Chapter05 Hydraulic Turbine Kaplan turbine Sub Fluids Mechanics

Chapter-05 Hydraulic Turbine Kaplan turbine Sub: Fluids Mechanics & Machinery Sub. Teacher Ms. Nilesha U. Patil

Program : Mechanical Engineering Course: Fluid Mechanics & Machinery CO-Select various types of turbine under specified condition.

Kaplan Turbine Invented by Prof. Viktor Kaplan of Austria during 1913 – 1922. The Kaplan is of the propeller type, similar to an airplane propeller. The difference between the Propeller and Kaplan turbines is that the Propeller turbine has fixed runner blades while the Kaplan turbine has adjustable runner blades. The kaplan's blades are adjustable for pitch and will handle a great variation of flow very efficiently. The kaplan turbine, unlike all other turbines, the runner's blades are movable. The application of Kaplan turbines are from a head of 2 m to 30 m.

Comparison with other turbines Pelton turbines are tangential flow impulse turbines operate above a head of 200 m and low discharge. low specific speed of 8. 5 to 30 for single jet and 30 to 51 for two or more jets. Francis turbine is a mixed flow reaction turbine operate under a head of 30 to 200 m and medium discharge specific speed of 51 to 255. and has minimum slow rate Kaplan turbine is axial flow reaction turbine operate under a head of 2 to 30 m and large discharge. a high specific speed of 255 to 860.

Major Parts of A Kaplan Turbine

Parts of kaplan turbine The main part of kaplan turbine are Scroll casing Guide vanes mechanism Runner of turbine Draft tube

Scroll casing: The water from penstock enters scroll casing and surrounds the runner. It provides an even distribution of water around the circumference of the turbine runner maintaining the constant velocity for the water distributed Stay ring: The function of stay ring is to direct the water from scroll casing to guide vanes. Guide vanes: The guide vanes direct the water at an appropriate angle and regulates the quantity of water supplied to the runner Runner blades: The blades are attached to the hub and so shaped that water flows axially through the runner

Draft tube: A Draft tube connects the runner exit to tail race. It is a pipe of gradually increasing area used for discharging water from exit of turbine to tail race. By using draft tube, the kinetic energy rejected at the outlet of turbine is converted to useful pressure energy. The turbine may be placed above the tail race and hence it can be inspected properly.

Types of Draft tubes: The following are the important type of draft tube which is used are a. Conical draft tubes b. Single elbow tubes c. Moody spreading tubes and d. Elbow draft tube with circular inlet and rectangular outlet. The conical draft tubes and moody spreading draft tubes is more efficient.

Operation of kaplan turbine The water from the penstocks enters the scroll casing and then moves to the guide vanes. From the guide vanes, the water turns through 90° and flows axially through the runner. For Kaplan Turbine, the shaft of the turbine is vertical. The lower end of the shaft is made larger and is called ‘Hub’ or ‘Boss’. The vanes are fixed on the hub and hence Hub acts as runner for axial flow turbine.

Important parameters for kaplan turbine The peripheral velocity at inlet and outlet are equal u 1=u 2= ∏Do. N/60 were Do is outer dia of runner • Velocity of flow at inlet and outlet are equal Vf 1=Vf 2 • Area of flow at inlet = area of flow at outlet A = (∏/4)(Do 2 -Db 2) , Db is diameter of hub • Specific speed of kaplan turbine is given by Ns = N√P/H 5/4 were P is shaft power in KW • Discharge Q=A*Vf 1 • Overall efficiency is given by ηo=P/(ρ*g*Q*H/1000)

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