Halliday, Resnick & Walker — Temperature, Heat, and the First Law of Thermodynamics: Problem 109

Composite slab conduction. A composite slab with face area \(A = 26\text{ ft}^2\) consists of \(2.0\text{ in.}\) of rock wool and \(0.75\text{ in.}\) of white pine. The thermal resistances for a \(1.0\text{ in.}\) slab are \(R_{rw} = 3.3\text{ ft}^2 \cdot {}^\circ\text{F} \cdot \text{h/Btu}\) and \(R_{wp} = 1.3\text{ ft}^2 \cdot {}^\circ\text{F} \cdot \text{h/Btu}\). The temperature difference between the slab faces is \(65\text{ F}^\circ\). What is the rate of heat transfer through the slab?