Wind Power
Template:EventLinksBox This event involves the construction of a device that can turn wind into energy and the answering of questions relating to alternative energy. This also refers to the C division event Physics Lab. See the original Physics Lab page for information about the old event.
The Basics of the Event
Half of your score for Physical Science Lab is how well you do on the building. You have to create a wind turbine-like object using a CD and other materials. During competition, they will attach your device to a CD motor. You will then place a fan in front of your device and turn it on. Your blade will spin therefore creating voltage. The higher your voltage, the better your score. You must include a standard CD in your wind turbine.
Safety spectacles with side shields are required for the blade testing portion of this event.
The Building Section
When you plan to build your device, there are many factors to consider. Some of them include:
- Wind turbine Diameter
- Weight
- Blade Width
- Curve of the Blade
- Blade Pitch
- Number of Blades
- Blade Material
- Alteration of CD or not
Something else you might want to think about is how heavy your device is. If your device is lighter, it can spin faster, therefore producing more voltage. You can use various items to construct your blades. Balsa wood is sometimes used as it is very light. You could also find different items around your house to use as blades. Plastic cups, when cut in half, can be a good idea. You just have to experiment with different factors. According to the New York Coaches Conference, taller towers increase energy production. They also say that doubling the diameter of the circle made by the blades produces a 4-fold increase in power.
When you research windmills, there is something that you must consider. The windmills for this event are not perfectly analogous to windmills in real life. Real life wind turbines have the objective of producing a large amount of power cheaply and safely. Our windmills have the objective of spinning as fast as possible, producing the most voltage.
Because of this, many teams have found that while real life windmills can create more power (not the same as voltage) by increasing the diameter of the blades, our windmills generally can spin faster by decreasing diameter.
Weight may be the most important factor in your voltage. The relationship between weight and voltage is simple- all other factors constant, a lighter windmill will produce higher voltage. You should try to cut weight in your turbine wherever possible. However, remember to not let cutting weight interfere with the success of your turbine, so make sure it is strong enough while being light. I'll touch on weight a bit more later.
For blade width, we should keep weight vs strength in mind. With thin blades, you have less weight, and therefore it can spin faster. However, there is a "limit". For a given material, if you make your blades too thin, they will obviously be weak. As well, you need some width for the wind to affect. Experimentation can show you the limit of blade width.
You may also want to introduce some curve into your blade, although it is not necessary to get a spinning windmill. A V-shape would also be ok. Depending on the material, you may be able to cut it into a curved shape, soak it in water and bend it into a curved shape, or just mold it into the right shape. Not a lot of curve is necessary.
Blade pitch refers to the angle of the blades relative to the CD. Generally, a lower pitch results in a higher speed and thus a higher voltage. I don't believe ridiculously low pitches, like 0-5 degrees, would work well (but I haven't tried it), but try to keep the pitch pretty low. Again, testing is the only way to see what will and will not work.
When considering number of blades, weight again comes into play, along with balance. More blades will be more forgiving balance-wise, but the extra weight will limit your voltage. Three blades tend to be a good trade off for a beginning or average builder, but, theoretically, two- or even one-bladed designs are better, as they are lighter and also have less drag.
Balance is also an important factor. If your turbine is terribly off balance, it may wobble on the mount, and could even break. As well, a well-balanced turbine will be able to spin faster, since it will not be bumping against the mount and wasting energy wobbling. You should make sure your turbine's center of gravity is at or very nearly at the center. You can adjust it by taking some mass off of the turbine on the heavy side, or by adding a small amount of clay on the lighter side.
With blade material, you must again consider weight vs strength. You can not use metal, which would probably be a bad material anyway, but you can use nearly any other material. So long as it is light and rigid under wind, any material will do. I'll leave finding the best material up to you.
Alteration of the CD is a good idea. You want to reduce mass, and the CD is just a lot of weight doing nothing for you. You can not alter the center hole, and you need a bit of plastic to attach your blades to, but you should probably cut off the rest. You can use scissors, a hole saw, a band saw, or a soldering iron may work as well. A whole CD is just dead weight that may even interfere with the airflow over your blades.
For the competition, you are allowed to bring in 2 turbines in Division B, but only 1 turbine in Division C. Also, make sure that your turbine is clearly within specs.
Written Portion
The other half of your score is the written portion. The rules recommend that you look at Alliant Energy and American Wind Energy Association. The main topics this year regard alternative energy and the physics of energy and heat. These topics involve several formulas.
Alternative Energy
Alternative energy is generally defined as energy that does not harm the environment directly. They usually do not produce carbon emissions and many times they are also renewable. There are several types of renewable energy, each with its own advantages and disadvantages.
- Solar power converts sunlight into energy via photovoltaic panels or concentration. It is generally constant as the Sun will shine constantly for millions of years unless a catastrophic event occurs, but it is costly and clouds can interfere with the efficiency.
- Wind power converts wind into energy, usually with turbines. Wind is plentiful and the method has no emissions, but turbines can be unwelcome both visually and environmentally. Also, periods of wind are more unpredictable than some other methods.
- Hydroelectric power converts the movement of water into energy, generally with turbines as well. the flow of water is abundant, constant, and hydroelectric plants can store energy for times when it is more necessary, but there are concerns in respect to the reservoirs created by dams.
- Tidal power is a major subset of hydroelectric power. It uses the movement of water created by tides to get energy. Tides are regular and predictable, but less power can be generated this way than some other ways.
- Ocean Thermal Energy Conversion (OTEC) utilizes the difference in temperature from shallow water to deeper water. When heat goes from the warmer water to cooler water, an engine converts the flow to energy. This is constant, but not very cost-effective and finding locations where this technology can be used is difficult.
- NOTE- In the 2010 rules, OTEC is incorrectly listed as meaning Oceanic Tidal Energy Currents. This error was corrected in the 2011 rules.
- Geothermal power converts underground heat into energy. This method is reliable, cost-effective, and environmentally friendly, but is mostly limited to areas with a high tectonic activity.
To conserve energy, the adage "reduce, reuse, recycle" can be followed. These three concepts can be applied to many techniques used to conserve energy.
Physics
There is also a section in the rules regarding energy, work, and heat and heat transfer concepts.
Energy
Energy is the capacity to perform work. Work, in turn, is when a force is exerted on an object and the object moves parallel to the direction of the force. Work, in joules (J), can be calculated by multiplying the force applied in Newtons (N) to the distance traveled in meters (m). Power is the rate at which this work is performed, and is found by dividing the work by the time. It is measured in watts.
There are two major types of energy:
- Kinetic energy is the energy contained by an object in motion
- Potential energy is how much work an outside force like gravity can do on an object depending on its position.
The Conservation of Energy principle states that energy cannot be created nor destroyed, and that it can only be transformed from one form to another.
Heat
Heat is the transfer of energy from a high-temperature object to a low-temperature object.
Temperature
Temperature is the average energy contained in the particles of an object. It is produced by the thermal energy in free particles. Many scales can measure temperature.
- Celsius scale
- was created in 1744
- is named after Anders Celsius
- bases its scale on the values of 0°C at water's freezing point and 100°C at water's boiling point
- Fahrenheit scale
- was created by Daniel Fahrenheit in 1724
- Places water's freezing point at 32°F and its boiling point at 212°F so they are 180° apart.
- Kelvin scale
- created by Lord Kelvin in 1848
- uses same scale as Celsius but puts 0 K at absolute zero (the hypothetical lowest temperature), making it always 273.15 units higher
- does not use ° symbol; is only K.
- Rankine scale
- created by William Rankine in 1859
- is Kelvin-Celsius equivalent to Fahrenheit; 0 °R is absolute zero and it is always 459.67 degrees higher than °F.
An important conversion factor is that between Celsius and Fahrenheit, and vice versa. The calculations are:
- [math]\displaystyle{ C=\frac {5}{9} \left ( F-32 \right ) }[/math]
- [math]\displaystyle{ F=\frac {9}{5} C +32 }[/math]
Where C is the temperature in Celsius and F is the temperature in Fahrenheit.
Heat Transfer
There are three main vehicles for transferring heat:
- Conduction is the transfer of heat by direct contact. The heat transfer for convection can be calculated by the following formula:
- [math]\displaystyle{ Q=\frac {kA\left (T_{hot}-T_{cold}\right )}{d} }[/math]
- Where
- Q is the heat transferred in [math]\displaystyle{ Watts }[/math]
- k is the barrier's thermal conductivity in [math]\displaystyle{ k=\frac {watts}{m K} }[/math]
- A is the cross-sectional area in [math]\displaystyle{ m^2 }[/math]
- T is the temperature in °C ([math]\displaystyle{ T_{hot} }[/math] represents the warmer temperature and [math]\displaystyle{ T_{cold} }[/math] represents the cooler temperature)
- d is the barrier's length in [math]\displaystyle{ m} }[/math]
- Convection is the transfer of heat from a solid or liquid to another fluid. Forced convection is a fluid flowing over a surface. Natural convection is when a fluid is heated and rises due to bouyancy such as when hot air rises and cooler air sinks, creating circular currents. The heat transfer for convection can be calculated by the following formula:
- [math]\displaystyle{ Q=hA(T_{hot}-T_{cold}) }[/math]
- Where
- Q is the heat transferred in [math]\displaystyle{ Watts }[/math]
- h is the film coefficient in [math]\displaystyle{ h=\frac{watts}{m^2 K} }[/math]
- A is the surface area in contact with the fluid in [math]\displaystyle{ m^2 }[/math]
- T is the temperature in °C ([math]\displaystyle{ T_{hot} }[/math] represents the warmer temperature and [math]\displaystyle{ T_{cold} }[/math] represents the cooler temperature)
- Radiation is where the heat is carried by electromagnetic waves. The Stefan-Boltzmann Law can help calculate this transfer:
- [math]\displaystyle{ P=e\sigma A \left (T^4-{T_C}^4\right ) }[/math]
- Where
- P is the radiated power in [math]\displaystyle{ Watts }[/math]
- e is the object's emissivity
- σ is Stefan's constant (equal to [math]\displaystyle{ 5.6703 \times 10^-8 \frac {W}{m^2K^4} }[/math])
- A is the radiating area in [math]\displaystyle{ m^2 }[/math]
- T is the temperature of the radiating source in K and [math]\displaystyle{ T_C }[/math] is the surrounding temperature.
Specific Heat
This is the amount of heat per unit mass needed to raise a substance's temperature by 1 °C. It is represented by the following formula:
[math]\displaystyle{ Q=mC\Delta T }[/math]
Where Q is the heat needed, C is the specific heat, m is the mass, and ΔT is the change in temperature. Every substance has its own specific heat. For example, water's specific heat is 4.184 J/g*K
The Competition
For the building set-up, there will be 2 stations: high speed and low speed. You will be given 5 minutes to set-up and test your device in front of each fan (5 minutes for high, 5 minutes for low). Once you are ready, you may tell the event supervisor to start the fan. The fan will run for one minute and the highest voltage within the time frame will be recorded as your score.
Once you have completed the device testing, you will get 40 minutes to complete the stations/written part.
Scoring
For this event, the highest score wins. Your voltage score is calculated like this:
- Voltage Score = Low speed voltage (mV) + High speed voltage (mV)
- Test Score = based on a 50 point scale (if you have 25 questions, each is worth 2 points.)
Final Score = 50 x (Part I score)/(Highest Part I score of all teams) + Station Score (50 point base)
The tiebreaker is the team that has the best high-speed performance.