Convection is the term used for heat transfer mechanism, which takes place in a fluid because of a combination of conduction due to the molecular interactions and energy transport due to the macroscopic (bulk) motion of the fluid itself. In the above definition, the motion of the fluid is essential otherwise, the heat transfer mechanism becomes a static conduction situation. When the term of convection is used, usually a solid surface is present next to the fluid. There are also cases of convection where only fluids are present, such as a hot jet entering into a cold reservoir. However, the most of the industrial applications involve a hot or cold surface transferring heat to the fluid or receiving heat from the fluid.