Abstract
ABSTRACT In liquid-liquid extraction contractors, mass transfer and stage efficiency are closely related to drop hydrodynamics. In the present study, hydrodynamic simulation of three standard liquid-liquid extraction systems recommended by the EFCE (European Federation of Chemical Engineering) has been investigated. Toluene/water, n-butyl acetate/water, and n-butanol/water with different drop diameters were considered in the simulations, representing systems with high, medium, and low interfacial tension respectively. In the current research, for the first time simulations have been carried out using the VOF-PLIC (Volume of Fluid - Piecewise Linear Interface Calculation) model, implementing two surface tension force models of CSS (Continuum Surface Stress) and CSF (Continuum Surface Force) as a source term in the momentum equation. Simulations have been carried out in an axisymmetric geometry with a moving droplet in the static zone. The stages of droplet acceleration, deformation, and stability in terms of shape and velocity have been captured through simulations. Simulation results show that the average relative error reduces by using the CSS model and the most enhanced effect is observed in the toluene/water system, followed by the n-butyl acetate/water and n-butanol/water systems, respectively. This is due to higher parasitic current effects in the highest surface tension system (toluene/water). The onset of oscillations in the toluene/water system was correctly predicted by the CSS model, while the CSF model could not. Droplet shapes, aspect ratio, terminal and transient velocity and streamlines were also reported in the two surface tension models and compared.
Highlights
The velocity of free rising or falling droplets has great importance in liquid-liquid extraction systems
In the field of liquid-liquid extraction, numerical simulations are confidently used in order to attain a better hydrodynamic insight
The results of the present study showed that the better performance of the level set method with respect to volume of fluid (VOF) is most evident in the toluene/water system
Summary
The velocity of free rising or falling droplets has great importance in liquid-liquid extraction systems. A swarm of droplets rather than single droplets exists in large industrial systems, deep understanding of this phenomenon will al., 2011). Numerical methods are widely used in different industrial applications (Ferreira et al, 2016; Oliveira et al, 2017, Pelissari et al, 2016), as well as in the new technologies of multiphase flow (Akbari et al, 2016; Goodarzi et al, 2014; Safaei et al, 2014 Safaei et al, 2016). In the field of liquid-liquid extraction, numerical simulations are confidently used in order to attain a better hydrodynamic insight. This work focuses on rising single drops using the volume of fluid (VOF) method
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