73255
Heat Transfer
- Surface & Radiation
- Every object EMITS
thermal radiation
- Dark, matt surfaces emit
more radiation than light ,
shiny surfaces
- DARK MATT SURFACES
- BETTER: absorbing
radiation than light
and shiny surfaces.
- BECAUSE
*has lots of
cavities -
which trap
and absorb
the radiation
- BECAUSE
*has lots of
cavities -
which trap
and absorb
the radiation
- BETTER: absorbing
radiation than light
and shiny surfaces.
- DARK MATT SURFACES
- Dark, matt surfaces emit
more radiation than light ,
shiny surfaces
- Every object EMITS
thermal radiation
- Conduction & Convection
- Metals conduct better than non metals
- BECAUSE * They contain FREE
ELECTIONS, which move around
randomly inside the metal and they hold
positive ions together.They collide with
each other and with the positive ions.
- IONS are
charged
particles
- EXAMPLE: a rod being heated, free
electrons on the hot end gain kinetic
energy and more faster.The electrons
then 'Defuse'/spread out and collide
with other free electrons = They transfer
kinetic energy to there electrons and
ions = energy transfer has occured
- IONS are
charged
particles
- BECAUSE * They contain FREE
ELECTIONS, which move around
randomly inside the metal and they hold
positive ions together.They collide with
each other and with the positive ions.
- Convection ONLY takes
place in Fluids (gases or
liquids)
- EXAMPLE: hot
water tank, hot water
from the boiler rises
and flows into the
tank where it rises to
the top.
- Takes place due to
CIRCULATION
CURRENTS in the
fluid
- EXAMPLE: hot
water tank, hot water
from the boiler rises
and flows into the
tank where it rises to
the top.
- Conduction
ONLY takes
place in Solids
- Metals conduct better than non metals
- Artificially modifying heat transfer at home
- Roof 25%
Windows 10%
Doors 15%
Walls 35% Floor
15%
- Sometimes we need o control heat
transfer, for example , a car engine which
overheats could go up in flames.
- Sometimes we need o control heat
transfer, for example , a car engine which
overheats could go up in flames.
- Roof 25%
Windows 10%
Doors 15%
Walls 35% Floor
15%
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