Introduction

Before we start to dive into the exciting topic of heat transfer, we should first start out by defining what heat transfer is and why it is important!

Heat transfer is the spatial movement of thermal energy due to a temperature difference. When there is a temperature difference, the heat will flow from high temperature to low temperature. This is due to Clausius' statement of the 2nd Law of Thermodynamics. Now, it should be noted if work is inputed into a system, heat can flow from low temperature to high temperature (like a refrigerator!), but naturally this does not occur.

Thermal Energy

Since heat transfer is the movement of thermal energy, that should be our next topic of conversation. Thermal energy in matter consists of two components: sensible and latent energy.

• Sensible energy - associated with random motion; this could be from translation, rotation, vibration, and electronic states of atomic structures.
• Latent energy - associated with changes in phases.

This relation between the two components can be explained via the heating of water.

Let's start with a pot of water at room temperature. Now, let's say the stovetop is turned on and heat is transferred through the pot to the water via conduction (we will talk more about conduction later). Now the water's sensible energy will increase as the temperature rises up to the boiling point of water. Now once the water reaches this point, it still requires more energy before the bonds between the atoms destabilize and break. This is where latent energy comes into play. When the required latent energy is added, then the water can evaporate into a gaseous state.

As some background, there is a term that is often used for liquids on the cusp of turning into a gaseous state, and that is a saturated liquid.

Modes of Heat Transfer

There are 3 types of heat transfer that can occur, conduction, convection, and radiation and we will dive into each of them throughout the guide.

• Convection - heat transfer through contact in a solid or a fluid that is stationary. This occurs from the random motion of constituent atoms, molecules, and/or electrons.
• Convection - heat transfer due to a moving fluid. This is from advection, or the combination of fluid dynamics and conduction.
• Radiation - heat transfer due to electromagnetic (EM) waves. EM waves are emitted from changes in electron configurations in atoms (they are constantly moving around!); radiation does not need a medium to travel in, but depending on the medium, it can affect how the radiation travels.

We will work our way through these modes of heat transfer one by one after we go through some more important fundamentals of heat transfer. Heat transfer occurs all the time, from warm water warming up cold ice cubes to you emitting EM radiation in the infrared range while reading this tutorial. Heat transfer is an exciting topic and is constantly occurring between thermal differences!