The heat transfer rate per unit o surface area q\'\' that occurs across a solid
ID: 1818128 • Letter: T
Question
The heat transfer rate per unit o surface area q'' that occurs across a solid one-dimensional wall is directly proportional to the temperature difference T across the wall and inversely proportional to the thermal resistance R of the wall:
q'' = T/R
Suppose the temperature difference across a wall is maintained at a constant 100 C. Determine the heat transfer rate across the wall if it is composed of the following materials:
a) copper with R = 1.25x10-3 K-m2/W
b) aluminum with R = 2.1x10-3 K-m2/W
c) stainless steel with R = 1.25x10-2 K-m2/W
d) brick with R = 0.38 K-m2/W
e) wood with R = 4.2 K-m2/W
f) cork with R = 12.8 K-m2/W
g) styrofoam with R = 19.2 K-m2/W
Which of these materials would you classify as good conductors of heat and which ones would you judge to be good thermal insulators?
Explanation / Answer
a) q'' = (273 + 100)K/ (1.25x10-3 K-m^2/W) = 298.4 KW/m^2 b) q'' = (273 + 100)K/ (2.1x10-3 K-m^2/W) = 177.61 KW/m^2 c) q'' = (273 + 100)K/ (1.25x10-2 K-m^2/W) = 29.84 KW/m^2 d) q'' = (273 + 100)K/ (0.38 K-m^2/W) = 981.57 W/m^2 e) q'' = (273 + 100)K/ (4.2 K-m^2/W) = 88.8 W/m^2 f) q'' = (273 + 100)K/ (12.8 K-m^2/W) = 29.14 W/m^2 g) q'' = (273 + 100)K/ (19.2 K-m^2/W) = 19.42 W/m^2 Copper is good heat conductor among all.
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