## Empirical prediction methods

Several empirical tray efficiency correlations are available in the literature. Of these, the O'Connell correlation has been the standard of the industry for several decades.

The O'Connell correlation (149, Fig. 7.5a). This correlation is based on test data from 31 plant columns, including hydrocarbon, chlorinated hydrocarbon, and alcohol separation columns. It evolved from an earlier correlation by Drickamer and Bradford (160), which empirically correlated efficiency test data for 54 refinery columns. The earlier correlation was modified by O'Connell to include nonhydrocarbon and h igh -relative-volatility system s.

Lockett (12) and King (126) noted some theoretical sense in O'Connell's correlation. Higher viscosity usually implies lower dif-fusivity, and therefore, greater liquid phase resistance and lower efficiency (12). Higher relative volatility increases the significance of the liquid phase resistance [Eq. (7.13)], thus reducing efficiency (126). Lockett expressed the O'Connell plot in equation form

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