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How Windmills Work

explanatory Essay
979 words
979 words
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How Windmills Work Should it be called a starmill?The windmill is driven by energy from the star which we call the sun. The sun is 71% hydrogen and 27% helium. The very high temperature and pressure inside the sun cause nuclear fusion: hydrogen and helium nuclei combine and produce vast quantities of heat. Fortunately, the sun is 150,000,000 kilometres away from us, and has enough hydrogen left to burn for billions of years.As the earth rotates and orbits the sun, radiation from the sun warms the atmosphere, the clouds, the surface of the ground, and the surface of the sea. As a result, different parts of the atmosphere are at different temperatures. This causes differences of pressure. The attempt to equalise the pressure in different parts of the atmosphere is known as wind.So a windmill could be called a starmill, a sunmill, or a nuclear fusion mill, but we call it by the energy source which is closest and most familiar to us, the wind. How the energy of the wind is capturedThe diagram on the left shows a board - seen from above - being held up in the wind. If you hold the board still, the moving air will mostly flow round the left-hand side. If you let the board go, the wind will push it back and to the right. If you only allow the board to move to the left or the right, the board will be pushed to the right. Windmills usually have four boards held at an angle to the wind.The sweep on the left is taken from the photograph on the Home Page. Its right edge is closer to you than the left edge. The wind blows from where you are, and will tend to flow round the left edge. The sweep cannot be blown backwards, because it is fixed to a central axle (called the windshaft) which points into the wind. If the windshaft is free to rotate, the sweep is pushed to the right. In other words, the windmill's sweeps or sails always rotate anticlockwise.In the Middle Ages, sails were made of cloth attached to lengths of wood. Later, they were made entirely of wood, and since the eighteenth century have often been called sweeps. Two problems To work efficiently, the sweeps must always face directly into the wind, the direction of which often changes. The sweeps must also be able to deal with changes in the strength of the wind, which are unpredictable.

In this essay, the author

  • Explains that a windmill is driven by energy from the sun, which is 71% hydrogen and 27% helium. the sun is 150,000,000 kilometres away, and has enough hydrogen to burn for billions of years.
  • Illustrates how the wind's energy is captured by a diagram on the left. if you hold the board still, the moving air will mostly flow round the right-hand side.
  • Explains that windmills have four boards held at an angle to the wind. the sweep is fixed to a central axle, and if the windshaft is free to rotate, it rotates anticlockwise.
  • Explains that in early mills, both problems required constant attention from the miller. two inventions in the eighteenth century made the life of millers easier.
  • Describes the fantail, which is like a small windmill fixed to the back of the cap, but the shaft faces across the wind instead of into it.
  • Describes the spring sail, which works like a venetian blind. the shutters can be closed or opened at different angles to reduce the force of the wind on the sweep.
  • Explains how the sweeps cause the windshaft to rotate. around the shaft is bolted an iron brakewheel 2.62 metres in diameter.
  • Illustrates how the brakewheel engages with teeth on a smaller wheel, the "wallower", which is connected to the great spur wheel two floors below it. it also drives the sack hoist.
  • Illustrates how the grain is tipped through apertures in the floor, and then directed down chutes to the rotating upper millstones.
  • Illustrates how the stone's shaft descending vertically ends in a fork which engages with the metal bracket fitted to the bottom of the upper stone.
  • Describes how the lower stone is supported on beams, with wedges used for levelling, and the upper stone on the vertical shaft upper centre, which rotates with the stone. the governor is driven via a leather belt.
  • Explains that the flour or animal feed produced by grinding could be collected in the bins themselves, or in sacks attached to the chutes.
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