Use Of Large Tower Mills example essay topic

The history of wind power shows a general evolution from the use of simple devices driven by drag forces to heavy material to efficient aerodynamic lift devices. Aerodynamic lift isn't a modern concept. The earliest known use of wind power was the sailboat. Ancient sailors understood lift although they didn't understand the physics to explain how it worked.

Early windmills were used for tasks like grain grinding and water-pumping. The earliest known design was the vertical axis system developed in Persia in about 500 AD. The first known documented design is also of a Persian windmill. It had vertical sails made of bundles of reeds, which were attached to the central vertical shaft by horizontal struts. Grain grinding was the first documented windmill application. A grinding stone was attached to the same vertical shaft.

The machinery was commonly enclosed in a building which featured a wall to block incoming wind. This prevented wind from slowing the drag-type rotor. Vertical axis windmills were also used in China. The belief that the windmill was invented in China more than two thousand years ago is widespread.

The earliest documentation of a Chinese windmill was in 1219 AD. The primary applications were grain grinding and water pumping. The first windmills to appear in Western Europe were of the horizontal-axis system. The reason for the sudden evolution from the vertical-axis design is unknown. European water wheels served as the technological model for early windmills.

These mills used wooden cog and ring gears to turn the grindstone. This gear was adapted for use on post mills from the horizontal-axis water wheel. As early as 1390 the Dutch set out to refine the tower mill design. It had first appeared in the Mediterranean. The Dutch fixed the standard post mill to the top of a multi story tower. The tower had separate floors devoted to grain grinding, removing chaff, storing grain and living quarters.

Living quarters were for the wind-smith so he had a place to live. Both the post mill and tower mill design was oriented into the wind manually, by pushing a large lever at the back of the mill. The wind-smith's jobs were protecting the mill from damage by furling the rotor sails during storms. A primary improvement of the European mills was their designer's use of sails that generated aerodynamic lift. This feature provided better rotor efficiency compared with Persian mills by allowing an increase in rotor speed. This allowed superior grain grinding and pumping action.

The process of perfecting the windmill sail in efficiency took 500 years. By the time the process was completed, windmill sails had all the major features recognized by modern designers as being crucial to performance. Windmills had camber along the leading edge. They also had a nonlinear twist of the blade from root to tip. Some models also featured aerodynamic brakes, flap and spoilers.

These mills were the "electrical motor" of pre-industrial Europe. Applications were diverse, ranging from the common water-well, irrigation or drainage pumping using a scoop wheel. They were also used for grain grinding, saw milling of timber and processing of other commodities such as spices, cocoa, paints and dyes. Tobacco was also another commodity.

While continuing well into the 19th century, the use of large tower mills declined with the increased use of the steam engine. The next spurt of wind power development occurred many thousands of miles to the west. For hundreds of years the most important application of windmills at the subsistence level has been mechanical water pumping. Small systems with rotor diameters of one to several meters were used for this.

These systems were perfected in the United States during the 19th century. The Holladay windmill in 1854 was the first then the Aer motor and Dempster designs. All are still in use today. The first windmills had four paddle-like wooden blades.

They were followed by mill with thin wooden slats nailed to wooden rims. Most of these mills had tails to direct them into the wind. Some were weather-van ing mills that operated downwind of the tower. Hinging sections of blades so that they would fold back like an umbrella in high winds provided speed control of some models. This action reduced the rotor capture area to reduce thrust. The most important refinement of the American fan-type windmill was the development of steel blades in 1870.

Steel blades could be made lighter and worked into more efficient shapes. They worked so well that their high speed required a reduction gear to turn the standard reciprocal pumps at the required speed. Between 1850 and 1970, over six million mostly small mechanical output wind machines were used to pump water in the United States alone. Very large windmills with rotors up to eighteen meters in diameter were used to pump water for steam railroad trains that provided the primary source of commercial transportation in areas where there were no navigable rivers. The first use of a large windmill to generate electricity was a system built in Cleveland, Ohio in 1888 by Charles F. Brush. The Brush machine was a post mill with a multiple bladed "picket-fence" rotor seventeen meters in diameter.

It featured a large tail hinged to turn the rotor out of the wind. It was the first windmill to incorporate a step-up gearbox in order to turn a direct current generator. Despite its relative success in operating for 20 years, the Brush windmill demonstrated the limitations of the low-speed, high-solidity rotor for electricity production applications. The twelve kilowatts produced by a modern lift-type rotor. In 1891, Dane Poul La Cour developed the first electrical output wind machine that displayed the aerodynamic design principles. It was used in European tower mills.

The higher speed of the La Cour rotor made these mills practical for electricity generation. By the end of World War I the use of electrical output machines had spread throughout Denmark, but cheaper and larger fossil-fuel steam plants soon put operations of these mills out of business. By 1920 the two dominate rotor configurations had both been tried and found to be inadequate for generating large amounts of electricity. Further development of wind generator electrical systems in the United States was inspired by the design of airplane propellers and monoplane wings. The first small electrical-output wind turbines simply used modified propeller to drive direct current generators. By the mid 1920's wind generator's developed by companies like Parris Dunn and Jacobs Wind-electric found widespread use in the rural areas of the Midwestern Great Plains.

These systems were installed at first to provide lighting for farms and to charge batteries used to power crystal radio sets. But their use was extended to an entire array of direct-current motor-driven appliances such as refrigerators, freezers, washing machines and power tools. But the more appliances were powered by the early wind generators, the more their operation became a problem. The demise of these systems was hastened by during the late 1930's and the 1940's by two factors: the demand of farmsteads forever-larger amounts of power, and the Great Depression. The Great Depression spurred the U.S. federal government to stimulate the depressed rural economics by extending the electrical grid throughout those areas.

While the market for a new small wind machine of any type had been largely eroded in the U.S. by 1950, the use of mechanical and electrical system continued throughout Europe. It also continued in windy, arid climates such as those found in parts of Africa and Australia. The development of bulk-power and utility-scale wind energy conversion systems was first created in Russia in 1931. This machine operated for about two years on the shore of the Caspian Sea. Experimental wind plants in the United States, Denmark, France, Germany and Great Britain during this period of 1935-1970 showed that large-scale wind turbines could work but failed to result in a practical large electrical wind turbine.

The largest was the 1.2-megawatt Smith-Puttnam machine, which was installed in Vermont in 1941. This horizontal axis design featured a two bladed, 175-ft. diameter rotor with a 16-ton stainless steel rotor. In 1945, after only several hundred hours of operation, one of the blades broke off near the hub. This was a cause of metal fatigue.

European developments continued after World War II when temporary shortages of fossil fuels led to higher energy costs. As in the U.S. the primary application for these systems was interconnection to the electric power grid. In Denmark the Gedser Mill wind turbine operated successfully until the early 1960's when declining fossil-fuel prices once again made wind energy uncompetitive with steam-powered generating plants. This machine featured a three-bladed upwind rotor with fixed pitch blades that used windmill technology with an airframe support structure. The design was much less complex than the Smith-Puttnam design. In Germany, Professor Ulrich Hitler developed a series of advanced, horizontal-axis designs of airfoil-type fiberglass and plastic blades with variable pitch to provide lightweight and high efficiencies.

This design approach sought to reduce bearing and structural failures. A unique feature that was used was the use of a bearing at the rotor hub that allowed the rotor to teeter in response to wind gusts. Hutter's advanced designs achieved over four thousand hours of operation before the experiments were ended in 1968. Post war activity in Denmark and Germany largely dictated the two major horizontal-axis design approaches of wind turbine development in the early 1970's. This refined the simple, fixed pitch, Gedser Mill design by utilizing advanced materials.

The engineering innovations of the lightweight and higher efficient German machines such as a teeter hub, which were used later by U.S. designers. G.J.M. Darrieus began the development of modern vertical-axis rotors in France in the 1970's. Of the several rotors Darrieus designed, the most important one is a rotor comprising slender. Major development work on this concept did not begin until the concept was reinvented in the late 1980's by two Canadian researchers.