An understanding of the eddy diffusivity on a distillation tray is important to accurately predict the distillation tray efficiency from the point efficiency. This article presents a new correlation to predict liquid-phase eddy diffusivity (De) on sieve trays. This correlation has been developed by modeling backmixing as the trajectory motion of liquid droplet elements through the two-phase layer height on the tray. The trajectory model indicates that De is a strong function of the two-phase layer height. An expression for froth height is derived.

The new De correlation offers two main improvements over existing literature correlations. First, this model is phenomenologically-based and, therefore, not limited to air/water. Second, the new De correlation gives significantly lower average actual and relative errors and a lower standard deviation of the actual error than do other available correlations.