Forced Convection Heat Transfer Principles
The mechanism of heat transfer by convection requires mixing of one portion of fluid with another portion due to gross movement of the mass of the fluid. The transfer of heat energy from one fluid particle or a molecule to another one is still by conduction but the energy is transported from one point in space to another by the displacement of fluid.
When the motion of fluid is created by the imposition of external forces in the form of pressure differences, the process of heat tra of fluid particles may be either laminar or turbulent and that depends upon the relative magnitude
of inertia and viscous forces, determined by the dimensionless parameter Reynolds number. In free convection, the velocity of fluid particle is very small in comparison with the velocity of fluid particles in forced convection, whether laminar or turbulent. In forced convection heat transfer, Gr/Re2<< 1, in free convection heat transfer, GrRe2>>1 and we have combined free and forced convection when Gr/Re2 »1.
Methods for Determining Heat Transfer Coefficient
The convective heat transfer coefficient in forced flow can be evaluated by:
(a) Dimensional Analysis combined with experiments;
(b) Reynolds Analogy –an analogy between heat and momentum transfer;
(c) Analytical Methods –exact and approximate analyses of boundary layer