A rectangular wall of a store-room measures and is built of burnt clay bricks thick…

PHYSICS · Subjective · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter

Problem

A rectangular wall of a store-room measures

15\,\text{m}\times3.0\,\text{m}

and is built of burnt clay bricks

0.25\,\text{m}

thick whose thermal conductivity is

0.80\,\text{W\,m}^{-1}\,\text{K}^{-1}

. In winter the inside surface of the wall is at

22^{\circ}\text{C}

while the outside surface remains at

2^{\circ}\text{C}

. The owner wishes to limit the heat flow through this wall to

9.0\times10^{2}\,\text{W}

by attaching an additional layer of glass-wool insulation on the inner side. (a) Write an expression for the total thermal resistance of the composite wall. (b) Calculate the minimum thickness of glass-wool (thermal conductivity

0.040\,\text{W\,m}^{-1}\,\text{K}^{-1}

) that must be added to achieve the desired limit, assuming steady one-dimensional conduction and neglecting surface convection.

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