What are the main components of a Francis turbine?
The main components are spiral casing, guide and stay vanes, runner blades, draft tube. The spiral casing also known as the volute casing or scroll case, has numerous openings at regular intervals which convert fluid's pressure energy into kinetic and allow the working fluid to impinge on the blades of the runner. This maintains a constant velocity despite the fact that numerous openings have been provided for the fluid to enter the blades, as the cross-sectional area of this casing decreases uniformly along the circumference. Guide and stay vanes convert the pressure energy of the fluid into kinetic energy. Runner blades are the centers where the fluid strikes and the tangential force of the impact produces torque causing the shaft of the turbine to rotate. Attention to blade angles at inlet and outlet is necessary, as these are major parameters affecting power production. The draft tube's primary function is to reduce the velocity of discharged water to minimize the loss of kinetic energy at the outlet.
What is the purpose of draft tube?
The efficiency of a reaction turbine, such as a Francis Turbine, increases with the increase in pressure difference between inlet and outlet pressures. As inlet pressure can't be increased further, since the inlet head of the turbine remains constant, the only way to improve efficiency is to decrease the outlet pressure and to create a negative head at the outlet. This is where Draft tubes comes into picture. Draft tubes are of different shapes and sizes, depending upon the magnitude of negative head to be produced at the outlet of the turbine. A draft tube can be imagined as a component with increasing area of cross section starting from the outlet of the turbine, to the tail race. Cross sections may be circular, rectangular, square or a specially designed one like a Siphon draft tube etc.
How to Calculate Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade?
Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade calculator uses Hydraulic Efficiency of Francis Turbine = (Whirl Velocity at Inlet of Francis Turbine*Velocity of Vane at Inlet For Francis Turbine+Whirl Velocity at Outlet of Francis Turbine*Velocity of Vane at Outlet For Francis Turbine)/(Acceleration Due to Gravity*Net Francis Turbine Head) to calculate the Hydraulic Efficiency of Francis Turbine, Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade is the ratio of the hydraulic power (useful power output) to the water power supplied to the turbine. The acute-angled outlet blades help in reducing energy losses due to fluid exit velocity, thus potentially improving the hydraulic efficiency of the turbine. Hydraulic Efficiency of Francis Turbine is denoted by ηh symbol.
How to calculate Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade using this online calculator? To use this online calculator for Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade, enter Whirl Velocity at Inlet of Francis Turbine (Vw1), Velocity of Vane at Inlet For Francis Turbine (u1), Whirl Velocity at Outlet of Francis Turbine (Vw2), Velocity of Vane at Outlet For Francis Turbine (u2), Acceleration Due to Gravity (g) & Net Francis Turbine Head (Hf) and hit the calculate button. Here is how the Hydraulic Efficiency of Francis Turbine with Acute Angled Outlet Blade calculation can be explained with given input values -> 0.726072 = (12.93*9.45+6.5*5.2)/(9.81*21.9).