Assume all temperatures to be exact. A large window measures 2.1 m by 3.0 m. At

Question

Assume all temperatures to be exact. A large window measures 2.1 m by 3.0 m. At what rate will heat be conducted through the window when the room temperature is 22 degree C and the outside temperature is 4 degree C if the window consists of a single pane of glass 4.3 mm thick. (Assume that there is a constant temperature difference and consider conduction only.) Express your answer using two significant figures. At what rate will heat be conducted through the window when the room temperature is 22 degree C and the outside temperature is 4 degree C if the window instead has a double pane of glass (a "thermopane" in which each pane is 2.2 mm thick, with an intervening air space of 1.4 mm? (Assume that there is a constant temperature difference and consider conduction only.) Express your answer using two significant figures.

Explanation / Answer

Part A )

the rate of heat transfer H = K A ( T2 - T1 ) / L

and H = dQ / dt

thermal conductivity of window K = 0.8

dQ / dt = 0.8 X 2.1 X 3 X ( 22 - 4 ) / 4.3 X 10-3

dQ / dt = 21097.67 W

or

dQ / dt = 21097.67 J/s

Part B )

the rate of heat transfer H = K A ( T2 - T1 ) / L

and H = dQ / dt

thermal conductivity of window K = 0.93

dQ / dt = 0.93 X 2.1 X 3 X ( 22 - 4 ) / ( 2.2 + 1.4 ) X 10-3

dQ / dt = 29295 W

or

dQ / dt = 29295 J/s

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