The composite wall of a refrigerator has a thermal conductivity of 0.05 W/m•K and a wall thickness of 50 mm. In a room of 25 °C, the refrigerated cold space inside the refrigerator is maintained at 4 °C. Assume the inner and outer convection heat transfer coefficients are 5 W/m2•K and 10 W/m2•K, respectively. Neglect radiation heat transfer.
Determine the rate of heat leaking into the refrigerator per unit surface area. [10 Marks]