Topic: Heat Transfer
It is required to insulate a kitchen oven with cork board (K=0.043 W/(m K)) so that the heat losses from the oven does not exceed 400 W/m² when the inner surface of the oven is at 225°C and the outer surface of the oven is at 40°C. The thickness of insulation required is nearly
- A. 1 cm
- B. 2 cm
- C. 3 cm
- D. 4 cm
Answer: B. 2 cm
Explanation: Applying Fourier's Law for heat conduction, the heat flux is given by $Q/A = k \frac{\Delta T}{\delta}$. The heat flux is 400 W/m², thermal conductivity $k = 0.043 \text{ W/m-K}$, and the temperature difference $\Delta T = 225 - 40 = 185°\text{C}$. Rearranging for thickness $\delta$ gives $\delta = \frac{0.043 \times 185}{400} = 0.01988 \text{ m}$. This is approximately 2 cm.