Answer:
a) 78.6 MJ b) 39.3 MJ
Explanation:
Assuming that the temperatures remain constant during the 5 hours, we can calculate the amount of the heat loss through the glass over this period, as follows:
ΔQ = [tex]\frac{k*A*(Ti-To)*t}{d}[/tex]
where k = thermal conductivity of glass = 0.78 W/m*K
A = area of the window = 2m * 2 m = 4 m²
Ti = temperature on the inner surface = 10ºC
Ti = temperature on the outer surface = 3ºC
d = glass layer thick = 0.5 cm = 0.005 m
t = time over which the heat is lost = 5 hs = 18,000 sec
Replacing these values in the equation above:
ΔQ =[tex]\frac{0.78 W/m*K*4 m2*7K*1.8e4s}{5e-3m} = 78.6 MJ[/tex]
If the glass layer were 1 cm thick, the above expression would become as follows:
ΔQ = [tex]\frac{0.78 W/m*K*4 m2*7K*1.8e4s}{1e-2m} = 39.3 MJ[/tex]
