CHAPTER 9. AGITATION AND MIXINGpages.mtu.edu/~fmorriso/cm310/fluids_lecture_15.pdf · CHAPTER 9....
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1 CHAPTER 9. AGITATION AND MIXING PRESENTATION OUTLINE -Definitions -Purposes of agitation -Devices to produce agitation -Power consumption of agitators -Blending and Mixing -Suspension of solid particles -Dispersion Operations -Agitator selection and Scale up ABRAHAM ROGELIO MARTIN GARCIA Copyright ©2003 A. R. Martin DEFINITIONS • Agitation: It refers to the induced motion of a “homogenous” material in a specified way • Mixing: It is the random distribution, into and through one another, of two or more initially separate phases PURPOSES OF AGITATION • Suspending solid particles • Blending miscible liquids • Dispersing a gas through the liquid • Dispersing a second liquid to form an emulsion or suspension • Promoting heat transfer Copyright ©2003 A. R. Martin
Transcript of CHAPTER 9. AGITATION AND MIXINGpages.mtu.edu/~fmorriso/cm310/fluids_lecture_15.pdf · CHAPTER 9....
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CHAPTER 9. AGITATION AND MIXING
PRESENTATION OUTLINE-Definitions-Purposes of agitation -Devices to produce agitation-Power consumption of agitators-Blending and Mixing-Suspension of solid particles-Dispersion Operations-Agitator selection and Scale up
ABRAHAM ROGELIO MARTIN GARCIA
Copyright ©2003 A. R. Martin
DEFINITIONS• Agitation: It refers to the induced motion of a
“homogenous” material in a specified way• Mixing: It is the random distribution, into and through one
another, of two or more initially separate phases
PURPOSES OF AGITATION• Suspending solid particles• Blending miscible liquids• Dispersing a gas through the liquid• Dispersing a second liquid to form an emulsion or
suspension• Promoting heat transfer
Copyright ©2003 A. R. Martin
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DEVICES TO PRODUCE AGITATION
IMPELLERS
• Propellers (high-speed, low viscosity)
• Turbines (Moderate viscosity)• High-efficiency impellers
Three-blademarinepropeller
Straight-bladeturbine
Disk turbine
Concave-blade CD-6 impellerPitched-blade turbine
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
DESIGN OF TURBINES
6
5
4
3
2
1
4
1
12
1
5
1
1
3
1
3
1
SD
L
SD
J
SD
W
SD
H
SD
E
SD
D
a
t
a
t
t
t
a
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
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POWER CONSUMPTION OF AGITATORS
� �� �� �> @
number) (Flow
tan1
3
3
aQ
a
aa
nD
qN
nDq
WDknDKq
v
� SES
It is a function of the volumetric flow rate and the kinetic energyValues of NQ
0.47HE-3 high-efficiency impeller
1.3Disk turbine
0.87Four-blade 45q turbine (W/Da)=1/6
0.5Marine propellers (square pitch)
NQImpeller
� �� �
number)(Power 2
2
22
53
22
53
2253
22
apQ
a
Qa
k
at
k
Dn
PNN
Dn
P
NDnP
EqP
nDV
E
U
SD
U
SDU
DSUU
¸̧¹
·¨̈©
§
�
Copyright ©2003 A. R. Martin
� �np SSSFrN ,...,,,Re, 21\
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
4
U
P
U
53
32
53
10000Re
10Re
aT
aL
ap
DnKP
For
DnKP
For
DnNP
!
�
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
BLENDING AND MIXING
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
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Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
SUSPENSION OF SOLID PARTICLES
13.0
45.0
2.01.085.0 BgDSDn pac ¸̧¹
·¨̈©
§ '
U
UQ
Shape factor S
6.58.59.5
442.5
344
Three-blade propellerNp=0.5
4.8812.5
444
234
Two-blade paddleDa/W=4Np=2.5
4.17.511.5
444
234
Six-blade turbineDa/W=5Np=6.2
SDt/E
Dt/D
aImpeller type
Copyright ©2003 A. R. Martin
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DISPERSION OPERATIONS
� �6.032
4.51058.0�
�
¸̧¹
·¨̈©
§�
V
U\
aC
a
S Dn
D
D
Source: McCabe et al. 2001Copyright ©2003 A. R. Martin
AGITATOR SELECTION AND SCALE UP
AGITATOR SELECTION• Depends on the viscosity of the liquid• For specific time of mixing, the best mixer is the one
that mixes in the required time with the smallest amount of power
SCALE UP• Maintaining constant power per unit volume and
geometric similarity
3
2
2
1
1
2¸̧¹
·¨̈©
§
a
a
D
D
n
n
Copyright ©2003 A. R. Martin
