Compressors

41. For supplying intermittent small quantity of air at high pressure, following compressor is best suited

  1. centrifugal
  2. reciprocating
  3. axial
  4. screw
  5. turbo jet.

Correct answer: (B)
reciprocating

42. Free air is the air at

  1. atmospheric conditions at any specific location
  2. 20°C and 1 kg/cm2 and relative humidity of 36%
  3. 0°C and standard atmospheric conditions
  4. 15°C and 1 kg/cm2
  5. 25°C, 1 kg/cm2 and relative humidity of 50%.

Correct answer: (A)
atmospheric conditions at any specific location

43. Gas turbine blades are given a rake

  1. equal to zero
  2. in the direction of motion of blades
  3. opposite to the direction of motion of blades
  4. depending on the velocity
  5. none of the above.

Correct answer: (B)
in the direction of motion of blades

44. Gas turbine cycle with regenerator

  1. increases thermal efficiency
  2. allows high compression ratio
  3. decreases heat loss is exhaust
  4. allows operation at very high altitudes
  5. permits high moisture content fuel to be used.

Correct answer: (A)
increases thermal efficiency

45. Gas turbine works on

  1. Brayton or Atkinson cycle
  2. Carnot cycle
  3. Rankine cycle
  4. Erricsson cycle
  5. Joule cycle.

Correct answer: (A)
Brayton or Atkinson cycle

46. Gas turbines for power generaion are normally used

  1. to supply base load requirements
  2. to supply peak load requirements
  3. to enable start thermal power plant
  4. in emergency
  5. when other sources of power fail.

Correct answer: (B)
to supply peak load requirements

47. Gas turbines use following type of air compressor

  1. centrifugal type
  2. reciprocating type
  3. lobe type
  4. axial flow type
  5. none of the above.

Correct answer: (D)
axial flow type

48. High air-fuel ratio is used in gas turbines

  1. to increase the output
  2. to increase the efficiency
  3. to save fuel
  4. to reduce the exit temperature
  5. none of the above.

Correct answer: (D)
to reduce the exit temperature

49. If infinite number of heaters be used in a gas turbine, then expansion process in turbine approaches

  1. isothermal
  2. isentropic
  3. adiabatic
  4. isochoric
  5. isobaric.

Correct answer: (A)
isothermal

50. If V, U and Vr represent the absolute velocity of fluid, velocity of blade, and relative velocity of fluid, and suffix i and o stand for entry and exit conditions, then in a rotary machine whose degree of reaction is unity

  1. Vi=V0
  2. Vt>V0
  3. U,<V0
  4. V,= U0
  5. Vri=Vm.

Correct answer: (A)
Vi=V0

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