Showing papers on "Transport phenomena published in 2008"
01 Jul 2008
TL;DR: In this paper, the authors used the nonequilibrium Green function theory for the derivation of the quantum kinetic equations for femtosecond laser-pulse spectroscopy.
Abstract: Nanoscale miniaturization and femtosecond laser-pulse spectroscopy require a quantum mechanical description of the carrier kinetics that goes beyond the conventional Boltzmann theory. On these extremely short length and time scales the electrons behave like partially coherent waves. This monograph deals with quantum kinetics for transport in low-dimensional microstructures and for ultra-short laser pulse spectroscopy. The nonequilibrium Green function theory is described and used for the derivation of the quantum kinetic equations. Numerical methods for the solution of the retarded quantum kinetic equations are discussed and results are presented for high-field transport and for mesoscopic transport phenomena. Quantum beats, polarization decay, and non-Markovian behaviour are treated for femtosecond spectroscopy on a microscopic basis. Since the publishing of the first edition in 1996 the nonequilibrium Green function technique has been applied to a large number of new research topics, and the revised edition introduces the reader to some of these areas, such as molecular electronics, noise calculations, build-up of screening and polaron correlations, and non-Markovian relaxation, among others. Connection to recent experiments is made, and it is emphasized how the quantum kinetic theory is essential in their interpretation. (orig.)
1,908 citations
TL;DR: In this paper, the authors show that, even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise and suggest that the presence of entanglement does not play an essential role for energy transport and may even hinder it.
Abstract: Transport phenomena are fundamental in physics. They allow for information and energy to be exchanged between individual constituents of communication systems, networks or even biological entities. Environmental noise will generally hinder the efficiency of the transport process. However, and contrary to intuition, there are situations in classical systems where thermal fluctuations are actually instrumental in assisting transport phenomena. Here we show that, even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise. We explain the underlying physical mechanisms behind this phenomenon and propose possible experimental demonstrations in quantum optics. Our results suggest that the presence of entanglement does not play an essential role for energy transport and may even hinder it. We argue that Nature may be routinely exploiting dephasing noise and show that the transport of excitations in simplified models of light harvesting molecules does benefit from such noise assisted processes. These results point toward the possibility for designing optimized structures for transport, for example in artificial nanostructures, assisted by noise.
941 citations
TL;DR: In this paper, a mathematical model for a complete lithium-sulfur cell is presented, which includes various electrochemical and chemical reactions, multicomponent transport phenomena in the electrolyte, and the charge transfer within and between solid and liquid phases.
Abstract: A mathematical model is presented for a complete lithium-sulfur cell. The model includes various electrochemical and chemical (precipitation) reactions, multicomponent transport phenomena in the electrolyte, and the charge transfer within and between solid and liquid phases. A change in the porosity of the porous cathode and separator due to precipitation reactions is also included in the model. The model is used to explain the physical reasons for the two-stage discharge profiles that are typically obtained for lithium-sulfur cells.
318 citations
TL;DR: In this paper, the authors investigated the complicated transport phenomena in spot hybrid laser-MIG keyhole welding and found that weld pool dynamics, cooling rate, and final weld bead geometry are strongly affected by the impingement process of the droplets in hybrid laser MIG welding.
151 citations
TL;DR: In this paper, a series of analysis methods are proposed to simulate the liquid-gas two-phase and multi-component transport phenomena in the gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC).
131 citations
TL;DR: The application of rapid prototyping of microfluidic networks with approximately 5000 channels, controllable wettability, and fluorescence-based analysis to the study of multiphase transport phenomena in porous media is demonstrated.
Abstract: We present a lab-on-chip approach to the study of multiphase transport in porous media. The applicability of microfluidics to biological and chemical analysis has motivated much development in lab-on-chip methodologies. Several of these methodologies are also well suited to the study of transport in porous media. We demonstrate the application of rapid prototyping of microfluidic networks with approximately 5000 channels, controllable wettability, and fluorescence-based analysis to the study of multiphase transport phenomena in porous media. The method is applied to measure the influence of wettability relative to network regularity, and to differentiate initial percolation patterns from active flow paths. Transport phenomena in porous media are of critical importance to many fields and particularly in many energy-related applications including liquid water transport in fuel cells, oil recovery, and CO(2) sequestration.
102 citations
TL;DR: In this article, a transport theory involving resistivity and the Hall coefficient on the basis of the microscopic Fermi liquid theory was proposed, where the current due to these excitations is called a current vertex correction (CVC).
Abstract: In this paper, we present recent developments in the theory of transport phenomena based on the Fermi liquid theory. In conventional metals, various transport coefficients are scaled according to the quasiparticles relaxation time, τ, which implies that the relaxation time approximation (RTA) holds well. However, such a simple scaling does not hold in many strongly correlated electron systems. The most famous example would be high-Tc superconductors (HTSCs), where almost all the transport coefficients exhibit a significant deviation from the RTA results. This issue has been one of the most significant unresolved problems in HTSCs for a long time. Similar anomalous transport phenomena have been observed in metals near their antiferromagnetic (AF) quantum critical point (QCP). The main goal of this study is to demonstrate whether the anomalous transport phenomena in HTSC is evidence of a non-Fermi liquid ground state, or just RTA violation in strongly correlated Fermi liquids. Another goal is to establish a unified theory of anomalous transport phenomena in metals with strong magnetic fluctuations. For these purposes, we develop a method for calculating various transport coefficients beyond the RTA by employing field theoretical techniques.In a Fermi liquid, an excited quasiparticle induces other excited quasiparticles by collision, and current due to these excitations is called a current vertex correction (CVC). Landau noticed the existence of CVC first, which is indispensable for calculating transport coefficients in accord with the conservation laws. Here, we develop a transport theory involving resistivity and the Hall coefficient on the basis of the microscopic Fermi liquid theory, by considering the CVC. In nearly AF Fermi liquids, we find that the strong backward scattering due to AF fluctuations induces the CVC with prominent momentum dependence. This feature of the CVC can account for the significant enhancement in the Hall coefficient, magnetoresistance, thermoelectric power, and Nernst coefficient in nearly AF metals. According to the present numerical study, aspects of anomalous transport phenomena in HTSC are explained in a unified way by considering the CVC, without introducing any fitting parameters; this strongly supports the idea that HTSCs are Fermi liquids with strong AF fluctuations. Further, the present theory also explains very similar anomalous transport phenomena occurring in CeMIn5 (M = Co or Rh), which is a heavy-fermion system near the AF-QCP, and in the organic superconductor κ-(BEDT-TTF).In addition, the striking ω-dependence of the ac-Hall coefficient and the remarkable effects of impurities on the transport coefficients in HTSCs appear to fit naturally into the present theory. Many aspects of the present theory are in accord with the anomalous transport phenomena in HTSCs, organic superconductors and heavy-fermion systems near their AF-QCPs. We discuss some of the open questions for future work.
100 citations
12 Jun 2008
TL;DR: Theoretical Investigations Special Topics in Thermal Phenomena Numerical Examples of Microscale Conduction Microscale Convective Heat Transfer Microscale Radiation Nanoscale Thermal phenomena Index as discussed by the authors.
Abstract: Preface Introduction to Microscale Heat Transfer Microscale Heat Transfer: A Recent Avenue in Energy Transport State of the Art: Some Introductory Remarks Overview of Microscale Transport Phenomena Discussions on Size-Effect Behavior Fundamental Approach for Microscale Heat Transfer Introduction to Engineering Applications of Microscale Heat Transfer Microscale Heat Conduction Review of Conduction Heat Transfer Conduction at the Microscale Space and Timescales Fundamental Approach Thermal Conductivity Boltzmann Equation and Phonon Transport Conduction in Thin Films Heat Conduction in Electronic Devices Measurement of Heat Conduction in the Microscale Conduction in Semiconductor Devices Fundamentals of Microscale Convection Introduction Convective Heat Transfer in Microtubes and Channels Engineering Applications of Microscale Convective Heat Transfer Introduction Research and Development Analysis of Systems for Engineering Applications Microscale Radiative Heat Transfer Macroscopic Approach Microscopic Approach Microscales in Radiative Transfer Investigations of Microscale Radiation Modeling of Microscale Radiation Radiation Properties in the Microscale Regime Recent Developments in Theoretical Modeling Nanoscale Thermal Phenomena Introduction Nanoparticles and Nanofluids Measurements in Nanofluids Theoretical Investigations Special Topics in Thermal Phenomena Numerical Examples Microscale Conduction Microscale Convective Heat Transfer Microscale Radiation Nanoscale Thermal Phenomena Index Concluding Remarks and References appear at the end of each chapter.
98 citations
TL;DR: In this paper, a three-dimensional model of polymer electrolyte fuel cells (PEFCs) is developed to investigate multiphase flows, species transport, and electrochemical processes in fuel cells and their interactions.
96 citations
TL;DR: In this paper, the authors considered the flow of a liquid film sheared by gas flow in a channel with a heater placed at the bottom wall and investigated the heat and mass transfer problem in the framework of a two-sided model.
86 citations
TL;DR: In this paper, the authors present a theoretical model describing the simultaneous transfer of momentum, heat and mass occurring in a convective drier where hot dry air flows under turbulent conditions around a food sample.
TL;DR: In this paper, a comprehensive numerical analysis has been conducted to explore the development of liquid-oxygen (LOX) flow in pressure swirl injectors operating at supercritical pressures, and various flow dynamics are investigated by means of the spectral and proper-orthogonaldecomposition techniques.
Abstract: A comprehensive numerical analysis has been conducted to explore the development of liquid-oxygen (LOX) flow in pressure swirl injectors operating at supercritical pressures. The model is based on full-conservation laws and accommodates real-fluid thermodynamics and transport phenomena over the entire range of fluid states of concern. Three different flow regimes with distinct characteristics, the developing, stationary, and accelerating regimes, are identified within the injector. Results are compared to predictions from classical hydrodynamics theories to acquire direct insight into the flow physics involved. In addition, various flow dynamics are investigated by means of the spectral and proper-orthogonal-decomposition techniques. The interactions between the hydrodynamic instabilities in the LOX film and acoustic oscillations in the gaseous core are clearly observed and studied. The influences of flow conditions (mass flowrate, swirl strength of the injected fluid, and ambient pressure) and injector g...
Book•
01 Feb 2008
TL;DR: In this article, the authors present a mathematical modeling and numerical simulation of fires, including a simulation of a pyrolysis model of a pool fire and a fire simulation of an exploding device in a JP-8 pool fire.
Abstract: Chapter 1: Mathematical modelling and numerical simulation of fires Introduction Turbulent combustion in fires Simulation and modelling Numerical method Boundary conditions and wall treatment Case study of upward flame spread over a PMMA board Chapter 2: Transport phenomena that affect heat transfer in fully turbulent fires Introduction Length and time scales within a fire Fluid dynamics within large fires Scalar transport and radiative properties Future of transport research in fires Chapter 3: Heat transfer to objects in pool fires Introduction Historical modeling approaches V&V as a foundation for predicting heat transfer to embedded objects in pool fires Surrogate fuel formulation Chemical kinetics for soot production from JP-8 Use of LES methods for pool fires Combustion/reaction models Turbulence/chemistry interactions Radiative heat transfer model Heat transfer to an embedded object in a JP-8 pool fire Prediction of heat flux to an explosive device in a JP-8 pool fire Predicting the potential hazard of an explosive device immersed in a JP-8 pool fire Toward predictivity: error quantification and propagation Summary Chapter 4: Heat and mass transfer effects to be considered when modelling the effect of fire on structures Introduction Building fires Methods of thermal analysis The boundary condition The compartment fire Solid-phase phenomena Conclusions Chapter 5: Weakly buoyant turbulent fire plumes in uniform still and crossflowing environments Introduction Structure of steady plumes in still environments Penetration of starting plumes in still environments Penetration and concentration properties of startingand steady plumes in crossflows Concluding remarks Chapter 6: Pyrolysis modeling, thermal decomposition, and transport processes in combustible solids Introduction Pyrolysis modeling and fire modeling Decomposition kinetics and thermodynamics Heat, mass, and momentum transfer Fire growth modeling Concluding remarks Chapter 7: Radiative heat transfer in fire modeling Introduction Radiative properties of combustion gases Radiative properties of soot Band models Global models Turbulence-radiation interactions Summary Chapter 8: Thermal radiation modeling in flames and fires Introduction Basic equations Solution of the RTE Radiation from flames Radiation from fires Summary Chapter 9: Combustion subgrid scale modeling for large eddy simulation of fires Introduction LES mathematical formulation Combustion SGS models Summary Chapter 10: CFD fire simulation and its recent development Introduction CFD simulation of conventional fire CFD simulation of spontaneous ignition in porous fuel storage Conclusions Chapter 11: The implementation and application of a fire CFD model Introduction Turbulence modelling Solution speed and stability Accounting for energy Liquid sprays Boundary and initial conditions The practice of modelling Assessing the model, assessing the results Examples Conclusions Chapter 12: CFD-based modeling of combustion and suppression in compartment fires Introduction Transient ignition and early fire growth Smoke filling and pre-flashover fire spread Flashover and transition to under-ventilated combustion Water-based fire suppression and fire control/extinction Conclusion
TL;DR: In this paper, the authors analyzed the chemistry and transport limitations in the partial oxidation of methane (POM) reaction carried out on Rh, supported on a foam catalyst, using spatially resolved measurements of temperature and concentration.
TL;DR: In this article, a three-dimensional numerical model of the proton exchange membrane fuel cells (PEMFCs) with conventional flow field designs (parallel flow field, Z-type flow field and serpentine flow field) has been established to investigate the performance and transport phenomena in the PEMFC.
TL;DR: In this paper, the volume-averaged porous media equations are employed to solve for transport through the porous arterial layers, and the Staverman filtration coefficient is incorporated to account for selective permeability of each porous layer to macromolecules.
TL;DR: In this paper, the authors demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the system Hamiltonian with pure dephasing induced by a fluctuating environment, in contrast to fully coherent hopping that leads to localization in disordered systems, and to highly incoherent transfer that is eventually suppressed by the quantum Zeno effect.
Abstract: Transport phenomena at the nanoscale are of interest due to the presence of both quantum and classical behavior. In this work, we demonstrate that quantum transport efficiency can be enhanced by a dynamical interplay of the system Hamiltonian with pure dephasing induced by a fluctuating environment. This is in contrast to fully coherent hopping that leads to localization in disordered systems, and to highly incoherent transfer that is eventually suppressed by the quantum Zeno effect. We study these phenomena in the Fenna-Matthews-Olson protein complex as a prototype for larger photosynthetic energy transfer systems. We also show that disordered binary tree structures exhibit enhanced transport in the presence of dephasing.
TL;DR: In this article, the authors investigated the hydrodynamic behavior of a TBR at high pressure (30 bar) in terms of pressure drop and liquid holdup after the development of a multiphase model by means of computational fluid dynamics (CFD) codes.
TL;DR: In this paper, it was shown that even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise and that entanglement does not play a supportive role.
Abstract: Transport phenomena are fundamental in Physics. They allow for information and energy to be exchanged between individual constituents of communication systems, networks or even biological entities. Environmental noise will generally hinder the efficiency of the transport process. However, and contrary to intuition, there are situations in classical systems where thermal fluctuations are actually instrumental in assisting transport phenomena. Here we show that, even at zero temperature, transport of excitations across dissipative quantum networks can be enhanced by local dephasing noise. We explain the underlying physical mechanisms behind this phenomenon, show that entanglement does not play a supportive role and propose possible experimental demonstrations in quantum optics. We argue that Nature may be routinely exploiting this effect and show that the transport of excitations in light harvesting molecules does benefit from such noise assisted processes. These results point towards the possibility for designing optimized structures for transport, for example in artificial nano-structures, assisted by noise.
TL;DR: In this paper, a thermodynamic theory for a difficult class of chemical processes undergoing in irreversible power-producing systems that yield mechanical work and are characterized by multiple (vectorial) efficiencies is developed.
TL;DR: Acts of electro-osmotic and osmotic motions, in addition to the classical Poiseuille flow, are studied at the canaliculus scale by deriving a coupled Darcy law.
Abstract: Fluid flow within cortical bone tissue is modeled through an upscaling approach of a local description of the fluid movement. At the pore scale, the coupled phenomena (Poiseuille effect, osmosis, and electro-osmosis) governing the interstitial fluid movement are considered. Thus, actions of electro-osmotic and osmotic motions, in addition to the classical Poiseuille flow, are studied at the canaliculus scale by deriving a coupled Darcy law. The addition of a Brinkman-like term in this macroscopic result helps us to take into account the influence of the pericellular matrix on the coupled transport phenomena. At the canaliculus scale, the general trends that can be drawn from this study are as follows: (i) The presence of the fibrous matrix tends to reduce the fluid flow considerably; (ii) the role of osmotic and electro-osmotic effects is no longer negligible for dense fibrous media.
TL;DR: In this article, a full 3D computational fluid dynamics model of a tubular-shaped proton exchange membrane (PEM) fuel cell has been developed, which accounts for the major transport phenomena in a PEM fuel cell: convective and diffusive heat and mass transfer.
TL;DR: In this paper, the authors provide an overview of the transport phenomena in polymer electrolyte membrane fuel cells, and a critical discussion of computational strategies to resolve processes in key components: polyethylene membrane, porous gas diffusion electrodes and microchannels.
Abstract: Fuel cells have emerged as one of the most promising energy conversion technologies to help mitigate pollution and greenhouse gas emissions. This relatively young and rapidly evolving technology offers scope for innovation in both computational modelling and design. The operation of a fuel cell depends on the optimised regulation of the flow of reactant gases, product water, heat and charged species in conjunction with reaction kinetics. These strongly coupled processes take place over a broad range of length and time scales, and in diverse structures and materials. This gives rise to a fascinating and challenging array of transport phenomena problems. This paper provides an overview of these transport phenomena in polymer electrolyte membrane fuel cells, and a critical discussion of computational strategies to resolve processes in key components: polymer electrolyte membrane, porous gas diffusion electrodes and microchannels. The integration of the various transport phenomena and components into a CFD framework is illustrated for single fuel cells and for manifolding and gas distribution in a stack. Multi-scale strategies and the coupling of CFD based models to multi-variable optimisation methods are also discussed and illustrated for catalyst layers. The paper closes with a perspective on some of the pacing items toward achieving truly functional computational design tools for fuel cells.
TL;DR: In this article, the Pauli Hamiltonian governing the leading relativistic corrections in condensed matter systems can be rewritten in a language of SU(2) covariant derivatives where the role of the non-Abelian gauge fields is taken by the physical electromagnetic fields.
TL;DR: In this article, the authors presented a mathematical model for modeling coupled heat conduction and mass diffusion of shrimp undergoing drying in a representative convective dryer, i.e., a jet spouted bed dryer.
TL;DR: The general TCAT framework and the mathematical foundation presented in previous works are built upon by formulating macroscale models for conservation of mass, momentum, and energy, and the balance of entropy for a species in a phase volume, interface, and common curve.
Book•
10 Oct 2008
TL;DR: In this article, the authors provide a brief introduction to Vectors, Tensors and Differential Operators, and a brief overview of the basic concepts in Fluid Mechanics.
Abstract: Fundamentals.- Basic Concepts in Fluid Mechanics.- Elementary Fluid Kinematics.- Fluid Forces.- Fluid Statics.- Conservation Principles.- Transport Theorems.- Integral Conservation Principles.- Constitutive Equations.- Differential Conservation Principles.- Dimensional Analysis. Theory and Applications.- Dimensional Analysis.- Dimensionless Equations and Numbers.- Transport Phenomena at Interfaces.- to the Boundary Layer.- Momentum, Heat and Mass Transport.- Self Evaluation.- Self Evaluation Exercises.- Appendices.- Collection of Formulae.- Classification of Fluid Flow.- Substance Properties.- A Brief Introduction to Vectors, Tensors and Differential Operators.- Useful Tools of Calculus.- Coordinate Systems.- Reference Systems.- Equations of State.- Multicomponent Reacting Systems.
TL;DR: In this article, the authors described the methods used for the measurement of diffusion and mass transfer of volatile compounds with their principles, main advantages and drawbacks, illustrated by some results obtained for flavoured model food products.
TL;DR: In this paper, a macroscopic model based on the Continuous Time Random Walk (CTRW) framework was developed to characterize the interaction between the fractured and porous rock domains by using a probability distribution function of residence times.
Abstract: The objective of this work is to discuss solute transport phenomena in fractured porous media, where the macroscopic transport of contaminants in the highly permeable interconnected fractures can be strongly affected by solute exchange with the porous rock matrix. We are interested in a wide range of rock types, with matrix hydraulic conductivities varying from almost impermeable (e.g., granites) to somewhat permeable (e.g., porous sandstones). In the first case, molecular diffusion is the only transport process causing the transfer of contaminants between the fractures and the matrix blocks. In the second case, additional solute transfer occurs as a result of a combination of advective and dispersive transport mechanisms, with considerable impact on the macroscopic transport behavior. We start our study by conducting numerical tracer experiments employing a discrete (microscopic) representation of fractures and matrix. Using the discrete simulations as a surrogate for the 'correct' transport behavior, we then evaluate the accuracy of macroscopic (continuum) approaches in comparison with the discrete results. However, instead of using dual-continuum models, which are quite often used to account for this type of heterogeneity, we develop a macroscopic model based on the Continuous Time Random Walk (CTRW) framework, which characterizes the interaction between the fracturedmore » and porous rock domains by using a probability distribution function of residence times. A parametric study of how CTRW parameters evolve is presented, describing transport as a function of the hydraulic conductivity ratio between fractured and porous domains.« less