Heat transfer
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Conduction , Convection and Radiation.
Transcript of Heat transfer
Modes of Heat Transfer
Conduction
Convection
Radiation
Conduction is the transfer of thermal energy through a substance , or between substances in contact, by the collision of particles.Conduction occurs in solids and liquids.
Convection is how the air contacted with heat material, which takes it to other materials with different temperatures. Convection occurs in liquids and gases.
The process in which energy is transferred waves. It is the combined processes of emission, transmission, and absorption of heat or light.Occurs in the presence of light in no medium.
CONDUCTION
Molecular vibration
Free electron diffusion
Occurs in all solids
Slow process
Occurs in metals only
Fast process
Two types of conduction Molecular vibration Free electron diffusionConductors and InsulatorsMaterials that can conduct heat easily and readily (eg. Metals) are known as conductors.Materials that do not conduct heat easily (eg. Water, air, plastic) are known as insulators.
What happens during convection?
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•Water at the bottom is heated first.
•Heated water expands.
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•When water expands density decreases
•Heated water of lower density starts to rise.
3
•Cooler water of higher density rushes in from sides to take its place.
•The cooler water gets heated and the cycle repeats.
Convection currents are set up.
Taking the example of heating water.
Convection
Hot water rises
Cooler water sinks
Convection currents
Cools at the
surface
Convection helps to make the Earth liveable as it removes excess heat from the Earth and transporting it high up into the atmosphere.
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Applications of convection.
Air con is usually placed at the top of a room.
Heating coil of a kettle is usually at the bottom
Formation of land and sea breezes
RadiationRadiation does not require a medium
to transfer heat. (can occur in a vacuum)
Sun releases electromagnetic waves (heat is contained in the waves as infra-red)
Hotter objects radiates more heat.
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Emitters and absorbers The Sun gives out the heat. It is known as an emitter / radiator The Earth takes in the heat. It is known as an absorber.
A good emitter would also be a good absorber.
A poor emitter would be a poor absorber.Good emitter/absorber
Poor emitter/absorber
Dull, black surfaceRough surface
Shiny, silver surfaceSmooth surface
Done By :Alefiya &
Disha.
