A)
For metals : Thermal conductivity - 50 to 1000 W/mK; CTE - 5 to 25 x 10-6 m/mK
For ceramic : Thermal conductivity - 80 to 300 W/mK; CTE - 2 to 12 x 10-6 m/mK
(Note : polymers and ceramics are different types of materials, thermal conductivity of polymers are lower and coefficient of thermal expansion larger as compared to ceramics.)
B)
Thermal conductivity of metal remains almost constant with change in temperature (may experience slight decrease). The slight change observed is due to the opposing effects of flow of electrons and molecular vibration at higher temperature. The conductivity depends on flow on electrons which is obstructed by the vibrating molecules at higher temperature.
C)
basis - taking maximum value of CTE
For metal :
Initial length - 10 cm. Initial temp - 25°C. Final temp - 300°C
CTE - 25 x 10-6 m/mK
Final length = 10+0.1*(300-25)*25x10-6 = 10.000687 cm
For ceramic
Initial length - 10 cm. Initial temp - 25°C. Final temp - 300°C
CTE - 12 x 10-6 m/mK
Final length = 10+0.1*(300-25)*12x10-6 = 10.00033 cm
5. 20 pts (A) What are typical values of thermal conductivity and coefficient of thermal expansion...
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