Drag Coefficients

Laminar Regime (Stokes Law Region)

Transitional Flow Regime (Intermediate Law Region) CD = 18.5/Re06; for 2 <Re < 500

Turbulent Flow Regime (Newton's Law Region)

The buoyant force is proportional to the mass of fluid displaced by the particle, that is, as the particle falls through the surrounding water, it displaces a volume of fluid equivalent to its own weight:

where pp = density of the solid particle p = density of the fluid

We now have all the information necessary to develop some working expressions for particle settling. Look back at equation 3 (the resistance force exerted by the water), and the expressions for the drag coefficient (sidebar discussion on page 261). The important factor for us to realize is that the settling velocity of a particle is that velocity when accelerating and resisting forces are equal:

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