Analysis Of Steam Engine ( Power Plant Engineering ) MCQs – Mechanical Engineering MCQs
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Mechanical Engineering MCQs – Analysis Of Steam Engine ( Power Plant Engineering ) MCQs
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Carnotinization of Rankine Cycle
1. In the T-S diagram of a Rankine cycle, the abscissa represents?
a) total entropy of turbine steam
b) partial entropy of turbine steam
c) partial enthalpy of turbine steam
d) none of the mentioned
Answer: a
Explanation: The T-S diagram of a Rankine Cycle has total entropy of turbine steam in the abscissa & temperature on the ordinate.
2. After the expansion of throttle steam, why is some steam extracted?
a) so that the total amount of steam in the entire system remains same
b) so that the variation in temperature is constant
c) so that pressure variation is constant
d) so that the total entropy is reduced
Answer: d
Explanation: The expansion of throttle steam is mainly to reduce the total entropy & the heat given up by this steam is added to feed water, thereby heating it.
3. The heat given up by the expansion of throttle steam is utilised in?
a) maintaining the heat flow in the system
b) reducing temperature variation in the system
c) heating the feedwater
d) cooling feedwater
Answer: c
Explanation: The expansion of throttle steam is mainly to reduce the total entropy & the heat given up by this steam is added to feed water, thereby heating it.
4. “Regenerative feedwater heating by turbine extraction” is often termed as?
a) Electrophoresis of Rankine cycle
b) Sterlinisation of Rankine cycle
c) Carnotization of Rankine cycle
d) None of the mentioned
Answer: c
Explanation: In the T-S diagram, the area of the parallelogram representing the cycle output will be equal to the area of the rectangle representing the output of the Carnot cycle. That is why we often term regenerative feedwater heating by turbine extraction as carnotization of rankine cycle.
5. A regenerative feedwater heating cycle with an infinite number of feedwater heaters has efficiency equal to?
a) Brayton cycle
b) Carnot cycle
c) Diesel cycle
d) Otto cycle
Answer: b
Explanation: In the T-S diagram, the area of the parallelogram representing the cycle output will be equal to the area of the rectangle representing the output of the Carnot cycle. Thus, the efficiency of a regenerative feedwater heating cycle with an infinite number of feedwater heaters is equal to that of a carnot cycle.
6. In the T-S diagram, the process of heating from condenser to boiler saturation temperature when the number of turbine extraction stages are finite is?
a) Reversible
b) Irreversible
c) Adiabatic
d) None of the mentioned
Answer: b
Explanation: When the number of extraction stages are finite, the process is irreversible. On the contrary, when there are infinite extraction stages, the process becomes reversible.
7. For the process of heating from condenser to boiler saturation temperature to be reversible, the number of extraction stages involved in the entire cycle should be?
a) Zero
b) One
c) Infinite
d) Finite
Answer: c
Explanation: When the number of extraction stages are finite, the process is irreversible. On the contrary, when there are infinite extraction stages, the process becomes reversible.
8. Which of the processes immediately follows the expansion of throttle steam?
a) heat given up by the steam is added to feedwater
b) heating from condenser to boiler saturation temperature
c) carnotization of rankine cycle
d) none of the mentioned
Answer: a
Explanation: The expansion of throttle steam is mainly to reduce the total entropy & the heat given up by this steam is added to feed water, thereby heating it.
9. The output from boiler goes to?
a) Turbine
b) Condenser
c) Pump
d) Economiser
Answer: a
Explanation: The sequence of flow is
Boiler, Turbine, Condenser, Pump, Economiser.
10. The area of parallelogram in the T-S diagram representing the cycle output is equal to?
a) area of rectangle representing the output of the Carnot cycle
b) area of the triangle representing the output of the Carnot cycle
c) area of the square representing the output of the Carnot cycle
d) none of the mentioned
Answer: a
Explanation: From the T-S diagram the area of parallelogram representing the cycle output is equal to the area of rectangle representing the output of the Carnot cycle.
Optimum Degree of Regeneration
1. What is the value of “beta” if h represents the local enthalpy on the given expansion line at a given pressure & hf is the enthalpy of saturated water at that pressure?
a) h + hf
b) h x hf
c) h – hf
d) none of the mentioned
Answer: c
Explanation: The expression for the value of “beta” if h represents the local enthalpy on the given expansion line at a given pressure & hf is the enthalpy of saturated water at that pressure is given as,
Beta = h – hf.
2. The expression for temperature rise t in feedwater heater when a & b are the temperatures of boiler saturation & condenser respectively, is given by which of the following expression?
a) t = 0.5 (a x b)
b) t = 0.5 (a / b)
c) t = 0.5 (a + b)
d) t = 0.5 (a – b)
Answer: d
Explanation: The expression for temperature rise t in feedwater heater when a & b are the temperatures of boiler saturation & condenser respectively, is given by,
t = 0.5 (a – b).
3. What happens to the feedwater that enters the economiser?
a) Feedwater is heated to the saturation temperature at the boiler pressure
b) Feedwater is heated to the boiler temperature at the saturation pressure
c) Feedwater is cooled to the saturation temperature
d) Feedwater is cooled at the boiler pressure
Answer: a
Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. Naturally, this is what happens to the feedwater in the Economiser.
4. The economiser can also be assumed as?
a) Feedwater cooler
b) Feedwater heater
c) Economiser has nothing to do with Feedwater
d) None of the mentioned
Answer: b
Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. Hence, it is assumed as ‘feedwater heater’.
5. The feedwater in the Economiser _________
a) is heated by bled turbine steam
b) is cooled by bled turbine steam
c) is heated by outgoing flue gases
d) is cooled by outgoing flue gases
Answer: c
Explanation: The function of an economiser is to heat the feedwater to the saturation temperature at the boiler temperature. This heating of feedwater occurs by the heat given to the feedwater by outgoing flue gases.
6. The temperature rise from condenser to boiler saturation is divided __________ among the feedwater heaters for maximum gain in efficiency.
a) unequally
b) partially
c) equally
d) remains undivided
Answer: c
Explanation: The total enthalpy rise or the temperature rise from condenser to boiler saturation is divided equally among the feedwater heaters for maximum gain in the efficiency.
7. What is the expression for enthalpy of each heater hper heater if a represents the enthalpy of heated feedwater from the economiser and b represents the enthalpy at condenser & n represents the number of heaters?
a) hper heater = (a-b)/ (n + 1)
b) hper heater = (a-b) x (n – 1)
c) hper heater = (a-b) + (n – 1)
d) hper heater = (a-b) – (n + 1)
Answer: a
Explanation: the expression for enthalpy of each heater h if a represents the enthalpy of heated feedwater from the economiser and b represents the enthalpy at condenser & n represents the number of heaters is given by,
hper heater = (a-b)/ (n + 1).
8. If n denotes the number of heater, tOA denotes the overall temperature difference & Tfw denotes the total temperature rise of feedwater. The expression for Tfw is?
a) (n/(n+1)) x tOA
b) (n/(n-1)) x tOA
c) (n/(n+1)) / tOA
d) (n/(n+1)) – tOA
Answer: a
Explanation: If n denotes the number of heater, tOA denotes the overall temperature difference & Tfw denotes the total temperature rise of feedwater. The expression for Tfw is given by the following relation,
Tfw = (n/(n+1)) x tOA.
9. The expression for the overall temperature difference TOA is given by?
a) tOA = boiler saturation temperature – condenser temperature
b) tOA = boiler saturation temperature + condenser temperature
c) tOA = boiler saturation temperature x condenser temperature
d) tOA = boiler saturation temperature / condenser temperature
Answer: a
Explanation: The expression for the overall temperature difference t is given by,
tOA = boiler saturation temperature – condenser temperature.
10. Efficiency gain follow the law of ____________
a) diminishing forward motion
b) increasing return
c) decreasing return
d) none of the mentioned
Answer: c
Explanation: The gain in cycle efficiency is proportional to the gain in feedwater temperature, the efficiency gain thereby follows the law of diminishing return with the increase in the number of heaters.
11. The number of heaters for a plant is fixed by?
a) Mass Balance
b) Energy balance
c) Heat balance
d) None of the mentioned
Answer: b
Explanation: The number of heaters for a plant is fixed by Energy Balance of the whole plant when it is found that cost of adding another heater does not justify the saving in heat supply or marginal increase in cycle efficiency.
12. The effect on the degree of regeneration due to an increase in feedwater temperature is?
a) degree of regeneration increases
b) degree of regeneration decreases
c) degree of regeneration remain same
d) degree of regeneration is optimised
Answer: d
Explanation: An increase in feedwater temperature reduces the heat absorption from the outgoing flue gases in the economiser & may cause a reduction in boiler efficiency. The number of heaters & the degree of regeneration thus get optimised.
13. The expression for efficiency when a & b are two constants corresponding to alpha & beta and c corresponds to gamma, is?
a) Efficiency = 1 – ((b2))/((b + c)(a + b – c)))
b) Efficiency = 1 + ((b2))/((b + c)(a + b – c)))
c) Efficiency = ((b2))/((b + c)(a + b – c)))
d) Efficiency = 1 / ((b2))/((b + c)(a + b – c)))
Answer: a
Explanation: The expression for efficiency when a & b are two constants corresponding to alpha & beta and c corresponds to gamma, is given as,
Efficiency = 1 – ((b2))/((b + c)(a + b – c))).
14. What is the relation between a & c if a & c correspond to alpha & gamma respectively, for maximum efficiency of a cycle?
a) a = 3c
b) c = 2a
c) c = (a/3)
d) a = 2c
Answer: d
Explanation: The relation between a & c if a & c correspond to alpha & gamma respectively, for maximum efficiency of a cycle is given by,
c = (a/2).
15. The expression for efficiency gain due to regeneration if a, b, n correspond to alpha, beta, cycle efficiency respectively, is?
a) n = ((a x a x b)/((a + b)(a + 2b)2))
b) n = ((a x a x b)/((a – b)(a + 2b)2))
c) n = ((a x a x b)/((a + b)(a + b)2))
d) n = ((a x a x b)/((a + b)(a + 2b)3))
Answer: a
Explanation: The expression for efficiency gain due to regeneration if a, b, n correspond to alpha, beta, cycle efficiency respectively is given by,
n = ((a x a x b)/(a + b)(a + 2b)2)).
Supercritical Pressure Cycle and Layout of a Stem Power Plant
1. Steam is generated in a _____________ boiler at a pressure above the critical point.
a) simple
b) once through
c) superficial
d) thrice through
Answer: b
Explanation: The steam generation in a supercritical pressure cycle is in a once through boiler when the steam is heated at a pressure above the critical point.
2. Apart from feedheating, what should a plant have to obtain a gain in thermal efficiency?
a) Lubrication
b) Differential heating
c) Reheating cycles
d) Regenerative cycles
Answer: c
Explanation: To obtain a gain in thermal cycle efficiency, apart from the feedheating, there should be multiple number of reheats.
3. The increment in thermal efficiency compared to the corresponding Subcritical cycle is gained at the expanse of?
a) compactness of the plant
b) simplicity of the plant
c) complexity of the plant
d) expanse of the plant
Answer: c
Explanation: The increment in thermal efficiency compared to the corresponding Subcritical cycle is gained at the expanse of complexity of the plant. Naturally, more the complexity, more this increment.
4. Which of the following needs to be incorporated to prevent the low pressure turbine exhaust wetness from being excessive?
a) Double regeneration
b) Double carnotization
c) Double reheat
d) Double cooling
Answer: c
Explanation: Incorporating double reheat is one way to prevent the low pressure turbine exhaust wetness from being excessive.
5. What is the critical point of steam generation in a “once through” boiler?
a) 221.5 bar
b) 221.4 bar
c) 221.3 bar
d) 221.2 bar
Answer: d
Explanation: Steam generation in a “once through” boiler is at the critical point of 221.2 bar.
6. In a typical layout of a 215MW reheat power plant, the feed in the boiler is at?
a) 280 degree Centigrade
b) 230 degree Centigrade
c) 238 degree Centigrade
d) 250 degree Centigrade
Answer: c
Explanation: In a typical layout of a 215MW reheat power plant, the feed in the boiler is at 238 degree Centigrade.
7. The input to the deaerator is from a __________ pressure feedwater heater.
a) high
b) low
c) medium
d) none of the mentioned
Answer: b
Explanation: The deaerator input is at low pressure feedwater heater and so the working of the deaerator comes into play.
8. The input to the low pressure feedwater heater is from?
a) Drain heater
b) Drain cooler
c) Drain pipe
d) None of the mentioned
Answer: b
Explanation: The input to the low pressure feedwater heater comes from the drain cooler which goes to the deaerator.
Steam Power Plant Appraisal
1. The thermal efficiency of a Watt’s Beam Engine is about?
a) 50%
b) 100%
c) 5%
d) 2%
Answer: d
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the efficiency of Watt’s Beam Engine is about 2%.
2. The thermal efficiency of a 1 MW locomotive steam engine is about?
a) 2%
b) 3%
c) 6%
d) 7%
Answer: d
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the efficiency of 1 MW locomotive steam engine is about 7%.
3. The number of feedwater heaters required in a Watt’s Beam Engine is?
a) 0
b) 4
c) 6
d) 8
Answer: a
Explanation: A Watt’s Beam Engine does not employ any feedwater heaters & hence the number of feedwater heaters in a Watt’s Beam Engine is ZERO.
4. Among 1 MW, 2 MW, 30 MW & 660 MW locomotive steam engines, the highest efficiency is?
a) 1 MW
b) 2 MW
c) 30 MW
d) 660 MW
Answer: d
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the efficiency of 1 MW locomotive steam engine is about 7%, 2 MW locomotive steam engine is about 20%, 30 MW locomotive steam engine is about 35%, 660 MW locomotive steam engine is about 44%.
5. The initial pressure of a Watt’s Beam Engine is about?
a) 1 bar
b) 2 bar
c) 3 bar
d) 4 bar
Answer: b
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the pressure of a Watt’s Beam Engine is about 2 bar.
6. What is the exhaust condition of a Watt’s Beam Engine?
a) near saturation
b) dry
c) wet
d) 0.9 dry
Answer: c
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the exhaust condition of a Watt’s Beam Engine is wet.
7. The number of feedwater heaters required for a 660 MW locomotive steam engine is?
a) 4
b) 0
c) 7
d) 8
Answer: c
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the number of feedwater heaters required by a 660 MW locomotive steam engine are 7.
8. Among 1 MW, 2 MW, 30 MW & 660 MW locomotive steam engines, the highest initial pressure is?
a) 1 MW
b) 2 MW
c) 30 MW
d) 660 MW
Answer: d
Explanation: From the performance table consisting of performance data of various steam power plants(Aschner), the initial pressure of 1 MW locomotive steam engine is about 15 bar, 2 MW locomotive steam engine is about 15 bar, 30 MW locomotive steam engine is about 40 bar, 660 MW locomotive steam engine is about 160 bar.
9. Among 1 MW, 2 MW, 30 MW & 660 MW locomotive steam engines, the highest initial temperature is?
a) 1 MW
b) 2 MW
c) 30 MW
d) 660 MW
Answer: d
Explanation: From the performance table consisting of performance data of various steam power plants (Aschner), the initial temperature of 1 MW locomotive steam engine is about 300 degree Celsius bar, 2 MW locomotive steam engine is about 250 degree Celsius, 30 MW locomotive steam engine is about 450 degree Celsius, 660 MW locomotive steam engine is about 540 degree Celsius.
10. Common size unit of a Steam Power Plant is?
a) 30 MW(e)
b) 300 MW(e)
c) 500 MW(e)
d) 150 MW(e)
Answer: c
Explanation: The most common size steam power plant is of 500 MW(e). Further large size plants have been built, but aren’t found in common usage.
Deaerator – 1
1. Deaerator is an ___________
a) closed heater
b) open heater
c) surface heater
d) none of the mentioned
Answer: b
Explanation: One of the feedwater heater is a contact type open heater, known as deaerator.
2. What is the purpose of deaerator?
a) to remove the dissolved oxygen and carbon dioxide
b) to remove the dissolved nitrogen
c) to remove the dissolved impurities
d) to supply more oxygen to feedwater
Answer: a
Explanation: Purpose of deaerator is to remove the dissolved oxygen and carbon dioxide in water which makes water corrosive.
3. What do you mean by vent condenser?
a) a condensing unit
b) a temperature measuring instrument
c) a heat exchanger
d) dissolves oxygen
Answer: c
Explanation: Feedwater is passed through a heat exchanger commonly called as vent condenser.
4. How dissolved oxygen and carbon dioxides are removed?
a) by allowing it to fall from height
b) by series of chemical reactions
c) by condensing feedwater
d) by heating feedwater to saturation temperature
Answer: d
Explanation: The solubility of these gases decreases with an increase in temperature.
5. What chemicals are added for residual dissolved oxygen and carbon dioxide?
a) sodium sulphite
b) hydrazine
c) alum
d) all of the mentioned
Answer: d
Explanation: Na2SO3 and N2H4 are used to remove residual gasses.
6. Why deaerator is installed at a certain height from the pump?
a) to provide a net positive suction head
b) to maintain less pressure
c) to avoid leakage
d) to maintain pressure
Answer: a
Explanation: Deaerator is installed at a certain height from the pump so as to maintain a optimum pressure before suction.
7. Why deaerator is not used in water cooled and moderated nuclear power plant?
a) radioactivity
b) not economical
c) not safe
d) not mechanically possible
Answer: a
Explanation: deaerator is not used in water cooled and moderated nuclear power plant because of the concern regarding radioactivity release with deaeration.
8. What is the location of high pressure heaters?
a) after the deaerator
b) before the deaerator
c) middle of deaerator
d) depends on pressure conditions
Answer: b
Explanation: The feedwater heaters before the deaerator are often called high pressure heaters(h.p.).
9. What is the location of low pressure heaters?
a) after the deaerator
b) before the deaerator
c) middle of deaerator
d) depends on pressure conditions
Answer: a
Explanation: The feedwater heaters after the deaerator are often called low pressure heaters(l.p.).
10. Steam used to heat water comes from?
a) boiler
b) turbine
c) condenser
d) external power source
Answer: b
Explanation: Steam from turbine is at high pressure and temperature.
Deaerator – 2
1. Which of the following type heater is known as deaerator?
a) Contact-type open heater
b) Contact-type closed heater
c) Closed heater
d) None of the mentioned
Answer: a
Explanation: A deaerator is a closed-type open feedwater heater while all the other heaters are closed heaters.
2. What is the solubility of dissolved gases at boiling or saturation temperature?
a) Positive
b) Negative
c) Zero
d) None of the mentioned
Answer: c
Explanation: The solubility of dissolved gases in water decreases with an increase in pressure and becomes zero at boiling or saturation temperature.
3. In the deaerator, the feedwater is heated to the saturation temperature by the steam extracted from?
a) compressor
b) turbine
c) pump
d) none of the mentioned
Answer: b
Explanation: The steam extracted from the turbine is used to heat the feedwater to the saturation temperature.
4. The heat exchanger after passing through which, the feedwater is sprayed from the top is called?
a) Vent condenser
b) Vent evaporator
c) Vent economiser
d) Vent heater
Answer: a
Explanation: Feedwater after passing through a heat exchanger, is sprayed from the top & bled steam from the turbine is fed from the bottom.
5. What kind of steam comes through the other side of the feedwater spray?
a) pure steam
b) bled steam
c) saturated steam
d) superheated steam
Answer: b
Explanation: Feedwater after passing through a heat exchanger, is sprayed from the top & bled steam from the turbine is fed from the bottom.
6. The chemical injected into the feedwater at the suction of the boiler feed pump is?
a) Sodium Sulphide
b) Sodium Sulphate
c) Sodium Sulphite
d) Sodium Hydride
Answer: c
Explanation: To minimise the effect of the residual dissolved oxygen & carbon dioxide gases in water, Sodium Sulphite & Hydrazine are injected in suitable calculated doses into the feedwater at the suction of the boiler feed pump.
7. Why is Sodium Sulphite added into the feedwater at the suction of the boiler feed pump?
a) to maximise the effect of dissolved gases
b) to minimise the effect of dissolved gases
c) to increase feedwater concentration
d) none of the mentioned
Answer: b
Explanation: To minimise the effect of the residual dissolved oxygen & carbon dioxide gases in water, Sodium Sulphite & Hydrazine are injected in suitable calculated doses into the feedwater at the suction of the boiler feed pump.
8. Name another chemical apart from Sodium Sulphite which is into the feedwater at the suction of the boiler feed pump?
a) Calcium peroxide
b) Hydroxide
c) Hydrazine
d) Oxymes
Answer: c
Explanation: To minimise the effect of the residual dissolved oxygen & carbon dioxide gases in water, Sodium Sulphite & Hydrazine are injected in suitable calculated doses into the feedwater at the suction of the boiler feed pump.
9. Where is the deaerator placed in the feedwater system?
a) in the beginning
b) in the middle
c) at the end
d) there is no deaerator in the feedwater system
Answer: b
Explanation: The deaerator is usually placed in the middle of the feedwater system so that the total pressure difference between the condenser & the boiler is shared equally between condensate pump & boiler feed pump.
10. Why is the deaerator placement in the feedwater system so important?
a) to maximise pressure difference between the condenser & the boiler
b) to minimise pressure difference between the condenser & the boiler
c) to make the pressure difference between the condenser & the boiler Zero
d) none of the mentioned
Answer: c
Explanation: The deaerator is usually placed in the middle of the feedwater system so that the total pressure difference between the condenser & the boiler is shared equally between condensate pump & boiler feed pump.
11. Which gases are vented out of the deaerator?
a) Oxygen only
b) Carbon dioxide only
c) Oxygen & Carbon dioxide
d) None of the mentioned
Answer: c
Explanation: The exhaust of the feedwater deaerator contains Oxygen & Carbon dioxide both.
12. Net positive suction head(NPSH) is provided because?
a) to prevent vapour lock
b) to prevent cavitation
c) to prevent friction
d) none of the mentioned
Answer: b
Explanation: In order to prevent the cavitation arising, a net positive suction head is provided for the pump. The deaerator is placed at a sufficient height from the basement.
13. The output of the boiler heat pump is to?
a) the high pressure heater
b) the low pressure heater
c) simultaneously to the low & high pressure heaters
d) none of the mentioned
Answer: a
Explanation: The Boiler feed pump give an output which goes to the high pressure heater.
14. Why is the deaerator not employed in water cooled & moderated nuclear power plant?
a) due to radioactivity release in degeneration
b) due to emissivity of degeneration
c) due to reheating
d) due to regeneration
Answer: a
Explanation: The deaerator is not employed in water cooled & moderated nuclear power plant because of the radioactivity released in degeneration.
15. Which among the following goes to the Vent Condenser along with Oxygen & Carbon dioxide?
a) Sodium sulphite
b) Carbon monoxide
c) Water vapour
d) None of the mentioned
Answer: c
Explanation: The gases Oxygen, Carbon dioxide & Water vapour are subjected to the vent condenser wherein the moisture gets absorbed & so the exhaust gases vented out are Oxygen & Carbon dioxide.
Efficiencies in a Steam Power Plant – 1
1. What percentage of fuel energy is actually converted to electrical energy?
a) 50%
b) 40%
c) 34%
d) 25%
Answer: c
Explanation: 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
Answer: a
Explanation: 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
Answer: b
Explanation: 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
Answer: a
Explanation: 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
Answer: d
Explanation: 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
Answer: c
Explanation: 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
Answer: d
Explanation: 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
Answer: a
Explanation: 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
Answer: b
Explanation: 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
Answer: b
Explanation: None.
Efficiencies in a Steam Power Plant – 2
1. The steam power plant is a bulk energy converter where fuel energy is converted to?
a) heat energy
b) electrical energy
c) chemical energy
d) none of the mentioned
Answer: b
Explanation: Energy conversion in a steam power plant is as below
Fuel energy to Electricity.
2. Rate of energy released by the combustion of the fuel is given by?
a) Fuel burning rate x Calorific Value of the fuel
b) Fuel burning rate / Calorific Value of the fuel
c) Fuel burning rate + Calorific Value of the fuel
d) Fuel burning rate – Calorific Value of the fuel
Answer: a
Explanation: Rate of energy released by the combustion of the fuel is given by,
Fuel burning rate x Calorific Value of the fuel.
3. The overall efficiency noverall of a steam power plant is given by?
a) noverall = (power available at the generator terminals / (Fuel burning rate x Calorific Value of the fuel))
b) noverall = (power available at the generator terminals + (Fuel burning rate x Calorific Value of the fuel))
c) noverall = (power available at the generator terminals – (Fuel burning rate x Calorific Value of the fuel))
d) none of the mentioned
Answer: a
Explanation: The overall efficiency noverall of a steam power plant is given by,
noverall = (power available at the generator terminals / (Fuel burning rate x Calorific Value of the fuel)).
4. Which of the following shows the correct relation? (nboiler denotes efficiency of a boiler)
a) nboiler = (rate of energy absorption by water to form steam / rate of energy released by the combustion of fuel)
b) nboiler = (rate of energy absorption by water to form steam + rate of energy released by the combustion of fuel)
c) nboiler = (rate of energy absorption by water to form steam – rate of energy released by the combustion of fuel)
d) nboiler = (rate of energy absorption by water to form steam x rate of energy released by the combustion of fuel)
Answer: a
Explanation: The efficiency of a boiler is given by the following expression,
nboiler = (rate of energy absorption by water to form steam / rate of energy released by the combustion of fuel).
5. The mechanical efficiency of a turbine is given by? (ntm denotes the mechanical efficiency)
a) ntm = (brake output of the turbine x internal output of the turbine)
b) ntm = (internal output of the turbine / break output of the turbine)
c) ntm = (brake output of the turbine / internal output of the turbine)
d) ntm = (brake output of the turbine – internal output of the turbine)
Answer: c
Explanation: The expression for the turbine mechanical efficiency is given by,
ntm = (brake output of the turbine / internal output of the turbine).
6. If Q1 represents the rate of heat addition to the cycle and Wnet represents net cycle work output, the expression for net cycle heat rate is?
a) Q1 + Wnet
b) Q1 / Wnet
c) Q1 / (1/Wnet)
d) Q1 x Wnet
Answer: b
Explanation: The expression for the net cycle heat rate is given by,
Net cycle heat rate(HR) = Q1 / Wnet.
7. The generator efficiency n of the electric alternator is?
a) n = (electrical output at generator terminals / Brake output of the turbine)
b) n = (electrical output at generator terminals x Brake output of the turbine)
c) n = (electrical output at generator terminals / (1/ Brake output of the turbine))
d) none of the mentioned
Answer: a
Explanation: The generator efficiency of the electric alternator is defined as the ratio of electrical output at generator terminals to the brake output of the turbine.
8. Which of these is not an auxiliary equipment in a power plant?
a) Fans
b) Crushers
c) Galvanisers
d) Conveyors
Answer: c
Explanation: The auxiliary equipment in a power plant are those equipment which are driven by the electricity taken from the generated power of the plant.
9. Which of these shows the formula for the efficiencies of the auxiliaries n1?
a) n1 = (net power transmitted by the generator x gross power produced by the plant)
b) n1 = (net power transmitted by the generator / gross power input to the plant)
c) n1 = (net power transmitted by the generator / gross power produced by the plant)
d) n1 = (net power transmitted by the generator / gross power transferred by the plant)
Answer: c
Explanation: The auxiliary equipment or auxiliaries in a power plant are those equipment which are driven by the electricity taken from the generated power of the plant. Their efficiency is given by,
n1 = (net power transmitted by the generator / gross power produced by the plant).
10. What approximate percentage of energy in the fuel is converted to electricity?
a) 55%
b) 45%
c) 35%
d) 25%
Answer: c
Explanation: Only 34% of the energy stored in the fuel is converted to electricity & 66% is lost. The maximum loss of energy takes place in the condenser where heat is rejected to cooling water.
11. Heat rejection in a condenser is to?
a) cooled water
b) coolant
c) cooling water
d) none of the mentioned
Answer: c
Explanation: The maximum loss of energy takes place in the condenser where heat is rejected to cooling water. This is the loss due to heat to work energy conversion in the cycle or the loss due to second law.
12. Heat rate indicates?
a) heat added per unit volume
b) heat added per unit of work produced
c) heat added per unit of mass stored
d) heat added per unit area
Answer: b
Explanation: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.
13. Which of the following parameters affects the fuel economy?
a) heat constant
b) specific heat
c) heat rate
d) heat consumption
Answer: c
Explanation: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.
14. Gross cycle heat rate is equal to?
a) (rate of heat addition / turbine output)
b) (rate of heat rejection / turbine input)
c) (heat rejected / turbine output)
d) none of the mentioned
Answer: a
Explanation: The gross cycle heat rate is given by,
Gross cycle heat rate = (rate of heat addition / turbine output).
15. The relation between heat rate & efficiency is?
a) both are directly proportional
b) both are inversely proportional
c) they are independent of each other
d) heat rate is also called efficiency
Answer: b
Explanation: The parameter which readily affects the fuel economy is the heat rate which is inversely proportional to the efficiency, and hence the lower its value the better. It broadly indicates the heat added per unit of work produced.
Cogeneration of Power & Process Heat
1. Having two separate units for process heat and power is?
a) useful
b) useless
c) pollution reducing
d) none of the mentioned
Answer: b
Explanation: Having two separate units for process heat & power is wasteful, for of the total heat supplied to the steam generator for power purposes, a greater part will normally be carried away by the cooling water in the condenser.
2. A plant producing both, electrical power & process heat simultaneously is?
a) Cogenital plant
b) Cogenerial plant
c) Cogeneration plant
d) Conglomerate plant
Answer: c
Explanation: Cogeneration plant is defined as a plant which produces electrical power and processes heat simultaneously.
3. In a back pressure turbine _____________
a) pressure at the exhaust from the turbine is the saturation pressure corresponding to the temperature desired in the process
b) pressure at the entrance of the turbine is the saturation pressure corresponding to the temperature desired in the process
c) pressure at the exhaust from the turbine is the saturation pressure corresponding to the pressure desired in the process
d) none of the mentioned
Answer: a
Explanation: The name back pressure turbine is given because pressure at the exhaust from the turbine is the saturation pressure corresponding to the temperature desired in the process.
4. In a by-product power cycle?
a) the power is produced initially
b) power production is in the middle stages of the cycle
c) power production is after the cycle has ended
d) none of the mentioned
Answer: c
Explanation: When the process steam is the basic need, and the power is produced incidentally as a by-product, the cycle is often called as the by-product power cycle.
5. Back pressure turbines are usually _________________ with respect to their power output.
a) large
b) small
c) very large
d) very small
Answer: b
Explanation: Back pressure turbines are usually small with respect to their power output because they have no great volume of exhaust to cope with, the density being high.
6. In terms of cost per MW compared to condensing sets of the same power, the back pressure turbines are?
a) more expensive
b) cheaper
c) costly
d) none of the mentioned
Answer: b
Explanation: Back pressure turbines are usually small with respect to their power output because they have no great volume of exhaust to cope with, the density being high. They are usually single cylinder and hence, usually cheaper in terms of cost per MW.
7. Which of these is not an application of back pressure turbine?
a) desalination of sea water
b) filtration of water
c) process industries
d) petrochemical installations
Answer: b
Explanation: The applications of back pressure turbine are desalination of sea water, process industries, petrochemical installations, district heating and also for driving compressors and feed pumps.
8. Back pressure turbine is placed between ____________
a) Turbine & Pump
b) Boiler & Pump
c) Turbine & Heat Exchanger
d) Boiler & Turbine
Answer: d
Explanation: In a cogeneration plant, the back pressure turbine is placed between the boiler & turbine.
9. Which of the following is a good medium for constant temperature heating?
a) Water
b) Steam
c) Coolant
d) Diesel
Answer: b
Explanation: For constant temperature heating (or drying), steam is a very good medium since isothermal condition can be maintained by allowing saturated steam to condense at that temperature and utilising the latent heat released for heating purposes.
10. The cogeneration plant efficiency nCO if WT, Qi, QH represents turbine work, heat input, heat output respectively is given by?
a) nCO = (WT + Qi) / QH
b) nCO = (WT – Qi) / QH
c) nCO = (WT + QH) / Qi
d) nCO = (WT + QH) / Qi
Answer: d
Explanation: The cogeneration plant efficiency nCO if WT, Qi, QH represents turbine work, heat input, heat output respectively is,
nCO = (WT + QH) / Qi.
11. The electricity fraction of total energy output if W1 and Q1 represents the turbine work and heat output is given by?
a) W1 / (W1 + Q1)
b) W1 / (W1 – Q1)
c) W1 / (W1Q1)
d) W1 / Q1
Answer: a
Explanation: The electricity fraction of total energy output if W1 and Q1 represents the turbine work and heat output is,
W1 / (W1 + Q1).
12. If e is the electricity fraction of the total energy output, m is the electric plant efficiency and n is the steam generator efficiency; the heat added per unit total energy output is given by?
a) (1 / m) + ((1 – e) / n)
b) (1 / n) + ((1 – e) / m)
c) (1 / m) + ((1 + e) / n)
d) (1 / n) + ((1 – e) / m)
Answer: a
Explanation: If e is the electricity fraction of the total energy output, m is the electric plant efficiency and n is the steam generator efficiency; the heat added per unit total energy output is given by?
(1 / m) + ((1 – e) / n).
13. Pass-out turbines are used in which of these cases?
a) relatively high back pressure
b) small heating requirement
c) only relatively low back pressure
d) both relatively high back pressure and small heating requirement
Answer: d
Explanation: Pass-out turbines are used in cases of relatively high back pressure and small heating requirements. They are used in cases where a certain quantity of steam is continuously extracted from the turbine at an intermediate stage for heating purposes at the desired temperature and pressure.
14. Which of these is not considered economical for cogeneration?
a) a high fraction of electric to total energy
b) a low fraction of electric to total energy
c) a low fraction of total energy to electric energy
d) none of the mentioned
Answer: b
Explanation: A low fraction of electric to total energy is considered as an economical condition for cogeneration. Cogeneration plant is defined as a plant which produces electrical power and processes heat simultaneously.