q =-k*(dT/dx) ] where q :heat flux/how much heat passes per unit area per unit time ; k: thermal conductivity (W/mk) ]]only valid for steady state heat flow(flux does not change with time)
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How is heat transported through solid materials?
Lattice vibrations(phonons), Free electrons
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How can the total thermal conductivity of a material be found?
It is the sum of the two contributions. K = k_l +k_e
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What determines the relative contribution of K_e to k_l?
The number of free electrons. (the concentration of free electrons.
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Explain why K_e increases with the increase in the concentration of free electrons?
As more electrons are available to participate in the heat transference process.
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What is more significant K_e or K_l for metals and why?
Free electrons are more significant than phonons.
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What is the Wiedemann-Franz law?
L= k/sT ] where s:electrical conductivity; T: Absolute temperature; L: a constant --> 2.44 *10^-8 W/(K)^2
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What happens at a fixed temperature for metals?
Thermal conductivity α Electrical conductivity
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What is primarily responsible for thermal conductivity in a ceramic?
Phonons (they are not that effective)
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Which is more conductive, glass or crystal and why?
Ceramic crystals are more conductive as they are ordered so phonons do not scatter.
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How can the thermal conductivity of a ceramic be increased?
The efficiency of the process increases with temperature due to radiant heat transfer.
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How is energy transfered in a polymer?
Through vibrations and rotation of the chain molecules.
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What does K depend on in polymers and why?
The degree of crystallinity. k_crystalline > k_amorphous. Since there is more effective coordination of vibration.
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How can a polymer be made to be more insulating?
By introducing small pores .(foaming).
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Other cards in this set
Card 2
Front
Give an equation for thermal conductivity
Back
q =-k*(dT/dx) ] where q :heat flux/how much heat passes per unit area per unit time ; k: thermal conductivity (W/mk) ]]only valid for steady state heat flow(flux does not change with time)
Card 3
Front
How is heat transported through solid materials?
Back
Card 4
Front
How can the total thermal conductivity of a material be found?
Back
Card 5
Front
What determines the relative contribution of K_e to k_l?
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