The wall of a refrigerator is constructed of fiberglassinsulation (k = 0.035 W/m·K) sandwiched between two layersof 1-mm-thick sheet metal (k = 15.1 W/m·K). The refrigeratedspace is maintained at 3°C, and the average heat transfercoefficients at the inner and outer surfaces of the wall are4 W/m2·K and 9 W/m2·K, respectively. The kitchen temperatureaverages 25°C. It is observed that condensation occurson the outer surfaces of the refrigerator when the temperatureof the outer surface drops to 20°C. Determine the minimumthickness of fiberglass insulation that needs to be used in thewall in order to avoid condensation on the outer surfaces.

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