Chapter 1, Problem 1.9P

A glass window of width $W=1\text{m}$ and height $H=2\text{m}$ is 5 mm thick and has a thermal conductivity of $k_g=1.4\text{W/m}\cdot \text{K}\text{.}$ If the inner and outer surface temperatures of the glass are $15°\text{C}$ and $-20°\text{C,}$ respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of $10°\text{C}$ and $-15°\text{C,}$ what is the rate of heat loss from a $1\text{m}\times 2\text{m}$ window? The thermal conductivity of air is $k_a=0.024\text{W/m}\cdot \text{K}\text{.}$