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Discover a new window to thermal engineering and thermodynamics through the study of thermal design
Thermal engineering is a specialized sub-discipline of mechanical engineering that focuses on the movement and transfer of heat energy between two mediums or altered into other forms of energy. Thermal engineers must have a strong knowledge of thermodynamics and the processes that convert generated energy from thermal sources into chemical, mechanical, or electrical energy — as such, thermal engineers can be employed in many industries, particularly in automotive manufacturing, commercial construction, and the HVAC industry. As part of their job, thermal engineers often have to improve a current system to make it more efficient, and so must be aware of a wide array of variables and familiar with a broad sweep of systems to ensure the work they do is economically viable.
In this significantly updated new edition, Thermal Design details the physical mechanisms of standard thermal devices while integrating essential formulas and detailed derivations to give a practical understanding of the field to students. The textbook examines the design of thermal devices through mathematical modeling, graphical optimization, and occasionally computational-fluid-dynamic (CFD) simulation. Moreover, it presents information on significant thermal devices such as heat sinks, thermoelectric generators and coolers, heat pipes, and heat exchangers as design components in larger systems — all of which are increasingly important and fundamental to numerous fields such as microelectronic cooling, green or thermal energy conversion, and thermal control and management in space.
Readers of the Second Edition of Thermal Design will also find:
Thermal Design is a useful reference for engineers and researchers in me chanical engineering, as well as senior undergraduate and graduate students in mechanical engineering.
HoSung Lee, PhD, is a Professor in the department of Mechanical and Aerospace Engineering at Western Michigan University, USA. His other areas of research include optimal design of thermoelectric generators and coolers and thermoelectric materials.
1 Introduction
1.1 INTRODUCTION
1.2 HUMANS AND ENERGY
1.3 THERMODYNAMICS
1.3.1 Energy, Heat, and Work
1.3.2 The First Law of Thermodynamics
1.3.3 Heat Engines, Refrigerators, and Heat Pumps
1.3.4 The Second Law of Thermodynamics
1.3.5 Carnot Cycle
1.4 HEAT TRANSFER
1.4.1 Introduction
1.4.2 Conduction
1.4.3 Convection
1.4.4 Radiation
REFERENCES
2 Heat Sinks
2.1 LONGITUDINAL FIN OF RECTANGULAR PROFILE
2.2 HEAT TRANSFER FROM FIN
2.3 FIN EFFECTIVENESS
2.4 FIN EFFICIENCY
2.5 CORRECTED PROFILE LENGTH
2.6 OPTIMIZATIONS
2.6.1 Constant Profile Area Ap
2.6.2 Constant Heat Transfer from a Fin
2.6.3 Constant Fin Volume or Mass
2.6.4 Optimum Dimensions of Rectangular Fin
2.6.5 Radial Fins
2.6.6 Optimization of Radial Fins
2.7 PLATE FIN HEAT SINKS
2.7.1 Free (Natural) Convection Cooling
2.7.2 Forced Convection Cooling
2.8 MULTIPLE FIN ARRAY II
2.8.1 Natural (Free) Convection Cooling
2.9 THERMAL RESISTANCE AND OVERALL SURFACE EFFICIENCY
2.10 FIN DESIGN WITH THERMAL RADIATION
2.10.1 Single Longitudinal Fin with Radiation
REFERENCES
PROBLEMS
3 Heat Pipes
3.1 OPERATION OF HEAT PIPE
3.2 SURFACE TENSION
3.3 HEAT TRANSFER LIMITATIONS
3.3.1 Capillary Limitation
3.3.2 Approximation for Capillary Pressure Difference
3.3.3 Sonic Limitation
3.3.4 Entrainment Limitation
3.3.5 Viscous Limitation
3.4 HEAT PIPE THERMAL RESISTANCE
3.4.1 Contact Resistance
3.5 VARIABLE CONDUCTANCE HEAT PIPES (VCHP)
3.5.1 Gas-Loaded Heat Pipes
3.5.2 Clayepyron–Clausius Equation
3.5.3 Applications
3.6 LOOP HEAT PIPES
3.7 MICRO HEAT PIPES
3.7.1 Steady-State Models
3.8 WORKING FLUID
3.8.1 Figure of Merit
3.8.2 Compatibility
3.9 WICK STRUCTURES
3.10 DESIGN EXAMPLE
3.10.1 Selection of Material and Working Fluid
3.10.2 Working Fluid Properties
3.10.3 Estimation of Operating Limits
3.10.4 Wall Thickness
3.10.5 Wick Selection
3.10.6 Maximum Arterial Depth
3.10.7 Design of Arterial Wick
3.10.8 Capillary Limitation
3.10.9 Performance Map
3.10.10 Check the Temperature Drop
REFERENCES
PROBLEMS
4 Compact Heat Exchangers
4.1 INTRODUCTION
4.2 FUNDAMENTALS OF HEAT EXCHANGERS
4.2.1 Counterflow and Parallel Flows
4.2.2 Overall Heat Transfer Coefficient
4.2.3 Log Mean Temperature Difference (LMTD)
4.2.4 Flow Properties
4.2.5 Nusselt Numbers
4.2.6 Effectiveness–NTU (ε-NTU) Method
4.2.7 Heat Exchanger Pressure Drop
4.2.8 Fouling Resistances (Fouling Factors)
4.2.9 Overall Surface (Fin) Efficiency
4.2.10 Reasonable Velocities of Various Fluids in Pipe Flow
4.3 DOUBLE-PIPE HEAT EXCHANGERS
4.4 SHELL-AND-TUBE HEAT EXCHANGERS
4.4.1 Baffles
4.4.2 Multiple Passes
4.4.3 Dimensions of Shell-and-Tube Heat Exchanger
4.4.4 Shell-Side Tube Layout
4.5 PLATE HEAT EXCHANGERS (PHEs)
4.5.1 Flow Pass Arrangements
4.5.2 Geometric Properties
4.5.3 Friction Factor
4.5.4 Nusselt Number
4.5.5 Pressure Drops
4.6 PRESSURE DROPS IN COMPACT HEAT EXCHANGERS
4.6.1 Fundamentals of Core Pressure Drop
4.6.2 Core Entrance and Exit Pressure Drops
4.6.3 Contraction and Expansion Loss Coefficients
4.7 FINNED-TUBE HEAT EXCHANGERS
4.7.1 Geometrical Characteristics
4.7.2 Flow Properties
4.7.3 Thermal Properties
4.7.4 Correlations for Circular Finned-Tube Geometry
4.7.5 Pressure Drop
4.7.6 Correlations for Louvered Plate-Fin Flat-Tube Geometry
4.8 PLATE-FIN HEAT EXCHANGERS
4.8.1 Geometric Characteristics
4.8.2 Correlations for Offset Strip Fin (OSF) Geometry
4.9 LOUVER-FIN-TYPE FLAT-TUBE PLATE-FIN HEAT EXCHANGERS
4.9.1 Geometric Characteristics
4.9.2 Correlations for Louver Fin Geometry
4.10 PLATE-FINNED HEAT PIPE HEAT EXCHANGER
4.10.1 Geometric Characteristics
4.10.2 Correlations for Plate-Finned Circular Tube Heat Exchanger
4.10.3 Fin Efficiency
4.10.4 Heat Pipes
4.10.5 Analytical Model for Plate-Finned Heat Pipe Heat Exchanger
PROBLEMS
REFERENCES
5 Thermoelectric Design
5.1 INTRODUCTION
5.1.1 Thermoelectric Effect
5.1.2 Seebeck Effect
5.1.3 Peltier Effect
5.1.4 Thomson Effect
5.1.5 Thomson (or Kelvin) Relationships
5.1.6 The Figure of Merit
5.1.7 New Generation Thermoelectrics
5.2 THERMOELECTRIC GENERATORS
5.2.1 Ideal Equations
5.2.2 Performance Parameters of a Thermoelectric Module
5.2.3 Maximum Parameters for a Thermoelectric Module
5.2.4 Normalized Parameters
5.2.5 Effective Material Properties
5.2.6 Comparison of Calculations with a Commercial Product
5.2.7 Figure of Merit and Optimum Geometry
5.3 THERMOELECTRIC COOLERS AND HEAT PUMPS
5.3.1 Ideal Equations
5.3.2 Maximum Parameters
5.3.3 Normalized Parameters for Thermoelectric Coolers
5.3.4 Normalized Parameters for Thermoelectric Heat Pumps
5.3.5 Effective Material Properties
5.4 OPTIMAL DESIGN
5.4.1 Introduction
5.4.2 Optimal Design for Thermoelectric Generators
5.4.3 Optimal Design of Thermoelectric Coolers and Heat Pumps
5.5 THOMSON EFFECT, EXACT SOLUTION, AND COMPATIBILITY FACTOR
5.5.1 Thermodynamics of Thomson Effect
5.5.2 Exact Solutions
5.5.3 Compatibility Factor
5.5.4 Thomson Effects
5.6 THERMAL AND ELECTRICAL CONTACT RESISTANCES FOR MICRO AND MACRO DEVICES
5.6.1 Modeling and Validation
5.6.2 Micro and Macro Thermoelectric Coolers
5.6.3 Micro and Macro Thermoelectric Generators
5.7 MODELING OF THERMOELECTRIC GENERATORS AND COOLERS WITH HEAT SINKS
5.7.1 Modeling of Thermoelectric Generators with Heat Sinks
5.7.2 Plate-Fin Heat Sinks
5.7.3 Modeling of Thermoelectric Coolers with Heat Sinks
5.8 APPLICATIONS
5.8.1 Exhaust Waste Heat Recovery
5.8.2 Solar Thermoelectric Generators (STEGs)
5.8.3 Automotive Thermoelectric Air Conditioner (TEAC)
PROBLEMS
REFERENCES
6 Thermoelectric Materials
6.1 CRYSTAL STRUCTURE
6.1.1 Atomic Mass
6.1.2 Unit Cells of a Crystal
6.1.3 Crystal Planes
6.2 PHYSICS OF ELECTRONS
6.2.1 Quantum Mechanics
6.2.2 Band Theory and Doping
6.3 DENSITY OF STATES, FERMI ENERGY, AND ENERGY BANDS
6.3.1 Current and Energy Transport
6.3.2 Electron Density of States
6.3.3 Fermi–Dirac Distribution
6.3.4 Electron Concentration
6.3.5 Fermi Energy in Metals
6.3.6 Fermi Energy in Semiconductors
6.3.7 Energy Bands
6.4 THERMOELECTRIC TRANSPORT PROPERTIES FOR ELECTRONS
6.4.1 Boltzmann Transport Equation
6.4.2 Simple Model of Metals
6.4.3 Power-Law Model for Metals and Semiconductors
6.4.4 Electron Relaxation Time
6.4.5 Multiband Effects
6.4.6 Nonparabolicity
6.5 PHONONS
6.5.1 Crystal Vibration
6.5.2 Specific Heat
6.5.3 Lattice Thermal Conductivity
6.6 LOW-DIMENSIONAL NANOSTRUCTURES
6.6.1 Low-Dimensional Systems
6.7 GENERIC MODEL OF BULK SILICON AND NANOWIRES
6.7.1 Electron Density of States for Bulk and Nanowires
6.7.2 Carrier Concentrations for Two-Band Model
6.7.3 Electron Transport Properties for Bulk and Nanowires
6.7.4 Electron Scattering Mechanisms
6.7.5 Lattice Thermal Conductivity
6.7.6 Phonon Relaxation Time
6.7.7 Input Data for Bulk Si and Nanowires
6.7.8 Bulk Si
6.7.9 Si Nanowires
6.8 THEORETICAL MODEL OF THERMOELECTRIC TRANSPORT PROPERTIES
6.8.1 Introduction
6.8.2 Theoretical Equations
6.8.3 Results and Discussion
6.8.4 Summary
PROBLEMS
REFERENCES
7 Solar Cells
7.1 INTRODUCTION
7.1.1 Operation of Solar Cells
7.1.2 Solar Cells and Technology
7.1.3 Solar Irradiance
7.1.4 Air Mass
7.1.5 Nature of Light
7.2 QUANTUM MECHANICS
7.2.1 Atomic Structure
7.2.2 Bohr’s Model
7.2.3 Line Spectra
7.2.4 De Broglie Wave
7.2.5 Heisenberg Uncertainty Principle
7.2.6 Schrödinger Equation
7.2.7 A Free Particle in a 1D Box
7.2.8 Quantum Numbers
7.2.9 Electron Configurations
7.2.10 Van der Waals Forces
7.2.11 Covalent Bonding
7.2.12 Energy Band
7.2.13 Pseudo-Potential Well
7.3 DENSITY OF STATES
7.3.1 Number of States
7.3.2 Effective Mass
7.4 EQUILIBRIUM INTRINSIC CARRIER CONCENTRATION
7.4.1 Fermi Function
7.4.2 Nondegenerate Semiconductor
7.4.3 Equilibrium Electron and Hole Concentrations
7.4.4 Intrinsic Semiconductors
7.4.5 Intrinsic Carrier Concentration, ni
7.4.6 Intrinsic Fermi Energy
7.4.7 Alternative Expression for n0 and p0
7.5 EXTRINSIC SEMICONDUCTORS IN THERMAL EQUILIBRIUM
7.5.1 Doping, Donors, and Acceptors
7.5.2 Extrinsic Carrier Concentration in Equilibrium
7.5.3 Built-in Voltage
7.5.4 Principle of Detailed Balance
7.5.5 Majority and Minority Carriers in Equilibrium
7.6 GENERATION AND RECOMBINATION
7.6.1 Direct and Indirect Band Gap Semiconductors
7.6.2 Absorption Coefficient
7.6.3 Photogeneration
7.7 RECOMBINATION
7.7.1 Recombination Mechanisms
7.7.2 Band Energy Diagram Under Nonequilibrium Conditions
7.7.3 Low-Level Injection
7.7.4 Band-to-Band Recombination
7.7.5 Trap-Assisted (SRH) Recombination
7.7.6 Simplified Expression of the SRH Recombination Rate
7.7.7 Auger Recombination
7.7.8 Total Recombination Rate
7.8 CARRIER TRANSPORT
7.8.1 Drift
7.8.2 Carrier Mobility
7.8.3 Diffusion
7.8.4 Total Current Densities
7.8.5 Einstein Relationship
7.8.6 Semiconductor Equations
7.8.7 Minority-Carrier Diffusion Equations
7.8.8 p–n Junction
7.8.9 Calculation of Depletion Width
7.8.10 Energy Band Diagram with a Reference Point
7.8.11 Quasi-Fermi Energy Levels
7.9 MINORITY CARRIER TRANSPORT
7.9.1 Boundary Conditions
7.9.2 Minority Carrier Lifetimes
7.9.3 Minority Carrier Diffusion Lengths
7.9.4 Minority Carrier Diffusion Equation for Holes
7.9.5 Minority Carrier Diffusion Equation for Electrons
7.10 CHARACTERISTICS OF SOLAR CELLS
7.10.1 Current Density
7.10.2 Current–Voltage Characteristics
7.10.3 Figures of Merit
7.10.4 Effect of Minority Electron Lifetime on Efficiency
7.10.5 Effect of Minority Hole Lifetime on Efficiency
7.10.6 Effect of Back Surface Recombination Velocity on Efficiency
7.10.7 Effect of Base Width on Efficiency
7.10.8 Effect of Emitter Width WN on Efficiency
7.10.9 Effect of Acceptor Concentration on Efficiency
7.10.10 Effect of Donor Concentration on Efficiency
7.10.11 Band Gap Energy with Temperature
7.10.12 Effect of Temperature on Efficiency
7.11 ADDITIONAL TOPICS
7.11.1 Parasitic Resistance Effects (Ohmic Losses)
7.11.2 Quantum Efficiency
7.11.3 Ideal Solar Cell Efficiency
7.12 MODELING
7.12.1 Modeling for a Silicon Solar Cell
7.12.2 Comparison of the Solar Cell Model with a Commercial Product
7.13 DESIGN OF A SOLAR CELL
7.13.1 Solar Cell Geometry with Surface Recombination Velocities
7.13.2 Donor and Acceptor Concentrations
7.13.3 Minority Carrier Diffusion Lifetimes
7.13.4 Grid Spacing
7.13.5 Antireflection, Light Trapping, and Passivation
REFERENCES
PROBLEMS
APPENDIX A: THERMOPHYSICAL PROPERTIES
APPENDIX B: OPTIMAL DIMENSIONLESS PARAMETERS FOR TEGS WITH ZT∞2 = 1
APPENDIX C: PIPE DIMENSIONS
APPENDIX D: PERIODIC TABLE
APPENDIX E: THERMOELECTRIC PROPERTIES
APPENDIX F: FERMI INTEGRAL
APPENDIX G: HALL FACTOR
APPENDIX H: CURVE FITTING OF WORKING FLUIDS
APPENDIX I: TUTORIAL I FOR 2D: ELECTRICAL WIRE
APPENDIX J: TUTORIAL II FOR 3D: DOUBLE-PIPE HEAT EXCHANGER
APPENDIX K: TUTORIAL TO SIMULATE A THERMOELECTRIC MODULE WITH HEATSINK IN ANSYS
APPENDIX L: TUTORIAL FOR MATHCAD
APPENDIX M: CONVERSION FACTORS
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