There are two main types of convection that students should be able to understand and explain following a course on convection heat transfer. They are forced convection, also known as assisted convection, and natural convection, also known as free convection. Forced convection is the result of an external force, such as a pump, inducing the flow of fluids. In contrast, natural convection is the result of natural buoyancy forces that cycle cold molecules down and warm molecules up.
All fluids flow according to one of two modes or flow regimes: laminar and turbulent. A fluid's flow regime determines how much friction a fluid will endure and how much energy is necessary to keep a fluid flowing. These factors are important for understanding how efficiently convection heat transfer can occur within specific systems. Also known as viscous or streamline flow, laminar flow occurs when multiple layers of fluid particles flow over one another at different speeds, without having the layers mix. The flow has a thick, viscous consistency and the molecules composing a laminar flow move in clear, observable paths or lines.
Unlike laminar flows, turbulent flows occur when fluids move irregularly with no definable frequency. The molecules composing turbulent flow fluids do not follow clear, observable lines and intermix as opposed to forming distinguishable layers.
Convection heat transfer courses may also cover the topics of boiling and condensation, both of which can occur as a result of the transferal of convection heat. When liquid-phase fluid molecules undergo convection and rise, their high temperatures can cause them to boil or evaporate. The result is that the fluid molecules enter a gaseous state. In contrast, when gaseous fluid molecules sink and cool as a result of convection, condensation occurs and they enter a liquid state.
Beyond the specific, informational objectives that courses on convection heat transfer can have, the overarching objective of convection classes is often to provide students with tools for understanding---and contributing to---the field of engineering. After finishing a convection heat transfer course, students should be able to apply what they have learned toward mathematically and physically solving convection heat transfer problems.