Presentation topic:

“Thermal conductivity”

Thermodynamics

Contents• Definition.• Explanation. • Methods to measure the thermal conductivity.• Experiment.• Application (importance).

……Use in industry.……Use in laboratory.

• Latest researches in this field.

Thermal:

MEANS

“HEAT.”Conductivity:

Means

“ability to convey”.

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.

Thermal Conductivity

Thermodynamics

x

Q/t Q/t

T1 T2

= T1-T2

Assume that no heat is lost through the edges of the disc.

Thermal Conductivity

Thermodynamics

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

TkA

x

Thermal Conductivity

Thermodynamics

k depends on the material and is called the thermal conductivity.

Rearranging in terms of k we can evaluate the units of k:

kQ

t Ax

Wm-2K-1m Wm-1K-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.

Methods to measure thermal conductivity.

• Main methods:

1.Steady state methods.2.Transient state

methods

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.

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.

METHODS:• IEEE Standard 442-1981, "IEEE guide for soil thermal resistivity measurements",

ISBN 0-7381-0794-8. See also soil thermal properties. [5] [1] • IEEE Standard 98-2002, "Standard for the Preparation of Test Procedures for the

Thermal Evaluation of Solid Electrical Insulating Materials", ISBN 0-7381-3277-2 [6] [2]

• ASTM Standard D5334-08, "Standard Test Method for Determination of Thermal Conductivity of Soil and Soft Rock by Thermal Needle Probe Procedure" [3]

• ASTM Standard D5470-06, "Standard Test Method for Thermal Transmission Properties of Thermally Conductive Electrical Insulation Materials" [7]

• ASTM Standard E1225-04, "Standard Test Method for Thermal Conductivity of Solids by Means of the Guarded-Comparative-Longitudinal Heat Flow Technique" [8]

• ASTM Standard D5930-01, "Standard Test Method for Thermal Conductivity of Plastics by Means of a Transient Line-Source Technique" [9]

• ASTM Standard D2717-95, "Standard Test Method for Thermal Conductivity of Liquids" [10]

• ISO 22007-2:2008 "Plastics -- Determination of thermal conductivity and thermal diffusivity -- Part 2: Transient plane heat source (hot disc) method" [11]

THERMAL CONDUCTIVITYAPPARATUS:

OBJECTIVES:

PROCEDUER:

• Take ice block ,find its weight and volume and place it on the material sheet.

• Then place it on the plate which is under observation

• Then provide steam for sometime then we the ice converted to water then measure the weight of the water (in beaker).

• Then place this values in the formula and calculate the conductivity.

Exp:

Formula:

K= Ro dx / A dT

• dx = thickness of material.

• dT =change in temperature.

Applications:As aluminums sheets are used in houses for blocking of

heat to come in and remain in cool inside.

Used in lab: Experiments are performed in lab for finding thermal conductivity of

different materials.

•

•Now a days different materials are used such like graphene and diamonds for

transferring heat which is also due to the techniques of finding thermal

conductivities.• Also because of this property of the material we can use desired elements in electric circuits like copper, steel etc according to their conductivity.

Latest researches.CARBON NANOTUBES

MAIN POINTS:

•Before carbon nanotubes the best thermal conductor was diamond.•Carbon nanotubes have extraordinary thermal conductivity properties.

STRUCTURAL IMAGE:

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.

Graphene:

Properties:

• has very high current capacity.•Used in high modified

circuit in which current gain is required

Group:

“ IEFRIANS”Talent participated:

HASSAN ALI (50+8)• HASSAN SULTAN(50-21)

TAUSEEF AWAN.(50-22)ANAS AMIN (50+6)

• M. AWAIS SATTAR.(50+4)

Special thanks to HASSAN ALI (YOUNG RUFFIANS)