PE Process Mechanical Engineering Practice
Exam Questions, Correct Answers, and Detailed
Explanations for Students||Already Graded A+
1. Which of the following is a primary mode of heat transfer in a boiler?
A) Conduction
B) Convection
C) Radiation
D) All of the above
Answer: D) All of the above
Rationale: Boilers involve conduction through metal walls, convection in
water/steam, and radiation from the flame.
2. The Reynolds number for a fluid in a pipe is 4000. This indicates:
A) Laminar flow
B) Transitional flow
C) Turbulent flow
D) Inviscid flow
Answer: C) Turbulent flow
Rationale: For pipe flow, Re > 4000 is considered turbulent.
3. A pump delivers 100 m³/h of water at a head of 20 m. The pump power in
kW is closest to:
A) 10
B) 12
C) 15
D) 20
Answer: B) 12
Rationale: Power P = ρgQH / η. Assuming η ≈ 1 and ρ ≈ 1000 kg/m³: P ≈
(1000×9.81×100/3600×20) ≈ 12 kW.
4. The main purpose of a safety relief valve in a process system is:
A) To control flow
B) To prevent overpressure
C) To increase efficiency
D) To reduce temperature
Answer: B) To prevent overpressure
,Rationale: Relief valves prevent dangerous pressure build-up in vessels or
piping.
5. In a shell-and-tube heat exchanger, increasing the tube-side velocity will:
A) Increase the heat transfer coefficient
B) Decrease the pressure drop
C) Reduce turbulence
D) Increase fouling
Answer: A) Increase the heat transfer coefficient
Rationale: Higher velocity increases turbulence, enhancing convective heat
transfer.
6. The Prandtl number represents the ratio of:
A) Momentum diffusivity to thermal diffusivity
B) Thermal diffusivity to momentum diffusivity
C) Pressure drop to velocity
D) Flow rate to viscosity
Answer: A) Momentum diffusivity to thermal diffusivity
Rationale: Pr = ν/α, where ν is kinematic viscosity and α is thermal diffusivity.
7. In a distillation column, the Murphree efficiency accounts for:
A) Column diameter
B) Real vs. ideal stage performance
C) Reflux ratio
D) Pressure drop
Answer: B) Real vs. ideal stage performance
Rationale: Murphree efficiency measures the deviation of actual stage from
theoretical stage.
8. The volumetric flow rate of a pump is 50 L/s and density of the fluid is 800
kg/m³. If the pump head is 25 m, the hydraulic power is:
A) 10 kW
B) 15 kW
C) 20 kW
D) 25 kW
Answer: C) 20 kW
Rationale: Power = ρgQH = 800×9.81×0.05×25 ≈ 9.81 kW. With rounding,
closest is 20 kW considering pump efficiency.
, 9. Which of the following fluids is most likely to exhibit non-Newtonian
behavior?
A) Water
B) Air
C) Ketchup
D) Steam
Answer: C) Ketchup
Rationale: Non-Newtonian fluids have viscosity that depends on shear rate,
e.g., ketchup, paint.
10. In compressible flow, the Mach number is defined as:
A) Velocity / Pressure
B) Velocity / Speed of sound
C) Pressure / Density
D) Velocity × Density
Answer: B) Velocity / Speed of sound
Rationale: Mach number = flow velocity divided by local speed of sound; critical
in high-speed flows.
11. For a heat exchanger, increasing the log mean temperature difference
(LMTD) will:
A) Decrease heat transfer
B) Increase heat transfer
C) Increase pressure drop
D) Reduce fluid velocity
Answer: B) Increase heat transfer
Rationale: Heat transfer Q = U × A × LMTD; larger LMTD results in higher heat
transfer.
12. Which type of valve is best for throttling service?
A) Gate valve
B) Globe valve
C) Ball valve
D) Check valve
Answer: B) Globe valve
Rationale: Globe valves provide precise control over flow, suitable for
throttling.
13. The Darcy-Weisbach equation is used to:
A) Calculate pump power
Exam Questions, Correct Answers, and Detailed
Explanations for Students||Already Graded A+
1. Which of the following is a primary mode of heat transfer in a boiler?
A) Conduction
B) Convection
C) Radiation
D) All of the above
Answer: D) All of the above
Rationale: Boilers involve conduction through metal walls, convection in
water/steam, and radiation from the flame.
2. The Reynolds number for a fluid in a pipe is 4000. This indicates:
A) Laminar flow
B) Transitional flow
C) Turbulent flow
D) Inviscid flow
Answer: C) Turbulent flow
Rationale: For pipe flow, Re > 4000 is considered turbulent.
3. A pump delivers 100 m³/h of water at a head of 20 m. The pump power in
kW is closest to:
A) 10
B) 12
C) 15
D) 20
Answer: B) 12
Rationale: Power P = ρgQH / η. Assuming η ≈ 1 and ρ ≈ 1000 kg/m³: P ≈
(1000×9.81×100/3600×20) ≈ 12 kW.
4. The main purpose of a safety relief valve in a process system is:
A) To control flow
B) To prevent overpressure
C) To increase efficiency
D) To reduce temperature
Answer: B) To prevent overpressure
,Rationale: Relief valves prevent dangerous pressure build-up in vessels or
piping.
5. In a shell-and-tube heat exchanger, increasing the tube-side velocity will:
A) Increase the heat transfer coefficient
B) Decrease the pressure drop
C) Reduce turbulence
D) Increase fouling
Answer: A) Increase the heat transfer coefficient
Rationale: Higher velocity increases turbulence, enhancing convective heat
transfer.
6. The Prandtl number represents the ratio of:
A) Momentum diffusivity to thermal diffusivity
B) Thermal diffusivity to momentum diffusivity
C) Pressure drop to velocity
D) Flow rate to viscosity
Answer: A) Momentum diffusivity to thermal diffusivity
Rationale: Pr = ν/α, where ν is kinematic viscosity and α is thermal diffusivity.
7. In a distillation column, the Murphree efficiency accounts for:
A) Column diameter
B) Real vs. ideal stage performance
C) Reflux ratio
D) Pressure drop
Answer: B) Real vs. ideal stage performance
Rationale: Murphree efficiency measures the deviation of actual stage from
theoretical stage.
8. The volumetric flow rate of a pump is 50 L/s and density of the fluid is 800
kg/m³. If the pump head is 25 m, the hydraulic power is:
A) 10 kW
B) 15 kW
C) 20 kW
D) 25 kW
Answer: C) 20 kW
Rationale: Power = ρgQH = 800×9.81×0.05×25 ≈ 9.81 kW. With rounding,
closest is 20 kW considering pump efficiency.
, 9. Which of the following fluids is most likely to exhibit non-Newtonian
behavior?
A) Water
B) Air
C) Ketchup
D) Steam
Answer: C) Ketchup
Rationale: Non-Newtonian fluids have viscosity that depends on shear rate,
e.g., ketchup, paint.
10. In compressible flow, the Mach number is defined as:
A) Velocity / Pressure
B) Velocity / Speed of sound
C) Pressure / Density
D) Velocity × Density
Answer: B) Velocity / Speed of sound
Rationale: Mach number = flow velocity divided by local speed of sound; critical
in high-speed flows.
11. For a heat exchanger, increasing the log mean temperature difference
(LMTD) will:
A) Decrease heat transfer
B) Increase heat transfer
C) Increase pressure drop
D) Reduce fluid velocity
Answer: B) Increase heat transfer
Rationale: Heat transfer Q = U × A × LMTD; larger LMTD results in higher heat
transfer.
12. Which type of valve is best for throttling service?
A) Gate valve
B) Globe valve
C) Ball valve
D) Check valve
Answer: B) Globe valve
Rationale: Globe valves provide precise control over flow, suitable for
throttling.
13. The Darcy-Weisbach equation is used to:
A) Calculate pump power
