Heat Transfer

Intoduction

Internal Energy

is the total stored energy of a body or a substance.

HEAT is a form of energy transfer/change

First Law of Thermodynamics

• The change in the internal energy (U) of a body or a system is equal to the work (W) done on a system plus the heat (Q) added to it.

Work vs Heat

To compare the molecular level of heat transfer to work as forms of energy

change

WORK• Energy transfer involving organized motion • When work is done on an object, the object’s

energy is increased as its molecules or atoms are stimulated to move in an orderly manner.

• “Energy in transition”

Heat

• Energy transfer involving the random disorderly motion of molecules, specifically called thermal motion.

• Heat is associated with the vibrational motion

of particles. • Energy in transit or on the move

ordered motion of molecules towards a particular direction

disordered and random movement of particles in heat transfer.

NOTE: The arrows represent the motion of molecules

Why does heat transfer occur from higher to lower temperature?

• Second Law of ThermodynamicsThe level of disorder in the universe is steadily and constantly increasing.

• Tendency is for objects having an ordered behavior to move in a more random disordered behavior.

Temperature

•is the measure of the internal energy an object

contains.

•is the average kinetic energy of particles

Modes of Heat Transfer

Conduction, Convection and Radiation

is heat transfer between two bodies which are in contact with each other.

is the heat transfer within liquids and gases through currents within the fluid.

heat transfer by electromagnetic waves involving the absorption or giving off electromagnetic waves.

Examples of Heat Transfer

Greenhouse Effect (Global Warming)• HOW?

Through radiation

Atmosphere• Air

– conductive and convective heat transfer

SunAround the core there is the radiative zone. In this region, energy is transported by radiation

Interface layer is the transition between the radiative and convection zones.

The convection zone is the outer-most layer of the interior where energy is transported by convection in this region.

http://www.cora.nwra.com/~werne/eos/text/convection_zone.html

Earth Surface• Conduction

Surface ocean, soil • Convection

Surface atmosphere

volcanoes are direct evidence of heat flowing out of Earth.

Soil

• Conduction occurs from heated gas and liquid molecules which come in contact with soil.

• It also happens among oil particles themselves.

Sea/Ocean

Heat is transferredRadiation ConvectionEvaporation of water and condensation

Heat is transferred within an ocean or sea through turbulent and convective mixing and by vertical and horizontal currents.

Hurricanes

Hurricanes• However, the trade-wind system is also

extremely important. – The trade winds are air flow from east to west and

toward the equator.

If they weaken, perhaps tropical storms will be more dispersed and less fearsome, or they may change their paths in ways that are difficult to tell.

Hurricanes

• Al Gore, an American politician, advocate and philanthropist and is currently an author and environmental activist.

• In his documentary An Inconvenient Truth, Al Gore said that when the oceans get warmer due to global warming, stronger storms form.

• He even mentioned Hurricane Katrina (2005).

References• http://physics.bu.edu/~duffy/py105/Secondlaw.html• http://physics.tutorvista.com/heat.html• Atkins’ Physical Chemistry by Atkins & De Paula, Eighth Edition, 2006• http://www.biocab.org/Heat_Transfer.html• http://www.clavius.org/heatxfer.html• http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html• http://www.school-for-champions.com/science/heat_transfer_earth.htm• http://www.bluffton.edu/~bergerd/nsc_111/thermo1.html• https://www.boundless.com/physics/heat-and-heat-transfer/global-warming/

greenhouse-gases-and-global-warming/• http://library.thinkquest.org/03oct/01424/How%20do%20hurrricanes%20form.htm• http://earthguide.ucsd.edu/virtualmuseum/climatechange1/09_2.shtml• http://www.skepticalscience.com/Did-global-warming-cause-Hurricane-

Katrina.html