Heat Transfer Conduction Convection and Radiation (PowerPoint) by xuyuzhu

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```									       Heat Transfer

Conduction, Convection, and
Heat
• Heat is thermal energy moving from one
object at one temperature to an object at a
different temperature.
How is heat transferred?
• There are THREE ways heat can move.
– Conduction

– Convection

Conduction
• Heat is transferred from one particle of matter
to another in an object without the
movement of the object.

• Conduction=CONTACT
Have you ever…
• Touched a metal spoon sitting in a pan of
boiling water only to be surprised by hot HOW
it is??
Example of Conduction
• Think of a metal spoon in a pot of hot water being
heated on an electric stove.
• The fast-moving particles of the hot electric coil (in the
stove) collide with the slow-moving particles of the cool
pot.
• Because of these collisions, the slower particles move
faster and heat is transferred.
• Then the particles of the pot collide with the particles
in the water, which collide with the particles at one end
of the spoon.
• As the particles move faster, the metal spoon gets
hotter. This process of conduction is repeated all along
the metal until the entire spoon is hot.
Examples of Conduction
• A piece of metal in a forge glows red as heat is
transferred to the metal from the forge.
Why does metal feel colder than wood, if they
are both at the same temperature?

Metal is a conductor, wood is an insulator. The metal conducts the
heat away from your hands, the wood does not conduct the heat
away from your hands as well as the metal, so the wood feels warmer
than the metal.
CONVECTION
• Convection is the movement that transfers
heat within the water.

• In convection, heat is transferred by the
movement of currents within a FLUID (liquid
OR gas)

• Convection=VENTS through air and liquid
particles
Have you ever…
• noticed that the air near the ceiling is warmer
than the air near the floor?
• Radiation is the transfer of energy by
electromagnetic waves.

• Radiation does NOT require matter to transfer
thermal energy. (Passes through a vacuum.)

Have you ever…
• sat too close to a campfire while cooking
marshmallows– enjoying the warmth-- only to
notice (when you move) that your skin is really
warm?
• You can FEEL the radiation from a bonfire from
several meters away!
• Think of the sun’s radiation…it travels through
MILLIONS of kilometers of empty space to
reach us.

• A blacksmith feels radiation from his forge.

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why are shiny foil blankets wrapped around marathon runners at the end of a
race?

The shiny metal reflects the heat radiation from the runner back in, this stops
the runner getting cold.

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