CPE Mechanical Systems & Equipment 4 — Questions and Answers
Question 1: In a shell-and-tube heat exchanger, baffles are installed to:
- Increase tube-side velocity to enhance heat transfer
- Direct shell-side flow across tubes and increase turbulence (Correct answer)
- Separate the tube-side and shell-side fluids
- Support the tube bundle and maintain tube spacing
Correct answer: Direct shell-side flow across tubes and increase turbulence
Baffles force the shell-side fluid to flow perpendicular to the tubes, increasing turbulence and heat transfer coefficient while also supporting the tube bundle.
Question 2: A plant engineer observes that a reciprocating compressor is running hot. Which cause should be investigated FIRST?
- Overspeed operation above rated RPM
- Fouled or leaking valves reducing volumetric efficiency (Correct answer)
- Incorrect lubricant viscosity grade
- Excessive discharge pipe length
Correct answer: Fouled or leaking valves reducing volumetric efficiency
Leaking or fouled compressor valves cause gas recirculation and recompression, which generates excessive heat and reduces capacity.
Question 3: The purpose of a pressure-compensated variable displacement pump in a hydraulic system is to:
- Maintain constant flow regardless of system pressure
- Maintain constant pressure by varying flow output (Correct answer)
- Convert hydraulic pressure to mechanical torque
- Filter contaminants from the hydraulic fluid
Correct answer: Maintain constant pressure by varying flow output
A pressure-compensated pump automatically reduces displacement to maintain a set pressure, delivering only the flow needed to sustain that pressure.
Question 4: Which lubrication regime is characterized by full separation of mating surfaces by a fluid film?
- Boundary lubrication
- Mixed-film lubrication
- Hydrodynamic (full-film) lubrication (Correct answer)
- Elastohydrodynamic lubrication
Correct answer: Hydrodynamic (full-film) lubrication
Hydrodynamic lubrication occurs when a pressurized oil film completely separates the surfaces, preventing metal-to-metal contact.
Question 5: A plant uses a chain drive instead of a belt drive for a conveyor. What is the main advantage?
- Lower noise and vibration at high speeds
- No slippage and positive mechanical drive (Correct answer)
- Better performance at elevated temperatures
- Requires no periodic lubrication
Correct answer: No slippage and positive mechanical drive
Chain drives engage sprocket teeth positively with no slippage, maintaining an exact speed ratio and enabling higher torque transmission.
Question 6: When performing a vibration analysis, what does the overall vibration level in velocity (in/s RMS) primarily indicate?
- The specific frequency causing the vibration
- The general severity of mechanical condition (Correct answer)
- The phase relationship between bearing locations
- The natural frequency of the machine structure
Correct answer: The general severity of mechanical condition
Overall velocity RMS gives a single number representing total vibration energy, which is compared to ISO standards to assess machine health severity.
Question 7: In a steam trap, the function is to:
- Control steam pressure to downstream equipment
- Discharge condensate and air while retaining steam (Correct answer)
- Measure steam flow rate in the distribution system
- Remove dissolved oxygen from feedwater
Correct answer: Discharge condensate and air while retaining steam
Steam traps automatically discharge condensate (and non-condensable gases) from steam lines while preventing live steam from escaping.
CPE Mechanical Systems & Equipment 4
In a shell-and-tube heat exchanger, baffles are installed to: