Thermal conductivity can be defined as the rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area.

1. “Thermal
conductivity”

2. Thermal:
MEANS
“HEAT.”
Conductivity:
Means
“ABILITY TO CONVEY”.

3. DEFINITION:
It is the property of a material that
indicates its ability to conduct heat.
 It is represented by k and is
measured in watts per kelvin per metre
(W·K−1·m−1).
The reciprocal of thermal conductivity
is thermal resistivity.

6. Thermal
Conductivity
x
Q / t Q / t
T1
T2
= T1-T2
Assume that no heat is lost
through the edges of the disc.

7. Thermal
Conductivity
x
Q/ t Q/ t
T1 T2
= T1-T2
For a uniform rod the rate of flow of heat through a
conductor ( Q/ t) is proportional to
•the cross sectional area (A) of the conductor
•the temperature gradient ( q/ x)
The constant of proportionality, k, is the thermal conductivity BUT note that heat
flows down a temperature gradient so we also introduce a negative sign to account
for this and obtain:
Q
T
kA
x

8. Thermal
Conductivity
k depends on the material and is called the thermal conductivity.
Rearranging in terms of k we can evaluate the units of k:
k
Q
t A
x
W m -2
K -1
m W m -1
K - 1
So k is defined as the rate of flow of
heat through unit area of cross
section of 1m of material when the
temperature difference between the
surfaces is 1K.

9. Methods to measure thermal conductivity.
• Main methods:
1.Steady stat methods
2.Transient state method

10. Steady state methods
 Definition:
• These methods are used when the materials are in
equilibrium state( means when temperature of the
materials is constant).
 Advantage :
• Accurate readings can be taken.
• It steady state implies
constant signals.
 Disadvantage:
• As material take to long time to reach
• equilibrium state so it is slow method

11. TRANSIENT STATE METHOD:
 Definition:
• These methods are used during
the heating of material.
 Advantage:
• Non-steady-state methods to measure the
thermal conductivity do not require the
signal to obtain a constant value.
• Readings can be taken during heating of
material.
 Disadvantage:
• Readings are not accurate
• Mathematical analysis of the data is in
general more difficult.

12. Thermal Conductivity of Metals
Metals are solids and as such they possess crystalline structure where the ions
(nuclei with their surrounding shells of core electrons) occupy translationally
equivalent positions in the crystal lattice. Metals in general have high electrical
conductivity, high thermal conductivity, and high density. Accordingly,
transport of thermal energy may be due to two effects:
•the migration of free electrons
•lattice vibrational waves (phonons).
When electrons and phonons carry thermal energy leading to conduction heat
transfer in a solid, the thermal conductivity may be expressed as:
k = ke + kph

14. Applications:
As aluminums sheets are used in houses for
blocking of heat to come in and remain in
cool inside.

15. Used in lab:
Experiments are performed in lab for finding
thermal conductivity of different materials.
•

16. • Now a days different materials are used
such like graphene and diamonds for
transferring heat which is also due to the
technique of finding thermal conductivity
• Also because of this property of
material we can use desired elements
in electric circuits like copper, steel etc
according to their conductivity.

17. Latest researches.
CARBON NANOTUBES

18. MAIN POINTS:
•Before carbon nanotubes the
best thermal conductor was
diamond.
•Carbon nanotubes have
extraordinary thermal
conductivity

19. STRUCTURAL
IMAGE:

20. RESEARCHES
• The record-setting anisotropic thermal
conductivity of carbon nanotubes is enabling
applications where heat needs to move from
one place to another.
• carbon nanotubes have the intrinsic
characteristics desired in material used as
electrodes in batteries and capacitors.

21. Graphene:

22. Properties:
• has very high current
capacity.
•Used in high modified
circuit in which current
gain is required

23. ThankYouAll Of U