Question 11.27: If the best exchanger in Illustrative Problem 11.26 is opera...
If the best exchanger in Illustrative Problem 11.26 is operated in parallel flow, determine the outside tube surface required.
From Figure 11.31,\theta_{A} = 215 – 60 = 155°F, and \theta_{B} = 125 – 90 = 35°F. Therefore,
(\Delta t)_{m}=\frac{\theta_{A}-\theta_{B}}{\ln \left(\theta_{A} / \theta_{B}\right)}=\frac{155-35}{\ln (155 / 35)}=80.6^{\circ} FBecause all other conditions are the same, \dot{Q} = 1836000 Btu/h.
1836000 = 40 × A × 80.6
Therefore, A = 569 ft .^{2} of the outside surface is required.
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