Chapter 19- Thermal Properties

# Chapter 19- Thermal Properties - Chapter 19 1 ISSUES TO...

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Unformatted text preview: Chapter 19 - 1 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? Chapter 19: Thermal Properties Chapter 19 - 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 capacity: ⋅ K kg J dT dQ C = T m Q c ∆ ∆ = Chapter 19 - 3 • Heat capacity...-- increases with temperature-- reaches a limiting value of 3 R • Atomic view:-- Energy is stored as atomic vibrations.-- As T goes up, so does the avg. energy of atomic vibr. Heat Capacity vs T Adapted from Fig. 19.2, Callister 7e . gas constant 3 R = 8.31 J/mol-K C v = constant Debye temperature (usually less than T room ) T (K) θ D C v C v =AT 3 Chapter 19 - 4 Energy Storage How is the energy stored? Phonons – thermal waves - vibrational modes Adapted from Fig. 19.1, Callister 7e . Chapter 19 - 5 increasing c p • Why is c p significantly larger for polymers? Selected values from Table 19.1, Callister 7e ....
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Chapter 19- Thermal Properties - Chapter 19 1 ISSUES TO...

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