.. d A is the area. The number of blades on a windmill varies. There are many different types of windmills. The following equation helps figure out how fast the a certain-bladed windmill will rotate in relation to windmills with different numbers of blades: Speed of windmill=”1″ / sq.
root of number of blades The aerofoils of a four bladed machine rotate 71% as fast as that of a 2 bladed machine. A six bladed machine rotates at 58% and an 8 bladed machine rotates at 56% as fast as a 2 bladed machine. Electricity and Storage of Energy As mentioned previously, the generators in a wind turbine can convert the mechanical energy produced by the rotation of the shaft into electrical energy, DC. From there, some windmills have synchronous inverters, complex electronic devices which convert the DC generated by the turbines into AC. This is an expensive option. There is a loss of power as well through its processes. Others have induction generators, which produce AC current without a synchronous inverter and less power loss.
The energy extracted from the wind and converted into mechanical energy then electrical energy by the generator must be stored, since it is not used generally used all at once. It is important to keep a surplus of energy for usage when the wind is not bl owing fast enough, despite the corrections that can be made in the pitch of the aerofoil blades and when the windmill is out of service or the demand is especially high. Storing the wind’s energy effectively is the key to its long-term use. Windmills used as water pumpers or air-compressors can pump excess water, hydrogen or air into reserve tanks. Today, there are a number of ways to store the wind’s energy. Windmills are used to charge Electrolyte batteries. Lead-acid or Lead-cobalt car batteries are commonly used as well.
However, batteries may be expensive and inefficient–they may lose 10-25% of the energy stored in them. Nickel-Iron, Nickel-cadmium, and zinc-a ir cells are often used as well. These tend to be more efficient. Some windmills are now using organic electrolyte batteries such as CuCl2, Ni Cl2, and NiF2 batteries as well as sodium-sulfur batteries, which operate at high temperature, are used. Although uncommon and still in experimental phases, some energy is stored not by being converted directly into electrical energy, but rather by being stored as thermal or electromagnetic energy, Sound Fluids are elastic. Pressure waves are constantly being created and propagated by the aerofoils and the turbine as a whole (entire components excepting the support). We can hear them in the sound given off. The sound intensity is directly proportional with the speed of the windmill.
The frequency of the waves is directly proportional to the angular speed of the blades on the rotor. The flutter you hear has aerodynamic and elastic properties. The higher speed the aerofoils are, the louder the sound a nd the louder the flutter they will make, as more pressure waves are being created and propagated. The generators are noisy. They often confuse birds and cause them to fly towards the turbine. Windmills can be very noisy. A 300 kW turbine at 1 mile away has a dB level equal to a traffic light 100 feet away (Gipe).
Windmill sound levels are regulate d. The sound level must be kept under 46 dB in a residential area. Wind turbines can cause interference, disturbances with TV and radio reception (ghost images on TVs), affect microwaves and disrupt satellite communication. These problems are currently being resolved. Many have already been fixed.
There is also a .009 probability of a bird or insect being struck by the blades. Windmill makers must use artificial sound or florescent paint or scents to scare away flying creatures. Brakes Mechanical brakes are used to hold windmills at rest when they are not needed, are not functioning, or are under repair. Greek windmills used sticks or logs jammed into the ground to keep the windmill stopped, but modern brakes are more sophisticated. Many windmills today use airbrakes like those used in planes. Other windmills have rope brakes.
Ropes connected to the aerofoils are simply pulled and tethered to a post to keep the aerofoils from turning. The torque on a rope brake can be calculated b y the equation (M-m)(R2 + r)g. The Types of Windmills There are a number of types of windmills. They are divided into Horizontal-Axis and Vertical-Axis types. Low speed horizontal-axis windmills are used for water pumping and air compressing.
American windmills (of the Midwest) are an example. Earlier wi ndmills such as the ones in England and Holland build a couple hundred years ago are another example. The horizontal-axis was invented in Egypt and Greece in 300 BCE. “It had 8 to 10 wooden beams rigged with sails, and a rotor which turned perpendicular to the wind direction” (Naar 5). This specific type of windmill became popular in Portugal and Greece.
In the 1200’s, the crusaders built and developed the post-mill, which where used to mill grain. It was first used to produce electricity in Denmark i n the late 1800’s and spread soon after to the U.S. In America, windmills made the great plains. They were used to pump water and irrigate crops. During World War I, farmers rigged windmills to generate 1 kW of DC current. They mounted their devices o n the tops of buildings and towers.
On western farms and railroad stations, the pumping windmill was 20-50 feet high with a 6-16 foot wheel diameter” (45)]. With 10-mph wind speed, a 6 foot-diameter wheel, a 2-foot diameter pump cylinder, a windmill-pump could lift 52 gallons per hour to a height of 38 feet. A 12-foot in diameter wheel could lift 80 gallons per hour to a height of 120 feet. (Naar, p. 46).
The growth of wind-electricity in America was greatly stunned in 1937 with the Rural Electrification Act, which made low-cost electricity more available. However, in the 1970’s, due to oil shortages, earlier prototypes of high-speed horizontal-axis windm ills were developed. High-speed horizontal-axis types are used for many purposes, come in many sizes. These include the typical windmills on a California windmill farm and other windmill farms, and any other wind turbines in which the shaft turned by th e aerofoils is horizontal. High-speed horizontal types may have 1, 2, 3, 4, or many aerofoils.
Low-speed types such as European ones have much larger aerofoils in relation to their height above the ground. Low speed types such as American Midwest ones are usually a pinwheel, with many small blades encircled with an outer frame like a wheel. Vertical-axis windmills were first developed in the Persians in 1500 BCE to mill corn. Sails were mounted on a boom, which was attached to a shaft that turned vertically. By 500 BCE, the technology had spread to Northern Africa and Spain.
Low-speed ve rtical-axis windmills are popular in Finland. They are about 150 years old. They consist of a 55-gallon oil drum split in half. They are used to pump water and aerate land. They are inefficient. High-speed vertical-axis windmills include the Darrieus models. These have long, thin, curved outer blades, which rotate at 3 to 4 times the wind speed.
They have a low starting torque and a high tip-speed ratio. They are inexpensive and are used for electricity generation and irrigation. There are three types, the delta, chi, and gamma models. All models are built on a tripod. The advantages to a Darrieus-windmill are that it can deliver mechanical power at ground level.
The generator, gearbox, and turbine components are on the ground, instead of at t he top of a tower as in horizontal-axis windmills. They cost much less to construct, because there is less material, and the pitch of the blades does not have to be adjusted. Another type of HSVAW’s are the Madaras and Flettner types, revolving cylinder s which sit on a tracked carriage. “The motion of a spinning cylinder causes the carriage to move over a circular track and the carriage wheels to drive an electric generator” (Justus). The Savonius model, which originated in Finland in the 1920’s, is a n S-shaped blade, which rotates and turns a vertical shaft. Today, these types of windmills are very popular with scientists and their technology is being developed.
Windmills Today Many windmills are used today: some estimates say 150,000 (Cheremisinoff 31), in the Midwest. They are used to heat water, refrigerate storage buildings or rooms, refrigerate produce, dry crops, irrigate crops, heat buildings, and charge batteries for tr actors on farms (33). Ever since the energy shortages of the 70’s, the growing concern of pollution due to the burning of fossil fuels and the depletion of natural resources, windmills have been greatly studied and developed. Today, Sandia National Laboratories, Alcoa, GE, Boe ing, Grumman, UTC, Westinghouse, and other scientists are researching and developing Darrieuses and new types of windmills. Today, windmills are used to operate sawmills and oil mills in Europe.
They are used in mining to extract minerals, to pump water , to generate electricity, and to charge batteries. “Windmills have been used on buoys moored far out in the ocean, the power being used for the collection and transmission of oceanographic and weather data. They also work in deserted places as an aid t o radio and telephone communications and they are used to work navigation lights on isolated hazards” (Calvert 77). My Windmill I built a windmill of my own. The goal of the windmill was to get as much electrical energy as possible.
This immediately ruled out any new-wave type windmill. Instead, I went to Home Depot and got a returned ceiling fan. I took off the white box wit h the motor and switches and left the spinning black box on. I mounted the blades on the black box. I put this on a post and a support.
Then I got a Maxon DC motor and, after fashioning a clamp-like device to hold the motor on to the support, I put a r ubber tire on the spinning shaft of the motor and adjusted it so that this rubber tire would be rotated by the spinning black box upon which the blades spun. Next, I attached two large wires to the motor. I then made a circuit. This circuit was a littl e difficult to make. It had a place for the wires from the motor, ran through resistors and a variable resistor, and then an Ammeter and then the place where I was to plug in the light. In parallel was a place for a battery and/or a voltmeter.
After a few minor adjustments, I was ready to test my product. At first, when the circuit was completed, the current flow was very low. There were a number of adjustments I had to make in order to make the windmill work better. First, I moved the fan that was blowing air on the blades, farther away. I added a seco nd fan and adjusted the angle of these two so that they were blowing at the center of the windmill. I turned the windmill around so that it faced away from the fans.
I loosened the screws that held the blades on. I inserted a piece of cardboard 1/3″ th ick into this space. This was to adjust the pitch angle of the blades so that they would “cut through” the air better. The adjustments I made were excellent. They worked.
When I connected everything, I began to notice an immediate change in the Ammete r. I was seeing as much as 20 milliamps and 6.1Volts. Before, there were 5 milliamps and 3.5 Volts. I began to experiment more with the angles of the fans, distances, and stuff like that. For my light source, I used a green light.
It had an internal resistance of 450 ohms. This bulb was 1/2 W. It lit up easily and was bright. The Future The Future will likely bring bigger and better things for the wind turbine. Many new wind turbine models are being built.
The wind turbine holds much promise for energy production in the years to come. BY DAN TORTORA Bibliography Calvert, N. G. Windpower Principles: Their application on the small scale. London: Charles Griffin and Co., Ltd., 1979. Cheremisinoff, Nicholas P. Fundamentals of Wind Energy.
Ann Arbor: Ann Arbor Science Publishers, Inc. 1978. Gipe, Paul. Wind Energy Comes of Age. New York: John Wiley and Sons, Inc. 1995.
Hau, E., J. Langenbrinck, and W. Palz. Large Wind Turbines. Berlin: Springer-Verlag, 1993. Hills, Richard L. Power From the Wind: A History of Windmill Technology.
London: Cambridge University Press, 1994. Justus, C. G. Winds and Wind System Performance. Philadelphia: The Franklin Institute Press, 1978.
Naar, Jon. The New Wind Power. New York: Penguin Books, 1982. Taylor, R. H. Alternative Energy Sources for the Centralized Generation of Electricity.
Bristol, England: Adam Hilger, Ltd. 1983. 14 7.