Distillation is the most widely used for unit operation separation in chemical and petrochemical industries but the prediction of tray efficiency remains a difficult task because of the complexity of hydrodynamics on the tray.In this paper

a three dimensional computational fluid dynamics(CFD)model is developed for describing the hydrodynamics on a sieve tray——Two-Layer Model

in which essential features of sieve tray are fully considered.On a sieve tray working under the foaming condition

two layers of liquid considered are jetting layer which is near the tray bottom resulting from high velocity gas phase emerging from the gas holes

and bubble layer——the upper layer in which gas exists in the form of gas bubbles resulting from the break-up of gas column due to much loss of gas energy.The two-equation k-ε turbulent model is used respectively to the two layers in modeling process considering the different types of interaction between phases.A sieve tray of 1.2 m in diameter is simulated

the results of calculation are reasonable.The calculation is carried out with commercial software Fluent 5.4 of Fluent Inc.