A composite wall is made of two different homogeneous layers joined in perfect…
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A composite wall is made of two different homogeneous layers joined in perfect thermal contact. In the steady state the inner surface of the wall is maintained at 90 °C while the outer surface is at 30 °C.
(i) State Fourier’s law of heat conduction.
(ii) Explain, with reasons, why the thermal resistances of two layers placed one after another along the direction of heat flow are additive, whereas the thermal conductances of two layers placed side by side (offering parallel paths for heat) are additive.
(iii) Draw a qualitative sketch of temperature versus position across the thickness of the wall and label the temperatures at the two surfaces and at the common interface.