A Fundamental Model for Prediction of Sieve Tray Efficiency

A phenomenological model for froth structure is proposed based on the analysis of froth images of an active sieve tray taken from a 0.153 m distillation column. Froth is defined as a combination of bubbles and continuous jets that break the surface of froth projecting liquid splashes and drops above the surface. To estimate the fraction of small bubbles in froth, a fundamentally sound theoretical expression is derived from turbulent break-up theory. A new model for predicting point efficiency of cross-flow sieve trays has been developed based on the hydrodynamics of an operating sieve tray represented by the proposed froth structure model. This efficiency model is applicable for both froth and spray regime. Fraction of by-passed or uninterrupted gas jet is considered as the determining factor for froth to spray transition. The net efficiency is estimated by adding up the contributions of both bubbles and jets present in the dispersion. The model is tested against the efficiency data of cyclo-hexane/n-heptane and i-butane/n-butane mixtures.