What is the primary purpose of a draft tube in a reaction turbine?
A
Increase pressure at turbine inlet
B
Increase velocity of water
C
Convert kinetic energy to pressure energy
D
Reduce water temperature
Analysis & Theory
A draft tube helps recover the kinetic energy of water leaving the runner by converting it into useful pressure energy.
Where is the draft tube located in a hydraulic turbine setup?
B
Between nozzle and runner
C
Between runner and tail race
Analysis & Theory
The draft tube is installed between the runner outlet and the tail race to help in energy recovery and discharge.
Which of the following is a benefit of using a draft tube?
A
Increases frictional losses
B
Reduces turbine efficiency
C
Allows turbine to be placed above tail race
D
Reduces water hammer effect
Analysis & Theory
By using a draft tube, the turbine can be positioned above the tail race without reducing efficiency.
Which type of turbine necessarily requires a draft tube?
Analysis & Theory
Kaplan turbines, being reaction turbines, require a draft tube to recover kinetic energy and operate efficiently.
What shape is typically used for efficient draft tubes?
Analysis & Theory
Gradually expanding tubes reduce velocity and help convert kinetic energy to pressure energy efficiently.
The pressure at the outlet of the turbine runner is usually:
C
Vacuum pressure (less than atmospheric)
D
Equal to inlet pressure
Analysis & Theory
The pressure at the runner outlet is often less than atmospheric, and the draft tube safely conveys water under this condition.
What is the main function of a conical draft tube?
A
Increase water temperature
D
Convert velocity head into pressure head
Analysis & Theory
A conical draft tube slows down water, converting velocity head into pressure head, improving energy recovery.
Which part of the hydraulic system assists in reducing pressure drop at the turbine outlet?
Analysis & Theory
The draft tube reduces pressure drop by safely conveying low-pressure water from the runner to the tail race.
Which of the following shapes is used in an elbow-type draft tube?
Analysis & Theory
Elbow-type draft tubes have a curved or 90-degree bend, often used in horizontal turbine installations.
What happens if the draft tube is poorly designed?
B
No impact on performance
C
Loss of energy recovery and possible cavitation
D
Increased water temperature
Analysis & Theory
A poorly designed draft tube can cause energy loss, turbulence, and even cavitation due to improper pressure recovery.