Question 6.CSGP.84: In a co-flowing (same direction) heat exchanger 1 kg/s air a......
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 \dot{ W }, \dot{ Q })
Continuity Eq.: \dot{ m }_1=\dot{ m }_3 \text { and } \dot{ m }_2=\dot{ m }_4
Energy Eq.6.10: \dot{ m }_1 h _1+\dot{ m }_2 h _2=\dot{ m }_1 h _3+\dot{ m }_2 h _4
Same exit T: h _3= h _4=\left[\dot{ m }_1 h _1+\dot{ m }_2 h _2\right] /\left[\dot{ m }_1+\dot{ m }_2\right]
Using conctant specific heat
T _3= T _4=\frac{\dot{ m }_1}{\dot{ m }_1+\dot{ m }_2} T _1+\frac{\dot{ m }_2}{\dot{ m }_1+\dot{ m }_2} T _2=\frac{1}{3} \times 500+\frac{2}{3} \times 300= 3 6 7 \,K
