Some empirical equations for heat transfer in free flow

3 Some empirical equations for heat transfer in free flow 

In the following some further empirical correlations, besides the relationships (3.328) and (3.331) for a vertical plate which we have already discussed, for heat transfer in free flow will be communicated. 

The characteristic length in the mean Nusselt and the Rayleigh number is an equivalent length L = A/U made up of the heat transfer area A and the perimeter U of the external edges of the plate. We can differentiate between the following cases Upper side of the plate is heated or underside is cooled in accordance with Figs. 3.47 and 3.48  

Upper side of the plate cooled or underside heated in accordance with Figs. 3.49 and 3.50  

Equation (3.331) holds for laminar and turbulent flow. The acceleration due to gravity g has to be replaced by its component parallel to the wall g cos p, in which p is the angle of incline to the vertical. The equation is now valid for inclined plates, as long as (p n/3 = 60°. 

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