Download - Heat Transfer By Design Lesson 4
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.