| A new and generalized model for the prediction of stage efficiency in sieve tray extractors has been developed. The model is mechanistic in nature and takes into account the several steps involved in the mass transfer process: jetting at the perforations, formation of drops, rise or fall of drops, and coalescence of the dispersed phase. It has been validated against a significant amount of experimental work performed by the author in a four-inch pilot plant extractor plus a considerable amount of data obtained by others and subjected to a careful examination for reliability. The model is expected to give a reliable prediction of local efficiency as a function of system properties, phase dispersed, direction of solute transfer, flow quantities, and column geometry. It fits the total data bank of 286 points with an accuracy of (+OR-) 35%, a greater accuracy than can be achieved with alternate mechanistic models.;It was concluded that the sieve tray extractor, which is a non-proprietary device without internal moving parts, can be designed for relatively high efficiencies. Thus it not only can be competitive with the proprietary devices but it has the advantages that go with a better understanding of the phase contacting process itself.;The dimensionless Weber number was found to be a key indicator of mass transfer capability, with higher values favoring higher efficiencies. Thus, systems with low interfacial tension or flow through larger perforations at higher dispersed phase velocities would be desirable for achieving the lower capital investment associated with higher stage efficiencies. The expected increased mass transfer effectiveness at higher tray spacings was found, but exploitation of this effect would depend upon the cost of the increase column height. |
