6 The walls of a refrigerator are typically constructed by sandwiching a layer of insulation between sheet metal panels. Consider a wall made from fiberglass insulation of thermal conductivity k;thickness

L; = 50 mm and steel panels, each of thermal conductivity k, = 60 W/m K and thickness L,, = 3 mm.If the wall separates refrigerated air at Tei = 4°C from ambient air at T = 25°C, what is the heat gain per unit surface area? Coefficients associated with natural convection at the inner and outer surfaces may be approximated as hi= ho 5w/m2 K

Fig: 1