Lecture 14 - Thermal Properties Thermal Properties ISSUES...

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1 Thermal Properties ISSUES TO ADDRESS. .. • How does a material respond to heat? • How do we define and measure. .. -- heat capacity -- coefficient of thermal expansion -- thermal conductivity -- thermal shock resistance • How do ceramics, metals, and polymers rank? Thermal Properties
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2 General: The ability of a material to absorb heat. • Quantitative: The energy required to increase the temperature of the material. heat capacity (J/mol-K) energy input (J/mol) temperature change (K) Heat Capacity Two ways to measure heat capacity: C p : Heat capacity at constant pressure. C v : Heat capacity at constant volume. C p > C v • Specific heat has typical units of K kg J dT dQ C = Heat Capacity, II What contributes to the heat capacity: Atomic vibrations Electronic excitations In metals only, Electrons close to Fermi level are only contributors Very small compared to vibrational contributions Magnetic order/disorder transitions Important only in magnetic materials Other order/disorder transitions: Configurational, for example
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3 Energy Storage- Vibrational Heat Capacity In most solids, thermal atomic vibrations are principal way of storing heat As atoms “heat up”, kinetic energy of atoms increases Restoring forces due to atomic bonds cause the atoms to oscillate around equilibrium position Vibrations are coordinated Traveling elastic waves (sound waves) Thermal energy consists of series of elastic waves with particular frequencies Energy Storage How is the energy stored?
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This note was uploaded on 06/24/2009 for the course MEEN 222 taught by Professor Radovic during the Fall '08 term at Texas A&M.

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Lecture 14 - Thermal Properties Thermal Properties ISSUES...

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