This turbine is used for high heads The water strikes the bucket along the

This turbine is used for high heads the water strikes

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This turbine is used for high heads. The water strikes the bucket along the tangent of the runner. Ex: Pelton Wheel Turbine. Reaction Turbine: If at the inlet of the turbine, the water possesses kinetic energy as well as pressure energy, the turbine is known as reaction turbine. As the water flows through the runner, the water is under pressure and the pressure energy goes on changing into kinetic energy. The runner is completely enclosed in an air-tight casing and the runner and casing is completely full of water. This turbine is used for medium heads. Ex: Francis Turbine. 72. Define Jet Ratio. It is defined as the ratio of the pitch diameter (D) of the Pelton wheel to the diameter of the jet (d). It is denoted by ‘m’ and is given as m = D/d
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73. Classification of hydraulic turbines: (a) Based on type of energy available at inlet Impulse turbine (Pelton wheel) Reaction turbine (Francis turbine, Kaplan turbine, Propeller turbine) (b) Based on head available at inlet High head turbine – [ > 250 m ] - (Pelton wheel) Medium head turbine – [ 60 to 250 m ] - (Francis turbine) Low head turbine – [ < 60 m ] – (Kaplan turbine, Propeller turbine) (c) Based on specific speed High specific speed turbine – (Kaplan turbine, Propeller turbine) Medium specific speed turbine - (Francis turbine) Low specific speed turbine - (Pelton wheel) (d) Based on direction of flow through runner Tangential flow turbine Radial flow turbine Axial flow turbine Mixed flow turbine 74. Define Radial flow reaction turbine and their types. If water flows in the radial direction in the turbine then it is referred as radial flow turbine. Types: Inward radial flow reaction turbine: If the water flows from outwards to inwards through the runner, the turbine is known as inward radial flow reaction turbine. Here the outer diameter of the runner is inlet diameter whereas the inner diameter of the runner is outlet diameter. Outward radial flow reaction turbine: If the water flows from inwards to outwards through the runner, the turbine is called as outward radial flow reaction turbine. Here the outer diameter of the runner is outlet diameter whereas the inner diameter of the runner is inlet diameter. 75. What is mean by Draft Tube? 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 sub-merged below the level of water in the tail race. 76. Why do draft tubes have enlarging passage area in the direction of flow? The pressure at the exit of the reaction turbine is generally less than atmospheric and this makes the water NOT to discharge directly to the tail race. By the introduction of draft tube, which has enlarged area in the direction of flow, the kinetic head reduces and pressure head increases. There by discharge of water to the tail race safely.
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