In water-driven turbines, the segment draft tube is extremely huge. In drive turbines, the stream vitality of the liquid is changed over to motor vitality by methods for the spout. In Reaction Turbines, some portion of the stream vitality is changed over to K.E however remaining vitality is as yet the weight vitality. Draft tubes are utilized in Reaction turbines to change over K.E into valuable weight vitality.
Draft tubes are a vital part of the response turbine. It is a course of a continuously expanding territory situated under the sprinter of the response turbine. The primary reason here is to change over the active vitality of the liquid into static weight vitality by decelerating the speed at the sprinter exit. Cast steel or established cement is utilized for the assembling of the draft tube.
In response turbines like Kaplan or Francis, both weight and dynamic vitality are utilized to influence the rotor to run. At the exit of the sprinter of these turbines, there is a negative weight created which is not as much as the air weight. So to enhance the work done this dynamic vitality is changed over to weight vitality again by the methods for the draft tube. What’s more, the water additionally moves out to tailrace.
Diverse kinds of Draft Tubes
Straightforward Elbow Draft Tube
Low head – This is straightforward in the plan. The approaching side and active side has a similar cross-area. Productivity 60%
Elbow with fluctuating cross segment
Gulf roundabout cross-area outlet rectangular cross-segment. For the most part, utilized in Kaplan Turbines – Proficiency 70%
Cranky Spreading Draft Tube
It lessens the spinning activity of water. It has one bay and two gulfs.
Tapered Diffuser or Divergent Draft Tube
The cone point is less than 10 degrees. On the off chance that the cone edge is all the more at that point there is a shot of cavitation.
For what reason Are Draft Tubes Not utilized in Impulse Turbines?
In an Impulse turbine, the Kinetic vitality is utilized to pivot the edges. Here no gadget is expected to change over the active vitality to weight vitality on the grounds that there is no loss of weight. The bay and outlet weight continues as before. The case of drive turbine is Pelton wheel. In Pelton wheel, the speed of the water is utilized to turn the sharp edge.