Friction factor solid sphere

Here, p is the density of the fluid, V is the relative velocity between the fluid and the solid body, and A is the cross sectional area of the body normal to the velocity vector V, e.g., nd1/4 for a sphere. Note that the definition of the drag coefficient from Eq. (11-1) is analogous to that of the friction factor for flow in a conduit, i.e.,... 

Friction Factor/Reynolds Number Correlation for Flow Around Spheres. The magnitude of the dynamic force exerted across the tlnid-solid interface provides the basis for macroscopic momentum transfer correlations. The component of this dynamic force in the primary flow direction. 

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