A Concrete Wall of a Cold Storage Room Measures 3

Multiple Choice

A concrete wall of a cold storage room measures 3.0 m high,5.0 m wide,and 20 cm thick.The inside wall is to be covered by a layer of wood in order to reduce the rate of heat flow through the wall by 90 percent.The inner surface of the wooden wall is maintained at -10°C and the outer surface of the concrete wall is at 20°C.The thermal conductivities of concrete and wood are 0.80 W/m ∙ K (concrete) and 0.040 W/m ∙ K (wood) .What should be the thickness of the layer of wood?

A) 60 mm
B) 70 mm
C) 80 mm
D) 90 mm
E) 100 mm