Transcript Convection

Convection
Material Flow

Objects at different temperatures may not be in direct
thermal contact.

An intermediate mechanism is needed to transfer
heat.

If the heat transfer is through the motion of a fluid,
then it is called convection.
Fluid Motion

Objects in a fluid have a
force of buoyancy.

Materials expand when they
are heated.
Fb = mg
• Increased volume
• Lower density

Warm fluids generally rise.
Fnet  coolVg   warmVg
Circulation

If one area in a fluid is
heated that are will become
less dense.

As it moves away it transfers
energy and cools

Cool fluid replaces the warm
fluid that left.
Home Heating

Convection causes heat to
circulate in a house.
• Water circulates in pipes
• Air circulates around
radiators.

Forced circulation uses a fan
to push heated air.
• Faster exchange of heat
Thunderstorm
Warm air rises in the storm over
a mass of colder air.
The moisture condenses as the
air cools.
The cool air in the storm
descends with precipitation.

Thunderstorms move heat
energy with convection.

Temperature difference is
between masses of warm
and cold air.
Global Circulation

Warm air at the equator also
rises.

As it moves poleward it
cools.

The cool air descends.

This forms a Hadley cell.
Global Circulation

The rotating earth breaks up
the Hadley cell.

Circulation moves heat in a
complex pattern that controls
the weather.
More Convection

Convection moves heat in many systems.
• Inside the oceans – ocean currents
• Inside the earth – continental drift
• Inside the sun - sunspots
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