Turbulent hydrodynamic stress induced dispersion and fragmentation of nanoscale agglomerates

High pressure dispersion nozzles of 2.5–10 mm length and 125 μm diameter have been characterized in terms of fluid dynamics and dispersion experiments at 100–1400 bar. Elongational stresses at the nozzle entry (5×105 Pa5×105 Pa) and turbulent stresses up to 105 Pa at a Reynolds number of 25,000 in turbulent channel flow are identified crucial for desagglomeration and aggregate fragmentation. Maximum stresses are calculated on representative particle tracks and related to agglomerate breakage. Agglomerates in the experimental study are in the range of the Kolmogorov micro scale (100–400 nm) and therefore break due to turbulent energy dissipation in viscous flow. Bond strength distributions could be determined experimentally from particle size distributions and fluid dynamics simulations, with primary particle erosion determined as dispersion mechanism for diffusion flame silica particles. Nanoscale agglomerates show a power law scaling for breakage with scaling exponents diverging from theory of floc dispersion. This is attributed to their strong bonding by sinter necks.

Turbulent hydrodynamic stresses exert shear on nanoscale agglomerates resulting in fragmentation. High pressure dispersion builds up these stresses.Figure optionsDownload as PowerPoint slide