Convection
This process of heat transfer from a solid surface to a moving liquid or gas is called convection. The motion of the fluid may be natural (driven by the heated or cooled solid) or forced (driven by external means such as a fan or a pump). The empirical equation governing the convective heat rate is often referred to as the Newton's law of cooling:
where the heat is transferred between a surface at uniform temperature Ts and a fluid with reference temperature of T? , As is the surface area, and is the mean coefficient of convection heat transfer; the unit for is W/(m2 ° C).