01-05-2017, 04:50 PM
The Pelton wheel is an impulse water turbine. It was invented by Lester Allan Pelton in the 1870s. The Pelton wheel draws energy from the urge to move water, as opposed to the dead weight of water as the traditional over water wheel. Many variations of impulse turbines existed prior to Pelton's design, but were less efficient than the Pelton design. The water coming out of those wheels typically still had high speed, taking away much of the dynamic energy brought to the wheels. The geometry of the Pelton palette was designed so that when the edge ran at half the speed of the water jet, the water left the wheel with very little speed; Thus its design extracted almost all the energy of the water impulse - which allowed a very efficient turbine.
The nozzles direct powerful, high-speed water streams against a rotating series of bucket-shaped spoons, also known as thrust blades, which are mounted around the circumferential edge of a drive wheel-also called a runner (see photo, Old Pelton As the water jet strikes the contoured blade blades, the direction of the water velocity changes to follow the contours of the bucket. In the system of the hub and wheel, by turning the wheel, the own water flow makes a "turn in U" and leaves the outer sides of the bucket, slowing down at low speed.In the process, Of water is transferred to the wheel and therefore to a turbine.Therefore, the "impulse" energy runs on the turbine.For maximum power and efficiency, the wheel and turbine system is designed Or in such a way that the speed of the water jet is twice the speed of the rotating hubs. A very small percentage of the original kinetic energy of the water jet will remain in the water, which will cause the bucket to empty at the same rate as it fills up (see conservation of mass) and thus allows the high input flow Pressure continues uninterrupted And without waste of energy. Typically, two buckets are mounted side by side on the wheel, which allows the water jet to be divided into two equal streams (see photo). This balances the lateral load forces on the wheel and helps ensure a smooth and efficient transfer from the moment of the fluid water jet to the turbine wheel.
Because water and most liquids are almost incompressible, almost all available energy is extracted in the first stage of the hydraulic turbine. Therefore, Pelton wheels have only one turbine stage, unlike gas turbines that run with compressible liquid.
Principle of operation of the Pelton turbine
The high velocity water jets that emerge from the nozzles hit the hubs in the dividers, placed in the center of a hub, from where the jets are divided into two equal currents. These flows flow along the inner curve of the cube and leave it in the opposite direction to that of the incoming jet. High-speed water jets that work with the Pelton Wheel Turbine are obtained by expanding the water at high pressure through the nozzles at atmospheric pressure. High pressure water can be obtained from any body of water located at some height or streams of water flowing through the hills.
The change in the momentum (direction and speed) of the water stream produces a boost in the blades of the Pelton Turbine wheel. This impulse generates torque and rotation on the Pelton Turbine shaft. To obtain the optimum output of the Pelton Turbine, the thrust received by the blades must be maximum. For this, the change in the moment of the water flow should be as much as possible. This is obtained when the water flow is diverted in the opposite direction to the one that hits the buckets and with the same speed with respect to the buckets.