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Mixing 283

and calculations for a jet system are given in the 10.28 Design of End-Around Baffle Mixing System
spreadsheet, Table CD10.12. Second and third rings Given
of jets are to be designed for installation in planes 150 An end-around mixing basin is considered for
and 300 mm downstream of the first ring; the flow alum coagulation. Let Q ¼ 0.044 m =s (1.0 mgd),
3
from each of the jet rings is radially toward the center w ¼ 0.330 m, slot ¼ 0.200 m.
of the pipe.
Required
Required Determine the power dissipated around the first bend
Design two jet rings. and G. Also determine, y 1 , y 2 , B(channel), V(channel).
10.25 Jet-Mixer System Test Program 10.29 Over-and-Under Baffle System Design for Initial
Given Mixing
Raw water is delivered to a WTP by a 1067 mm Given
(42 in.) pipeline from Horsetooth Reservoir with 3
Let Q 0.088 m =s (2 mgd) with variation, 0.044
water surface elevation 61 m (200 ft) above the plant. Q 0.132 m =s(1 Q 3 mgd) Also let T ¼ 208C
3
Over the annual cycle, 2 T 168C. Second and third and assume C(alum) 20 mg=LasAl 2 (SO 4 ) 3 14H 2 O
rings of jets are installed in planes 150 and 300 mm and is fed as liquid alum by means of a manifold
downstream of the first ring; the flow from each of the placed above the water surface in the plane of the
jet rings is radially toward the center of the pipe. If weir plate. Let the weir plates be adjustable (such as
used, these rings would require higher operating by wooden slats each about 10 cm (4 in. height); also
expense. The jets were installed because the philoso- assume the sluice gate can be raised or lowered as
phy of the plant management was to provide for uncer- needed. A reference is Harhoff (1998).
tainty in operating effectiveness if only small added
Required
capital expenses are involved.
Determine the baffle settings for the two weirs and the
Required sluice for the minimum, average, and maximum
(a) Outline a test program to determine optimum jet flows such that G 1 1000 s 1 for each flow. Show
flow for a jet-mixer system. in a drawing, the water surface profiles. Table
(b) Describe alternative feed points for alum and how CDprob10.29 may be used to facilitate calculations.
you would test for which is most effective. 10.30 Static-Mixer Design
(c) Outline a test program to determine whether the
Given
downstream jet rings should be placed in oper- 3
Let Q ¼ 0.348 m =s (10 mgd) for flow through a static
ation.
mixer.
(d) Indicate, in your opinion, the effect of temperature
variation. Required
(a) Recommend a raw-water pipe diameter.
10.26 Rationale for Design of Jet-Mixer System
(b) Recommend a pipe diameter for a static mixer in
Given
the raw-water line (possibly resulting in a smaller
Table 10.10 from Kawamura (2000) shows that most
pipe size).
of the operating plants have much lower power per
(c) Calculate the associated G and repeat with as
unit of flow values than seen in Table CD10.12 (for
many trials as needed to arrive at a G value that
right columns).
seems most appropriate.
Required (d) Calculate the monthly energy cost for each alter-
Discuss reasons for the differences. Would you design native.
based upon the Kawamura data as a guide or would 10.31 Design of Elbow Assembly Rapid Mix
you apply the rationale of Example 10.9 and the asso-
Given
ciated computational algorithm of Table CD10.12?
Flow of water is 76 L=min (20 gpm) into a pilot plant
10.27 Static Mixer for Alum Addition
with a 51 mm (2 in.) PVC raw-water pipe. An elbow
Given assembly is proposed as a rapid mix. A coagulant is to
A Kenics KMS Model 6 helical static mixer is to be be added at the entrance to the assembly.
3
used for alum mixing. Assume Q ¼ 1.0 m =s and let
Required
d(pipe) ¼ 457 mm (18 in.). From Table 10.13, for
Determine the size, d(pipe), for each elbow and the
d(pipe) ¼ 457 mm (18 in.), L(static mixer) ¼ 3258
number, n(elbows), in the sequence.
mm (128 in.). Assume liquid alum is to be fed; alum
concentration ¼ 25 mg Al 2 (SO 4 ) 3 14H 2 O.
ACKNOWLEDGMENTS
Required
Determine the headloss across the six-element static Professor Bogusz J. Beinkiewicz, Department of Civil Engin-
mixer and the P=V value. Reference is Section eering, Colorado State University, spent several sessions with
10.4.4.3. me to review the topic of turbulence with particular attention