Using DEM-CFD method to model colloids aggregation and deposition Florian CHAUMEIL Supervisor: Dr...
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Transcript of Using DEM-CFD method to model colloids aggregation and deposition Florian CHAUMEIL Supervisor: Dr...
Using DEM-CFD method to model colloids aggregation and
deposition
Florian CHAUMEIL
Supervisor: Dr Martin Crapper
1
BACKGROUND
Why modelling particulate matter deposition ?
It is of great importance in many industrial processes
such as• micro-contamination control of microelectronics • membrane filtration and fouling of heat exchangers • surface deposition in micro-fluidic devices
In nature, micro-particle deposition is of great interest in • microbial pathogen removal through natural granular filtration of surface
water.
2
BACKGROUND
Results from literature
• hydrodynamic drag mitigates deposition and drives re-entrainment of both biological and non-biological colloids.
• re-entrainment was found to be a monotonic function of the extent of deposition.
• Bigger deposited agglomerates increase floc re-suspension. Therefore, particle-particle interactions in a flowing fluid are shown to be as critical as surface interaction.
• Electrostatic interaction of charged colloids is still a challenging problem for researchers. In the present work surface charges are not hindering deposition.
3
AIM
What will we be looking at ?
Mechanisms of deposition
Mechanisms of deposition mitigation:• Hydrodynamic Drag• Cluster Scouring • Impaction
i.e. what drives particles to deposit in the first place and eventually re-suspend?
4
Numerical Tools
• CFD Package– Simulates
hydrodynamics (velocity and pressure field, shear forces, turbulence intensity)
• DEM Package– Simulates particulate
matter dynamics
couplingData computed by one package influence the data of the other
5
Question
how to model colloidal agglomeration ?
1) What force model :
- DLVO
- Brownian forcesGaussian random numbers (Gi) of zero mean and unit variances
2) How to describe surrounding fluid : - CFD -> Drag- Analytic Near the wall retardation
22222
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3
32
baRbaR
abRnFlvdw
3
1iiiB eNF
C
Bp
ii Ct
TkrGN
.
2.6
6
colloids aggregation and deposition in a constricted tube
7
METHODOLOGY
100μm
1-2μm 36μm
80μm inw
in
VAC
.0
Particle concentration
8
Results Collection efficiency
9
Results Collection efficiency
gen
dep
in
w
N
N
A
A.
Collection efficiency decreases when:
•Concentration Decreases•Flow rate increases•Particle size decrease
There is a variability between different runs of a same configurations due to the random particle generation 10
Results Effect of Brownian motion
mean collection efficiency for each configuration
Brownian particles have a lower collection efficiency
Random forces have an adverse effect on deposition, because they are applied at each time step in random directions
11
Results Identification of scouring mechanism
1. Particles deposit and form aggregates
2. Aggregates grow bigger by accumulating/catching free flowing particles and flocs
3. Free flowing cluster impacts deposited aggregate
4. Re-suspension
12
Results Effect of scouring on deposition
1. Particles deposit and form aggregates
2. Aggregates grow bigger by accumulating/catching free flowing particles and flocs
3. Free flowing cluster impacts deposited aggregate
4. Re-suspension
13
Results Rolling mechanism
Aggregates loosely attached to the wall roll along the surface until re-suspension or until a larger amount of their particles attach.
Identifiable by the tailed peak on the curve
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Resultscollisions correlation with collection efficiency
15
Conclusion
• Quantify number of deposited particle
• Observe the effect of Brownian motion
• Identify scouring and impact mechanisms
• Identify of rolling mechanism
• Particle to particle collisions correlation with collection
efficiency
What CFD-DEM help us achieve
16
colloids deposition in membrane filtration spacers
17
What are membrane spacers
They separate membrane sheets in water filtration system in order for the feed to flow through it
18
Spacer modeling
NALTEX-51 commercial range of spacers as this has already been subject to published studies, both experimental and computational and
has therefore a well defined geometry, with specifications readily available
19
Simulations
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Conclusion
• Initial deposition pattern appear in region of low shear stresses
• preferred deposition patterns that depends on spacer orientation is also predicted
• particle accumulation around Naltex51-1 filament junction
• No agglomeration observed at particle concentration considered
What CFD-DEM help us achieve
21