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Using DEM-CFD method to model colloids aggregation and deposition

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Presentation on theme: "Using DEM-CFD method to model colloids aggregation and deposition"— Presentation transcript:

1 Using DEM-CFD method to model colloids aggregation and deposition
Florian CHAUMEIL Supervisor: Dr Martin Crapper 1

2 Why modelling particulate matter deposition ?
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

3 Results from literature
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

4 What will we be looking at ?
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

5 Numerical Tools CFD Package DEM Package
Simulates hydrodynamics (velocity and pressure field, shear forces, turbulence intensity) DEM Package Simulates particulate matter dynamics Data computed by one package influence the data of the other coupling 5

6 how to model colloidal agglomeration ?
Question how to model colloidal agglomeration ? What force model : DLVO Brownian forces Gaussian random numbers (Gi) of zero mean and unit variances 2) How to describe surrounding fluid : CFD -> Drag Analytic Near the wall retardation 6

7 colloids aggregation and deposition in a constricted tube
7

8 Particle concentration
METHODOLOGY 100μm 80μm 1-2μm Particle concentration 36μm 8

9 Collection efficiency
Results Collection efficiency 9

10 Collection efficiency
Results Collection efficiency 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

11 mean collection efficiency for each configuration
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

12 Identification of scouring mechanism
Results Identification of scouring mechanism Particles deposit and form aggregates Aggregates grow bigger by accumulating/catching free flowing particles and flocs Free flowing cluster impacts deposited aggregate Re-suspension 12

13 Effect of scouring on deposition
Results Effect of scouring on deposition Particles deposit and form aggregates Aggregates grow bigger by accumulating/catching free flowing particles and flocs Free flowing cluster impacts deposited aggregate Re-suspension 13

14 Identifiable by the tailed peak on the curve
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 14

15 collisions correlation with collection efficiency
Results collisions correlation with collection efficiency 15

16 What CFD-DEM help us achieve
Conclusion What CFD-DEM help us achieve 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 16

17 colloids deposition in membrane filtration spacers
17

18 What are membrane spacers
They separate membrane sheets in water filtration system in order for the feed to flow through it 18

19 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

20 Simulations 20

21 What CFD-DEM help us achieve
Conclusion What CFD-DEM help us achieve 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 21


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