Compressors, Gas Turbines and Jet Engines - Set 08 - ObjectiveBooks

# Compressors, Gas Turbines and Jet Engines - Set 08

### Practice Test: Question Set - 08

1. Rotary compressors are used for delivering
(A) Small quantities of air at high pressures
(B) Large quantities of air at high pressures
(C) Small quantities of air at low pressures
(D) Large quantities of air at low pressures

2. More than one stage will be preferred for reciprocating compressor if the delivery pressure is more than
(A) 2 kg/cm²
(B) 6 kg/cm²
(C) 10 kg/cm²
(D) 14.7 kg/cm²

3. Only rocket engines can be propelled to space because
(A) They can generate very high thrust
(B) They have high propulsion efficiency
(C) These engines can work on several fuels
(D) They are not air breathing engines

4. The advantage of multistage compression over single stage compression is
(A) Lower power consumption per unit of air delivered
(B) Higher volumetric efficiency
(C) Decreased discharge temperature
(D) All of the above

5. Reheating in a gas turbine
(A) Increases the thermal efficiency
(B) Increases the compressor work
(C) Increases the turbine work
(D) Decreases the thermal efficiency

(A) Better lubrication is possible advantages of multistage
(B) More loss of air due to leakage past the cylinder
(C) Mechanical balance is better
(D) Air can be cooled perfectly in between

7. 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

8. 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

9. 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

10. Losses in a centrifugal compressor are due to
(A) Inlet losses
(B) Impeller channel losses
(C) Diffuser losses
(D) All of the above

11. The axial flow compressor is preferred in aircraft gas turbines because of
(A) Low frontal area
(B) Higher thrust
(C) High pressure rise
(D) None of these

12. 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%

13. If p₁, is the pressure of air entering the L.P. cylinder and p₂ is the pressure of air leaving the L.P. cylinder (or inter-cooler pressure), then the ratio of cylinder diameters for a single acting, two stage reciprocating air compressor with complete intercooling is given by (where D₁ = Dia. of L.P. cylinder, and D₂ = Dia. of H.P. cylinder)
(A) D₁/D₂ = p₁ p₂
(B) D₁/D₂ = p₁/p₂
(C) D₁/D₂ = p₂/p₁
(D) None of these

14. 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

15. Which of the following statement is correct?
(A) The ratio of the discharge pressure to the inlet pressure of air is called compressor efficiency
(B) The compression ratio for the compressor is always greater than unity
(C) The compressor capacity is the ratio of work-done per cycle to the stroke volume
(D) During isothermal compression of air, the work-done in a compressor is maximum

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