Methods of Heat Transfer Notes

Temperature – measurement of the average kinetic energy of the molecules in a substance

Kinetic Energy – energy in the motion of molecules

Heat flow – thermal energy travels as heat from an area of high temperatures to an area of low temperature (warmer to cooler objects)

Thermal equilibrium – heat flow from a warmer object to the cooler object, back and forth until they are both the same temperature

1st Law of thermodynamics – the heat lost by one object is equal to the heat gained by the other object

Heat Transfer Methods

  1. Conduction
  2. Transfer of heat by direct contact of particles of matter (from molecule to molecule)
  3. Occurs between two materials at different temperatures when they are touching each other
  4. The atoms of the hotter material have more kinetic energy and therefore transfer this energy to the cooler material by the collisions of atoms until thermal equilibrium is reached
  5. Thermal conductivity – the degree to which something can conduct heat; measures how good of a conductor a material is
  6. Thermal Conductors: conduct heat easily. They tend to be dense and/or metallic solids which conduct heat and electricity better than liquids and gases
  7. Thermal Insulators: poor conductors of heat. Tend to be less dense and/or non-metallic (wood, air, Styrofoam, glass, rubber, plastic)
  8. Convection
  9. Transfer of heat by the actual motion of a fluid (gases or liquids) in the form of currents
  10. Warm fluids are less dense and rise
  11. Cool fluids are more dense and sink
  12. Natural convection
  13. Causes global winds- a result of the unequal heating of the globe because of Earth’s tilt, local winds (land and sea breezes)- a result of unequal heating based on specific heat differences of sand and water, and the boiling of fluids
  14. Forced convection
  15. The use of mechanical devices like heaters and pumps to circulate a fluid
  16. Radiation
  17. Transfer of heat by electromagnetic waves that occur in the presence or absence of (vacuum) of matter
  18. Radiation can transfer heat through space whereas convection and conduction must take placed in the presence of matter
  19. Electromagnetic radiation is in the form of all the different light types from the electromagnetic spectrum (visible light, infrared, ultraviolet, radio, micro , x-ray and gamma)
  20. Radiation is reflected or absorbed in varying amounts by objects
  21. Absorbers – absorb heat/light well and are dark colored
  22. Reflectors – reflect heat/light well and are light colored or shin and metallic
  23. Emitters – those objects that can reemit (give off) heat by radiation, conduction, convection
  24. Color temperature relationship exists for objects that emit visible light
  25. ROYGBIV – with red being the least hot and violet being the most hot