CFD–PBM Simulation of Liquid–Liquid Dispersions in a Pump-Mixer

Abstract

The approach coupling computational fluid dynamics and a population balance model (PBM) was adopted to simulate the hydraulic performance of liquid–liquid dispersions in a pump-mixer. Behaviors of the drop breakage and coalescence were considered in the PBM. To validate simulation methods and strategies, simulated drop size distributions were compared with experimental data and a good agreement was obtained. Flow structures in the pump-mixer were analyzed and two recirculation loops were observed. Holdup profiles reveal that the dispersed phase is unevenly distributed in space, which is more obvious at lower rotating speeds. Simulation results show that breakup regions are mainly located near the impeller where high energy dissipation rates exist, while coalescence regions were observed in the whole mixer. Distributions of the drop mean diameter were displayed. It indicated that the drop size is uniformly distributed in space at higher rotating speeds.

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

“…However, these two models are verified to lack generality. , Considering this limitation, extensive work was performed to develop the appropriate mechanisms and constraints of droplet breakup in the literature. Among all of those efforts, the novel breakup kernel based on the surface oscillation breakup mechanism which is proposed in our previous work , (named the Zhou model in this study) was verified to be accurate and general for droplet breakup modeling under turbulent conditions. , Using the novel breakup model, liquid–liquid dispersions in a pump-mixer were accurately modeled in our previous work; the model was thus adopted in the present work.…”

“…For dilute dispersions, the temporal evolution of the DSD is typically dominated by droplet breakup behaviors. 1,4 Comparatively, the influence of drop coalescence on the DSD evolution can be omitted. In such a scenario, source terms in eq 1 reduce to the following two terms: In the past few decades, various breakup kernels were established based on different modeling frameworks.…”

“…Among all of those efforts, the novel breakup kernel based on the surface oscillation breakup mechanism which is proposed in our previous work 15,17 (named the Zhou model in this study) was verified to be accurate and general for droplet breakup modeling under turbulent conditions. 1,15 Using the novel breakup model, liquid−liquid dispersions in a pumpmixer were accurately modeled in our previous work; 1 the model was thus adopted in the present work.…”

“…In the stirred tank, the dispersed phase is broken up with the turbulence that is induced by the rotating impeller. Due to the heterogeneous distribution of the turbulence intensity, local droplet behaviors of droplet breakup and coalescence have a strong spatial dependence. − As the DSD is directly determined by droplet breakup and coalescence in the stirred tank, it is necessary to construct the corresponding description method to quantify the relationship between the evolution of the droplet size and droplet behaviors.…”

“…To apply the PBM, sub-kernels including droplet breakup frequency, daughter droplet size distribution (DDSD), and droplet coalescence frequency should be first obtained. For dilute dispersions, the temporal evolution of the DSD is typically dominated by droplet breakup behaviors. , Comparatively, the influence of drop coalescence on the DSD evolution can be omitted. In such a scenario, source terms in eq reduce to the following two terms: Herein, Ω­( r , d ) is the breakup frequency function, and β­( d , d ′) is the DDSD function.…”