This document defines key concepts related to heat transfer including: - Heat is the transfer of energy between objects due to temperature differences and is measured in Joules. - Temperature is determined by the motion of particles in a substance, with faster motion indicating a higher temperature. - The three primary methods of heat transfer are conduction, convection, and radiation. Conduction involves direct contact, convection involves the transfer of heat by a liquid or gas, and radiation involves the transfer of heat through electromagnetic waves. - Equations are provided to calculate heat transfer via conduction, convection, and radiation based on factors like thermal conductivity, heat transfer coefficient, surface area, and temperature differences.

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2. Energy that flows from something warm to
something cooler
A hotter substance gives KE to a cooler one
Heat is the transfer of energy between two objects
due to temperature differences
Heat is measured in Joules (J) because it is a form
of energy
Heat

3. Heat
 The name of the transfer process is heat. What gets
transferred is energy.
 Heat is NOT a substance although it is very
convenient to think of it that way.
In fact, it used to be thought that heat was a
substance.
There is a circular nature to the definitions used:
(a) energy does work or produces heat, but
(b) heat is a transfer of energy.

4. Temperature
 Temperature is the property which determines the
direction heat will flow when two objects are
brought into contact
 Based on the motion of the particles in a
substance
Fast motion = high temperature
Slower motion = lower temperature
 Relatively describes how the particles collide with
the surface of the thermometer
 Collisions transfer energy

5. Temperature Scales
 Fahrenheit
Common in the US
Freezing point of water is 32ºF
Boiling point of water is 212ºF
 Celsius
Common in the rest of the world (SI)
Freezing point of water is 0ºC
Boiling point of water is 100ºC
 Kelvin
Used for science
Freezing point of water is 273K
Boiling point of water is 373K

6. Temperature and the Phases
of Matter
 In the Fahrenheit scale, water freezes at 32
degrees and boils at 212 degrees
 The Celsius scale divides the difference between
the freezing and boiling points of water into 100
degrees (instead of 180).

7. Temperature and the Phases
of Matter
 All thermometers are based
on some physical property
(such as color or volume)
that changes with
temperature.
 A thermometer is a device
that changes its electrical
resistance as the
temperature changes.
 A thermocouple is another
electrical sensor that
measures temperature.

8. Heat and Thermal Energy
 Temperature is NOT the same as thermal energy.
 Thermal energy is energy stored in materials
because of differences in temperature.
 The thermal energy of an object is the total
amount of random kinetic energy for all the atoms
in the object.
 Remember, temperature measures the random
kinetic energy of each atom.

9. Heat and Thermal Energy
 Imagine heating a cup of
coffee to a temperature of
100°C.
 Next think about heating
up 1,000 cups of coffee to
100°C.
 The final temperature is
the same in both cases but
the amount of energy
needed is very different.

10. First Law of Thermodynamics
 Energy loss is equal to energy gain.

11. Second Law of
Thermodynamics

12. Energy and Heat flow
There Energy, in the process we call heat or heat flow,
is constantly flowing into and out of all objects,
including living objects.
 Heat flow moves energy from a higher temperature to
a lower temperature.
The bigger the difference in temperature between two
objects, the faster heat flows between them.
When temperatures are the same there is no change in
energy due to heat flow.
Radiation and Conduction are the two methods of heat
transfer. Convection is a special type of conduction.
Heat has the units of energy; heat flow has the units of
power.

13.  Heat flow is energy moving. It has the same units as
power - energy per unit time .
 It means that during the given amount of time, during
which heat is flowing, a certain amount of energy is
transferred or moved from one place to another place
Energy and Heat flow

14.  Three easy things to know about the way heat flows:
1) There has to be a temperature difference. Energy
only flows as heat if there is a temperature difference.
2) Energy as heat flows from a higher temperature to a
lower temperature.
3) The greater or larger the difference in temperature,
the faster the energy flows.
Heat flow

15.  The science of how heat flows is called heat transfer.
 There are three ways heat transfer works:
conduction, convection, and radiation.
 Heat flow depends on the temperature difference.
Heat flow

16. Heat flow

17. Heat Conduction
 Conduction occurs when two object at
different temperatures are in contact
with each other.
 Heat flows from the warmer to the
cooler object until they are both at the
same temperature.
 Conduction is the movement of heat
through a substance by the collision of
molecules. At the place where the two
object touch, the faster-moving molecules
of the warmer object collide with the
slower moving molecules of the cooler
object.

18. Heat Conduction
 Conduction is the transfer of heat through materials
by the direct contact of matter.
 Dense metals like copper and aluminum are very
good thermal conductors.
 A thermal insulator is a material that conducts heat
poorly.

19. Thermal Conductivity
 The thermal conductivity of a material describes
how well the material conducts heat.

20. Heat Conduction Equation
PH = k A (T2 -T1)
L
Area of cross section (m2)
Length (m)
Thermal conductivity
(watts/moC)
Heat flow
(watts)
Temperature
difference (oC)

21. Convection
Convection is the transfer of
heat by the motion of liquids
and gases.
– Convection in a gas occurs
because gas expands when
heated.
– Convection occurs because
currents flow when hot gas rises
and cool gas sink.
– Convection in liquids also
occurs because of differences in
density.

22. Convection
 When the flow of gas or
liquid comes from
differences in density and
temperature, it is called
free convection.
 When the flow of gas or
liquid is circulated by
pumps or fans it is called
forced convection.

23. Convection
 Both free and forced convection help to heat
houses and cool car engines.

24. Convection
 Convection depends on speed and surface area.
 Motion increases heat transfer by convection in all
fluids.
 If the surface contacting the fluid is increased, the rate
of heat transfer also increases.

25. Convection and Sea
Breezes
 On a smaller scale near
coastlines, convection is
responsible for sea breezes.
 During the daytime, land is
much hotter than the ocean.
 A sea breeze is created when
hot air over the land rises due
to convection and is replaced
by cooler air from the ocean.
 At night the temperature
reverses so a land breeze
occurs.

26. Heat Convection Equation
PH = h A (T2 -T1)
Area contacting fluids (m2)Heat transfer coefficient
(watts/m2oC)
Heat flow
(watts)
Temperature
difference (oC)

27. Radiation
 Radiation is heat transfer by
electromagnetic waves.
 Thermal radiation is
electromagnetic waves
(including light) produced by
objects because of their
temperature.
 The higher the temperature
of an object, the more
thermal radiation it gives off.

28. • Radiation
Radiation
 Heat from the sun is the
best example of radiation.
The sun is rays reach the
earth without having any
material medium in
between the earth and the
sun.
The electromagnetic rays
carry energy from the sun is
surface to the earth and
heat up the earth and its
atmosphere.

29. Radiant Heat
 We do not see the thermal
radiation because it occurs
at infrared wavelengths
invisible to the human eye.
 Objects glow different colors
at different temperatures.

30.  The graph of power versus wavelength for a perfect
blackbody is called the blackbody spectrum.
Radiant Heat
 A perfect blackbody is a surface that reflects nothing
and emits pure thermal radiation.

31. Radiant Heat
 The total power emitted as thermal radiation by a
blackbody depends on temperature (T) and surface
area (A).
 Real surfaces usually emit less than the blackbody
power, typically between 10 and 90 percent.
 The Kelvin temperature scale is used in the Stefan-
Boltzmann formula because thermal radiation
depends on the temperature above absolute zero.

32. Stefan-Boltzmann
formula
P = s AT4
Surface area (m2)
Stefan-Boltzmann constant
5.67 x 10-8 watts/m2K4)
Power
(watts)
Absolute temperature
(K)

33. The End
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