Definition of Draft Tube, Efficiency of Draft Tube, specific speed and Unit Speed

Draft Tube:

Reaction turbine usually discharges through a draft tube, the function of which is to reconvert the kinetic energy to flow energy by gradual expansion of X sectional area.

Efficiency of Draft Tube:

Efficiency of draft tube is defined as the ratio of regain of pressure head to the velocity head of outer surface of water.

Specific Speed:

Specific Speed is defined as the speed which geometrically similar (homogeneous series )turbines would run under unit head of water producing unit power.

i. All linear dimension are principle of similarity.

ii. All angles are constant.

Unit Speed:

Unit Speed defined as the speed of a turbine under unit head of water.

U=πDn/60

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