The wall of a refrigerator is constructed of fiberglass insulation (k = 0.035 w/m·k) sandwiched between two layers of 1-mm-thick sheet metal (k = 15.1 w/m·k). 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·k and 9 w/m2·k, 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. determine the minimum thickness of fiberglass insulation that needs to be used in the wall in order to avoid condensation on the outer surfaces.