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A fluorimetric technique was used to determine detailed residence time and R. B. SOLAR1 and R. L. BELL velocity distribution on commercial sieve trays installed in a five-tray, 1.22 m dia. air/water simulator. Results show a strong effect of the gas rate on the residence time distribution. At low air rates, isochron lines of high residence time are found at the column wall. and the variance distributions suggest the existence of zones of Department of Chemical Engineering University of California Davis, CA 95616 I different degrees of mixing. The velocity profiles at F, (vapor velocity load) factors less than 0.65 show severe flow nonuniformities characterized by a high velocity at the centerline and stagnant zone close to the wall. At higher F, factors the velocity maldistribution seems to be relatively mild. Correlations are presented to estimate the velocity distribution on the tray as a function of the gas rate.

The effect of nonuniform velocity distributions and retrograde flow on Murphree tray efficiency has been studied. Both types of nonuniformities were shown to substantially reduce the efficiency of the tray. The results show that the presence of flow nonuniformity alone may result in significant deviations from the efficiency predicted by the AIChE model. RICHARD L. BELLand RODOLFO B. SOLAR1 Department of Chemical EngineeringUniversity of California Davis, California 95616Although tray-type contacting equipment has been in common use for years, the prediction of the mass transfer efficiency of these devices without data from similar services is at best imprecise. The most commonly used methods for predicting tray efficiency are based on that proposed in the AIChE Bubble Tray Design Manual (1958). This method first requires a prediction of gas and liquid phase transfer units which yield a point efficiency. The second step is to use the point efficiency in a mathematical model of liquid and gas motion on the tray to obtain an overall tray efficiency. These are separate steps and errors in either could independently result in errors in the prediction of tray efficiency.The AIChE tray model assumes that the liquid phase flows from the tray inlet to outlet with a uniform velocity and with no velocity gradient in the direction normal to flow. However, it has recently been demonstrated that severe, nonuniform flow patterns exist on commercialscale sieve trays (Bell, 1972a,b). These patterns ranged from simple nonuniform velocity distributions to extensive reverse or retrograde flow near the walls. In the latter case there was a high speed flow through the center of the tray and a tendency for pooling on either side of the centerline. The pooling resulted from regions in which the circulation was closed and as shown in the film by Keller and Yanagi (1970), the movement of fluid elements out of this region can be very slow. The AIChE Bubble Tray Design Manual, as well as other authors have drawn attention to the inefficiency which can accompany nonuniform flow distributions (Williams et al., 1960;Foss et al., 1958;Gerster et al., 1958). Although the effect of small-scale eddy dispersion on tray efficiency has been studied extensively, very little work has been done on the effects of deviation from the uniform velocity distribution.Direct bypassing of fluid from the tray outlet to inlet was considered by Warzell (1955), Crozier (1955, and Oliver and Watson (1956). Strand (1963) experimentally determined a bypassing factor and showed that better agreement could be obtained between predicted and observed efficiencies by using his bypassing factor correlation. In each of these cases, however, a uniform velocity distribution was assumed and the bypassing stream did not participate in the mass transfer process.Lebedev and co-workers (1968) have calculated the effect of n nonuniform velocity distribution by considering 2 flow paths which consist of several well mixed chambers. By use of this mixed hydrodynamic model the flow rat...

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A model was developed to predict the flowdynamic behavior of bale-type catalytic packings, which are widely used in the industry for several applications. The new model takes into account the effect of the catalyst properties and packing characteristics as well as the properties of the fluids, flow rates, and column diameter to predict liquid hold-up, pressure drop, and the loading and flooding points. The particle model concepts were used as the basis for the generation of the model, introducing considerations that account for a proper representation of a wide variety of data obtained in tests performed in this work or reported previously in the literature. It was found that the nature of the catalyst contained in the "bales" strongly affects the liquid hold-up due to solid-liquid interactions. A factor was also introduced in the model to account for the strong effect of the wall on small-diameter columns. The new model 855 ORDER REPRINTS significantly improved the prediction of the flowdynamic parameters such as hold-up and pressure drop as well as loading and flooding points, which showed deviations smaller than 10 -30%.