heat transfer

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  • Created by: helen
  • Created on: 13-01-13 18:14
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  • heat transfer
    • thermal radiation = infra-red radiation.
    • dark matt surfaces emit more radiation then shiny light ones.
      • they also absorb radiation better.
      • shiny, light surfaces reflect radiation the best.
    • conduction: free electrons are given where heated and diffused- this energy is passed on as electrons collide.
      • a conductor can pass on energy quicker.
    • convection occurs with only liquids or gases.
      • Hot, light air rises, whilst cold, dense air sinks. This causes convectioncurrent in gases and liquids.
        • fluids expand when heated making them lighter
    • vacuum cuts out heat transfer by conduction and convection.
      • glass is a poor conductor so little heat conducted here.
      • glass surfaces are silvery to reduce radiation from outer wall.
    • double glazed windows with vacuum reduces conduction.
      • cavity wall insulates reducing heat loss
      • loft insulation reduces heat loss through roof.

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