Transport Of Binary Mixtures Research Articles

Diffusivities in Binary Mixtures of n-Hexane or 1-Hexanol with Dissolved CH4, Ne, Kr, R143a, SF6, or R236fa Close to Infinite Dilution

This work is a continuation of previous studies focusing on the influence of intermolecular interactions on the diffusive mass transport in mixtures consisting of liquids with dissolved gases by determining the Fick diffusion coefficient of the mixtures or self-diffusion coefficient of the gas solutes. Dynamic light scattering, Raman spectroscopy, and molecular dynamics simulations are applied to study the interplay between the liquid structure and diffusive mass transport in binary mixtures consisting of methane, neon, krypton, sulfur hexafluoride, and the two refrigerants R143a and R236fa dissolved in n-hexane or 1-hexanol. Experiments and simulations were performed at the macroscopic thermodynamic equilibrium close to infinite dilution of the solute at temperatures between 303 and 423 K. The obtained Fick diffusion coefficients increase with increasing temperature and are always smaller in mixtures based on 1-hexanol compared to those of n-hexane. For both solvents, a decreasing molar mass of the solutes leads to increasing Fick diffusion coefficients with the exception of methane and neon showing the opposite behavior. Next to a general discussion and comparison with the literature, the present diffusivity data are compared with values predicted by a semiempirical model, which was previously developed to predict mass diffusivities in binary mixtures consisting of n-alkanes or 1-alcohols with dissolved gases close to infinite dilution.

Transport of Binary Mixtures in Pervaporation through a Microporous Silica Membrane: Shortcomings of Fickian Models

This study explores the applicability of the adsorption‐diffusion mechanism to describe the transport of binary “methanol‐water” and “ethanol‐water” mixtures in pervaporation through a commercial microporous silica membrane. Two different adsorption‐diffusion models are considered: one based on Fick's diffusion equation and another based on the Maxwell‐Stefan formulation. Basic models (Fick) assume concentration independent parameters; more complex models (Maxwell‐Stefan) incorporate flux coupling and other non‐idealities. The influence of feed temperature (40°C–90°C) on permeation flux was analysed in terms of activation energy for flux, permeability and diffusion, and heat of adsorption and vaporization. Also the occurrence of coupling effects was studied by determining the effect of feed composition (entire composition range) on permeation flux, permeability and selectivity. Adsorption‐diffusion models based on Fick's diffusion equation can be used to describe coupling effects if they are modified with concentration dependent diffusion and/or sorption coefficients. They are incapable of describing drag effects by water on alcohols. These drag effects should be modeled through models based on the Maxwell‐Stefan theory.

Principles of polymer processing

1. History, Structural Formulation of the Field Through Elementary Steps, and Future Perspectives. 1.1 Historical Notes. 1.2 Current Polymer Processing Practice. 1.3 Analysis of Polymer Processing in Terms of Elementary Steps and Shaping Methods. 1.4 Future Perspectives: From Polymer Processing to Macromolecular Engineering. 2. The Balance Equations and Newtonian Fluid Dynamics. 2.1 Introduction. 2.2 The Balance Equations. 2.3 Reynolds Transport Theorem. 2.4 The Macroscopic Mass Balance and the Equation of Continuity. 2.5 The Macroscopic Linear Momentum Balance and the Equation of Motion. 2.6 The Stress Tensor. 2.7 The Rate of Strain Tensor. 2.8 Newtonian Fluids. 2.9 The Macroscopic Energy Balance and the Bernoulli and Thermal Energy Equations. 2.10 Mass Transport in Binary Mixtures and the Diffusion Equation. 2.11 Mathematical Modeling, Common Boundary Conditions, Common Simplifying Assumptions, and the Lubrication Approximation. 3. Polymer Rheology and Non-Newtonian Fluid Mechanics. 3.1 Rheological Behavior, Rheometry, and Rheological Material Functions of Polymer Melts. 3.2 Experimental Determination of the Viscosity and Normal Stress Difference Coefficients. 3.3 Polymer Melt Constitutive Equations Based on Continuum Mechanics. 3.4 Polymer Melt Constitutive Equations Based on Molecular Theories. 4. The Handling and Transporting of Polymer Particulate Solids. 4.1 Some Unique Properties of Particulate Solids. 4.2 Agglomeration. 4.3 Pressure Distribution in Bins and Hoppers. 4.4 Flow and Flow Instabilities in Hoppers. 4.5 Compaction. 4.6 Flow in Closed Conduits. 4.7 Mechanical Displacement Flow. 4.8 Steady Mechanical Displacement Flow Aided by Drag. 4.9 Steady Drag-induced Flow in Straight Channels. 4.10 The Discrete Element Method. 5. Melting. 5.1 Classification and Discussion of Melting Mechanisms. 5.2 Geometry, Boundary Conditions, and Physical Properties in Melting. 5.3 Conduction Melting without Melt Removal. 5.4 Moving Heat Sources. 5.5 Sintering. 5.6 Conduction Melting with Forced Melt Removal. 5.7 Drag-induced Melt Removal. 5.8 Pressure-induced Melt Removal. 5.9 Deformation Melting. 6. Pressurization and Pumping. 6.1 Classification of Pressurization Methods. 6.2 Synthesis of Pumping Machines from Basic Principles. 6.3 The Single Screw Extruder Pump. 6.4 Knife and Roll Coating, Calenders, and Roll Mills. 6.5 The Normal Stress Pump. 6.6 The Co-rotating Disk Pump. 6.7 Positive Displacement Pumps. 6.8 Twin Screw Extruder Pumps. 7. Mixing. 7.1 Basic Concepts and Mixing Mechanisms. 7.2 Mixing Equipment and Operations of Multicomponent and Multiphase Systems. 7.3 Distribution Functions. 7.4 Characterization of Mixtures. 7.5 Computational Analysis. 8. Devolatilization. 8.1 Introduction. 8.2 Devolatilization Equipment. 8.3 Devolatilization Mechanisms. 8.4 Thermodynamic Considerations of Devolatilization. 8.5 Diffusivity of Low Molecular Weight Components in Molten Polymers. 8.6 Boiling Phenomena: Nucleation. 8.7 Boiling-Foaming Mechanisms of Polymeric Melts. 8.8 Ultrasound-enhanced Devolatilization. 8.9 Bubble Growth. 8.10 Bubble Dynamics and Mass Transfer in Shear Flow. 8.11 Scanning Electron Microscopy Studies of Polymer Melt Devolatilization. 9. Single Rotor Machines. 9.1 Modeling of Processing Machines Using Elementary Steps. 9.2 The Single Screw Melt Extrusion Process. 9.3 The Single Screw Plasticating Extrusion Process. 9.4 The Co-rotating Disk Plasticating Processor. 10. Twin Screw and Twin Rotor Processing Equipment. 10.1 Types of Twin Screw and Twin Rotor-based Machines. 10.2 Counterrotating Twin Screw and Twin Rotor Machines. 10.3 Co-rotating, Fully Intermeshing Twin Screw Extruders. 11. Reactive Polymer Processing and Compounding. 11.1 Classes of Polymer Chain Modification Reactions, Carried out in Reactive Polymer Processing Equipment. 11.2 Reactor Classification. 11.3 Mixing Considerations in Multicomponent Miscible Reactive Polymer Processing Systems. 11.4 Reactive Processing of Multicomponent Immiscible and Compatibilized Immiscible Polymer Systems. 11.5 Polymer Compounding. 12. Die Forming. 12.1 Capillary Flow. 12.2 Elastic Effects in Capillary Flows. 12.3 Sheet Forming and Film Casting. 12.4 Tube, Blown Film, and Parison Forming. 12.5 Wire Coating. 12.6 Profile Extrusion. 13. Molding. 13.1 Injection Molding. 13.2 Reactive Injection Molding. 13.3 Compression Molding. 14. Stretch Shaping. 14.1 Fiber Spinning. 14.2 Film Blowing. 14.3 Blow Molding. 15. Calendering. 15.1 The Calendering Process. 15.2 Mathematical Modeling of Calendering. 15.3 Analysis of Calendering Using FEM. Appendix A: Rheological and Thermophysical Properties of Polymers. Appendix B: Conversion Tables to the International System of Units (SI). Appendix C: Notation. Author Index. Subject Index.

Percolating ion transport in binary mixtures with high dielectric loss

We investigate the ion transport percolation properties of a binary system of an ion conductor (NaCl) and an insulator (ethyl cellulose) for which the ac component of the conductivity is non-negligible over the entire measured frequency range. We find that the dc conductivity, extracted from a well-defined range of frequencies, can be described by a low percolation threshold, ϕc=0.06 three-dimensional conducting network. The low ϕc was explained by the water-layer-assisted ion conduction in micrometer-sized ethyl cellulose channels between NaCl grains. The present findings provide valuable knowledge for the analysis and design of a broad class of ion conducting functional materials.

Soret coefficient for liquid argon-krypton mixtures via equilibrium and nonequilibrium molecular dynamics: a comparison with experiments.

The Soret and the other transport coefficients, characterizing the heat and mass transport in binary mixtures, have been obtained by equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively). Two state points of the argon-krypton mixture are considered, for which experimental values of the Soret coefficient are available. To attempt a comparison between simulations and experiments the common enthalpy-diffusion-free expression for the heat flux has been chosen. The comparison of the simulations with the experiments shows a remarkable agreement, for all the several utilized EMD and NEMD techniques (dynamical and stationary). The techniques, used over 0.3 micros of total simulation time span, are slow convergent but have comparable performances.

A note on the time-lags for the transport of gas mixtures

A general expression has been obtained which relates the time-lag for transport of a gas mixture through a membrane to the corresponding time-lags for the components of the mixture. The derivation, being based only on conservation of mass and attainment of steady-state transport, is independent of any assumed equation of flow and of the nature of the membrane. Some applications to the transport of binary mixtures are considered.

Steady-State and Dynamic Mass Transfer of Gases in Porous Materials

The diffusion of binary gas mixtures through a porous asymmetric tubular membrane has been studied experimentally. A modified Wicke-Kallenbach diffusion cell consisting of two gas compartments separated by the membrane was used. Steady-state experiments with pure gases and binary mixtures were carried out in order to determine the transport parameters of the membrane with respect to the dusty gas model. To verify these parameters, the dynamic transport of binary mixtures was examined applying the dynamic diffusion cell technique proposed by Novak et al. The measured transients were in relative good agreement with the model predictions.

Critical exponent of the heat of transport of water– isobutyric acid mixtures

The Dufour effect (diffusion thermoeffect) has been used to obtain the critical exponent of the heat of transport in binary mixtures of isobutyric acid and water near the liquid–liquid critical point. As the critical temperature is approached experimentally, the heat of transport vanishes with a critical exponent of about 2/3. The i critical exponent for the Onsager coefficient Ω01 is zero. This value is consistent with the semidefinite positive entropy production r requirement and is identical to the best literature value for the critical exponent of the reciprocal Onsager coefficient Ω10. In order to explain the observed critical behavior of the heat of transport a new molecular interpretation based on the random thermal motion model for diffusion is suggested.

FLUCTUATIONS AND TRANSPORT IN BINARY MIXTURES

FLUCTUATIONS AND TRANSPORT IN BINARY MIXTURES

Fundamental Studies on the Bearman–Kirkwood Theory of Transport. I. The Diffusion Coefficient Ratio

Although the Bearman–Kirkwood theory of transport in binary mixtures was developed as a theory of the liquid state, it is formally possible to carry out calculations of the self-diffusion coefficient ratio, D1 / D2, at all densities at which radial distribution functions are available for a given intermolecular potential. These calculations can be used to check the internal consistency of the theory at any density. For, except at unit mole fraction of solvent, the theory provides three alternative expressions for D1 / D2, which should agree when the theory is consistent. For Lennard-Jones parameters of a model system corresponding to argon and krypton, explicit calculation shows that at each mole fraction and temperature, the three expressions disagree except at a density characteristic of a liquid or dense fluid. At the densities of consistency, D1 / D2 assumes a not unreasonable value and remains quite independent of temperature in agreement with available data on argon and krypton. At unit mole fraction, another consistency test is available which qualitatively justifies the application of the theory to so-called “regular solutions” and quantitatively gives densities of consistency smoothly connected to those at other mole fractions.