Convection (heat transfer)

Note that this definition of convection is only applicable in Heat transfer and thermodynamic contexts.

After heating has stopped, mixing and conduction from this natural convection eventually result in a nearly homogeneous density, and even temperature.

Without the presence of gravity (or conditions that cause a g-force of any type), natural convection does not occur, and only forced-convection modes operate.

This motion is associated with the fact that, at any instant, large numbers of molecules are moving collectively or as aggregates.

An external flow occurs when a fluid extends indefinitely without encountering a solid surface.

[citation needed] The bulk temperature, or the average fluid temperature, is a convenient reference point for evaluating properties related to convective heat transfer, particularly in applications related to flow in pipes and ducts.

Since they bring in an added complexity due to the undulations in the surfaces, they need to be tackled with mathematical finesse through elegant simplification techniques.

Also, they do affect the flow and heat transfer characteristics, thereby behaving differently from straight smooth surfaces.

The convection currents of the red liquid may be seen to rise and fall in different regions, then eventually settle, illustrating the process as heat gradients are dissipated.

Simulation of thermal convection in the Earth's mantle . Hot areas are shown in red, cold areas are shown in blue. A hot, less-dense material at the bottom moves upwards, and likewise, cold material from the top moves downwards.
This color schlieren image reveals thermal convection from a human hand (in silhouette form) to the surrounding still atmosphere.