(461c) Effect of Primary Particle Size on Steady-State Aggregates Size and Structure Under Turbulent Conditions in Stirred Tank

Authors: 
Ehrl, L., ETH Zurich
Morbidelli, M., Institute of Chemical and Bioengineering, ETH Zurich
Moussa, A. S., ETH Zurich


The evolution of the steady-state size and structure of aggregates produced under turbulent conditions in stirred tank for primary particle diameters equal to 120nm, 420nm, and 810nm was studied experimentally for various values of the volume average shear rate and solid volume fraction. The steady-state aggregate structure was characterized by image analysis of two-dimensional pictures of the aggregates obtained by confocal microscopy. The mass fractal dimension showed to be invariant to primary particle size and applied shear rate with a value equal to 2.64±0.18. The absolute values of the root-mean-square radius of gyration obtained from small-angle static light scattering measured for similar solid volume fraction and hydrodynamic conditions proved to be independent from the primary particle size. The root-mean-square radius of gyration for all studied conditions follows a power-law scaling with the volume average shear rate with an exponent equal to -1/2, which is in agreement with our previous data and data published in the literature. Using these values combined with a force balance approach leads to an aggregate strength independent from the aggregate size and the obtained values agree well with values published in the literature. Relating the two measured moments of the cluster mass distribution, namely the root-mean-square radius of gyration and the zero-angle intensity, with the independently measured aggregates structure can be used to evaluate the effect of multiple scattering within the aggregates.

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