Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 7 :: Mechanical Engineering

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Q1. The compressor capacity is defined as the

(A) Actual volume of the air delivered by the compressor when reduced to normal temperature and pressure conditions
(B) Volume of air delivered by the compressor
(C) Volume of air sucked by the compressor during its suction stroke
(D) None of the above

Answer: (B) Volume of air delivered by the compressor


Q2. An ideal air compressor cycle without 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: (A) One adiabatic, two isobaric, and one constant volume


Q3. Ratio of indicated H.P. and brake H.P. is known as

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

Answer: (A) Mechanical efficiency


Q4. Which of the following statement is correct as regard to centrifugal compressors?

(A) The flow of air is parallel to the axis of the compressor
(B) The static pressure of air in the impeller increases in order to provide centripetal force on the air
(C) The impeller rotates at high speeds
(D) The maximum efficiency is higher than multistage axial flow compressors

Answer: (B) The static pressure of air in the impeller increases in order to provide centripetal force on the air


Q5. Volumetric efficiency of air compressors is of the order of

(A) 20 – 30%
(B) 40 – 50%
(C) 60 – 70%
(D) 70 – 90%

Answer: (D) 70 – 90%


Q6. In a compressor, free air delivered is the actual volume delivered at the stated pressure reduced to

(A) N.T.P. conditions
(B) Intake temperature and pressure conditions
(C) 0°C and 1 kg/cm²
(D) 20°C and 1 kg/cm²

Answer: (B) Intake temperature and pressure conditions


Q7. The volumetric efficiency of a compressor falls roughly as follows for every 5°C increase in atmospheric temperature

(A) 0.1%
(B) 0.5%
(C) 1%
(D) 5%

Answer: (C) 1%


Q8. The type of rotary compressor used in aeroplanes, is of

(A) Centrifugal type
(B) Axial flow type
(C) Radial flow type
(D) None of these

Answer: (B) Axial flow type


Q9. For maximum work, the reheating should be done to an intermediate pressure of
(Where p₁ = Maximum pressure, and p₂ = Minimum pressure)

(A) (p₁ – p₂)/2
(B) (p₁ + p₂)/2
(C) p₁/p₂
(D) p₁ p₂

Answer: (D) p₁ p₂


Q10. In the aircraft propellers

(A) The propulsive matter is caused to flow around the propelled body
(B) Propulsive matter is ejected from within the propelled body
(C) Its functioning does not depend on presence of air
(D) All of the above

Answer: (D) All of the above


Q11. The area of actual indicator diagram on an air compressor as compared to area of ideal indicator diagram is

(A) Less
(B) More
(C) Same
(D) More/less depending on compressor capacity

Answer: (B) More


Q12. The thrust of a jet propulsion power unit can be increased by

(A) Injecting water into the compressor
(B) Burning fuel after gas turbine
(C) Injecting ammonia into the combustion chamber
(D) All of the above

Answer:(D) All of the above


Q13. The ratio of the volume of free air delivery per stroke to the swept volume of the piston, is known as

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

Answer:(B) Volumetric efficiency


Q14. Isothermal compression efficiency can be attained by running the compressor

(A) At very high speed
(B) At very slow speed
(C) At average speed
(D) At zero speed

Answer: (B) At very slow speed


Q15. The velocity of air entering in a rocket is _ as compared to an aircraft.

(A) Zero
(B) Less
(C) More
(D) Same

Answer: (A) Zero


Q16. The blades of gas turbine are made of

(A) High nickel alloy
(B) Stainless steel
(C) Carbon steel
(D) High alloy steel

Answer: (A) High nickel alloy


Q17. The indicated work per unit mass of air delivered is

(A) Directly proportional to clearance volume
(B) Greatly affected by clearance volume
(C) Not affected by clearance volume
(D) Inversely proportional to clearance volume

Answer:(C) Not affected by clearance volume


Q18. Phenomenon of choking in compressor means

(A) No flow of air
(B) Fixed mass flow rate regardless of pressure ratio
(C) Reducing mass flow rate with increase in pressure ratio
(D) Increased inclination of chord with air steam

Answer: (B) Fixed mass flow rate regardless of pressure ratio


Q19. The pressure ratio of an ideal vaned compressor with increase in mass flow rate

(A) Increases
(B) Decreases
(C) Remain constant
(D) First decreases and then increases

Answer: (C) Remain constant


Q20. In a jet propulsion unit, the products of combustion after passing through the gas turbine are discharged into

(A) Atmosphere
(B) Vacuum
(C) Discharge nozzle
(D) Back to the compressor

Answer: (C) Discharge nozzle


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