A window has a glass surface of 3574 cm2 and a thickness of 4 mm. Find the rate

Question

A window has a glass surface of 3574 cm2 and a thickness of 4 mm. Find the rate of energy transfer by conduction through this pane when the temperature of the inside surface of the glass is 78F and the outside temperature is 90 F. Assume the thermal conductivity of window glass is 0.8 J/s · m · C . Answer in units of kW. 003 (part 2 of 2) 10.0 points Find the rate of energy transfer for the same inside temperature and an outside temperature of 0F. Answer in units of kW.

I can't get the part when the outside temp is 0F Thanks! it says it's not -4.36

Explanation / Answer

A = 3574 cm2 = 0.3574 m2

L = 4 mm = 0.004 m

k = 0.8 J/s · m · C

(1) P = k A T/L

P = (0.8 * 0.3574 * (90-78) * 5/9) / 0.004

P = 476.53 Watts

P = 0.47653 kW

(2) P = k A T/L

P = (0.8 * 0.3574 * (78-0) * 5/9) / 0.004

P = 3097.47 Watts

P = 3.09747 kW

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