8.1.1 State that 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.
The conversion of energy needs to be cyclical in order to provide enough work for a machine. The cyclical conversion of energy also requires some of that energy to be released into the environment. An example would be the internal combustion engine, where chemical energy is converted to mechanical energy. In order for this process to work, it needs to be cyclical and some energy needs to be released.
8.1.2 Explain what is meant by degraded energy.
A typical power station may be only 35% efficient, so that 65% of the energy is degraded and transferred to the surroundings of the power station. This released energy is also known as degraded energy, it cannot be used to perform work. Degraded energy mostly comes in the form of heat. The higher the temperature of the input and the lower the temperature of the output, the higher the efficiency of the system. An example would be a light bulb, where 100J are put in, but not all are used. The light bulb heats up as a result of the degraded energy.
8.1.3 Construct and analyze energy flow diagrams (Sankey diagrams) and identify where the energy is degraded.
Sankey diagrams indicate how much energy remains after a series of transformations. The arrows pointing upwards indicate exhaust while the arrows pointing downwards indicate loss due to heat, friction or other factors. The thickness of the lines should be proportional to the percentage of energy being represented. Exercises with Sankey diagrams include identifying where energy is degraded, calculating overall efficiency and drawing diagrams to represent energy conversions.
Using Sankey diagrams, we can calculate the efficiency of a process. Efficiency can be calculated by:
(Useful Energy Output ÷ Total Energy Input) x 100
It is a percentage value with no units.
Using Sankey diagrams, we can calculate the efficiency of a process. Efficiency can be calculated by:
(Useful Energy Output ÷ Total Energy Input) x 100
It is a percentage value with no units.
8.1.4 Outline the principle mechanisms involved in the production of electrical power.
Electricity can be produced mechanically, chemically or through photovoltaic cells. It can also be stored chemically in the form of batteries.
Mechanical energy is converted to electrical power through an electric generator. Electric generators are powered through steam, water or air. Generators come in the form of AC (alternating current) or DC (direct current). Most generators have a wired loop or coil that is rotated in a magnetic field to produce a current, this is called electromagnetic induction. The wired loop or coil is attached to a turbine that will turn when it is impacted by steam, wind or water, thus creating a current.
Mechanical energy is converted to electrical power through an electric generator. Electric generators are powered through steam, water or air. Generators come in the form of AC (alternating current) or DC (direct current). Most generators have a wired loop or coil that is rotated in a magnetic field to produce a current, this is called electromagnetic induction. The wired loop or coil is attached to a turbine that will turn when it is impacted by steam, wind or water, thus creating a current.