In a co-flowing (same direction) heat exchanger 1 kg/s air at 500 K flows into one channel and 2 kg/s air flows into the neighboring channel at 300 K. If it is infinitely long what is the exit temperature? Sketch the variation of T in the two flows.
C.V. mixing section (no W˙,Q˙)
Continuity Eq.: m˙1=m˙3 and m˙2=m˙4
Energy Eq.6.10: m˙1h1+m˙2h2=m˙1h3+m˙2h4
Same exit T: h3=h4=[m˙1h1+m˙2h2]/[m˙1+m˙2]
Using conctant specific heat
T3=T4=m˙1+m˙2m˙1T1+m˙1+m˙2m˙2T2=31×500+32×300=367K