Effect of a Window in a Door. A carpenter builds a solid wood door with dimensions 2.00 m X 0.95 m X 5.0 cm. Its thermal conductivity is k = 0.120 W/m· K. The air films on the inner and outer surfaces of the door have the same combined thermal resistance as an additional 1.8·cm thickness of solid wood. The inside air temperature is 20.0oC, and the outside air temperature is -8.0oC.
(a) What is the rate of heat flow through the door?
(b) By what factor is the heat flow increased if a window 0.500 m on a side is inserted in the door? The glass is 0.450 cm thick, and the glass has a thermal conductivity of 0.80 W/m. K. The air films on the two sides of the glass have a total thermal resistance that is the same as an additional 120 cm of glass.