Showing papers on "Transport phenomena published in 2014"

Homotopy simulation of nanofluid dynamics from a non-linearly stretching isothermal permeable sheet with transpiration

Abstract: In this article we derive semi-analytical/numerical solutions for transport phenomena (momentum, heat and mass transfer) in a nanofluid regime adjacent to a nonlinearly porous stretching sheet by means of the Homotopy analysis method (HAM). The governing equations are reduced to a nonlinear, coupled, non-similar, ordinary differential equation system via appropriate similarity transformations. This system is solved under physically realistic boundary conditions to compute stream function, velocity, temperature and concentration function distributions. The results of the present study are compared with numerical quadrature solutions employing a shooting technique with excellent correlation. Furthermore the current HAM solutions demonstrate very good correlation with the non-transpiring finite element solutions of Rana and Bhargava (Commun. Nonlinear Sci. Numer. Simul. 17:212–226, 2012). The influence of stretching parameter, transpiration (wall suction/injection) Prandtl number, Brownian motion parameter, thermophoresis parameter and Lewis number on velocity, temperature and concentration functions is illustrated graphically. Transpiration is shown to exert a substantial influence on flow characteristics. Applications of the study include industrial nanotechnological fabrication processes.

Molecular Dirac Fermion Systems — Theoretical and Experimental Approaches —

Abstract: The transport phenomena of zero-gap conductors are one of the central subjects in condensed matter physics. α-(BEDT-TTF)2I3 [BEDT-TTF = bis(ethylenedithio)-tetrathiafulvalene] is a typical zero-gap conductor consisting of two-dimensional multiple two-dimensional layers. Under high pressures of above 1.5 GPa, it undergoes a phase transition to a zero-gap state, in which it exhibits unusual transport phenomena. This paper reviews the recent progress in clarifying the physics of α-(BEDT-TTF)2I3. In particular, the effect of a magnetic field on the behavior of electrons is investigated. On the basis of the interlayer magnetoresistance, evidence of the Landau level with the index N = 0 was obtained. The collaboration of experiments and theory has opened a new field of exploring the interlayer electron transport in two-dimensional layered zero-gap conductors. Furthermore, these phenomena have been observed by NMR and specific heat measurements in contrast to the case of graphene. The paper also reviews some rec...

Comparative numerical study of single-phase and two-phase models for bio-nanofluid transport phenomena

Abstract: A computational fluid dynamics (CFD) simulation of laminar convection of Al2O3–water bio-nanofluids in a circular tube under constant wall temperature conditions was conducted, employing a single-phase model and three different two-phase models (volume of fluid (VOF), mixture and Eulerian). The steady-state, three-dimensional flow conservation equations were discretised using the finite volume method (FVM). Several parameters such as temperature, flow field, skin friction and heat transfer coefficient were computed. The computations showed that CFD predictions with the three different two-phase models are essentially the same. The CFD simulations also demonstrated that single-phase and two-phase models yield the same results for fluid flow but different results for thermal fields. The two-phase models, however, achieved better correlation with experimental measurements. The simulations further showed that heat transfer coefficient distinctly increases with increasing nanofluid particle concentration. The physical properties of the base fluid were considered to be temperature-dependent, while those of the solid particles were constant. Grid independence tests were also included. The simulations have applications in novel biomedical flow processing systems.

Influence of heat generation and heat flux on peristaltic flow with interacting nanoparticles

Abstract: In the current study, we have examined the peristaltic flow of three different nanoparticles with water as base fluid under the influence of slip boundary conditions through a vertical asymmetric porous channel in the presence of MHD. The selected nanoparticles are titanium dioxide ( TiO2 , copper oxide (CuO) and silicon dioxide ( SiO2 . The Brownian motion shows that the effective conductivity increases to result in a lower temperature gradient for a given heat flux. To examine these transport phenomena thoroughly, we also consider the thermal conductivity model of Brownian motion for nanofluids, this increases the effect of the particle size, particle volume fraction and temperature dependence. The mathematical formulation is presented. Exact solutions are obtained from the resulting equations. The obtained expressions for pressure gradient, temperature and velocity profile are described through graphs for the various relevant parameters. The streamlines are drawn for some physical quantities to discuss the trapping phenomenon.

The effects of plasma diffusion and viscosity on turbulent instability growth

Abstract: We perform two-dimensional simulations of strongly–driven compressible Rayleigh–Taylor and Kelvin–Helmholtz instabilities with and without plasma transport phenomena, modeling plasma species diffusion, and plasma viscosity in order to determine their effects on the growth of the hydrodynamic instabilities. Simulations are performed in hydrodynamically similar boxes of varying sizes, ranging from 1 μm to 1 cm in order to determine the scale at which plasma effects become important. Our results suggest that these plasma effects become noticeable when the box size is approximately 100 μm, they become significant in the 10 μm box, and dominate when the box size is 1 μm. Results suggest that plasma transport may be important at scales and conditions relevant to inertial confinement fusion, and that a plasma fluid model is capable of representing some of the kinetic transport effects.

Introductory Transport Phenomena

Abstract: 0. The Subject of Transport Phenomena 1. Viscosity and the Mechanisms of Momentum Transport 2. Shell Momentum Balances and Velocity Distributions in Laminar Flow 3. The Equations of Change for Isothermal Systems 4. Velocity Distributions in Turbulent Flow 5. Dimensional Analysis for Isothermal Systems 6. Interphase Transport in Isothermal Systems 7. Macroscopic Balances for Isothermal Flow Systems 8. Non-Newtonian Liquids 9. Thermal Conductivity and the Mechanisms of Energy Transport 10. Shell Energy Balances and Temperature Distributions in Solids and Laminar Flow 11. The Equations of Change for Nonisothermal Systems 12. Temperature Distributions in Turbulent Flow 13. Dimensional Analysis in Nonisothermal Systems 14. Interphase Transport in Nonisothermal Systems 15. Macroscopic Balances for Nonisothermal Systems 16. Energy Transport by Radiation 17. Diffusivity and the Mechanisms of Mass Transport 18. Concentration Distributions in Solids and in Laminar Flow 19. The Equations of Change for Binary Mixtures 20. Concentration Distributions in Turbulent Flow 21. Dimensional Analysis for Flowing Mixtures 22. Interphase Transport in Nonisothermal Mixtures 23. Macroscopic Balances for Multicomponent Systems 24. Other Mechanisms for Mass Transport

Heat transport as torsional responses and Keldysh formalism in a curved spacetime

Abstract: Heat transport phenomena are of scientific and technological importance. Especially the thermal Hall effect is an interesting phenomenon in which the heat current flows perpendicular to a temperature gradient. Recent experiments revealed the effects of inelastic scattering on the anomalous Hall effect in ferromagnetic metals [1] and detected the magnon Hall effect in a ferromagnetic insulator [2]. A systematic framework for calculating the thermal Hall conductivity (THC) is highly desired. Theoretically, the Kubo formula for the thermal conductivity is well established by introducing a gravitational potential [3], while that for the THC alone is not sufficient and should be augmented with the heat magnetization (HM) [4, 5]. Previous theories are unsatisfactory; it remains unclear how the scaling assumptions on the charge and heat currents are justified and furthermore how the theories are practically applied to disordered or interacting systems. In this talk, we revisit the basics of heat transport from the gauge-theoretical viewpoint [6]. We begin with the Noether theorem and gauge principle and explain why a theory of heat transport involves gravity. A vielbein is a gauge field of gravity which is coupled to the energy current and induces a field strength called torsion. A torsional electric field is equivalent to a temperature gradient, and a torsional magnetic field is conjugate to the HM. Such a gauge-theoretical discussion yields the natural definition of the HM. We also develop the Keldysh formalism in a curved spacetime to calculate these gravitational responses [6]. This is a natural extension of the gaugecovariant Keldysh formalism [7] by taking into account gauge fields of gravity. We derive the Green-function formulas for the Kubo-formula contribution and the HM applicable to disordered or interacting systems. In the clean and noninteracting limit, we reproduce the Berry-phase formula for the THC which satisfies the Wiedemann-Franz law [5].

Channeling of particles and associated anomalous transport in a two-dimensional complex plasma crystal

Abstract: Implications of the recently discovered effect of channeling of upstream extra particles for transport phenomena in a two-dimensional plasma crystal are discussed Upstream particles levitated above the lattice layer and tended to move between the rows of lattice particles An example of heat transport is considered, where upstream particles act as moving heat sources, which may lead to anomalous heat transport The average channeling length observed was 15–20 interparticle distances Other features of the channeling process are also reported

Simulation of cuttings transport with foam in deviated wellbores using computational fluid dynamics

Abstract: Foam is non-Newtonian pseudo-plastic fluid, which is used for drilling, well intervention, and stimulation. Predicting the cutting transport efficiency of foam in the wellbore annulus is very important to optimize the drilling process. In this paper, the cuttings transport process with foam is numerically simulated using an Eulerian two-phase model in inclined wellbores. A computational fluid dynamics (CFD) software package called FLUENT was used for this goal. The effect of foam quality, foam velocity, drill pipe rotation, and wellbore inclination on cuttings transport phenomena in both concentric and eccentric annulus was investigated. The simulation results are compared to the experimental data from previous studies, with a relative error less than 8 %. This study shows the reliability of the CFD simulation in replicating the actual physical process.

Mathematical Modeling of the Coupled Transport Phenomena and Color Development: Finish Drying of Trellis-Dried Sultanas

Abstract: A mathematical model for simulation of simultaneous heat and mass transport was developed to describe the drying kinetics during finish drying of trellis-dried sultanas. In this model, the governing partial differential equations for heat and mass transfer for a solid spherical body were numerically solved using a finite difference technique. In addition, a kinetic model was coupled to the heat and mass transfer calculations to simultaneously predict the evolution of product color during the drying process. This allows predictions of moisture content, temperature, and color profiles of the product in a space–time domain during the drying process as a function of various operating conditions. Predictions compared well with the experimental values, implying that the proposed numerical model can be used with confidence for the simulation of the important transport phenomena in optimizing the design and operation of a drying system for sultanas that maximizes the retention of the desired product color. The wo...

Comprehensive modeling and CFD simulation of absorption of CO2 and H2S by MEA solution in hollow fiber membrane reactors

Abstract: A comprehensive mathematical model has been developed for the simulation of simultaneous chemical absorption of carbon dioxide and hydrogen sulfide by means of Monoethanolamine (MEA) aqueous solution in hollow fiber membrane reactors is described. In this regard, a perfect model considering the entrance regions of momentum, energy, and mass transfers was developed. Computational Fluid Dynamics (CFD) techniques were applied to solve governing equations, and the model predictions were validated against experimental data reported in the literature and excellent agreement was found. Effects of different disturbances on the dynamic behavior of the reactor were investigated. Moreover, effects of various parameters such as wetting fraction, gas and liquid inlet velocities, inlet temperature of the solvent, MEA concentration, and CO2 and H2S compositions were carefully studied. It was found that for large values of gas velocity or small values of liquid velocity, the thermal energy equation can play an important role in the model predictions. © 2013 American Institute of Chemical Engineers AIChE J 60: 657–672, 2014

Stress-gradient induced migration of polymers in corrugated channels

Abstract: We study the flow of a dilute polymer solution in a wavy channel under steady-state flow conditions by employing the nonequilibrium thermodynamics two-fluid model [Mavrantzas and Beris, Phys. Rev. Lett. 69, 273–276 (1992)], allowing for the coupling between polymer concentration and polymer stresses. The resulting highly complex system of partial differential equations describing inhomogeneous transport phenomena in the fluid are solved with an efficient implementation of the mixed finite-element method. We present numerical results for polymer concentration, stress, velocity, and fluxes of polymer as a function of the nondimensional parameters of the problem (the Deborah number De, the Peclet number Pe, the Reynolds number Re, the ratio of the solvent viscosity to the total fluid viscosity β, and the constriction ratio of the channel width cr). We find that the constricted part of the wall is depleted of polymer, when the polymer diffusion length scale, expressed by the ratio of De/Pe, increases. The mig...

Continuum Model for the Phase Behavior, Microstructure, and Rheology of Unentangled Polymer Nanocomposite Melts

Abstract: We introduce a continuum model for polymer melts filled with nanoparticles capable of describing in a unified and self-consistent way their microstructure, phase behavior, and rheology in both the linear and nonlinear regimes. It is based on the Hamiltonian formulation of transport phenomena for fluids with a complex microstructure with the final dynamic equations derived by means of a generalized (Poisson plus dissipative) bracket. The model describes the polymer nanocomposite melt at a mesoscopic level by using three fields (state variables): a vectorial (the momentum density) and two tensorial ones (the conformation tensor for polymer chains and the orientation tensor for nanoparticles). The dynamic equations are developed for nanoparticles with an arbitrary shape but then they are specified to the case of spherical ones. Restrictions on the parameters of the model are provided by analyzing its thermodynamic admissibility. A key ingredient of the model is the expression for the Helmholtz free energy A ...

Atomistic simulation of transport phenomena in nanoelectronic devices.

Abstract: Computational chemistry deals with the first-principles calculation of electronic and crystal structures, phase diagrams, charge distributions, vibrational frequencies, or ion diffusivity in complex molecules and solids. Typically, none of these numerical experiments allows for the calculation of electrical currents under the influence of externally applied voltages. To address this issue, there is an imperative need for an advanced simulation approach capable of treating all kind of transport phenomena (electron, energy, momentum) at a quantum mechanical level. The goal of this tutorial review is to give an overview of the “quantum transport” (QT) research activity, introduce specific techniques such as the Non-equilibrium Green's Function (NEGF) formalism, describe their basic features, and underline their strengths and weaknesses. Three examples from the nanoelectronics field have been selected to illustrate the insight provided by quantum transport simulations. Details are also given about the numerical algorithms to solve the NEGF equations and about strategies to parallelize the workload on supercomputers.

Mathematical modelling of laser materials processing

Abstract: Laser materials processing involves a wide range of transport phenomena, power density (up to 1012W/cm²) and interaction time (up to picoseconds) for processing objects with sizes ranging from nanometres to metres The art of modelling this novel process is to develop a proper understanding in selecting the appropriate transport phenomena and boundary conditions for specific applications This paper summarizes modelling efforts to date, on laser heat treatment, non–equilibrium synthesis, alloying, cladding, welding, cutting, drilling, chemical vapour deposition, and ablation processes For each process, the transport phenomena, boundary conditions, governing equations, solution techniques and applicability and limitations are reviewed An extensive bibliography is provided for further reading of the interested scientists and engineers

Modelling of dendritic growth during alloy solidification under natural convection

Abstract: A two-dimensional (2D) lattice Boltzmann method (LBM)-cellular automaton model is presented to investigate the dendritic growth of binary alloys in the presence of natural convection. The kinetic-based LBM is adopted to calculate the transport phenomena by the evolution of distribution functions of moving pseudo-particles. To numerically solve natural convection thermal and solute transport simultaneously, three sets of distribution functions are employed in conjunction with the lattice Bhatnagar–Gross–Krook scheme. Based on the LBM calculated local temperature and concentration at the solid/liquid interface, the kinetics of dendritic growth is determined according to a local solute equilibrium approach. Thus, the physics of a complete time-dependent interaction of natural convection, thermal and solutal transport, and dendritic growth during alloy solidification is embedded in the model. Model validation is performed by comparing the simulated results with literature data and analytical predictions. The model is applied to simulate dendritic growth in binary alloys under the influence of natural convection. The effects of Rayleigh numbers and initial undercooling on dendrite growth are investigated. The results show that natural buoyancy flow, induced by thermal and solutal gradients under gravity, transports the heat and solute from the lower region to the upper region. The dendritic growth is thus accelerated in the downward direction, whereas it is inhibited in the upward direction, yielding asymmetrical dendrite patterns. Increasing the Rayleigh number and undercooling will enhance and reduce, respectively, the influence of natural flow on the dendritic growth.

Progress on High Magnetic Field-Controlled Transport Phenomena and Their Effects on Solidification Microstructure

Abstract: The recent contributions on changes induced by high magnetic fields in transport phenomena, such as convection, solute diffusion, solute or phase migration in the liquid, are reviewed and analyzed. Selectivity provided by the Lorentz, thermoelectromagnetic (a special kind of Lorentz force), and magnetic forces or combinations enables the control of transport phenomena in liquids. This possibility, together with the capability of the transport phenomena to affect solidification in alloys, allows a level of control over solidification microstructures. As a result, recent relevant work can be found dealing with the effects of high magnetic fields on transport phenomena and the corresponding solidification microstructure evolution of alloys, based on the Lorentz, thermoelectromagnetic, and magnetic forces or combinations thereof.

Physics of Semiconductor Devices

Abstract: Part I A Review of Analytical Mechanics and Electromagnetism.- Analytical Mechanics.- Coordinate Transformations and Invariance Properties.- Applications of the Concepts of Analytical Mechanics.- Electromagnetism.- Applications of the Concepts of Electromagnetism.- Part II Introductory Concepts to Statistical and Quantum Mechanics.- Classical Distribution Function and Transport Equation.- From Classical Mechanics to Quantum Mechanics.- Time-Independent Schrodinger Equation.- Time-Dependent Schrodinger Equation.- General Methods of Quantum Mechanics.- Part III Applications of the Schrodinger Equation.- Elementary Cases.- Cases Related to the Linear Harmonic Oscillator.- Other Examples of the Schrodinger Equation.- Time-Dependent Perturbation Theory.- Part IV Systems of Interacting Particles- Quantum Statistics.- Many-Particle Systems.- Separation of Many-Particle Systems.- Part V Applications to Semiconducting Crystals.- Periodic Structures.- Electrons and Holes in Semiconductors at Equilibrium.- Part VI Transport Phenomena in Semiconductors.- Mathematical Model of Semiconductor Devices.- Generation-Recombination and Mobility.- Part VII Basic Semiconductor Devices.- Bipolar Devices.- MOS Devices.- Part VIII Miscellany.- Thermal Diffusion.- Thermal Oxidation- Layer Deposition.- Measuring the Semiconductor Parameters.