# Uses of Energy.

## Presentation on theme: "Uses of Energy."— Presentation transcript:

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
We use released heat from fuels to transform to other types of E we use to do work. Turn a piston or a turbine.

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.

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.

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

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.

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

Sankey Diagrams – some more specific about heat losses.

a. Calculate the overall efficiency of the engine.
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.

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

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

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

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

List some energy not from the sun.
Tidal Nuclear geothermal

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

Wood = 4765 kg Coal = 2492 kg Oil= 1727 kg
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

Energy Density 235U = 9 x 107 MJ/kg

Power Plants 5:30 min

Nuclear problem Hamper 187.