USCG Exam PracticeRefrigeration principles and systems
In a marine shell-and-tube condenser, non-condensable gas that enters the system will collect where, and what is the operational consequence?
- A. It collects at the bottom of the receiver and restricts liquid flow to the metering device, starving the evaporator
- ✓ It collects at the top of the condenser and receiver, raising head pressure without contributing to heat rejectionCorrect
- C. It collects in the compressor crankcase, diluting the lubricating oil and reducing bearing protection
- D. It collects in the evaporator coil, insulating the coil surface and reducing heat absorption
Why B is correct
NAVEDTRA 14075 §6-3 states that non-condensable gas (air) collects in the top of the condenser and receiver, raising head pressure without doing any cooling, and must be removed by purging. This elevated head pressure causes the compressor to work harder and can trip the high-pressure cutout.
Cited:NAVEDTRA 14075 §6-3