uses of energy
DESCRIPTION
Uses of Energy. 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. Fuels release Thermal Energy. - PowerPoint PPT PresentationTRANSCRIPT
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Uses of Energy
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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.
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Fuels release Thermal Energy
We use released heat from fuels to transform to other types of E we use to do work.
Turn a piston or a turbine.
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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.
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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.
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Steam turns a turbine. Convert Heat > KE > Electric + Heat
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• Most processes involve significant E lost to (unwanted) heat.
• Degraded E define
• Flashlight battery puts out 100 units, only 10 units transferred to light the rest is degraded “lost” to heat.
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Sankey Diagrams show E transfer.Straight arrow shows % useful work.Curved shows % degraded work.
Straight branch useful.
Branch width = proportion.
Coal Fired Plant
input
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Sankey Diagrams – some more specific about heat losses.
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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.
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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 %
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We like to convert E to electricity.
• Need some fuel to get a turbine spinning.
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Power Plant
Fuel source:Coal, Gas, OilNukes.
Heat/Steam
Coils MagnetsElectric
Recycle water
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List some energy that depend on the sun.
• Coal
• Oil
• Wood
• Solar
• Wind
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List some energy not from the sun.
• Tidal
• Nuclear
• geothermal
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Energy Density
• Fuels rated by density
• The amount of energy per kg fuel.
• Oil much denser than wood.
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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 kg
Oil= 1727 kg
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Energy Density 235U = 9 x 107 MJ/kg
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Power Plants 5:30 min
http://www.youtube.com/watch?v=20Vb6hlLQSg&feature=endscreen&NR=1
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Nuclear problem Hamper 187.