Thermal Conductivity Presentation

1. In the name of Allah, the Most Merciful, the Most Kind

2. Experimental Methods to Find
Thermal Conductivity
Presented to:
Dr. Anis-Ur-Rehman
Muhammad Ahsan
CIIT/FA20-PPH-001/ISB

3. Outlines
• Thermal Conductivity
• Experimental Methods
• Steady State Method
• Guarded Hot Plate Method
• Concentric Sphere Method
• Unsteady State Method
• Transient Plane Source Method
• Laser Flash Method

4. “Ability to Convey”
Thermal:
“Heat”
Conductivity:
Means
Means

5. Thermal conduction is the phenomenon by which heat is transported from
high to low temperature regions of a substance.
The property that characterizes the ability of a material to transfer heat is the
thermal conductivity.
It is best defined in terms of the expression:
𝑄 = 𝑘𝐴
𝑑𝑇
𝑑𝑥
heat flux
thermal conductivity
temperature gradient
Thermal Conductivity

6. Several thermal conductivity measurement methods exist, and the
proper method depends on many factors, such as sample type,
temperature range, and available resources.
Some of the methods are:
• Steady State Methods • Unsteady State Methods
(constant temperature) (temperature varies with time)
Experimental Methods to Find
Thermal Conductivity

7. Definition:
These methods are used when the materials are in equilibrium state.
(when temperature of the materials is constant)
Advantages:
• Accurate readings can be taken.
• Its steady state implies constant signals.
Disadvantage:
As material takes long time to reach equilibrium state so it is slow method.
Steady State Methods

8. • A solid sample of material is placed between
two plates. One plate is heated and the other is
cooled or heated to lesser extent.
• Temperature of the plates is monitored using
thermo couple until they are constant.
• The steady state temperatures, the thickness of
the sample and the heat input to the hot plate
are used to calculate thermal conductivity.
Guarded Hot Plate Method

9. • The apparatus consists of two concentric
thin spherical chambers with grain sample
filled inside the annular space properly.
• The inner sphere is heated electrically, and
the outer space is cooled in a water bath.
The thermal conductivity ‘k’ will be:
Q=kA₂A₁(T₂ - T₁ / R₂ - R₁)
Where Q= rate of heat flow
A= area
T= temperature
1,2 is suffix for outer and inner sphere
Concentric Sphere Method

10. Definition:
These methods are used during the heating of material.
Advantage:
• 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.
Unsteady State Methods

11. Transient Plane Source Method
• It utilizes a plane sensor and a special mathematical model describing
the heat conductivity, combined with electronics, enables the method to
be used to measure “k”.
• Range between at least 0.01-500 W/m/K

12. • The Transient Plane Source technique typically employs two samples
halves, in between which the sensor is sandwiched.
• The sensor is placed between two halves of the sample to be measured.
• During the measurement, a constant electrical effect is passes through
the conducting spiral, increasing the sensor temperature.
• The heat generated dissipates into the sample on both sides of the
sensor, at a rate depending on the thermal transport properties of the
material.
• By recording temperature vs. time response in the sensor, the thermal
conductivity, thermal diffusivity and specific heat capacity of the
material can be calculated.
Transient Plane Source Method

13. • This method is used to measure thermal diffusivity of a thin disc in the
thickness direction.
• This method is based upon the measurement of the temperature rise at
the rear face of the thin-disc specimen produced by a short energy
pulse on the front face.
• With a reference sample specific heat can be achieved and with known
density the thermal conductivity results as follows
α=k/ρC
• It is suitable for a multiplicity of different materials over a broad
temperature range (−120°C to 2800°C).
Laser Flash Method

14. Laser Flash Method