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Heat Transfer

Heat Transfer. Thermal Equilibrium. Thermal energy is transferred from a region of higher temperature to a region of lower temperature. Regions of equal temperature will be in thermal equilibrium. Objectives. Thermal Equilibrium Conduction Convection Radiation. Conduction.

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Heat Transfer

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  1. Heat Transfer

  2. Thermal Equilibrium • Thermal energy is transferred from • a region of higher temperature to a • region of lower temperature. • Regions of equal temperature will • be in thermal equilibrium.

  3. Objectives • Thermal Equilibrium • Conduction • Convection • Radiation

  4. Conduction • The transfer of thermal energy through • matter from particle to particle. It is the • transfer and distribution of heat energy • from atom to atom within a substance. • It is the transfer of heat within a solid.

  5. Conduction

  6. Conduction If heat is applied directly to one part of a solid object, the electrons become excited. This causes molecular collisions that travel along the object, heating as it passes through.

  7. Conduction - Non Metals Wooden Rod

  8. Conduction - Metals

  9. Metals vs Non-Metals CONDUCTORS INSULATORS A poor conductor is a good insulator.

  10. Discussion Time! • What is the best insulator? • Why are liquids and gases poor • conductors of heat?

  11. Convection Convection is the process by which heat is transmitted from one place to another by the movement of heated particles of a gas or liquid.

  12. Convection Cold air being denser and sinks. Hot air becomes less dense and rises.

  13. difference in density Convection When a fluid at the bottom is heated It becomes less dense and starts to rise The colder fluid at the top being denser will sink to replace the hotter fluid Convection currents are set up

  14. Discussion Time! Why does convection only in fluids (liquids and gases) but not in solids?

  15. Radiation • Radiation is the process by which heat • energy is transmitted as electromagnetic • waves (or infrared radiation ). • It does not require any medium. • It can take place a vacuum. • Heat is transmitted at the speed of light.

  16. RADIATE the heat to you!!! Hehehe…. Oh.. You poor thing… Let me give you some heat… Don’t worry…. Cos I can……. Oops… Sorry.. Hope you like it… hehehe… Grrr….. I am feeling very cool….. Conduction & convection can’t take place… But how??!! There’s a VACUUM between us…. Oh.. That’s too much.. But.. Thank you…

  17. Emission of Radiation • A surface’s temperature falls when it emits radiation. • 3 factors: • Surface temperature • The hotter the surface, the more heat it emits. • Surface area • The bigger the surface area exposed to the surroundings, the faster heat is emitted. • Colour and texture of the surface • Dull, black surfaces are better emitters than shiny, white surfaces.

  18. Emission of Radiation

  19. Absorption of Radiation • A surface’s temperature rises when it absorbs radiation. • The ability to absorb radiation depends on the colour and texture of the surface.

  20. Absorption of Radiation

  21. A good emitter is also a good absorber.

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