USCG Exam PracticeThermodynamics and heat exchangers
A lube-oil cooler aboard a vessel is found to be losing cooling capacity gradually over several weeks of operation. Based on heat-exchanger theory, what is the most probable cause?
- A. The log-mean temperature difference has increased, reducing the driving force for heat transfer.
- ✓ Fouling — scale, sludge, or oil films — has added thermal resistance to the tube surfaces.Correct
- C. The counter-flow arrangement has reverted to parallel flow, reducing thermal efficiency.
- D. Non-condensable gases have accumulated in the shell side, blanketing the tubes.
Why B is correct
DOE-HDBK-1018 Vol.1 §2-1 identifies fouling — scale, sludge, marine growth, or oil films — as the most common reason a cooler gradually loses capacity, because it adds thermal resistance to the surfaces.
Cited:DOE-HDBK-1018 Vol.1 §2-1