Fenske tray efficiency

There are two common definitions of tray efficiency (rj). The Fenske tray efficiency is applied to the whole column... 

The combined Fenske-Underwood-Gillilland method developed by Frank [100] is shown in Figure 8-47. This relates product purity, actual reflux ratio, and relative volatility (average) for the column to the number of equilibrium stages required. Note that this does not consider tray efficiency, as discussed elsewhere. It is perhaps more convenient for designing new columns than reworking existing columns, and should be used only on at acent-key systems. 

Overall effect. A procedure for evaluating the overall effect (combining the direct and indirect effects on tray efficiency) was developed by Nelson, Olson, and Sandler (156). This method is based on the Fenske, Underwood, and Gilliland (Eduljee version) shortcut relationships (Secs. 3.2.1 to 3.2.5) and was shown to work well when comparing to a more rigorous procedure. An example (using an x-y diagram) in Sec. 7.3.6 demonstrates how differences between true and apparent volatility affect efficiencies calculated from test data. 

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