Now days Water Turbines are used to convert hydraulic energy into mechanical energy. These water turbines are developed from water wheels which were used in olden days. There are different types of water wheels used according to requirements. At present, Water Wheels has no more use in practice but as a mechanical engineering professional, we have to have knowledge of this useful invention.In olden days, following types of Water Wheels had been used.
01) Overshot Water Wheel
In these types of water wheel, the water enters into buckets at the top of the periphery. Actually this wheel runs entirely by weight of the water but some it may run by the impulse of the water. The water from slightly upper position, which is called as the head race, is allowed to enter into buckets through an adjustable sluice gate.The buckets are forced downwards due to the weight of the water and water wheel starts rotating. The water filled buckets are get emptied in the lower position, called tail race.To utilized maximum water energy, the buckets are arranged in proper manner. When the crown of the wheel made slightly below the head race, the water strikes the buckets at some initial velocity and wheel starts rotating partly by impulse of the water.Overshot Water Wheel is useful in water head from 10 to 25 meters and for such a high head; the diameter of the wheel is from 3 to 20 meters. We can achieve 60 to 80 percentage efficiency from this wheel at 4 to 8 R.P.M. (Rotation per Minuet). The 8 to 10 numbers of buckets are sufficient in its construction.
02) Breast Water Wheel
In this type of water wheel, the water enters the buckets at the breast height of the wheel and wheel runs partly by weight and partly by impulse of the water.With the help of rock and pinion arrangement, the water from head race is entering the buckets without shock through a number of passages. The wheel starts rotating due the weight of the water and buckets starts moving downwards.Breast Water Wheel had two main special features, first is its bottom is immersed in the tail race of the water and second is the diameter of the wheel is more than the head of water available.This water wheel is useful in 1 to 5 meters water head, with diameter 4 to 8 meters. The efficiency of this water wheel is 50 to 60 percentages at 3 to 7 R.P.M.
03) Undershot Water Wheel
In this type of water wheel, the water in the form of jet impinges on the vanes at the bottom of its periphery. This wheel entirely runs by the impulse of the water. The jet of the water strikes on the vanes and this makes wheel to rotate. Before water strikes the buckets or vanes of the wheel, the available water head is first converted into velocity head.Undershot Water Wheel is useful where available water head is less than 2 meters with the diameter of wheel 2 to 4 times of water head. The efficiency of this type of wheel is only 35 to 45 percentages at 2 to 4 R.P.M.
04) Poncelet Water Wheel
This is the improvement of Undershot Water Wheel. In this type of water wheel, curved vanes are used to replace straight vanes. This wheel entirely runs by the impulse of the water.The vanes are curved in such an angle, that the jet of water enters the vanes without shock. The water flows down to the tail race without spill over at the outlet due to its sufficiently long vanes.The Poncelet Water Wheel is useful in 2 to 3 meters water head at diameter of wheel is 2 to 4 times of the water head. The efficiency is 50 to 65 percentages with 2 to 5 R.P.M. The inlet angle of the vane is 15 degree.
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