Topic 8 - Energy, power and climate change Flashcards
What is the problem in converting thermal energy to work?
Thermal energy may be completely converted to work in a single process, but the continuous conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.
What is meant by degraded energy?
The energy that spreads into the surroundings (dissipates) and that cannot be recovered to do any useful work
Draw an energy flow diagram (Sankey diagram) for a fossil fuel power station and identify where the energy is degraded
Energy is degraded whenever it is lost as thermal energy
Outline the principal mechanisms involved in the production of electrical power
Heat engines: The thermal energy from a reaction is used to raise the temperature of water in a boiler and turn it into high pressure steam. The steam rotates turbines that are connected to coils. The coils rotating in strong magnetic fields induce electrical energy. The steam exits the turbines and is cooled and condensed, and the water is pumped back into the boiler.
Identify different world energy sources
- Fossil fuels
- Nuclear power
- Renewable energy sources
Define renewable energy source
An energy source that is continuously replaced by natural processes, and the source will not be used up.
Give examples of renewable energy sources
- Biomass/biofuels
- Hydroelectricity
- Solar heating
- Wind power
- Geothermal energy
- Photovoltaic cells
- Wave power
Define non-renewable energy source
An energy source that cannot be replaced once it has been used up. Supplies will run out at some point.
Give examples of non-renewable energy sources
- Fossil fuels
- Nuclear power
Define the energy density of a fuel
The energy transferred from a unit mass of fuel. Measured in Jkg-1
State the relative proportions of the different energy sources available in the world
Oil = 38 %
Natural gas = 23 %
Coal = 25 %
Renewable sources = 8 %
Nuclear = 6 %
Outline the issues to consider about different energy sources (idk stupid question)
- Greenhouse gas emissions and possible effects on global warming
- Risks to human health
- Possible pollution and environmental effects
- Whether the source is renewable or non-renewable
- Expense
- Energy density
- Whether the energy is continuososusly available, or dependent on factors such as weather or the time of the day
Outline the historical and geographical reasons for the widespread use of fossil fuels
When the Industrial Revolution began there was a high demand for fuels, which in that time was mainly coal. Coal was cheap, plentiful, and energy dense. Later on coal and other fossil fuels were continued on using because they are simpler ways of producing energy and renewable energy is still a relatively new form of energy.
Define the power output of a power station
P = efficiency X mass of fuel burned every second X energy density
What are the advantages and disadvantages of transporting and storing fossil fuels?
Because of its high energy density, the cost of transporting is small compared to other expenses of fuels. Fuels can also be stored for many weeks ahead. Disadvantages include the risk of accidents and environmental harm
State the efficiency of power stations powered by different fossil fuels
- Natural gas = 45% efficient
- Oil = 40% efficient
- Coal = 35% efficient
Outline the environmental problems associated with the recovery of fossil fuels and their use
- Green house gas emissions → global warming
- Chemical pollution during mining and burning (e.g. acid rain)
- Non-renewable sources
- Mining can damage the environment and be dangerous to health
- Oil leakage can cause environmental harm
How can the neutrons produced in a fission reaction be used to initiate further fission reactions (chain reaction)?
Each fission releases three neutrons that can each initiate another nuclear fission, causing a chain reaction
List the stages of converting nuclear energy into electrical energy
Nuclear energy in fuel → kinetic energy of fission fragments → internal energy of water and steam → kinetic energy of steam → kinetic energy of turbines and coils → electrical energy
What are fission fragments
The resulting nuclei after a nuclear fission
In what shape is nuclear fuel usually stored and used?
The shape of rods
What kind of neutrons favour fission reactions?
Low-energy neutrons (≈ 1 eV).
What is critical mass?
The minimum mass needed for a self-sustaining chain reaction.
Distinguish between controlled and uncontrolled nuclear fission
In controlled, the number of fissions per second is constant.
In uncontrolled, each fission produces more than one further fission and the number of fissions per second increases rapidly.
What is fuel enrichment?
The process of increasing the amount of desired isotope to a certain percentage (e.g. U-235). This way nuclear fission is more likely to occur.
What does a moderator do? Give two examples
It slows down the neutrons to 1 eV or less so that the probability of fission is more likely. Graphite and cold water are often used.
What does a heat exchanger do?
It transfers the thermal energy from the water from the reaction vessel to a separate system of water. This water is then turned to steam, which goes to turbines to generate electricity.
What are control rods?
Rods usually made of boron that are used for adjusting the rate of the fission by absorbing neutrons if necessary. The rods are moved into and out of the system when needed.
Show how a uranium-238 results in the production of plutionium-239 by neutron capture
Uranium goes through beta emission to neptunium, which goes through beta emission to plutonium
What are the advantages of using plutonium-239?
It is more easily fissible than uranium-235 and releases slightly more energy per fission. Also used as a fuel in other types of reactors
What are the safety issues of nuclear power?
- The possibility of thermal meltdown
- Nuclear waste
- Problems with mining uranium (radon gas from decay)
- The possibility of a nuclear power station used to produce nuclear weapons
What are the problems of using nuclear fusion?
Maintaining and confining a very high-temperature, high-density plasma of hydrogen.
Distinguish between a photovoltaic cell and a solar heating panel
In a photovoltaic cell the solar energy is transferred to electrical energy.
In a solar heating panel the solar energy is transferred to raise the internal energy of water
Define radiation intensity
What are photovoltaic cells used for?
For low power devices like calculators and isolated single devices like emergency phones
Where are solar heating panels used?
In individual homes
List the reasons for seasonal and regional variations in the solar power incident per unit area
- The weather/climate
- The geographical latitude of the location
- Time of day
- The angle of the surface to the horizontal at the location
Outline the disadvantages of solar power
- Variation of output energy
- Panels and cells are expensive to construct and install
- Photovoltaic cells have some pollution issues during construction and recycling
- Low energy density
List the different hydroelectric schemes
- Water storage in lakes
- Tidal water storage
- Pump storage
Outline the function of water storage power generation
- Water is stored at high altitude in lakes or artificial reservoirs
- Water is allowed to drop downwards and electrical energy can be generated by turbines at the bottom of the fall
Outline the function of tidal water storage power generation
- Water is stored behind a dam at high tide and is released at low tide through turbines to generate electricity
Describe the energy transformations that take place in hydroelectric schemes
Outline the basic features of a wind generator
A conventional horizontal-axis machine
Outline the energy transformation in wind power plants
Determine the theoretical maximum power of a wind generator
See data booklet for
P = ½Apv3
Describe the principle of an oscillating water column (OWC) wave energy converter
When a crest of a wave enters the chamber it pushes air out and past turbine blades, which generate a potential difference.
When a trough enters the chamber, a partical vacuum is created in the chamber and air is forced to flow in the opposite direction and a potential difference is generated.
Determine the power per unit length of a wavefront
Power per unit length = ½A2pgv
Define the intensity of the Sun’s radiation incident on a planet
P = power of the Sun = 3.84 X 1026 W
r = distance from the Sun
Define albedo
The ratio of the total scattered or reflected power to the total incident power:
State the factors that determine a planet’s albedo
Albedo varies daily and is dependent on season, surface and latitude. Oceans have a low value (because they absorb light) but snow and ice have a high value (reflect). The Earth’s average albedo is 0.3 (30%)
Define the greenhouse effect
The natural effect of a planet’s atmosphere has in increasing the temperature of the planet to a value higher than it would be without an atmosphere
Identify the main greenhouse gases and their sources
- Methane, CH4
- Water vapour, H2O
- Carbon dioxide, CO2
- Dinitrogen monoxide, N2O
Each of the gases has natural and man-made origins
Explain the molecular mechanisms by which greenhouse gases absorb infrared radiation
Due to resonance, the molecules absorb photons of the same natural frequency. The natural frequency of the molecules of greenhouse gases is in the infrared region.
Define transmittance
A measure of the absorption of radiation in a gas. (100% means that nothing is absorbed)
Define black-body radiation
The radiation emitted from a perfect emitter, a black body.
Define black body
An idealised object which absorbs all the electromagnetic radiation that falls upon it.
Draw a graph of the emission spectra of black bodies at different temperatures
State Stefan-Boltzmann law
The total power emitted per unit area is proportional to the fourth power of the absolute temperature:
What does the total power radiated from a surface depend on?
- Surface area, A
- Surface temperature, T
- Nature of the surface
Define emissivity
The power radiated by a surface divided by the power radiated from a black body of the same surface area and temperature
Define surface heat capacity, Cs
The energy required to raise the temperature of unit areaa of a planet’s surface by one degree, measured in Jm-2K-1
List the possible models of global warming
- Enhanced greenhouse effect
- Variation in the inclination of the Earth’s axis
- Increased solar flare activity
- Volcanic activity
- Changes in the Earth’s orbital
Outline the effect of enhanced greenhouse effect on global warming
- Increase in the concentration of greenhouse gases
- Reduced intensity of radiation emitted from the Earth
- Increased combustion of fossil fuels has released extra CO2
- Possibly the most important cause of global warming
Outline the effect of variation of the inclination of the Earth’s axis on global warming
- Responsible for ice ages and other extreme conditions
Outline the effect of increased solar flare activity on global warming
- Varies over an 11 year period
- Periodically changes the Earth’s temperature slightly
Outline the effect of volcanic activity on global warming
- Produce more greenhouse gases
- Scatter ash, which reflects more sunlight resulting in a slight cooling effect
Outline the effect of changes in the Earth’s orbit global warming
- Alter the Earth’s distance from the Sun, thus affecting the temperature on Earth
What is meant by the enhanced greenhouse effect?
Due to human activities the concentration of greenhouse gases has increased, which has potentially increased the temperature of the atmosphere
Describe the evidence that links global warming to increased levels of greenhouse gases
- Ice extracted from somewhere has been studied to find out the CO2 concentration over the years
- There is a correlation between global temperatures and the CO2 concentration in the atmosphere
What may increase the rate of global warming?
- Global warming reduces ice and snow cover which increases the albedo → more heat is absorbed
- Temperature increase reduces the solubility of CO2 in the sea → more CO2 is left in the atmosphere
- Deforestation causes carbon fixation
Define coefficient of volume expansion
The fractional change in volume per degree change in temperature
What is another possible effect of the enhanced greenhouse effect?
The rise in mean sea levels
What are the possible reasons for a predicted rise in mean sea level?
Precise preditctions are difficult to make due to factors such as:
- Anomalous expansion of water
- Different effects of ice melting on sea water compared to ice melting on land
What is climate change an outcome of?
Enhanced greenhouse effect
What are some possible solutions to reduce the enhanced greenhouse effect?
- Greater efficiency of power production
- Replacing the use of coal and oil with natural gas
- Use of combined heating and power systems (CHP)
- Increased use of renewable energy sources and nuclear power
- Carbon dioxide capture and storage
- Use of hybrid vehicles
What are the international efforts to reduce the enhanced greenhouse effect?
- Intergovernmental Panel on Climate Change (IPCC)
- Kyoto Protocol
- Asia-Pacific Partnership on Clean Development and Climate (APPCDC)
