2. Characteristics and Motion of Sédiments
27
for B < 39
where,
r /
_ \ 1 0-7
v/= (^)s
_ \
r
/
-> 39 < B < 104
Vf —
SZW0.91
\ P J
Ps~ P
P
gD^/v2
-> 104 < B
(2-14)
(2.15)
(2.16)
Figure 2.3 shows that for 400 < Re < 200,000, the Cd is almost a
constant. From Eq. (2.17) this would give
p3 — p
Vf = const x I --------gD
(2.17)
jtfD/v
Fig. 2.3 Typical variation of Cjj with Re falling in an infinité fluid.
At 20°C the fall velocity for particles of médian size 60 x 10 6 <
<
6000 x 10~6 m is given by
= 0.447(log £>5o)2 + 1.961 logO50 + 2.736
(2-18)
The expressions obtained for a sphere are not directly applicable to
grains of sédiment because of the différence in shape. The effect of variations