Question

Find the amount of thermal energy that will flow through a concrete wall 20.0 m long,1.80 m high, and 12.0 cm wide, in a period of 24.0 hr, if the inside temperature of the wall is 15.0◦Cand the outside temperature of the wall is 0.00◦C. (For concrete,k= 1.30 (J/m s◦C).)

Answer 1

The formula for rate of heat transfer is given by

where , the thermal conductivity

, the cross-sectional area

, the temperature difference on either side of the wall. While convention dictates we must use Kelvin, we can express temperature difference in Celsius as well, as the Celsius scale is simply a shifted Kelvin scale.

, the thickness of the wall.

Putting in our values, we will get the rate of heat transfer.

To get the amount of energy transferred, we multiply the rate of heat transfer by the number of seconds in 24 hours.