Steam nozzles and turbine mcq

Steam nozzles and turbine most imp mcq

01. The difference of supersaturated temperature and saturation temperature at that pressure is called

degree of undercooling

02. The ratio of the useful heat drop to the isentropic heat drop is called

nozzle efficiency.

Note:-

The nozzle efficiency is high when the nozzle has a smooth bell shape

03. The efficiency of steam turbines may be improved by

reheating of steam

regenerative feed heating

binary vapour plant

any one of these

04. In a reaction turbine, when steam flows through the fixed blades,

pressure decreases while velocity increases.

Note:-

Reaction Turbines are turbines used in hydroelectric power. These turbines are used commonly in situations where the water has a medium to low head, and a fairly high flow rate. The water from the comes in to the turbines at a right angle to the blades.

05. The discharge of steam in a convergent-divergent nozzle__________ after the throat (i.e. in the divergent portion of the nozzle)

remains constant

06. The rate of discharge through the

nozzle increases when the exit pressure is

gradually reduced.

07. The velocity of steam leaving the nozzle (V) is given by (where K = Nozzle coefficient or nozzle

efficiency, and hd = Enthalpy or heat drop during expansion of steam in a nozzle)

C.V = 44.72 K hd

08. In a nozzle, whole frictional loss is assumed to occur between

throat and exit

Note:-

The flow in the throat is sonic which means the Mach number is equal to one in the throat.

09. The critical pressure ratio for initially wet steam is

0.582

10. The impulse reaction turbine has its driving force

partly as an impulsive force and partly as a reaction force

11. The efficiency of reaction turbine is maximum when (where α = Angle made by the absolute velocity (V) at inlet)

Vb = V cos α

12. A regenerative steam cycle renders

decreased work output per unit mass of steam as well as increased thermal efficiency

13. De-Laval turbine is a

single rotor impulse turbine.

Note:-

De Laval's impulse turbine is simpler, less expensive and does not need to be pressure-proof. It can operate with any pressure of steam, but is considerably less efficient.

14. The turbine, in which the general direction of the steam flow is parallel to the turbine axis, is called

axial flow turbines

15. The critical pressure gives the velocity of steam at the throat equal to the

velocity of sound.

16. The reheat factor is the ratio of the

cumulative heat drop to the isentropic heat drop

17. Thermal equilibrium means that the flow of steam is

isentropic

18. When the back pressure of a nozzle is below the designed value of pressure at exit of nozzle, the nozzle is said to be

underdamping

19. The ratio of the workdone on the

blades to the energy supplied to the blades, is called

blading efficiency

20. The discharge is maximum at

critical pressure.

21. The supersaturated flow of steam through a nozzle as compared to a stable flow, the available heat drop

decreases

22. The steam leaves the nozzle at a

low pressure and a high velocity

23. The critical pressure gives the velocity of steam at the throat

equal to the velocity of sound

24. The Parsons' reaction turbine has

identical fixed and moving blades.

25. The action of steam in a steam turbine is

dynamic

26. The blade velocity coefficient is ratio of relative velocity of steam at outlet tip of the blade to the relative velocity of steam

at inlet tip of the blade.

27. Multi-stage steam turbines are of the

velocity compounded type

reaction type

pressure compounded type

all of these

28. Which of the following statement is correct?

The expansion of steam in a nozzle follows Rankine cycle.

The friction in the nozzle increases the dryness fraction of steam.

The pressure of steam at throat is called critical pressure.

all of the above

29. A binary vapour plant consists of

steam turbine

steam condenser

mercury boiler

all of these

30. The stage efficiency (ηS) is given by (where ηB = Blading efficiency, and ηN = Nozzle efficiency)

ηS = ηB x ηN

31. In a convergent divergent nozzle, the discharge depends upon the initial conditions of steam and the

area of nozzle at throat.

32. Parson's reaction turbine is a 50 percent

reaction turbine.

33. The turbine blades are

curved

34. The variation of steam pressure in the nozzle depends upon

velocity of steam

specific volume of steam

dryness fraction of steam

all of these

35. Steam turbines are used for

large marine propulsion

electric power generation

direct drive of fans, compressors, pumps

all of these

36. Parson's turbine is a

simple reaction turbine

37. The steam enters the nozzle at a

high pressure and a low velocity

38. When the nozzle operates with the maximum mass flow, the nozzle is said to be

choked

39. In a velocity compounded impulse turbine, when steam flows through the second row of moving blades,

velocity decreases

40. A steam nozzle converts converts

heat energy of steam into kinetic energy

41. The maximum discharge of steam through a convergent-divergent nozzle depends upon

area of nozzle at throat

initial pressure and volume of steam

both of the above.

42. De-Laval turbine is a

simple impulse turbine

43. The impulse turbine rotor efficiency will have a maximum value of 0.5 cos2 α, where α is the nozzle exit flow angle, if the

blades are equiangular and frictionless

44. When the cross-section of a nozzle increases continuously from entrance to exit, it is called a

divergent nozzle

45. Rateau turbine is

pressure compounded turbine

46. The ratio of the work delivered at the turbine shaft to the heat supplied is called

overall thermal efficiency of turbine.

47. In a single stage impulse turbine, the velocity of steam approaching nozzles is

negligible.

48. Curtis turbine is a

pressure-velocity compounded turbine.

49. The velocity of steam at throat of the nozzle is equal to the

velocity of sound.

50. The critical pressure ratio for initially dry saturated steam is

0.577

      

51. The discharge through a nozzle is maximum for a certain value of exit pressure. This pressure is known as

critical pressure.

52. The velocity of steam, in reaction turbines, is increased in the fixed blades as well as in

moving blades.

53. The critical pressure ratio for gases is

0.528

54. The efficiency of a pressure velocity compounded impulse turbine is less as compared to

pressure compounded impulse turbine.

55. The effect of supersaturation is that the

mass of the steam discharged increases

entropy and specific volume of the steam increases

exit velocity of steam reduces

all of these.

56. The effect of friction on the flow of steam through a nozzle is to

decrease the mass flow rate and to decrease the wetness of steam.

57. The ratio of the isentropic heat drop to the heat supplied, is called

Rankine efficiency.

Note:-

The Rankine cycle is a model used to predict the performance of steam turbine systems. The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work while undergoing phase change.

58. When the cross-section of a nozzle first increases from its entrance to throat, and then decreases from its throat to exit, it is not a

convergent divergent nozzle.

59. The efficiency ratio is the ratio of total useful heat drop to the total

isentropic heat drop.

60. The purpose of governing in steam turbines is to

maintain the speed of the turbine.

Note:-

Steam turbine governing is the procedure of controlling the flow rate of steam to a steam turbine so as to maintain its speed of rotation as constant. The variation in load during the operation of a steam turbine can have a significant impact on its performance.

61. De-Laval turbines are mostly used

for small power purposes and high speeds

62. The reheat factor depends upon

initial pressure and superheat

exit pressure

turbine stage efficiency

all of these

63. In an impulse turbine

the steam is expanded in nozzles only and there is a pressure drop and heat drop.

64. A nozzle is said to be a divergent nozzle

when the cross-section of the nozzle increases continuously from entrance to exit.

65. The ratio of the cumulative heat drop to the isentropic heat drop is called

reheat factor.

66. The compounding of turbines is done in order to

reduce speed of rotor

improve efficiency

reduce exit losses

all of these

67. The pressure of steam decreases while flowing through a

nozzle.

68. The process of maintaining the speed of the turbine constant for various load conditions, is known as

governing

69. Reheating of steam in a turbine

increases the workdone through the turbine

increases the efficiency of the turbine

reduces wear on the blades

all of these

70. Which of the following statement is correct for steam turbines as compared to reciprocating steam engines?

A steam turbine develops higher speeds,

The efficiency of steam turbine is higher,

The steam consumption is less,

all of these.

71. The density of supersaturated steam is about 8 times that of the ordinary saturated vapour at the

corresponding pressure.

72. The ratio of the workdone on the blades per kg of steam to the total energy supplied per stage per kg of steam is called

stage efficiency.

73. The diagram efficiency is the ratio of

work done on the blades to the energy supplied to the blades.

74. Blading efficiency is also known as

diagram efficiency.

75. The pressure of steam, in reaction turbines, is reduced in the fixed blades as well as in

moving blades.

76. In order to reduce the rotor speed of an impulse turbine, the method employed is

velocity compounding

pressure compounding

pressure velocity compounding

all of these

77. The nozzle efficiency is the ratio of

energy supplied to the blades per kg of steam to the total energy supplied per stage per kg of steam.

78. The friction in the nozzle decreases exit

velocity of steam.

79. In a reaction turbine

the expansion of steam takes place partly in the fixed blades and partly in the moving blades

80. A stage, in reaction turbine, is represented by

each row of blades

81. In a De-Laval impulse turbine, the nozzle is kept

very close to the blades.

82. The flow of steam is super-sonic

in the divergent portion of the nozzle

83. The pressure of steam at throat of a steam nozzle is called

critical pressure.

84. For maximum efficiency of an impulse turbine, the steam should leave the blades at

right angles to their motion.

85. In a nozzle, the effect of

supersaturation is to

increase the entropy

86. Which of the following statement is correct?

The efficiency of steam turbines is greater than steam engines.

87. The pressure velocity compounded impulse turbine allows a bigger pressure drop and hence

less number of stages are required.

88. If the critical pressure ratio for steam is 0.546, then the steam is initially

superheated steam

89. The maximum efficiency of a De- Laval turbine is (where α = Nozzle angle)

cos2 α

90. The pressure compounded impulse turbine as compared to velocity compounded turbine require more

number of stages.

91. In a reaction turbine when the degree of reaction is zero, then there is

no heat drop in moving blades

92. The effect of friction in the nozzle increases

dryness fraction of steam.

93. When the cross-section of a nozzle decreases continuously from entrance to exit, it is called a

convergent nozzle.

94. In an ideal impulse turbine, the

      

relative velocity at the inlet of the moving blade is equal to that at the outlet

95. During flow through a nozzle,

no heat is supplied or rejected by the steam.

96. In a reaction turbine, when steam flows through the moving blades,

pressure and velocity both decreases

97. In velocity compounding of an impulse turbine, the expansion of steam takes place in a nozzle or a set of nozzles from the

boiler pressure to condenser pressure.

98. The critical pressure ratio is given by (where p1 = Initial pressure of steam, and p2 = Pressure of steam at throat or critical pressure)

p2/p1

99. A steam turbine, in which a part of the steam after partial expansion, is used for process heating and the remaining steam is further expanded for power generation, is known as

pass out turbine

100. Stage efficiency is also known as

gross efficiency

101. A single stage turbine is not used because it requires large reduction gearing due to

very high rotational speed.

102. In turbines, the fluid undergoes a continuous steady flow process and the speed of flow is

very high

103. A nozzle is said to be a

convergent-divergent nozzle, when the cross-section of a nozzle first

decreases from its entrance to throat and then increases from its throat to exit.

104. In an impulse reaction turbine, the pressure drops gradually and continuously over

both fixed and moving blades

105. When the inlet pressure of steam is equal to the exit pressure, then

there is no pressure drop and fluid does not flow through the nozzle

106. The blade friction in the impulse turbine reduces the velocity of steam by 10 to 15% while it

passes over the blades.

107. The effect of bleeding is that

it increases the thermodynamic efficiency of the turbine

boiler is supplied with hot water

it decreases the power developed by the turbine

all of the above

108. The expansion of steam, as it flows over the blades in reaction turbine, represents

isentropic process

109. The critical pressure ratio for initially superheated steam is less as compared to initially dry

saturated steam.

110. For a Parson's reaction turbine, if α1 and α2 are fixed blade angles at inlet and exit respectively and β1 and β2 are the moving blade angles at entrance and exit respectively, then

α1 = β1 and α2 = β2

111. The velocity of whirl at outlet for an axial discharge turbine is

zero

112. In impulse turbines, when friction is neglected, the relative velocity of steam at outlet tip of the blade is equal to the relative velocity of steam at

inlet tip of the blade.

113. The friction present between the steam and the nozzle surfaces reduces the heat drop by

10 to 15 percent

114. An impulse turbine as compared to a reaction turbine, for a given power has

more row of blades.

115. Degree of reaction is defined as the ratio of

heat drop in moving blades to the heat drop in fixed blades plus heat drop in moving blades

116. The expansion of steam in a nozzle follows

Rankine cycle

117. Steam turbines may be classified according to

direction of steam flow

number of stages

mode of steam action

all of these

118. The process of draining steam from the turbine, at certain points during its expansion and using this steam for heating the feed water in feed water heaters and then supplying it to the boiler is known as

bleeding

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