USCG Exam PracticeThermodynamics and heat exchangers
Why is counter-flow arrangement preferred over parallel-flow in most shipboard heat exchangers?
- A. Counter-flow allows both fluids to enter at the same end, simplifying piping connections
- ✓ Counter-flow produces a more uniform temperature difference along the exchanger length and allows the cold fluid outlet to exceed the hot fluid outlet temperatureCorrect
- C. Counter-flow eliminates the need to calculate the log-mean temperature difference
- D. Counter-flow reduces fouling because the two streams move in opposite directions and flush scale from the surfaces
Why B is correct
DOE-HDBK-1018 Vol.1 §2-2 explains that in counter-flow the temperature difference is more uniform along the length, the exchanger is thermally more efficient, and the cold fluid can leave hotter than the hot fluid's outlet — none of which is achievable in parallel-flow. The log-mean temperature difference applies to both arrangements.
Cited:DOE-HDBK-1018 Vol.1 §2-2