Fans are used when natural convection is insufficient to remove heat.

It frequently arises in the study of situations involving natural convection.

Combined forced and natural convection, however, can be generally described in one of three ways.

The driving force for natural convection is buoyancy, a result of differences in fluid density.

The fuel is to be cooled by natural convection of air.

If there are also buoyancy effects, for example hot air rising, then natural convection can occur.

The reactor is then only cooled by natural convection of the water.

However the distinction between natural and forced convection is particularly important for convective heat transfer.

A common example of natural convection is the rise of smoke from a fire.

It is a very important dimensionless parameter in analyzing natural or free convection.