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Dr. Mohamed Reda SalemLecturer at Faculty of Engineering at Shoubra
Benha University, Egypt
mohamed.abdelhamid@feng.bu.edu.egme_mohamedreda@yahoo.com
https://www.facebook.com/Dr.Mohamed.Reda.Salem
Heat Transfer and Industrial Furnaces
Code : MEP2932014/2015
GRADING POLICYTotal Degrees : 125
Assignments/Class Work : 20%Oral Exam : 20%Final Exam : 60%
REFERENCES Course Notes:
Course notes prepared by instructor.
Essential Books (Text Books)
Theodore L. Bergman, Adrienne S. Lavine, Frank P.Incropera, and David P. Dewitt, “Fundamentals of Heat andMass Transfer”, 7th Edition, John Wiley & Sons, Inc., 2011.
J.P. Holman “Heat Transfer”, 10th Edition, 2010.
Yunus A. Cengel, “Heat Transfer: A Practical Approach”, 2nd
Edition, July 2002.
Chapter (1)
Fundamentals of Heat Transfer
Lecture (1)
Topics to be Covered in Lecture (1) Heat Transfer Concept
Modes of Heat Transfer
Conduction Heat Transfer
Convection Heat Transfer
Radiation Heat Transfer
Heat Transfer Concept
The heat energy is the form of energy called thermal energy, which can
be transferred from one system to another as a result of temperature
difference.
The science, which deals with the determination of the rates of heat
energy, is called Heat Transfer.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Introduction
Examples are everywhere
Heat flows in the body
Home heating/cooling systems
Refrigerators, air conditioning, ovens, furnaces, other appliances
Automobiles, power plants, the sun, etc.
During heat transfer, the thermal energy always moves in the same
direction:
Heat energy only flows when there is a temperature difference from a
warmer area to a cooler area.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Introduction
HOT COLD
Modes (Mechanisms) of Heat Transfer
There are three fundamental modes in which heat is transferred:
Conduction heat transfer,
Convection heat transfer,
Radiation heat transfer.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Introduction
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Introduction
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Introduction
Conduction Heat Transfer is the transfer of heat energy through
stagnant (stationary) medium as solids and non-movable fluids from
the more heated particles of the substance to the adjacent, less heated
ones as a result of contact of atoms.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
The Physical Mechanism of Conduction Heat Transfer
In Solids: Conduction heat transfer is due to the combination of the
vibrations of the molecules in a lattice and the energy transport by
free electrons.
In Fluids (gases and liquids): Conduction heat transfer is due to the
collisions of the molecules during their random motion.
How are the particles arranged in a solid, a liquid and a gas?
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
Solid Liquid Gas
Metal
as
Cu, Al, Fe
Non-Metal
as
Graphite
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
How do non-metals conduct heat?
Taking the graphite as example of non-metals that is a good conductor
of heat.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
As the graphite rod is heated, the carbon atoms near the heat source
begin to vibrate. These vibrations make the adjacent atoms vibrate, and
so on along the rode. This is how heat energy travels along a non-metal.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
Heat
How do metals conduct heat?
Metals are good conductors of heat. The outer electrons of metal atoms
are not attached to any particular atom. They are free to move between
the atoms. So, heat transfer is due to the combination of the vibrations
of the molecules in a lattice and the energy transport by free electrons.
When a metal is heated, the free electrons
gain kinetic energy.
This means that the free electrons move faster
and transfer the energy through the metal.
This makes heat transfer in metals very
efficient.
Insulators do not have free electrons and so
they do not conduct heat as well as metals.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
T1
L x
QA
T2
w
H
The parameters that affect the rate of
heat conduction:
Surface area of wall normal to heat
flow (Q A)
Temperature difference across the wall
(Q T)
Wall thickness (Q 1/L)
Wall material (Q k)
L
TTA Q 21
cond
Conduction Heat Transfer is expressed by Fourier’s Law of conduction as
L
TTA k Q 21
cond
L
TTA k 12
dx
dTA k For Plane Wall
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
Where:
Qcond is the conduction heat transfer rate (W)
k is the thermal conductivity (W/m.C or W/m.K)
A is the heat transfer area normal to the heat transfer (m2)
dT/dx is the temperature gradient across the wall (C/m or K/m)
T1, T2 are surfaces temperatures (C or K)
−e sign refers to that the heat moves in the direction of temperature
decreasing
dx
dTA k
L
TTA k Q 21
cond
For Plane Wall
The thermal conductivity is a physical property of the wall material. The
significance of the thermal conductivity of a material comes from that; it
is a measure of how fast heat will be conducted in that material.
Convection heat transfer is the transfer of heat energy between a
surface and the adjacent moving fluid. It involves the combined effect
of conduction and fluid motion.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Modes (Mechanisms) of Convection Heat Transfer
According to the source of fluid motion, there are two modes of
convection heat transfer;
(a) Natural (Free) convection heat transfer and
(b) Forced convection heat transfer.
Natural (Free) Convection
The fluid motion is due to buoyancy
force caused due to density difference
due to temperature difference .
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
T
Ts
Forced Convection:
The fluid motion is due to inertia force
caused by external means of motion
as a fan, pump, or the wind.....
Ts
Forced
flow Fluid
T
Convection heat transfer is expressed by Newton’s Law of Cooling as:
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
TTA h Q ssconv
Where:
Qconv is the convection heat transfer rate (W)
h is the convection heat transfer coefficient (W/m2.C or W/m2.K)
As is the surface area (m2)
Ts is the surface temperature (C or K)
T is the fluid temperature (C or K)
Example for free convection: When the kettle is turned on, the heating element worms
up and heats the water around it. The heated water becomes less dense than the cold
water above. This means that the heated water rises up the kettle. As the heated water
rises, it displaces the cold water. The colder, denser water falls to the bottom, where it is
then warmed by the heating element. This creates circular movements of water.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Why is the freezer compartment at the top of a fridge?
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
At the bottom of the fridge, it is
warmer. This warmer air rises and so a
convection current is set up inside the
fridge, which helps to keep the fridge
cool.
The freezer cools the air at the top and
this cold air cools the food on the way
down.
Report:
Why is it windy at seaside??
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Radiation heat transfer is the transfer of heat energy in the form of
electromagnetic waves (or photons) as a result of the changes in the
electronic configurations of the atoms or molecules.
Any body have temperature larger than absolute zero (0 K = −273C),
emit heat by radiation.
Radiation heat transfer needs no medium to transmit.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Radiation Heat Transfer
Stefan-Boltzmann Law
“The emissive radiation of a body over all wave lengths is proportional
to fourth power of temperature”.
4
srad T Q
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Radiation Heat Transfer
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Radiation Heat Transfer
Radiation heat transfer is expressed by Stefan-Boltzmann Law as:
Where:
Qrad is the radiation heat transfer rate (W)
is the surface emissivity, 0 ≤ ≤ 1
As is the surface area (m2)
is Stefan-Boltzmann constant; = 5.67*10−8
(W/m2.K4)
Ts is the surface temperature (K)
Tsur is the surrounding temperature (K)
4
sur
4
ssrad TT A Q
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Notes
q is the amount of heat energy (J)
Q is the heat transfer rate (W), Q = q/t
q is the heat transfer rate per unit length (W/m), q = Q/w
q is the heat transfer rate per unit area (Heat Flux) (W/m2), q = Q/A
q is the heat transfer rate per unit volume (Heat Generation) (W/m3),
q = Q/V
Awall = w*H Vwall = w*H*L
As, cylinder = DL = 2Rl Vcylinder = D2L/4 = r2L
Ac, cylinder = D2/4 = r2
Asphere = D2 = 4r2 Vsphere = D3/6 = 4r3/3
The heat energy
Heat Transfer
Modes (Mechanisms) of Heat Transfer
Conduction Heat Transfer
Convection Heat Transfer
Radiation Heat Transfer
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Summary
L
TTA k Q 21
cond
TTA h Q ssconv 4
sur
4
ssrad TT A Q
Thank You
QUESTIONS?
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Example for free convection: During the day, the land is warmer than the sea. The heat
of the land warms the air above the land. This warm air rises because it is less dense
than the surrounding cooler air. The cold air then moves from the sea to take the place of
the warm air that has risen above the land. This movement of air sets up a convection
current and creates the seaside breeze.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Example for free convection: During the day, the land is warmer than the sea. The heat
of the land warms the air above the land. This warm air rises because it is less dense
than the surrounding cooler air. The cold air then moves from the sea to take the place of
the warm air that has risen above the land. This movement of air sets up a convection
current and creates the seaside breeze.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Example for free convection: at night, the land becomes cooler than the see. The warm
air above the sea rises and is replaced by cold air from the land. This means that
convection now occurs in the opposite direction.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Convection Heat Transfer
Example for free convection: at night, the land becomes cooler than the see. The warm
air above the sea rises and is replaced by cold air from the land. This means that
convection now occurs in the opposite direction.
Chapter (1): Fundamentals of Heat Transfer (Lect. 1)
Conduction Heat Transfer
HEAT TRANSFER
CONDUCTION CONVECTION RADIATION
q12sT14 sT2
4
q1 q2
11
11
A
22
21
A
121
1
FA
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