P1.2.1 Energy transfers and efficiency

When energy is transferred only part of it may be usefully transferred, the rest is 'wasted'
1. this wasted energy is eventually transferred to the surroundings, which become warmer
  1. the wasted energy becomes increasingly spread out (it's dissipated)
    1. and so becomes less useful
    2. useful energy eventually transfers to the surroundings too
key principles
1. Energy can be transferred usefully, stored or dissipated
  1. but cannot be created or destroyed
  2. the Conservation of Energy
2. energy is only useful- when it can be converted from one form to another
All energy transfers taking part in a process can be summarised with a Sankey diagram
All energy processes taking part in a process can be summarised with a Sankey Diagram
to calculate the efficiency of a device
1. use one of the two equations on the P1 equations sheet
  1. the greater the percentage of the energy that is usefully transferred in a device, the more efficient the device is
you need to think about cost-effectiveness
1. when choosing new appliances
  1. low energy light bulbs
    1. is about 4 x more efficient than an ordinary lightbulb
    2. are also more expensive
      1. but, as they last longer, are energy-saving/efficient light bulbs are generally more cost-effective
  2. LED light bulbs are even more efficient than low-energy bulbs
    1. and last even longer than them (long)
      1. but are more expensive
        and give out less light than the other two types
  3. light bulbs
    1. replacing old appliances with energy efficient ones
      1. new, efficient appliances are cheaper to run
        but are more expensive
        to work out if a appliance is cost effective, work out its
        payback time
        the time it takes for the annual saving on energy bills to equal the initial cost
        = initial cost/ annual saving
2. and efficiency
making waste energy useful
1. heat exchangers
  1. 1) Pump a cool fluid through the escaping heat
    1. 2) The temperature of this fluid rises as it gains heat energy
      1. 3) This heat energy can then be converted into a useful form
        4) either in the original appliance or for another function
        e.g. heat from a car's engine can be transferred to the air in the passenger compartment- thus warming it
Ultimately, all energy ends up as heat energy
1. If you use an electric drill, it gives out various types of energy, but they all quickly end up as heat
2. Meaning, an electric heater is perhaps the only appliance that is 100% efficient
  1. as all the electricity is given out as 'useful' heat
types of energy
1. chemical energy
  1. is energy stored in fuel (inc food. this energy is released when chemical reactions take place
2. kinetic energy
  1. is the energy of a moving object
3. gravitational potential energy
  1. the energy of an object due to its position
4. elastic potential energy
  1. the energy stored in a springy object when we stretch or squash it
    1. these types of energy are forms of stored energy
      2. e.g. they are waiting to be turned into another form
5. electrical energy
  1. energy transferred by an electric current

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