Compressors, Gas Turbines and Jet Engines MCQ Practice Test – Set 4 :: Mechanical Engineering

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Q1. The overall thermal efficiency of an ideal gas turbine plant is (where r = Pressure ratio)

(A) r ɣ-1
(B) 1 – r ɣ-1
(C) 1 – (1/r) ɣ-1/ɣ
(D) 1 – (1/r) ɣ/ɣ-1

Answer: (C) 1 – (1/r) ɣ-1/ɣ

Q2. The volume of air sucked by the compressor during its suction stroke is called

(A) Free air delivery
(B) Compressor capacity
(C) Swept volume
(D) None of these

Answer: (C) Swept volume

Q3. Which of the following statement is correct?

(A) The reciprocating compressors are best suited for high pressure and low volume capacity
(B) The effect of clearance volume on power consumption is negligible for the same volume of discharge
(C) Both (A) and (B)
(D) None of these

Answer: (C) Both (A) and (B)

Q4. The efficiency of jet engine is

(A) Lower at low speed
(B) Higher at high altitudes
(C) Same at all altitudes
(D) Higher at high speed

Answer: (B) Higher at high altitudes

Q5. The process, which causes the air to enter the impeller blades of a centrifugal compressor at __ velocity (without effecting the mass of air to flow and velocity of flow) is known as prewhirl.

(A) Reduced
(B) Increased
(C) Zero
(D) None of these

Answer: (A) Reduced

Q6. The net work input required for compressor with increase in clearance volume

(A) Increases
(B) Decreases
(C) Remains same
(D) Increases/decreases depending on compressor capacity

Answer: (C) Remains same

Q7. A compressor at high altitude will draw

(A) More power
(B) Less power
(C) Same power
(D) More/less power depending on other factors

Answer: (B) Less power

Q8. For perfect intercooling in a three stage compressor

(A) p₂/p₁ = p₃/p₂ = p₄/p₃
(B) p₃/p₁ = p₄/p₂
(C) p₁ p₂ = p₃ p₄
(D) p₁ p₃ = p₂ p₄

Answer:(A) p₂/p₁ = p₃/p₂ = p₄/p₃

Q9. Which one of the following is the effect of blade shape on performance of a centrifugal compressor?

(A) Backward curved blades has poor efficiency
(B) Backward curved blades lead to stable performance
(C) Forward curved blades has higher efficiency
(D) Forward curved blades produce lower pressure ratio

Answer:(D) Forward curved blades produce lower pressure ratio

Q10. The efficiency of roots blower __ with the increase in pressure ratio.

(A) Decreases
(B) Increases
(C) Does not change
(D) None of these

Answer: (A) Decreases

Q11. Pick up the correct statement

(A) Large gas turbines use radial inflow turbines
(B) Gas turbines have their blades similar to steam turbine
(C) Gas turbine’s blade will appear as impulse section at the hub and as a reaction section at tip
(D) Gas turbines use both air and liquid cooling

Answer: (C) Gas turbine’s blade will appear as impulse section at the hub and as a reaction section at tip

Q12. Which is false statement about multistage compression?

(A) Power consumption per unit of air delivered is low
(B) Volumetric efficiency is high
(C) It is best suited for compression ratios around 7:1
(D) The moisture in air is condensed in the inter-cooler

Answer: (B) Volumetric efficiency is high

Q13. Mining industry usually employs following motive power

(A) A.C. electric motor
(B) Compressed air
(C) Petrol engine
(D) Diesel engine

Answer: (B) Compressed air

Q14. Compression efficiency is compared against

(A) Ideal compression
(B) Adiabatic compression
(C) Isentropic compression
(D) Isothermal compression

Answer: (D) Isothermal compression

Q15. The overall isothermal efficiency of compressor is defined as the ratio of

(A) Isothermal h.p. to the BHP of motor
(B) Isothermal h.p. to adiabatic h.p.
(C) Power to drive compressor to isothermal h.p.
(D) Work to compress air isothermally to work for actual compression

Answer:(A) Isothermal h.p. to the BHP of motor

Q16. For minimum work required to compress and deliver a quantity of air by multistage compression

(A) The compression ratio in each stage should be same
(B) The intercooling should be perfect
(C) The work-done in each stage should be same
(D) All of the above

Answer: (D) All of the above

Q17. In a single acting reciprocating air compressor, without clearance, the compression of air may be

(A) Isothermal
(B) Polytropic
(C) Isentropic
(D) Any one of these

Answer: (D) Any one of these

Q18. The ratio of outlet whirl velocity to blade velocity in case of centrifugal compressor is called

(A) Slip factor
(B) Velocity factor
(C) Velocity coefficient
(D) None of the above

Answer: (A) Slip factor

Q19. Diffuser in a compressor is used to

(A) Increase velocity
(B) Make the flow streamline
(C) Convert pressure energy into kinetic energy
(D) Convert kinetic energy into pressure energy

Answer: (D) Convert kinetic energy into pressure energy

Q20. Axial flow compressor has the following advantage over centrifugal compressor

(A) Larger air handling ability per unit frontal area
(B) Higher pressure ratio per stage
(C) Aerofoil blades are used
(D) Higher average velocities

Answer: (A) Larger air handling ability per unit frontal area

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