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# Problem 14-2 - Example 14-2 Air flows through a tube with...

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Example 14-2 Air flows through a tube with an inside diameter of 1.5 cm and outside diameter of 2.5 cm. The tube has a thermal conductivity of 52 W/m·K and is 5 m long. The inlet temperature is 42°C, the required outlet temperature is 52°C, and the flow rate is 50 kg/h. Steam condenses on the outside of the tube with a heat transfer coefficient of 1000 W/m 2 K. What steam temperature is required to obtain this outlet air temperature? What is the steam pressure? Use the ε – NTU method. Solution: The total heat transferred is () ,, CC o C i QCT T =− ± max min , , o C i H iC i CT T Q Q T ε == ± ± min , , H i T ±

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The steam temperature is constant ,, H iH oH TT T == max C →∞ min p Cm c = ± air side () , pH C i Qm c T T ε =− ± ± Because the steam is condensing, 1e x p NTU ( ) , x p C i QN T U m c T T ⎡⎤ ⎣⎦ ± ± min p UA UA NTU c ± pC o C i cT T ± ± , x p o C i C i p UA mc T T mc T T mc ⎛⎞ −= ⎢⎥ ⎜⎟ ⎝⎠ ±± ± , x p Co Ci p HC i UA mc ± To find U , we need h i . The average air temperature is
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Problem 14-2 - Example 14-2 Air flows through a tube with...

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