Use the exact values you enter in previous answer(s) to make later calculation(s

Question

Use the exact values you enter in previous answer(s) to make later calculation(s).

Energy-efficient windows are constructed with two panes of glass separated by an air gap (see figure below). In a typical window of this type, the air gap makes a huge difference in the rate of heat flow. The heat-flow rate is much smaller for an energy-efficient window than for a single pane of glass because the thermal conductivity of the air gap is much less than that of a glass pane.

(a) To compare heat flow for the different types of windows, first calculate the heat-flow rate for a single-pane window. Assume the glass is 3.6 mm thick, it has an area of 0.55 m2, and the temperatures on the two sides of the glass differ by 31

Explanation / Answer

Q/t = k A(delta T)/L Q=heat gain/loss t=time so Q/t is time rate of heat conduction k= thermal conductivity and is the key player here A=area, L=length, delta T is temp difference on either side of the material if everything is being held constant, the key difference is the value of the thermal conductivity coefficients for glass and air for air, this constant = 0.023 J/(s m C) for glass, it is 0.84 J/(sm C) so the ratio of values for air to glass is 0.023/0.84=0.027, so 0.027 times as much energy conducts through air each sec as through glass this means you would need a pane of glass 1 cm x (1/0.027) thick to have the same rate of energy conduction

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