Consider a 1. 0. m-high and 1. 0. m-wide double-pane window consisting of two 3-

Question

Consider a 1. 0. m-high and 1. 0. m-wide double-pane window consisting of two 3-mm-thick layers of glass (k = 07. 8 W/m . C) separated by a 12. mm-wide stagnant air space (k = 0. 026 W/m . C). Determine the steady rate of heat transfer through this double-pane window and the temperature of its inner surface for a day during which the room is maintained at 20 C while the temperature of the outdoors is 0 C. Take the convection heat transfer coefficients on the inner and outer surface of the window to be h1 = 10 W/m2 . C and h2 = 25 W/m2 . C, rexpectly, an disregard any heat transfer by radiation.

Explanation / Answer

Area A = 1 * 1 = 1 m^2

Total thermal resistance = 1/h1A + 2*t1/k1A + t2/k2A + 1/h2A

= 1/(10*1) + 2*0.003/(0.78*1) + 0.012/(0.026*1) + 1/(25*1)

= 0.609 deg C/W

Q = (T1-T2)/R

Q = (20-0)/0.609 = 32.8 W

Q = kA(dT/dx)

32.8 = 0.78*1*(20-T1')/0.003

T1' = 19.87 deg C

32.8 = 0.78*1*(T2'-0)/0.003

T2' = 0.126 deg C

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