#### Question

The north wall of an electrically heated home is 20 ft long, 10 ft high, and 1 ft thick, and is made of brick whose thermal conductivity is $k=0.42 \mathrm{Btu} / \mathrm{h} \cdot \mathrm{ft} \cdot ^{\circ} \mathrm{F}.$ On a certain winter night, the temperatures of the inner and the outer surfaces of the wall are measured to be at about $62^{\circ} \mathrm{F}$ and $25^{\circ} \mathrm{F},$ respectively, for a period of 8 h. Determine (a) the rate of heat loss through the wall that night and (b) the cost of that heat loss to the home owner if the cost of electricity is \$0.07/kWh.

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#### Step 1

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$\textit{\textbf{Assumptions:} \\ (1) Thermal properties of the wall are constant. \\ (2) Heat transfer through the wall is by conduction. }$

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#### Fundamentals of Thermal-Fluid Sciences

5th EditionJohn Cimbala, Robert Turner, Yunus A. Cengel
2,403 solutions