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 2° 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 24°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.

Transcribed Image Text:

Sheet metal Insulation 1 mm L FIGURE P17-31 Kitchen air 24C Refrigerated space 2°C mm