draft tube

16
Draft-tube

Upload: swargpatel283

Post on 21-Aug-2015

172 views

Category:

Engineering


24 download

TRANSCRIPT

Page 1: Draft tube

Draft-tube

Page 2: Draft tube

Definition

The draft-tube is a pipe of gradually increasing area which connects the outlet of the runner to the tail race.

One end of the draft tube is connected to the outlet of the runner while the other end is submerged below the level of water in the tail race.

Page 3: Draft tube

Why it is needed?

In an Impulse turbine the available head is considerably high and there is no significant effect on the efficiency if the turbine is placed a couple of meters above the tailrace.

But in the case of Reaction turbines, if the net head is low and if the turbine is installed above the tailrace, there can be appreciable loss in available pressure head.

Page 4: Draft tube

Why it is needed?

If the pressure at the exit of the turbine is lower than the pressure of fluid in the tailrace, a back flow of liquid into the turbine can result in significant damage. By placing a diffusing pipe at the exit of the runner, the pressure head is increased by decreasing the exit velocity, and both the overall efficiency and the output of the turbine can be improved.

 Turbines need to have a minimum amount of water to propel them in order to produce enough energy. Without these tubes, the pressure could drop because of lack of water, and in turn, the entire turbine could fail to work and power could be lost.

Page 5: Draft tube

Function

The primary purpose of the draft tube is to monitor the influx of water.

The turbine has something called a "tail race," which is the lowest portion of a dam or construction project where water pools. The tube connects the turbine to this tail race, permitting the turbine to be outside of the water but still have access to the water.

Reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet.

Page 6: Draft tube
Page 7: Draft tube

Function

It permits negative head to be established at the outlet of the runner and thereby increase the net head on the turbine .

The turbine may be placed above the tail race without any loss of net head and hence turbine may be inspected properly.

Page 8: Draft tube

Function

It converts a large portion of the kinetic energy rejected at the outlet of the turbine into useful pressure energy. Without the draft tube ,the kinetic energy rejected at the outlet of the turbine will go waste to the tail race.

The draft tube prevents the splashing of water coming out of the runner and guides the water to the tail race.

Page 9: Draft tube

Theory

Page 10: Draft tube

Theory

Page 11: Draft tube

Efficiency

The efficiency of a draft tube is defined as the ratio of actual conversion of kinetic head into pressure head in the draft tube to the kinetic head at the inlet of the draft tube

Page 12: Draft tube

Types of Draft tube

Conical draft tube

Page 13: Draft tube

Types of Draft tube

Simple elbow tubes

Page 14: Draft tube

Types of Draft tube

Moody spreading tube

Page 15: Draft tube

Types of Draft tube

Elbow draft tube with circular inlet and rectangular outlet

Page 16: Draft tube