Heat Transfer

Heat Transfer

1. Heat energy can be transferred in three different ways:

   • Radiation
     • Emitted by solids, liquids and gases
     • An object that is hotter than its surroundings emits more than it absorbs
     • Radiation depends on surface colour and texture
       • Dark, matt surfaces:
         • Absorb infrared radiation better
         • Emit much more
       • Light, shiny surfaces:
         • Reflect more infrared radiation
   • Conduction
     • Mainly occurs in solids
     • CONDUCTION OF HEAT ENERGY IS WHERE VIBRATING PARTICLES PASS ON THEIR EXTRA KINETIC ENERGY TO NEIGHBOURING PARTICLES
     • Metals are good conductors due to their free electrons
       • The electrons can move freely meaning that it is a much faster way of transferring energy
   • Convection
     • Only occurs in liquids and gases
       • Can't happen in solids because the particles can't move
       • Other processes that only happen in liquids and gases:
         • Condensation
           • This is when gas turns into a liquid
             • If the temperature gets cold enough and the particles get close enough condensation takes place
         • Evaporation
           • This is when a liquid turns into a gas
             • The particles with the most kinetic energy are most likely to evaporate
     • CONVECTION OCCURS WHEN THE MORE ENERGETIC PARTICLES MOVE FROM THE HOTTER REGION TO THE COOLER REGION- AND TAKE THE HEAT WITH THEM
     • Convection currents are all about changes in DENSITY
       • Heating a room with a radiator relies on convection currents
         • Hot, less dense air near the radiator rises and so denser, cooler air flows to replace it

2. By Stephen Thompson