Windmill

A device in which wind is used to rotate the blades of a fan like structure is called a windmill. The windmill works on a very simple principle. When the blowing wind strikes across the blades of a windmill it exerts a force which rotates its blades.

The rotational effect is due to a special design of the blades similar to those of an electric fan. In other words, the windmill can be thought of an electric fan working in the reverse order. The rotating fan blows air while the blowing air rotates the blades of the windmill. The earliest windmills were made in Persia and it was spread to China, Europe and the other parts of the world.

Sub Topics

Windmill for Grinding
Windmill Running Water Pumps

Windmill for Grinding

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It contains a set of blades made of wood or metal. The blades are attached to a horizontal shaft to which a toothed wheel (like a gear) is fixed. The toothed wheel is in contact with a gear wheel mounted on a vertical shaft. The other end of the shaft is connected to a heavy, disc-shaped stone called a millstone which rotates over another millstone which is kept fixed. The grain to be ground is fed to the pair of millstones from the hopper. The machinery of the windmill (except the blades) is kept inside the building and the blades are projected outside facing the wind.

When wind strikes the blades of the windmill, the blades rotate setting the shaft and wheel into motion. The teeth of the wheel press against the gearwheel and it starts rotating.

The vertical shaft also rotates and millstone begins to grind the grains.

Windmill Running Water Pumps

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Wind energy has been extensively used for driving windmills for centuries. However they are used to operate water lifting pumps too. In a water pump a piston moves up and down and draws water from underground sources of water. The figure shows the design of a windmill used to run a water pump. It consists of large blades fixed to a rod called crank which contains a 'U' shaped bend to which the piston rod is connected. As the wind blows, it rotates the blades of the windmill thereby rotating the crank. As the 'U' shaped bend rotates, the piston rod moves up and down inturn the pump moving vertically and drawing water from the source.

Windmill