Teaching Nanoscale Transport Phenomena.Pdf

Total Page:16

File Type:pdf, Size:1020Kb

Teaching Nanoscale Transport Phenomena.Pdf Teaching Nanoscale Transport Phenomena Pamela Norris Professor Department of Mechanical and Aerospace Engineering University of Virginia Charlottesville, VA 22902 VIRGINIA 1 • UVa – MAE 612 – Microscale Heat Transfer • Berkeley – ME 259 – Microscale Thermophysics and Heat Transfer • MIT – ME 2.57 – Nano-to-Macro Transport Processes • Ga Tech – ME 8833 Nano/Microscale Heat Transfer and Thermophysics • U Penn – ME 572 – Micro/Nanoscale Energy Transport • UC Boulder – MCEN 5228 – Nano-to-Macroscale Transport Processes • U Mich – ME 539 – Heat Transfer Physics (with a focus on size effects) Several more examples can be found…. 2 • Microscale Heat Transfer Courses – Graduate Level Courses in Mechanical Engineering • “advanced statistical thermodynamics, nonequilibrium thermodynamics, and kinetic theory concepts used to analyze thermophysics of microscale systems...” -UC Berkeley ME 259 course description – Typical Prerequisites • Undergraduate thermo • Undergraduate heat transfer • Graduate thermo/statistical physics • Note---no solid state physics, quantum mechanics, statistical mechanics, or kinetic theory exposure is typically required 3 Microscale Heat Transfer has been taught for a decade at UVA (once every two years) • First half of the course focuses on developing the solid state background required (with Kittel, Ashcroft and Mermin as the texts) with assigned homework • The second half of the course uses current research papers in the field and relies on open discussion • The final two weeks of the course are dedicated to student presentations of a current research topic • Class size is typically 7 grad and 1 undergrad (all Mechanical and Aerospace Engineers) 4 • Microscale Heat Transfer Text Books G. Chen, 2005, Nanoscale Energy Transport and Z. M. Zhang, 2007, Nano/Microscale Heat Transfer, Conversion: A Parallel Treatment of Electrons, (McGraw Hill). 5 Molecules, Phonons, and Photons, (Oxford University Press, New York). “The challenge for the profession and engineering education is to ensure that the core knowledge advances in nanoscience, and other areas yet to be discovered are delivered to engineering students so they can leverage them to achieve interdisciplinary solutions to engineering problems in their engineering practice.” (The Engineer of 2020: visions of engineering in the new century, National Academy of Engineering) 6 Proposal: Undergraduate Microscale Heat Transfer Course • Interdisciplinary approach to microscale heat transfer • Teach theory of heat transfer physics and microscale heat transfer phenomena driven by applications of nanotechnology and nanodevices in all disciplines Being developed with Patrick Hopkins, PhD student and NSF fellow. To be team taught in the Spring 2008. 7 • Focus: Undergraduate engineering majors • Relevant ABET Curriculum – 2 semesters intro physics (mechanics + E&M) – 1 semester general chemistry – ordinary differential equations • Goal: Microscale heat transfer class for undergraduates 8 • Undergraduate course for all engineers should focus on concepts – Basic thermodynamics (macro) – Quantum mechanics – Solid state physics – Statistical mechanics – Basic heat transfer (macro) – Kinetic theory – Nonequilibrium thermodynamics 9 • Supplement the aforementioned topics with examples and motivating applications in various fields of nanotechnology and engineering – IC development, processor speed, Moore’s Law, FETs – Quantum wells, VCSELs and waveguides – Quantum dots – Hard drive “read” head and magnetic materials – Thermoelectric devices – Current microscale heat transfer research and phenomena driven by applications (electron- phonon coupling, TBR, EPRT) E. L. Wolf, 2004, Nanophysics and Nanotechnology: An introduction to modern concepts of nanoscience, (Wiley-VCH, Weinheim). 10 • Basic thermodynamics – Historical development – Equilibrium thermo – Selected sections in Chapters 1-6 D. Kondepudi and I. Prigogine, 1998, Modern Thermodynamics: From Heat Engines to Dissipative Structures, (John Wiley and Sons, Inc., New York). 11 • Mechanics – Harmonic motion of particles (Ch. 3 and 4) – Lagrangian mechanics (Ch. 10) – Dynamics of oscillating systems (Ch. 11) Fowles and Cassiday, 1999, Analytical Mechanics 6th Ed., (Harcourt Brace, Orlando). 12 • Origins of quantum theory – History – BB radiation – Photoelectric effect – de Broglie postulate – Uncertainty principle – Sections in Chapters 3 – 5 Llewellyn and Tipler, 2000, Modern Physics 3rd Ed., (Freeman, New York). 13 • Quantum mechanics – Schrodinger – Free particles – Potential well 14 Griffiths, 2000, Introduction to Quantum Mechanics 2nd Ed., (Prentice Hall, New Jersey). • Statistical mechanics – Partition functions – Particle development of basic thermo – Energy storage on the microscale Reif, 1965, Fundamentals of statistical and thermal physics, (McGraw-Hill, Inc.,New York). 15 • Solid state physics – Crystal structure – Vibrations – Phonon properties and link to statistical – Electron properties and link to statistical Kittel, 2005, Introduction to Solid State Physics, 8th Ed., (John Wiley and Sons, New Jersey). 16 • Basic heat transfer and kinetic theory – Modes of heat transfer – Particle view of heat transfer – electrons and phonons – Phenomena in microscale heat transfer using theory previously developed through nanoscale applications: what happens when device x is shrunk down to y length scale? How is transport affected based on quantum mechanics, solid state physics, and statistical mechanics? Reif, 1965, Fundamentals of statistical and thermal physics, (McGraw-Hill, Inc.,New York). 17 • Non-equilbrium thermodynamics – Wrap up with 1-2 lectures pointing to the differences and where this can go and how non-equilibrium effects are starting to become increasingly important – Part IV, Chapters 15-17 D. Kondepudi and I. Prigogine, 1998, Modern Thermodynamics: From Heat Engines to Dissipative Structures, (John Wiley and Sons, Inc., New York). 18 It is our hope that by teaching students the fundamentals of the physics of heat transport with a bottom up approach even before they have seen the entire system or the macroscale, they will be able to better understand how effects at the nanoscale influence and limit system performance and that we can train students that are better able to find interdisciplinary solutions to practical design problems. 19.
Recommended publications
  • HEAT TRANSFER PHYSICS, SECOND EDITION This Graduate Textbook Describes Atomic-Level Kinetics (Mechanisms and Rates) of Thermal E
    Cambridge University Press 978-1-107-04178-3 - Heat Transfer Physics: Second Edition Massoud Kaviany Frontmatter More information HEAT TRANSFER PHYSICS, SECOND EDITION This graduate textbook describes atomic-level kinetics (mechanisms and rates) of thermal energy storage, transport (conduction, convection, and radiation), and transformation (various energy conversions) by principal energy carriers. The approach combines the fundamentals of molecular orbitals-potentials, sta- tistical thermodynamics, computational molecular dynamics, quantum energy states, transport theories, solid-state and fluid-state physics, and quantum optics. The textbook presents a unified theory, over fine-structure/molecular- dynamics/Boltzmann/macroscopic length and time scales, of heat transfer kinetics in terms of transition rates and relaxation times, and its modern applica- tions, including nano- and microscale size effects. Numerous examples, illustra- tions, and homework problems with answers to enhance learning are included. This new edition includes applications in energy conversion (including chem- ical bond, nuclear, and solar), expanded examples of size effects, inclusion of junction quantum transport, and discussion of graphene and its phonon and electronic conductances. New appendix coverage of phonon contributions to the Seebeck coefficient, Monte Carlo methods, and ladder operators is also included. Massoud Kaviany is a Professor in the Department of Mechanical Engineering and in the Applied Physics Program at the University of Michigan, where he has been since 1986. His area of teaching and research is heat transfer physics, with a particular interest in porous media. His current projects include atomic structural metrics in high-performance thermoelectric materials (both electron and phonon transport) and in laser cooling of solids (including ab initio cal- culations of photon-electron and electron-phonon couplings), and the effect of pore water in polymer electrolyte transport and fuel cell performance.
    [Show full text]
  • Downloadable in Supplementary Materials of Ref[190], and the Training Process Is Performed Using the QUIP Package
    THERMAL CONDUCTIVITY OF COMPLEX CRYSTALS, HIGH TEMPERATURE MATERIALS AND TWO DIMENSIONAL LAYERED MATERIALS By XIN QIAN B.S. Huazhong University of Science and Technology, 2014 A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Mechanical Engineering 2019 i This thesis entitled: Thermal Conductivity of Complex Crystals, High Temperature Materials and Two Dimensional Layered Materials written by Xin Qian has been approved for the Department of Mechanical Engineering Prof. Ronggui Yang, Chair Prof. Baowen Li Date: The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above mentioned discipline. ii ABSTRACT Xin Qian (Ph.D, Mechanical Engineering) Thermal Conductivity of Complex Crystals, High Temperature Materials and Two Dimensional Layered Materials Thesis directed by Professor Ronggui Yang Thermal conductivity is a critical property for designing novel functional materials for engineering applications. For applications demanding efficient thermal management like power electronics and batteries, thermal conductivity is a key parameter affecting thermal designs, stability and performances of the devices. Thermal conductivity is also the critical material metrics for applications like thermal barrier coatings (TBCs) in gas turbines and thermoelectrics (TE). Therefore, thermal conductivities of various functional materials have been investigated in the past decade, but most of the materials are simple and isotropic crystals at low temperature. This is because the first-principles calculation is limited to simple crystals at ground state and few experimental methods are only capable of measuring thermal conductivity along a single direction.
    [Show full text]
  • A Fast Synthetic Iterative Scheme for the Stationary Phonon Boltzmann Transport Equation
    A fast synthetic iterative scheme for the stationary phonon Boltzmann transport equation Chuang Zhanga, Songze Chena, Zhaoli Guoa,∗, Lei Wub,∗ aState Key Laboratory of Coal Combustion, Huazhong University of Science and Technology,Wuhan, 430074, China bJames Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde, Glasgow G1 1XJ, UK Abstract The heat transfer in solid materials at the micro- and nano-scale can be described by the mesoscopic phonon Boltzmann transport equation (BTE), rather than the macroscopic Fourier's heat conduction equa- tion that works only in the diffusive regime. The implicit discrete ordinate method (DOM) is efficient to find the steady-state solutions of the BTE for highly non-equilibrium heat transfer problems, but converges extremely slowly in the near-diffusive regime. In this paper, a fast synthetic iterative scheme is developed to accelerate convergence for the implicit DOM based on the stationary phonon BTE. The key innovative point of the present scheme is the introduction of the macroscopic synthetic diffusion equation for the tempera- ture, which is obtained from the zero- and first-order moment equations of the phonon BTE. The synthetic diffusion equation, which is asymptomatically preserving to the Fourier's heat conduction equation in the diffusive regime, contains a term related to the Fourier's law and a term determined by the second-order moment of the distribution function that reflects the non-Fourier heat transfer. The mesoscopic kinetic equation and macroscopic diffusion equations are tightly coupled together, because the diffusion equation provides the temperature for the BTE, while the BTE provides the high-order moment to the diffusion equa- tion to describe the non-Fourier heat transfer.
    [Show full text]
  • Heat Transfer Physics, Winter 2011 Tu & Th, 11:30-1:00, 104 EWRE 3 Credits, Prerequisite: Heat Transfer (ME 335 Or Equivalent), Instructor: M
    ME 539 (AP 639), Heat Transfer Physics, Winter 2011 Tu & Th, 11:30-1:00, 104 EWRE 3 Credits, Prerequisite: Heat Transfer (ME 335 or equivalent), Instructor: M. Kaviany Department of Mechanical Engineering, University of Michigan, Ann Arbor OBJECTIVE Heat Transfer Physics is a graduate course describing atomic-level kinetics (mechanisms and rates) of thermal energy storage, transport (conduction, convection, and radiation), and transformation (various energy conversions) by principal energy carriers. These carriers are: phonon (lattice vibration wave also treated as quasi-particle), electron (as classical or quantum entity), fluid particle (classical particle with quantum features), and photon (classical electromagnetic wave also as quantum-particle), as show in figure below. The approach combines fundamentals (through survey and summaries) of following fields. Molecular orbitals/potentials, statistical thermodynamics, computational molecular dynamics (including lattice dynamics), quantum energy states, transport theories (e.g., the Boltzmann and stochastic transport equations and the Maxwell equations), solid-state (including semiconductors) and fluid-state (including surface interactions) physics, and quantum optics (e.g., spontaneous and stimulated emission, photon– electron–phonon couplings). These are rationally connected to atomic-level heat transfer (e.g., heat capacity, thermal conductivity, photon absorption coefficient) and thermal energy conversion (e.g., ultrasonic heating, thermoelectric and laser cooling). The course presents a unified theory, over fine-structure/molecular-dynamics/Boltzmann/macroscopic length and time scales (as shown in figure below), of the heat transfer kinetics which are the transition rates and relaxation times. The fundamentals are also relates to modern applications (including nano- and microscale size effects). The prerequisite is ME 335 (Heat Transfer) or consensus of the instructor.
    [Show full text]
  • 1 Introduction and Preliminaries
    Cambridge University Press 978-1-107-04178-3 - Heat Transfer Physics: Second Edition Massoud Kaviany Excerpt More information 1 Introduction and Preliminaries The macroscopic heat transfer rates use thermal-energy related properties, such as the thermal conductivity, and in turn these properties are related to the atomic-level properties and processes. Heat transfer physics addresses these atomic-level pro- cesses (e.g., kinetics). We begin with the macroscopic energy equation used in heat transfer analysis to describe the rates of thermal energy storage, transport (by means of conduction k, convection u, and radiation r), and conversion to and from other forms of energy. The volumetric macroscopic energy conservation (rate) equation is listed in Table 1.1.† The sensible heat storage is the product of density and specific heat capacity ρcp, and the time rate of change of local temperature ∂T/∂t. The heat flux vector q is the sum of the conductive, convective, and radiative heat flux vec- tors. The conductive heat flux vector qk is the negative of the product of the thermal conductivity k, and the gradient of temperature ∇T , i.e., the Fourier law of conduc- ‡ tion. The convective heat flux vector qu (assuming net local motion) is the product of ρcp, the local velocity vector u, and temperature. For laminar flow, in contrast to turbulent flow that contains chaotic velocity fluctuations, molecular conduction of the fluid is unaltered, whereas in turbulent flow this is augmented (phenomenolog- ically) by turbulent mixing transport (turbulent eddy conductivity). The radiative heat flux vector qr = qph (ph stands for photon) is the spatial (angular) and spectral integrals of the product of the unit vector s and the electromagnetic (EM), spectral (frequency dependent), directional radiation intensity Iph,ω, where ω is the angular frequency of EM radiation (made up of photons).
    [Show full text]
  • First-Principles Modeling of Thermal Transport in Materials
    International Journal of Thermophysics (2020) 41:9 https://doi.org/10.1007/s10765-019-2583-4 First‑principles Modeling of Thermal Transport in Materials: Achievements, Opportunities, and Challenges Tengfei Ma1 · Pranay Chakraborty1 · Xixi Guo1 · Lei Cao1 · Yan Wang1 Received: 9 August 2019 / Accepted: 30 November 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Thermal transport properties have attracted extensive research attentions over the past decades. First-principles-based approaches have proved to be very useful for predicting the thermal transport properties of materials and revealing the phonon and electron scattering or propagation mechanisms in materials and devices. In this review, we provide a concise but inclusive discussion on state-of-the-art frst-prin- ciples thermal modeling methods and notable achievements by these methods over the last decade. A wide range of materials are covered in this review, including two- dimensional materials, superhard materials, metamaterials, and polymers. We also cover the very recent important fndings on heat transfer mechanisms informed from frst principles, including phonon–electron scattering, higher-order phonon–phonon scattering, and the efect of external electric feld on thermal transport. Finally, we discuss the challenges and limitations of state-of-the-art approaches and provide an outlook toward future developments in this area. Keywords Density functional theory · Electron · First principles · Phonon · Thermal transport 1 Introduction 1.1 Overview Thermal transport is of fundamental importance in a number of modern technologi- cal drivers, for instance, transistors, optoelectronics, photovoltaics, and thermoelectric energy conversion [1–3]. The materials used in these applications vary in size, lattice structure, constituting elements, type and number of defects, etc., imposing great chal- lenges for optimal thermal design of the devices.
    [Show full text]
  • 1 Applications of Heat Transfer Fundamentals to Fire Modeling O.A
    Applications of Heat Transfer Fundamentals to Fire Modeling O.A. Ezekoye1, M. J. Hurley2, J.L. Torero3, and K.B. McGrattan4 1 Dept. of Mechanical Engineering, The University of Texas at Austin and 2Society of Fire Protection Engineers and 3The University of Queensland and 4National Institute of Standards and Technology Abstract The fire industry relies on fire engineers and scientists to develop materials and technologies used to either resist, detect, or suppress fire. While combustion processes are the drivers for what might be considered to be fire phenomena, it is heat transfer physics that mediate how fire spreads. Much of the knowledge of fire phenomena has been encapsulated and exercised in fire modeling software tools. Over the past 30 years, participants in the fire industry have begun to use fire modeling tools to aid in decision making associated with design and analysis. In the rest of this paper we will discuss what the drivers have been for the growth of fire modeling tools, the types of submodels incorporated into such tools, the role of model verification, validation, and uncertainty propagation in these tools, and possible futures for these types of tools to best meet the requirements of the user community. Throughout this discussion, we identify how heat transfer research has supported and aided the advancement of fire modeling. Introduction On this occasion of the 75th anniversary of the ASME Heat Transfer Division, we provide an overview of the fire industry and discuss how heat and mass transfer fundamentals are applied in fire modeling. The fire industry, which will be discussed shortly, relies on fire engineers and fire scientists to advance materials and technologies used to either resist, detect, or suppress fire.
    [Show full text]
  • A Review of Simulation Methods in Micro/Nanoscale Heat Conduction
    ES Energy & Environment REVIEW PAPER View Article Online A Review of Simulation Methods in Micro/Nanoscale Heat Conduction Hua Bao,1* Jie Chen,2* Xiaokun Gu3* and Bingyang Cao4* Significant progress has been made in the past two decades about the micro/nanoscale heat conduction. Many computational methods have been developed to accommodate the needs to investigate new physical phenomena at micro/nanoscale and support the applications like microelectronics and thermoelectric materials. In this review, we first provide an introduction of state-of-the-art computational methods for micro/nanoscale conduction research. Then the physical origin of size effects in thermal transport is presented. The relationship between the different methods and their classification are discussed. In the subsequent sections, four commonly used simulation methods, including first-principles Boltzmann transport equation, molecular dynamics, non-equilibrium Green’s function, and numerical solution of phonon Boltzmann transport equation will be reviewed in details. The hybrid method and coupling scheme for multiscale heat transfer simulation are also briefly discussed. Keywords: Heat conduction; First-principles; Boltzmann transport equation; Molecular dynamics; Non-equilibrium Green’s function Received 4 September 2018, Accepted 7 October 2018 DOI: 10.30919/esee8c149 1. Introduction dimensional materials,7,8 and considerable work is devoted into The miniaturization of devices and structures, higher power density laboratory studies on superlattices, nanofluids, as well as special of the novel electronic and optic cells and more severe thermal nanostructures and interfaces at micro/nanoscale.9,10 conditions pose huge challenges to the thermal management and Despite the rapid progress of experimental measurements, it is energy conversion issues.
    [Show full text]
  • The Heat Transfer Module User's Guide
    Heat Transfer Module User’s Guide Heat Transfer Module User’s Guide © 1998–2019 COMSOL Protected by patents listed on www.comsol.com/patents, and U.S. Patents 7,519,518; 7,596,474; 7,623,991; 8,457,932; 8,954,302; 9,098,106; 9,146,652; 9,323,503; 9,372,673; 9,454,625; and 10,019,544. Patents pending. This Documentation and the Programs described herein are furnished under the COMSOL Software License Agreement (www.comsol.com/comsol-license-agreement) and may be used or copied only under the terms of the license agreement. COMSOL, the COMSOL logo, COMSOL Multiphysics, COMSOL Desktop, COMSOL Compiler, COMSOL Server, and LiveLink are either registered trademarks or trademarks of COMSOL AB. All other trademarks are the property of their respective owners, and COMSOL AB and its subsidiaries and products are not affiliated with, endorsed by, sponsored by, or supported by those trademark owners. For a list of such trademark owners, see www.comsol.com/trademarks. Version: COMSOL 5.5 Contact Information Visit the Contact COMSOL page at www.comsol.com/contact to submit general inquiries, contact Technical Support, or search for an address and phone number. You can also visit the Worldwide Sales Offices page at www.comsol.com/contact/offices for address and contact information. If you need to contact Support, an online request form is located at the COMSOL Access page at www.comsol.com/support/case. Other useful links include: • Support Center: www.comsol.com/support • Product Download: www.comsol.com/product-download • Product Updates: www.comsol.com/support/updates • COMSOL Blog: www.comsol.com/blogs • Discussion Forum: www.comsol.com/community • Events: www.comsol.com/events • COMSOL Video Gallery: www.comsol.com/video • Support Knowledge Base: www.comsol.com/support/knowledgebase Part number: CM020801 Contents Chapter 1: Introduction About the Heat Transfer Module 20 Why Heat Transfer Is Important to Modeling .
    [Show full text]
  • Thermal Energy at the Nanoscale Week 5: Carrier Scattering and Transmission Lecture 5.3: Phonon-Phonon Scattering Fundamentals
    Thermal Energy at the Nanoscale Week 5: Carrier Scattering and Transmission Lecture 5.3: Phonon-Phonon Scattering Fundamentals By Tim Fisher Professor of Mechanical Engineering Purdue University 1 Anharmonic Scattering • Spring stiffness, g, changes with strain • A strain caused by one wave will be seen as a different stiffness • Anharmonic scattering is also known as intrinsic scattering because it can happen in a pure crystal 2 3-Phonon Scattering • 3-phonon interactions (phonon- phonon)K 1 K3 K1 + K 2 = K 3 ω1 + ω2 = ω3 (A) Normal K 2 (N) K3 K1 K1 = K 2 + K 3 ω = ω + ω 1 2 3 (B) K K 2 K 2 1 Umklapp + = + ω + ω = ω (C) K1 K 2 K 3 G 1 2 3 (U) Where G is the reciprocal lattice vector 3 Brillouin Zone G K2 K3 K2 K 1 Γ K1 K3 4 Consequences for Heat Conduction • N processes do not impede phonon momentum, therefore, do not impede heat flow ‘directly’ – Affect heat flow by re-distributing phonon energies • U processes do impede phonon momentum and do impede heat flow – Dominate thermal conductivity of semiconductors and insulators 5 Finding the Scattering Rate G K2 K3 K2 K 1 Γ K1 K3 Surface of energy imbalance Δω for the process ZA(K1)+ZA(K2)→TA(K3) 6 Line Segment of Energy Balance: LA phonons Type 2 Type 1 4) LA+ZATO, K =13.2 nm-1 1) LA ZO+LA, K =11.8 nm-1 1 1 5) LA+ZALO, K =11.8 nm-1 -1 1 2) LA ZO+TA, K1 =11.8 nm -1 -1 6) LA+ZA LA, K1 =8.8 nm 3) LA ZA+TA, K1 =11.8 nm -1 7) LA+ZOLO, K1 =5.8 nm 7 Scattering Analysis and Models • Quantum mechanics + perturbation theory required for full scattering analysis, called “Fermi’s Golden Rule” (see Kaviany, Heat Transfer Physics, 2008 Appendix E).
    [Show full text]
  • A Comprehensive Review of Heat Transfer in Thermoelectric Materials and Devices
    A Comprehensive Review of Heat Transfer in Thermoelectric Materials and Devices Zhiting Tian, Sangyeop Lee and Gang Chen Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge, MA 02139, USA Abstract Solid-state thermoelectric devices are currently used in applications ranging from thermocouple sensors to power generators in satellites, to portable air-conditioners and refrigerators. With the ever-rising demand throughout the world for energy consumption and CO2 reduction, thermoelectric energy conversion has been receiving intensified attention as a potential candidate for waste-heat harvesting as well as for power generation from renewable sources. Efficient thermoelectric energy conversion critically depends on the performance of thermoelectric materials and devices. In this review, we discuss heat transfer in thermoelectric materials and devices, especially phonon engineering to reduce the lattice thermal conductivity of thermoelectric materials, which requires a fundamental understanding of nanoscale heat conduction physics. Key words: Heat Transfer, Thermoelectric, Nanostructuring, Phonon Transport, Electron Transport, Thermal Conductivity Nomenclature Constant: = Boltzmann constant, ћ = reduced Planck constant, Symbols: A = cross-sectional area, m2 C = spectral volumetric specific heat, J m-3 Hz-1 K-1 D = density of states per unit volume per unit frequency interval, m-3 Hz-1 e = charge per carrier, C = Fermi level (i.e. electrochemical potential) relative to conduction band edge , J = band gap energy
    [Show full text]
  • Discrete Unified Gas Kinetic Scheme for Multiscale Heat Transfer With
    Discrete unified gas kinetic scheme for multiscale heat transfer with arbitrary temperature difference Chuang Zhanga, Zhaoli Guoa,∗ aState Key Laboratory of Coal Combustion, Huazhong University of Science and Technology,Wuhan, 430074, China Abstract In this paper, a finite-volume discrete unified gas kinetic scheme (DUGKS) based on the non-gray phonon transport model is developed for multiscale heat transfer problem with arbitrary temperature difference. Un- der large temperature difference, the phonon Boltzmann transport equation (BTE) is essentially multiscale, not only in the frequency space, but also in the spatial space. In order to realize the efficient coupling of the multiscale phonon transport, the phonon scattering and advection are coupled together in the present scheme on the reconstruction of the distribution function at the cell interface. The Newtonian method is adopted to solve the nonlinear scattering term for the update of the temperature at both the cell center and interface. In addition, the energy at the cell center is updated by a macroscopic equation instead of taking the moment of the distribution function, which enhances the numerical conservation. Numerical re- sults of the cross-plane heat transfer prove that the present scheme can describe the multiscale heat transfer phenomena accurately with arbitrary temperature difference in a wide range. In the diffusive regime, even if the time step is larger than the relaxation time, the present scheme can capture the transient thermal transport process accurately. Compared to that under small temperature differences, as the temperature difference increases, the variation of the temperature distribution behaves quite differently and the average temperature in the domain increases in the ballistic regime but decreases in the diffusive regime.
    [Show full text]