Lecture 1 2nd Year Mining 1

Introduction to Heat Transfer

&

Refrigeration and Air

Conditioning

Lecture 1 2nd Year Mining 2

References

1.) “Fundamentals of Heat and Mass

Transfer,” Frank P. Incropera and David P.

De Witt, 7th Edition.

2.) “Heat Transfer: A Practical Approach,”

Yunus A. Cengel, 2nd Edition.

3.) “Refrigeration and Air Conditioning,”

P.L. Ballaney

Lecture 1 2nd Year Mining 3

What is Heat Transfer?

“Energy that can be transferred due to

temperature difference.”

Lecture 1 2nd Year Mining 4

Heat Transfer Vs. Thermodynamics

Thermodynamics tells us:

• How much heat is transferred (Q)

• How much work is done (W)

• Final state of the system

Heat transfer tells us:

• How (with what modes) Q is transferred

• At what rate Q is transferred

• Temperature distribution inside the body

Lecture 1 2nd Year Mining 5

Applications of Heat Transfer

Lecture 1 2nd Year Mining 6

Applications of Heat Transfer

• Energy production and conversion

• Steam power plant, solar energy conversion, … etc.

• Refrigeration and air-conditioning

• Domestic applications

• Ovens, stoves, toaster

• Cooling of electronic equipment

• Manufacturing / materials processing

• Welding, casting, soldering, laser machining

• Automobiles / aircraft design

• Nature (weather, climate, …etc.)

Lecture 1 2nd Year Mining 7

Heat Transfer MechanismsHeat can be transferred in three different modes:

conduction, convection, and radiation.

In all modes, heat transfer

requires temperature difference.

from the high-temp. medium to a lower-temp. one.

Conduction• Needs matter (solids, liquids, or gases)

• In gases and liquids collisions and diffusion of the molecules

• In solids vibrations of the molecules in a lattice and the energy transport by free electrons.

Lecture 1 2nd Year Mining 8

Conduction by lattice vibration

Conduction by particle collision

Lecture 1 2nd Year Mining 9

Materials such as

copper and silver that

are good electric

conductors are also

good heat conductors

while wood is both

electrically and thermally

insulator.

Lecture 1 2nd Year Mining 10

Heat Transfer MechanismsConvection

• Needs matter (liquids, or gases)

• Natural (or free) and forced convection.

Lecture 1 2nd Year Mining 11

Natural convection

Lecture 1 2nd Year Mining 12

Heat Transfer MechanismsRadiation

• Does not needs matter

• Transmission of energy by electromagnetic

waves (or photons)

• Fast (at speed of light).

• Occurs in vacuum, ex. energy from the sun

reaches the earth.

Lecture 1 2nd Year Mining 13

Basic Equations

ConductionFourier’s law of heat conduction (1822)

Lecture 1 2nd Year Mining 14

Lecture 1 2nd Year Mining 15

dT/dx is the temperature gradient which is the slope of the temperature curve on a T-x diagram.

Lecture 1 2nd Year Mining 16

Thermal Conductivity (k)

Lecture 1 2nd Year Mining 17Variation of the thermal conductivity with temperature

Lecture 1 2nd Year Mining 18

Lecture 1 2nd Year Mining 19

Determination of Thermal Conductivity

Lecture 1 2nd Year Mining 20

• Specific heat ….

Thermal Diffusivity (α)

Lecture 1 2nd Year Mining 21

ConvectionNewton’s law of cooling

Lecture 1 2nd Year Mining 22

Lecture 1 2nd Year Mining 23

Basic Equations

RadiationStefan-Boltzmann law

Lecture 1 2nd Year Mining 24

Lecture 1 2nd Year Mining 25

Lecture 1 2nd Year Mining 26

Lecture 1 2nd Year Mining 27

Simultaneous Heat Transfer

Mechanisms

Lecture 1 2nd Year Mining 28

Example

Lecture 1 2nd Year Mining 29

Example

Lecture 1 2nd Year Mining 30

• No CHEATING in exams

• Be ACTIVE student (reward)

Class Rules

• Do NOT come late•

• TURN your mobile OFF (vibration is

OK)

• ATTENDANCE will be taken

Please ….