heat transfer

heat transfer

1. conduction

   • transfer of heat energy through the vibration of particles
   • pan on hob
     • heat energy from hob causes particles in the pan to vibrate more and gain heat energy
       • when food is placed into the hot pan energy is transferred from the particles in the pan to the particles in the food
   • metals are good conductors of heat
     • why pans are made out of metal

2. convection

   • transfer of heat energy through gases or liquids
   • when you heat up a liquid, the liquid near the heat source warms up faster
     • the warmer liquid rises above its colder surroundings
       • as the warm liquid rises, cooler liquid takes its place
         • as the process continues, you end up with a circulation of fluid (convection currents)
   • also occurs in ovens
     • hot air rises and cooler air falls

3. radiation

   • transfer of heat energy through waves of radiation
   • no direct contact between the heat source and the food
   • cookers and grills use radiation to cook food
     • they emit waves of radiation
       • when these waves reach the food, they are absorbed and heat up the food
   • microwaves use radiation to heat up the fat, sugar and water molecules in our food