Empirical correlations for the prediction of mass transfer coefficients for single drops are presented. Published experimental results for both circulating and oscillating drops are considered. Correlation for the individual continuous-phase mass transfer coefficient, which is based on data from 596 measurements taken from 10 different groups of investigators, reproduces the data with an average absolute error of 14.1%. This is then used to determine a correlating equation for the individual dispersed-phase mass transfer coefficient on the basis of data for overall dispersed-phase mass transfer coefficient taken from 21 sources. The average absolute value of the relative error in the predicted values of overall dispersed-phase mass transfer coefficient from the experimental points by using the correlations for individual mass transfer coefficients is 24.5%. It is further shown that by allowing for the effects of power input per unit mass and dispersed-phase hold-up, the correlations for single drops can be extended to extraction columns. The correction factors required for this purpose have been obtained by using simulated values of overall mass transfer coefficients for pulsed perforated-plate, Karr reciprocating-plate, Kuhni, and rotating disc columns.

Correlations for Prediction of Mass Transfer Coefficients in Single Drop Systems and Liquid–Liquid Extraction Columns

Correlation of the average drop size in eight different types of extraction columns, namely, rotating disk, asymmetric rotating disk, Kuhni, Wirz-II, pulsed perforated-plate, Karr reciprocating-pla...

Unified Correlations for the Prediction of Drop Size in Liquid−Liquid Extraction Columns

The mathematical derivation of solutions for longitudinal dispersion in chemical-process equipment is extended to the case of cocurrent flow. The extent of completion of the process, in dimensionless form, is given as an analytical function of rates of dispersion in the two phases, over-all heat- or mass- transfer coefficient, partition coefficient, rates of fluid flow, and fractional height in the equipment. Numerical results for a large number of typical conditions are given in tubular form. (auth)

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Longitudinal dispersion in two-phase continuous-flow operations: solution and tables for cocurrent flow

Mathematical models are reviewed for different types of commonly used extraction columns, viz. pulsed sieve plate column, rotating disc contactor, Kuhni column, spray column, Scheibel extractor, packed column, Oldshue-Rushton contactor and reciprocating plate column. In addition, numerical techniques, process simulators and some estimation methods for model parameters have also been included. The review cites over 120 references.

Modeling of liquid-liquid extraction column: a review

A precise model for predicting liquid-liquid extraction column efficiency based upon assumed hydrodynamic, axial mixing and mass transfer behaviour has been formulated and solved numerically.



The complex nature of the dispersed phase can be better described by drop-size-dependent residence time distribution (RTD). Both the variation of axial velocities due to drops of different sizes, i.e. forward mixing, and the axial dispersion for the drops of the same size have been considered in this model.



The computed results reveal that the effects of both varying velocities and dispersion of drops on extraction efficiency are appreciable and cannot be neglected, and the efficiency may be overestimated if only a forward mixing model is adopted. The comparison of the experimental values of NODP with those predicted shows that the mass transfer data obtained in RDC agree well with the values predicted by the present model for the case of solute transfer in cd direction, and are slightly higher than the predicted ones for the transfer in dc direction.



On a formule et resolu numeriquement un modele precis pour prevoir l'efficacite d'une colonne d'extraction liquide-liquide base sur un comportement hydrodynamique hypothetique, le melange axial et le transfert de masse ayant ete formules et resolus numeriquement.



On peut mieux decrire la nature complexe de la phase dispersee par une distribution de temps de sejour qui depend de la dimension des gouttes. On a considere, dans ce modele, a la fois la variation des vitesses axiales avec la dimension des gouttes (melange devance) et la dispersion axiale pour les gouttes de memes dimensions.



Les resultats calcules revelent que l'effet de la variation des vitesses et celui de la dispersion des gouttes sur l'efficacite d'extraction sont appreciables et ne peuvent etre negliges; l'efficacite peut etre surestimee si seul un modele de melange devance est adopte. La comparaison des valeurs experimentales de Nodp avec les valeurs predites indique que les donnees de transfert de matiere obtenues dans RDC concordent bien avec les valeurs prevues par ce modele dans le cas du transfert du solute dans la direction c d; les valeurs experimentales sont legerement plus elevees que les valeurs prevues dans le cas du transfert dans la direction d c.

A model for liquid‐liquid extraction column performance — The influence of drop size distribution on extraction efficiency

Correlations for predicting characteristic velocity both above and below the critical rotor speed have been obtained under conditions with and without solute transfer.



It has been found that (1) above the critical rotor speed, the characteristic velocity U0 is proportional to g/DrN2, whereas below this value a transition region exists where Uo is proportional to (g/DrN2)0.26; (2) multiple regression analysis of the experimental data of continuous phase axial mixing shows that the axial dispersion coefficient varies not only with the rotor speed and modified velocity of continuous phase but also with the velocity of dispersed phase.



With varying RDC operations, the true value of Kod corrected for axial mixing changes continually between the limiting values predicted from stagnant and fully turbulent drop models. However, the highest experimental values were only 30 to 40% of those predicted by the Handlos-Baron model at the same drop Peclet number.

S. H. Zhang

Papers

Hydrodynamicst axial mixing and mass transfer in rotating disk contactors