Compressors

21. Atmospheric pressure is 1.03 kg/cm and vapour pressure is 0.03 kg/cm . The air pressure will be

  1. 1.03 kg/cm2
  2. 1.06 kg/cm2
  3. 1.00 kg/cm2
  4. 0.53 kg/cm2
  5. 0.5 kg/cm2.

Correct answer: (C)
1.00 kg/cm2

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

  1. larger air handling ability per unit frontal area
  2. higher pressure ratio per stage
  3. aerofoil blades are used
  4. higher average velocities
  5. none of the above.

Correct answer: (A)
larger air handling ability per unit frontal area

23. Axial flow compressor resembles

  1. centrifugal pump
  2. reciprocating pump
  3. turbine
  4. sliding vane compressor
  5. none of the above.

Correct answer: (C)
turbine

24. Choose the correct statement

  1. gas turbine requires lot of cooling water
  2. gas turbine is capable of rapid start up and loading
  3. gas turbines have flat efficiency at part loads
  4. gas turbines have high standby losses and require lot of maintenance
  5. gas turbines can be used to generate power only.

Correct answer: (B)
gas turbine is capable of rapid start up and loading

25. Clearance volume in actual reciprocating compressors is essential

  1. to accommedate Valves in the cylinder head
  2. to provide cushioning effect
  3. to attain high volumetric efficiency
  4. to avoid mechanical bang of piston with cylinder head
  5. to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.

Correct answer: (E)
to provide cushioning effect and also to avoid mechanical bang of piston with cylinder head.

26. Compression efficiency is compared against

  1. ideal compression
  2. adiabatic compression
  3. botii isothermal and adiabatic compression
  4. isentropic compression
  5. isothermal compression.

Correct answer: (E)
isothermal compression.

27. Cylinder clearance in a compressor should be

  1. as large as possible
  2. as small as possible
  3. about 50% of swept volume
  4. about 100% of swept volume
  5. none of the above.

Correct answer: (B)
as small as possible

28. Diffuser in a compressor is used to

  1. increase velocity
  2. make the flow stream-line
  3. convert pressure energy into kinetic energy
  4. convert kinetic energy into pressure energy
  5. increase degree of reaction.

Correct answer: (D)
convert kinetic energy into pressure energy

29. During base load operation, the best method of controlling compressor is

  1. start-stop motor
  2. constant speed unloader
  3. relief valve
  4. variable speed
  5. none of the above.

Correct answer: (A)
start-stop motor

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

  1. start-stop motor
  2. constant speed unloader
  3. relief valve
  4. variable speed
  5. none of the above.

Correct answer: (B)
constant speed unloader

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