| Heat energy transfers between a solid and a
fluid when there is a temperature difference between the fluid and
the solid. This is known as "convection heat transfer". Generally,
convection heat transfer can not be ignored when there is a
significant fluid motion around the solid.
The temperature of the solid due to an external field such as
fluid buoyancy can induce a fluid motion. This is known as "natural
convection" and it is a strong function of the temperature
difference between the solid and the fluid. Blowing air over the
solid by using external devices such as fans and pumps can also
generate a fluid motion. This is known as "forced convection".
Fluid mechanics plays a major role in determining convection heat
transfer. For each kind of convection heat transfer, the fluid flow
can be either laminar or turbulent. Laminar flow generally occurs in
relatively low velocities in a smooth laminar boundary layer over
smooth small objects, while turbulent flow forms when the boundary
layer is shedding or breaking due to higher velocities or rough
geometries. | 
