| First, an experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of ∼10 mum latex spheres suspended in an aqueous solution undergoing laminar and turbulent Taylor-Couette flow was carried out, according to the following program. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in-situ optical imaging method) and with predictions using spatial average shear rates. The mean particle size evolution predicted by CFD and QMOM using appropriate kinetic expressions that incorporate information concerning the particle morphology (fractal dimension) and the local fluid viscous effects on aggregation collision efficiency matches well with the experimental data. Second, CFD simulation of turbulent reactive precipitation in a poorly micromixed plug-flow reactor has been investigated in this work. The predictions of multi-environment and transported PDF models are compared. For the first time, DQMOM is formulated and applied to approximate the composition PDF transport equation. When properly chosen, the resulting DQMOM correction terms enforce agreement between selected lower-order moments of the mixture-fraction PDF and the exact moment transport equations. Likewise, for reacting scalars, the multi-environment PDF model provides a closure for the chemical source term, and the DQMOM correction terms enforce the correct behave of the lower-order moments under the influence of turbulent diffusivity. Results for reactive precipitation show that the DQMOM-IEM model agrees closely with a transported PDF model. Since the multi-environment PDF model is much less computationally intensive than the transported PDF model, it is easy and extremely promising to couple the simple Eulerian-based multi-environment PDF models with a commercial CFD code for realistic industrial problems. Third, a novel algorithm, in-situ adaptive tabulation, has been implemented in a CFD code for the integration of reactive precipitation. A speed-up of ∼10 was achieved. |
