Cross-sectional area of draft tube in reaction turbine

Q.  The water from runner in reaction turbine is discharged into tail race through a draft tube which has ____________ cross sectional area.
- Published on 16 Sep 15

a. constant
b. gradually decreasing
c. gradually increasing
d. uneven

ANSWER: gradually increasing
 

    Discussion

  • Pankaj   -Posted on 12 Oct 15
    In reaction turbine the water enters the runner under pressure having some velocity head. The pressure of water is gradually converted into velocity head while the water passes over the runner. This pressure is reduced to atmospheric pressure along with the change in kinetic energy. The rotation of runner and production of mechanical work is the result of impulse action.

    As the water flows under pressure over the runner, above atmospheric it is necessary that the runner must run full of water. This water coming out from runner is discharged into tail race through closed tube of gradually increasing cross-sectional area called as draft tube.

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