Convection:

The transfer of heat by the bulk movement of molecules which

only occurs in fluids or gases.

This continues flow is called a “convection current”.

What happens to the particles in a liquid or a gas when you heat

them?

The particles spread out and become less dense.

Convection in Fluids

• Cooler, more dense, fluids sink through warmer, less dense

fluids.

• Warmer liquids and gases rise up. Cooler liquids and gases sink

• The air is least dense and rises to the

top.

• The water is the most dense and sinks

to the bottom.

The density of a substance depends on how far apart its particles

are.

Water

Oil

Air

Hot water

rises

Cooler

water sinks

Convection

current

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=1DsAQy6nigFx3M&tbnid=oaizexYvYIRleM:&ved=0CAUQjRw&url=http://www.mlms.loganschools.org/~mlowe/LoweHome/SciberText/SciberStandard4Movement of energy.html&ei=r4Y0U7yVDbHLsQSH9oLABg&psig=AFQjCNHeUvmTP7ZDK2NmPPCmJ7ysx1ou_w&ust=1396037641464266

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CONVECTION

IN GASES

Why is the freezer

compartment put in a

fridge at the top?

Freezer

compartment

It is put at the top,

because cool air

sinks, so it cools the

food on the way

down.

It is warmer at the

bottom, so this

warmer air rises and

a convection current

is set up.

Concept on ventilation of a room with fire place

Concept on ventilation of a room with a radiator

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There are two Types of Convection: 1.) Natural 2.) Forced

Natural Convection: 1. Heating Water on a Pan 2. Cooling a Refrigerator 3. Land/Sea Breeze 4. Mountain/Valley Breezes

Forced Convection: 1. Fan on computer / projector 2. Hair Dryer 3. Car pump circulating radiator fluid 4. Furnace 5. Convection Oven