Dispersed-phase Volume Fraction and Flow Regimes in Oscillatory Liquid-Liquid Two-Phase Flow in Annuli: Comparison of Sieve-Plate and Baffle-Plate Internals

ABSTRACT

Liquid-liquid two-phase flows are central to solvent extraction processes. In a columnar solvent extraction contactor, the turn-down ratio can be increased by imposing oscillatory flow over steady flow. This study compares dispersed phase volume fraction and flows regimes for oscillatory liquid-liquid two-phase flow in annuli having sieve-plate and baffle-plate internals. Such flows in annuli are important for specific solvent extraction applications requiring a high surface-to-volume ratio in the contactor geometry. For identical conditions, the volume fraction of the dispersed phase is found to be more in the annulus having baffle plates compared to the annulus having sieve plates. For both types of internals, an increase in dispersed phase velocity or continuous phase velocity, or oscillation velocity leads to enhancement in the volume fraction of the dispersed phase. The dispersed phase volume fraction increases when the spacing between sieve plates or baffle plates is reduced or when the fractional open area is reduced. Retention of the dispersed phase is more in the annulus having a smaller equivalent diameter. The annulus having baffle plates shows a faster transition from mixer-settler to dispersion regime or dispersion regime to the quasi-emulsion regime. Higher dispersed phase volume fraction in the annulus having baffle-plate internals suggests that it is more suitable for mass transfer than the annulus having sieve-plate internals. However, faster regime transitions in the annulus having baffle plates indicate that it is more prone to flooding than the annulus having sieve plates. The correlations that can be used to estimate the volume fraction of the dispersed phase are proposed. These correlations will be useful for design calculations.

KEYWORDS:

• Annulus
• flow regime
• holdup
• multiphase
• oscillatory flow

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