Single Phase Axial Mixing in Rotating Disc Contactors

Abstract

The degree of single phase axial-mixing and back-mixing in liquid-liquid extraction rotating disc contactors has been studied using several measurement techniques, i.e. single phase unsteady-state pulse injection, stationary phase axial-mixing (with no flow), and steady-state injection of tracer. Emphasis was placed on understanding the effect of column diameter, the experimental columns used having diameters of 152, 600 and 710 mm, and on the effect of operating at zero rotor speed in large columns, with the objective of more certain estimation of axial mixing in existing commercial RDCs of 3 to 4 m diameter, for which no data are available. Published data on columns of 64, 640 and 2180 mm were also used. The existence of a cylindrical region of dead space at the shaft, increasing in amount as continuous phase velocity increases, but with little dependence on rotor speed, was demonstrated. It was found that correlation of axial-mixing dispersion coefficients measured at zero rotor speed was best made using a combination of column diameter and compartment height as a characteristic length parameter. General agreement is found for the effect of agitation studied by others, but not for the effect of continuous phase flow rate.