Chapter 6: Controlling Heat Transfer
Introduction
 Fire-walkers amaze tourists.
 They aim to convince their audiences that they have
some sort of special abilities.
 But! Fire-walkers have learned to reduce the transfer
of thermal energy from the red-hot coals to their feet.
 But how is this done?

Moisture on the walkers
feet vaporizes.
Ace Ventura: Pet Detective
 Ace Ventura
https://www.youtube.com/watch?v=ZlAA0G_WrVI
Introduction
 *Hint: Cooks test to see if a skillet is hot enough by
dropping water into it.
 The pan is hot enough if the water drops dance across
the surface of the skillet.
Introduction
 We will re-visit the secrets of fire-walking later.
 We control heat transfer every day.
 Knowledge of differences in heat absorption is used in
many ways.
6.1 Absorbing and Losing Heat
 Recall from Chapter 5:
 Water moderates the temperature of the land around it.
 In this chapter we will discuss another reason why that
happens.
 Different materials absorb heat at different rates.
 This is referred to as heat absorption.
6.1 Absorbing and Losing Heat
 Specific Heat Capacity
 Different substances require different amounts of
thermal energy to raise their temperature the same
amount.
 This is true for all substances.
 Each substance requires a unique amount of heat gain or
loss to change its temperature.
6.1 Absorbing and Losing Heat
 Specific heat capacity – measures a substance’s ability
to absorb or lose heat
 Measured in joules per gram degrees Celsius
6.1 Absorbing and Losing Heat
 The specific heat capacity of a substance can change
depending on its state. For example, solid water (ice)
has a lower specific heat capacity than liquid water.
 This has to do in part with the relative attraction
between the molecules. Molecules that are close
together, as in a solid, have a stronger attraction to
each other. They require more energy to get moving.
 The joule is named after James Prescott Joule (1818–
1899), a brewer and physicist. It is represented by the
symbol J.
6.1 Absorbing and Losing Heat
 Example
 The specific heat capacity for water is
 What does this mean?


One gram of water absorbs 4.19 joules of heat to raise its
temperature 1°C
One gram of water loses 4.19 joules of heat to lower its
temperature 1°C
 Regardless of the amount of water, the amount of heat
needed to change the temperature does not change.
6.1 Absorbing and Losing Heat
 Another example:
 The specific heat capacity of sand is
 This means:
 To increase the temperature of 1 gram of sand by
1 °C would require 0.66 J of energy.
6.1 Absorbing and Losing Heat
 Consider:
 SHC of water =
 SHC of sand =
 Which has a higher specific heat capacity?
6.1 Absorbing and Losing Heat



Water!
This means that it takes more energy to
increase the temperature of water than it does
to increase the temperature of sand.
This is why sand on a sunny beach is much
warmer than the shallow water nearby.
6.1 Absorbing and Losing Heat
Substance
Specific Heat Capacity
Water
4.19
Motor oil
2.00
Vegetable oil
1.97
Air
0.995
glass
0.84
sand
0.66
Iron
0.45
copper
0.38
6.1 Absorbing and Losing Heat
 Warming Up and Cooling Down with Oceans
 Recall: oceans moderate shore areas
 Also, water has a high specific heat capacity.
 Oceans store more heat energy or thermal energy than
you might expect.
6.1 Absorbing and Losing Heat
 With water’s large SHC, water can absorb, store or
release much more thermal energy than land.
 That is another reason for land heating and cooling
quicker than lakes and oceans.
 SHC also affects climate in other ways:
 On a hot day, water will absorb heat. This slows down
the rise of temperature in the surrounding area.
 At night, water will release heat. This slows cooling in
the surrounding area.
6.1 Absorbing and Losing Heat
 The secrets of fire-walking
 Water has a very high specific heat capacity (4.184 kJ/K
kg), whereas coals have a very low one. Therefore the
foot's temperature tends to change less than the coal's.
 Water also has a high thermal conductivity, and on top
of that, the rich blood flow in the foot will carry away
the heat and spread it. On the other hand, coal has a
poor thermal conductivity, so the hotter body consists
only of the parts of the coal which is close to the foot.
6.1 Absorbing and Losing Heat
 When the coal cools down, its temperature sinks
below the flash point, so it stops burning, and no new
heat is generated.
 Firewalkers do not spend very much time on the coals,
and they keep moving.
 Calluses on the feet may offer an additional level of
protection, even if only from pain; however, most
people do not have calluses that would make any
significant difference.
6.1 Absorbing and Losing Heat
 Practice!
 Check Your Understanding p. 110 #1-5
6.2 Keeping Heat at Home
 Recall: heat moves from hot toward cold.
 This happens especially in the winter.
 Heat often leaks through windows, doors, and roofs.
 Proper insulation can help this problem.
 Insulation slows heat transfer.
6.2 Keeping Heat at Home
 With energy costs rising, Canadians want to make sure
heat stays inside the house in winter.
 For Canadians, 50 to70 percent of energy costs go
toward heating or cooling our homes.
 If insulation is inadequate, much energy is wasted.
 This is bad for the environment and for the home
budget.
6.2 Keeping Heat at Home
 With insulation you get two benefits for the price of
one.
 The same insulation that keeps heat in during the
winter keeps heat out on a hot summer day.
 Knowledge of heat transfer teaches you how to keep
your home warm in the winter and cool in the
summer.
 But what makes a good insulator?
6.2 Keeping Heat at Home
 Insulation reduces heat transfer. A good insulator is
the opposite of a good conductor.
 With good insulation, the three forms of heat transfer
are slowed.
6.2 Keeping Heat at Home
 Heat convection and heat conduction can be
minimized in two ways:
 First, create a partial vacuum between the areas to be
insulated. This is done in vacuum bottles and in some
double-glazed windows with an inert gas between the
panes.
 Second, use trapped air. Still air provides 15 000 times
better insulation than metal.
6.2 Keeping Heat at Home
 Substances used for insulation are chosen for their low
thermal conductivity and their ability to trap air.
 Good conductors include cork, felt, cotton batting,
magnesium carbonate, and spun glass or fibreglass.
 Asbestos is an excellent insulator but it is a health
hazard and no longer used in construction.
6.2 Keeping Heat at Home
 Insulators work best when the air is dry. Moist air acts
as a much better heat conductor than dry air.
 To keep insulation dry, fibreglass is covered with
plastic sheeting before drywall is installed. Without
the plastic sheet, moisture from inside the house —
from cooking, bathing, and breathing — would
infiltrate the insulation and reduce its effectiveness.
 Radiant heat loss can be lessened by installing
aluminum foil, semi-reflective windows, and
metal roofing.
6.2 Keeping Heat at Home
 R-value
 Air transfers heat when it is moved by convection
currents.
 Air is an excellent insulator when it is held still.
 R-value is a measure of how well an insulating material
slows heat transfer.
 Materials with high R-values are better insulators than
those with low R-values.
i.e.) R-12 loses heat faster than one with R-16
6.2 Keeping Heat at Home
 When materials are used together, the total R-value is
the sum of the R-values of each material used.
 Example
 Walls in your home have 25 mm of expanded
polystyrene and 25 mm of rigid urethane foam. What is
the R-value of the insulation?
3.96 + 7.50 = R 11.46
Thickness of insulating material
Approximate R-Value
25 mm of air space in a wall cavity
2.04
25 mm of air space with reflective surface on inside
of wall cavity
5.54
25 mm of expanded polystyrene
3.96
25 mm of rigid urethane foam
7.50
25 mm of fibreglass
4.25
25 mm of solid wood
1.25
25 mm of wood shavings
2.42
25 mm of clay brick
0.11
25 mm of concrete
0.19
One thickness of glass
1.00
Thermal glass (2 thicknesses with air space)
1.80
Will Aluminum Foil Keep You Warm Lab??
Initial
Beaker
Aluminum Wrapped
Beaker
30 Minutes Later
6.2 Keeping Heat at Home
 Other Ways to Keep the Heat in Your House
 The empty space between the inside and outside wall of
a house is called a wall cavity.
 Filling the cavity with insulation stops convection
currents.
6.2 Keeping Heat at Home
 When insulation fills a wall cavity, there are many
pickets of trapped, still air.
 Foam pellets and poured insulation work in this
way.
6.2 Keeping Heat at Home
 Windows and Doors That Keep Heat In
 Windows and doors are two weak points when you try
to keep a house warm.
 A single pane of glass is a poor insulator.
 Heat escapes quickly through glass.
 Leaks also develop around the panes and around the
edge of the windows.
6.2 Keeping Heat at Home
 Older houses use double windows and doors – called
storm windows and storm doors – to keep heat in.
 Today’s exterior doors and windows use double
glazing.
 This provides a space of still air.
 Insulation value of this still air in improved when air is
mixed with a gas such as argon.
Unit Heat Loss Rates
6.2 Keeping Heat at Home
 Exterior doors used to be solid wood.
 Modern doors are cavities filled with insulation.
 Some are metal covered.
 To prevent heat transfer, there is a break in the metal
between the inside and outside.
6.2 Keeping Heat at Home
 Did You Know?
 Even the smallest crack (1.5 mm) around the outside of
one window, your furnace may burn an extra litre of fuel
per day!
6.2 Keeping Heat at Home
 Controlling Heat Transfer
 Pizza parlours keep pizza warm by transporting it in
insulated containers.
 As well as limiting heat transfer, the envelope must be
washable.
 This limitation prevents the use of some materials.
6.2 Keeping Heat at Home
 A vacuum bottle uses several of the same
technologies that keep your house warm in order to
keep food and beverages warm.
 Inside is a double glass jar. One jar is fitted inside the
other – similar to windows with a double pane.
 Some air is removed from between the two jars. That is
where the name comes from. The space between is a
partial vacuum.
6.2 Keeping Heat at Home
 Rubber or plastic keeps the glass away from the outer
case.
 The cap is insulated.
6.2 Keeping Heat at Home
 Kitchen and Workshop
 Large appliances (i.e. Stoves, refrigerators, freezers,
even dishwashers) are all insulated.
 Insulation slows heat transfer, keeping ovens hot and
freezers cold.
 What makes a good insulator?

Non-metals (i.e. Wood and plastic)
6.2 Keeping Heat at Home
 Examples:
 Plastic and/or wooden handles on kitchen utensils
or pots and pans
 Aprons and oven mitts
6.2 Keeping Heat at Home
 Practice!
 Check Your Understanding p. 119 #1-6
6.3 Keeping Yourself Warm
 The same techniques that keep our
houses warm, keeps our bodies warm.
 For example, on a cold day we may
choose to wear several layers.
 We choose inner layers for their open
weave and thickness.
 Air trapped in the material serves as
insulation.
 A windproof outer layer keeps warm air
from escaping.
6.3 Keeping Yourself Warm
 Clothing insulates by holding air between fibres.
 The better clothes trap air, the better insulators they
are.
 This is why thicker clothing tends to be warmer than
thinner.
 Thicker clothing reduces air flow and maintains still
air.
 Windproof material reduces or eliminates airflow
through the fibres.
6.3 Keeping Yourself Warm
 Some of the warmest winter clothing
contain down.
 Birds grow fluffy, down feathers.
 These feathers keep birds warm.
 Down is often quilted between the outer
shell and inner lining of a vest or jacket.
 When down is fluffed, it holds air in place.
 The jacket material keeps air from blowing
through the down and changing cold air for
warm.
6.3 Keeping Yourself Warm
 Recall: a dry body is a warm body.
 Vigorous activity causes sweat. Water causes cooling as
it evaporates.
 When working or playing outside, you want to protect
yourself from getting and staying damp.
 When you start to sweat, remove one layer, possibly
another.
 This allows heat to transfer out and your body to stay at
the right temperature.
 When you stop moving you can replace those layers.
6.3 Keeping Yourself Warm
 On a cold day, up to 40 percent of body heat is lost
through the head.
 Covering the head is important for heat retention.
 When a person becomes overheated in winter, a hat is
often the first piece of clothing removed to cool the
body and reduce perspiration.
6.3 Keeping Yourself Warm
 People of the North
 Inuit designed clothing is the
warmest.
 Traditionally, Caribou Inuit
clothes have two complete suits
on cold days.
 The inner set is worn with fur
next to the body.
 Body moisture is transferred
through the fur and through the
leather skin.
6.3 Keeping Yourself Warm
 Caribou fur is dense; individual hairs are hollow.
 Air trapped between and inside the hair provides
insulation.
 The outer parka is worn with the fur outside – this is
important for very cold days.
 The parka hood traps air in front of the wearer’s face.
 Frigid air is warmed before being breathed.
 This protects the wearer’s lungs.
6.3 Keeping Yourself Warm
 During extremely cold weather, water
vapour from the lungs can condense and
freeze on people’s faces and clothing.
 The hoods are designed to prevent
condensation.
 The edge of the hood, where ice might
form, is trimmed with fur.
 Ice does not stick to wolverine, wolf, or
some dog fur.
6.3 Keeping Yourself Warm
 Caribou and Copper Inuit wear up to four layers on
their feet in winter.
 Seal skin is preferred to boots because it is waterproof.
 Inuit parkas are much larger than we might expect.
 The large size allows wearers to bring their arms inside
this warm space.
6.3 Keeping Yourself Warm
 Did You Know?
 Some motorcyclists have clothing with built in
heaters!
 Heating elements are sewn into the clothing and warm
areas of the body such as the torso where a lot of heat
can be lost.
 The clothing runs off of a motorcycle battery and uses
less power than a headlight.
 The amount of heat can be controlled using a palmsized computer.
6.3 Keeping Yourself Warm
 Did You Know?
 People outside in winter protect themselves from
frostbite. Frostbite usually freezes hands, feet and the
face.
 One way to warm a cold hand is to tuck it into your
armpit for a few minutes!
6.3 Keeping Yourself Warm
 Keeping Cool
 Ever notice that people who live in
warmer climate areas where more
clothes?
 This is because they want to
minimize heat transfer.
 They wear long, thick robes to
protect the body from the Sun’s rays.
 These clothes are usually light in
colour to help reflect heat and to
allow body heat to escape.
6.3 Keeping Yourself Warm
 Oven mitts work in a similar manner.
 Their quilted material reduces heat transfer.
 Some include reflective material that also reduces heat
transfer.
6.3 Keeping Yourself Warm
 Dressing for Intense Heat – or Cold
 Firefighters and deep-sea divers have to deal with major
changes in temperature.
 But how?
6.3 Keeping Yourself Warm
 Firefighters’ suits are made of a
special material.
 Many contain flame retardant
chemicals.
 When flames or sparks come into
contact with the suit, the fabric
chars but does not burn.
 The charred material produces a
layer of insulation that protects the
firefighter from too much heat.
6.3 Keeping Yourself Warm
 Firefighters can suffer from heat stroke if




their body temperature increases too much.
Material on the inside of their fire suit
absorbs body moisture.
This helps to keep them cool.
Firefighters must monitor their own bodies.
If they get too hot, they could suffer from
heatstroke – even if it’s in the winter!
6.3 Keeping Yourself Warm
 The fabrics used in firefighters’ suits are tested to
determine their fire resistant qualities.
 They are tested by Scientists to see if they are safe
enough for firefighters to wear.
 This is done by dressing a mannequin in fire gear and
setting it on fire.
 These mannequins are equipped with sensors to
measure the rate and amount of heat transfer from the
fire.
6.3 Keeping Yourself Warm
 Even in hot climates, temperatures deep underwater




can be as cold as winter.
As a result, a diver’s suit should fit snugly.
Tight diving suits prevent cold water next to the skin
from causing cooling by conduction.
If cold ocean water moved in and out of the suit, a
diver would soon be cold.
Water could pick up heat from the diver’s body and
carry it off into the ocean.
6.3 Keeping Yourself Warm
 Dive suits are made of neoprene that has bubbles of
nitrogen trapped in the fabric.
 The more gas trapped in the fabric, the higher the
thermal value.
 These neoprene suits are well insulated to keep body
heat inside.
6.3 Keeping Yourself Warm
 Dive suits also have hoods for the
same reason that winter parkas have
hoods.
 Underwater, a great amount of heat
can be lost from a diver’s head.
 Some dive suits have titanium added
to the side of the fabric that is next
to the skin.
 The shiny titanium reflects heat
back into the body.
6.3 Keeping Yourself Warm
 Practice!
 Check Your Understanding p. 125 #1-6
Review
 Complete review questions on pg. 126
 Hand-in Assignment #6