The space between the panes of a doubleglazed window note th

The space between the panes of a double-glazed window (note the windows are completely enclosed) is filled with air at 1 atmosphere. The window is 1.5m high and the spacing is 37.5mm. The outside temperature is - 10 degree C and the inside temperature it 20 degree C. Calculate the heal transfer across the double pane window. Assume radiation it negligible. Show all of your work and units.

Solution

A double pane glass window has two glass surfaces separated by air entrapped.

Height of the glass window = 1.5m

Assume the glass is 1m in length. therefore the area of glass surface, A= 1.5 m²

Temperature Out= -10⁰C, Temperature In = 20⁰C

therefore change in temperature, = 20- (-10) = 30⁰C

we have the equation for heat transfer, dQ/dt = k* A* (Tin - Tout) /L

In this case we have 3 layers( 2 glass layers and 1 air layer)

therefore heat transfer dQ/dt = A * (Tin- Tout) / {(L1/k1)+ (L2/k2) + (L3/k3)}

k = heat conductivity constant in J/ sec m ⁰C

L= length of the path heat has to travel in metres

we have k for glass = 0.8 J/ sec m ⁰C

k for air = 0.024 J/ sec m ⁰C.

Heat transfer across the window:

dQ/dt = 1.5 * 30 / {(0.005/0.8) + (0.0375/0.024) + (0.005/0.8) }

= 45/ 1.575

= 28.57 J/sec or 28.57 Watts.