(a) What is the heat flow through a glass window of dimensions 0.50 m x 0.50 m a

Question

(a) What is the heat flow through a glass window of dimensions 0.50 m x 0.50 m and thickness 4.0 mm, when the inside temperature is 25 celsius and the outside temperature is -15 celsius. (thermal conductivity of glass is 0.8 W/mK and of air is 0.024 W/mK)

(b) What is the heat flow when a thicker glass window of 8.0 mm is used?

(c) Estimate the heat flow when a double pane of glass is used with a 4.0 mm air gap between the panes? Each individual glass sheet is 4.0 mm thick.

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Explanation / Answer

a) Q/t = k A dT/L = 0.8*0.5^2*40/4.0E-3=2000

b) double the thickenss halves the flow, so 1000

c) 1/R = L/kA + L/kA + L/kA = 8.0E-3/(0.8*0.5^2) + 4.0E-3/(0.024*0.5^2)=1/R

R=1.4151

so Q/T = 1.4151*40=56.6

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