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Conduction and Radiation Heat

Transfer

ME 301

Course Teacher:

Dr. Mohammad Arif Hasan Mamun

&

Dr. Aloke Kumar Mozumder

Professor

Department of Mechanical Engineering

BUET

Detail Outline of Course:

�Basic modes of heat transfer;

�General conduction equation for one dimensional

and three dimensional situation;

�Steady state conduction in different geometrics and

composite structures for one dimensional situation;

� Effect of variable thermal conductivity;

�Analysis of heat conduction of system with heat

sources and heat transfer from finned surfaces;

� Transient heat conduction in solids with negligible

internal resistance and with internal and surface

resistance;

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�Use of Heisler charts; Analytical and numerical

solutions of conduction heat transfer problems.

�Heat transfer by the mechanism of radiation; Laws

of radiation heat transfer;

�Blackbody radiation and radiative properties of

surfaces;

�Angle factor;

�Net radiation interchange between two infinite

parallel planes, concentric spheres and long cylinders;

�Simple enclosure problems;

�Radiation shield;

�Solar radiation and its prospects in Bangladesh.

Reference Books:

1. Principle of Heat Transfer

-Kreith

2. Heat Transfer

- M.N. Ozisik

3. Heat Transfer

-Halman

4. Heat Transfer

-Chapman

5. Fundamentals of Heat Transfer

-F.P. Incorpera & D.P. DeWitt

6. Heat and Mass Transfer

-Y. A. Çengel

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Heat Transfer

�Heat transfer is a term applied to a study in which

transfer of energy in the form of heat takes place as a

result of temperature difference.

�The temperature is a thermal state of a body which

distinguishes a hot body from a cold body.

�The temperature of a body is proportional to the stored

molecules energy i.e. the average molecules kinetic energy of

the molecules in a system.

�Thermal energy is related to the temperature of matter.

� For a given material and mass, the higher the temperature,

the greater its thermal energy.

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Question?

�Why study Heat Transfer?

�What is Thermodynamics?

�What is the difference b/w Thermodynamics and Heat

Transfer?

Thermodynamics

�It is a science of the relation ship b/w Heat, Work and

Properties of the system – it deals with equilibrium

states, it does not deal with Rate of Energy (Heat )

Transfer.

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Heat Transfer

�It obeys the laws of thermodynamics.

�In Heat Transfer, rate (i.e. time) is very important which

is absent in thermodynamics.

�Mechanism of Heat Transfer is not in Thermodynamics.

Objectives of our study:

�Mechanism by which heat is transferred.

�Parameters involved

�Rate of heat transfer and total quantity of heat transfer

over a certain period of time.

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Applications of Heat Transfer:

Heat Transfer From Finned Surfaces

The thin plate fins of a car radiator

greatly increase the rate of

heat transfer to the air

Some innovative fin designs.

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Modes of Heat Transfer

1. Conduction

2. Convection

3. Radiation

Conduction:

�It is a mechanism by which heat flows from a region of

higher temperature to a region of lower temperature within a

medium or between different medium by kinetic motion of

molecules or by direct impact as in fluids or by electron flow as

in solid.

�Conduction is the transfer of heat through solids or stationery

fluids.

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�When you touch a hot object, the heat you feel is transferred

through your skin by conduction.

�Two mechanisms explain how heat is transferred by conduction:

lattice vibration and particle collision.

�Conduction through solids occurs by a combination of the two

mechanisms;

�Heat is conducted through stationery fluids primarily by

molecular collisions.

Figure 1 Conduction by lattice vibration

�In solids, atoms are bound to each other by a series of bonds,

analogous to springs as shown in Figure 1.

�When there is a temperature difference in the solid, the hot

side of the solid experiences more vigorous atomic movements.

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�The vibrations are transmitted through the springs to the

cooler side of the solid.

�Eventually, they reach an equilibrium, where all the atoms

are vibrating with the same energy.

Figure 2 Conduction by particle collision

�Solids, especially metals, have free electrons, which are not

bound to any particular atom and can freely move about the solid.

�The electrons in the hot side of the solid move faster than those

on the cooler side. This scenario is shown in Figure 2.

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�As the electrons undergo a series of collisions, the faster

electrons give off some of their energy to the slower electrons.

�Eventually, through a series of random collisions, an

equilibrium is reached, where the electrons are moving at the

same average velocity.

�Conduction through electron collision is more effective than

through lattice vibration; this is why metals generally are better

heat conductors than ceramic materials, which do not have many

free electrons.

�In fluids, conduction occurs through collisions between

freely moving molecules.

�The mechanism is identical to the electron collisions in

metals.

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Convection:

It is a study of the heat transfer process caused by the flow of

fluids and is a mode of heat transfer between a solid surface

and a liquid or gas.

Figure 1.4 Natural convection

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�Convection uses the motion of fluids to transfer heat.

�In a typical convective heat transfer, a hot surface heats the

surrounding fluid, which is then carried away by fluid

movement such as wind.

�The warm fluid is replaced by cooler fluid, which can draw

more heat away from the surface.

�Since the heated fluid is constantly replaced by cooler fluid,

the rate of heat transfer is enhanced.

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