| Distillation column with trays is playing a very important role in the distillation equipment. One of the main aspects of research on distillation column with trays is the fluid field and mass transfer on the trays by the method of Computational Fluid Dynamics (CFD).Firstly, based on the present research all over the world, a 3D quasi-single phase model is built together with K-εequations. The special feature of this model is taking account of the influence of interaction between liquid and gas, that is to say, the influence of interphase drag force, lifting force perpendicular to the relative velocity, virtual mass force and gas or liquid volume fraction in the fluid field have been considered. A 3D two-fluid model is also built in order to describe more accurately the fluid flow on distillation trays by comparing the computational results of quasi-single phase mathematical model with of two-fluid mathematical model. Secondly, for the first time, by volume average concept and Reynolds time-average method, a 3D quasi-single phase mass transfer model of distillation tray is deduced by considering the effects of velocity fluctuation, concentration fluctuation and volume fraction of gas and liquid on mass transfer. A source item Sc for interphase mass transfer is considered. By applying conventional method of estimating the interphase mass transfer coefficient, a formula for Sc is obtained.The finite volume method and the STAR-CD software are used to compute the fluid flow process and mass transfer process of one tray and for the first time of the whole distillation column (10 trays) under the total reflux. The computed results are as follows:1. Since the previous research did not show the comparison between the computational results and the measured values of 3D fluid field on a distillation tray, attention is paid to present work in this paper. Good agreement is obtained between present CFD predictions and published experimental data of Solari and Bell[77]. The maximum standard error of the result is 18.9%. The results can reflect the phenomena of different circulation area along the height of liquid layer and above the inlet baffle.Because of the complexity of gas-liquid cross-flow, the computed results show the necessary of further research on the two-fluid model.2. Computational results of the whole column (10 trays) under total reflux show that the velocity distribution of the tenth tray (the top tray) is identical with a single tray. The inlet velocity of the tenth tray is uniformly one-dimensional and the others is 3D at the gap of the downcomer. Thus, at the bottom of the other trays there is no recirculation, which is different from the tenth tray. Above the bottom of the other trays the flow trend is the same as on a single tray.3. Computed results of liquid concentration distribution on a single tray show that there exists concentration recirculation in the liquid layer below and above the inlet baffle. The average concentration decreases as the liquid layer moves upward. Concentration recirculation is not found in the upper liquid layer. The computational concentration of ten trays of Cyclohexane-n-Heptane at the outlet under total reflux and the measured are compared [108],The result shows that the simulation of concentration distribution on the trays is successful. A new method by rotating the probe of X-type hot-film anemometer in a plane to measure 3D velocity on a 1.2m diameter sieve tray is presented. Comparison with computational results forcefully proves the accuracy of this new method.
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