Topic 8 Energy Production Flashcards
the law of conservation of energy
“energy cannot be created nor destroyed, only changed from one form to another”
(usually to transfer energy, work must be done, exception: transfer of thermal energy)
sankey diagram
show the flow of energy through a system and identify where energy is lost to the surroundings
fuels:
- are sources of energy
- release energy by changing their chemical or nuclear structure
- in releasing energy their atoms lose Ep and gain Ek (heat)
- an engine or machine is needed if the heat produced is to do work eg. car engine (heat from petrol is used to move the car)
- some heat is always lost to the surroundings (second law of thermodynamics: “it is not possible to convert heat completely into work”)
- this lost energy is known as degraded energy - because this energy is no longer able to perform useful work
specific energy in fuels
the energy liberated per unit mass of fuel consumed
unit: Jkg^–1 (MJkg^–1)
eg. coal = 30 MJkg^–1
uranium = 80 000 000 MJkg^–1
energy density in fuels
the energy liberated per unit volume of fuel consumed
unit: Jm^–3 (MJm^–3)
primary sources definition
has not been transformed or converted before use by a consumer
eg. burning coal to release its chemical potential energy for hearing or using the kinetic energy of the wind to turn a windmill to grind corn.
secondary sources
results from the transformation of a primary source
eg. the electrical energy generated by coal-fired power stations or wind turbines is a secondary source of energy.
non-renewable energy sources definition
energy sources that can be used up because they are used at a greater rate than they are produced
eg. coal, oil, gas, uranium
renewable energy sources definition
energy sources that cannot be used up or are used at a rate that effectively means the sources will NOT run out
ie. rate of production is greater than the rate of usage
eg. hydro, wind, solar, tidal, wave, geothermal
total global fuel use of coal
38%
total global fuel use of coal to produce electrical energy
40%
generating electrical energy: generator
- a conductor is moved relative to a magnetic field,
- then a force is exerted on the electrons in the conductor and a voltage difference will be induced across the conductor.
- If the conductor is part of a circuit a current will flow
fluids typically used in turbines to convert the flow of a fluid into mechanical motion within the generator
- steam
- water
- hot gas
- wind
production and usage of electrical energy measurement unit:
1 kilowatt-hour (kWh) = 3.60 x 10^6 J
a kilowatt-hour is the amount of energy used by a 1kW device in one hour
advantages and disadvantages of fossil fuels
Advantages:
- very high energy density
- easy to transport
- cheap
- can be used directly or heating
- power stations can be built almost anywhere
Disadvantages:
- combustion products produce pollution (e.g. acid rain), “greenhouse” gases
- fuel extraction can damage the environment
- non-renewable
- power stations need large amounts of fuel
how do nuclear power stations generate energy
nuclear fission that releases energy
most common fuel source of nuclear power
uranium-235
splits into barium-141 and krypton-92
how does uranium-235 undergo fission to produce energy
a neutron source such as americium-241 and beryllium-9 is used to initiate the fission process.
if the mass of uranium-235 is large enough (critical mass) then enough neutrons produced by fission will collide with further uranium nuclei to sustain fission before being lost from the surface of the fuel - this is know as a chain reaction
what percentage of uranium is uranium-235 and what percentage does it need to be at to be used to produce power
0.7%
needs to be at around 5% before it can be used in a nuclear reactor
what does a moderator do in nuclear power station
the high energy neutrons must be slowed down so that collisions with U-235 nuclei cause fission to occur.
(collisions between the moderator’s nuclei and the neutrons reduce the kinetic energy of the neutrons from several MeV to just several eV)
makes fission happen
eg. water, graphite
what do control rods do in nuclear power station
the control rods absorb neutrons.
(by lowering the rods into, or raising them out of, the reactor ore the fission reaction can be controlled. an uncontrolled chain reaction is like totally bad - it’s a nuclear bomb)
control the rate of fission
eg. cadmium
what does a heat exchanger do in nuclear power station
water heated by the fission reactions enters the heat exchanger and its thermal energy is transferred to cold water in a seperate circuit to convert it into steam to drive the turbines
energy flow diagram of nuclear power generator
Ek of fission products ––> thermal energy of water ––> Ek of turbines ––> Ek of generator ––> electrical energy
advantages and disadvantages of nuclear power
advantage:
- uranium has a very high specific energy (need 10x more coal)
- relatively large reserves of uranium
- no greenhouse gases are produced during energy production
disadvantage:
- radioactive waste is produced (safe storage is needed)
- high risk if things go wrong (radioactive contamination)
- non-renewable (but uranium reserves will last a long time)
