Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5 cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.

GIVEN

Wood wall

Two layers 0.025 m thick each

Nail cross sectional area of nails = 0.5% of wall area

Temperature difference (???T) = 25°C

ASSUMPTIONS

One dimensional heat transfer through the wall

Steady state prevails

Contact resistance between the wall layers isnegligible

AT= 25C Nals Wood 2.5 in