Steam Nozzles and Turbines

Q1: The critical pressure gives the velocity of steam at the throat equal to the velocity of sound.

A Agree

B Disagree

Q2: The critical pressure ratio for initially wet steam is

A 0.546

B 0.577

C 0.582

D 0.601

Q3: The pressure at which the steam leaves the nozzle is known as back pressure.

A Correct

B Incorrect

Q4: Parson's turbine is a

A simple impulse turbine

B simple reaction turbine

C impulse-reaction turbine

D none of these

Q5: The discharge is __________ at critical pressure.

A zero

B minimum

C maximum

Q6: The Parsons' reaction turbine has

A only moving blades

B only fixed blades

C identical fixed and moving blades

D fixed and moving blades of different shape

Q7: The value of the reheat factor varies from

A 1.02 to 1.06

B 1.08 to 1.l0

C 1.2 to 1.6

D 1.6 to 2

Q8: When the back pressure of a nozzle is below the designed value of pressure at exit of nozzle, the nozzle is said to be

A choked

B underdamping

C overdamping

D none of these

Q9: 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

A 3.3 bar

B 5.46 bar

C 8.2 bar

D 9.9 bar

Q10: The turbine blades are

A straight

B circular

C curved

Q11: A turbine is said to have an axial discharge when the steam leaves the blade tip at __________ to the direction of the blade motion.

A 60°

B 90°

C 180°

D 270°

Q12: Thermal equilibrium means that the flow of steam is

A isothermal

B isentropic

C hyperbolic

D polytropic

Q13: A nozzle is said to be a convergent nozzle

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

B when the cross-section of the nozzle decreases continuously from entrance to exit

C when the cross-section of the nozzle first decreases from entrance to throat and then increases from its throat to exit

D none of the above

Q14: 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.

A True

B False

Q15: Multi-stage steam turbines are of the

A velocity compounded type

B reaction type

C pressure compounded type

D all of these

Q16: The turbine, in which the general direction of the steam flow is parallel to the turbine axis, is called axial flow turbines

A True

B False

Q17: The difference of supersaturated temperature and saturation temperature at that pressure is called

A degree of supersaturation

B degree of superheat

C degree of undercooling

D none of these

Q18: The discharge of steam in a convergent-divergent nozzle __________ after the throat (i.e. in the divergent portion of the nozzle)

A remains constant

B decreases

C increases

Q19: The efficiency of steam turbines may be improved by

A reheating of steam

B regenerative feed heating

C binary vapour plant

D any one of these

Q20: In a convergent divergent nozzle, the discharge depends upon the initial conditions of steam and the area of nozzle at throat.

A Correct

B Incorrect

Q21: The steam leaves the nozzle at a

A high pressure and a low velocity

B high pressure and a high velocity

C low pressure and a low velocity

D low pressure and a high velocity

Q22: The critical pressure ratio (p2/p1) is given by

A

B

C

D

Q23: 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

A 0.4

B 0.56

C 0.67

D 1.67

Q24: The maximum efficiency of a reaction turbine is

A

B

C

D

Q25: Which of the following statement is correct?

A The expansion of steam in a nozzle follows Rankine cycle.

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

C The pressure of steam at throat is called critical pressure.

D all of the above

Q26: The efficiency of reaction turbine is maximum when (where α = Angle made by the absolute velocity (V) at inlet)

A Vb = 0.5 V cos α

B Vb = V cos α

C Vb = 0.5 V2 cos α

D Vb = V2 cos α

Q27: In a nozzle, whole frictional loss is assumed to occur between

A inlet and thoroat

B inlet and outlet

C throat and exit

D all of these

Q28: The rate of discharge through the nozzle __________ when the exit pressure is gradually reduced.

A remains same

B decreases

C increases

Q29: De-Laval turbine is a

A single rotor impulse turbine

B multi-rotor impulse turbine

C impulse reaction turbine

D none of these

Q30: The turbine blades do not change the direction of steam issuing from the nozzle.

A True

B False

Q31: The ratio of the useful heat drop to the isentropic heat drop is called

A condenser efficiency

B nozzle efficiency

C boiler efficiency

D vacuum efficiency

Q32: A regenerative steam cycle renders

A increased work output per unit mass of steam

B decreased work output per unit mass of steam

C increased thermal efficiency

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

Q33: The variation of steam pressure in the nozzle depends upon

A velocity of steam

B specific volume of steam

C dryness fraction of steam

D all of these

Q34: The critical pressure gives the velocity of steam at the throat

A equal to the velocity of sound

B less than the velocity of sound

C more than the velocity of sound

D none of these

Q35: The flow through a nozzle is regarded as

A constant volume flow

B constant pressure flow

C isothermal flow

D isentropic flow

Q36: In a reaction turbine, when steam flows through the fixed blades,

A pressure increases while velocity decreases

B pressure decreases while velocity increases

C pressure and velocity both decreases

D pressure and velocity both increases

Q37: The steam enters the nozzle at a

A high pressure and a low velocity

B high pressure and a high velocity

C low pressure and a low velocity

D low pressure and a high velocity

Q38: The stage efficiency (ηS) is given by (where ηB = Blading efficiency, and ηN = Nozzle efficiency)

A ηS = ηB x ηN

B ηS = ηBN

C ηS = ηNB

D none of these

Q39: The critical pressure ratio for initially dry saturated steam is more as compared to initially wet steam.

A Yes

B No

Q40: The impulse reaction turbine has its driving force

A as an impulsive force

B as a reaction force

C partly as an impulsive force and partly as a reaction force

D none of the above

Q41: A binary vapour plant consists of

A steam turbine

B steam condenser

C mercury boiler

D all of these

Q42: 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)

A V = 44.72 hd K

B V = 44.72 K hd

C V = 44.72 K hd

D V = 44.72 K hd

Q43: The ratio of the workdone on the blades to the energy supplied to the blades, is called

A blading efficiency

B nozzle efficiency

C gross or stage efficiency

D mechanical efficiency

Q44: The action of steam in a steam turbine is

A static

B dynamic

C static and dynamic

D neither static nor dynamic

Q45: Steam turbines are used for

A large marine propulsion

B electric power generation

C direct drive of fans, compressors, pumps

D all of these

Q46: In reaction turbines, the axial thrust is due to

A pressure drop across the rotor

B change in axial velocity

C both (a) and (b)

D none of these

Q47: The reheat factor is the ratio of the

A cumulative heat drop to the isentropic heat drop

B isentropic heat drop to the heat supplied

C total useful heat drop to the total isentropic heat drop

D none of the above

Q48: The supersaturated flow of steam through a nozzle as compared to a stable flow, the available heat drop

A remains the same

B increases

C decreases

D is unpredictable

Q49: Parson's reaction turbine is a __________ reaction turbine.

A 40 percent

B 50 percent

C 60 percent

D 70 percent

Q50: The ratio of total useful heat drop to the total isentropic heat drop, is called

A stage efficiency

B internal efficiency

C Rankine efficiency

D none of these


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