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Using DEM-CFD method to model colloids aggregation and deposition

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

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Using DEM-CFD method to model colloids aggregation and deposition

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

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

  9. Results Collection efficiency 9

  10. 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. 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. 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. 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. 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. Results collisions correlation with collection efficiency 15

  16. 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. 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

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