Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 5 :: Mechanical Engineering

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Q1. The degree of reaction is usually kept __ for all types of axial flow compressors.

(A) 0.2
(B) 0.3
(C) 0.4
(D) 0.5

Answer: (D) 0.5

Q2. Standard air is the air at __ and relative humidity of 36 percent.

(A) 0.1 bar and 20°C
(B) 1 bar and 20°C
(C) 0.1 bar and 40°C
(D) 1 bar and 40°C

Answer: (B) 1 bar and 20°C

Q3. The reason for volumetric efficiency of reciprocating compressor being less than 100 percent is

(A) Pressure drop across the valves
(B) Superheating in compressor
(C) Clearance volume and leakages
(D) All of these

Answer: (D) All of these

Q4. High air-fuel ratio in gas turbines

(A) Increases power output
(B) Improves thermal efficiency
(C) Reduces exhaust temperature
(D) Do not damage turbine blades

Answer: (C) Reduces exhaust temperature

Q5. In a centrifugal compressor, the ratio of the __ to the blade velocity is called slip factor.

(A) Inlet whirl velocity
(B) Outlet whirl velocity
(C) Inlet velocity of flow
(D) Outlet velocity of flow

Answer: (D) Outlet velocity of flow

Q6. Ratio of indicated h.p. to shaft h.p. in known as

(A) Compressor efficiency
(B) Isothermal efficiency
(C) Volumetric efficiency
(D) Mechanical efficiency

Answer: (D) Mechanical efficiency

Q7. During peak load periods, the best method of controlling compressors is

(A) Start-stop motor
(B) Constant speed unloader
(C) Relief valve
(D) Variable speed

Answer: (B) Constant speed unloader

Q8. When the temperature of air leaving the inter-cooler, in a two stage compression with inter-cooler, is __ the original atmospheric air temperature, then the intercooling is known as perfect or complete intercooling.

(A) Equal to
(B) Less than
(C) More than
(D) None of these

Answer: (A) Equal to

Q9. A closed cycle gas turbine consists of a

(A) Compressor
(B) Heating chamber
(C) Cooling chamber
(D) All of these

Answer: (D) All of these

Q10. The maximum temperature in a gas turbine is

(A) 200°C
(B) 500°C
(C) 700°C
(D) 1000°C

Answer: (C) 700°C

Q11. Ram compression in turbojet involves

(A) Reduction of speed of incoming air and conversion of part of it into pressure energy
(B) Compression of inlet air
(C) Increasing speed of incoming air
(D) Lost work

Answer: (A) Reduction of speed of incoming air and conversion of part of it into pressure energy

Q12. Out of the following, from where you will prefer to take intake for air compressor

(A) From an air conditioned room maintained at 20°C
(B) From outside atmosphere at 1°C
(C) From coal yard side
(D) From a side where cooling tower is located nearby

Answer:(D) From a side where cooling tower is located nearby

Q13. In jet propulsion power unit, the inlet duct of diverging shape is used in order to

(A) Collect more air
(B) Convert kinetic energy of air into pressure energy
(C) Provide robust structure
(D) Beautify the shape

Answer: (B) Convert kinetic energy of air into pressure energy

Q14. An ideal air compressor cycle with clearance on P-V diagram can be represented by following processes

(A) One adiabatic, two isobaric, and one constant volume
(B) Two adiabatic and two isobaric
(C) Two adiabatic, one isobaric and one constant volume
(D) One adiabatic, one isobaric and two constant volumes

Answer: (B) Two adiabatic and two isobaric

Q15. The most efficient method of compressing air is to compress it

(A) Isothermally
(B) Adiabatically
(C) Isentropically
(D) Isochronically

Answer:(A) Isothermally

Q16. In a jet engine, the air-fuel ratio is

(A) 30:1
(B) 40:1
(C) 50:1
(D) 60:1

Answer: (D) 60:1

Q17. The temperature of air at the beginning of the compression stroke is __ the atmospheric temperature.

(A) Equal to
(B) Less than
(C) More than
(D) None of these

Answer: (C) More than

Q18. Losses in a centrifugal compressor are due to

(A) Inlet losses
(B) Impeller channel losses
(C) Diffuser losses
(D) All of the above

Answer: (D) All of the above

Q19. The ratio of isentropic work to Euler’s work is known as

(A) Compressor efficiency
(B) Isentropic efficiency
(C) Euler’s efficiency
(D) Pressure coefficient

Answer:(D) Pressure coefficient

Q20. Actual compression curve is

(A) Same as isothermal
(B) Same as adiabatic
(C) Better than isothermal and adiabatic
(D) In between isothermal and adiabatic

Answer: (D) In between isothermal and adiabatic

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