Page 19 - DJJ20063- Thermodynamics 1

DJJ20063- Thermodynamics 1

1.6 Energy Conversions

Energy conversion is the process of transforming energy from one form into another.

Examples of sets of energy conversions in machines

For instance, a coal-fired power plant involves these power transfers:

i. Chemical energy in the coal converted to thermal energy
ii. Thermal energy converted to kinetic energy in steam

iii. Kinetic energy converted to mechanical energy in the turbine

iv. Mechanical energy of the turbine converted to electrical energy, which is the

ultimate output

In such a system, the last step is almost perfectly efficient, the first and second steps are

fairly efficient, but the third step is relatively inefficient. The most efficient gas-fired

electrical power stations can achieve 50% conversion efficiency. Oil and coal fired stations
achieve less. In a conventional automobile, these power transfers are involved:

i. Potential energy in the fuel converted to kinetic energy of expanding gas via

combustion

ii. Kinetic energy of expanding gas converted to linear piston movement
iii. Linear piston movement converted to rotary crankshaft movement

iv. Rotary crankshaft movement passed into transmission assembly

v. Rotary movement passed out of transmission assembly

vi. Rotary movement passed through differential
vii. Rotary movement passed out of differential to drive wheels

viii. Rotary movement of drive wheels converted to linear motion of the vehicle.

Other energy conversions
There are many different machines and transducers that convert one energy form into

another. A short list of examples follows:

• Thermoelectric (Heat → Electricity)
• Geothermal power (Heat→ Electricity)

• Heat engines, such as the internal combustion engine used in cars, or the steam

engine (Heat → Mechanical energy)
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