Study of axial mixing, holdup and slip velocity of dispersed phase in a pulsed sieve plate extraction column using radiotracer technique.
Axial mixing, holdup and slip velocity of dispersed phase which are parameters of fundamental importance in the design and operation of liquid-liquid extraction pulsed sieve plate columns have been investigated. Experiments for residence time distribution (RTD) analysis have been carried out for a range of pulsation frequency and amplitude in a liquid-liquid extraction pulsed sieve plate column with water as dispersed and kerosene as continuous phase using radiotracer technique. The column was operated in emulsion region and (99m)Tc in the form of sodium pertechnetate eluted from a (99)Mo/(99m)Tc generator was used to trace the dispersed phase. Axial dispersed plug flow model with open-open boundary condition and two points measurement method was used to simulate the hydrodynamics of dispersed phase. It has been observed that the axial mixing and holdup of dispersed phase increases with increase in pulsation frequency and amplitude until a maximum value is achieved while slip velocity decreases with increase in pulsation frequency and amplitude until it approaches a minimum value. Short lived and low energy radiotracer (99m)Tc in the form of sodium pertechnetate was found to be a good water tracer to study the hydrodynamics of a liquid-liquid extraction pulsed sieve plate column operating with two immiscible liquids, water and kerosene. Axial dispersed plug flow model with open-open boundary condition was found to be a suitable model to describe the hydrodynamics of dispersed phase in the pulsed sieve plate extraction column.
Mixing Analysis in a Stirred Tank Using Computational Fluid Dynamics
In this study computational fluid dynamics (CFD) approach was used to study mixing in an Industrial gold leaching tank. The objective was to analyze the extent of mixing in the tank by producing visual images of the various mixing zones in the tank domain. Eddy viscosity plots that characterise the extent of mixing in the tank were generated in the flow field obtained by an Eulerian-Eulerian approach. The extent of mixing was found to be greatest in the circulation loops of the impeller discharge region and least at the top and bottom portions of the tank. Trailing vortices that contribute to some level of mixing were identified in between the impeller blades. This approach could be used to enhance optimum design of mixing vessels and to eliminate the need for pilot plants.
Longitudinal mixing in reciprocating and pulsed sieve‐plate column‐single phase flow
Longitudinal mixing in reciprocating and pulsed sieve-plate columns has been investigated for single-phase flow and is described by a model in which both back-mixing between stages and axial mixing within stages is considered. The model proposed expresses the effect of the amplitude, frequency, flow-rates, distance between trays, their fractional free area and hole size on longitudinal mixing. The relations proposed have been verified by experiments, and the values of the constants in the correlation have been determined. 
 
 
 
On a etudie, dans le cas d'un ecoulement a phase simple, le melange fait en direction longitudinale dans des colonnes pourvues d'une plaque criblee soumise a un mouvement alternatif et des colonnes pulsees; on le decrit au moyen d'un modele ou il se fait a la fois un retro-melange entre les stades et un melange axial durant les stades. Le modele propose indique l'influence sur le melange en direction horizontales de l'amplitude, de la frequence et des debits ainsi que de la distance entre les plateaux, leur surface libre fractionnee et les dimensions de leurs ouvertures. On a verifie experimentalement les relations proposees et trouve les valeurs des constantes dans la correlation.