D

a'gDDp

in which ¡x(v) is the dynamic (kinematic) viscosity of the fluid, and Rep = wsDf/v is the particle Reynolds number. For spherical (a = p = 1), Euclidean (nf = 3) particles in the Stokes' regime, for which Rep ^ 1, the well-known Stokes' formula for a stationary settling particle is retrieved:

Figure 12.5 presents the settling velocity as established with Equation (12.5) with a = p = 1, Dp = 4 ¡m (which is a typical value found by Van Leussen5 for Ems mud), ps = 2650 kg/m3, pw = 1020 kg/m3, and x = 10-3 Pasec, for three values of nf, that is, nf = 1.7, 2, and 2.3, together with observations. These observations comprise of data on settling velocity and floc size measured in the Delft Hydraulics settling column, in the Ems estuary and in the North Sea (Van Leussen5; VIS in Figure 12.5 means size and settling velocity measurements with a Video In Situ camera system), in Chesapeake Bay (Gibbs17), and in the Tamar estuary (Fennessy et al.18). It is observed that Equation (12.5) matches the data adequately. This is also the case for data presented by Hawley,19 who summarizes the work of Japanese researchers c a v

10p o

10,000

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