Thermal Conduction, Thermal Conductivity – Problems and Solutions

07. The brick wall of a house is 35 cm thick with an area of 28 m². The temperature inside and outside the house are 21 ^oC and 16 ^oC respectively.
a. Calculate the heat loss per hour through the wall.
b. If the wall is covered with a layered of plastic 15 mm thick on the inside surface, find the heat loss per hour for the same temperature difference.
— Thermal Conductivity of plaster = 0.004 W m^-1 K^-1, and of brick = 0.4 Wm^-1 K^-1 .–

Solutions

a. the heat loss per second through the wall.

$\\\\ \frac {dQ}{dt}= -kA \frac {d\theta}{dx}\\\\ \frac {dQ}{dt}= -0.4 x 28 x \left(\frac {16 - 21}{35 x 10^-2} \right) \\\\ \frac {dQ}{dt}= 160 Js^{-1} \\\\$

the heat loss per hour through the wall.

$\\\\ \frac {dQ}{dt}= 160 x 60 x 60 = 5.76 x 10^5 J \\\\$

Source : Physics Problems

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