solar passive

8/10/2019 solar passive

1/23

Understanding Heat Transfer,Conduction, Convection and

Radiation


2/23

Heat Transfer

Heat always moves from a warmer place toa cooler place.

Hot objects in a cooler room will cool toroom temperature.

Cold objects in a warmer room will heat upto room temperature.


3/23

Question

If a cup of coffee and a red popsickle wereleft on the table in this room what wouldhappen to them? Why?

The cup of coffee will cool until it reachesroom temperature. The popsickle will melt

and then the liquid will warm to roomtemperature.


4/23

Heat Transfer Methods

Heat transfers in three ways:

Conduction Convection Radiation


5/23

Conduction

When you heat a metal strip at one end, the heattravels to the other end.

As you heat the metal, the particles vibrate, thesevibrations make the adjacent particles vibrate, and so onand so on, the vibrations are passed along the metal andso is the heat. We call this?

Conduction


6/23

Metals are different

The outer e______ of metal atomsdrift, and are free to move.

When the metal is

heated, this sea ofelectrons gain k_____energy and transfer itthroughout the metal.

Insulators, such as w___ and p____, do nothave this sea of electrons which is why theydo not conduct heat as well as metals.

lectrons

kinetic

ood lastic


7/23

Why does metal feel colder than wood, if theyare both at the same temperature?

Metal is a conductor, wood is an insulator. Metalconducts the heat away from your hands. Wooddoes not conduct the heat away from your hands aswell as the metal, so the wood feels warmer than

the metal.


8/23

Convection

What happens to the particles in a liquid or agas when you heat them?

The particles spread out andbecome less dense.

This effects fluid movement.


9/23

Fluid movement

Cooler, more d____, fluidssink through w_____, lessdense fluids.

In effect, warmer liquids andgases r___ up.

Cooler liquids and gases s___.

ensearmer

ise

ink


10/23

Water movement

Hot waterrises

Cooler

water sinks

Convection

current

Cools at the

surface


11/23

Why is it windy at the seaside?


12/23

Cold air sinks

Where is thefreezercompartment

put in a fridge?

Freezercompartment

It is put at thetop, becausecool air sinks,so it cools the

food on theway down.

It is warmerat thebottom, so

this warmerair rises anda convection

current isset up.


13/23

The third method of heat transfer

How does heat energy getfrom the Sun to the Earth?

There are no particlesbetween the Sun and theEarth so it CANNOTtravel by conduction or

by convection.

?RADIATION


14/23

Radiation

Radiation travels in straight lines

True/False

Radiation can travel through a vacuum

True/False

Radiation requires particles to travel

True/False

Radiation travels at the speed of light

True/False


15/23

Emission experiment

Four containers were filled with warm water. Whichcontainer would have the warmest water after ten minutes?

Shiny metal

Dull metal

Dull black

Shiny black

The __________ container would be the warmest after ten

minutes because its shiny surface reflects heat _______ backinto the container so less is lost. The ________ containerwould be the coolest because it is the best at _______ heatradiation.

shiny metal

radiationdull blackemitting


16/23

Absorption experiment

Four containers were placed equidistant from a heater. Whichcontainer would have the warmest water after ten minutes?

The __________ container would be the warmest after tenminutes because its surface absorbs heat _______ the best.The _________ container would be the coolest because it isthe poorest at __________ heat radiation.

dull black radiationshiny metal

absorbing

Shiny metal

Dull metal

Dull black

Shiny black


17/23

Convection questions

Why are boilers placed beneath hot watertanks in peoples homes?

Hot water rises.

So when the boiler heats the water, and the hot waterrises, the water tank is filled with hot water.

Why does hot air rise and cold air sink?

Cool air is more dense than warm air, so thecool air falls through the warm air.


18/23

Radiation questions

Why are houses painted white in hot countries?

White reflects heat radiation and keeps the house cooler.

Why are shiny foil blankets wrapped around marathonrunners at the end of a race?

The shiny metal reflects the heat radiation from the runnerback in, this stops the runner getting cold.


19/23

1. Which of the following is not amethod of heat transfer?

A. Radiation

B. InsulationC. Conduction

D. Convection


20/23

2. In which of the following arethe particles closest together?

A. Solid

B. LiquidC. Gas

D. Fluid


21/23

3. How does heat energy reachthe Earth from the Sun?

A. Radiation

B. ConductionC. Convection

D. Insulation


22/23

4. Which is the best surface forreflecting heat radiation?

A. Shiny white

B. Dull whiteC. Shiny black

D. Dull black


23/23

5. Which is the best surface forabsorbing heat radiation?

A. Shiny white

B. Dull whiteC. Shiny black

D. Dull black

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