Consider a double-paned window consisting of two panes of glass, each with a thi

Question

Consider a double-paned window consisting of two panes of glass, each with a thickness of 0.600cm and an area of 0.775m^2 , separated by a layer of air with a thickness of 1.55cm . The temperature on one side of the window is 0.00 degree celsius ; the temperature on the other side is 25.0 degree celsius. In addition, note that the thermal conductivity of glass is roughly 36 times greater than that of air. a)Approximate the heat transfer through this window by ignoring the glass. That is, calculate the heat flow per second through 1.55cm of air with a temperature difference of 25.0 degree celsius . (The exact result for the complete window is 28.6 J/s.) b)Use the approximate heat flow found in part A to find an approximate temperature difference across each pane of glass. (The exact result is 0.264 degree celsius .)

Explanation / Answer

Qdot = kappa * A *delta(T)/D For air, kappa = 0.025 W / m C, so Qdot = 0.025 J/s / (m C) * 0.775m^2 * 20.0C/(0.0175m) = 20.6 J/s (b) That same heat flow is through a pane, so 20.6 J/s = 36*0.025W/(m C) * 0.720m^2 * Delta(T) / (0.005 m) => Delta(T) = 0.157 C

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