Hydro and Wind Mills from olden days

Oct 31, 2012   //   by admin   //   Knowledge Base  //  No Comments

Hydro and Wind Mills from olden days

Water Energy and Wind Energy are the oldest form of renewable energy. Since ancient times it has been used as a perennial source of energy. Given below is a brief description of water mills and wind mills in ancient times: –

Watermills:

The ancient Greek people were the first to use underwater and breast shot water mills. They invented two main components – water wheel and tooth gearing along with romans. Some instances from Alexandrian war also explains how Caesar’s enemies used geared water wheels to pour sea water from elevated places on the position of the trapped Romans. The Romans used both fixed and floating water wheels and introduced water power. “Roman Mills” were different from traditional “greek mills”. Greek style mills are water wheels with a horizontal wheel and vertical shaft.  They are older and simpler of the two designs, but only operate well with high water velocities and with small diameter millstones. While Roman style mills have vertical wheels with horizontal shaft & are more complicated as they require gears to transmit the power from a shaft with a horizontal axis to one with a vertical axis.

A typical traditional mill used a diversion or impoundment to divert water to a turbine or water wheel via a pipe or a channel. The force of water movement or kinetic energy of water will in turn rotate the axle which drives other machineries. Water mills can be classified in to two types – Horizontal & vertical water mills. The horizontal water mills are the oldest. In these mills the force of water after striking the water wheel turned a runner stone balanced on a shaft. Vertical mills were of three kinds: Under shot, Over shot and Breast Shot. Undershot water wheel was simple set up in main stream of water & was driven by the main thrust of water. Over shot wheels were used by pouring water on the top of the wheel. The water fills buckets built into the wheel, as the bucket fills wheel is turned by the weight of the water. These require a construction of a small dam or millpond. Breast shot water wheels used water power of water poured at point of one- third of the height of the wheel, causing the wheel to revolve in a direction opposite to that of the flow of the water in mill race.

By the end of 19th century Pelton wheel came into existence which extracted energy from the impulse of water. Like traditional overshot waterwheels these are driven by weight of water. As water flows into the spoon shaped bucket mounted on the edge, the direction of the water velocity changes to follow the contour of the bucket. When the water-jet contacts the bucket, the water exerts pressure on the bucket and the water is decelerated as it does a “U-turn” and flows out the other side of the bucket at low velocity. In the process, the water’s momentum is transferred to the turbine. And the impulse produced works on the turbine. Pelton wheels were more efficient than other forms and hence were used for generating hydropower.

 

Windmills: –

Windmills were used mainly for grinding grain for food production and other industrial uses like to pump water, generating electricity, extracting groundwater etc. The wind wheel of the Greek engineer Heron of Alexandria in the 1st century AD is the earliest known instance of using a wind-driven wheel to power a machine. However the first known practical use were in Sistan. Another instance from Chinese history in 4th century as “prayer wheels”. Babylonians used windmills for irrigation purposes in 17th century. There were two types of windmills depending upon their configurations: Horizontal and vertical windmills.

Horizontal windmills had sails that rotated in a horizontal plane around a vertical axis. “Panemone windmills” were among the earliest known windmills which were used by Persians in 9th century. These “Panemone” were vertical axle windmills, which had long vertical drive – shafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water, and were used in the grist milling and sugarcane industries. Some types of windmills with vertical axis were used by Chinese for irrigation in 13th century. Horizontal windmills were also used in Europe in eighteenth and nineteenth century for e.g. Fowler’s mill and Hopper’s mill. Fowler’s mill had a three storey base with twelve sided structure, wind mill was mounted on this structure. The main advantage of an vertical axis turbine is that they does not need to be pointed into the wind to be effective. This is having much advantage where the speed of wind is variable. And the main disadvantage is that they have low rotational speed with higher torque hence are less power coefficient.

Vertical windmills have horizontal axis turbines and sails into vertical direction. It was first used in North-Western Europe in 12th century. These were used to grind cereals. There were three common types of vertical windmills in Europe: –  Post Mills, Tower Mills  and Smock Mills.

Post Mills were the earliest type of European windmills. The mills were mounted on a single vertical post, around which it can be turned to bring the sails into the wind. Some post mills are also “Hollow Post Mills”. In these mills machinery is driven in the base or roundhouse. Tower Mills consists of a brick or stone tower which can rotate to bring the sails into the wind. These have advantages over traditional Post Mills as they could stand much higher, bear larger sails, and thus afford greater reach into the wind. It is not necessary to turn the whole mill. These more efficient then watermills hence were used for grinding spices, powering sawmills and were used to change pulp into paper. Smock mills are even more practical version of Tower mills, Smock mills have a wooden framework “smock” which is an octagonal plan, though examples with more, or fewer, sides exist. The smock is thatched, boarded or covered by other materials like slate, sheet metal or tar paper. These were used for a variety of industrial purposes.

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