Ch heat transfer,_kinetic_theory,_insulation,_uvalues

Introduction to
Heating & Cooling

Starter
Use the particle model to show what the
particles of a solid, liquid and a gas look like:
Solid Liquid Gas

Learning Objectives
• Know that all objects absorb and emit heat
energy
• Describe how particles move and transfer
energy in solids, liquids and gases
• Explain the process of conduction

Particle Simulation
• http://phet.colorado.edu/en/simulation/state
s-of-matter

Heat Energy
• Infra-red radiation
• All objects absorb and emit heat energy

Kinetic theory
• Kinetic theory describes how particles move in
solids liquids and gases
In your books
– Explain how the movement of particles is different
in solids liquids and gases.
– Discuss how materials change between the 3
states of matter

Methods of Heat Transfer
• Conduction
• Convection
• Radiation

Conduction
• Type of thermal energy transfer which occurs
in solids
• Vibrating particles pass on extra kinetic energy
(or heat) to neighbouring particles.
• This eventually results in a rise in temperature
at the other side of the solid.

Thermochromic paper
• Make a prediction as to which metal will be the
best conductor and why
• Describe how thermochromic paper works
• Explain why the different pieces of paper
changed colour at different rates
• Explain the process of conduction
• Which metal do you conclude was the best
conductor? Why?

Homework
• Outline what happens in conduction
• Prediction & explanation
• Method
• Conclusion

Draw one of these and explain what is
happening

Starter
Match the key words to the definitions and their
explanations (don’t copy it out!)
1) Conduction
2) Convection
3) Radiation
3) Type of thermal energy
transfer which occurs in
solids
transfer which occurs in
liquids and gases
transfer which does not
require matter in order to
travel
1) Vibrating particles pass on
extra kinetic energy (or heat) to
neighbouring particles. This
eventually results in a rise in
temperature at the other side of
the solid.
3) Liquid and gas particles are
free to move. Particles with
more kinetic energy move from
hotter regions to cooler
regions, taking their thermal
energy with them.
2) Thermal energy travels as
waves.
It travels at the speed of light.
It can travel through a vacuum.
This is the only way heat can
reach us from the sun.

Learning Objectives
• Understand how heat is transferred in liquids
and gases
• Explain how heat can be transferred in terms
of convection currents
• Apply your knowledge of the 3 methods of
heat transfer to exam style questions

Convection
• Type of thermal energy transfer which occurs
in liquids and gases
• Liquid and gas particles are free to move.
• Particles with more kinetic energy move from
hotter regions to cooler regions, taking their
thermal energy with them.

Convection Currents
• Hot air/liquid is less dense than cooler air/
liquid so it rises
• Cool air/liquid is more dense so it falls/sinks
• The rising and falling of particles with
more/less thermal energy results in a
convection current
• http://www.bbc.co.uk/schools/gcsebitesize/sc
ience/aqa/energy/heatrev1.shtml

Radiation
• Method of heat transfer which does not
require particles
• Heat energy travels as waves
• This is how heat from the sun reaches Earth
Remember! Not all radiation is dangerous!

Starter
• Here are 2 cubes of the same dimensions, made
from the same material:
• If both cubes have a starting temperature of
100°C and are left on a cool surface, which cube
will have cooled down the most after 10
minutes? Explain your answer.

Learning Objectives
• Know that all surfaces emit and absorb some
thermal radiation
• Explain why surfaces emit and absorb
radiation at different rates
• Predict the rate at which objects will cool
compared to others based on their surfaces

• All objects absorb and emit some radiation
• Some surfaces are better at this than others
Colour Finish Ability to
absorb
thermal
radiation
Ability to emit
thermal
radiation
Dark Dull or matt Good Good
Light Shiny Poor Poor

Drawing tables
• Independent variable
• Dependent variable

Drawing tables
Independent Variable Dependent Variable

Time (min) Temperature of water (°C)
Black
container
Shiny
container
Insulated
container
Bare metal
container
0
5
10
15
20
25
30

Safety
goggles
You will need:
• 4 copper containers with different
surfaces/coverings
• 100ml boiling water in each
(use a glass beaker to carry the water!)
• Thermometer
• Watch with a second hand/stopwatch
• Investigation sheet with results table
• Graph paper

Condensation & Evaporation
• Starter: Exam style question
A wet towel is left on a radiator in a room
turned on at 30°C. Another wet towel of the
same size and material is hung on a washing
line outside. The temperature is 15°C and
there is a steady breeze. Which towel will dry
the quickest and why?

Learning objectives
• Define what is meant by evaporation and
condensation
• Explain how the 2 processes occur in terms of
particles and kinetic energy
• Tackle some exam style questions on heat
transfers

Evaporation & Condensation
Evaporation
Process by which a liquid becomes a gas.
Evaporation takes thermal energy away from the surface on
which it is occurring.
Particles move further appart due to more kinetic energy
Condensation
Process by which a gas becomes a liquid.
Particles move closer together as they have less kinetic energy

Insulation
Starter
• What do we mean by insulation?
• List as many ways as you can think of in which
we can insulate our homes

Learning objectives
• List some examples of how we could insulate
our homes
• Explain how each of these methods reduces
heat transfer and cuts energy costs
• Understand what is meant by a U-value

Cavity wall insulation
• Air is a poor conductor of heat.
• Filling a wall cavity with fibreglass of
polystyrene traps pockets of air between the
walls.
• This reduces heat transfer by conduction.

Double glazing
• An air gap is created
• This reduces heat loss
by conduction

Double glass bottle
Vacuum
Silvering

U-values
• A measure of heat loss.
• The ‘overall heat transfer coefficient’
• The lower the U-value, the better the insulation
provided by the material.
• The U-valure currently required for a new-build
external wall is approx. 0.25.

You DO NOT need to know this for the
exam
U-value = W/m² x k
Heat loss in square metres of roof/glass etc
When the temperature (k) is 1°C lower outside
than inside

Questions
1. What does a U-value measure?
2. Why would a U-value be relevant to someone living in a
warm climate?
3. Give 2 advantages of using materials with a low
U-value in a building.
4. Will a building that loses less energy have a low or a
high U-value?
5. Describe the effect adding insulation to a building has
on its U-value and heat loss to the surroundings.
IN FULL SENTENCES PLEASE!

Payback Time
Starter
Last lesson we talked about ways of insulating
buildings.
List as many ways of doing this as you can
remember.

Learning Objectives
• Understand what is meant by the term
‘payback time’
• Start to tackle some exam-style calculations
on payback time.

Effectiveness
• The more effective a method of insulation, the
better it is at conserving heat energy.
• What does this tell you about its U-value?

Payback Time
• The time taken to recoup an investment
Payback time = Cost of insulator ÷ annual fuel saving

Ch heat transfer,_kinetic_theory,_insulation,_uvalues

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