(480e) CFD Analysis of Flow of Two Immiscible Fluids in a Disk and Doughnut Pulsed Column | AIChE

(480e) CFD Analysis of Flow of Two Immiscible Fluids in a Disk and Doughnut Pulsed Column

Authors 

Bose, M. - Presenter, Indian Institute of Technology Bombay
Saini, R., Indian Institute of Technology



Solvent extraction is one of the key unit operations in the process industry. Among various
types of solvent extraction units, the pulsed columns are emerging as one of the best choices
because of their much smaller footprints compared to the most commonly used mixer-settler
type extraction units [1]. Optimal design of a pulsed column requires a thorough
understanding of the multi-phase flow dynamics as the mass transfer efficiency directly
depends on the inter-facial area which in turn, is influenced by the extent of the turbulent
mixing in the unit.

The objective of the present work is to investigate the pulsatile flow of single and two
immiscible liquids in a disk and doughnut pulsed column (DDPC) using the techniques of
computational fluid dynamics (CFD), in order to understand the effect of the geometry and
the operation conditions on the distribution of the drop size of the dispersed phase. To that
end, model geometry is selected based on the dimensional analysis of the large scale
columns. A DDPC can be described as a circular column with an internal fitting that has
several units stacked vertically in a repeated manner. Each unit comprises of a disk placed
between two ring shaped baffles (the doughnuts). The height between the ring and the disk
remains uniform throughout the column. All the geometric parameters such as the aperture of
the ring (dr), the diameter of the disk (dD), the height between the ring and the disk (h), are
non-dimensionalised by the diameter of the column.

These ratios (dr/dc, dD/dc, h/dc) are modified to investigate the influence of geometry on the
mixing. The effect of turbulence in the continuous phase is modelled using low Reynolds
number k − ε model. Simulation results are validated against the experimental work [2].
The results obtained from simulation of the scaled down DDPC is in very good agreement
with the experimental observation.

We have also determined the spatial distribution of the turbulent kinetic energy to
estimate the maximum size of the droplet formed [3]. The estimated droplet size is used in
the simulations of two immiscible fluids in a pulsed column using Eulerian-Eulerian
approach, where, both the phases are considered to be interpenetrating continua. Effect of the
column geometry, frequency and amplitude of pulsation and the location of the feeding for
the secondary phase on the dispersion will be discussed in the presentation.

References:

1. Angelov, G., Gourdon, C., 2012. Pressure drop in pulsed extraction columns with internals
   of discs and doughnuts. Chemical Engineering Research and Design, 90 (7), 877-883.

2. Bujalski, J., Yang, W., Nikolov, J., Solnordal, C., Schwarz, M., 2006. Measurement and
   cfd simulation of single-phase flow in solvent extraction pulsed column. Chemical
   Engineering Science 61 (9), 2930 -2938, fluid Mixing VIII International Conference.

3. Angelov, G., Gourdon, C., 2009. Turbulent flow in pulsed extraction columns with
   internals of discs and rings: Turbulent kinetic energy and its dissipation rate during the
   pulsation. Chemical Engineering and Processing: Process Intensification 48 (2), 592 -599.

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