### Interview Questions on Steam Nozzles and Turbines

1. A steam nozzle covert
1. heat energy of steam into kinetic energy
2. potential energy of steam into kinetic energy
3. kinetic energy of steam into mechanical energy
4. heat energy of steam into mechanical energy
2. The discharge of steam in a convergent-divergent nozzle __________ after the throat (i.e. in the divergent portion of the nozzle)
1. remains constant
2. decreases
3. increases
3. In pressure velocity compounding
2. fixed nozzles are used
4. All of the above are used
4. The rate of discharge through the nozzle __________ when the exit pressure is gradually reduced.
1. remains same
2. decreases
3. increases
5. If K= Nozzle coefficient, hd=Enthalpy or heat drop during expansion of steam in a nozzle and V= velocity of steam leaving the nozzle then
1. V = 44.72 hd K
2. V = 44.72 K hd
3. V = 44.72 K hd
4. V = 44.72 K hd
6. The critical pressure ratio for initially wet steam is
1. 0.546
2. 0.577
3. 0.582
4. 0.601
7. Maximum efficiency in reaction steam turbine is
1. 2Cos^2α/(1+ Cos^2α)
2. Cos2α/(1+ Cos^2α)
3. Cos(α/2) /(1+ Cos^2α)
4. Cosα/(1+ Cos^2α)
###### Where α is nozzle angle
8. The isentropic enthalpy drop in moving blade is two-third of the isentropic enthalpy drop in fixed blades of a turbine. The degree of reaction will be
1. 0.4
2. 0.56
3. 0.67
4. 1.67
9. The efficiency of reaction turbine is maximum when (where α = Angle made by the absolute velocity (V) at inlet)
1. Vb = 0.5 V cos α
2. Vb = V cos α
3. Vb = 0.5 V2 cos α
4. Vb = V2 cos α
10. A regenerative steam cycle renders
1. increased work output per unit mass of steam
2. decreased work output per unit mass of steam
3. increased thermal efficiency
4. increased thermal efficiency and decreased work output per unit mass of steam
11. e-Laval turbine is a
1. single rotor impulse turbine
2. multi-rotor impulse turbine
3. impulse reaction turbine
4. none of these
12. Degree of reaction is given by
1. Heat drop in moving blades / total heat drop in the stage
2. Heat drop in fixed blades / total heat drop in the stage
3. Heat drop in moving blades / Heat drop in fixed blades
4. total heat drop in the stage / Heat drop in fixed blades
13. The turbine, in which the general direction of the steam flow is parallel to the turbine axis, is called axial flow turbines
1. True
2. False
14. The critical pressure gives the velocity of steam at the throat equal to the velocity of sound.
1. Agree
2. Disagree
15.The reheat factor is the ratio of the
1. cumulative heat drop to the isentropic heat drop
2. isentropic heat drop to the heat supplied
3. useful heat drop to isentropic heat drop
4. none of the above
16. The turbine blades do not change the direction of steam issuing from the nozzle.
1. True
2. False
17. Thermal equilibrium means that the flow of steam is
1. Isothermal
2. Isentropic
3. Hyperbolic
4. Polytropic
18. Which of the following is a steam turbine?
1. De laval
2. Kaplan
3. Francis
4. Bulb
19. If back pressure of a nozzle is below the designed value of pressure at exit of nozzle, then nozzle is
1. Choked
2. Underdamping
3. Overdamping
4. none of these
20.The ratio of the workdone on the blades to the energy supplied to the blades, is called
2. nozzle efficiency
3. gross or stage efficiency
4. mechanical efficiency
21. The discharge is __________ at critical pressure.
1. Zero
2. minimum
3. maximum
22. A turbine is said to have an axial discharge when the steam leaves the blade tip at __________ to the direction of the blade motion.
1. 60°
2. 90°
3. 180°
4. 270°
23. Maximum efficiency in impulse steam turbine is
1. 2Cosα
2. Cos2α
3. Cos(α/2)
4. Cos^2α
###### Where α is nozzle angle
24. The velocity of steam at the throat due to critical pressure is
1. equal to the velocity of sound
2. less than the velocity of sound
3. more than the velocity of sound
4. none of these
25. The Parsons' reaction turbine has
3. identical fixed and moving blades
4. fixed and moving blades of different shape
26. The action of steam in a steam turbine is
1. static
2. dynamic
3. static and dynamic
4. neither static nor dynamic
27. The ratio of relative velocity of steam at outlet tip of the blade to the relative velocity of steam at inlet tip of the blade is called blade velocity coefficient
1. True
2. False
28. Multi-stage steam turbines are of the
1. velocity compounded type
2. reaction type
3. pressure compounded type
4. all of these
29. The flow through a nozzle is regarded as
1. constant volume flow
2. constant pressure flow
3. isothermal flow
4. isentropic flow
30. In reaction turbines, the axial thrust is due to
1. pressure drop across the rotor
2. change in axial velocity
3. both (a) and (b)
4. none of these
31. A binary vapour plant consists of
1. steam turbine
2. steam condenser
3. mercury boiler
4. all of these
32. The steam leaves the nozzle at a
1. high pressure and a low velocity
2. high pressure and a high velocity
3. low pressure and a low velocity
4. low pressure and a high velocity
33. In a De-Laval nozzle expanding superheated steam from 10 bar to 0.1 bar, the pressure at the minimum cross-section (i. e. pressure at throat, p2) will be
1. 3.3 bar
2. 5.46 bar
3. 8.2 bar
4. 9.9 bar
34. If ηB=Blading efficiency, ηN=Nozzle efficiency then stage efficiency (ηS) is
1. ηS = ηB x ηN
2. ηS = ηBN
3. ηS = ηNB
4. none of these
35. The critical pressure ratio for initially dry saturated steam is more as compared to initially wet steam
1. Yes
2. No
36. Discharge of a convergent-divergent nozzle depends upon the initial conditions of steam and the area of nozzle at throat.
1. Correct
2. Incorrect
37. Parson's reaction turbine is a __________ reaction turbine.
1. 40 percent
2. 50 percent
3. 60 percent
4. 70 percent
1. Straight
2. Circular
3. curved
39. The variation of steam pressure in the nozzle depends upon
1. velocity of steam
2. specific volume of steam
3. dryness fraction of steam
4. all of these
40. Steam turbines are used for
1. large marine propulsion
2. electric power generation
3. direct drive of fans, compressors, pumps
4. all of these
41. In pressure compounding, steam is passed through
42. Ratio of total useful heat-drop to the total isentropic heat-drop, is known as
1. stage efficiency
2. internal efficiency
3. Rankine efficiency
4. none of these
43. Parson's turbine is a
1. simple impulse turbine
2. simple reaction turbine
3. impulse-reaction turbine
4. none of these
44. The purpose of governing in steam turbines is to
1. maintain the speed of the turbine
2. reduce the effective heat drop
3. reheat the steam and improve its quality
4. completely balance against end thrust
45. The value of the reheat factor varies from
1. 1.02 to 1.06
2. 1.08 to 1.l0
3. 1.2 to 1.6
4. 1.6 to 2
46. The steam enters the nozzle at a
1. high pressure and a low velocity
2. high pressure and a high velocity
3. low pressure and a low velocity
4. low pressure and a high velocity
47. Difference of supersaturated-temperature and saturation-temperature at that pressure is known as
1. degree of super saturation
2. degree of superheat
3. degree of undercooling
4. none of these
48. In velocity compounding, steam is passed through
49. Ratio of the useful heat-drop to the isentropic heat-drop is known as
1. condenser efficiency
2. nozzle efficiency
3. boiler efficiency
4. vacuum efficiency
50. The efficiency of steam turbines may be improved by
1. reheating of steam
2. regenerative feed heating
3. binary vapour plant
4. any one of these
51. The maximum discharge of steam through a convergent-divergent nozzle depends upon
1. area of nozzle at throat
2. initial pressure and volume of steam
3. final pressure of steam leaving the nozzle
4. both (a) and (b)
52. In a reaction turbine, when steam flows through the fixed blades,
1. pressure increases while velocity decreases
2. pressure decreases while velocity increases
3. pressure and velocity both decreases
4. pressure and velocity both increases
53. A single stage impulse turbine with a diameter of 1.2 m runs at 3000 r.p.m. Calculate the inlet velocity of steam if the blade speed ratio is 0.42.
1. 79 m/s
2. 188 m/s
3. 450 m/s
4. 900 m/s
54. In a De-Laval impulse turbine, the nozzle is kept very close to the blades.
1. Yes
2. No
55. The flow of steam is super-sonic
1. at the entrance to the nozzle
2. at the throat of the nozzle
3. in the convergent portion of the nozzle
4. in the divergent portion of the nozzle
56. The smallest section in nozzle is known as
1. throat
2. venturi
3. convergent
4. divergent
57. The pressure of steam at throat of a steam nozzle is called critical pressure.
1. Agree
2. Disagree
58. For maximum efficiency of an impulse turbine, the steam should leave the blades at right angles to their motion.
1. Correct
2. Incorrect
59. De-Laval turbine is a
1. simple impulse turbine
2. simple reaction turbine
3. impulse-reaction turbine
4. none of these
60. If α is the nozzle exit flow angle then the impulse turbine rotor efficiency will have a maximum value of 0.5 cos2 α when
2. blade velocity coefficient is unity
3. blades are equiangular and frictionless
61. When the cross-section of a nozzle increases continuously from entrance to exit, it is called a
1. divergent nozzle
2. convergent nozzle
3. convergent-divergent nozzle
4. none of these
62. Rateau turbine is
1. simple reaction turbine
2. velocity compounded turbine
3. pressure compounded turbine
4. pressure-velocity compounded turbine
63. The ratio of the work delivered at the turbine shaft to the heat supplied is called overall thermal efficiency of turbine.
1. True
2. False
64. Velocity of steam approaching nozzle is negligible in a single-stage impulse-turbine
1. True
2. False
65. The following are the method for compounding except
1. velocity compounding
2. pressure compounding
3. volume compounding
4. reaction turbine
66. Curtis turbine is a
1. simple reaction turbine
2. velocity compounded turbine
3. pressure compounded turbine
4. pressure-velocity compounded turbine
67. The velocity of steam at throat of the nozzle is __________ the velocity of sound.
1. equal to
2. less than
3. more than
68. Critical Pressure ratio for initially dry-saturated steam is
1. 0.546
2. 0.577
3. 0.582
4. 0.601
69. The discharge through a nozzle is maximum for a certain value of exit pressure. This pressure is known as critical pressure.
1. Agree
2. Disagree
70. The critical pressure ratio for gases is
1. 0.528
2. 0.546
3. 0.577
4. 0.582
71. The efficiency of a pressure-velocity compounded impulse turbine is __________ as compared to pressure compounded impulse turbine.
1. same
2. less
3. more
72. In reaction turbine the fixed blade
1. alter the direction of steam
2. allow steam to expand to a larger velocity
3. functions as same of nozzle
4. All of the above
73. The effect of super saturation is that the
1. mass of the steam discharged increases
2. entropy and specific volume of the steam increases
3. exit velocity of steam reduces
4. all of these
74. The ratio of the isentropic heat drop to the heat supplied, is called
1. reheat factor
2. stage efficiency
3. internal efficiency
4. Rankine efficiency
75. If the cross-section of a nozzle first increases from its entrance to throat, and then decreases from its throat to exit, then it is not a convergent-divergent nozzle.
1. Yes
2. No
76. The efficiency ratio is the ratio of total useful heat drop to the total isentropic heat drop.
1. Agree
2. Disagree
77.In a velocity compounded impulse turbine, when steam flows through the second row of moving blades,
1. velocity increases
2. velocity decreases
3. velocity remains constant
4. pressure remains constant
78. The reheat factor depends upon
1. initial pressure and superheat
2. exit pressure
3. turbine stage efficiency
4. all of these
79. The steam turbine can be governed by the following methods except
1. Throttle governing
2. Nozzle governing
3. By pass governing
4. Reaction governing
80. The compounding of turbines is done in order to
1. reduce speed of rotor
2. improve efficiency
3. reduce exit losses
4. all of these
81. The pressure of steam __________ while flowing through a nozzle.
1. Increases
2. Decreases
3. remains constant
82. The process of maintaining the speed of the turbine constant for various load conditions, is known as
1. Bleeding
2. Reheating
3. Governing
4. none of these
83. Reheating of steam in a turbine
1. increases the work done through the turbine
2. increases the efficiency of the turbine
3. reduces wear on the blades
4. all of these
84. Which of the following statement is correct for steam turbines as compared to reciprocating steam engines?
1. A steam turbine develops higher speeds
2. The efficiency of steam turbine is higher
3. The steam consumption is less
4. all of these
85. The correct order in which energy is converted from one form to another, in steam power plant is
1. Kinetic energy – potential energy – mechanical energy – electrical energy
2. Kinetic energy – potential energy– electrical energy – mechanical energy
3. potential energy – Kinetic energy –mechanical energy – electrical energy
4. mechanical energy – potential energy – Kinetic energy –electrical energy
86. Ratio of workdone on the blades per kg of steam to the total energy supplied per stage per kg of steam is called
2. nozzle efficiency
3. stage efficiency
4. mechanical efficiency
87. Rankine efficiency depends upon total useful heat-drop and total isentropic heat-drop.
1. Correct
2. Incorrect
88. Blading efficiency is also known as
1. stage efficiency
2. diagram efficiency
3. nozzle efficiency
4. none of these
89. In order to reduce the rotor speed of an impulse turbine, the method employed is
1. velocity compounding
2. pressure compounding
3. pressure-velocity compounding
4. all of these
90. The maximum velocity of steam at throat is
1. a. {2(n/n+1) p1v1}^1/2
2. b. {2(n/n+1) p1v1}^3/2
3. c. {2(n/2n+1) p1v1}^1/2
4. d. {2(n/2n+1) p1v1}^3/2
Where, n=1.135 for saturated steam and 1.3 for superheated steam. p1= initial pressure of steam, v1=initial volume of 1 kg of steam at pressure p1
91. The nozzle efficiency is the ratio of
1. work done on the blades to the energy supplied to the blades
2. work done on the blades per kg of steam to the total energy supplied per stage per kg of steam
3. energy supplied to the blades per kg of steam to the total energy supplied per stage per kg of steam
4. none of the above
92. In a nozzle, whole frictional loss is assumed to occur between
1. inlet and throat
2. inlet and outlet
3. throat and exit
4. all of these
93. The friction in the nozzle __________ exit velocity of steam.
1. has no effect on
2. Decreases
3. Increases
94. A stage, in reaction turbine, is represented by
1. number of casing
2. number of entries of steam
3. number of exits of steam
95. When the nozzle operates with the maximum mass flow, the nozzle is said to be
1. Choked
2. Underdamping
3. Overdamping
4. none of these
96. Which of the following is true for steam flow through nozzle?
1. The flow is assumed to be adiabatic
2. The steam loses its pressure and heat while passing through nozzle
3. The work done is equal to the adiabatic heat drop
4. All of the above
97. The ratio of the energy supplied to the blades per kg of steam to the total energy supplied per stage per kg of steam is called mechanical efficiency.
1. Yes
2. No