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| Water Turbine |
Water is very heavy and its flow energetic. The Power available in flowing water is described by;
where:
• Power( Joules/sec or Watts)
• turbine efficiency
• density of water (Kg/meter3)
• accelaration of gravity (9.8 meters/sec2)
• head (meters, this is the height at which still, unimpeded water starts falling from)
• flow rate (meters3/sec)
Theory of operation
Water turbines are divided into two groups; reaction turbines and impulse turbines.
Impulse turbines change the direction of flow of the water, leaving the exit flow with diminished energy. The water's energy is converted to kinetic energy by a nozzle prior to hitting the turbine blades. No pressure change occurs at the turbine blades and the turbine doesn't require a housing for operation. Impulse turbines are more often used in high head applications.
Reaction turbines are acted on by water changing pressure as it moves through the turbine. The turbine must be cased to contain the water pressure (or fully submerged in the water flow). Reaction turbines are more often used in low head applications.
Turbine designs often combine both these concepts.
The critical speed of a water turbine is the speed at which water flows through the turbine without resistance and no energy is extracted from the water flow. The operating speed is always less than the critical speed.
Some water turbines are designed to reverse flow and turn into a pump. They can fill a high reservoir during off-peak electrical hours and revert to a turbine for power generation during peak electrical demand.
Types of turbines
Reaction turbines:
• Francis
• Propeller
• Kaplan
• Tyson
• Water Wheel
Impulse turbines:
• Pelton
• Turgo
• Banki(Crossflow)
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