heat transfer materials storage, transport, and transformation part i: physics
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A Short Course by Reza Toossi, Ph.D., P.E. California State University, Long Beach. Heat Transfer Materials Storage, Transport, and Transformation Part I: Physics. Outline. Atomic and Molecular Bonds Energy Carriers Specific Heat Thermal Conductivity Discussions. History. - PowerPoint PPT PresentationTRANSCRIPT
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Heat Transfer MaterialsStorage, Transport, and TransformationPart I: Physics
A Short Course byReza Toossi, Ph.D., P.E.California State University, Long Beach
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Outline
Atomic and Molecular Bonds Energy Carriers
Specific Heat Thermal Conductivity
Discussions
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History Aristotle (384 BC–323 BC) Antoine Lavoisier (1743-1794) John Dalton (1766 - 1844) Benjamin Thompson (Count Rumford) (1753-1814) Robert Mayer (1814-1878) William Thompson (Lord Kelvin) (1824-1907) Gustav Boltzmann (1844-1906) James Maxwell (1831–1879) Max Planck (1858 –1947) Neil Bohr (1855–1962) Wolfgang Pauli (1900–1958) Erwin Schrodinger (1887–1961) Enrico Fermi (1901–1954)
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Heat Transfer Medium
Gases▪ Vapors, ideal gases, and plasmas
Liquids▪ Organics▪ Inorganics
▪ Metals and Nonmetals
Solids▪ Conductors (metals)▪ Insulators (nonmetals)▪ Semiconductors
Composites ▪ Layered and non-layered
▪ Liquid-gas (aerosol spray)▪ Liquid-Liquid (emulsion)▪ Solid-solid (wood, resin-filled fiberglass)▪ Solid-gas (coal, membrane)▪ Solid-liquid-gas (nucleate boiling on a solid surface)
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Thermochemical and Thermophysical Properties
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Microscopic Heat Transfer
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Microscopic Energy Carriers
Particles Waves Quasi-Particles
▪ Phonon ▪ Acoustic▪ Optical
▪ Photon▪ Electron (and Hole)
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Strong and Weak Bonds
Strong Bonds Ionic Covalent Metallic
Weak Bonds (~kcal/mole)
Van der Waals▪ Hydrogen▪ Electrostatic
(ionic)
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Strong (Primary) Bonds
Ionic (metal to nonmetal) NaCl
Covalent (nonmetal to nonmetal) Diamond, organic matters
Metallic bonding (metal to metal) Silver
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Weak (Secondary) Bonds Hydrogen Forces (H2O, NH3)
Van der Waals Dipole-Dipole Forces (HCl-HCl)
London Dispersion Forces (Xe-Xe)
Ion-Dipole Forces
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Bond Strength
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Bonding Between Neutral Atoms
Attractive force @ large distances (van der Waals) Repulsive force @ short distances (Pauli repulsion) Models▪ Quantum mechanical (Dipole-dipole and London forces)▪ Classical (LJ)
V is the energy potential Is the equilibrium distancee is the energy of interaction (depth of the potential well)r is the distance of separation
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Cohesion and Adhesion
Cohesion: Intermolecular attraction between molecules of the same kind or phase (viscosity in fluid)
Adhesion: Intermolecular attraction between molecules of different kind or phase (water wetting of a glass, oil droplets in a hot skillet)
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Transport Phenomena
Conduction Macroscale (> 1 mm, Fourier’s Law ) Microscale (1-100 μm, Thermalization) Nanoscale (1-100 nm, Non-equilibrium)
Surface Tension Macroscale Microscale
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Continuum Approach Continuity
Species
Momentum (Navier-Stokes)
Energy
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Continuum Flow Limitations
Continuum regime (Kn < 0.01)Slip flow regime (0.01 < Kn <
0.1)Transition regime (0.1 < Kn < 3)Free molecular flow regime (Kn
> 3)
Knudsen Number:
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Statistical Approach
Boltzmann Transport Equation
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Nanoscale Considerations Nonequilibrium Phenomenon
Ultra small dimensions Ultrafast processes
Different conduction equations for electrons and the lattice Nucleation
Laser Irradiation
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Example: Laser Processing of Material
Melting of Gold Films Short-pulsed laser melting of thin films
involves two non-equilibrium processes. (1) Deposition of laser energy (2) Energy transfer between electrons and lattice (3) Melting
One –Step Model
Two –Step Model
Electron:
Lattice: Kuo, L.S., and Qui, T.Q., 1996, “Microscale Energy Transfer During Picosecond Laser Melting of Metal Films,” ASME HTD-Vol. 323, Vol. 1, pp.149-157.
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Results (Gold film with L = 1000 nm, tp =20 ps)
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Specific Heat of Various Substances
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Heat Storage
Specific Heat Capacities: Cp and Cv Gases
▪ Translational▪ Rotational▪ Vibrational▪ Electronic
Solids (metals, dielectrics, and semiconductors)▪ Lattice vibration (phonons)▪ Free electrons
Liquids▪ Near critical point (behaves like a gas)▪ Away from critical point (behaves like a solid)
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Modes of Energy Storage (H2)
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Cp 0 to ∞
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Cp for GasesSpecific Heat of Selected gases at 300 K
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Cp for solids
Einstein (Classic) Model cv = 3 k (per molecule), 3R (per mole)
Debye Model cv increases until TD
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Cp for liquids
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Cp for Water
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Thermal Conductivity
Thermal Conductivity (k) Gases Solids
▪ Metals (Drude classical theory)▪ Nonmetals (Debye model)▪ Semiconductors
Liquids Composites
▪ Effective conductivity
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Contributions from Heat Carriers
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Equilibrium vs. Transport
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Mechanism of Heat Conduction in Gases
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Mechanism of Heat Conduction in Solids Roles of the conduction electrons and the thermal
lattice vibration are significant Conduction electrons (Drude Model)
Lattice (phonons) vibration (Callaway Model)▪ Amorphous (non-periodic)▪ Crystalline (Periodic)
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k = km+ ke + kp
Molecular For an ideal monatomic gas For an ideal polyatomic gas
Electronic Contribution to thermal
conductivity
Contribution to electrical conductivity
Phonons
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Metals, Nonmetals, and Semiconductors
Metals Excellent heat conductor Excellent electrical conductor
Nonmetals Poor heat conductor Poor electrical conductor
Semiconductors Fair heat conductor Good electrical conductor
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Thermal Conductivities of Solids
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Thermal Materials:From Ideal Insulators to Perfect Conductors
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Thermal Conductivity of Liquids
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Thermal Conductivity of Composites
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Further Readings Lee, J., Sears, F. W, and Turcotte, D. L., “Statistical
Thermodynamics,” Addison-Wesley, 1963. Tien, C. L., and Lienhard, J. H., “Statistical
Thermodynamics,” Holt, Rinehart and Winston, 1971.
Kaviany, M., “Principal of Heat Transfer,” Wiley, 2002.
Atkins, P. W., “Molecular Quantum Mechanics,” Clarendon Press, 1970.
Siegal, R., and Howell, J. R., “Thermal Radiation Heat Transfer,” Hemisphere Publishing Corporation, 3rd Ed., 1992