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Understanding Energy and Power: Conversion, Work, and Conservation

Explore the uses of energy in various forms, from converting energy to doing work to power plants and energy density. Learn about energy conservation, thermal energy transfer, engines, and Sankey diagrams. Discover how different fuels release thermal energy and how energy can be lost in processes.

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Understanding Energy and Power: Conversion, Work, and Conservation

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  1. Uses of Energy

  2. Energy, Work, Power, Climate • We like to convert E to do work. • Conservation of E says we cannot create E, but we can transfer E between objects. • E can be transferred by inputting thermal E to object.

  3. Fuels release Thermal Energy We can use released heat from fuels to transform to other types of E we use to do work. Turn a piston or a turbine.

  4. A Cyclic Process needed to do continuous work. • Engines convert fuel to KE. • In order to have continuous work, system must be returned to original state. • E is “lost” when system returns to original state.

  5. Hamper ex: hot air balloon rises to force rope to rotate a spool thus doing work. Once rope is used up, balloon must cool to return to ground & be re-heated a cycle. Some heat is “lost” in the process when balloon cools to return to ground.

  6. Steam turns a turbine. Convert Heat > KE > Electric + Heat

  7. Electric CurrentChem E (battery) > KE e- > Light (lamp) + Heat

  8. Most processes involve significant E lost to (unwanted) heat.Degraded E.Flashlight battery puts out 100 units, only 10 units transferred to light the rest is degraded “lost” to heat.

  9. Sankey Diagrams show E transfer.Straight arrow shows % useful work.Curved shows % degraded work. Coal Fired Plant Branch width = proportion. input Straight branch useful.

  10. Sankey Diagrams – some more specific about heat losses.

  11. Ex 1: In a car engine chemical E is converted to KE of the wheels as shown. • a. Calculate the overall efficiency of the engine. • b. Calculate the engine efficiency ignoring frictional losses.

  12. Eff = useful work x 100 %tot work • a. 300 J/ 1000 J x 100% = 30% • ~ 550 J “lost” to friction. • b. (300 + 550) J /1000 J x 100% = 85 %

  13. We like to convert E to electricity. • Need some fuel to get a turbine spinning.

  14. Power Plant Heat/ Steam Coils Magnets Electric Fuel source: Coal, Gas, Oil Nukes. Recycle water

  15. List some energy that depend on the sun. • Coal • Oil • Wood • Solar • Wind

  16. List some energy not from the sun. • Tidal • Nuclear • geothermal

  17. Energy Density • Fuels rated by density • The amount of energy per kg fuel. • Oil much denser than wood.

  18. Ex 2. Use the Energy density table Hamper to calculate the following:A steam engine has 4500 kW of power. If we wish to run the engine for 5 hours, how many kg of each type of fuel will be needed? Wood = 4765 kg Coal = 2492 kgOil= 1727 kg

  19. Energy Density 235U = 9 x 107 MJ/kg

  20. Hwk Nuclear Power wksht w/reading.

  21. Power Plants 5:30 min http://www.youtube.com/watch?v=20Vb6hlLQSg&feature=endscreen&NR=1

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