250+ TOP MCQs on Efficiency of Francis Turbine and Answers

By engineer / May 26, 2024

Answer: d
Clarification: With the given information, we can find the volumetric efficiency and not the mechanical efficiency. If you got this question wrong, its advised to read the question carefully before answering.

9. The volumetric efficiency of a Francis turbine is given to be 90%. If the volume flow rate through the turbine is 25 m³/s. What is the flow rate of water over the runner blades (in m³/s)?
a) 20
b) 25
c) 22.5
d) 21.5
Answer: c
Clarification: The definition of volumetric efficiency in a Francis turbine states that it is the ratio between the total volume of water flowing over the runner blades to the volume of water entering the turbine. Hence, if Q = 25 m3/s, the volume of water over runner blades = 0.9*25 = 22.5 m³/s.

10. The volumetric efficiency of a given turbine is 80%. If volume flow rate of water in given to be 30 m³/s, find the volume of water (m³) NOT flowing over the runner blades per second?
a) 5
b) 6
c) 10
d) 12
Answer: b
Clarification: The volume of water flowing over runner blades = 0.8*30 = 24 m³/s. The volume of water NOT flowing over the runner blades would then be 30 – 24 = 6 m³/s.

11. The power available at the shaft of a Francis turbine is 1 MW. The volume flow rate of water in 25 m³/s, whirl velocity at inlet is 10 m/s and blade velocity is 5 m/s. Find the mechanical efficiency (in %)?
a) 65
b) 75
c) 80
d) 90
Answer: c
Clarification: Mechanical efficiency is given by ηm = shaft power / ρQVw1u1. Substituting the given values into this equation, we get mechanical efficiency = 80%.

12. The whirl velocity at inlet is 15 m/s and blade velocity is 10 m/s. The volume flow rate of water in 20 m³/s. Find the power output available at the shaft if the mechanical efficiency is 95% (in MW)?
a) 2.85
b) 3.075
c) 6.55
d) 0.285
Answer: a
Clarification: Mechanical efficiency is given by ηm = shaft power / ρQV_w1u1. Substituting the given values into this equation, we get shaft power = 2.85 MW.

13. The power output of the shaft is 5 MW. The volume flow rate of water in 10 m³/s at an available head of 60 m. Find the overall efficiency of the turbine in % (g = 10 m/s²)?
a) 80
b) 82.5
c) 83.3
d) 85
Answer: c
Clarification: The overall efficiency of a Francis turbine is given by ηo = shaft power/ ρQgH. Substituting the given values in this equation, we get overall efficiency = 83.33 %.

14. The volume flow rate of water in 10 m³/s at an available head of 60 m (g = 10 m/s³). Find the shaft power (in MW) if the overall efficiency of the turbine is 90%.
a) 54
b) 5.4
c) 540
d) 0.54
Answer: b
Clarification: The overall efficiency of a Francis turbine is given by ηo = shaft power/ ρQgH. Substituting the given values in this equation, we get shaft power = 5.4 MW.

15. The hydraulic efficiency of a Francis turbine is 90%, the mechanical efficiency is 95% and the volumetric efficiency is assumed to be 100%. Fine the overall efficiency (in %)?
a) 80
b) 85.5
c) 87.5
d) 83.3
Answer: b
Clarification: Overall efficiency is also given by ηo = ηh*ηm*ηv. So, ηo = 0.90*0.95*1 = 0.855 = 85.5%.