This document discusses different methods of heat transfer, specifically conduction and convection. It defines conduction as the direct transfer of heat between objects in contact, explaining that it occurs faster in metals due to their structure and free-moving electrons. Convection is defined as the transfer of heat by the movement of fluids like liquids and gases, such as in boiling water where hot water rises and cold sinks, creating convection currents. The document provides illustrations of these processes and their practical applications.

1. Heat Transfer: Conduction
and Convection

2. After going through this module, you are expected to:
1. observe heat transfer between objects;
2. identify the different methods of heat transfer;
3. explain and compare how conduction and convection
occur; and
4. cite the practical application of heat transfer.

3. PRETEST
Choose the letter of the best answer. Write your answer on a
separate sheet of paper.
1. Heat is the form of energy that is transferred
between two substances at different temperatures. Which of
the following statements is TRUE about heat transfer?
a. The energy flows in circular motion.
b. The energy flows in different directions.
c. The direction of energy flow is from the substance of
higher temperature to the substance of lower temperature.
d. The direction of energy flow is from the substance of
lower temperature to the substance of higher temperature.
2. Three types of heat transfer include conduction,
convection, and radiation. What type of heat transfer is
involved when heat is transferred via solid material?
a. conduction b. convection C. diversion
D. radiation

4. 3. Chocolate candy in your hand will eventually melt as
heat is conducted from your hand to the chocolate. How does
conduction occur?
a. It occurs when two objects with the same
temperature are in direct contact.
b. It occurs when two objects with different
temperature are placed near each other.
c. It occurs when two things with different temperature
are in direct contact and energy flows from colder object to
hotter object at the point of contact.
d. It occurs when materials with different temperature
touch each other and energy directly transfers from the hotter
object to the colder object at the point of contact.
4. How does convection occur?
a. It occurs when heat is transferred by the movement
of solids.
b. It occurs when heat is transferred by the movement
of gases only.
c. It occurs when heat is transferred by the movement
of liquids only.
d. It occurs when heat is transferred by the movement
of liquids or gases.

5. 5. Heat is a concept that is important to understand in
various engineering fields. Why is study of heat transfer
particularly relevant for civil, mechanical and chemical
engineers?
a. Heat transfer is needed in the field of engineering.
b. Heat transfer plays a key role in machinery efficiency.
c. Engineers need to apply heat transfer to build
infrastructures.
d. Heat transfer plays a key role in material selection
and machinery efficiency.

6. RECAP
Direction: Fill in each blank with a correct word found in the
box to review your past lesson in science.
liquid temperature increase gas thermal
Heat is the form of energy that is transferred between systems
or objects with different (1) __________. It is also referred to
as heat energy or (2) ________ energy. Fast moving particles
‘excite’ nearby particles. If heated sufficiently, the movement of
particles in a solid (3) ___________ and overcome the bonds
that hold the particles together. The substance changes its
state from solid to (4) __________. If the movement of the
particles increases further in liquid, then a stage is reached
where the substance changes into a (5) ________ .

7. LESSON
Temperature and heat are not the same thing because
temperature is a measure of how hot something is; and heat is
a measure of the thermal energy contained in an object.
Temperature is measured in 0C (Degree Celsius) while heat
energy is measured in J (Joules).
Heat energy can flow by conduction, convection or radiation. It
always flows from a region of high temperature to a region of
low temperature

8. There are three (3) types of thermal energy transfer or
commonly called as heat transfer: Conduction, convection, and
radiation. Conduction is the transfer of heat from one
substance to another by direct contact. Convection is a transfer
of heat through a fluid (liquid or gas) caused by a molecular
motion. And radiation is transmitted in the form of rays or
waves or particles.
Observe the illustration in figure 1 below.

9. Figure 1: Three Ways of Heat Transfer

10. Conduction in solids
The atoms of a solid are held together by chemical bonds. The
atoms are fixed in place but are free to vibrate. When part of a
solid absorbs heat energy the atoms vibrate faster and with
bigger amplitude. These vibrations pass from atom to atom
transferring heat energy as they do so. This process happens in
all solids when heated but is a slow process.

11. Conduction in Metals
Some of the electrons in a piece of metal can leave their atoms
and move about in the metal as free electrons. The parts of the
metal atoms left behind are now positively charged metal ions.
When the free electrons absorb heat energy, they move much
faster. As they move through the metal, free electrons crash
into metal ions.
Observe the illustration in figure 2 below. Two kids are roasting
marshmallows. Who will burn their hands first, the kid using a
wooden stick or the one holding a metal rod? Why? You will
learn more about heat transfer in our activity and discussion
today.

12. Figure 2: Why does heat travel faster along metal than
in glass?

13. Why does heat travel faster along metal than in glass? In metals
(and minerals and crystals) the atoms are arranged in parallel
rows while in glass they are all mixed up. Metals conduct
electricity because some electrons become detached from
atoms and are free to move throughout the metals. Glass is a
very poor heat conductor. It has one of the lowest possible
heat conductions a solid (without air trapped in it) can possibly
have, this is mostly due to its lack of ordered crystal structure.
Since it's an insulator, the electronic contribution to the
thermal conductivity is very small.

14. Convection in Fluids
Heat can be transferred in liquids or gases by convection.
Liquids and gases are fluids because they can be made to flow.
The particles in these fluids can move from place to place.
Convection occurs when particles with a lot of heat energy in a
liquid or gas move and take the place of particles with less heat
energy.

15. Figure 3: Heat Transfer in boiling water

16. Look at the figure above. How does heat transfer occur in
boiling water? The water particles at the bottom of the pot are
hotter than the particles at the top. Hot water molecule is less
dense so it rises while cold water molecule which is denser
sinks. The movement of particles continues until all particles
are heated. The continuous rising of hot particles and sinking of
cold particles create convection current in water.