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GATE Past Year Questions: Power Plant Engineering

Q1: Consider an air-standard Brayton cycle with adiabatic compressor and turbine, and a regenerator, as shown in the figure. Air enters the compressor at 100kPa and 300 K and exits the compressor at 600kPa and 550 K. The air exits the combustion chamber at 1250 K and exits the adiabatic turbine at 100kPa and 800 K. The exhaust air from the turbine is used to preheat the air in regenerator. The exhaust air exits the regenerator (state 6) at 600 K. There is no pressure drop across the regenerator and the combustion chamber. Also, there is no heat loss from the regenerator to the surroundings. The ratio of specific heats at constant pressure and volume is cp/cv = 1.4. The thermal efficiency of the cycle is _____ % (answer in integer).   [GATE ME 2024]
GATE Past Year Questions: Power Plant EngineeringAns:
40 to 40
GATE Past Year Questions: Power Plant EngineeringT1 = 300 K
T2 = 550 K 
T= 1250 K 
T= 800 K 
T6 = 600 K 
γ = 1.4 
Wnet = CP(T4-T5) - CP(T2-T1)
QR = CP(T6-T1)
QS = Wnet +QR
So, η = Wnet /Qs
GATE Past Year Questions: Power Plant Engineering

Q2: Which one of the following statements regarding a Rankine cycle is FALSE?   [GATE ME 2024]
(a) Superheating the steam in the boiler increases the cycle efficiency.
(b) The pressure at the turbine outlet depends on the condenser temperature.
(c) Cycle efficiency increases as a condenser pressure decreases.
(d) Cycle efficiency increases as boiler pressure decreases.
Ans: (d)
Superheating in Rankine cycle increases the cycle efficiency because of increase in mean temperature of heat addition.
With increase in pressure of boiler, the cycle efficiency increases. So, the given statement is wrong.
With decrease in condenser pressure, the cycle efficiency increases because of decrease in mean temperature of heat rejection.
The pressure of turbine outlet is governed by the condenser temperature. Decreasing the cooling water temperature, creates more vacuum in condenser which results in pressure drop and vice-versa.

Q1: Consider an isentropic flow of air (ratio of specific heats = 1.4) through a duct as shown in the figure.
The variations in the flow across the cross-section are negligible. The flow conditions at Location 1 are given as follows:
??P= 100kPa, ρ= 1.2 kg/m3, u= 400m/s
The duct cross-sectional area at Location 2 is given by A2 = 2A1, where A1 denotes the duct cross-sectional area at Location 1. Which one of the given statements about the velocity u2 and pressure P2 at Location 2 is TRUE?  [GATE ME 2023]
GATE Past Year Questions: Power Plant Engineering(a) u2 < u1, P2 < P1
(b) u2 < u1, P2 > P1
(c) u2 > u1, P2 < P1
(d) u2 > u1, P2 > P1
Ans:
(c)
Step -1: First identify type of flow - Subsonic or Supersonic by finding out Mach number
GATE Past Year Questions: Power Plant EngineeringMach no at start of flow
Ma = u1/C1, where, C1 = GATE Past Year Questions: Power Plant Engineering
u1 is velocity of gas
C1 is velocity of sound
P1 = ρ1RT1
GATE Past Year Questions: Power Plant Engineering
= 341.56 m/sec
Ma1 = 400/341.56 = 1.017
Flow is supersonic flow. Hence, diverging duct is nozzle so u2 > u1 and P2 < P1.

Q1: In a steam power plant based on Rankine cycle, steam is initially expanded in a high-pressure turbine. The steam is then reheated in a reheater and finally expanded in a low-pressure turbine. The expansion work in the high-pressure turbine is 400 kJ/kg and in the low-pressure turbine is 850 kJ/kg, whereas the pump work is 15 kJ/kg. If the cycle efficiency is 32%, the heat rejected in the condenser is ________ kJ/kg (round off to 2 decimal places).   [GATE ME 2022 SET-1]
Ans:
2620 to 2630
GATE Past Year Questions: Power Plant EngineeringWHPT = 400 kJ/kg
WLPT = 850 kJ/kg
WP = 15kJ/kg
η = 0.35 = Wnet/QS
Q= 3859.375 kJ/kg
∴ Wnet = QS - QR
QR = 3859.375 - 1235
QR = 2624.37 kJ/kg

Q1: Consider the open feed water heater (FWH) shown in the figure given below:
GATE Past Year Questions: Power Plant Engineering

Specific enthalpy of steam at location 2 is 2624 kJ/kg, specific enthalpy of water at location 5 is 226.7 kJ/kg and specific enthalpy of saturated water at location 6 is 708.6 kJ/kg. If the mass flow rate of water entering the open feed water heater (at location 5) is 100 kg/s then the mass flow rate of steam at location 2 will be kg/s (round off to one decimal place).   [GATE ME 2021 SET-2]
Ans: 
25 to 25.4
GATE Past Year Questions: Power Plant EngineeringGATE Past Year Questions: Power Plant Engineering100h+ (x - 100)h2 = xh6
100 × 226.7 + (x - 100)2624 = 708.6x
22670 + 2624x - 262400 = 708.6x
2624x - 708.6x = 239730
1915.4x = 239730
x = 125.159 GATE Past Year Questions: Power Plant Engineering125.2 kg/s
Mass flow rate at state 2(x - 100) = 25.2 kg/s

Q2: Consider a steam power plant operating on an ideal reheat Rankine cycle. The work input to the pump is 20 kJ/kg. The work output from the high pressure turbine is 750 kJ/kg. The work output from the low pressure turbine is 1500 kJ/kg. The thermal efficiency of the cycle is 50 %. The enthalpy of saturated liquid and saturated vapour at condenser pressure are 200 kJ/kg and 2600 kJ/kg, respectively. The quality of steam at the exit of the low pressure turbine is ________ % (round off to the nearest integer).   [GATE ME 2021 SET-1]
Ans:
92 to 96
GATE Past Year Questions: Power Plant Engineeringhf = 200 kJ/kg
hg = 2600 kJ/kg
wp = 20 kJ/kg = h- h5
h1 - h2 = 750 kJ/kg
h- h4 = 1500 kJ/kg
GATE Past Year Questions: Power Plant Engineering
GATE Past Year Questions: Power Plant Engineering
Q= 4460 kJ/kg
η = 1 - (QR/QS)
(QR/QS) = 0.5
Q= 2230 kJ/kg
Q= h4 - h5
2230 = h4 - 200
h= hf + x(hg - hf)
2430 = 200 + x(2600 - 200)
x = 0.9291
x  = 93%

Q1: The values of enthalpies at the stator inlet and rotor outlet of a hydraulic turbomachine stage are h1 and h3 respectively. The enthalpy at the stator outlet (or, rotor inlet) is h2. The condition (h- h1) = (h3 - h2) indicates that the degree of reaction of this stage is  [GATE ME 2020 SET-2]
(a) zero
(b) 50%
(c) 75%
(d) 100%
Ans: 
(b)
As enthalpy across stator and rotor is equal it is 50% reaction stage.

MULTIPLE CHOICE QUESTION

Try yourself: Boiler rating is usually defined in terms of

[1992]

A

Maximum temperature of steam in kelvin

B

Heat transfer rate in kJ/hr

C

Heat transfer area in meter2

D

Steam output in kg/hr

MULTIPLE CHOICE QUESTION

Try yourself: The equivalent evaporation (kg/hr) of a boiler producing 2000 kg/hr of steam with enthalpy content of 2426 kJ/kg from feed water at temperature 40°C (liquid enthalpy =168 kJ/kg) is (enthalpy of vaporization of water at 100°C = 2258 kJ/kg)

[1993]

A

2000

B

2149

C

186

D

1649

MULTIPLE CHOICE QUESTION

Try yourself: Which among the following is the boiler mounting?

[1997]

A

Blow off cock

B

Feed pump

C

Economizer

D

Super heater

MULTIPLE CHOICE QUESTION

Try yourself: When initially dry and saturated steam flows through a nozzle, the ratio of actual discharge to calculated discharge is

[1990]

A

Equal to 1.0

B

Greater than 1.0

C

Less than 1.0

D

Independent of inlet conditions

MULTIPLE CHOICE QUESTION

Try yourself: Subsonic and supersonic diffusers have the following geometry.

[1992]

A

Divergent and convergent respectively

B

Both divergent

C

Both convergent

D

Convergent and divergent respectively

MULTIPLE CHOICE QUESTION

Try yourself: The isentropic heat drop in the nozzle of an impulse steam turbine with a nozzle efficiency 0.9, blade velocity ratio 0.5 and mean blade velocity 150 m/s in kJ/kg is

[1998]

A

50

B

40

C

60

D

75

MULTIPLE CHOICE QUESTION

Try yourself: In the Rankine cycle when superheated steam is used

[1990]

A

Thermal efficiency increases

B

Steam consumption decreases

C

Steam dryness after expansion increases

D

All of the above

MULTIPLE CHOICE QUESTION

Try yourself: In a Rankine cycle heat is added

[1991]

A

Reversibly at constant volume

B

Reversibly at constant temperature

C

Reversibly at constant pressure and temperature

D

Reversibly at constant pressure

MULTIPLE CHOICE QUESTION

Try yourself: In steam and other vapour cycle, the process of removing non-condensable is called

[1992]

A

Scavenging process

B

Deaeration process

C

Exhaust process

D

Condensation process

MULTIPLE CHOICE QUESTION

Try yourself: A gas turbine cycle with heat exchange and reheating improves

[1993]

A

Only the thermal efficiency

B

Only the specific power output

C

Both thermal efficiency and specific power output

D

Neither thermal efficiency nor specific power output

MULTIPLE CHOICE QUESTION

Try yourself: For a given set of operating pressure limits of a Rankine cycle the highest efficiency occurs for

[1994]

A

Saturated cycle

B

Superheated cycle

C

Reheat cycle

D

Regenerative cycle

MULTIPLE CHOICE QUESTION

Try yourself: A gas turbine cycle with infinitely large number of stages during compression and expansion leads to

[1994]

A

Stirling cycle

B

Atkinson cycle

C

Ericson cycle

D

Brayton cycle

MULTIPLE CHOICE QUESTION

Try yourself: Consider an actual regenerative Rankine cycle with one open feed water heater. For each kg steam entering the turbine, if m kg steam with a specific enthalpy of h1 is blade from the turbine, and the specific enthalpy of liquid water entering the heater is h2, then h3 the specific enthalpy of saturated liquid leaving the heater is equal to

[1997]

A

mh1 – (h2 – h1)

B

h1 – m(h2 – h1)

C

h2 – m(h2 – h1)

D

mh2 – (h2 – h1)

MULTIPLE CHOICE QUESTION

Try yourself: The efficiency of superheat Rankine cycle is higher than that of simple Rankine cycle because

[2002]

A

the enthalpy of main steam is higher for superheat cycle

B

the mean temperature of heat addition is higher for superheat cycle

C

the temperature of steam in the condenser is high

D

the quality of steam in the condenser is low

MULTIPLE CHOICE QUESTION

Try yourself: In Rankine cycle, regeneration results inhigher efficiency because

[2003]

A

pressure inside the boiler increases

B

heat is added before steam enters the low pressure turbine

C

average temperature of heat addition in the boiler increases

D

total work delivered by the turbine increases

MULTIPLE CHOICE QUESTION

Try yourself: In a gas turbine, hot combustion products with the specific heats cp = 0.98 kJ/kgK, and cv = 0.7538 kJ/kgK enters the turbine at 20 bar, 1500 K and exits at 1 bar. The isentropic efficiency of the turbine is 0.94. The work developed by the turbine per kg of gas flow is

[2003]

A

689.64 kJ/kg

B

794.66 kJ/kg

C

1009.72 kJ/kg

D

1312.00 kJ/kg

MULTIPLE CHOICE QUESTION

Try yourself: The compression ratio of a gas power plant cycle corresponding to maximum work output for the given temperature limits of Tmin and Tmax will be

[2004]

A

GATE Past Year Questions: Power Plant Engineering

B

GATE Past Year Questions: Power Plant Engineering

C

GATE Past Year Questions: Power Plant Engineering

D

GATE Past Year Questions: Power Plant Engineering

MULTIPLE CHOICE QUESTION

Try yourself: Given below is an extract from steam tables.
GATE Past Year Questions: Power Plant Engineering
​Specific enthalpy of water in kJ/kg at 150 bar and 45°C is

[2006]

A

203.60

B

200.53

C

196.38

D

188.45

MULTIPLE CHOICE QUESTION

Try yourself: Determine the correctness or otherwise Assertion (A) and the Reason (R).
Assertion (A): In a power plant working on a Rankine cycle, the regenerative feed water heating improves the efficiency of the steam turbine.
Reason (R): The regenerative feed water heating raises the average temperature of heat addition in the Rankine cycle.

[2006]

A

Both (A) and (R) are true and (R) is the correct reason for (A)

B

Both (A) and (R) are true but (R) is NOT the correct reason for (A)

C

Both (A) and (R) are false

D

(A) is false but (R) is true

MULTIPLE CHOICE QUESTION

Try yourself: Determine the correctness or otherwise of the following Assertion (A) and the Reason (R).
Assertion (A) : Condenser is an essential equipment in a steam power plant.
Reason (R): For the same mass flow rate and the same pressure rise, a water pump requires substantially less power than a steam compressor.

[2006]

A

Both (A) and (R) are true and (R) is the correct reason for (A)

B

Both (A) and (R) are true but (R) is NOT the correct reason for (A)

C

Both (A) and (R) are false

D

(A) is false but (R) is true

MULTIPLE CHOICE QUESTION

Try yourself: Which combination of the following statements is correct?
The incorporation of reheater in a steam power plant:
P : Always increases the thermal efficiency of the plant.
Q : Always increases the dryness fraction of steam at condenser inlet.
R : Always increases the mean temperature of heat addition.
S : Always increases the specific work output.

[2007]

A

P and S

B

Q and S

C

P, R and S

D

P, Q, R and S

MULTIPLE CHOICE QUESTION

Try yourself: A thermal power plant operates on a regenerative cycle with a single open feedwater heater, as shown in the figure. For the state points shown, the specific enthalpies are: h1 = 2800 kJ/kg and h2 = 200 kJ/kg. The bleed to the feedwater heater is 20% of the boiler steam generation rate. The specific enthalpy at state 3 is

GATE Past Year Questions: Power Plant Engineering

[2008]

A

720 kJ/kg

B

2280 kJ/kg

C

1500 kJ/kg

D

3000 kJ/kg

MULTIPLE CHOICE QUESTION

Try yourself: The values of enthalpy of steam at the inlet and outlet of a steam turbine in a Rankine cycle are 2800 kJ/kg and 1800 kJ/kg respectively.Neglecting pump work, the specific steam consumption in kg/kW hour is

[2011]

A

3.60

B

0.36

C

0.06

D

0.01

MULTIPLE CHOICE QUESTION

Try yourself: An ideal Brayton cycle, operating between the pressure limits of 1 bar and 6 bar, has minimum and maximum temperatures of 300 K and 1500 K. The ratio of specific heats of the working fluid is 1.4. The approximate final temperature in Kelvin at the end of the compression and expansion processes are respectively

[2011]

A

500 and 900        

B

900 and 500

C

500 and 5400      

D

900 and 900

MULTIPLE CHOICE QUESTION

Try yourself: In a power plant, water (density = 1000 kg/m3) is pumped from 80 kPa to 3 MPa. The pump has an isentropic efficiency of 0.85. Assuming that the temperature of the water remains the same, the specific work (in kJ/kg) supplied to the pump is

[2014,Set-1]

A

0.34

B

2.48

C

2.92

D

3.43

MULTIPLE CHOICE QUESTION

Try yourself: The thermal efficiency of an ai r-standard Brayton cycle in terms of pressure ratio rp and y(= cp/cv) is given by

[2014,Set-2]

A

GATE Past Year Questions: Power Plant Engineering

B

GATE Past Year Questions: Power Plant Engineering

C

GATE Past Year Questions: Power Plant Engineering

D

GATE Past Year Questions: Power Plant Engineering

MULTIPLE CHOICE QUESTION

Try yourself: For a gas turbine power plant, identify the correct pair of statements.
P. Smaller in size compared to steam power plant for same power output
Q. Starts quickly compared to steam power plant
R. Works on the principle of Rankine cycle
S. Good compatibility with solid fuel

[2014,Set-3]

A

P and Q

B

R and S

C

Q and R

D

P and S

MULTIPLE CHOICE QUESTION

Try yourself: The INCORRECT statement about regeneration in vapor power cycle is that

[2016,Set-1]

A

it increases the irreversibility by adding the liquid with higher energy content to the steam generator

B

heat is exchanged between the expanding fluid in the turbine and the compressed fluid before heat addition

C

the principle is similar to the principle of Stirling gas cycle

D

it is practically implemented by providing feed water heaters

MULTIPLE CHOICE QUESTION

Try yourself: Which one of the following modifications of the simple ideal Rankine cycle increases the thermal efficiency and reduces the moisture content of the steam at the turbine outlet?

[2019,Set-2]

A

Increasing the turbine inlet temperature

B

Decreasing the condenser pressure

C

Increasing the boiler pressure

D

Decreasing the boiler pressure

MULTIPLE CHOICE QUESTION

Try yourself: The current level of the maximum temperature of steam turbine inlet.is much lower than that at gas turbine inlet because

[1989]

A

The fuel combustion temperature in a steam generator is lower than that in a gas turbine engine

B

Of the corrosive nature of high temperature steam on super heater tubes

C

The materials used for the gas turbine blades are not suitabie for the steam turbine blades

D

Unlike the gas turbine blades the steam turbine blades cannot be cooled

MULTIPLE CHOICE QUESTION

Try yourself: For a single stage impulse turbine with rotor diameter of 2 m and a speed of 3000 rpm when the nozzle angle is 20°, the optimum velocity of steam in m/s is

[1994]

A

334

B

356

C

668

D

711

MULTIPLE CHOICE QUESTION

Try yourself: A steam power plant has the boiler efficiency of 92%, turbine efficiency (mechanical) of 94%, generator efficiency of 95% and cycle efficiency of 44%. If 6% of the generated power is used to run the auxiliaries, the overall plant efficiency is

[1996]

A

34%

B

39%

C

45%

D

30%

MULTIPLE CHOICE QUESTION

Try yourself: The following data pertain to a single stage impulse steam turbine:
Nozzle angle = 20°
Blade velocity = 200 m/s
Relative steam velocity at entry = 350 m/s
Blade inlet angle = 30°
Blade exit angle = 25°
If blade friction is neglected the work done per kg steam is

[1997]

A

124 kJ

B

164 kJ

C

169 kJ

D

174 kJ

MULTIPLE CHOICE QUESTION

Try yourself: If VN and α are the nozzle exit velocity and nozzle angle in an impulse turbine, the optimum blade velocity is given by

[1998]

A

VN cos 2α

B

VN sin 2α

C

VN cos (α/2)

D

GATE Past Year Questions: Power Plant Engineering

MULTIPLE CHOICE QUESTION

Try yourself: A Curtis stage, Rateau stage and a 50% reaction stage in a steam turbine are examples of

[1998]

A

different types of impulse stages

B

different types of reaction stages

C

a simple impulse stage, a velocity compounded impulse stage and reaction stage

D

a.velocity compounded impulse stage, a pressure compounded impulse stage and a reaction stage

MULTIPLE CHOICE QUESTION

Try yourself: Which of the following is a pressure compounded turbine?

[2000]

A

Parsons

B

Curtis

C

Rateau

D

All of three

MULTIPLE CHOICE QUESTION

Try yourself: The Rateau turbine belongs to the category of

[2001]

A

pressure compounded turbine

B

reaction turbine

C

velocity compounded turbine

D

radial flow turbine

MULTIPLE CHOICE QUESTION

Try yourself: Considering the variation of static pressure and absolute velocity in an impulse steam turbine, across one row of moving blades

[2003]

A

both pressure and velocity decrease

B

pressure decreases but velocity increases

C

pressure remains constant, while velocity increases

D

pressure remains constant, while velocity decreases

MULTIPLE CHOICE QUESTION

Try yourself: In the velocity diagram shown below, u = blade velocity, C = absolute fluid velocity and W = relative velocity of fluid and the subscripts 1 and 2 refer to inlet and outlet. This diagram is for

GATE Past Year Questions: Power Plant Engineering

[2005]

A

an impulse turbine

B

a reaction turbine

C

a centrifugal compressor

D

an axial flow compressor

MULTIPLE CHOICE QUESTION

Try yourself: Specific enthalpy and velocity of steam at inlet and exit of a steam turbine, running under steady state, are as given below:

GATE Past Year Questions: Power Plant Engineering
The rate of heat loss from the turbine per kg of steam flow rate is 5 kW. Neglecting changes in potential energy of steam, the power developed in kW by the steam turbine per kg of steam flow rate, is

[2014]

A

901.2

B

911.2

C

17072.5

D

17082.5

The document GATE Past Year Questions: Power Plant Engineering is a part of the Mechanical Engineering Course Thermodynamics.
All you need of Mechanical Engineering at this link: Mechanical Engineering

FAQs on GATE Past Year Questions: Power Plant Engineering

1. What are the major types of power plants covered in Power Plant Engineering?
Ans. The major types of power plants include thermal power plants, hydroelectric power plants, nuclear power plants, and renewable energy power plants such as wind and solar. Each type has its own operational principles, advantages, and disadvantages, which are essential for understanding the overall landscape of power generation.
2. How is the efficiency of a thermal power plant calculated?
Ans. The efficiency of a thermal power plant is calculated using the formula: Efficiency = (Output Energy / Input Energy) × 100%. Output energy is the electrical energy generated, while input energy is the thermal energy produced from burning fuel. Factors such as heat losses and operational conditions significantly affect the overall efficiency.
3. What are the environmental impacts of power plants?
Ans. Power plants can have various environmental impacts, including air and water pollution, habitat destruction, and greenhouse gas emissions. Thermal power plants emit CO2 and other pollutants, while hydroelectric plants can disrupt local ecosystems. Understanding these impacts is crucial for developing sustainable energy solutions.
4. What is the role of a boiler in a thermal power plant?
Ans. A boiler in a thermal power plant is responsible for converting water into steam by heating it using combustion of fuel. The steam produced is then used to drive turbines that generate electricity. The efficiency and design of the boiler significantly influence the overall performance of the power plant.
5. What are some common questions asked in GATE related to Power Plant Engineering?
Ans. Common questions in the GATE exam related to Power Plant Engineering may include topics like thermodynamic cycles, efficiency calculations, types of power plants, environmental regulations, and energy conversion methods. Familiarity with these areas can help in effectively preparing for the exam.
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