8.1 Energy degradation and power generation

8.1.1 Thermal Energy and Work

Thermal energy may be completely converted to work in a single process, but that continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.

Energy Conversion Example
source: http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html

Jet_Turbine.jpg Vijayavithal Bongale, Asst. Professor in Mechanical Engg, MCE, Hassan
The air intake is not cycled through and is all exhasted. This allows thermal energy to be completely converted to work.

Steam_Turbine.jpg Vijayavithal Bongale, Asst. Professor in Mechanical Engg, MCE, Hassan
Water (steam) is reused and energy is transfered out of the system (labeled QL)

8.1.2 Explain what is meant by degraded energy

In any process that involves energy transformations, the energy that is transferred to the surroundings (thermal energy) is DEGRADED ENERGY and is no longer available to perform useful work.

[insert examples here and leave your name and source if you used one]
  • a match [Kenny]
  • A computer (the computer heats up)
  • A car engine (heat released out of the exhaust pipe cannot be reused (lost to the atmosphere) [Jessie]
  • A steam engine (the energy is transformed from heat to kinetic energy, however, there are certain amount of energy lost during this process) [Sang Keun]
  • Iron?, as in ironing a shirt... not all energy goes to smoothing out the wrinkles. [Jessica]
  • Electronic heater [Mr. O (Hiroki)]
  • a cooking plate (not all the energy goes to heat up what we want to cook, some is lost to the atmosphere and cannot be used again) [Manon]
  • Desk light [Mr. Q (Sean)]
  • Electricity [Hao]. Electricity is not 100% efficient as some of it becomes thermal energy through resistance.

8.1.3 Construct and analyze energy flow diagrams (Sankey diagrams) and identify where the energy is degraded.

Energy flow diagrams (Sankey diagrams) show us energy conversions. An arrow is draw from left to right represents the energy changes taking place. The width of the arrow represents the power or energy involved. Degraded energy is usually drawn turning downward.

Car efficiency
A Sankey diagram for the energy in driving a car
source: http://www.antonine-education.co.uk/Physics_A2/Options/Module_7/Topic_5/topic_5_second_law_of_thermodyna.htm

Electrical power production from coal
Degraded energy of electrical power production from coal to use.
source: http://www.wbcsd.org/plugins/DocSearch/details.asp?type=DocDet&ObjectId=MTk1MjU

8.1.4 Outline the principal mechanisms involved in the production of electrical power.

Electrical energy may be produced by rotating coils of wire in a magnetic field. An EMF is induced by the change of the magnetic field density in the coil. The device with the magnets and rotating coil is called a GENERATOR.

A animated generator http://www.walter-fendt.de/ph11e/generator_e.htm