Study on Air-Water & Water-Water Heat Exchange in a Finned Tube Exchanger
Heat transfer seminar
1. MODES OF HEAT TRANSFER
Amaljo Joju E
s3 EEE
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EEE Dept. SCET
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How ‘Heat’ Moves
• Define “Heat”:
Heat is the movement of
thermal energy from a
substance at a higher
temperature to another
substance at a lower
temperature.
EEE Dept. SCET
3. 3
How ‘Heat’ Moves
Thermal energy in the form of
heat can move in three ways.
Conduction
Convection
Radiation
EEE Dept. SCET
4. 4
Conduction
CONDUCTION:
• The transfer of heat from one
particle of matter to another by
direct particle to particle contact.
– Conduction occurs primarily in solids because
the particles are tightly packed together.
– The particles themselves DO NOT change
positions.
EEE Dept. SCET
5. Metals are different
The outer e______ of metal atoms
drift, and are free to move.
When the metal is
heated, this ‘sea of
electrons’ gain k_____
energy and transfer it
throughout the metal.
Insulators, such as w___ and p____, do not
have this ‘sea of electrons’ which is why they
do not conduct heat as well as metals.
lectrons
inetic
ood lastic
EEE Dept. SCET
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6. Why does metal feel colder than wood, if they
are both at the same temperature?
Metal is a conductor, wood is an insulator. Metal
conducts the heat away from your hands. Wood
does not conduct the heat away from your hands as
well as the metal, so the wood feels warmer than
the metal.
EEE Dept. SCET
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7. 7
Convection
Convection: the transfer of
thermal energy (heat) through
the bulk movement of matter.
– Convection occurs in FLUIDS (liquids
and gases).
– Convection produces CURRENTS in
both gases and liquids.
– Thermal Energy heat is carried by the
particles as they move from one location to
another.
EEE Dept. SCET
8. Convection
What happens to the particles in a liquid or a
gas when you heat them?
The particles spread out and
become less dense.
This effects fluid movement.What is a fluid?A liquid or gas.
EEE Dept. SCET
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9. Fluid movement
Cooler, more d____, fluids
sink through w_____, less
dense fluids.
In effect, warmer liquids and
gases r___ up.
Cooler liquids and gases s___.
ense
armer
ise
ink
EEE Dept. SCET
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10. Why is it windy at the seaside?
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11. 11
Radiation
• Radiation: the transfer of
(thermal) energy by electromagnetic
waves.
– Radiation does not require matter to
transfer thermal energy.
• All the sun’s energy that reaches Earth
travels through millions of kilometers of
empty space (a vacuum).
– All matter can radiate energy.
• You feel the radiation of thermal energy
from a bonfire, a heat lamp and a light
bulb. EEE Dept. SCET
12. The third method of heat transfer
How does heat energy get
from the Sun to the Earth?
There are no particles
between the Sun and the
Earth so it CANNOT
travel by conduction or
by convection.
?
RADIATION
EEE Dept. SCET
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13. Absorption experiment
Four containers were placed equidistant from a heater. Which
container would have the warmest water after ten minutes?
The __________ container would be the warmest after ten
minutes because its surface absorbs heat _______ the best.
The _________ container would be the coolest because it is
the poorest at __________ heat radiation.
dull black
radiation
shiny metal
absorbing
Shiny metal
Dull metal
Dull black
Shiny black
EEE Dept. SCET
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15. 15
Conduction
• Direct
contact of
particles
• Solids/liquids
/gases
• The handle
of a cooking
utensil
• Transfer of
energy by
waves
• Only radiant
energy that
is absorbed
becomes
thermal
energy
• Lightbulb
• Fireplace
• Transfer of
energy by
bulk
movement of
matter
(fluids)
• Currents
(wind,water)
• Hot air
balloon
Radiation Convection
EEE Dept. SCET
