Chapter 13, Problem 13.112P

Consider a vertical, double-pane window for the conditions prescribed in Problem 9.94. That is, vertical panes at temperature of $T_1=22°\text{C}$ and $T_2=-20°\text{C}$ are separated by atmospheric air, and the critical
Rayleigh number for the onset of convection is $R{a}_{L,c}=2000$ .
(a) What is the conduction heat flux across the air gap for the optimal spacing $L_{\text{op}}$ between the panes?
(b) If the glass has an emissivity of ${\epsilon }_g=0.90$ , what is the total heat flux across the gap?
(c) What is the total heat flux if a special, low emissivity coating $\left({\epsilon }_c=0.10\right)$ is applied to one of the panes at its air-glass interface? What is the total heat flux if both panes are coated?