Assessment of gel formation in colloidal dispersions during mixing in turbulent jets

Abstract

Onset of gel formation upon mixing between colloidal dispersions and coagulant solutions in turbulent jets was studied using a combination of computational fluid dynamics (CFD) and population balance equation (PBE). To describe the interaction between turbulence fluctuations and particle aggregation, a micromixing model based on presumed probability density function was implemented inside the CFD code. Furthermore, effect of the solid phase on the fluid flow was modeled through an effective viscosity of the mixture evaluated from PBE. The results are presented in the parameter space of the primary particle diameter and the solid volume fraction where strong interplay between mixing and aggregation mechanisms controls the gelation phenomena and consequently also the fluid dynamics. Simulation results are in good agreement with observations from gelation experiments of concentrated nanoparticle suspensions injected into coagulant solutions

Study of the Shear-Thinning Effect between Polymer Nanoparticle Surfaces during Shear-Induced Aggregation

“…To compare the impact of the shear rate, the data are plotted as a function of dimensionless time (α⟨ G ⟩ tϕ ), − where the prefactor α is a function of primary particle’s Peclet number ( Pe ), through power-law dependency, α = Pe – n . The scaling parameter, n , is a function of the interparticle interactions, characterized with the ratio of the Hamaker constant and k B T and Pe , as n = 0.18 – (0.82 bPe 0.82 )/(1 – exp ( bPe 0.82 )) with b = 4­( A H /12 k B T ) 0.18 . − As can be seen, the initial aggregation period was rather fast, and at the dimensionless time equal to two, all conditions already reached the steady state that is characterized by the dynamic equilibrium between aggregation and breakup. ,, When comparing the steady-state sizes, it can be seen that by increasing the vessel averaged shear rate, the size of aggregates becomes smaller as a result of a stronger impact of the breakup. This observation is in agreement with the available data in the literature. ,,,,,, Somehow surprising is the dramatic increase of the steady-state aggregate sizes when temperature rises from 5 to 25 °C, almost by 1 order of magnitude.…”

0D Homogeneous Simulation of Droplet Size Evolution in a Turbulent Stirred Tank

“…Due to the heterogeneous turbulence in the turbulent stirred tank, droplet size evolutions can be hardly predicted with only the PBM solved. To take account of the heterogeneity, computational fluid dynamics (CFD) is commonly introduced, and the two-way coupled CFD-PBM method can be developed. ,,− For the coupled CFD-PBM method, governing equations of the CFD and PBM are solved by traversing each grid of the calculation domain, resulting in a large computational cost when executing the CFD-PBM simulations. To address this limitation and thus improve the simulation efficiency, some researchers made efforts to develop novel numerical processing methods for the PBM, e.g., method of moments (MOM), quadrature method of moments (QMOM), etc.…”