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Windmill
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Windmill is a machine that converts wind to useful, productive
energy. The energy is derived due to the force of
wind acting on oblique blades (sails) that spread out from the
shaft. This shaft may be connected to machinery used to
perform work such as milling grain, pumping water or
generating electricity. When the shaft is connected to the
load such as a pump, then the device is known as windmill.
Windmill can also be used to generate electricity. This kind
of windmill is called wind turbine generator.
The history
of windmills goes back to 650 AD. The first windmills were noted in Sistan in Eastern Persia. It is
believed that it was invented by a slave, Abu Lulua, as the outcome of a challenge. Lulua boasted
that he could harness the wind and the caliph challenged him
to prove it. Till this day, Sistan operates the windmill
designed by him.
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How to make a
windmill? The ancient windmill was a tall building of
sun-dried bricks. The vanes within were made of reed matting,
attached to a vertical wind shaft that ran up the centre of
the building and caught the wind. The shaft turned the upper
millstone as they were combined directly. Two apertures were
cut into the tower - one, which allowed the prevailing
wind to encroach upon the waves on one side of the shaft, and
the other that allowed it to escape. The vanes on the other
side of the building were secure from the
wind. One of the main
disadvantages of this kind of windmill was that it can only
work in a region where there was a steady prevailing wind.
This was because the working of the apertures depended upon
the apertures being aligned with the wind so as to pass
through one and come out through the other. Thus, this type of
windmill was not of much use to places outside Persia, where
the steady wind blew for three months of the year.
By
950 AD, windmills were very common in Persia. The first known
windmills in Europe appeared two centuries after that. They were an
invention on their own because they did seem to have anything common
to the Persian Windmills. |
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A Windmill |
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The first
European windmill looked more like a small wooden mill house
with a gabled roof. It was supported on a single, wooden post
about which it could rotate. It is therefore referred to as
post mill. There is no evidence about the precise origin
of the windmill. It is likely to have originated from Northern
France and Southern England where in the 12th
century, domestic buildings were made of wood. Also the
monastic orders, especially the Cistercians, were showing
increasing interest in many forms of engineering.
The post was held to the ground by cross beams and ties. Its
upper end had an iron bearing that was engaged in an equally
sturdy cross beam within the mill. The rotor was made of four
lattice sweeps that were covered with cloth, also called
sails. |
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A painting depicting an ancient windmill |
These
were motorized into the windshaft. The windshaft was tilted at an
angle of about 10 degrees from the horizontal level, and rotated
through bearings in front and rear timbers of the mill house. The
teeth of a wooden crown wheel on windshaft was engaged between the
spokes of a cage-wheel, the axle of which drove the upper milestone.
Thus there was a gearing between the windshaft and millstone of a
ratio that allowed rapid movement of the stone.
Around 1180 AD, windmills were a popular sight in Western Europe.
They appeared not only on hilltops and in open countryside but also
on walls of cities and castles. |
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