Wind Power

Physical Science Lab, known as Physics Lab in 2010 and Wind Power in 2011 for Division C, involves the construction of a device that can turn wind into energy and the answering of questions relating to alternative energy. For the 2006 event, see the original Physics Lab page.

The Basics of the Event
Half of your score for Wind Power 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:


 * 1) Wind turbine Diameter
 * 2) Weight
 * 3) Blade Width
 * 4) Blade Thickness
 * 5) Curve of the Blade
 * 6) Blade Pitch
 * 7) Number of Blades
 * 8) Blade Material
 * 9) Alteration of CD or not

This event has changed since last year, instead of trying to get the blades to spin as fast as possible with no resistance that it has to "push" against, Now you have 5 to 7.5 ohms of resistance, which should be wired into the setup. You can buy a resistor of that size or wire 2 in parallel, ie two 14 ohm resistors in parallel = 7 ohms of resistance.

Lighter blades will spin faster, but since this year you must produce power (due to the resistors) a slightly heavier blade will have a higher momentum. 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.

Similar to real life wind turbines, our turbines need to be designed to generate power, because the resistors which have been added to the setup this year, It means your turbine actually has to "push" against the resistance, unlike last year when resistors were not a part of the setup, and the goal then was to get them to spin as fast a possible with nothing as far as resistance goes holding them back. The resistance found on the setups must be between 5 and 7.5 ohms.

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, one will want to do this because unlike last year, we now must generate power, not voltage.

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. You are going to want any curve to simulate an airfoil. You will want the wind from the fan blowing on the outside of the blades curve, this is not what most people do. Most people curve it so that the wind hits the inside of the curve, this provides quick acceleration (which should be relatively fast since the average voltage is measured) but a top speed that is lower than the other direction of curve.

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 power (it will have a much slower acceleration but a high top speed. The blades I make aren't so much "curved" but the back edge is completely flat and the front edge you are going to want at a higher pitch the closer you get to the center of the turbine. ie 20 degrees towards the center and make the front edge gradually get lower until around 5-10 degrees or so at the outside.

The number of blades is another adjustable variable. I find that 2-3 blades is best. Remember that more weight will get you more momentum but there is a point where there is too much weight and your top speed will not be very high. I feel like this occurs when you have 4 blades, it's just too heavy... However if your blade is a lighter material, ie Balsa, then 4 might actually better than 2 or 3.

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. A way to help make sure that you build your blade as balanced as possible is to make a device with a thin 1 ft by 1ft thin piece of ply wood with a metal/wood rod sticking straight out, and lines can be drawn on the sheet of ply going away from the rod at equal increments for which you can line up your blades as you glue them to the CD.

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 a Dremel, 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. So just the center circle that is around the hole is a good thing to cut out and glue to the center of the blade, just make sure it mounts to the CD holder properly.

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 and labelled with your team's name.

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:


 * $$C=\frac {5}{9} \left ( F-32 \right )$$
 * $$F=\frac {9}{5} C +32$$

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:


 * $$Q=\frac {kA\left (T_{hot}-T_{cold}\right )}{d}$$


 * Where


 * Q is the heat transferred in $$Watts$$


 * k is the barrier's thermal conductivity in $$k=\frac {watts}{m K}$$


 * A is the cross-sectional area in $$m^2$$


 * T is the temperature in °C ($$T_{hot}$$ represents the warmer temperature and $$T_{cold}$$ represents the cooler temperature)


 * d is the barrier's length in $$m}$$




 * 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:


 * $$Q=hA(T_{hot}-T_{cold})$$


 * Where


 * Q is the heat transferred in $$Watts$$


 * h is the film coefficient in $$h=\frac{watts}{m^2 K}$$


 * A is the surface area in contact with the fluid in $$m^2$$


 * T is the temperature in °C ($$T_{hot}$$ represents the warmer temperature and $$T_{cold}$$ represents the cooler temperature)




 * Radiation is where the heat is carried by electromagnetic waves. The Stefan-Boltzmann Law can help calculate this transfer:


 * $$P=e\sigma A \left (T^4-{T_C}^4\right )$$


 * Where


 * P is the radiated power in $$Watts$$


 * e is the object's emissivity


 * σ is Stefan's constant (equal to $$5.6703 \times 10^-8 \frac {W}{m^2K^4}$$)


 * A is the radiating area in $$m^2$$


 * T is the temperature of the radiating source in K and $$T_C$$ 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:

$$Q=mC\Delta T$$

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 "x" amount of minutes to complete the stations/written part.

Scoring
For this event, the highest score wins. Your voltage score is calculated like this:


 * Voltage Score = High speed voltage with resistance factored in and Low speed voltage and resistance factored in.
 * 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.

Links

 * New York Coaches Conference
 * HyperPhysics
 * Scientific American
 * [[Media:Physics_Lab_Nationals_2010_Results_B.xlsx|Physics Lab Nationals 2010 Results B]]
 * [Alternate Energy's Environmental Impacts]