The wall of a refrigerator is constructed of fiberglass insulation (k = 0.035 W/m·
°C) sandwiched between two layers of 1-mm-thick sheet metal (k = 15.1 W/m·
°C) as shown in Fig. 3. The refrigerated space is maintained at 3°C, and the average heat transfer coefficients at the inner and outer surfaces of the wall are 4 W/m2· °C and 9 Wm2· °C, respectively. The kitchen temperature averages 25 °C. It is observed that condensation occurs on the outer surfaces of the refrigerator when the temperature of the outer surface drops to 20 °C. Take the surface area of the refrigerator is 1 m 2.
a. Sktech the thermal resistance network diagram for the above system
b. Determine the minimum thickness of fiberglass insulation that needs to be
used in the wall in order to avoid condensation on the outer surfaces.