A composite refrigerator wall is composed of 5 cm of corkboard sandwiched between a 1.2-cm-thick layer of oak and a 0.8-mm-thick layer of aluminum lining on the inner surface. The average convection heat transfer coefficients at the interior and exterior wall are 11 and 8.5 W/ (m² K) respectively. 

(a) Draw the thermal circuit. 

(b) Calculate the individual resistances of the components of this composite wall and the resistances at the surfaces. 

(c) Calculate the overall heat transfer coefficient through the wall. 

(d) For an air temperature of –1°C inside the refrigerator and 32°C outside, calculate the rate of heat transfer per unit area through the wall.