Convection Modes and Heat Transfer Coefficient

Irrespective of this classification of convection heat transfer modes, the overall effect is given by a convection rate equation governed by Newton s law cf cooling expressed as 

Combining Equations 6.35 and 6.38, we have the defining equation for convection heat transfer coefficient 

The convection heat transfer coefficient depends on a number of factors such as surface geometry, flow field, and the thermophysical and transport properties of fluid. In order to determine the convection heat transfer coefficient and hence the convection heat transfer, it is necessary to solve the energy equation for the temperature distribution along with the equation of motion for the velocity field. 

Convection heat transfer coefficients are derived for many flow conditions in the form of a correlation. For forced convections, the correlations are of the form 

represent the characteristic length and velocity in the problem. For free convection, the heat transfer correlations are given in terms of the Grashof number, Gr, and Prandtl number as  

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