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- 1. Energy Efficiency Reducing the amount lost—also known as increasing efficiency—is as important to our energy future as finding new sources because gigantic amounts of energy are lost every minute of every day in conversions.
- 2. Conservation of Energy vs. Energy Conservation <ul><li>Energy Conservation is about reducing consumption by lifestyle changes and technological fixes. </li></ul><ul><li>Conservation of Energy is a law of nature that states that the amount of energy in the universe is constant and that energy is neither created nor destroyed, only transformed from one form to another. </li></ul>
- 3. Energy is Conserved <ul><li>When we use energy, it doesn’t disappear. We change it from one form of energy into another. </li></ul><ul><li>Don’t we create energy at a power plant? </li></ul><ul><ul><li>No , we simply transform energy at our power plants </li></ul></ul><ul><li>Doesn’t the sun create energy? </li></ul><ul><ul><li>No—it exchanges mass for energy </li></ul></ul><ul><li>The net energy of the entire Universe is constant. The best we can do is scrape up some useful crumbs </li></ul>
- 4. Energy Conversions <ul><li>Though the total energy of a system is constant, the form of the energy can change. </li></ul><ul><li>A simple example is that of a simple pendulum, in which a continual exchange is converted between kinetic and potential energy </li></ul>
- 5. Energy Conversions <ul><li>There are three primary sources of energy readily available for human consumption </li></ul><ul><ul><li>Chemical Energy </li></ul></ul><ul><ul><ul><li>Fossil Fuels and Biomass </li></ul></ul></ul><ul><ul><li>Nuclear Energy </li></ul></ul><ul><ul><ul><li>radioactive minerals and geothermal </li></ul></ul></ul><ul><ul><li>Radiant Energy </li></ul></ul><ul><ul><ul><li>solar and wind </li></ul></ul></ul><ul><li>We convert these primary sources into more useful energy through energy conversion devices. </li></ul>
- 6. Energy Conversion Devices <ul><li>An energy conversion device converts one form of energy into another. </li></ul>
- 7. Energy Conversion Devices
- 8. Energy Conversion Devices
- 9. Review of Work and Energy <ul><li>Work is a force over a distance. </li></ul><ul><li>Energy is the ability to do work. </li></ul><ul><li>Too put it another way…… </li></ul>Energy is money in the bank Work is when you use that money by cash, credit card, check, etc
- 10. Review of Work and Energy <ul><li>Energy can do work as </li></ul><ul><li>Work against inertia </li></ul><ul><li>Work against gravity </li></ul><ul><li>Work against friction </li></ul><ul><li>Work against shape </li></ul><ul><li>Work against combinations of above </li></ul>
- 11. Law of Energy Conservation <ul><li>The Law of Energy Conservation states that when work is done the energy can be converted from one form to another but the total energy remains constant. </li></ul>The energy input should be equal to the energy output as the woman overcomes inertia and friction to do work by pushing the box.
- 12. Work and Energy <ul><li>Work is a way to transfer energy to an object. </li></ul><ul><li>The box obtains energy by the work perform by the woman to overcome inertia and friction. </li></ul>The total work is to the change in potential and kinetic energy added to the box from the woman. W = Δ ( KE + PE ) Δ means “change in”
- 13. Thermal Energy <ul><li>All matter is made of atoms/molecules, which move around randomly </li></ul><ul><li>Thermal Energy is the energy available in the internal motion of atoms or molecules </li></ul><ul><li>Thermal Energy increases when atomic motion increases </li></ul><ul><li>Friction and other contact forces generate thermal energy by increasing the atomic motion along the surface of contact. </li></ul>
- 14. Work and Thermal Energy <ul><li>As the woman pushes the box, the molecules of the box in contact with the floor increase in motion due to friction </li></ul><ul><li>Thus the box obtains additional energy by the thermal energy generated due to friction. </li></ul>The total work can now be represented . W = Δ ( KE + PE +TE ) Δ means “change in”
- 15. Work and Energy Change <ul><li>The result of work is that one or all of the following energy changes has taken place: </li></ul><ul><ul><li>Increased kinetic energy (Work against Inertia) </li></ul></ul><ul><ul><li>Increased potential energy (Work against Gravity and Shape) </li></ul></ul><ul><ul><li>Increased thermal energy (Work against Friction) </li></ul></ul>
- 16. Perpetual Motion?? <ul><li>A simple example is that of a simple pendulum, in which a continual exchange goes on between kinetic and potential energy </li></ul><ul><li>Why won’t the pendulum swing back and forever? </li></ul>
- 17. “Waste Heat” <ul><li>As the pendulum swings back and forth in encounters air resistance and friction </li></ul><ul><li>This converts some of the energy in this system to thermal energy which is transferred to the surrounding environment as heat. </li></ul><ul><li>Total Energy = Δ ( KE + PE + TE ) </li></ul><ul><li>The TE is wasted because is not useful in the original system (pendulum) </li></ul>
- 18. High Vs Low Quality Energy <ul><li>When energy is converted in a system, two types of energy occur: </li></ul><ul><li>High Quality (USEFUL) Energy </li></ul><ul><ul><li>Organized and Concentrated </li></ul></ul><ul><ul><li>Great ability to perform USEFUL work. </li></ul></ul><ul><li>Low Quality Energy </li></ul><ul><ul><li>Disorganized and Dilute </li></ul></ul><ul><ul><li>Little ability to do work. </li></ul></ul><ul><ul><li>Usually in the form of “Waste Heat” </li></ul></ul>
- 19. Energy Flow in a System <ul><li>1) The total energy in the system is constant </li></ul><ul><li>Energy Input = Energy Output </li></ul><ul><li>2) Some of the energy input will be converted into less useful thermal energy and transferred into the surrounding environment as “waste heat.” </li></ul><ul><li>Useful Energy Output < Total Energy Input </li></ul>
- 20. Energy Conversion Devices and Efficiency <ul><li>The efficiency of an energy conversion device is a quantitative expression of the balance between energy input and useful energy output. </li></ul><ul><li>The meaning of the word ‘useful’ depends on the purpose of the device. </li></ul>
- 21. Energy Conversion Devices and Useful Energy
- 22. Incandescent Light Bulb <ul><li>Very thin tungsten filament that is housed inside a glass sphere. </li></ul><ul><li>Electricity runs through the filament, since the filament is so thin it offers a good bit of resistance to the electricity. </li></ul><ul><li>This resistance then turns electrical energy into heat. </li></ul><ul><li>The heat is enough to make the filament white hot and the “white” part is light. </li></ul><ul><li>The filament literally incandesces because of the heat. </li></ul>
- 23. Energy Conservation in an Incandescent Light Bulb <ul><li>When a convince device such as an incandescent light bulb converts electrical energy to radiant energy, the energy input is equal to the energy output . </li></ul>Electrical Energy In Radiant Energy Out Incandescent Light Bulb
- 24. However……. <ul><li>If we were to measure the energy in and the energy out of the incandescent bulb for one second, we might get energy numbers that look something below. </li></ul><ul><li>This would suggest that energy is not conserved!!! Where did the other 95 J of energy go? </li></ul>Electrical Energy In 100 J (joules) Radiant Energy Out 5 J (joules) Incandescent Light Bulb
- 25. “ Missing Energy” <ul><li>Energy can change into more than one form simultaneously. </li></ul><ul><li>If you feel a light bulb it is very hot. The "missing" energy was converted into low quality thermal energy. </li></ul>Electrical Energy In 100 J (joules) Radiant Energy Out 5 J (joules) Thermal Energy Out 95 J (joules) Incandescent Light Bulb
- 26. Efficiency of an Incandescent Light Bulb <ul><li>Suppose you paid $100 a year to light your home with incandescent light bulbs. </li></ul><ul><li>Since these light bulbs have an efficiency of 5%, only five dollars of this payment went toward paying for the light! </li></ul><ul><li>The other $95 of energy was wasted as unused thermal energy! </li></ul>
- 27. Efficiencies of common energy conversion devices <ul><li>The table on the next slide shows the energy efficiency of common energy conversion devices </li></ul><ul><li>The numbers shown are typical but they can be different for different models of the same type of device details or for the same device, depending on whether it is used and maintained properly. </li></ul><ul><ul><li>For example, your car engine will be more efficient if you change the oil regularly. </li></ul></ul><ul><li>Note that the most efficient devices are those that produce heat as the use energy output (electric drier and electric heater) </li></ul>
- 28. Efficiencies of common energy conversion devices
- 29. <ul><li>In a multistep system, the overall efficiency is equal to the product of the individual efficiencies. </li></ul><ul><li>For example, in a electrical power plant there are three main energy conversion devices: the boiler, the turbine, and the generator. </li></ul>Overall Efficiency
- 30. The Boiler <ul><li>The boiler converts chemical energy from the energy source (coal, natural gas, uranium) to thermal energy in order to generate steam. </li></ul><ul><li>A boiler has an efficiency of 88%. </li></ul>
- 31. The Turbine <ul><li>The turbine converts the thermal energy from the boiler to mechanical energy to spin the generator. </li></ul><ul><li>A turbine has an efficiency of 40%. </li></ul>
- 32. The Generator <ul><li>The generator converts the mechanical energy from the turbine to electrical energy. </li></ul><ul><li>A generator has an efficiency of 98%. </li></ul>
- 33. Efficiency of a Power Plant <ul><li>The efficiency of the power plant can be calculated by multiply the individual efficiencies of the boiler, turbine and the generator. </li></ul>
- 34. Conservation of Energy Chemical Energy in Fuel Electricity (Useful Energy) Waste Heat Total Energy In = Total Energy Out 100% Use Energy Input = 35% Use Energy Output
- 35. Thermal Pollution <ul><li>65% of the potential use energy of the power plant is released into the environment as “waste heat” </li></ul><ul><li>This unwanted heat alters the surrounding environment and is referred to as thermal pollution </li></ul>Thermal Pollution Thermal Pollution
- 36. Overall Efficiency of a Light Bulb <ul><li>Once the energy is generated at the power plant, it has to be transmitted to building to be used by energy conversion devices. </li></ul><ul><li>The efficiency of most power lines is 90% </li></ul><ul><li>What is the overall efficiency of an incandescent light? </li></ul>
- 37. Overall Efficiency of a Light Bulb
- 38. Compact Fluorescent Light Bulb <ul><li>A compact fluorescent light bulb (CFL) produces less waste heat than an incandescent bulb, so the overall efficiency rises to around 5%— better, but still a small fraction of the original. </li></ul><ul><li>Although CFLs cost more upfront, they last longer an a household could save up to $40.00 per light bulb for a 5 year period by using CFL instead of incandescent bulbs. </li></ul>
- 39. Light Emitting Diode <ul><li>Light Emitting Diodes (LEDs) generate relatively little heat, last 100 times longer than an incandescent lightbulb, and convert about 25% to 35% of electrical energy to light. </li></ul><ul><li>Additionally, they do not require bulky sockets or fixtures and could be embedded directly into ceilings or walls. </li></ul>
- 40. Cost Comparison between LEDs, CFLs and Incandescent light bulbs $652.50 $159.75 $95.95 Total cost for 50k hours $52.50 $19.75 $35.95 Equivalent 50k hours bulb expense 42 5 1 Bulbs needed for 50k hours use $600 $140 $60 Cost of electricity (@ 0.20per KWh) 3000 700 300 KWh of electricity used over 50,000 hours $1.25 $3.95 $35.95 Cost per bulb 60 14 6 Watts per bulb (equiv. 60 watts) 1,200 hours 10,000 hours 50,000 hours Light bulb projected lifespan Incandescent CFL LED

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