Rankine Cycle Questions and Answers

Power Plant Questions and Answers – Rankine Cycle

This set of Power Plant Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Rankine cycle”.

1. 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

Explanation: In the Rankine cycle, the working fluid goes through four processes: expansion in the turbine, heat addition in the boiler, heat rejection in the condenser, and compression in the pump.

2. Match the following:

i) Boiler                 A. reversible adiabatic expansion of steam
ii) turbine               B. constant pressure heat heat addition
iii) Condenser            C. reversible adiabatic compression
iv) pump                  D. constant pressure heat rejection

a) i-B ii-A iii-D iv-C
b) i-A ii-C iii-D iv-A
c) i-B ii-D iii-C iv-A
d) i-A ii-D iii-B iv-C

Explanation: In the Rankine cycle, the working fluid goes through four processes: expansion in the turbine, heat addition in the boiler, heat rejection in the condenser, and compression in the pump.

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

Explanation: The TIT(Turbine Inlet Temperature) is of the range 500-570C.

4. 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%

Explanation: Efficiency of Rankine cycle in actual working condition is found to be between 35 to 45%.

5. 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

Explanation: 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%.

6. 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

Explanation: 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%.

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

Explanation: Heat rate is the rate of input required to produce unit shaft output.

8. 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

Explanation: In comparison to the Carnot cycle, the Rankine cycle will have a larger area under the P-V curve.

9. 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

Explanation: The temperature of the cooling water is lower in the winter, which boosts the effectiveness of the condenser.

10. 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

Explanation: The Rankine cycle is a reversible cycle with two processes of constant pressure and temperature.

11. 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

Explanation: Work output(turbine) = h1 – h2.

The Rankine cycle is an idealised thermodynamic cycle that describes the process by which mechanical work can be taken from a fluid as it passes between a heat source and a heat sink in certain heat engines, such as steam turbines or reciprocating steam engines. William John Macquorn Rankine, a Scottish polymath professor at Glasgow University, is the inspiration for the Rankine cycle. The system receives heat energy from a boiler, which converts the working fluid (usually water) to a high-pressure gaseous state (steam) in order to power a turbine.

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