title: Breakup of Finite-Size Colloidal Aggregates in Turbulent Flow Investigated by Three-Dimensional (3D) Particle Tracking Velocimetry.
abstract: Aggregates grown in mild shear flow are released, one at a time, into homogeneous isotropic turbulence, where their motion and intermittent breakup is recorded by three-dimensional particle tracking velocimetry (3D-PTV). The aggregates have an open structure with a fractal dimension of ∼2.2, and their size is 1.4 ± 0.4 mm, which is large, compared to the Kolmogorov length scale (η = 0.15 mm). 3D-PTV of flow tracers allows for the simultaneous measurement of aggregate trajectories and the full velocity gradient tensor along their pathlines, which enables us to access the Lagrangian stress history of individual breakup events. From this data, we found no consistent pattern that relates breakup to the local flow properties at the point of breakup. Also, the correlation between the aggregate size and both shear stress and normal stress at the location of breakage is found to be weaker, when compared with the correlation between size and drag stress. The analysis suggests that the aggregates are mostly broken due to the accumulation of the drag stress over a time lag on the order of the Kolmogorov time scale. This finding is explained by the fact that the aggregates are large, which gives their motion inertia and increases the time for stress propagation inside the aggregate. Furthermore, it is found that the scaling of the largest fragment and the accumulated stress at breakup follows an earlier established power law, i.e., dfrag ∼ σ(-0.6) obtained from laminar nozzle experiments. This indicates that, despite the large size and the different type of hydrodynamic stress, the microscopic mechanism causing breakup is consistent over a wide range of aggregate size and stress magnitude.
authors.affiliation: Department of Applied Physics, Eindhoven University of Technology , 5600 MB, Eindhoven, The Netherlands.
authors.forename: Debashish
authors.initials: D
authors.lastname: Saha
authors.affiliation: Department of Chemical Engineering and Technology, KTH Royal Institute of Technology , SE-10044 Stockholm, Sweden.
authors.forename: Matthaus U
authors.initials: MU
authors.lastname: Babler
authors.affiliation: Environmental Fluid Mechanics, Institute of Environmental Engineering, ETH Zurich , 8093 Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Holzner
authors.affiliation: Faculty of Chemical Engineering, Department of Chemical Engineering, University of Chemistry and Technology Prague , Technicka 3, 166 28 Praha 6-Dejvice, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Soos
authors.affiliation: Photrack AG, Ankerstr. 16a, 8004, Zurich, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Lüthi
authors.affiliation: School of Mechanical Engineering, Tel Aviv University , Tel Aviv 69978, Israel.
authors.forename: Alex
authors.initials: A
authors.lastname: Liberzon
authors.affiliation: ETH Zurich , 8093 Zurich, Switzerland.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kinzelbach