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

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

## 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

## 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

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

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

## 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

## Q9. A closed cycle gas turbine consists of a

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

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

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

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

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

## 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