A thermopane window consists of two glass panes, each 0.50 cm thick, with a 1.0-

Question

A thermopane window consists of two glass panes, each 0.50 cm thick, with a 1.0-cm-thick sealed layer of air in between. (Use 0.8 J/s · m · °C for the thermal conductivity of glass and 0.0234 J/s · m · °C for the thermal conductivity of air to answer the following.)

(a) If the inside surface temperature is 23.7°C and the outside surface temperature is 0.0°C, determine the rate of energy transfer through 1.85 m2 of the window.
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(b) Compare your answer to (a) with the rate of energy transfer through 1.85 m2 of a single 1.0-cm-thick pane of glass. Disregard surface air layers.
W

Explanation / Answer

A = 1.85 m^2
T = 23.7°C
1x = 0.50 cm = 0.005 m
2x = 1.0 cm = 0.01m
3x = 0.50 cm = 0.005 m
K1 = 0.0234
k2 = 0.8
K3 = 0.0234

Now that we know these, you must plug them into this equation: http://upload.wikimedia.org/math/2/0/f/20f80e46fc929fe8b63923b32ce2f4f2.png
First, multiply A by T to get 43.845. Then divide this by number by 0.005/0.0234 + 0.01/0.8 + 0.005/0.0234

I ended up with 99.68 J/s.

For the single pane window, just plug into this equation:
J/s (Single pane window) = -KA(T/x) = -(0.8)(1.85)(-23.7/0.01) = 3507.6 J/s

Therefore, using significant digits:
J/s (Thermopane window) = 99.68 J/s
J/s (Single pane window) = 3507.6J/s
The thermopane window transfers a lot less heat per second than the single window, so it is a better insulator.

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