External Natural Convection — Lesson 3

What is the one thing that is common between the cooling of hot coffee in a mug sitting on a table and the formation of sea/land breeze? In both scenarios, the natural convection heat transfer, more specifically, external natural convection, is the primary mechanism driving air motion. As the hot coffee warms the air up in its proximity, this warm air rises up, moves away from the mug and gets replaced with cooler air. By just placing a hot coffee mug on a table, a natural movement of air is established.

During the day, as the sun heats up the land, the land in turn heats up the air above it. This warmer, less dense air rises due to buoyancy effects, and it is replaced by cooler air over the sea. This flow of cooler air from the sea onto the land is known as sea breeze. At night, the land cools down faster than the sea, and the cycle is reversed, resulting in land breeze.

It is quite complicated to properly model and analyze the external natural convection heat transfer phenomena in real-world applications such as those mentioned above. However, for the purpose of preliminary analysis, most real-world geometries can be approximated by canonical configurations such as spheres, cylinders, etc. For example, land and water bodies can be assumed to be flat plates. In this lesson, we will learn about the external natural convective heat transfer characteristics of some simple configurations such as spheres, vertical and horizontal flat plates, and cylinders.

Alternate video link.

Here are the handouts for this lesson.