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is reciprocally proportional to the viscosity of water, i.e.,
ω
sfT
1
ω
sfT
2
=
µ
T
2
(11.3)
µ
T
1
µ
T
1
and
µ
T
2
are the dynamic viscosities of water at temperatures
T
1
and
T
2
,
where
respectively.
In addition, organic matters also have significant influence on flocculation. Organic
matters usually have a positive charge, which enlarges the binding forces among sedi-
ment particles and thus intensifies flocculation. However, quantification of this effect
needs to be investigated further.
11.1.3 Formulas of floc settling velocity
The Migniot formula (11.1) and the Thorn formula (11.2) can be used to determine
the settling velocity of flocs. However, each of them only considers the effect of a
single factor. Yue (1983) proposed a formula of floc settling velocity that considers
the effects of sediment concentration, size, and non-uniformity, as well as salinity:
sa
C
1
/
3
d
1
/
4
ζβ
−
1
/
6
C
3
/
4
ω
sf
=
0.18
(11.4)
50
where
C
sa
is the salinity (ppt),
C
is the sediment concentration by volume,
β
=
1
+
0.14
d
−
1
/
2
50
2
.
Eq. (11.4) introduces a monotonous function between the floc settling velocity and
sediment concentration and thus cannot represent the general trend shown in Fig. 11.5.
Lick and Lick (1988) and Gailani
et al
. (1991) proposed a formula to determine the
floc diameter:
1
/
, and
ζ
=
(
d
80
/
d
20
)
α
0
CG
1
/
2
d
f
=
(11.5)
where
d
f
is the median diameter of flocs (cm),
C
is the sediment concentration
cm
−
3
),
G
is the fluid shear stress (dynes
cm
−
2
), and
(g
0
is an experimentally
determined coefficient. For fine-grained, cohesive sediments in freshwater,
·
·
α
10
−
8
.
According to Burban
et al
. (1990), for the same floc diameter, a larger settling
velocity is observed for the floc produced at a higher fluid shear because the effective
density and shape of the floc are affected by the conditions in which it is produced.
Burban
et al
. proposed a formula for the floc settling velocity
α
=
0
s
−
1
) based on
ω
sf
(cm
·
experiments on flocculated, cohesive sediments in freshwater:
ad
f
ω
sf
=
(11.6)
)
−
0.85
,
b
10
−
4
, and
where
a
=
B
1
(
CG
=−[
0.8
+
0.5 log
(
CG
−
B
2
)
]
,
B
1
=
9.6
×
10
−
6
(Gailani
et al
., 1991).
B
2
=
7.5
×
