1. Why Rankine cycle is modified?The work obtained at the end of the expansion is very less. The work is too inadequate toovercome the friction. Therefore the adiabatic expansion is terminated at the point before the endof the expansion in the turbine and pressure decreases suddenly, while the volume remainsconstant.2. Name the various vapour power cycle.

Carnot cycle and Rankine cycle.

3. Define efficiency ratio.The ratio of actual cycle efficiency to that of the ideal cycle efficiency is termed as efficiencyratio.4. Define overall efficiency.It is the ratio of the mechanical work to the energy supplied in the fuel. It is also defined as theproduct of combustion efficiency and the cycle efficiency.5. Define specific steam consumption of an ideal Rankine cycle.It is defined as the mass flow of steam required per unit power output.6. Name the different components in steam power plant working on Rankine cycle.

Boiler, Turbine, Cooling Tower or Condenser and Pump.7. What are the effects of condenser pressure on the Rankine Cycle?By lowering the condenser pressure, we can increase the cycle efficiency. The maindisadvantage is lowering the back pressure in release the wetness of steam. Isentropiccompression of a very wet vapour is very difficult.8. Mention the improvements made to increase the ideal efficiency of Rankine cycle.1. Lowering the condenser pressure.2. Superheated steam is supplied to the turbine.3. Increasing the boiler pressure to certain limit.4. Implementing reheat and regeneration in the cycle.9. Why reheat cycle is not used for low boiler pressure?At the low reheat pressure the heat cycle efficiency may be less than the Rankine cycleefficiency.Since the average temperature during heating will then be low.10. What are the disadvantages of reheating?Reheating increases the condenser capacity due to increased dryness fraction, increases the costof the plant due to the reheats and its very long connections.11. What are the advantages of reheat cycle?

1. It increases the turbine work.2. It increases the heat supply.3. It increases the efficiency of the plant.4. It reduces the wear on the blade because of low moisture content in LP state of the

turbine.12. Define latent heat of evaporation or Enthalpy of evaporation.The amount of heat added during heating of water up to dry steam from boiling point is knownas Latent heat of evaporation or enthalpy of evaporation.13. Explain the term super heated steam and super heating.The dry steam is further heated its temperature raises, this process is called as superheating andthe steam obtained is known as superheated steam.

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14. Explain heat of super heat or super heat enthalpy.The heat added to dry steam at 100oC to convert it into super heated steam at the temperatureTsup is called as heat of superheat or super heat enthalpy.15. Explain the term critical point, critical temperature and critical pressure.In the T-S diagram the region left of the waterline, the water exists as liquid. In right of the drysteam line, the water exists as a super heated steam. In between water and dry steam line thewater exists as a wet steam. At a particular point, the water is directly converted into dry steamwithout formation of wet steam. The point is called critical point. The critical temperature is thetemperature above which a substance cannot exist as a liquid; the critical temperature of water is374.15oC. The corresponding pressure is called critical pressure.16. Define dryness fraction (or) what is the quality of steam?It is defined as the ratio of mass of the dry steam to the mass of the total steam.17. Define enthalpy of steam.It is the sum of heat added to water from freezing point to saturation temperature and the heatabsorbed during evaporation.18. How do you determine the state of steam?If V>vg then super-heated steam, V= vg then dry steam and V< vg then wet steam.19. Define triple point.The triple point is merely the point of intersection of sublimation and vapourisation curves.20. Define heat of vapourisation.The amount of heat required to convert the liquid water completely into vapour under thiscondition is called the heat of vapourisation.21. Explain the terms, Degree of super heat, degree of sub-cooling.The difference between the temperature of the superheated vapour and the saturation temperatureat the same pressure. The temperature between the saturation temperature and the temperature inthe sub cooled region of liquid.22. What is the purpose of reheating?The purpose of reheating is to increase the dryness fraction of the steam passing out of the laterstages of the turbine.23. What are the processes that constitute a Rankine cycle?Process 1–2: Isentropic expansion of the working fluid through the turbine from saturated vaporat state 1 to the condenser pressure.Process 2–3: Heat transfer from the working fluid as it flows at constant pressure through thecondenser with saturated liquid at state 3.Process 3–4: Isentropic compression in the pump to state 4 in the compressed liquid region.Process 4–1: Heat transfer to the working fluid as it flows at constant pressure through the boilerto complete the cycle.

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1. A vessel of volume 0.04m3 contains a mixture of saturated water and steam at atemperature of 2500 C. The mass of the liquid present is 9 kg. Find the pressure, mass,specific volume, enthalpy, entropy and internal energy. (8)

(May/June 2003, Nov/Dec 2012)2. A rigid tank of 0.03m3 capacity contains wet vapour at 80 kPa. If the wet vapour mass

is 12kg, calculate the heat added and the quality of the mixture when the pressureinside the tank reaches 7 Mpa. (Nov/ Dec 2005)

3. 3 kg of steam at 18bar occupy a volume of 0.2550m3. During a constant volumeprocess, the heat rejected is 1320kJ. Determine final internal energy and final initialdryness and work done. (May/June 2008)

4. Steam initially at 0.3Mpa, 2500C is cooled at constant volume. At what temperaturewill the steam become saturated vapour? What is the quality at 800C.Also find what isthe heat transferred per kg of steam in cooling from 2500 C to 800C. (12)

(Nov / Dec 2013)5. Ten kg of water of 45oC is heated at a constant pressure of 10 bars until it becomes

superheated vapour at 3000C. Find the changes in volume, enthalpy, internal energyand entropy. (May / June 2005 )

6. 2 kg of water at 2000C are contained in a 20m3 vessel. Determine the pressure,enthalpy, mass and volume of vapor within the vessel. (8)

(May / June 2007)7. Steam at 30 bar and 3500 C is expanded in a non flow isothermal process to a pressure

of 1 bar. The temperature and pressure of the surroundings are 250C and 100 kParespectively. Determine the maximum work that can be obtained from this process perkg of steam. Also find the maximum useful work. (10)

(May/June 2013)8. 1 kg of steam initially dry saturated at 1.1 MPa expands in a cylinder following the

law pv1.13= C. The pressure at the end of expansion is 0.1MPa. Determine: (i) Thefinal volume (ii) final dryness fraction (iii) work done (iv) The change in internalenergy (v) the heat transferred. (16)

(Nov/Dec 2006)9. Steam at a pressure of 15bar and 2500C expands according to the law pV1.25=C to a

pressure of 1.5 bar. Evaluate the final conditions, work done, heat transfer and changein entropy. The mass of the system is 0.8kg. (Nov/Dec 2008)

10. In steam generator compressed water at 10 MPa, 300C enters a 30 mm diameter tubeat the rate of 3 litres /sec. Steam at 9 MPa and 4000C exit the tube. Find the rate ofheat transfer. (8)

(Nov/Dec 2003, May/June 2012)

11. Steam at 0.8 MPa, 2500C and flowing at the rate of 1 kg/s passes into a pipe carryingwet steam at 0.8 MPa, 0.95 dry. After adiabatic mixing the flow rate is 2.3 kg/s.Determine the properties of the steam after mixing. (Nov/Dec 2004)

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12. A vessel having a capacity of 0.05 m3 contains a mixture of saturated water andsaturated steam at a temperature of 2450C. The mass of the liquid present is 10 kg.find the following

(i) The pressure,(ii) The mass,(iii) The specific volume(iv) The specific enthalpy,(v) The specific entropy, and(vi) The specific internal energy. (16)

(May/June 2014)13. Steam flows steadily through a turbine with a mass flow rate of 3 kg/sec. the steam is

at 70 bar and 5000C while entering the turbine and at 0.2 bar on leaving the turbine.The expansion process may be considered as isentropic. Determine the turbine outputpower. (May/June 2004)

14. Steam expands in a nozzle from 1 MPa, 2500C to 10 kPa, the flow rate being 1 kg/sec.determine the velocity of steam at the exit of the nozzle and the exit area of thenozzle. The steam velocity at the inlet to the nozzle may be ignored.

(May/June 2004)15. Two streams of steam, one at 2 MPa, 3000C and the other at 2 MPa, 4000C, mix in a

steady flow adiabatic process. The rates of flow of the two streams are 3 kg/min and 2kg/min respectively. Evaluate the final temperature of the emerging steam, if there isno pressure drop due to the mixing process. What would be the rate of increase in theentropy of the universe? This steam with negligible velocity now expandsadiabatically in a nozzle to a pressure of 1 kPa. Determine the exit velocity of thestream and exit area of the nozzle. (16)

(Nov/Dec 2011)16. A 0.5 m3 vessel contains 10 kg refrigerant 134a at -20°C. Determine the pressure, the

total internal energy and the volume occupied by the liquid phase. (6)(Nov/Dec 2010)

17. A rigid tank with a volume of 2.5 m3 contains 15 kg of saturated liquid vapourmixture of water at 75°C. Now the water is slowly heated. Determine the temperatureat which the liquid in the tank is completely vaporized. Also, show the processes onT-v diagram with respect to saturation lines. (10)

(Nov/Dec 2010)18. Steam flows through a small turbine at the rate of 5000 kg/h entering at 15 bar, 3000C

and leaving at 0.1bar with 4% moisture. The steam enters at 80m/s at a point 2 mabove the discharge and leaves at 40m/s. compute the shaft power assuming that thedevice is adiabatic but considering kinetic and potential energies. Calculate thediameters of the inlet and discharge tubes. (8)

(May/June 2010)19. Steam expands isentropically in a nozzle from 1 MPa, 2500C to 10 kPa. The steam

flow rate is 1 kg/s. find the velocity of steam at the exit from the nozzle, and the exitarea of the nozzle. Neglect the velocity of steam at inlet to the nozzle. The exhauststeam from the nozzle flows in a condenser and flows out as saturated water. The

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UNIT – III QUESTION BANK

V.ANBARASAN, AP/MECH

cooling water enters the condenser at 250C and leaves at 350C. Determine the massflow rate. (8)

(May/June 2010)20. In a closed vessel the 100 kg of steam at 100 kPa, 0.5 dry is to be brought to a

pressure of 1000 kPa inside vessel. Determine the mass of dry saturated steamadmitted at 2000 kPa for raising pressure. Also determine the final quality. (16)

(May/June 2011)21. A steam power plant running on Rankine cycle has steam entering HP turbine at 20

MPa, 5000C and leaving LP turbine at 90% dryness. Considering condenser pressureof 0.005 MPa and reheating occurring up to the temperature of 5000C determine,

(i) The pressure at which steam leaves HP turbine(ii) The thermal efficiency.(iii) Work done. (16)

(May/June 2011)22. In a Rankine cycle, the steam at inlet to turbine is saturated at a pressure of 35 bar and

the exhaust pressure is 0.2 bar. The flow rate of steam is 9.5 kg/s. Determine (1) thepump work (2) the turbine work (3) Rankine efficiency (4) condenser heat flow (5)work ratio and (6) specific steam consumption. (10)

(Nov/Dec 2011)23. Steam at a pressure of 2.5 MPa and 500°C is expanded in a steam turbine to a

condenser pressure of 0.05 MPa. Determine for Rankine cycle:(i) The thermal efficiency of Rankine cycle(ii) Specific steam consumption.If the steam pressure is reduced to 1 MPa and the temperature is kept same 500°C.Determine the thermal efficiency and the specific steam consumption. Neglect feedpump work, (16)

(Nov/Dec 2006)24. Consider a steam power plant operating on the ideal Rankine cycle. Steam enters the

turbine at 3 MPa and 623 K and is condensed in the condenser at a pressure of 10 kPa.Determine (i) the thermal efficiency of this power plant, (ii) the thermal efficiency ifsteam is superheated to 873 K instead of 623 K, and (iii) the thermal efficiency if theboiler pressure is raised to 15 MPa while the turbine inlet temperature is maintained at873 K. (16)

(Nov/Dec 2009)25. Consider a steam power plant operating on the ideal reheat Rankine cycle. Steam

enters the high-pressure turbine at 15 MPa and 873 K and is condensed in thecondenser at a pressure of 10 kPa. If the moisture content of the steam at the exit ofthe low-pressure turbine is not to exceed 10.4 percent, determine (i) the pressure atwhich the steam should be reheated and (ii) the thermal efficiency of the cycle.Assume the steam is reheated to the inlet temperature of the high-pressure turbine.

(16)(Nov/Dec 2009)

26. Consider a steam power plant that operates on a reheat Rankine cycle and has a netpower output of 80 MW. Steam enters the high-pressure turbine at 10 MPa and 500°Cand the low-pressure turbine at 1 MPa and 500°C. Steam leaves the condenser as asaturated liquid at a pressure of 10 kPa. The isentropic efficiency of the turbine is 80percent, and that of the pump is 95 percent. Show the cycle on a T-s diagram withrespect to saturation lines, and determine

(i) The quality (or temperature, if superheated) of the steam at the turbine exit,

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(ii) The thermal efficiency of the cycle, and ‘(iii) The mass flow rate of the steam. (16)

(Nov/Dec 2010)27. A steam boiler generates steam at 30bar, 3000C at the rate of 2kg/s. this steam is

expanded isentropically in a turbine to a condenser pressure of 0.05bar, condensed atconstant pressure and pumped back to boiler.

(i) Draw the schematic arrangement of the above plant and T-S diagramof Rankine cycle.

(ii) Find heat supplied in the boiler per hour.(iii) Determine the quality of steam after expansion.(iv) What is the power generated by the turbine?(v) Estimate the Rankine efficiency considering pump work.

(May/June 2004)28. A cyclic steam power plant is to be designed for a steam temperature at turbine inlet

of 633K and an exhaust pressure of 8kPa. After isentropic expansion of steam in theturbine, the moisture content at the turbine exhaust is not to exceed 15%. Determinethe greatest allowable steam pressure at the turbine inlet, and calculate the Rankinecycle efficiency for these steam conditions. Estimate also the mean temperature ofheat addition. (16)

(Nov/Dec 2007)29. Steam at 20bar, 3600C is expanded in a steam turbine to 0.08bar. It then enters a

condenser, where it is condensed to saturated liquid water. The pump feeds back thewater into the boiler.(i) Assuming ideal processes find the net-work and the cycle efficiency per kg of

steam.(ii) If the pump and the turbine have 80% efficiency, find the percentage reduction

in the net-work and cycle efficiency. (8)(May/June 2012)

30. In a steam power plant operating on an ideal reheat Rankine cycle, the steam entersthe high-pressure turbine at 3MPa and 4000C. After expansion to 0.6 MPa, the steamis reheated to 4000C and then expanded the low-pressure turbine to the condenserpressure of 10kPa. Determine the thermal efficiency of the cycle and the quality of thesteam at the outlet of the low pressure turbine.

(Nov/Dec 2002)31. In a thermal power plant operating on a Rankine cycle, superheated steam at 50 bar

and 5000C enters a turbine, the isentropic efficiency of which is 0.8. The condenserpressure is 0.05 bar and it delivers saturated liquid to a feed pump, the isentropicefficiency of which is 0.7. Determine the thermal efficiency of the power plant andthe mass flow rate of steam required for 50 MW net power generation. (8)

(May/June 2010)32. A reheat cycle operating between 30 and 0.04bar has a superheat and reheat

temperature of 4500C. The first expansion takes place till the steam is dry saturatedand then reheat is given. Neglecting feed pump work. Determine the ideal cycleefficiency. (Nov/Dec2003)

33. A steam power plant operates on a theoretical reheat cycle. Steam at boiler at 150 bar,5500C expands through the high pressure turbine. It is reheated at a constant pressureof 40bar to 5500C and expands through the low pressure turbine to a condenser at 0.1bars. Draw T-s and h-s diagrams. Find :

(i) Quality of steam at turbine exhaust

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(ii) Cycle efficiency(iii) Steam rate in kg/kWh. (16)

(May/June2004, May/June 2014)34. In a reheat steam cycle, the maximum steam temperature is limited to 773K. The

condenser pressure is 10kPa and the quality at turbine exhaust is 0.8778. Had therebeen no reheat, the exhaust quality would have been 0.7592. Assuming idealprocesses, determine (i) reheat pressure (ii) the boiler pressure (iii) the cycleefficiency (iv) the steam rate. (16)

(Nov/Dec2007)35. In a regenerative cycle, the steam pressure at turbine inlet is 30bar and the exhaust is

at 0.04bar. The steam is initially saturated. Enough steam is bled off at the optimumpressure of 3bar to heat the feed water. Determine the cycle efficiency. Neglect pumpwork. (Nov/Dec2003)

36. In a single heater regenerative cycle the steam enters the turbine at 30bar and 4000Cand the turbine exhaust pressure is 0.10bar. The condensate is heated in a directcontact type heater which operates at 5bar. Find the efficiency and the steam rate ofthe cycle and the increase in mean temperature of heat addition, efficiency and steamrate as compared to the Rankine cycle. Neglect pump work. (May/June2004)

37. Steam enters the turbine at 3MPa and 4000C and is condensed at 10kPa. Somequantity of steam leaves the turbine at 0.6MPa and enters open feed water heater.Compute the fraction of the steam extracted per kg of steam and cycle thermalefficiency. (10)

(Nov/Dec2005, Nov/Dec2012)38. In an ideal reheat cycle, the steam enters the turbine at 30bar and 5000C. After

expansion to 5bar, the steam is reheated to 5000C and then expanded to the condenserpressure of 0.1 bar. Determine the cycle thermal efficiency, mass flow rate of steam.Take power output as 100 MW. (10)

(May/June2007)39. Steam at 50bar, 4000C expands in a Rankine cycle to 0.34 bar. For a mass flow rate of

150 kg/s of steam, determine(i) Power developed(ii) Thermal efficiency(iii) Specific steam consumption. (8)

(May/June 2013)39. Steam at 4800C, 90 bar is supplied to a Rankine cycle. It is reheated to 12bar and

4800C. The minimum pressure is 0.07 bar. Find the work output and cycle efficiencyusing steam tables with and without considering pump work. (16)

(Nov / Dec 2013)

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