Jennifer Straka – Page 2 – SCI-184 Blog: Fall 2015

The Stirling Heat Engine & Peltier Device

What is the Stirling Heat Engine? The Stirling engine was invented by Robert Stirling in 1816. There hasn’t been a successful mass-market application for the Stirling engine. The gasses used inside a Stirling engine never leave the engine. There are no exhaust valves that vent high-pressure gasses, as in a gasoline or diesel engine, and there are no explosions taking place making Stirling engines very quiet. The Stirling cycle uses an external heat source, which could be anything from gasoline to solar energy to the heat produced by decaying plants. No combustion takes place inside the cylinders of the engine.

Modern Day Applications? Stirling engines are used only in some very specialized applications, like in submarines or auxiliary power generators for yachts, where quiet operation is important.

What is the Peltier Device? Peltier devices, otherwise known as thermoelectric coolers, are solid-state heat pumps that operate according to the Peltier effect: a theory that claims a heating or cooling effect occurs when electric current passes through two conductors. A voltage applied to the free ends of two dissimilar materials creates a temperature difference. With this temperature difference, Peltier cooling will cause heat to move from one end to the other. The Peltier Effect was discovered by Jean Peltier in 1834.

A typical thermoelectric cooler will consist of p- and n- type semiconductor elements that act as the two dissimilar conductors. It is possible to shift the balance of electrons and holes in a silicon crystal lattice by “doping” it with other atoms. Atoms with one more valence electron than silicon are used to produce “n-type” semiconductor material. Atoms with one less valence electron result in “p-type” material.

The array of elements is soldered between two ceramic plates, electrically in series and thermally in parallel. As a DC current passes through one or more pairs of elements from n- to p-, there is a decrease in temperature at the junction (“cold side”), resulting in the absorption of heat from the environment. The heat is carried through the cooler by electron transport and released on the opposite (“hot”) side as the electrons move from a high- to low-energy state. The heat-pumping capacity of a cooler is proportional to the current and the number of pairs of n- and p- type elements (or couples).

Modern day applications? Peltier elements are commonly used in consumer products including camping products, portable coolers, cooling electronic components and small instruments. The cooling effect of Peltier heat pumps can also be used to extract water from the air in dehumidifiers. Climate-controlled jackets are beginning to use Peltier elements. Thermoelectric coolers are used to replace heat sinks for microprocessors. They are also used for wine coolers.

References:

1. How Stuff Works

http://auto.howstuffworks.com/stirling-engine.htm

2. II-VI Marlow

http://www.marlow.com/resources/general-faq/6-how-do-thermoelectric-coolers-tecs-work.html

3. PV Education

http://www.pveducation.org/pvcdrom/pn-junction/doping

Museum of Science

Catching the Wind:

How do wind turbines generate electricity? Wind turbines catch the energy of the wind and change it into a form we can use. As the wind turns a turbine’s blades, the machinery inside the machine coverts the energy into electricity.

What factors need to be considered when selecting and siting them? The decision to install a wind turbine is generally based on a location’s wind speed and duration over the course of a year. Other factors include how much energy a wind turbine is capable of generating, efficiency, cost, the time it will take for the turbine to return a profit, how wildlife will be affected, and acceptance by the community.

What are the tradeoffs?

Renewable:

Wind- Wind is only available at certain times and in certain parts of the country, often times in areas far from large amounts of energy consumption. Also, an efficient method of storing excess energy produced by windmills has not been invented.

Solar- Solar energy is only available for half of the day and can be lessened with weather conditions. Also, the technology for solar panels is expensive.

Hydropower- Dams can negatively affect the ecosystems in the water and can also potentially contribute to the pollution of the surrounding water.

Biomass- The tradeoffs for biomass include that it is expensive, it is not as efficient as fossil fuels, and it creates methane gas when burned which is harmful to the environment.

Non-renewable:

Coal- Burning coal emits harmful waste such as carbon dioxide, sulphur dioxide, nitrogen oxides, sulphuric acids, arsenic and ash into the air, acid rain, mining can negatively affect the ecosystem, miners and employees can suffer from coal related health issues, and there is a limited amount of coal to be used.

Nuclear Power- Radioactive wastes are produced and either have to be recycled or disposed of safely, safety of nuclear power and weapons use, limited amount of uranium, and nuclear accidents are tradeoffs to consider.

Natural Gas- Natural gas use produces greenhouse gas emissions, it is toxic and flammable, not as efficient as gasoline for transportation, and its supply is also limited.

Conserve @ Home:

Changes to make to energy “budget”-

>buying a car that gets 30.7 mpg vs 20 = 13.5% savings

>carpool to work = 4.2% savings

>install more efficient furnace = 2.9% savings

>lower winter thermostat = 2.8%

>replace single pane windows with more efficient ones = 2.8%

>lower highway speed from 70 mph to 60 mph = 2.4% savings

>buy low rolling resistance tires = 1.5% savings

>reduce washing machine temp. = 1.2% savings

>line dry clothing for 5 months of year = 1.1% savings

What’s a watt? The hair dryer used considerable more energy (1000 watts) versus the mixer (250 watts).

Energized: I went through all the interactive exhibits and found the solar energy ones to be intriguing. It was interesting to see the reading on the solar panel change depending on where you put it representing different times of day.

Investigate!: This exhibit went over the four steps of an at-home investigation- Ask a question. Make a guess. Check it out. Investigate further.

References:

1. Conserve Energy Future

http://www.conserve-energy-future.com/Advantages_Disadvantages_BiomassEnergy.php

2. Fossil Fuel

http://fossil-fuel.co.uk/coal/the-disadvantages-of-coal

3. Museum of Science

http://www.mos.org/

Generator Activity

My partner and I did the generator lab demonstrating Faraday’s Law that states that changing magnetic fluxes through coiled wires generate electricity. The greater the change in magnetic flux, the greater the currents and voltages. We used a flashlight shake generator to demonstrate this and are results were in accordance with Faraday’s Law.

To conduct the experiment my partner shook the tube for thirty seconds at a constant rate. She counted the the number of times she shook it and I recorded the number. Using excel, we took the sum of the square of the voltages and recorded that number. We repeated this four more times at different rates of shakes. Below are our results and a graph with a trend line representing what we learned from Faraday’s Law. The more shakes, the higher the sum of the square of the voltages.

Labs

Tesla Electric Car

How does the Tesla electric car work? The Tesla uses a three-phase Alternating Current (AC) Induction motor. The motor has two primary components: a rotor and a stator. The rotor is a shaft of steel with copper bars running through it. It rotates and, in doing so, turns the wheels. The stationary stator surrounds, but does not touch, the rotor. The stator has two functions: it creates a rotating magnetic field and it induces a current in the rotor. The current creates a second magnetic field in the rotor that chases the rotating stator field. The end result is torque. The magnetic field is created completely from electricity. The stator is assembled by winding coils of copper wire through a stack of thin steel plates called laminations. The copper wire conducts the electricity fed into the motor from the Power Electronics Module. There are three sets of wires – each wire conducts one of the three phases of electricity. The three phases are offset from each other such that combing the rises and falls of each phase creates a smooth supply of current—and therefore power. The flow of alternating current into the copper windings creates a magnetic field. This is electromagnetism. And just as the current in each phase constantly rises and falls, the magnetic field also varies between “North” and “South”. -Tesla

Use of technology- Nikola Tesla emigrated to America from Croatia to work for Thomas Edison. The partnership did not last long and soon after he ended up going out on his own and launched a small company and development laboratory in 1886 in New York. In 1887 Tesla files his first patents for a two-phase AC system with four electric power lines, which consists of a generator, a transmission system and a multi-phase motor. The image below is a picture of one of many patents he filed for.

George Westinghouse licensed his AC induction motor and transformer and Tesla also worked for a short time as a consultant for Westinghouse. Tesla also made many other discoveries in fields such as lighting and radio technology. Below is a picture of Tesla around 1890.

Charging stations- The Tesla can charge wherever there is an outlet, 120v or 240v! The Tesla can be programmed to charge at a certain time of day. The recommended time is between midnight and 6 am when the cost of electricity may be lowest. Tesla also offers high power charging stations for home use that greatly increase the speed at which the car charges. Another option are Superchargers- stations on the road users can rapidly charge their cars at. There are also public charging stations across the country Tesla cars can use with an adapter. The map below shows the Supercharge stations as of January 2015.

References:

1. Tesla

http://my.teslamotors.com/roadster/technology/motor

http://www.teslamotors.com/models-charging#/onthego

2. Explain That Stuff

http://www.explainthatstuff.com/induction-motors.html

3. KIT

https://www.eti.kit.edu/english/1390.php

4. Hybrid Cars

http://www.hybridcars.com/tesla-updates-map-of-supercharger-sites/

Pulley Lab

My partner Jill Swan and I did the pulley lab together. The lab consisted of exploring Newton’s 2^nd Law- the law of conservation of energy, velocity and acceleration, and power. We used the Lego Mindstorm robot to see how acceleration changed when mass changed and power was fixed and when power changed and mass was fixed.

Does the acceleration vary with mass? Yes. When we changed the masses- .05 kg, .1 kg, .15 kg, .2 kg, and .25 kg, with the power level left constant at 75, the acceleration decreased. The first graph is a representation of our results. It shows the trend line angled in a downward slope in regards to acceleration vs. mass.

Does the acceleration vary with power level? Yes. When we changed the power level- 50, 60, 70, 80, and 90, with the mass left constant at .1 kg, the acceleration level increased. The second graph is a representation of our results. It shows the trend line angled in an upward slope in regards to power vs. acceleration.

Is the linear trend line as expected? Yes. The linear trend line reflected what I expected the results to be based on the lecture and understanding the formula F=ma.

17.5 cm- to bottom of pulley

9 cm- height of weights

Electricity Generation

Electricity Generation:

How does a coal power plant work? The process begins when coal is ground to a powder. It is then blown into a boiler where the coal dust is burned, thus creating heat energy. Why grind the coal? Grinding it into a powder creates more surface are which, in turn, allows for faster and hotter burning producing more heat and less waste. The burning of the coal heats water in pipes coiled around the boiler, turning it into steam. Pressure is created by keeping the steam in pipes where it expands and the pressure drives the steam over the blades of a steam turbine. The steam turbine spins and mechanical energy is produced. A shaft connects the steam turbine to the turbine generator, so as the steam turbine spins, the generator does as well. Using an electromagnetic field, the generator converts the mechanical energy into electrical energy. The byproducts are ash and exhaust gas. The ash is collected from the bottom of the boiler and often sold to be used in building materials and the gases enter the exhaust stack. The exhaust stack has filters to remove the dust and ask before the gas is released into the air.How does a natural gas power plant work? The first step at a natural gas power plant is pumping the natural gas into the turbine. There it is mixed with air and burned, creating heat energy. Combustion gas is also created. The heat causes the combustion gas to expand causing a buildup of pressure. The pressure drives the combustion gas over the blades of the gas turbine, causing it to spin, converting some of the heat energy into mechanical energy. A shaft connects the gas turbine to the gas turbine generator so when the turbine spins, the generator spins as well. Using an electromagnetic field, the generator converts the mechanical energy into electrical energy. The combustion gas is then piped to the heat recovery steam generator where it is used to heat pipes of water, turning the water to steam, before leaving through the exhaust stack. The hot steam expands in the pipes and emerges under high pressure. These high-pressure steam jets spin the steam turbine. The steam turbine is connected by a shaft to the steam turbine generator, which converts the turbine’s mechanical energy into electrical energy.

How does a nuclear power plant work? The nuclear power plant begins the process in a reactor vessel- a tough steel capsule that houses the fuel rods, sealed metal cylinders containing pellets of uranium oxide. When a neutron, a neutrally charged subatomic particle, hits a uranium atom, the atom sometimes splits, releasing two or three more neutrons. This process converts the nuclear energy that binds the atom together into heat energy. When atoms in the fuel split, the neutrons they release are likely to hit other atoms and make them split as well creating a chain reaction producing large amounts of heat. Water flows through the reactor vessel, where the chain reaction heats it to around 300°C. The water needs to stay in liquid form for the power station to work, so the pressuriser stops it from boiling. The reactor coolant pump circulates the hot pressurised water from the reactor vessel to the steam generator. Here, the water flows through thousands of looped pipes before circulating back to the reactor vessel. A second stream of water flows through the steam generator, around the outside of the pipes. This water is under much less pressure, so the heat from the pipes boils it into steam. The steam then passes through a series of turbines, causing them to spin, converting the heat energy produced in the reactor into mechanical energy. A shaft connects the turbines to a generator, so when the turbines spin, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.There are similarities in the three types of power plants. They all use hot water, steam, turbines, and electromagnetic fields in their production process. There are a couple big differences I think are worth mentioning- the ability to control when and how much power is made and environmental impact. While nuclear power plants are in full effect at all times, natural gas and coal production can increase and decrease as needed to meet the demands, a definite benefit. On the note of environmental efficiency, nuclear is the clear winner producing carbon-free electricity as well as being a renewable resource. Natural gas produces less greenhouse gases than coal, about half as much, but the goal should eventually be no gas emissions so natural gas is not a perfect solution. It is abundant and cheap at the moment making it an appealing source of energy for now.

References:

1. EDF Energy- Coal

http://www.edfenergy.com/energyfuture/coal-generation

2. EDF Energy- Natural Gas

http://www.edfenergy.com/energyfuture/generation-gas

3. EDF Energy- Nuclear Power

http://www.edfenergy.com/energyfuture/generation-nuclear

4. Oil Price

http://oilprice.com/Alternative-Energy/Nuclear-Power/Natural-Gas-Threatens-U.S.-Nuclear-Future.html

Lego Mindstorm Lab Activity #2

My teammate, Jill Swan, and I experimented with three power settings for the motors, keeping both motors the same. We did three trials per power setting. The results are as follows:

Wheel Diameter= .055 m Circumference= .1728 m

The experiments show that the more power the motors had, the farther the robots went. In order to make a full rotation, the power needs to be over 55, as our experiments show that 55 just slightly not enough for an entire 360 degree rotation. The margin of error varied across all the studies anywhere from less than a percent to 12% error with no definitive link between the variation of results. The experience was helpful to reinforce the concepts of distance, velocity, and dealing with diameter, radius, and circumference from the lecture. It also was beneficial in learning to work with the robots and the computer software associated with them.

Fracking

What is fracking? Fracking, otherwise known as hydraulic fracturing, has been in use since the 1940’s but has recently seen a rise in the United States in part due to the economic benefit it brings to the communities where these resources are located and also because of the desire for energy security. The process of fracking begins with a well drilled vertically or horizontally 1-2+ miles into the Earth. In order to reduce the risk of leakage into the groundwater, the well is encased in steel and/or cement. At the time the vertical well reaches the layer of rock where the oil or natural gas is located, the well curves to about 90 degrees to drill horizontally along the rock layer, extending potentially over a mile. Next, fracking fluid is pumped into the well at pressures high enough to fracture the surrounding rock, creating fissures that allow oil or gas to flow through. This fracking fluid, also called slickwater, while mostly water, contains a range of additives and chemicals as well. Proppants are also pumped into the well and are used to keep the fractures open so the oil or natural gas can flow freely through the fissures. The reservoirs of oil or natural gas are then pumped back to the surface along with flowback liquid containing numerous contaminates. The flowback liquid is eventually injected deep in the ground below groundwater or disposed of at wastewater treatment facilities. The image below provides a graphic representation of how fracking works.

Pros:

>Fracking provides economic benefits such as jobs in the communities where the wells are located. (Reference 2)

>Fracking allows the US to produce their own energy resources, decreasing dependency on imported oil and fossil fuels and the costs associated with that. (Reference 2)

>Fracking can stimulate new production from older wells. (Reference 1)

Cons/Environmental Impact:

>An average of 400 tanker trucks are required to carry water and supplies to and from the site, contributing to air pollution and use of fossil fuels. (Reference 3)

>Millions of gallons of water are used in each fracturing job.

>About 40,000 gallons of chemicals (up to 600 types of chemicals such as lead, uranium, and mercury) are used in a fracturing job.

>Groundwater used by nearby towns for drinking water can be contaminated from leaching of the chemicals during the fracking process sometimes causing health complications.

>Up to 50% of the fracking fluid (not biodegradable) is not recovered and is left in the ground.

>Fracking fluid left to evaporate releases harmful VOC’s into the atmosphere contributing to acid rain, contaminated air, and ground level ozone.

References:

1. What is fracking?

http://www.what-is-fracking.com/what-is-hydraulic-fracturing/

2. Live Science

http://www.livescience.com/34464-what-is-fracking.html

3. Dangers of Fracking

http://www.dangersoffracking.com/

US Energy Grid

What is the energy grid?- The energy grid, or power grid in the United States is the system by which electricity is distributed to consumers across the country. The grid connects the energy producers and the consumers through a complex electrical system composed of three interconnected systems.

What composes the infrastructure of the energy grid?- As stated above the energy grid is composed of three interconnected systems. The systems are divided into the Western Interconnection, the Eastern Interconnection and the Texas Interconnection. According to the US Energy Information Administration, “The interlinked systems now include about 2,000 electric distribution utilities, more than 300,000 miles of transmission and distribution lines, millions of customers, and 7,000 power plants.” The image below is a graphic representation of the energy grid, showing the three interconnections.

How does the energy grid work?- The first step of the grid is the power source, whether that be a from a renewable source such as a hydro-electric plant or a non-renewable source such as a coal plant. Once the power is generated, it is stepped up at a transmission substation in order to be able to travel long distances. In order for the power to be used, it comes off the transmission grid to the distribution grid where it is stepped down at a distribution substation. On the distribution grid it is then stepped down a second time through the transformers so the power is now at the 120 or 240 Volts that we use in our homes and businesses.What are Smart Grids?- Smart grids are a way of modernizing the power grid by adding technology to the current grid such as meters, sensors, and synchrophasors. This incorporation of digital technology enables communication between the grid, consumers, and the operating network providing data on consumption, voltage, damage, and potential problems among others. According to the US Energy Information Administration, “A smarter grid makes the electrical system more reliable and efficient by helping utilities reduce electricity losses and to detect and fix problems more quickly. The smart grid can help consumers conserve energy, especially at times when demand reaches significantly high levels or when an energy demand reduction is needed to support system reliability.”

Pros:

1. Provides power to the country

2. Contributes to the economy in ways such as providing jobs anywhere from at the power plants to the installation of new lines.

Cons:

1. Security threats: “In fiscal year 2014, there were 79 hacking incidents at energy companies that were investigated by the Computer Emergency Readiness Team, a division of the Department of Homeland Security. There were 145 incidents the previous year.” CNN

2. Siting new transmission lines when there is opposition to construction.

3. Reaching renewable energy generation sites can be challenging.

References:

1. US Energy Information Administration: http://www.eia.gov/energy_in_brief/article/power_grid.cfm

2. CNN: http://money.cnn.com/2014/11/18/technology/security/energy-grid-hack/

3. How Stuff Works: http://science.howstuffworks.com/environmental/energy/power4.htm

4. Office of Electricity Delivery & Energy Reliability: http://energy.gov/oe/services/technology-development/smart-grid