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Multiple choice question for engineering

Set 1

1. What is the unit of Heat rate?
a) kJ/KW
b) KW/kJ
c) kJ
d) KW

View Answer

Answer: a [Reason:] Heat rate is the rate of input required to produce unit shaft output.

2. Rankine cycle operating on low pressure limit of p1 and high pressure limit of p2
a) has higher thermal efficiency than the Carnot cycle operating between same pressure limits
b) has lower thermal efficiency than Carnot cycle operating between same pressure limits
c) has same thermal efficiency as Carnot cycle operating between same pressure limits
d) may be more or less depending upon the magnitudes of p1 and p2

View Answer

Answer: a [Reason:] Area under P-V curve for Rankine will be more as compared to Carnot cycle.

3. Rankine efficiency of a Steam Power Plant
a) improves in Summer as compared to that in Winter
b) improves in Winter as compared to that in Summer
c) is unaffected by climatic conditions
d) none of the mentioned

View Answer

Answer: b [Reason:] In winters, temperature of cooling water is low, which increases Condenser’s efficiency.

4. Rankine cycle comprises of
a) two isentropic processes and two constant volume processes
b) two isentropic processes and two constant pressure processes
c) two isothermal processes and two constant pressure processes
d) none of the mentioned

View Answer

Answer: b [Reason:] Rankine cycle is a reversible cycle which have two constant pressure and two constant temperature processes.

5. In Rankine cycle, the work output from the turbine is given by
a) change of internal energy between inlet and outlet
b) change of enthalpy between inlet and outlet
c) change of entropy between inlet and outlet
d) change of temperature between inlet and outlet

View Answer

Answer: b [Reason:] Work output(turbine) = h1-h2.

6. Which of the following contributes to the improvement of efficiency of Rankine cycle in a Thermal Power Plant?
a) reheating of steam at intermediate stage
b) regeneration use of steam for heating Boiler feed water
c) use of high pressures
d) all of the mentioned

View Answer

Answer: d [Reason:] The regenerative features effectively raise the nominal cycle heat input temperature, by reducing the addition of heat from the Boiler/fuel source at the relatively low feedwater temperatures that would exist without regenerative feedwater heating.

7. Match the following:

a) Boiler            1. reversible adiabatic expansion of steam
b) turbine           2. constant pressure heat heat addition
c) Condenser         3. reversible adiabatic compression
d) pump              4. constant pressure heat rejection

View Answer

Answer: a-2 b-1 c-4 d-3 [Reason:] Working fluid in Rankine cycle undergoes 4 processes, expansion in turbine, heat addition in Boiler, heat rejection in Condenser and compression in pump.

8. What is the actual turbine inlet temperature in Rankine cycle?
a) 700C
b) 800C
c) 550C
d) 1150C

View Answer

Answer: c [Reason:] The TIT(Turbine Inlet Temperature) is of the range 500-570C.

9. Rankine cycle efficiency of a good Steam Power Plant may be in the range of?
a) 15 to 20%
b) 35 to 45%
c) 70 to 80%
d) 90 to 95%

View Answer

Answer: b [Reason:] Efficiency of Rankine cycle in actual working condition is found to be between 35 to 45%.

10. A simple Rankine cycle operates the Boiler at 3 MPa with an outlet temperature of 350°C and the Condenser at 50 kPa. Assuming ideal operation and processes, what is the thermal efficiency of this cycle?
a) 7.7
b) 17.7
c) 27.7
d) 37.7

View Answer

Answer: c [Reason:] Fixing the states; h1 = 340.5 kJ/kg, h2 = h1 + v1 (P2 – P1) = 343.5 kJ/kg, h3 = 3115.3 kJ/kg, s3 = 6.7428 kJ/kg – K, x4 = 0.869, and h4 = 2343.9 kJ/kg. Thus, η = 1 – Qout / Qin = 1 – (h4 – h1) / (h3 – h2) = 27.7%.

11. A simple Rankine cycle produces 40 MW of power, 50 MW of process heat and rejects 60 MW of heat to the surroundings. What is the utilization factor of this co generation cycle neglecting the pump work?
a) 50
b) 60
c) 70
d) 80

View Answer

Answer: b [Reason:] Application of the first law to the entire cycle gives Qin = Qp + Qreject + W = 150 MW. The utilization factor is then = (Qp + W) / Qin = 60%.

Set 2

1. What is the basic principle of regeneration?
a) Steam after coming out of condenser is circulated to boiler
b) Steam after coming out of condenser is circulated to turbine
c Steam after coming out of turbine is circulated to boiler
d) Two stage turbine is used

View Answer

Answer: b [Reason:] In regeneration steam from condenser is circulated through turbine to increase steam temperature before it enters boiler.

2. Ideal regenerative rankine cycle
a) Increases efficiency
b) Increases work output
c) Increases the heat supplied
d) does not effect efficiency

View Answer

Answer: a [Reason:] Feedwater is preheated so as to decrease the fuel consumption which increases efficiency.

3. Mean temperature of heat addition is _______ due to Regeneration
a) Decreases
b) not effected
c) Increases
d) varied exponentially

View Answer

Answer: c [Reason:] Since less heat is required in the boiler so mean temperature of heat addition increases.

4. Name the coolants commonly used for fast breeder reactors?
a) Liquid metal (Na (or) Na K)
b) Helium (He)
c) Carbon dioxide
d) All of the mentioned

View Answer

Answer: d [Reason:] Liquid metals are commonly used, in some plants He and CO2 are also used.

5. Why trash rack is used?
a) To prevent the entry of debris
b) To prevent steam overflow
c) It is used as an insulter
d) Prevents back flow

View Answer

Answer: a [Reason:] The trash rack is used to prevent the entry of debris, which might damage the turbine runners and chock up the nozzle of impulse turbine.

6. What is the use of surge tank?
a) To store condensate
b) To prevent surging
c) To provide better regulation of water pressure in the system
d) To prevent chocking

View Answer

Answer: c [Reason:] The surge tank controls the water when the load on the turbine decreases and supplies water when the load on the turbine increases.

7. What is the function of Fore bay?
a) Temporary water storage
b) Steam passage
c) Water flow in penstock
d) condensate storage

View Answer

Answer: a [Reason:] It is temporary water storage when the load on the plant is reduced and provides water for initial increment on increasing load.

8. What is the use of draft tube?
a) To regain kinetic energy
b) To regain potential energy
c) Passage for water
d) Stores energy

View Answer

Answer: a [Reason:] The draft tube is used to regain the kinetic energy of water coming out of reaction turbine. It enables the reaction turbine to be placed over tailrace level.

9. Is regenerative cycle alone useful?
a) Yes
b) No
c) may be
d) depends on other factors

View Answer

Answer: a [Reason:] Feedwater is preheated so as to decrease the fuel consumption which increases efficiency.

10. Function of surge tank?
a) Regulation of water pressure
b) Regulation of steam pressure
c) Storage
d) Regulation of lubricants

View Answer

Answer: a [Reason:] The surge tank controls the water when the load on the turbine decreases and supplies water when the load on the turbine increases

Set 3

1. Why Reheating of steam is used?
a) to increase efficiency
b) to increase work output
c) to increase Turbine Inlet Temperature
d) to reduce amount of fuel used

View Answer

Answer: b [Reason:] Work output = work done by turbine – work done by compressor.

2. Reheating of steam
a) decreases steam rate
b) increases steam rate
c) no effect on steam rate
d) none of the mentioned

View Answer

Answer: a [Reason:] Since work output increases the steam rate decreases.

3. Efficiency of cycle will increase due to Reheating if
a) mean temperature of heat addition in boiler is higher than in reheat process
b) mean temperature of heat addition in boiler is lower than in reheat process
c) it will increase without any conditions
d) it will not increase

View Answer

Answer: a [Reason:] Efficiency = work output / heat supplied, heat supplied is less in this condition only.

4. Why don’t we use more than two reheats?
a) not economical
b) increased mechanical stresses
c) net efficiency is decreased
d) all of the mentioned

View Answer

Answer: d [Reason:] The mechanical stresses increases in much higher proportion than the pressure pressure because of the prevailing high temperature.

5. The cycle efficiency in a single reheat plant is influenced by
a) pressure at tubine inlet
b) pressure at which steam is reheated
c) temperature at which steam is reheated
d) temperature at tubine inlet

View Answer

Answer: b [Reason:] The cycle efficiency is a function of the ratio of reheat to initial pressure.

6. The optimum reheat pressure for the most of the modern power plants is ___________ of the initial steam pressure
a) 0.1-0.5
b) 0.2-0.3
c) 0.2-0.25
d) 0.25-0.3

View Answer

Answer: c [Reason:] In this range of reheat pressure efficiency is maximum.

7. What is the effect of reheat on steam quality?
a) increases
b) decreases
c) does not change
d) depends on several parameters

View Answer

Answer: a [Reason:] Because this steam is undergoing expansion two times.

8. What should be the dryness fraction at the time of exhaust?
a) 0.88
b) 0.80
c) 0.90
d) 0.75

View Answer

Answer: a [Reason:] For modern turbines the admissible dryness fraction of exhaust steam (at the turbine exit) should be not less than x = 0.86 to 0.88.

9. Reheat is preferred for the plants having efficiency greater than
a) 150MW
b) 200MW
c) 100MW
d) 250MW

View Answer

Answer: c [Reason:] For producing power less than this reheat will not be economical.

10. Which one of the following is an advantage of reheat cycle
a) the size of the Low pressure (LP) turbine blades is reduced because specific volume is reduced by 7 to 8%
b) the reheating reduce 4 to 5% fuel consumption with a corresponding reduction in the fuel handling
c) lower steam pressures and temperatures and less costly materials can be used to obtain the required thermal performance
d) all of the mentioned

View Answer

Answer: d [Reason:] Reheat increases work output.

Set 4

1. How can we classify steam generators on the basis of application
a) utility steam generators
b) industrial steam generator
c) marine steam generator
d) all of the mentioned

View Answer

Answer: d [Reason:] Steam generators can be classified in a number of ways, on the basis of application these three generators are known.

2. What is the critical pressure of steam?
a) 221.2 bar
b) 220 bar
c) 120 bar
d) 300 bar

View Answer

Answer: a [Reason:] Below 221.2 its sub critical and above 221.2 its super critical.

3. An air preheater is installed
a) between the economiser and chimney
b) before the superheater
c) before the economiser
d) none of the mentioned

View Answer

Answer: a [Reason:] Preheater is used to increase the temperature of steam.

4. The length of shell of a Locomotive boiler is
a) 5m
b) 4m
c) 3m
d) 2m

View Answer

Answer: b [Reason:] It is fixed due to mechanical constraints.

5. Which of the following statement is correct ?
a) A simple vertical boiler has one fire tube.
b) A fire tube boiler occupies less space than a water tube boiler, for a given power.
c) Steam at a high pressure and in large quantities can be produced with a simple vertical boiler.
d) all of the mentioned

View Answer

Answer: a [Reason:] A typical vertical boiler can have only one fire tube for the flow of fire or heat.

6. The object of producing draught in a boiler is
a) to discharge the gases of combustion to the atmosphere through the chimney
b) all of the mentioned
c) to exhaust the gases of combustion from the combustion chamber
d) to provide an adequate supply of air for the fuel combustion

View Answer

Answer: b

7. The natural draught is produced by
a) team jet
b) chimney
c) centrifugal fan
d) none of the mentioned

View Answer

Answer: b [Reason:] When air or flue gases flow due to the difference in density of the hot flue gases and cooler ambient gases.

8. Which of the following statement is wrong ?
a) Water tube boilers are internally fired.
b) Locomotive boiler is a water tube boiler.
c) La-mont boiler is a low pressure water tube boiler.
d) all of the mentioned

View Answer

Answer: d [Reason:] Water tube boilers are externally fired where as fire tube boilers are internally fired.

9. Which of the following boiler is best suited to meet the fluctuating demand of steam ?
a) Locomotive boiler
b) Lancashire boiler
c) Babcock and Wilcox boiler
d) Cornish boiler

View Answer

Answer: a [Reason:] Because forced draught is provided in the locomotive boiler by injecting exhausted steam back into the exhaust via a blast pipe in the smokebox.

Set 5

1. What percentage of fuel energy is actually converted to electrical energy?
a) 50%
b) 40%
c) 34%
d) 25%

View Answer

Answer: c [Reason:] In overall process due to losses the 66% of energy is lost.

2. Maximum energy of a power plant is lost in?
a) condensor
b) pump
c) boiler
d) environment

View Answer

Answer: a [Reason:] In a condensor heat is rejected to cooling water.This is the loss due to heat to work energy conversion in the cycle.

3. The lower is the value of heat rate, __________ is the efficiency.
a) lower
b) higher
c) same
d) depends on further parameters

View Answer

Answer: b [Reason:] The parameter that readily reflects the fuel economy is the heat rate, which is inversely proportional to the efficiency.

4. Overall efficiency is the ratio of power available at generator terminals to rate of energy released by combustion of fuel.
a) true
b) false
c) can’t say
d) not true for all conditions

View Answer

Answer: a [Reason:] Efficiency is power generated / power supplied.

5. The steam from steam generator of a nuclear power plant is best described as
a) superheated steam
b) supercritical steam
c) saturated dry steam
d) saturated wet steam

View Answer

Answer: d [Reason:] Steam contains moisture after coming out of boiler.

6. Under certain conditions, the specific enthalpies of dry steam, saturated water and wet steam are 2783 kJ/kg, 1219 kJ/kg and 2750 kJ/kg respectively. Determine the dryness fraction of wet steam.
a) 0.01
b) 0.02
c) 0.021
d) 0.03

View Answer

Answer: c [Reason:] Specific enthalpies of saturated water (hl) and dry steam (hs) are 1219 kJ/kg and 2783 kJ/kg. Substituting these values in the equation “hws= xdhg+(1-xd)hl” gives the dryness fraction as 0.021.

7. What includes fixed cost?
a) cost of land, Cost of building, Cost of equipment, Cost of installation
b) interest
c) management cost
d) all of the mentioned

View Answer

Answer: d [Reason:] These are the parameters that cannot be neglected and come under the fixed cost.

8. Name the major isotope present in steam generated in a Boiling Water Reactor.
a) N-16
b) D-32
c) N-32
d) D-16

View Answer

Answer: a [Reason:] It is more economical and more efficient.

9. Efficiency of a power plant is more in summers or winters?
a) summers
b) winters
c) same in both
d) depends on variation

View Answer

Answer: b [Reason:] In summers the heat loss is more so efficiency is less.

10. What is the mechanical efficiency of turbine?
a) brake output / internal output
b) internal output / brake output
c) blade energy / energy supplied
d) none of the mentioned

View Answer

Answer: b