2-4 Find the heat transfer per unit area through the composite wall in Figure P2-4. Assume one-dimensional heat flow. Figure P2-4

KA=150W/m℃ ΔXA=2.5×10-2m AA=0.1m2

KB=30 ΔXB=ΔXD=7.5×10-2m AB=AD=0.05m2

KC=50 ΔXC=5×10-2m AC=0.1m2

KD=70

AB=AD RA=0.025/(150*0.1)=0.00166℃/W RB=0.075/(30*0.05)=0.05℃/W RC=0.05/(50*0.1)=0.01℃/W RD=0.075/(70*0.05)=0.021℃/W Rth=0.00166+{1/[(1/0.05)+(1/0.021)]}+0.1=0.026448732℃/W q=(370-66)/0.026448732=11692.30769 W