HEAT TRANSFER

ANDREW PURDY

M3 SCIENCE

The heat is on

Temperature and atoms

Why do some things feel cold and some hot?

• When an object feels hot, the atoms inside it are moving fast, and when it feels cold, they are moving slowly.

So when I'm heating something, I'm just making its atoms move faster?

Exactly. If the object is a solid the atoms are vibrating back and forth, and if it is a gas like the air, the atoms are flying around much like little balls.

Absolute Zero

The hotter the atoms the faster they move. When atoms are cold enough they stop moving we call this absolute zero. Absolute zero is the lowest temperature that could ever be (-273 Celsius)

Types of heat transfer

How can heat move from one thing to another?

There are 3 ways to transfer heat:

1. Conduction

2. Convection

3. Radiation

ConductionWow. Ajarn Andrew you are so smart. Can you tell me how conduction works?

Of course, this one is easy.

If something is hot, then the atoms inside of it are moving around a lot. When the atoms move, they bump into the atoms next to them, making them move.This starts a chain reaction and the heat spreads through the whole object. This is what's happening if you've ever set a pan on the stove. The handle gets warm even though only the bottom touches the burner because the metal conducts the heat .

Conduction Pictures

Convection What about convection?

When a gas or a liquid is heated, hot areas of the material flow and mix with the cool areas.This type of heating is called convection. Convection transfers heat over a distance faster than by conduction

Convection- gas/ liquid

Hot water rises, cools, and falls.

                           

Heated air rises, cools, then falls. Air near heater is replaced by cooler air, andthe cycle repeats.

              

           What if coils were atthe bottom?

 

Radiation

Wow. So cool. What about the last one?

A third method to transfer heat is by radiation.A warm or hot object gives off infrared electromagnetic radiation, which can be absorbed in another object, heating it up. Transfer of heat by radiation travels at the speed of light and goes great distances. We are heated from the Sun through radiation transfer of heat

“Convection" is heat transferred by an air (or water) current: the air heats up, moves to another place, heats up that place.

“Conduction" is heat moving from one solid object to another: a hot piece of metal is place against a cold piece of metal and heat moves from one to the other.

“Radiation" is heat moving from one place to another a

s electro-magnetic (mainly infra-red) radiation.

Remember!

Thanks Ajarn Andrew