National Institute of Technology Karnataka, SurathkalFourth Semester Mechanical

Subject: Applied ThermodynamicsAssignment

PART-A (M11+M21 Batches)

1. a) Steam is supplied; dry saturated at 40 bar to a turbine and the condenser pressure is 0.035 bar. If the plant operates on the Rankine cycle, calculate, per kilogram of steam:(i) The work output neglecting the feed-pump work;(ii) The work required for the feed pump;(iii) The heat transferred to the condenser cooling water, and the amount of cooling water required through the

condenser if the temperature rise of the water is assumed to be 5.5K; (iv) The heat supplied;(v) The Rankine efficiency;(vi) The specific steam consumption

b) For the same steam condition calculate the efficiency and the specific steam consumption for a Carnotcycle operating with wet steam. (986kj, 4kj, 1703kj, 74kg,2685kj,36.6%, 3.67kg/kWh;42.7%,4.92kg/kWh)

2. A Steam plant operates with an initial pressure at 20 bar and temperature 4000C,and exhaust to a heating system at2 bar. The condensate from the heating system is return to the boiler plant at 65 0C and the heating

system utilizes for its intended purpose 90% of the energy transferred from the steam it receives. The turbine efficiency is 70%. (a) what fraction of the energy supplied to the steam plant serves a

useful purpose? (b) if two superate steam plants had been set up to produce the same useful energy, one to generate heating steam at 2 bar, and the other to generate power through a cycle working between 20 bar, 4000C and 0.07 bar , what fraction of the energy supplied would have served a useful purpose? (91.2%,64.5%.)3.

3 A generating station is to give a power output of 200MW. The superheat outlet pressure of the boiler is to be 170 bar and the temperature 600oC. After expansion through the first-stage turbine to a pressure of 40 bar, 15% of the steam is extracted for feed heating. The remainder is reheated at 600oC and is then expanded through the second turbine stage to a condenser pressure of 0.035 bar. For preliminary calculations it is assumed that the actual cycle will have an efficiency ratio of 70% and that the generator mechanical and electrical efficiency is 95%. Calculate the maximum continuous rating of the boiler in kilograms per hour. (632000kg/h)

4 A steam turbine is to operate on a simple regenerative cycle. Steam is supplied dry saturated at 40 bar, and is exhausted to a condenser at 0.07 bar. The condensate is pumped to a pressure of 3.5 bar at which it is mixed with bleed steam from the turbine at 3.5bar. The resulting water which is at saturation temperature is then pumped to the boiler. For the ideal cycle calculate, neglecting feed-pump work,

(i) the amount of bleed steam required per kilogram of supply steam; (ii)the cycle efficiency of the plant; (iii)the specific steam consumption. (0.1906;37%;4.39kg/kWh)

PART-B (M12+M22 Batches)

1. (a) Steam is supplied; at 40 bar and 350 0 C to a turbine and the condenser pressure is 0.035 bar. If the plant operates on the Rankine cycle, calculate, perkilogram of steam:

(i) The work output neglecting the feed-pump work; (ii) The work required for the feed pump; (iii) The heat transferred to the condenser cooling water, and the amount of cooling water required through the condenser if the temperature rise of the water is assumed to be 5.5K; (iv) The heat supplied;

(v) The Rankine efficiency; (vi)The specific steam consumption (1125 KJ, 4kj, 1857kj, 80.7kg, 2978kj, 37.6%, 3.21kg/kWh)

2. Steam is supplied to a two-stage turbine at 40 bar and 350oC.It expands in the first turbine until it is just dry saturated, then it is re-heated to 350oC and expanded through the second-stage turbine. The condenser pressure is 0.035 bar. The isentropic efficiencies are 84% and 78% respectively in the first stage and the second stage expansion, calculate the work output and the heat supplied per kilogram of steam for the plant, assuming ideal processes and neglecting the feed-pump term. Calculate also the cycle efficiency, the specific steam consumption and wetness of the steam leaving the turbine.(1028kj,331kj,31.1%,3.5kg/kWh)

3. In a nuclear power plant saturated steam at 30 bar enters a h.p. turbine and expands isentrophically to a pressure at which its quality is 0.841. At this pressure the steam is passed through a moisture superator which removes all the liquid. Saturated vapour leaves the superator and is expanded isentrophically to 0.04 bar in i.p. turbine, while the saturated liquid leaving the superator is returned via a feed pump to the boiler the condensate leaving the condenser at 0.04 bar is also returned to the boiler via a second feed pump. Calculate the cycle efficiency and turbine outlet quality taking in to account the feed pump term. Recalculate the same quantities for a cycle with the same boiler and condenser preasures but without moisture seperation. (35.5%, 0.824; 35%;0.716)

4. In a regenerative steam cycle employing three closed feed heaters the steam is supplied to the turbine at 42 bar and 500oC and is exhausted to the condenser at 0.035 bar. The bleed steam for feed heating is taken at pressures of 15, 4 and 0.5 bar. Assuming ideal processes and neglecting pump work, calculate:

(i) the fraction of the boiler steam bled at each stage;(ii) the power output of the plant per unit mass flow rate of boiler steam;(iii) The cycle efficiency. (.0952,.0969,0.0902; , 1133.6Kw per kg/s;43.6%)

PART-C (M13+M23 Batches)

1. A Simple steam power cycle uses solar energy for the heat input.Water in the cycle enters the pump as a saturated liquid at 400C,and is pumped to 2 bar. It then evaporates in the boiler at this pressure, and enters the turbine as saturated vapour. At the turbine exhaust the conditions are 400C and 10% moisture. The flow rate is 150kg/hr. Determine (a) the turbine isentropic efficiency,(b) The net work output,(c) The cycle efficiency, and (d) The area of solar collected needed if the collectors pick up 0.58 kW/m2. (c)2.78%;(d)18.2m2.

2. Steam is supplied to a two-stage turbine at 40 bar and 350oC. It expands in the first turbine until it is just dry saturated, then it is re-heated to 350oC and expanded through the second-stage turbine. The condenser pressure is 0.035 bar. Calculate the work output and the heat supplied per kilogram of steam for the plant, assuming ideal processes and neglecting the feed-pump term. Calculate also the specific steam consumption and the cycle efficiency. (1290kj;3362kj,2.79kg/kWh;38.4%)

3. Steam is supplied to a two-stage turbine at 40bar and 500oC.In the first stage the steam expands isentropically to 3.0 bar at which pressure 2500 kg/h of steam is extracted for process work. The remainder is reheated to 500oC and then expanded isentropically to 0.06 bar. The by-product power from the plant is required to be 6000KW.Calculate the amount of steam required from the boiler, and the heat supplied. Neglect feed-pump terms, and assume that the process condensate returns at the saturation temperature to mix adiabatically with the condensate from the condenser. (11950kg/h;, 15880Kw)

4. The net power out put of an ideal regenerative-reheat steam cycle is 80MW. Steam enters the h.p.turbine at 80 bar,5000C and expands till it becomes saturated vapour. Some of the steam then goes to and open feed water heater and the balance is reheated to 4000C, after which it expands in the I.p. turbine to 0.07 bar. Compute (a) the reheat pressure, (b) the steam flow rate to the h.p.turbine, and (c) the cycle efficiency .Neglect pump work. (6.5 bar, 58.4kg/s,43.7%)

PART-D (M14+M24 Batches)

1 A geothermal power plant utilizes steam produced by natural means underground. Steam well are drilled to tap this steam supply which is available at 4.5 bar and 175 = C. The steam leaves the turbine at 100 mm Hg absolute pressure. The turbine isentropic efficiency is 0.75. Calculate the efficiency of the plant. If the unit produces 12.5MW, what is the steam flow rate?

2 In a reheat cycle, the initial steam pressure and maximum temperature are 150 bar and 550 = C respectively. If the condenser pressure is 0.1 bar and the moisture at the condenser inlet is 5%, and assuming ideal processes, determine (a) the reheat pressure, (b) the cycle efficiency, and (c) the steam rate. (Ans, 13.5 bar, 43.6%,2.05 kg/kwh)

3 The net power output of the turbine in an ideal reheat-regenertive cycles 100MW. Steam enters the high – pressure (H.P) turbine at 90 bar, 550 = C. After expansion to 7 bar, some of the steam goes to an open heater and the balance is reheated to 400 = C, after which it expands to 0.07 bar. (a) What is the steam flow rate to the H.P. turbine? (b) What is the total pump work? (c) Calculate the cycle efficiency. (d) If there is a 10 = C rise in the temperature of the cooling water. What rate of flow of the cooling water in the condenser? (e) If the velocity of the steam flowing from the turbine to the condenser is limited to a maximum of 130m/s, find the diameter of the connecting pipe.

4 In a steam power plant, the condition of steam at turbine inlet is 80 bar, 500 = C and the condenser pressure is 0.1 bar. The heat source comprises a steam of exhaust gases from a gas turbine discharging at 560 = C and 1 atm pressure. The minimum temperature allowed for the exhaust gas steam is 450 K. The mass flow rate of the hot gases is such that the heat input rate to the stream cycle is 100MW. The ambient condition is given by 300Kand 1 atm. Determine ƞI, work ratio and eƞII of the following cycles: (a) basic Rankine cycle, without superheat, (b) Rankine cycle with superheat, (c) Rankine cycle with reheat such that steam expand in the h.p. turbine until it exits as dry saturated vapour ,(d) ideal regenerative cycle, with the exit temperature of the exhaust gas steam taken as 320 = C , because the saturation temperature of steam at 80 bar is close to 300 = C

PART E(To be answered by all)

1] What are the desirable properties of the working fluid for a vapour power cycle 2] Explain with necessary diagrams the regenarativecycle with closed feedwater heater

3] Explain with necessary diagrams the binary vapour power cycle’.

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