Learning objectives

What factors affect heat transfer from hot materials.

How heat losses can be reduced.

“Energy can neither be created or destroyed, just changed in form.”

You need to remember that whenever energy is changed from one form to another, some energy is always ______.

In what two forms is energy usually wasted?

1._________

2._________Sound

Heat

wasted

If you can hear a device that is not designed to make noise then energy is wasted as sound.

If a device gets warm and it is not designed to get warm then energy is wasted as heat.

Heat Transfer

Heat always moves from a warmer place to a cooler place.

Hot objects in a cooler room will cool to room temperature.

Cold objects in a warmer room will heat up to room temperature.

Can you name some devices that waste energy as sound?

_____________

_____________

_____________

_____________

_____________

_____________

_____________

_____________Hairdryer

Washing machine

Car engine

Computer

Microwave

Bunsen burner

Wind turbine

Dish washer

Can you name some devices that waste energy as heat?

_____________

_____________

_____________

_____________

_____________

_____________

_____________

_____________

Computer

Turbine

Motor

Transformer

Any electrical device

Television

Radio

Car engine

Wasted e_____ spreads out (d_______) into the s_________.

This makes the energy harder to r____.

Remember energy can not be c______ or d_______.

What happens to the wasted energy you get whenever energy is changed from one form to another?

This is why it is important to r_____ the amount of wasted energy there is.

reated estroyed

nergy issipatedurroundings

e-use

educe

Heat Loss from Homes

Reducing Heat Loss From The HomeHow can Heat be lost at our homes?

These include:RoofWallsGaps around doors and windowsFloorsWindows

Reducing Heat Loss From The Home

We can reduce heat loss from our homes by using different methods of insulation.

These include:Double glazingLoft InsulationCavity Wall InsulationCarpets, Curtains, Draught Excluders

(You will need to know more detail about how these methods reduce heat loss)

The vacuum flaskThe vacuum

prevents conduction and convection

The silvered surfaces reduces radiation

Cap and base are made of good insulators to reduce conduction

Double Glazed

Double GlazerImproved thermal insulation - reduces heat loss

more effectively.Promotes passive solar heat gain - free heat from

the sun passes easily through the glass helping to warm your home.

Improved energy efficiency - reduced need for heating helps to save energy and protect the environment whilst saving you money on heating bills.

More comfortable rooms - improved thermal insulation means fewer cold spots and drafts near windows and doors.

Less condensation - the inner surface of the glass stays warmer reducing internal condensation and prolonging the life of your window.

Heat Transfer:Questions

An engineer wishes to pump hot fluid from one place to another with as little loss of heat as is possible.

a) What physical characteristics should the pipe have? (2)

Narrow bore, shiny surface, low thermal conductivity, low heat capacity........

b) Should it necessarily be wide?

c) Is the rate of flow of fluid important?

No, it might increase the SA so much that more heat is lost - but that is unlikely in most cases.

Yes, the less time it is in the pipe, the less energy it is likely to lose.

Heat Transfer:

RadiationReduce surface area and used highly polished, shiny surfaces.Evaporation

Reduce exposed surface area - use a lid - float polystyrene balls on surface.

Methods of decreasing heat transfer - Methods of decreasing heat transfer - insulation (continued)insulation (continued)

Note that generally the rate of cooling

increases with increased excess temperature.

Heat Transfer:

ConductionLeave a fluid (air gap) between surfaces - if the gap is “large” you might increase convection - introduce a vacuum jacket.

Convection

Reduce surface area and restrict the flow of the fluid - introduce a vacuum jacket.