Bernoulli Equation states the sum of kinetic energy and potential energy of a fluid flow steam line is constant at any place.
According to Torricelli's theorem velocity out from a tank is equal to speed of a free body falling a distant similar to water head.This velocity has to be considered at the discharging orifice. But there can an acceleration take place on the water column moving along the pipe due to the continues gravitational force exerting on this water column until it reaches the discharging end.
Let us consider the flow of fluid through a duct having inlet and outlet sectional area are A1, and A2 consecutively. According to Continuity Equation A1.v1 = A2.V2= Constant. Reservoir with constant level H from L1 to L2 to B, by decreasing the pipe diameter, pressure will increase at discharging point B, without changing any other factors. This length would be approximately 5 times the pressure head H. Diameter of the pipe is recommended to reduce to 20%, considering losses due to friction and bends. This method is equally applicable to Pelton wheel as well.
Water flowing in a river is a turbulent flow. The river flow speed is controlled by the surface roughness and the gradient of the river bed. Water flowing through a pipe is a streamline flow. In a pipeline water flow is not subjected to friction and it will flow at a higher speed than the river.
Due to it's operational method hydro turbines are categorized as Impulse turbines and Reaction turbines.
Reaction turbines convert water pressure in to mechanical force, while Impulse turbines convert potential energy of water in to kinetic energy by a nozzle and focused on the turbine. Usually impulse turbines are used in very high head applications.
Renewable Energy Hydraulics Environmental pollution