions using the virial method for nitrogen for the simulated range of temperatures in this study, and for water for reduced temperatures above 0.7. In addition, the FEI method results agree well with other established theoretical techniques for predictions of the surface tension of sulfur hexafluoride close to the critical point.     

Turbulent conjugate heat-and mass transfer in chemical conversions in a tubular reactor

A model of turbulent heat-and mass transfer with nonlinear sources (sinks) that appear as a result of chemical reactions of the first and second orders has been developed. The conjugation condition (equality of temperatures and local fluxes) at the reactor — coolant interface was used for this purpose. A finite-difference numerical solution by the alternating direction method is obtained. The influence of the coefficients of turbulent viscosity on heat-and mass transfer is investigated. The model has been tested on the example of modeling fast polymerization processes. It has been established in practical calculations of the processes of fast polymerization that instead of the model with variable coefficients of transfer and velocities of liquid motion one can use its approximation with constant coefficients of transfer and velocities of liquid motion. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 73–85, November–December, 2007.     

Correlation for the Carbon Dioxide and Water Mixture Based on The Lemmon–Jacobsen Mixture Model and the Peng–Robinson Equation of State

Models representing the thermodynamic behavior of the CO₂–H₂O mixture have been developed. The single-phase model is based upon the thermodynamic property mixture model proposed by Lemmon and Jacobsen. The model represents the single-phase vapor states over the temperature range of 323–1074 K, up to a pressure of 100 MPa over the entire composition range. The experimental data used to develop these formulations include pressure–density–temperature-composition, second virial coefficients, and excess enthalpy. A nonlinear regression algorithm was used to determine the various adjustable parameters of the model. The model can be used to compute density values of the mixture to within ±0.1%. Due to a lack of single-phase liquid data for the mixture, the Peng–Robinson equation of state (PREOS) was used to predict the vapor–liquid equilibrium (VLE) properties of the mixture. Comparisons of values computed from the Peng–Robinson VLE predictions using standard binary interaction parameters to experimental data are presented to verify the accuracy of this calculation. The VLE calculation is shown to be accurate to within ±3 K in temperature over a temperature range of 323–624 K up to 20 MPa. The accuracy from 20 to 100 MPa is ±3 K up to ±30 K in temperature, being worse for higher pressures. Bubble-point mole fractions can be determined within ±0.05 for CO₂.     

Effect of electrode pore geometry modeled using Nernst–Planck–Poisson-modified Stern layer model

A planar electrode containing cylindrical pores with semi-circular ends is modeled using a finite element implementation of the transient nonlinear 2D Nernst– Planck–Poisson-modified Stern (NPPMS) model. The model uses a modified Stern layer to account for finite ion size. The study includes the effects of pore radius and depth on the predicted electric potential, ion concentration, surface charge density, surface energy density, and charging time. The ion concentration and electric potential are found to be sensitive to the change in radii of the pore and insensitive to the pore depth. The surface charge density is slightly higher within the pore than along the vertical flat regions of the electrode. The increase in surface area due to porosity increases the charging time.     

Modeling Erosion Wear Rates in Slurry Flotation Cells

In processes using slurry as the working fluid, wear due to solid particles impinging on elements of the process units is a serious reliability issue. This study considers modeling wear damage in flotation cells, which are widely used in mineral processing. Flotation cells are typically cylindrical vessels where an impeller is used to agitate the fluid, enabling the liberation of the minerals from the slurry. Some solids, particularly those entrained in the impeller stream, can impact on the wall of the cell, leading to material loss and eventually to loss of structural integrity. The problem of predicting the remaining life of the unit due to erosion requires understanding of various sub-processes: flow modeling, particle–fluid interaction, energy interactions at the surface, and the mechanism of erosion itself. In this study, empirically developed equations for the flow field of cylindrical mixing vessel with a Rushton turbine are used in formulating a model relating and the damage accumulation rate to a simple set of measurable variables. To validate a model, a PIV technique was used to measure velocities in the flow field and near the wall on a physical model of the cell with transparent walls and particles that match the refractive index of the fluid. An Eulerian–Langrangian approach has been used to determine the particle trajectories and the effect of a squeeze film is incorporated into the model to modify the velocity distribution of particles prior to impacts. An analytical model based on equations of impulse and momentum for a particle of any shape striking a flat massive surface has been used to describe the energy lost at the walls. Finally, a damage model is developed that takes into account impact velocity, attack angle, properties of the impinging particles and the surface. This model is verified against a second physical model that measures material loss rate at different locations within the cell.     

One-velocity model of a multicomponent heat-conducting medium

A model of a one-velocity heat-conducting heterogeneous medium with the Fourier relaxation law of heat transfer has been constructed. It is shown that the model’s equations are of hyperbolic type. The results of numerical experiments for a three-component mixture of ideal gases carried out with the use of the Courant–Isaacson–Rees scheme are presented.     

Simulation of the turbulent mixing of a passive impurity in a jet mixer

Results of numerical simulation of the mixing of a turbulent jet with a cocurrent incompressible-fluid flow (Schmidt number Sc ≈ 1000) in a cylindrical channel of circular cross section (axisymmetric mixer) with the use of the standard k-ε turbulence model and different models for the averaged value of the mixture fraction and its variance have been given. For the problem of mixing of an inert passive impurity, two regimes of flow — the regime with the formation of a recirculation zone and that without its formation — have been considered. The formulated statistical model has been verified with the use of experimental data and results of calculation by large-eddy simulation. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 666–681, July–August, 2008.     

Surface changes during pyrolytic conversion of hybrid materials to oxycarbide glasses

Hybrid materials from TEOS–TBOT–PDMS have been prepared and pyrolyzed between 400 and 1,000 °C. The surface characteristics of this type of materials have been studied by nitrogen adsorption, mercury intrusion porosimetry, and inverse gas chromatography at infinite dilution (IGC). IGC has been used for obtaining the dispersive and acid–base surface energies of the different materials. The specific surface areas and pore volumes of the studied samples have resulted to increase the pyrolysis temperatures ranging between 400 and 600 °C and decrease for higher temperatures. On the other hand, surface energies increase when the materials are pyrolyzed between 400 and 800 °C and then decrease after pyrolysis at 1,000 °C. When the material is pyrolyzed at the highest temperature, the surface energies are close to that of typical glasses. It has been observed that pyrolyzing at 800 °C the material has the highest values of both components of the surface free energy (dispersive and specific). The surface energy–pyrolysis temperature variation does not correspond to the formation of micropores in the material during the pyrolysis process. Therefore, it has been assumed that high energy active sites must be formed on the surface when the materials are pyrolyzed at 800 °C.