Title 8.1 Energy sources, Nuclear ractors and safety.pdf ✅

8.1 – Energy sources Specific energy and energy density of fuel sources • Specific energy and energy density are useful measures of the energy that will be released from a given weight or volume of fuel when it is burned. • Specific energy is the energy per unit mass of the fuel and can be given by energy/mass (J/kg) • Energy density is the energy per unit volume of a fuel and can be given by energy/volume (J/m3 ) Sankey diagrams Sankey diagrams show the total input on the left and where this energy goes on the right/below. Energy that flows to the right is useful output, energy that flows downwards is degraded (wasted) energy. The width of each arrow is proportional to the amount of energy in that section The Sankey diagram below is for a fossil fuel power station Energy degradation While energy may be completely converted into work in a single process, a cyclical process is required to convert thermal energy to work continuously. In accordance with the second law of thermodynamics, some energy will be lost to the surroundings and cannot be used to perform useful work. The unavailable energy is called degraded energy. This Photo by Unknown Author is licensed under CC BY-SA
Primary energy sources Primary energy sources are found in nature and have not been subjected to any conversion or transformation process. Examples of use of primary energy sources are shown in the chart below: Electricity as a secondary and versatile form of energy Electricity is a secondary source because it has to be generated from primary sources. It is a versatile and convenient form of energy. It gives us a continuous supply of energy that can power a range of appliances and is clean at the point of use. Production of electrical power: A fuel is burnt to release heat, which is used to boil water to produce pressurised steam. The pressurised steam drives a turbine which is connected to a generator. When the turbine rotates, the generator rotates. Electrical power is produced via electromagnetic induction in the generator. Renewable and non-renewable energy sources • There are two categories of primary energy sources: renewable energy resources and non-renewable energy resources. • Renewable energy sources are the ones which cannot be depleted. • Non-renewable energy sources can be used up and become depleted. • Most energy sources derive their energy from the sun directly (e.g. solar power) or indirectly (e.g. fossil fuels).
Solar power • Solar heating panel: sunlight directly used to heat up water.
• Photovoltaic cells: sunlight directly converted into direct electrical current (dc), as the light incident on the panel releases electrons and establishes a potential difference across the cell. Wind power • Equation: maximum theoretical value of the available power = 1⁄2 ρAv3 where ρ = density of air = 1.3 kg m–3 A = area swept out by blades per revolution (=area of circle or radius = blade length); v = wind speed o Assumptions: no wind, no friction or turbulence. • Ideal places: off-shore and top of hills, due to higher wind speeds. Hydroelectric power • Process: potential energy of a mass of water transferred into electricity. • Formula: Power = Energy/time = mgh/∆t = ρ∆Vgh/∆t = ρQgh, where Q = volume flow rate and ρ the water density. • Reverse process (pumped storage system): storing energy on a large scale when needed, this requires more energy than will be gained.