fluent simulation
TRANSCRIPT
FLUENT SIMULATIONS
Clearwater AIChE - June 2006
SCOPE
• What is FLUENT ?• What are objectives and interests ?• Focus on Agitation operation• Some general examples of agitation
results• Conclusions
FLUENT
WHAT IS FLUENT ?WHAT IS FLUENT ?
Presentation of FLUENT
• Program for Fluids simulations in anygeometry (standard and not standard)
• Based on Computational Fluid Dynamics• Based on resolution of equations for
conserved properties:– Heat transfer– Mass transfer– Momentum transfer
FLUENT strategy
• Modelisation of the geometric system• Meshing of this geometry: discretization
in small cells• Resolution of continuity equations by
successive calculations in each cell
FLUENT strategy
• Geometrydefinition
• meshing
FLUENT strategy
FLUENT
WHAT ARE THE OBJECTIVES WHAT ARE THE OBJECTIVES AND INTERESTS ?AND INTERESTS ?
FLUENT objectivesObjectives: to be able
– To study and visualize the fluid motion in any size tank
– To improve process performances by simulating alternative designs
– To have flexiblity for changing quickly anyparameters (optimization)
FLUENT objectivesNUMERICAL SIMULATIONS allow:
⇒To create a large potential of investigation⇒To obtain prediction of fluid motion⇒To favour development, optimization and innovation⇒To save time, money and man power
FLUENT activities
Main FLUENT interests for chemical process:
– Chemical reactions– Heat and mass transfer– Sedimentation of solids particles– Multi-phasis systems (absorption, separation, …)– Agitation operation– Etc….
FLUENT simulations
FOCUS ON AGITATION
Agitation with FLUENT
How to design a good agitator ?
Stirred tank
Agitation with FLUENT
– Quick dispersion and homogeneization– Adequate pumping flow– Efficient solids suspension– Efficient mixing and chemical reaction– Minimum of dead zone and by-pass
flows– Optimization of power consumption
Loocking for :
FLUENT simulations
AGITATION PARAMETERS
• type of impeller (axial or radial)• type of tank• Number of impeller• position of impeller(s)• Standard or not standard geometry
Type of impeller
Types of tank
Number of impeller
FLUENT simulations
SOME GENERAL EXAMPLES...
- flow patterns- blending time- solids suspension- some ‘’sexy’’ video
FLUENT simulations
Tank fitted with1 or 2 impellers
Case 0• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=1600 mm• Down pumping
FLUENT simulations
H
D
Dag1Hag1
N
Impellers 4 PPR30°
Single impellerPoor agitation on upper zone
OK
NOT OPTIMAL
FLOW FIELD
single vs multi impeller(s)
Position of single impeller:• To avoid solids sedimentation• Risk to create poor agitation on surface
Solution:• Increase rotation speed? No (danger abrasion)• Install a second impeller? Yes but…
Case A• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=2.5 m• Dag2 =2500 mm• Hag2 = 5.5 m
FLUENT simulations
H
D
Dag1Hag1
N
Dag2
Hag2
Impellers 4 PPR30°
Multi impellers• Baffles effect
• Second impelleraction
Multi impellers2 impellers could
improve the mixing,
BUT…
Multi impellers
• Poormixing attank bottom
OK
BAD
Multi impellers
Multi impellers
• Incorrect distribution of fluidvelocity
• Danger if solids
BAD
OK
Multi impellers
• No cleaningeffect atthe bottom
• Not down pumpingaction
Case B (change ofposition)
• N=55 rpm• D=6600 mm• H=7200 mm• Dag1=2500 mm• Hag1=1.6 m• Dag2 =2500 mm• Hag2 = 5.1 m
FLUENT simulations
H
D
Dag1Hag1
N
Dag2
Hag2
Impellers 4 PPR30°
Multi impellers
• Better fluidmotion andmixing atthe bottom
OK
Multi impellers
• Goodagitation atthe bottom
Multi impellers
• Correct velocityfield
OK
Multi impellers•Cleaningeffect on thebottom
FLUENT simulationsInfluence of impellers position
and number:
Impact on flow patterns
Impact on agitation efficiency
Impact on blending time
Impact on solids suspension
FLUENT simulations
Influence of impellers position
Impact on solidssuspension
Solids suspension
Case A Case B
Initial situation (solids deposit at bottom)
solids
liquid
Case A Case B
Solids suspension
37 sec 6 sec
Case A Case B
Solids suspension
115 sec 20 sec
Case A Case BSolids suspension
Very slow suspension
quickersuspension
2317 sec 720 sec
FLUENT simulations
Impact on theBlending time
Influence of impellers…number
Blending timeWhat is the
target ?What is it ?What is it ?
• Required time for uniformity• Based on pulse of tracer• Monitoring over time of
concentration at # locations• To be minimized• To have good mixing• To avoid over-concentration• To avoid loss of recovery
as P2O5 UN and CO
top
mid
bottomcone
Blending timeCase BCase A
2 impellers1 impeller
+/- 80 sec +/- 60 sec
FLUENT simulations
EXCITING DYNAMIC VIDEOS
FLUENT simulations
CONCLUSIONSON FLUENT
Conclusions• Large potential of utilities• Development and improvement of designs• Save time and $$• PRAYON uses CFD to optimize its technologies
Thank you
Have a good day