Terminology
The term convection may have slightly different but related usages in different scientific or engineering contexts or applications. The broader sense is in fluid mechanics, where convection refers to the motion of fluid regardless of cause. However in thermodynamics "convection" often refers specifically to heat transfer by convection.
Additionally, convection includes fluid movement both by bulk motion (advection) and by the motion of individual particles (diffusion). However in some cases, convection is taken to mean only advective phenomena. For instance, in the transport equation, which describes a number of different transport phenomena, terms are separated into "convective" and "diffusive" effects, with "convective" meaning purely advective in context. A similar differentiation is made in the Navier–Stokes equations. In such cases the precise meaning of the term may be clear only from context.
Read more about this topic: Convection