The cabinet of a refrigerator is 40 cm wide, 110 cm high and 50 cm deep. The side walls, door and top consist of an inner layer of plastic (kp = 0.25 W/mK), a middle layer of grass wool (kg = 0.035 W/m-K), and an outer layer of steel (ks = 12.1 W/m-K), of thicknesses 2 mm, 60 mm and 1.5 mm respectively. When the refrigerator is operating steadily and the temperature of the surroundings is 25 C, the temperature of the contents, which may be assumed to be uniform, is 5 C. The convection heat transfer coefficients on the internal and the external surfaces are 4.0 W/mK and 6.0 W/mK respectively. Heat transfer through the base is negligible. Neglect the difference in area between the internal and external surfaces of the cabinet. 1. Estimate the heat transfer rate into the cabinet assuming radiation heat transfer is negligible. 2. Verify if it is reasonable to neglect radiation heat transfer in part 1, assume the emissivity of the wall is between 0.5 and 0.9. 3. Use the natural convection correlation to verify if it is a good estimation to use a convection coefficient of 6 W/m-K on the external side wall. (Natural convection will be covered in the week 9 lecture.)