Discussion
The log mean temperature difference (LMTD) correction factor is not required during heat transfer rate calculation in
Answer: B
No correction factor is needed for a 1 shell pass and 1 tube pass heat exchanger.
The LMTD formula is exact only for pure parallel flow or pure counterflow. A 1-1 shell-and-tube exchanger is one of these: the shell fluid and tube fluid each make a single pass, so the exchanger is analysed directly as counterflow (or parallel flow) with F = 1.
In 1-2 and 2-4 shell-and-tube exchangers the tube fluid reverses direction, so part of the exchanger runs in parallel flow and part in counterflow; the true mean temperature difference is less than the counterflow LMTD and a correction factor F below 1 is applied. Plate heat exchangers are also normally treated with a correction factor, because their pass and channel arrangements depart from pure counterflow; the key takes the 1-1 shell-and-tube exchanger as the case that needs none.
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