Applying Force on the Body - Report Example

1. Energy and Work Mechanical Work or Work is said to be done on an object or a system when force and the object moves a certain distance as a result. It is a scalar quantity- meaning that it has magnitude but no specific direction. For example, if we push a shopping cart (the object) and it covers a certain distance; some work has been done. However, the system applying the force on the other body in order to do some work must have some energy. In the earlier example, we should "have some energy" in order to push the shopping before any work is done. The unit of work, and in turn energy, in SI is Joule or Nm. 1 Joule is defined as amount of energy used when a force of 1 N moves a system through a distance of 1 m. It is important to note that in the process of doing work, the body doing the work transfers the energy to the body on which work is done. For example, when we throw a ball, a certain amount of energy has been imparted to the ball. Similarly, when water stored in a reservoir falls on a water-wheel the energy stored in water is transferred and the wheel starts to turn. This leads us to the important Law of Conservation of energy, which state that: Total amount of energy in a system remains constant over time or it is conserved. It can change its form but can neither be created nor destroyed. Energy has different forms which include Potential Energy (based on the position of the system), kinetic (based on the motion), chemical energy (based on composition) and nuclear energy. 2. Energy from Fuels Most common form of energy we use in our daily lives is heat. Heat energy is released when we burn coal, wood, natural gas and gasoline. That is, the Chemical Energy stored in these materials is released in the process of combustion and is available to us for work. These material are referred to as Hydrocarbon fuels, Fossil Fuels or simply Fuels. At the basic chemical level, these material consist of carbon and hydrogen. In the process of combustion, these react with the atmospheric oxygen producing carbon oxides(monoxide and dioxides) and significant amount of heat energy. Coal Coal is the oldest and perhaps the most abundantly used fuel in the history of mankind. It is a fossil fuel and it is was formed from huge amounts of organic material that was buried under soil and rock overtime due to natural events like floods. As time passed on, the overburden (and the pressure) due to soil continued to increase and in an atmosphere lacking oxygen, the organic matter converted to coal. It is important to note that the plant matter had depended on the sun as source of energy until it was buried. Hence, it can be argued that the original or primary source of energy was from the sun itself. Figure 1 Process of Coal Formation (Source: National Energy Education Development Project) Coal is extracted from the earth through mining. The depth at which coal is found can vary from few feet to several hundred feet. In todays age the mining processes have become very efficient and safe compared to those in the past. In 2010, total amount of coal mined throughout the world was around 7.9 billion short ton of coal. While U.S. alone approximately produced 1.08 billion short tons of coal, most of which was used to produce electricity. US relies on coal for meeting 46.1% of its electricity needs. (U.S. Energy Information Agency, EIA) The amount of energy contained in coal depends on carbon content. Besides carbon, coal also contains sulfur, mercury and other heavy trace metals. Based on the carbon-content coal is generally classified as Anthracite (86-97% carbon), Bituminous (45-86% carbon), Sub-Bituminous(34-45% carbon) and Lignite (25-45%) carbon. (U.S. Energy Information Agency, EIA) However, for commercial purposed it is classified by the heat-content or Calorific Heating Value. Heating value is defined as the amount of energy released when a specific amount of coal or any fuel is burned in standard conditions. Indicative heating values of different grades or rank of coal is provided in the Figure 2. Petroleum Oil Petroleum Oil or Oil is the second most consumed form of fossil fuels. It was created in the same way as coal, when dead-plant and organic materials (specially diatoms- the single cell organisms) was compressed under soil, water and other overburden over long period of time. While coal is mined and used without much processing (other than simple cleaning and sizing), crude oil undergoes significant processing in specially built refineries. Refining results is products like kerosene, Light Furnace Oil (LFO), Heavy Furnace Oil (HFO), Naphtha, diesel oil and gasoline. The last two are perhaps the most commonly used and known fuels. Petroleum has a very high energy density- it contains 83-87% carbon by composition and hence a significantly high heating value of 20,000 BTU/lb (or 9,091 BTU/kg). (National Institute of Standards & Technology, NIST) Petroleum, like coal, is categorized as non-renewable source of energy as it is believed that there are finite amount of oil reserves. In 2010, U.S. produced around 5.5 million barrels of crude oil per day and imported around 9.1 million barrel /day to meet its requirements. Natural Gas Natural gas is a mixture of gases which are locked between rocks and layers of overburden under the earth surface. The origin of natural gas is very similar to petroleum oil. In many cases, the two are found in close proximity. It is an odorless and colorless gas (however, additives are added later on to give it a smell and facilitate tracing of leaks). Natural gas mostly consists of methane (CH4 ), other gases like ethane, butane, propane and some other impurities are also found. Crude gas is treated to reduce moisture and other impurities before use for heating and electricity generation. The Heating value for natural gas varies significantly depending up on its compositions. Average heating value of natural gas produced in US is 36.26MMBTU /m3 . (U.S. Energy Information Agency, EIA) Natural gas is one of the cleanest hydrocarbon fuels. Recently, US is seeing a surge in indigenous natural gas production resulting in historic low gas prices. 3. Heat to motion in a car Car engines convert the chemical energy stored in the fuel in to useable mechanical energy which is used to drive the car through a transmission and drive system. The central part of a car engine is the cylinder block, consisting of 4, 8 or as many as 16 cylinders arrange in a sequence. Most common are in-line cylinders. Some modern cars have cylinder arranged in a V-shape and hence called V-type engines. Figure 3 V-type engine Figure 4 4-Cyliner In line engine block showing pistons Each cylinder consists of cylinder, piston and associated valves. A simplified 4-stroke engine cycle is show in Figure 5 and explained as following: Cylinders are generally hollow bores created in a cast metal block, referred to engine block. The size of the bore is closely matched with the size of the matching piston. There is very little clearance left, so as to avoid any leakage of hot gases or fuels. Piston consists of a head, piston rings (which seal the moving surface between the cylinder and piston head and connecting rod). Valve ports and valves provide the openings for intake of fuel and air mixture and exhaust of spent gases from the cylinder. Opening and closing of these valves is controlled through a cam shaft or an electronic system (in modern cars). Using these parts, the engine delivers the power in four repeating steps or strokes: Intake stroke: The piston is at the bottom end (withdrawn), the fuel port opens. Fuel and air mixture enter the cylinder. The exhaust port is closed. Compression stroke: The piston starts to move, using the energy stored by a flywheel (external to the engine block) from the last cycle or a starting motor. The piston head continues to move towards the top-end while compressing the air-fuel mixture. Both the fuel and exhaust ports are closed during this stroke. Power Stroke: In the power stroke, the air fuel mixture is ignited using a spark plug. The compressed air-fuel mixtures burns efficiently and produce hot gases. The piston head is pushed back towards the bottom end in a violent motion inter delivering power to the transmission system trough the connective road (linear motion of piston is converted in to rotary motion). Exhaust Stroke: In the exhaust stroke, the exhaust post opens and spent gases are exhausted to the environment. 4. Heat in to motion in a generator? Generators often refer to diesel engine driven generators. The diesel engine are based on a diesel-cycle which compresses the diesel fuel rapidly resulting in ignition in contrast to the petrol engine explained earlier which relies on external source of ignition like a spark plug. Because of this high compression ratio, diesel engine has the highest efficiency of all the internal combustion designs and hence the use in powering heavy trucks and buses. Figure 7 A simple Diesel Engine Figure & shows a simplified cut-out of a diesel engine. Generally, the size of the pistons in diesel engines is larger because of the high compression ratio and the resulting high forces that the piston faces. The fuel injector injects the diesel in form a small particles in the cylinder to facilitate ignition. Turbochargers and Superchargers are additions to the simple diesel engine. The purpose of these add-ons is to compress the intake air entering the engine to further increase in efficiency. Turbochargers, essentially air compressors, rely on exhaust gases for the drive. In contrast, Superchargers use direct drive from the engine. Diesel engines are extensively used as drivers for Electricity generators. 5. How generators work? As described above, diesel engines are used extensively as prime movers for producing electricity through Electricity Generators. Other example of prime-movers which used heat energy from fuels include steam turbines and gas turbines. In general, all these prime-movers are referred to as engines. While the electricity generator is referred to as a generator. The operating principle of an electricity generator is called The Generator Principle what states that: When an electrical conductor is moved through a magnetic field, electrical potential is developed across the ends of the conductor. A simple of demonstration of this principle is shown in the Fig 8. As the simple coil is rotated through the magnetic field of a permanent magnet , we see a potential developing across the terminals AD. This potential can drive electric current and hence deliver electrical power. This demonstration produces Direct Currents (DC). However, in real life, most electricity generators are Alternating Current (AC). The construction of AC generators is relatively more complex. However, the concept remains the same. In typical industrial sized AC generators (or alternator), the coil or winding remains stationary and is referred to as Armature. Instead the magnetic field (produced by an electromagnet) is made to rotate at a constant speed. The electromagnet is called the Field and is mounted on a rotors. As described earlier, the prime-movers are used to drive the generator. Actually, the prime-mover drives or rotates the rotor at a constant speed. Based on the generator principle a potential difference develops across the stationary armature. The magnitude of electrical potential (or voltage) will depend on the strength of the electromagnet. While, the speed of rotation will determine the frequency of AC. In US, electricity is generated at 60Hz frequency. The magnitude of voltage in most industrial scale generators is 6000 V and above. 6. Ethanol Ethanol is a bio-fuel prepared from sugarcane or corn. Chemically , it is Ethyl Alcohol which in its purest form is colorless, highly volatile and flammable chemical. However, ethanol as a fuel contains certain additives to improve its stability and combustion properties. There are a variety of chemical process that convert sugarcane or corn in to ethanol. However, essentially all the processes involve fermentation and ethylene hydration. Fermentation relies on certain types of yeasts to break the sugar in the grains to produce ethanol and carbon dioxide. While in ethylene hydration, ethanol is produced by catalytic hydration of ethylene. Again, it is important to note that the sugarcane and corn plants relied on suns energy to grow. Hence, it can be argued that ethanol is derived from the suns energy. Ethanol, is claimed to burn more cleanly (producing less Greenhouse gases). The heating value of pure ethanol is 26 MJ/kg. However, it mostly used in blended form. Most common blend is referred to as E85 (85% ethanol, 15% gasoline) Brazil, is the world leader in ethanol production and consumption. There ethanol is used as a substitute for gasoline in cars. The automobile engines require special modifications in order to use ethanol-rich fuel. However, a normal car can safely use E10 (10% Ethanol, 90% gasoline). (Energy Information Agency, EIA) 7. Energy from flowing water and how in a way it also relies on energy from the sun. Flowing water can be a source of energy when it is used to drive water or hydro-turbines, which in turn produce electricity. Mostly, water is captured in huge reservoirs by making Dams on the flowing water. The Potential energy stored in this captured water is released in controlled manner by managing the flow through turbines. One can argue that this method of electricity generation also relies on energy from the sun. How? well availability of water depends on the phenomenon called the Water Cycle. Water cycle Energy from the sun, heats the water in large bodies of water like oceans, seas, lake and rivers. Water turns in to vapors and ultimately clouds. At the same time, suns energy also heats the air. The heating of the air varies, on and around the land mass, and results in flow of winds. The winds, in turn carry the clouds from the sea to the land. The heavy moisture carrying clouds release their water as rain or snow over the land. Melting of snow recharges the flow of rivers and the underground water reservoirs. Hence the ability to produce electricity depends on availability of flowing water. Which in turn depends on the water cycle. Countries which depend extensively on hydal energy, sometimes see shortage of electricity when there is a dry period (as the dams deplete the stored water and have insufficient recharging because of lack of rains). 8. Solar Power The energy from the sun, much of it in form of radiation and some of it in form of light, travels through the earths atmosphere. Earths atmosphere shield us from the immense amount of radiation by rejecting almost 31% of the total energy coming toward the earth. (Houghton, Griggs and Noguer) According to Houghton, the average amount of radiation or energy that makes it to the surface of earth is 198 W/m2 (of which 30 W/m2 is reflected by the surface). We can say that this is the total amount available for conversion either for heating purposes or electricity generation. In homes generally, the solar energy is converted to electricity using Photovoltaic Panels, commonly referred to as Solar Panels. Most of the commercially available solar panels have an efficiency of only 18-20%. Hence, the amount of energy that can be actually converted to electricity is limited to 39.6 W/m2 (calculated as 192 x 20% = 39.6 W/m2). Assuming, an average 2000 sqft house, we can calculate the surface area of the roof. Approximately, 185 m2 of surface is available. Hence, a total of 7.32 KW of electricity (approx.) can be produced. This is calculated as (Area x electricity produced / m2 = 185 x 39.6= 7326 W). Assuming that a month consists of 700 hours and a day consists of 12 hrs, the amount of total energy produced will be 2,564 KWh. An average house of this size consumes about 500-1000 units (KWh) of electricity in a month. However, the above calculation is over simplistic and leads to very enticing but incorrect conclusion. This is for the following reasons: - The cells which are fixed on roof top will not always get the same amount of radiations as the angle will continue to change over the day. - Changing weather conditions, like cloud cover, can also severely impact the capacity of the system. - Most solar systems employ DC to AC current convertors, which have their own inherent efficiency losses. Further reducing the available energy. 9. Solar Cells Solar cells are made of special semiconductor materials. When light falls on them, a certain amount of the energy is absorbed in the material when it knocks out loose electrons, allowing the electrons to move freely. This results in an electric current. Many sells are connected together to form a module or a panel to harvest significant amount of current. With unlimited amount of available solar energy, one can might think that we have access to unlimited amount of readily available energy. However, this is not case. In truth, the process is a lot more complicated and may other factors limit the overall efficiency of a solar cell. Presently, the average efficiency of a solar cell is 18-20% (U.S. Department of Enenrgy, Energy Efficiency & Renewable Energy). As already mentioned, Solar systems produce DC currents, which in turn are converted to AC currents using Inverter Systems which employ electronics and batteries. 10. It Takes energy to make cold The basic principle of Refrigeration is based on the phenomenon of evaporation. A liquid evaporates (changes its phase from liquid to gas) when it absorbs heat from the surface or system it is in contact with. As a results the temperature of the surface, which lost the heat, falls down and it becomes cold. In a refrigerator, the liquid that evaporates (and changes phase) is called the coolant or refrigerant. However, it is maintained in closed system or loop. So, it is keeps on flowing through the system, changing in to gas (on absorbing heat) and turning back in liquid (on rejecting the heat). The first refrigerators used ammonia as a coolants, later it was replaced by Chlorofluorocarbon (CFC) and now most units use non-CFC refrigerants. Refrigerator consists of four key components: A compressor, which compresses the refrigerant, which is in gaseous state, and increases its temperature (as energy is being added to it by the work done by the compressor). Electrical energy is consumed in running a compressor. The compressed and relatively hot gas flow in to the Outer heat-exchanger tubes. Outer heat exchanger (tubes), allow compressed gas to lose the heat while maintaining high pressure. The gas changes its phase and turn in to high pressure liquid which enters next the expansion valve. Fans are generally used to improve the heat transfer. expansion valve is nothing but a nozzle with very small hole. When high pressure liquid passes through the valve it immediately cools down and starts to boil (turning in to gas). and inner heat exchanger (tubes) the cold gaseous- refrigerant flows through the tubes. It absorbs the heat from the inner of the box (and from the items placed in it). All the time, the gas is being sucked towards the compressor and the cycle starts all over again. So we can conclude that even cooling down things (refrigeration) takes energy. A refrigerator is very similar to air-conditioner. Air conditioner, in addition to the above mentioned four key components also uses two large fans to facilitate the heat exchange (one on each heat-exchanger tubing). 11. Efficiency and Thermodaynamics While we note that almost all electrical energy can be converted in to heat energy (as in an electrical iron), the converse is not true. This phenomenon is explained by Carnots theorem which states: No engine operating between two heat reservoirs can be more efficient than a Carnot engine operating between the same reservoir. Where Carnot Engine is a hypothetical device which does some useful work while transferring heat energy (Source- Hot) from a high energy reservoir to a low energy reservoir (Sink- Cold). The theoretical efficiency of this engine is given by the equation: where; n = efficiency of the Carnot engine W = Work done QH = Energy in the Source Tc and Th are temperatures of sink and source respectively. The Carnots theorem also offer an important result according to which all the reversible systems (or engines) between same Source and Sink will have to have same efficiency. As we already noted that the efficiency of the engine depends on the temperature of the source or the sink. Therefore, it can be conclude that only an ideal and truly reversible engine will be able to completely transform wasted energy back in to the original form. 12. Sun and Earth- A cosmic engine The estimated surface temperature of the sun is around 5,778 degree K. (NASA). In contrast, earth has an average temperature of 288.15 deg K (NASA). While the temperature of the space that exists between the two is extremely cold. It is estimated at 2.7 K, which in essence is just temperature of surrounding background radiation. (Keohane) Knowing the Carnot cycle discussed above, we can say that the sun (source at high temperature) and the earth ( at relatively low temperatures). 13. Nuclear Fission and Uranium Nuclear fission is defined as a process in which nucleus of an atom splits in to smaller parts accompanied by release of huge amount of energy. Figure 11 Fission (Source:Thinkquest.org) According to scientists, metals including uranium were created during supernovas- violent deaths of stars through implosion. Supernova is followed by release of huge amount of energy (according to some theorists, the energy is in order of the total energy emitted by our sun in its lifetime) massive shockwave which spreads the dead stars remnants in to the space. Since, our sun is similar to other stars in the universe, it can be argues that Uranium also comes from the sun. 14. Fusion Nuclear fusion is a reaction in which two or more nuclei combine to form a heavier nucleus (and hence a new element is formed). During the course of process, immense amount of heat energy is released. Scientists believe that stars are like huge reactors in which the process of fusion is ongoing creating huge amount of material as well as energy. In, a way we can call the stars the factories that make the materials we find all across the universe. Smaller stars, like our sun, are believed to form lighter gas like Helium as a product of fusion. However, larger stars can produce metals like iron, cobalt, lead and uranium. As discussed earlier, when these stars die and implode as a supernova, these materials are spewed in to the space. 15. Summary To summarize the entire discussion, we note that: Energy is the ability to do useful work. It can change forms within the system but cannot be created or destroyed. It is not possible to create an ideal and perfectly reversible system. Hence, it is not practically possible to convert all of the heat (which was produced after expending energy back) in to its previous state. It can be argued that all the energy comes from stars, much like our sun. Today, we rely heavily on hydrocarbons to meet our energy needs. These are hydrocarbons were produced from decayed organic material over period of many thousand years. When alive, these organisms relied on the energy from sun to survive, grow and propagate. Stars are the factories that not only produces vast amount of energy but also huge amount of materials including metals. Works Cited Energy Information Agency, EIA. http://www.eia.gov/energyexplained/index.cfm?page=biofuel_home. 19 March 2012. 4 April 2012. Fenley, Adam. http://motorsportengineering.blogspot.com/2011/04/vehicle-design-piston-design-101.html. 4 April 2011. 13 April 2012. Houghton, J. T., Ding, Y., et al. "Climate Change 2001: The Scientific Basis." Cambridge, UK: Cambridge University Press, 2001. http://2tengines.com/485/. n.d. Keohane, Jonathan. http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/980301b.html. 1 March 1998. 14 April 2012. NASA. nasa.gov. n.d. 15 4 2012. National Institute of Standards & Technology, NIST. http://webbook.nist.gov/chemistry/. n.d. 13 April 2012. U.S. Department of Enenrgy, Energy Efficiency & Renewable Energy. http://www.eere.energy.gov/basics/renewable_energy/pv_cell_conversion_efficiency.html. 12 August 2011. 14 April 2012. U.S. Energy Information Agency, EIA. "2010 Key World Energy Statistics." Statistics. 2010. —. http://www.eia.gov/energyexplained/index.cfm?page=coal_home. 9 January 2012. 13 April 2012. Read More