Fire Unit

• Heat


  The average kinetic energy of molecules (when we burn fossil fuels, absorb solar energy)
• Light


  The energy associated with photons, either from the sun or from artificial light
• The bulk of energy on the planet comes from the sun, which drives processes like photosynthesis (net storage of energy)
• Chemical energy


  Stored in batteries, photovoltaics convert the sun into electrical energy
• Mechanical energy

  When there is a potential difference that generates an electromagnetic force, this can drive pressure, volume, work etc of atoms
• Kinetic energy

  • Depends on how fast and object with mass is moving
  • Can be ordered, high quality kinetic energy with no entropy component to it (best for work recovery) transferred through work
  • Can also be disordered in no particular direction, transferred through heat
• Potential energy


  Energy associated with particles in some field (gravitational), may also include electrostatic energy, and nuclear energy
• Every time energy is converted, energy is lost
• The Schrodinger equation gives the location and energy of electrons
• Laws of thermodynamics


  • Conservation of energy
  • Entropy always increased (spontaneousness)
• Maxwell Boltzmann distribution


  Tells us the probability of having a molecule/atom at a particular speed. The maxima in the graph corresponds to a given temperature that is the average kinetic energy of all particles in the system
• Collision of molecules


  1. Transfer of elastic energy (sticky collisions)

  2. They stay together sometimes after collision which results in some energy loss

  3. A system that's a equilibrium/steady state will have elastic collisions (no loss so Temp and Pressure remain constant)

  4. During expansion, you will see inelastic collisions where there is some loss as work and the gas cools
• Second law (Entropy)


  The number of ways you can disperse energy and arrangements of systems. Processes that happen spontaneously will increase entropy in the universe. When we put in work and energy into a process, entropy will be dispersed somewhere else in the universe. We reach equilibrium when entropy is zero. The system will tend towards the micro state that has the most individual micro states (most random)
• You need a difference in temperature to run an engine which is then converted to work
• Carnot cycle

  1. First isothermal expansion in a piston with added heat (reversible)

  2. Insulate and run adiabatic expansion, gas cools

  3. Isothermal compression in a piston with cold reservoir

  4. Adiabatic cooling as the gas condenses
• Most cars only have 20% heat to work efficiency
• Coal power plant

  1. Chemical energy in the form of fossil fuels is combusted and converted to thermal energy

  2. Thermal energy heats steam to produce mechanical energy in a turbine

  3. Mechanical energy is converted to electrical energy
• Unusable forms of energy

  • Heat
  • Sound
  • Light (from combustion fire)
• Two thirds of energy in the USA is rejected energy lost to the environment, of which the transportation sector is the most wasteful
• Non-renewable sources of energy

  • Fossil fuels
  • Natural gas
  • Nuclear
• Geothermal energy is the only renewable source of energy that doesn't come from the sun, but the planet itself
• Hydrogen is often used as a carrier for electricity but it is not a source
• Turbines


  • Used to convert thermal energy (steam) to mechanical energy
  • The steam causes a shaft connected to an alternator to rotate and produce electricity
  • There are two types: impulse turbines and reaction turbines
• Impulse turbine


  Has a nozzle for the steam to impact the blades to spin while pressure remains constant
• Reaction turbine


  Has a guide mechanism for the steam that creates pressure and kinetic energy, the blades increase in length to increase efficiency
• Steam turbines have low maintenance, low costs, and are reliable, but take time to start and stop
• Gas turbines have compressed air and fuels at high temperatures and pressures
• You can combine gas and steam turbines through a combined cycle process where hot exhaust from gas turbine heats steam in steam turbine, this allows 50% more power to be generated
• Carbon capture is done to reduce CO2 emissions but requires energy to do so, thus reducing the efficiency of the plant
• In nuclear power generation, the water in the reactor is kept as a liquid by maintaining high pressures
• The largest solar power plants are located in India, China, and Egypt which cover over 50 square kilometers of land (example for Bola solar park in Rajasthan)
• Solar cells have inverters which convert DC current to AC current and the transformed to an appropriate voltage
• Thermal energy storage


  Heating a storage medium to later convert into heat (heat reservoirs)
• Kinetic energy storage


  Storing energy in the energy of motion (flywheel)
• Mechanical and potential energy storage

  • Putting energy into springs
  • Compressed air
  • Raised weights
• Chemical storage


  Using chemical compounds or potential difference such as batteries to store energy
• Aim of energy storage


  • Have small space needed for higher energy and power densities
  • Avoid losses in storage or through self-discharge
  • Long lifetimes
  • Low emissions
  • Safe and reliable in various conditions
• In the USA, pumped hydro is the most common but the pipeline trend is towards electrochemical and thermal storage
• Pumped hydro


  • Used for large scale storage
  • Can supply 1000 watts over a large discharge time (hours)
• Compressed air energy storage (CAES)

  • 2 plants in Germany and Alabama
  • Compresses air and stores in a cavern or salt mine
  • Expanded in a turbine to generate electricity
  • Allows for long period and seasonal storage
  • Efficiency around 42% for diabatic process and 70% for adiabatic process