Thermal Energy Transfer

There are 3 common methods for Energy Transfer.

1. Conduction
2. Convection
3. Radiation

Let's start by having a look at Conduction.

Conduction is the process of thermal energy transfer without any flow of the material medium.

• Metals contain free electrons which move randomly between the atoms and molecules, thus they are good conductors of heat. Whereas non-metals do not have free electrons, thus they are poor conductors of thermal energy.

How the thermal energy transfer works.

The particles vibrate, however when heat is implemented, the particles at the hot end vibrate more vigorously due to the higher temperature (KPT)

The particles collide with neighbouring particles, causing them to vibrate as well

Kinetic Energy of vibrating particles is transferred to the neighbouring conductors.

As the atom vibrates, the free electrons in good conductors of heat move at high speeds towards the cold end.

Because the particles are far apart in liquid and gases, the transfer of thermal energy is inefficient.

Convection

Convection is thermal energy transferred by hot fluid rising and cooler fluid sinking.

1. cold air contracts, so with the same number of particles, it is more dense, causing it to sink
2. When fluids (liquids and gases) are heated, they expand and become less dense
3. The less dense fluids tend to rise from the heating source.
4. Cooler fluids, being more dense, sink to replace the less dense fluids.
5. This movement of fluid due to a difference in its density sets up a convection current.

When fluids are heated they expand and become less dense (the particles have more space).

Convection currents occur only in fluids such as liquids and gases but not in solids (due to the involvement of movement of the fluids which carry with them thermal energy.

Radiation

Radiation is the continual emission of infrared waves from the surface of all bodies transmitted without the aid of a medium.

Hence, thermal energy is released in the form of radiation. Molecules can absorb and emit EM radiation (mostly infrared radiation) in the form of molecules and electrons vibrations. When particles vibrate so vigorously, the emit a form of light as well.

Radiation can take place in a vacuum (does not require a medium)

The Sun emits electromagnetic waves, part of it comprises of infrared waves.

All objects emit some infrared radiation.

The hotter the object, the greater the radiation. The absorption of thermal energy (infrared radiation) causes a temperature rise.

In general, good emitter is also a good absorber. ž Conversely, poor emitter is also a poor absorber.

1. Factors affecting Radiation
1. Colour : black vs white
2. ž Texture: dull vs shiny
3. ž Surface temperature
4. ž Surface area

Thus, thermal energy can be transferred via Conduction, Convection and Radiation.