The draft tube is an important component of a Francis turbine which influences the hydraulic performance. It is located just under the runner and
allowed to decelerate the flow velocity exiting the runner, thereby converting the excess of kinetic energy into static pressure
.
What are the functions of a draft tube?
The draft tube is a conduit which connects the runner exit to the tail race where the water is being finally discharged from the turbine. The primary function of the draft tube is
to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet
.
What is the function of draft tube in turbine?
Draft Tube is a diverging tube fitted at the exit of runner of turbine and
used to utilize the kinetic energy available with water at the exit of runner
. ‘. This draft tube at the end of the turbine increases the pressure of the exiting fluid at the expense of its velocity.
Why draft tube is used in Kaplan turbine?
Draft tube is very important component of Kaplan turbines
due to high amount of kinetic energy leaving the runner and entering the draft tube
. As was presented by many papers [Lit], there is still problem to simulate reasonably the real flow in the draft tube with elbow.
Is draft tube used in impulse turbine?
The draft tube is used only in
reaction turbine
as there is a change in pressure energy involved. In an impulse turbine, there is no change in pressure so no need of a draft tube.
Why is it used in a reaction turbine?
When the water enters the turbine runner,
a part of the available energy of water is converted into kinetic energy
, and the remaining part is converted into pressure energy. Pressure varies throughout the turbine. … Francis, propeller, and Kaplan are some commonly used reaction turbines.
Is draft tube used in Pelton turbine?
Draft tubes
are not used in Pelton
wheels. Draft tube is a tube that is installed in power turbines. Explanation: The draft tube at the exit of the nozzle increases the pressure in the fluid. … The efficiency of the draft tube is defined as the ratio of actual conversion of kinetic energy into the pressure energy.
Where is turbine used?
Turbines are used in
wind power, hydropower, in heat engines, and for propulsion
. Turbines are extremely important because of the fact that nearly all electricity is produced by turning mechanical energy from a turbine into electrical energy via a generator.
What is the function of draft?
The main function of draft tube is
to decelerate the velocity and increase the pressure of the fluid flowing from the runner exit to tail race
. Water enters into the penstock and strikes the turbine vanes and reduces its pressure.
Which principle is used in hydraulic turbine?
Answer:
Newton’s second law of motion
The hydraulic turbine’s principle is based on Newton’s second law of motion. The force is directly proportional to the change in momentum, according to this law. Any change in the momentum of the water results in the generation of a force.
What is difference between impulse and reaction turbine?
The main difference between the impulse turbine and the reaction turbine is that,
in the former, there is a pressure drop across the fixed blades only
, whereas in the latter, there is a pressure drop across both the fixed and the moving blades.
Why draft tube is submerged in water?
The outlet of draft tube is always submerged in water. The draft tube
increases the pressure of the exiting fluid in expense of its kinetic energy and velocity
. It increases the efficiency of turbines. It is located just under the runner and allow to decelerate the flow velocity exit from the runner.
What type of turbine is Kaplan turbine?
A Kaplan turbine is
a type of propeller hydro turbine (specifically a reaction turbine)
used in hydroelectric plants. Water flows both in and out of Kaplan turbines along its rotational axis (axial flow).
Which is an example of impulse turbine?
Artwork:
A Pelton water wheel
is an example of an impulse turbine. It spins as one or more high-pressure water jets (blue), controlled by a valve (green), fire into the buckets around the edge of the wheel (red).
What is the main principle of draft tube?
The principal purpose of the draft tube is
to convert water kinetic energy into pressure energy
. To decrease the velocity of the water and to raise the pressure of the water before joining the tailrace, the pipe is used to steadily increase the cross-sectional area.
What is the reason for the absence of draft tube in an impulse turbine?
Draft tubes are not required for impulse turbine since the runner must be located above the maximum tail water to permit operation at atmospheric pressure. Without a draft tube,
the pressure could drop because of lack of water
, and in turn, the entire turbine could fail to work and power could be lost.
