Question

A double-plane window consists of two glass sheets each of area $1$ and thickness 0.01 m separated by a 0.05 m thick stagnant air space. In the steady state, the room glass interface and the glass outdoor interface are at constant temperature of $27$ and $0$ respectively. The rate of heat flow through the window pane is (Given, $K_{glass}=0.8W{m}^{-1}{K}^{-1},K_{air}=0.08W{m}^{-1}{K}^{-1}$ )

• A. 41.5 W
• B. 31.5 W
• C. 21.5 W
• D. 11.5 W

Answer 1

The correct option is A 41.5 W

Total thermal resistanceis
$R=\frac{t_1}{K_1{A}_1}+\frac{t_2}{K_2{A}_2}+\frac{t_1}{K_1{A}_1}$

$R=2\times \frac{0.01}{0.8\times 1}+\frac{0.05}{0.08\times 1}=0.65W^{}K$

$\therefore$ Heat current, $H=\frac{\Delta T}{R}=\frac{27-0}{0.65}=41.5W$