IT IS A PPT MADE FOR YOU GY

1. Modes of
heat
transfer
BY : -
ARIANA ANWAR
7 F

2. Content
1)What is heat ?
2)What is heat transfer ?
3) Different methods of
heat transfer.
4) ACTIVITIES to prove
the process
5)An google form on the
basis of your
reading

3. Heat
• According to heat definition, it is
one of the essential forms of
energy for the survival of life on
earth. Transfer of heat takes place
from one body to another due to
differences in temperature as per
thermodynamics. We use heat
energy for various activities like
cooking, ironing, transportation,
recreation, etc. This form of
energy also plays a vital role in
nature. The occurrence of the
wind, rain, change of seasons,
etc., depends on the gradient
created due to uneven heating of
different regions

4. Heat as a form of
energy
• Heat as a form of energy can be
converted to other forms of energy.
For example, in motorized vehicles,
heat is converted to mechanical
energy. In electric bulbs, it is
converted to light energy. In
thermal power plants, it is finally
converted to electrical energy.
•

5. ACTIVITY

6. • Let us take three beakers, first with cold water, the second
with hot and the third with water at normal temperature
• . If we dip our fingers in beaker 1 and then in beaker 3,
we will observe that the water in beaker 3 is hot compared
to that in beaker
• 1. Whereas, if we dip our fingers in beaker 2 and then in
beaker 3, we will observe that the water in beaker 3 is
colder as compared to that in beaker
• 2. This shows that we cannot rely on our sense of touch to
judge the hotness or coldness of something, and that’s
why the degree of hotness or coldness of any object is
measured in terms of temperature.
• Temperature is the measure of hotness or coldness of the
body. Celsius (C) or Fahrenheit (F) scale, or in Kelvins
(K). Relations are established on the amount of heat
added to taken out from the body.

7. Different
methods of
heat transfer

8. • Any matter which is made up of
atoms and molecules has the
ability to transfer heat. The
atoms are in different types of
motion at any time. The motion
of molecules and atoms is
responsible for heat or thermal
energy and every matter has this
thermal energy. The more the
motion of molecules, more will
be the heat energy. However,
talking about heat transfer, it is
nothing but the process of
transfer of heat from a high-
temperature body to a low
temperature one.

9. What is Heat Transfer?
According to thermodynamic systems, heat transfer
is defined as
“The movement of heat across the border of the
system due to a difference in temperature between
the system and its surroundings.”
Interestingly, the difference in temperature is said to
be a ‘potential’ that causes the transfer of heat from
one point to another.

10. Heat can travel from one place to
another in several ways.
The different modes of heat transfer
include:
Conduction
Convection
Radiation
Meanwhile, if the temperature
difference exists between the two
systems, heat will find a way to
transfer from the higher to the lower
system.

11. conduction

12. What is Conduction?
Conduction is defined as
The process of transmission of energy from
one particle of the medium to another with
the particles being in direct contact with
each other.
An area of higher kinetic energy transfers
thermal energy towards the lower kinetic
energy area. High-speed particles clash
with particles moving at a slow speed, as a
result, slow speed particles increase
their kinetic energy. This is a typical form of
heat transfer and takes place through
physical contact. Conduction is also known
as thermal conduction or heat conduction.
This Photo by Unknown author is licensed under CC BY.

13. Extra
information

14. Conduction equation
The rate of conduction can be calculated by the following equation:
Where,
•Q is the transfer of heat per unit time
•K is the thermal conductivity of the body
•A is the area of heat transfer
•Thot is the temperature of the hot region
•Tcold is the temperature of the cold region
•d is the thickness of the body
The coefficient of thermal conductivity shows that a metal body conducts
heat better when it comes to conduction.

15. Following are the examples of
conduction:
Ironing of clothes is an example of
conduction where the heat is
conducted from the iron to the
clothes.
Heat is transferred from hands to
ice cube resulting in the melting
of an ice cube when held in
hands.
Heat conduction through the sand
at the beaches. This can be
experienced during summers.
Sand is a good conductor of
heat.

16. Convection

17. What is
convection ??
• Convection is defined as
• The movement of fluid molecules from
higher temperature regions to lower
temperature regions.
• Convection Equation
• As the temperature of the liquid increases,
the liquid’s volume also has to increase by
the same factor and this effect is known as
displacement. The equation to calculate
the rate of convection is as follows:
• Q = hc ∙ A ∙ (Ts – Tf)

18. Where,
Q is the heat transferred per
unit time
hc is the coefficient of
convective heat transfer
A is the area of heat transfer
Ts is the surface temperature
Tf is the fluid temperature

19. Convection Examples
Examples of convection include:
Boiling of water, that is molecules that are
denser move at the bottom while
the molecules which are less dense move
upwards resulting in the circular motion
of the molecules so that water gets heated.
Warm water around the equator moves
towards the poles while cooler water at
the poles moves towards the equator.
Blood circulation in warm-blooded animals
takes place with the help of convection,
thereby regulating the body temperature.
This Photo by Unknown author is licensed under CC BY-NC.

20. RADIATION

21. • Radiant heat is present in some or other form in our
daily lives. Thermal radiations are referred to as
radiant heat. Thermal radiation is generated by the
emission of electromagnetic waves. These waves
carry away the energy from the emitting body.
Radiation takes place through a vacuum or
transparent medium which can be either solid or
liquid. Thermal radiation is the result of the random
motion of molecules in matter. The movement of
charged electrons and protons is responsible for the
emission of electromagnetic radiation. Let us know
more about radiation heat transfer.
• Radiation heat transfer is measured by a device
known as thermocouple. A thermocouple is used for
measuring the temperature. In this device
sometimes, error takes place while measuring the
temperature through radiation heat transfer.

22. • Radiation Equation
As temperature rises, the wavelength
in the spectra of the radiation emitted
decreases and shorter wavelengths
radiations are emitted. Thermal
radiation can be calculated by
Stefan-Boltzmann law:
Where,
P is the net power of radiation
A is the area of radiation
Tr is the radiator temperature
Tc is the surrounding temperature
e is emissivity and σ is Stefan’s
constant (σ = 5.67 × 10-8Wm-2K-4

23. Radiation Example
Following are the examples of
radiation:
Microwave radiation emitted in
the oven is an example of
radiation.
UV rays coming from the sun is
an example of radiation.
The release of alpha particles
during the decaying of Uranium-
238 into Thorium-234 is an
example of radiation.

24. Heat energy can move from one
body to another or from one
location of a body to another, as
long as there is enough heat.
Studying how heat energy is
passed on is called heat transfer.
There must be a temperature
differential between two bodies for
heat to travel between them. The
two bodies must be at two
different temperatures, one higher
than the other, so that that heat
can move from the one with higher
temperature to the one with lower
temperature.

25. QUIZ TIME

26. 1) What is meant by convection? Explain with the help of
an example?
2) Define radiation?
3) Why the Sun’s heat not reach earth by conduction or
convection?
4) Define the term conduction?
5) Name the three ways in which heat can flow?

27. ANSWER

28. 1)Convection is the process of heat transfer in fluids by the actual motion of
matter.
It happens in liquids and gases.
It may be natural or forced.
It involves a bulk transfer of portions of the fluid.
When a fluid is heated from below, thermal expansion takes place. The lower
layers of the fluid, which are hotter, become less dense. We know that colder
fluid is denser. Due to buoyancy, the less dense, hotter part of the fluid rises
up. And the colder, denser fluid replaces it. This process is repeated when this
part also gets heated and rises up to be replaced by the colder upper layer.
This is how the heat is transferred through convection

29. 2)Radiation is energy that comes from a source and travels through space at
the speed of light. This energy has an electric field and a magnetic field
associated with it, and has wave-like properties. You could also call radiation
“electromagnetic waves
3)As there is vacuum after the earth's atmosphere there is no material and
no particles, so due to no particles there is no scope for conduction and
convection except radiation for the transmission of heat from sun to the
earth
4) Conduction is the transfer of energy in the form of heat or electricity from
one atom to another within an object by direct contact. Conduction occurs in
solids, liquids, and gases. However, solids transfer energy most efficiently
since the molecules in solids are most tightly packed, and the molecules are
closer together.

30. • 5)There are three ways heat is
transferred into and through
the atmosphere:
• radiation.
• conduction.
• convection.

31. This Photo by Unknown author is licensed under CC BY-NC.