P.16-19

P.16-19

1. Rate of Heat Transfer

   • The rate of heat energy transfer depends on many things
     • Surface area
       • The larger the surface area the faster the rate of heat transfer
     • Volume
       • The larger the volume the slower the rate of heat transfer
     • Type of material
       • Objects made from good conductors transfer heat away quicker
   • Some devices are designed to limit heat transfer
   • Humans and animals have ways of controlling heat transfer too
     • In the cold, the hairs on your skin stand up to trap a layer of air around your body
       • This prevents convection
     • When you're too warm, your body diverts blood to flow nearer to the surface of your skin
       • This causes more radiation

2. Energy Transfer

   • There are nine types of energy:
   • Electrical Energy
   • Light Energy
   • Sound Energy
   • Kinetic Energy
   • Nuclear Energy
   • Thermal Energy
   • Gravitational Potential Energy
   • Elastic Potential Energy
   • Chemical Energy
     • These are forms of stored energy
   • Energy can be transferred usefully from one form to another stored or dissipated- but it can never be created or destroyed
   • Energy is only useful when it can be converted from on form to another

3. Specific Heat Capacity

   • Specific Heat Capacity tells you how much energy materials can store
     • It takes more heat energy to increase the temperature of some materials than others
   • E = m x c x ϑ
   • Energy transferred = Mass x specific heat capacity x temperature change
   • J = kg x J/kg°C x °C
   • Heaters are designed to have high heat capacities to store lots of energy

4. Energy efficiency in the home

   • Effectiveness and cost-effectiveness are not the same thing
     • The most effective methods of insulation give you the biggest annual saving
       • The money you've saved on heating bills will equal the initial cost
         • This is the payback time
     • The most cost-effectiveness methods tend to be the cheapest
       • They have a short payback time
   • Cavity wall insulation, Loft insulation, Draught-Proofing, Hot water tank jacket, and Thick curtains
     • U-Values show how fast heat can transfer through a material

5. By Stephen Thompson