Chapter 13, Problem 13.113P

Consider the double-pane window of Problem 9.95, for which $1\text{m}\times 1\text{m}$ panes are separated by a 25-mm gap of atmospheric air. The window panes are approximately isothermal and separate quiescent room air at $T_{\infty ,i}=20°\text{C}$ from quiescent ambient air at $T_{\infty ,o}=-20°\text{C}$ .
(a) For glass panes of emissivity ${\epsilon }_g=0.90$ , determine the temperature of each pane and the rate of heat transfer through the window.
(b) Quantify the improvements in energy conservation that may be effected if the space between the panes is evacuated and/or a low emissivity coating $\left({\epsilon }_c=0.1\right)$ is applied to the surface of each pane adjoining the gap.