Heat transfer is the exchange of thermal energy between physical bodies.

1. Heat Transfer
By Prof. Liwayway Memije-Cruz

2. The transfer of heat is normally from a
high temperature object to a lower
temperature object. Heat transfer changes
the internal energy of both systems involved
according to the First Law of
Thermodynamics.

3. Heat Transfer

4. Conduction

5. Conduction is the transfer of
heat between substances
that are in direct contact
with each other. The better
the conductor, the more
rapidly heat will be
transferred. Metal is a good
conduction of heat.
Conduction occurs when a
substance is heated,
particles will gain more
energy, and vibrate more.
These molecules then bump
into nearby particles and
transfer some of their
energy to them. This then
continues and passes the
energy from the hot end
down to the colder end of
the substance.

6. Convection

7. Thermal energy is
transferred from hot places
to cold places by convection.
Convection occurs when
warmer areas of a liquid or
gas rise to cooler areas in
the liquid or gas. Cooler
liquid or gas then takes the
place of the warmer areas
which have risen higher. This
results in a continuous
circulation pattern. Water
boiling in a pan is a good
example of these convection
currents. Another good
example of convection is in
the atmosphere. The earth's
surface is warmed by the
sun, the warm air rises and
cool air moves in.

8. Applications of Convection:
1. The air, which we breathe out, is warmer and lighter. It moves up in the room to go out of the
ventilators, near the top of side walls. The fresh air comes through the windows and doors. It is
cool and takes the place of exhaled air rising upward.
2. In winter, hotels and other buildings are heated centrally on the principle of convection
currents.
3. Land and sea breezes are convection currents. During the day the land absorbs the heat of
the sun more quickly than the sea. As a result, the temperature of land rises much higher than
that of sea water.
4. Convection of currents causes trade winds. The sun heats up land and water which receive
same amount of heat for equal areas. This heating is greatest at the tropics. The heated earth
heats the air coming in coming with it. The hot air expands and becomes less dense than the
air from the temperate and polar regions. This hot air rises up and cool air from the temperate
and polar regions rushes in to take its place. This convection of air is the cause of (trade)
winds.
5. Convection currents of heat cause oceanic currents. Water near the equator gets heated
up, whereas water near the poles is comparatively cold. The warm water is lighter than cold
water. The cold water near the poles sinks and the surface water flows to take its place. So
convection currents are produced by warm water flowing from equator towards the poles.
Convection current of cold water flows from poles towards the equator below the surface of
oceans. These convection currents are called oceanic currents. They control the temperature
of ocean.

9. Radiation

10. Radiation is a method of
heat transfer that does not
rely upon any contact
between the heat source
and the heated object as is
the case with conduction
and convection. Heat can be
transmitted through empty
space by thermal radiation
often called infrared
radiation. This is a type
electromagnetic radiation.
No mass is exchanged and
no medium is required in the
process of radiation.
Examples of radiation is the
heat from the sun, or heat
released from the filament
of a light bulb.

12. References:
http://www.edinformatics.com/math_science/how_is_heat_transferred.ht
m
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html
http://www.preservearticles.com/201012261699/applications-of-
convection-currents-of-heat.html