Vapour Power Cycle In Engineering Thermodynamics by PK Nag (Chapter 12)

A: Governing principle: Overpressure protection is sized for credible upset, not normal operation. Here, loss of load with continued firing drives pressure faster than MCR assumptions, so the relief basis collapses. Option D traps engineers who know once-through boilers behave differently, then apply that distinction to relief philosophy where it doesn't belong.

A: Governing principle: Mass transfer can control metal loss when protective films are unstable. High velocity strips magnetite faster than it reforms, even with low oxygen, matching the observed pattern. Option D catches people who see low pH and stop there, dropping the velocity term that actually sets the rate.

A: Governing principle: Regeneration trades hardware for cycle efficiency and chemistry control. Closed heaters boost efficiency without direct mixing, keeping oxygen and contaminants out of the feedwater. Option B tempts engineers from smaller plants where simplicity rules, but it breaks chemistry control at this scale.

A: Governing principle: Non-condensables raise partial pressure without changing cooling water duty. Normal CW conditions with pressure rise point to air leakage rather than heat transfer loss. Option B traps those who default to fouling, ignoring that fouling tracks CW temperature rise, which isn't present.