9.24 A refrigerator door has a height and width of H-1m and W- 0.65 m, respectively, and is situated in a large room for which the air and walls are at T s 25°C. The door consists of a layer of...

9.24 A refrigerator door has a height and width of H-1m and W- 0.65 m, respectively, and is situated in a large room for which the air and walls are at T s 25°C. The door consists of a layer of polystyrene insulation (k-o.03 W/m s K) sandwiched between thin sheets of steel (E0.6) and polypropylene. Under normal operating conditions, the inner surface of the door is maintained at a fixed temperature of Tsi 5°C. a) Estimate the rate of heat gain through the door for the worst-case condition corresponding to no insulation (1-0). b) Compute the rate of heat gain with an outside surface temperature Ts,o 20 °C and an insulation thickness of L = 15 mm.