A wall is constructed of a 5 cm layer of fibro board (R = 1) and 15 cm of fibreglass batting (R = 3). If the temperature on the outside surface of the fibreglass board is 40$\degree$C and the temperature on the inside surface of the fibreglass batting is 20$\degree$C, what is the temperature (in $\degree$C) at the interface?

Question

Quizplus · Accepted Answer

The temperature drop across each layer is proportional to its thermal resistance. The total resistance is 4 (1 for fibro board + 3 for fibreglass). The temperature drop across the fibro board is (1/4) of the total temperature difference (20°C), which is 5°C. Therefore, the temperature at the interface is 40°C - 5°C = 35°C.

A Wall Is Constructed of a 5 Cm Layer of Fibro