Interesting Facts About Green Eyes
For safety and efficiency reasons wind turbines are subject to operating limits depending on the wind conditions and the system design. In other projects Wikimedia Commons. A newborn can actually inherit any eye color, no matter the eye color of the parents — though ancestry and heritage are other two factors that play an important role. To retain the optimum angle of attack as wind speed increases a fixed pitch blade must increase its rotational speed accordingly, otherwise, for fixed speed rotors, variable pitch blades must be used. Leave A Reply Cancel Reply. Argon is the most abundant noble gas in Earth's crust, comprising 0.
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Argon Chemical elements Noble gases Industrial gases. Rural Installations The economics of rural and remote locations make wind power more attractive than for urban locations. Domestic wind turbines located between buildings in urban environments rarely operate at peak efficiency suffering from turbulence as well as being shielded from the wind by buildings and trees. Though the turbine works with winds speeds right up to the cut-out wind speed, its efficiency is automatically reduced at speeds above the rated speed so that it captures less of the available wind energy in order to protect the generator. For a person to get green eyes, The yellow colored stroma should be present in the eyes.
Just as with aircraft wings, the lift resulting from the incident wind force increases as the angle of attack increases from 0 to a maximum of about 15 degrees at which point the smooth laminar flow of the air over the blade ceases and the air flow over the blade separates from the aerofoil and becomes turbulent. Above this point the lift force deteriorates rapidly while drag increases leading to a stall. See more about the angle of attack. For a given wind speed the apparent wind will be different at the root of the blade from the apparent wind at the tip of the blade because the rotational relative wind speed is different.
For a given speed of rotation, the tangential velocity of sections of the blade increases along the length of the blade towards the tip, so that the pitch of the blade must be twisted to maintain the same, optimum angle of attack at all sections along the length of the blade. The blade twist is thus optimised for a given wind speed. As the wind speed changes however, the twist will no longer be optimum.
To retain the optimum angle of attack as wind speed increases a fixed pitch blade must increase its rotational speed accordingly, otherwise, for fixed speed rotors, variable pitch blades must be used. The number of blades in the turbine rotor and its rotational speed must be optimised to extract the maximum energy from the available wind. While using rotors with multiple blades should capture more wind energy, there is a practical limit to the number of blades which can be used because each blade of a spinning rotor leaves turbulence in its wake and this reduces the amount of energy which the following blade can extract from the wind.
This same turbulence effect also limits the possible rotor speeds because a high speed rotor does not provide enough time for the air flow to settle after the passage of a blade before the next blade comes along. There is also a lower limit to both the number of blades and the rotor speed.
With too few rotor blades, or a slow turning rotor, most of the wind will pass undisturbed through the gap between the blades reducing the potential for capturing the wind energy.
The fewer the number of blades, the faster the wind turbine rotor needs to turn to extract maximum power from the wind. The notion of the Tip Speed Ratio TSR is a concept used by wind turbine designers to optimise a blade set to the shaft speed required by a particular electricity generator while extracting the maximum energy from the wind. For safety and efficiency reasons wind turbines are subject to operating limits depending on the wind conditions and the system design.
The cut-out speed is specified to be as high possible consistent with safety requirements and practicality in order to capture as much as possible of the available wind energy over the full spectrum of expected wind speeds See diagram of Wind Speed Distribution below. Windmills can only extract the maximum power from the available wind when the plane of rotation of the blades is perpendicular to the direction of the wind. To ensure this the rotor mount must be free to rotate on its vertical axis and the installation must include some form of yaw control to turn the rotor into the wind.
For small, lightweight installations this is normally accomplished by adding a tail fin behind the rotor in line with its axis. Any lateral component of the wind will tend to push the side of the tail fin causing the rotor mount to turn until the fin is in line with the wind. When the rotor is facing into the wind there will be no lateral force on the fin and the rotor will remain in position. Friction and inertia will tend to hold it in position so that it does not follow small disturbances.
Large turbine installations have automatic control systems with wind sensors to monitor the direction of the wind and a powered mechanism to drive the rotor into its optimum position. Electrical generating equipment is usually specified at its rated capacity. This is normally the maximum power or energy output which can be generated in optimal conditions.
Since a wind turbine rarely works at its optimal capacity the actual energy output over a year will be much less than its rated capacity. Furthermore there will often be periods when the wind turbine can not deliver any power at all. These occur when there is insufficient wind to power the turbine system, or other periods, fortunately only a few, when the wind turbine must be shut down because the wind speed is dangerously high and exceeds the system cut-out speed.
The capacity factor is simply the wind turbine generator's actual energy output for a given period divided by the theoretical energy output if the machine had operated at its rated power output for the same period.
Typical capacity factors for wind turbines range from 0. Thus a wind turbine rated at 1 MegaWatt will deliver on average only about kiloWatts of power.
For comparison, the capacity factor of thermal power generation is between 0. Though the force and power of the wind are difficult to quantify, various scales and descriptions have been used to characterise its intensity.
The Beaufort scale is one measure in common use. The lowest point or zero on the Beaufort scale corresponds to the calmest conditions when the wind speed is zero and smoke rises vertically. At force 3, wind speeds range from 3. Wind conditions are described as "light" and leaves are in movement and flags begin to extend. Wind conditions are described as "strong" and whole trees are in motion. Wind power has the advantage that it is normally available 24 hours per day, unlike solar power which is only available during daylight hours.
Unfortunately the availability of wind energy is less predictable than solar energy. At least we know that the sun rises and sets every day. Nevertheless, based on data collected over many years, some predictions about the frequency of the wind at various speeds, if not the timing, are possible. Care should be taken in calculating the amount of energy available from the wind as it is quite common to overestimate its potential.
You can not simply take the average of the wind speeds throughout the year and use it to calculate the energy available from the wind because its speed is constantly changing and its power is proportional to the cube of the wind speed. You have to weigh the probability of each wind speed with the corresponding amount of energy it carries. Experience shows that for a given height above ground, the frequency at which the wind blows with any particular speed follows a Rayleigh Distribution.
An example is shown below. An empirical formula developed by D. The histogram below shows this relationship. The histogram below shows the resulting distribution of the wind energy content superimposed on the Rayleigh wind speed distribution above which caused it. Unfortunately not all of this wind energy can be captured by conventional wind turbines.
For a given wind speed the wind energy also depends on the elevation of the wind turbine above sea level. This is because the density of the air decreases with altitude and the wind energy is proportional to the air density. This effect is shown in the following histogram. Turbulent conditions will reduce the amount of energy which can be extracted from the wind reducing in turn the overall efficiency of the system. This is more likely to be the case over land than over the sea.
Raising the height of the turbine above the ground effectively lifts it above the worst of the turbulence and improves efficiency. Domestic wind turbines located between buildings in urban environments rarely operate at peak efficiency suffering from turbulence as well as being shielded from the wind by buildings and trees.
Grid connected systems are dimensioned for average wind speeds 5. While offshore plants benefit from higher sustainable wind speeds, their construction and maintenance costs are higher. Large scale wind turbine generators with outputs of up to 8 MWe or more with rotor diameters up to metres are now functioning in many regions of the world with even larger designs in the pipeline. Large rotor blades are necessary to intercept the maximum air stream but these give rise to very high tip speeds.
The tip speeds however must be limited, mainly because of unacceptable noise levels, resulting in very low rotation speeds which may be as low as 10 to 20 rpm for large wind turbines. The operating speed of the generator is however is much higher, typically rpm, determined by the number of its magnetic pole pairs and the frequency of the grid electrical supply. Consequently a gearbox must be used to increase the shaft speed to drive the generator at the fixed synchronous speed corresponding to the grid frequency.
Note that a "synchronous generator" is one whose electrical output frequency is synchronised to its shaft speed. It is not necessarily synchronised to the grid frequency, although that is usually an objective and extra, external controls are necessary to achieve this.
A typical fixed speed system employs a rotor with three variable pitch blades which are controlled automatically to maintain a fixed rotation speed for any wind speed. The rotor drives a synchronous generator through a gear box and the whole assembly is housed in a nacelle on top of a substantial tower with massive foundations requiring hundreds of cubic metres of reinforced concrete.
Fixed speed systems may however suffer excessive mechanical stresses. Because they are required to maintain a fixed speed regardless of the wind speed, there is no "give" in the mechanism to absorb gusty wind forces and this results in high torque, high stresses and excessive wear and tear on the gear box increasing maintenance costs and reducing service life.
At the same time, the reaction time of these mechanical systems can be in the range of tens of milliseconds so that each time a burst of wind hits the turbine, a rapid fluctuation of electrical output power can be observed. For these reasons, variable speed systems are preferred over fixed speed systems. See more about the properties of synchronous generators. A variable speed generator is better able to cope with stormy wind conditions because its rotor can speed up or slow down to absorb the forces when bursts of wind suddenly increase the torque on the system.
The electronic control systems will keep the generator's output frequency constant during these fluctuating wind conditions. Rather than controlling the turbine rotation speed to obtain a fixed frequency synchronised with the grid from a synchronous generator, the rotor and turbine can be run at a variable speed corresponding to the prevailing wind conditions. This will produce a varying frequency output from the generator synchronised with the drive shaft rotation speed.
This output can then be rectified in the generator side of an AC-DC-AC converter and the converted back to AC in an inverter in grid side of the converter which is synchronised with the grid frequency. The grid side converter can also be used to provide reactive power VArs to the grid for power factor control and voltage regulation by varying the firing angle of the thyristor switching in the inverter and thus the phase of the output current with respect to the voltage.
See an explanation and more details of why reactive power is needed in the section about Power Quality and Voltage Support as used in the utility grid. The range of wind speeds over which the system can be operated can be extended and mechanical safety controls can be incorporated by means of an optional speed control system based on pitch control of the rotor vanes as used in the fixed speed system described above.
One major drawback of this system is that the components and the electronic control circuits in the frequency converter must be dimensioned to carry the full generator power. The doubly fed induction generator DFIG overcomes this difficulty.
DFIG technology is currently the preferred wind power generating technology. The basic grid connected asynchronous induction generator gets its excitation current from the grid through the stator windings and has limited control over its output voltage and frequency. The doubly fed induction generator permits a second excitation current input, through slip rings to a wound rotor permitting greater control over the generator output.
The DFIG system consists of a 3 phase wound rotor generator with its stator windings fed from the grid and its rotor windings fed via a back to back converter system in a bidirectional feedback loop taking power either from the grid to the generator or from the generator to the grid.
See the following diagram. The feedback control system monitors the stator output voltage and frequency and provides error signals if these are different from the grid standards. The frequency error is equal to the generator slip frequency and is equivalent to the difference between the synchronous speed and the actual shaft speed of the machine.
The excitation from the stator windings causes the generator to act in much the same way as a basic squirrel cage or wound rotor generator, See more about the properties of induction generators and how they work.
Without the additional rotor excitation, the frequency of a slow running generator will be less than the grid frequency which provides its excitation and its slip would be positive.
Conversely if it was running too fast the frequency would be too high and its slip would be negative. The rotor absorbs power from the grid to speed up and delivers power to the grid in order to slow down. When the machine is running synchronously the frequency of the combined stator and rotor excitation matches the grid frequency, there is no slip and the machine will be synchronised with the grid.
As with the in-line converter described above, by adjusting the timing of the GSC inverter switching, the GSC converter also provides variable reactive power output to counterbalance the reactive power drawn from the grid enabling power factor correction as in the in-line frequency control system described above. When the generator is running too slowly, its frequency will be too low so that it is essentially motoring.
The machine side converter takes DC power from the DC link and provides AC output power at the slip frequency to the rotor to eliminate its motoring slip and thus increase its speed.
If the rotor is running too fast causing the generator frequency to be too high, the MSC extracts AC power from the rotor at the slip frequency causing it to slow down, reducing the generator slip, and converts the rotor output to DC passing it through the DC link to the GSC where it is converted to the fixed grid voltage and frequency and is inserted into the grid.
The frequency of the rotor currents induced by transformer action from the stator is the same as the slip frequency and this is equivalent to the frequency error signal in the feedback loop.
The additional direct excitation of the rotor adds a second set of controlled currents to the currents already induced in the rotor by transformer action from the stator. These additional currents affect the rotation speed of the rotor in the same way as the stator induced currents, producing an additional driving torque on the rotor except that the additional rotor currents are independent of the speed of the rotor. The frequency of the control current supplied by the MSC can be precisely controlled to match and thus neutralise the slip frequency so that, with zero slip, the generator rotates at the synchronous frequency determined by the grid.
The greater the slip, the greater the compensating frequency required. To increase the speed of a slow running rotor, the phase sequence of the rotor windings is set so that the rotor magnetic field is in the same direction as the generator rotor producing negative slip to counteract and thus neutralise the rotor's positive slip. To reduce the rotor speed, the phase sequence of the rotor windings is set in opposite direction from the generator's rotation producing positive slip to counteract the rotor's negative slip.
When operating at synchronous speed the rotor current will be DC current and there will be no sip and no power flow through the rotor. The generator output voltage is determined by the magnitude of the excitation current supplied to the rotor and this can be adjusted by means of the rotor input voltage provided by the MSC. A chopper or pulse width modulator PWM is used to generate the variable DC control voltage necessary.
The converter feedback controls thus enable the excitation current to be regulated by the MSC to neutralise the voltage error signal and thus obtain a constant bus voltage matched to the grid voltage. Compared to xenon , argon is cheaper and has a distinct scintillation time profile, which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to 39 Ar contamination, unless one uses argon from underground sources, which has much less 39 Ar contamination.
The 39 Ar activity in the atmosphere is maintained by cosmogenic production through the knockout reaction 40 Ar n,2n 39 Ar and similar reactions. As a result, the underground Ar, shielded by rock and water, has much less 39 Ar contamination.
Neutrino experiments include ICARUS and MicroBooNE , both of which use high-purity liquid argon in a time projection chamber for fine grained three-dimensional imaging of neutrino interactions. Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents argon has the European food additive code E Aerial oxidation, hydrolysis, and other chemical reactions that degrade the products are retarded or prevented entirely.
High-purity chemicals and pharmaceuticals are sometimes packed and sealed in argon. In winemaking , argon is used in a variety of activities to provide a barrier against oxygen at the liquid surface, which can spoil wine by fueling both microbial metabolism as with acetic acid bacteria and standard redox chemistry. Argon is sometimes used as the propellant in aerosol cans for such products as varnish , polyurethane , and paint, and to displace air when preparing a container for storage after opening.
Since , the American National Archives stores important national documents such as the Declaration of Independence and the Constitution within argon-filled cases to inhibit their degradation. Argon is preferable to the helium that had been used in the preceding five decades, because helium gas escapes through the intermolecular pores in most containers and must be regularly replaced.
Argon may be used as the inert gas within Schlenk lines and gloveboxes. Argon is preferred to less expensive nitrogen in cases where nitrogen may react with the reagents or apparatus. Argon may be used as the carrier gas in gas chromatography and in electrospray ionization mass spectrometry ; it is the gas of choice for the plasma used in ICP spectroscopy.
Argon is preferred for the sputter coating of specimens for scanning electron microscopy. Argon gas is also commonly used for sputter deposition of thin films as in microelectronics and for wafer cleaning in microfabrication. Cryosurgery procedures such as cryoablation use liquid argon to destroy tissue such as cancer cells. It is used in a procedure called "argon-enhanced coagulation", a form of argon plasma beam electrosurgery. The procedure carries a risk of producing gas embolism and has resulted in the death of at least one patient.
Blue argon lasers are used in surgery to weld arteries, destroy tumors, and correct eye defects. Argon has also been used experimentally to replace nitrogen in the breathing or decompression mix known as Argox , to speed the elimination of dissolved nitrogen from the blood. Incandescent lights are filled with argon, to preserve the filaments at high temperature from oxidation.
It is used for the specific way it ionizes and emits light, such as in plasma globes and calorimetry in experimental particle physics. Argon is also used for blue and green argon-ion lasers. Argon is used for thermal insulation in energy-efficient windows.
Compressed argon gas is allowed to expand, to cool the seeker heads of some versions of the AIM-9 Sidewinder missile and other missiles that use cooled thermal seeker heads. The gas is stored at high pressure. Argon, with a half-life of years, has been used for a number of applications, primarily ice core and ground water dating. Also, potassium—argon dating and related argon-argon dating is used to date sedimentary , metamorphic , and igneous rocks.
Argon has been used by athletes as a doping agent to simulate hypoxic conditions. In , the World Anti-Doping Agency WADA added argon and xenon to the list of prohibited substances and methods, although at this time there is no reliable test for abuse. It is difficult to detect because it is colorless, odorless, and tasteless. A incident, in which a man was asphyxiated after entering an argon-filled section of oil pipe under construction in Alaska , highlights the dangers of argon tank leakage in confined spaces and emphasizes the need for proper use, storage and handling.
From Wikipedia, the free encyclopedia. This article is about the chemical element. For other uses, see Argon disambiguation. Pure and Applied Chemistry. Kirk Othmer Encyclopedia of Chemical Technology. Chemical Rubber Company Publishing. See Group periodic table. Retrieved 14 October Argon's not so noble after all — researchers make argon fluorohydride". Journal of Chemical Physics. Historical Remarks on the Discovery of Argon: The First Noble Gas.
University of Chicago Press. The Discovery of the Rare Gases. Proceedings of the Royal Society. A New Constituent of the Atmosphere". Philosophical Transactions of the Royal Society A.
The New York Times. Retrieved 1 February National Nuclear Data Center. Retrieved 14 January Archived from the original on 7 October Retrieved 8 March Archived from the original on 9 May Retrieved 7 March A review of matrix isolated Group 12 to Group 18 complexes". Journal of Physical Chemistry Letters. Retrieved 13 December Retrieved 12 September Recent Advances in Poultry Slaughter Technology.
Archived from the original PDF on 24 July Retrieved 1 January Journal of Applied Animal Welfare Science. Journal of Fire Protection Engineering.
Patent 6,, Issue date: Retrieved 7 July Aviation, Space, and Environmental Medicine. Retrieved 1 August Retrieved 2 March Archived from the original on 22 December State of Alaska Department of Public Health. Retrieved 29 January
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Argon is also used in incandescent , fluorescent lighting , and other gas-discharge tubes. Other noble gases would be equally suitable for most of these applications, but argon is by far the cheapest.
It is not necessarily synchronised to the grid frequency, although that is usually an objective and extra, external controls are necessary to achieve this. So what makes this type of eyes so interesting and attention-grabbing? Argon, with a half-life of years, has been used for a number of applications, primarily ice core and ground water dating.
High wind speeds cause high rotation speeds speed dating rayleigh high stresses in the wind turbine which can can result in serious damage to the installation. When the rotor is facing into the wind there will be no lateral force on the fin and the rotor will remain in position. For safety and efficiency reasons wind turbines are subject to operating limits depending on the wind conditions and the system design. Speed dating rayleigh well designed typical three-bladed rotor would have a tip speed ratio of around 6 to 7. A review vating matrix isolated Group 12 to Group speed dating nordjylland complexes". Furthermore, larger, speed dating rayleigh efficient wind power installations are possible and the prevailing winds will also be higher.
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