Multiphase Modeling in ANSYS CFD - ANSYS - Simulation Driven

49 Pages·2012·4.72 MB·English

by  Gilles Eggenspieler

Multiphase Models in
ANSYS CFD
Gilles Eggenspieler
Senior Product Manager
1 © 2011 ANSYS, Inc. May 14, 2012
Which Reactor is Better?
Depends!
When gas dissolution is important Solid catalyst particles
Higher hold up! Much better mixing!
2 © 2011 ANSYS, Inc. May 14, 2012
ANSYS CFD: A Platform for Modeling
Multiphase Flows
3 © 2011 ANSYS, Inc. May 14, 2012
Introduction
Multiphase flow involves the simultaneous flow of two or
more immiscible interacting phases
Many industrial processes involve multiphase flow
• Gasoline sprays in automobile combustion engines
•• GGaassiiffiiccaattiioonn aanndd ccooaall ccoommbbuussttiioonn iinn ppoowweerr ppllaannttss
• Fluid catalytic cracking in refineries
• Aeration in water treatment plants
• Icing on aircrafts
• And several others …
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Challenges Involving Multiphase Flows
Engineering operations often involve “non-spontaneous”
processes
• Mixing -- Keep a mixture of components that separate
naturally, mixed. Desire to improve contact between the
phases to improve and enhance interfacial transfer processes
•• SSeeppaarraattiioonn ---- NNeeeedd ttoo sseeppaarraattee ccoommppoonneennttss tthhaatt aarree ddiiffffiiccuulltt
to separate, such as fine dust from flue gases
Flow dynamics crucial to the efficiency of these processes
Non-linear effect of parameters and geometry on
processes
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Lower Dimensional Simulations
Tools like Aspen, HYSYS, gProms
• Quick
• System wide simulation
Need to be supplemented with
detailed engineering analysis
•• EEnnggiinneeeerriinngg aannoommaalliieess
– Flow mal-distribution, hot spots,
stress concentrations
• Insights on off-design performance
• Effect of geometry
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The Need for Detailed Simulations
• Include all relevant phenomena
• Effect of inlets, outlets, internals
and other geometric details
captured
•• SSccaallee iinnddeeppeennddeenntt
• Qualitative and quantitative
information
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Appropriate Models for Multiphase Flow
What is the engineering
problem of interest?
What is the flow regime?
• Length scale of interface in
relation to the domain?
•• RReeggiimmee cchhaannggee??
Other important physics?
• Impact of flow on size?
• Heterogeneous and
homogeneous reactions
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Modeling Multiphase Flows
Length scale of equipment - L
Length scale of flow that is resolved (mesh) – l
Interfacial length scale (droplet or bubble size) – d
• l >> d
––
DDiissppeerrsseedd ffllooww
–
Droplets, bubbles or particles unresolved!
–
Need to model interactions (momentum, heat and mass)
• l << d or d ≈ L
–
Separated flow
–
Interfacial interactions resolved as part of solution
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Separated or Dispersed?
Bubble columns
Fluidized beds
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