(98c) Comparison of Breakup Kernels in the CFD-PBM Simulation of a Pulsed Disc and Doughnut Column
Pulsed disc and doughnut column (PDDC) is a widely used type of liquid-liquid extraction equipment. Both research and design for this kind of device require a penetrating knowledge of the dispersed doplet size distribution(DSD). The coupling of computational fluid dynamics (CFD) and population banlance model (PBM) has shown its great potential to predict the DSD taking breakage and coalescence into account. In the present work, a CFD-PBM simulation is applied to predict the droplet size distribution and local flow behaviors in a PDDC with square section. Small dispersed phase flow rate is used so that the droplet coalescence can be ignored and breakup kernels can be compared. Two breakup kernel functions, a semi-theortical one by Coulaloglou and Tavlarides [1977. Description of interaction processes in agitated liquidâliquid dispersions. Chemical Engineering Science 32, 1289â1297] and an empirical correlation by Zhou et al. [2017. Direct measurement of droplet breakage in a pulsed disc and doughnut column. AIChE Journal, 63(9), 4188-4200] are indiviually implemented in the CFD code on the CFX platform. Class method with fixed pivot techinique is adopted to solve the population balance equations. The model of Zhou predicts the droplet size distribution more accurately than that of Coulaloglou and Tavlarides regarding to experimental results. CFD-PBM simulation results with the kernel functions of Zhou et al. are then used to investigate specific issues. Influences of droplet size range and inlet droplet size conditions on the predicted size distribution are discussed. Hydraulic performace by simulation agrees well with experimental work. Local flow field variations are illustrated and depict the typical flow behaviors of the PDDC. The simuation results suggest that CFD-PBM method is a promising method for the simulation of liquid-liquid flow when a precise kernel function is firstly determined.
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