Heat Transfer

We are interested in the movement of thermal energy to provide energy services.

There are three main modes of heat transfer:

• Conduction
• Convection
• Radiation

Conduction

Is the transfer of thermal energy through a solid object through atomic vibrations

• Frying pan handles

Convection

The transfer of thermal energy through the movement of a gas or liquid

• Hair dryer
• Clothes dryer

Radiation

The transfer of thermal energy through photon radiation

• Campfires
• Cats and sunbeams

Energy Balance

As energy moves, it is always conserved. Tracking the flow of energy is a common problem solving technique.

Let’s say we have a covered pot of water on a stove.

Thermal energy is being added to the pot by the heating element on the stove.

This thermal energy goes toward heating the pot and heating the water. Some of this thremal energy also leaves the pot through convection and radiation.

We can write an equation saying that the energy entering the pot from the stove is equal to the energy to heat the pot and the water and the energy leaving the pot.

While the relative amount of energy going to heating the water and leaving the pot will change, the overall equation will remain true.