The diffusion model applies to axial dispersion in the continuous phase of liquid-liquid spray columns. Continuous-phase axial dispersion coefficients were determined for methyl isobutyl ketone dispersed in water.A sodium chloride tracer, insoluble in the dispersed phase, was injected into the column and its steady-state concentration was measured upstream in the continuous phase from the plane of injection. The dispersion coefficient was unaffected by continuous-phase superficial velocity over the velocity range investigated, but decreased with increased dispersed-phase superficial velocity. It increased with column diameter but was unaffected by column length. It increased with drop size at constant dispersed-phase superficial velocity; however, it remained approximately constant with drop size when the number of drops per unit volume of column was maintained constant. Some disagreement with earlier results was noted; however, dispersion numbers calculated from the present study superimpose roughly on those published earlier for liquids in packed beds.Internal sampling of liquid-liquid spray extraction columns, begun by Geankoplis and Hixson (1950) and continued by others-e.g., Gier and Hougen (1953), Vogt and Geankoplis (1954), and Cavers and Ewanchyna (1957)-revealed a sharp change, or end effect, in the continuous-phase concentration at the inlet of that phase to the column. Newman (1952) pointed out that this end effect could be explained in terms of backmixing of the continuous phase; however, part of it arises from mass transfer between the continuous phase and the drops while these are agitated at the column interface prior to coalescence (Cavers and Ewanchyna, 1957). Miyauchi and Vermeulen (1963), among others, considered longitudinal dispersion from the standpoint of theory, and Brutvan (1958) and Hazlebeck and Geankoplis (1963) studied it experimentally in spray towers. Letan and Kehat (1965, 1968) from heat transfer work in such columns, confirmed that the main mechanism of backmixing is transport in drop wakes, in accord with the findings of Hendrix et al. (1967) for mass transfer. Recently, the whole subject of the effect of axial mixing on mass transfer in extraction columns ivas reviewed by Li and Ziegler (1967); Mixon et al. (1967)

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