Breakup of finite size colloidal aggregates in turbulent flow

Transcription

1 Breakup of finite size colloidal aggregates in turbulent flow Matthäus Bäbler Dept. Chemical Engineering and Technology, KTH Stockholm, Sweden In collaboration with: D. Saha (TU Eindhoven) M. Holzner (ETH Zurich) M. Soos (UCT Prague) B. Lüthi (Photrack AG) A. Liberzon (Tel Aviv Univ.) W. Kinzelback (ETH Zurich) And L. Biferale (Univ. Rome) A.S. Lanotte (CNR Lecce) COST Workshop Lagrangian transport: from complex flows to complex fluids, Lecce, March 7-10, 2016

2 Breakup of aggregates Lecce, Matthäus Bäbler, 2

3 Breakup of aggregates Processing of industrial colloids, flocculation in (waste)water treatment 10 m Pictures: M. Soos, D. Marchisio, J. Sefcik, AIChE J. (2013) and Soos, et al., J. Colloid Interface Sci. (2008) Lecce, Matthäus Bäbler, babler@kth.se 3

4 Breakup of aggregates Processing of industrial colloids, flocculation in (waste)water treatment Dispersion of powder agglomerates (inhalation drugs, powder burners) Picture: Getty images ( ), Göktepe et al. Fuel Process. Technol. (2016) Lecce, Matthäus Bäbler, 4

5 Breakup of aggregates Picture: Satellite image River Plate Estuary, ( ) Processing of industrial colloids, flocculation in (waste)water treatment Dispersion of powder agglomerates (inhalation drugs, powder burners) Evolution and transport of sediments and marine snow in natural waters Lecce, Matthäus Bäbler, 5

6 Aggregate breakup in turbulence Mechanism of breakup Dynamics of breakup Lecce, Matthäus Bäbler, 6

7 Experimental setup Stationary turbulence, monitored by 3D PTV Tracer particles High speed cameras Lüthi, Tsinober, Kinzelbach, J. Fluid Mech. 528 (2005) 87 Lecce, Matthäus Bäbler, 7

8 Experimental setup Stationary turbulence, monitored by 3D PTV Inject a single preformed aggregate Tracer particles High speed cameras Lüthi, Tsinober, Kinzelbach, J. Fluid Mech. 528 (2005) 87 Lecce, Matthäus Bäbler, babler@kth.se 8

9 Experimental setup Stationary turbulence, monitored by 3D PTV Inject a single preformed aggregate Follow the aggregate until (and beyond) breakup Tracer particles Determine local flow conditions that prevail at breakup Lüthi, Tsinober, Kinzelbach, J. Fluid Mech. 528 (2005) 87 High speed cameras Lecce, Matthäus Bäbler, babler@kth.se 9

10 Experimental setup Feeding pipe Aggregates Made out of polystyrene colloids, d p = 420 nm Flow device R cm 2 /s mm Grown in-situ in the feed pipe, under oscillatory flow d agg = mm Fractal dimension d f 2.2 Liberzon, Guala, Lüthi, Kinzelbach, Phys. Fluids 17 (2015) Lecce, Matthäus Bäbler, babler@kth.se 10

11 Breakup experiments Example of a breakup experiment R cm 2 /s mm d agg 1.4 mm Lecce, Matthäus Bäbler, babler@kth.se 11

12 Breakup experiments Example of a breakup experiment R cm 2 /s mm d agg 1.4 mm time Lecce, Matthäus Bäbler, babler@kth.se 12

13 Hydrodynamic stress Aggregate motion d agg / 9 ± 3 Aggregate Stokes number Aggregate motion is influenced by inertia Lecce, Matthäus Bäbler, babler@kth.se 13

14 Hydrodynamic stress Filter size to estimate u Aggregate motion d agg / 9 ± 3 Aggregate Stokes number Aggregate motion is influenced by inertia Shear stress Drag stress Lecce, Matthäus Bäbler, babler@kth.se 14

15 Breakup mechanism: limiting cases Soft aggregates (slow breakup) Brittle aggregates (fast breakup) Bond breakup due to thermal motion of the colloids [1]. Breakup caused by an abrupt breakup of bonds [2]. Depends on the duration the aggregate is subject to hydrodynamic stress. If true: weak aggregates (=large aggregates) break earlier than stronger ones. Occurs when the hydrodynamic stress exceeds a critical threshold. If true: the hydrodynamic stress at breakup correlates with the aggregate size. [1] B. O Conchuir, A. Zaccone, PRE 87 (2013) [2] M. Vanni, A. Gastaldi, Langmuir 27 (2011) Lecce, Matthäus Bäbler, babler@kth.se 15

16 Experimental results Time lag from release to breakup Shear stress at breakup Drag stress at breakup weak Aggregate strength strong weak Aggregate strength strong weak Aggregate strength strong Lecce, Matthäus Bäbler, 16

17 Experimental results Accumulation of shear stress Accumulation of drag stress Lecce, Matthäus Bäbler, 17

18 Breakup mechanism 3D PTV with large aggregates Sub-Kolmogorov aggregates 10 m Hydrodynamic stress dominated by drag Breakup is caused by weak accumulation of stress Lecce, Matthäus Bäbler, babler@kth.se 18

19 Breakup mechanism 3D PTV with large aggregates Sub-Kolmogorov aggregates 10 m Hydrodynamic stress dominated by drag Drag originates from the finite aggregate size Stress on small aggregates (in liquid) dominated by shear Breakup is caused by weak accumulation of stress Lecce, Matthäus Bäbler, babler@kth.se 19

20 Breakup mechanism 3D PTV with large aggregates Sub-Kolmogorov aggregates 10 m Hydrodynamic stress dominated by drag Drag originates from the finite aggregate size Stress on small aggregates (in liquid) dominated by shear Breakup is caused by weak accumulation of stress Bonds within the aggregate store elastic energy Small aggregates exhibit faster response Lecce, Matthäus Bäbler, babler@kth.se 20

21 Aggregate breakup in turbulence Mechanism of breakup Dynamics of breakup Lecce, Matthäus Bäbler, 21

22 Numerical experiments Stationary turbulent flow, release of few pre-formed aggregates Lecce, Matthäus Bäbler, 22

23 Numerical experiments Stationary turbulent flow, release of few pre-formed aggregates Aggregates are small and heavy Move as if they were heavy point particles Lecce, Matthäus Bäbler, 23

24 Numerical experiments Stationary turbulent flow, release of few pre-formed aggregates Aggregates are small and heavy Move as if they were heavy point particles Subject to shear and drag stress + K.A. Kusters (1991), Bagster and Tomi, Chem. Eng. Sci. (1974) Lecce, Matthäus Bäbler, babler@kth.se 24

25 Numerical experiments Stationary turbulent flow, release of few pre-formed aggregates Aggregates are small and heavy Move as if they were heavy point particles Subject to shear and drag stress Predefined rule for breakup + Babler, Biferale, Lanotte (2012) Lecce, Matthäus Bäbler, babler@kth.se 25

26 Numerical experiments Stationary turbulent flow, release of few pre-formed aggregates Aggregates are small and heavy cr Move as if they were heavy point particles Subject to shear and drag stress Aggregate breakup rate Predefined rule for breakup Babler, Biferale, Lanotte (2012) Lecce, Matthäus Bäbler, 26

27 Numerical experiments Turbulent trajectories for heavy point particles in HIT are available on (as part of EuHIT program) cr Resolution Re λ = 400 Aggregate breakup rate Babler, Biferale, Lanotte (2012) Lecce, Matthäus Bäbler, babler@kth.se 27

28 Aerosols aggregates in HIT Aggregates of size R/ = 0.1 and varying density Tracers Lecce, Matthäus Bäbler, babler@kth.se 28

29 Aerosols aggregates in HIT Aggregates of size R/ = 0.1 and varying density St=0.16 St=40 Tracers St Lecce, Matthäus Bäbler, babler@kth.se 29

30 Aerosols aggregates in HIT Aggregates of size R/ = 0.1 and varying density St=0.16 St=40 Tracers St Lecce, Matthäus Bäbler, babler@kth.se 30

31 Aerosols aggregates in HIT Aggregates of size R/ = 0.1 and varying density St=0.16 St=40 3D-PTV Experiments R/ = 18, St 0.3 Tracers Experiments St 0.3 St Lecce, Matthäus Bäbler, babler@kth.se 31

32 Conclusions We studied the breakup of finite size aggregates made out of fully destabilized polystyrene colloids in homogeneous isotropic turbulence by means of 3D-PTV. Major findings are: Hydrodynamic stress is dominated by drag. Breakup is caused by weak accumulation of stress. Both these findings are an effect of the large aggregate size. Ref. D. Saha, M.U.B., M. Holzner, M. Soos, B. Lüthi, A. Liberzon, W. Kinzelbach, Langmuir (2016) doi: /acs.langmuir.5b03804 Lecce, Matthäus Bäbler, 32

33 Conclusions Numerical simulations of small and brittle aggregates show that the breakup rate as a function of aggregate strength exhibits power law behavior for weak aggregates, followed by a sharp cut-off as the aggregate strength increases. Power law is controlled by the smooth part of the flow whose statistics are close to Gaussian. The sharp cut-off is causes by rare intermittent turbulent events. Lecce, Matthäus Bäbler, babler@kth.se 33

34 Acknowledgements Swedish Research Council VR, grant nr EU-COST Action MP1305 Flowing Matter Lecce, Matthäus Bäbler, 34

35 Backup slide Breakup mechanism 3D PTV with large aggregates Sub-Kolmogorov aggregates 10 m Hydrodynamic stress dominated by drag Drag originates from the finite aggregate size Stress on small aggregates (in liquid) dominated by shear Breakup is caused by weak accumulation of stress Finite stress propagation inside the aggregate Small aggregates exhibit faster response Lecce, Matthäus Bäbler, babler@kth.se 35

36 Breakup of aggregates Aim: Investigating the mechanism of breakup in turbulence by monitoring individual breakup events in well controlled experiments Lecce, Matthäus Bäbler, 36

37 Aim of this work Previous work: Dynamics of breakup This work: Mechanism of breakup Lecce, Matthäus Bäbler, 37

38 Aim of this work Previous work: Dynamics of breakup This work: Mechanism of breakup Lecce, Matthäus Bäbler, 38