2. The data at inlet and exit of the turbine, running under steady flow, is given below.

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1 3 rd week quiz 1. Identify the correct path of fluid flow in a steam power plant. a) Steam turbine-pump-boiler-condenser. b) Economizer- evaporator- superheater. c) Pump-turbine-condenser-evaporator. d) Steam turbine-boiler-pump. Ans: b. 2. The data at inlet and exit of the turbine, running under steady flow, is given below. Specific Enthalpy ( kj Kg ) Inlet Condition 3250 Outlet Condition 2360 The rate of heat loss per kg of steam is 10 kj. The changes in potential and kinetic energy of steam is negligible. Calculate turbine work developed (kj/kg) a) 430 b) 880 c) 170 d) 1550 Ans: The changes in potential and kinetic energy of steam is negligible. Here, w = hi he + (-q) = = 880 kj/kg (b) 3. In a simple power plant, the change of state of the working fluid and the hot product of combustion during the heating process is schematically represented by:

2 Ans: a

3 4. Select the advantages obtained from the use of reheat in steam power plant Ans: a, b. a) Improves the total work output and dryness fraction. b) Work output per unit mass of circulating fluid increases. c) Decrease size of boiler. d) Less heating is required in economizer 5. Match the following Ans: 1 a) Regenerative cycle i) Direct contact b) Reheat Cycle ii) Increases mean temperature of heat addition c) Closed feed water heater iii) Improves work output d) Open feed water heater iv) Indirect contact 1) a-ii, b-iii, c-iv, d-i 2) a-iii, b-iv, c-i, d-ii 3) a-iv, b-iii, c-i,d-ii 4) a-i, b-iv, c-iii, d-ii 6. A steam power plant operates on a Rankine cycle with reheating. The cycle is shown in a T-s plane. Which one is representing heating process?

4 (a) A-B, (b) B-C, (c) C-D (d) D-E Ans: (c) C-D 7. A steam power plant is represented in a T-s diagram. What are the processes associated with it? (a) Reheating, (b) Regeneration, (c) 2 open feed water heating, (d) None of these. Ans: a, b, c 8. Regarding feed water heaters (FWH) of a steam power plant the following statements are made. Identify the correct statement(s).

5 (a) FWHs are used for heating the condensate from the waste heat of the boiler. (b) In open FWHs condensate is heated using the exhaust gas. (c) Open FWHs are given such a name as they can be opened easily for the purpose of maintenance. (d) Open FWHs have three terminal temperatures only. Ans: (d) 9. Identify the correct statements. In a utility steam power plant, (a) a combination of reheat and regeneration is used. (b) combination of reheat and regeneration should be avoided. (c) regeneration is not preferred as it reduces the work output. (d) regeneration feed heating reduces the work output for a specified flow of the working fluid. Ans: a, d. 10. The condensing temperature of a Rankine cycle is 27 ºC. One may approximate the heat transfer in the boiler to be equivalent to heat transfer from a source at a constant temperature of 600 K. The equivalent Carnot efficiency of the cycle is (a) 80 %, (b) 50%, (c) 33 %, (d) Can not be calculated from the given data. Ans: Carnot T 1 T (b) 11. In a steam power plant, a saturated liquid water coming out from condenser enters into a pump and the pump feeds back the water into the boiler. The condenser and the boiler pressures are 0.08 bar and 20 bar, respectively. The specific volume of the water at the condenser outlet is m 3 /kg. Find out the pump work (kj/kg) required to feed unit mass of water. Isentropic efficiency of the pump is 80 %. (a) 2.008, (b) 1.6, (c) 2.51, (d) Insufficient data.

6 Ans: P1 P2 = = bar = kn/m 2 v3 = m 3 /kg WP, isentropic = h4s h3 = v3 (P1 P2) = = kj/kg ηp = 80% = WP, isentropic/wp,actual WP,actual = 2.008/0.8 = 2.51 kj/kg (c) 12. A steam power plant operates on an ideal regenerative Rankine cycle with one open feed water heater. Determine the fraction of steam extracted from the turbine. T-s diagram of the cycle is shown in the figure. The enthalpies of various states are given. h2 = kj/kg h4 = kj/kg h6 = kj/kg Neglect pump work and kinetic and potential energy changes. (a) 0.554, (b) 0.227, (c) 0.133, (d) 0.884

7 Ans: h2 = kj/kg h4 = kj/kg = h5 (neglecting pump work) h6 = kj/kg By energy balance for the feed water heater: m(h2 h6) = (1 m)( h6 h5) m = (b) 13.

8 Process 1-3 shows the actual expansion in a turbine. Process 1-2 is the isentropic expansion from boiler pressure to condenser pressure. (a) h2 > h3 (b) h2 < h3 (c) Nothing can be said regarding the relationship between h2 and h3. (d) Actual expansion curve is wrongly represented; it should be on the left side of curve 1-2. Ans: (b) 14. Referring to the above diagram (problem 13), the isentropic efficiency of the turbine is η (a) s s s s (b) h h h h (c) T ds T ds (d) None of the above Ans: (b) 15. Identify the correct statements. In a Rankine cycle with regenerative feed heating is introduced. (a) Mass flow rate through the boiler and the condenser remains the same. (b) The size of the low pressure stage of turbine reduces. (c) We need to burn less fuel in the boiler. (d) Size of the economizer reduces. Ans: b, c, d.