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Modes of
heat
transfer
BY : -
ARIANA ANWAR
7 F
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
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
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.
•
ACTIVITY
• 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.
Different
methods of
heat transfer
• 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.
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.
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.
conduction
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.
Extra
information
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.
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.
Convection
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)
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
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.
RADIATION
• 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.
• 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
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.
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.
QUIZ TIME
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?
ANSWER
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
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.
• 5)There are three ways heat is
transferred into and through
the atmosphere:
• radiation.
• conduction.
• convection.
This Photo by Unknown author is licensed under CC BY-NC.

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Modes of heat transfer ( ARIANA ANWAR 7 F).pptx

  • 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. •
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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?
  • 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.