Heat Transfer

Heat Transfer

1. Surface & Radiation

   • Every object EMITS thermal radiation
     • Dark, matt surfaces emit more radiation than light , shiny surfaces
       • DARK MATT SURFACES
         • BETTER: absorbing radiation than light and shiny surfaces.
           • BECAUSE *has lots of cavities - which trap and absorb the radiation

2. Conduction & Convection

   • Metals conduct better than non metals
     • BECAUSE * They contain FREE ELECTIONS, which move around randomly inside the metal and they hold positive ions together.They collide with each other and with the positive ions.
       • IONS are charged particles
       • EXAMPLE: a rod being heated, free electrons on the hot end gain kinetic energy and more faster.The electrons then 'Defuse'/spread out and collide with other free electrons = They transfer kinetic energy to there electrons and ions = energy transfer has occured
   • Convection ONLY takes place in Fluids (gases or liquids)
     • EXAMPLE: hot water tank, hot water from the boiler rises and flows into the tank where it rises to the top.
     • Takes place due to CIRCULATION CURRENTS in the fluid
   • Conduction ONLY takes place in Solids

3. Artificially modifying heat transfer at home

   • Roof 25% Windows 10% Doors 15% Walls 35% Floor 15%
     • Sometimes we need o control heat transfer, for example , a car engine which overheats could go up in flames.