It gives a brief details about the ways of transfer of energy which will clear the concepts of the students easily.

1. TRANSFER OF HEAT
ENERGY
PHYSICS-5054
BY:
ENGR. MUHAMMAD AHSAN RAUF

2. LEARNING OBJECTIVES
Students will be able to:
(a) describe how to distinguish between good and bad conductors of heat.
(b) describe, in terms of the movement of molecules or free electrons, how
heat transfer occurs in solids.
(c) describe convection in fluids in terms of density changes.
(d) describe the process of heat transfer by radiation.
(e) describe the effect of surface colour (black or white) and texture (dull or
shiny) on the emission, absorption and reflection of radiation.
(f) describe how to distinguish between good and bad emitters and good and
bad absorbers of infra-red radiation.
(g) describe how heat is transferred to or from buildings and to or from a
room.
(h) state and explain the use of the important practical methods of thermal
insulation for buildings.

3. Transfer of Thermal Energy
Transfer of Thermal Energy
1) Transfer of thermal energy takes place when there is
a temperature difference. Thermal energy is
transferred from a hotter region to a colder region.
2) When 2 bodies are at the same temperature, there is
no net flow of thermal energy between then and they
are said to be in thermal equilibrium.

4. Modes of Heat Transfer
Conduction
Convection
Radiation

5. Heat Transfer In Solids
• When a substance (object) is heated at one end,
the particles at the region gains thermal energy
and vibrate faster.
• These molecules collide with the less energetic
neighboring particles and transfer KE to them.
• In this way, thermal energy is transferred along
the entire substance (object) by molecular
collisions from the hot end of the substance
(object) to the cooler end.

6. Why is metal a better conductor of
heat than non-metals?
In metals, apart from transferring heat energy by
the relatively slow process of molecular collision,
another faster process of free electron diffusion
takes place.
Metals contain free electrons that are mobile.
When heated, these free electrons gains KE and
will diffuse to the cooler end at high speeds.
In the process, they will collide with atoms at the
cooler end and transfer kinetic energy to them.

7. Why is metal a better conductor of
heat than non-metals?
In metals, apart from transferring heat energy by
the relatively slow process of molecular collision,
another faster process of free electron diffusion
takes place.
Metals contain free electrons that are mobile.
When heated, these free electrons gains KE and
will diffuse to the cooler end at high speeds.
In the process, they will collide with atoms at the
cooler end and transfer kinetic energy to them.

8. Explain why materials such as
fiberglass, wool, polystyrene, fur
are commonly used as heat
insulators
• Fibreglass, wool, polystyrene and furs are
poor conductors of heat because they are non-
metals.
• In addition, they contain trapped, still air,
which is a poor thermal conductor as well.

9. Heat Transfer In Fluids
• When a fluid is heated at the base, it will expand,
become less dense and rise.
• The cooler fluid at the top being denser, will sink.
• This continuous, cyclic movement of the fluid known
as convection current will eventually heat up the entire
whole fluid evenly.

10. Heat Transfer By Radiation
• Radiation is the continual emission of the infra red
waves from the surface of all bodies transmitted
without the aid of a medium. Example, transfer of
thermal energy from sun to earth.
• Infrared radiation is absorbed and emitted by all
objects and surfaces.
• Dull black surfaces are better absorbers and emitters
of infrared radiation than shiny white surfaces.

11. Factors Affecting Rate Of Radiation

12. Applications Of Thermal Energy
Transfer

13. Comparison Between 3 Methods
Of Heat Transfer In Different
States

14. Question???
Describe how is heat
transferred to or from
buildings and to or from a
room?

15. Answer!!!
• Heat energy is transferred from homes by conduction through the
walls, floor, roof and windows.
• It is also transferred from homes by convection. For example, cold air
can enter the house through gaps in doors and windows, and
convection currents can transfer heat energy in the loft to the roof
tiles.
• Heat energy also leaves the house by radiation - through the walls,
roof and windows.

16. Practical Methods Of Thermal
Insulation For Buildings
There are several different ways to reduce heat loss:
• Simple ways to reduce heat loss include fitting carpets, curtains and
draught excluders. It is even possible to fit reflective foil in the walls or on
them.
• Heat loss through windows can be reduced by using double glazing.
These special windows have air or a vacuum between two panes of glass. If
the double glazing has a vacuum there will be no conduction or convection.
If the double glazing is made with air between the glass then convection is
minimised because there is little room for the air to move. Air is a poor
conductor so there will be very little heat loss by conduction.

17. Practical Methods Of Thermal
Insulation For Buildings
• Heat loss through walls can be reduced using cavity wall insulation.This
involves blowing insulating material into the gap between the brick and
the inside wall. Insulating materials are bad conductors and so this reduces
the heat loss by conduction.The material also prevents air circulating
inside the cavity, therefore reducing heat loss by convection.
• Heat loss through the roof can be reduced by laying loft insulation.This
works in a similar way to cavity wall insulation.

18. LEARNING OBJECTIVES
Students will be able to:
(a) describe how to distinguish between good and bad conductors of heat.
(b) describe, in terms of the movement of molecules or free electrons, how
heat transfer occurs in solids.
(c) describe convection in fluids in terms of density changes.
(d) describe the process of heat transfer by radiation.
(e) describe the effect of surface colour (black or white) and texture (dull or
shiny) on the emission, absorption and reflection of radiation.
(f) describe how to distinguish between good and bad emitters and good and
bad absorbers of infra-red radiation.
(g) describe how heat is transferred to or from buildings and to or from a
room.
(h) state and explain the use of the important practical methods of thermal
insulation for buildings.

19. ThankYou