Flooding prediction, holdup

Flood prediction by the Billet and Schultes correlation. Billet and Schultes (79,80) modified the GFDC to take liquid holdup into account. The important parameter was left out of earlier versions of the correlation. Its inclusion improves the theoretical validity of the correlation at the expense of greater complexity. Billet and Schultes derived their flood-point correlation from their liquid holdup equation by postulating that at the flood point, a small increase in vapor or liq-... 

This model apphes in the region belowthe loading point, and it cannot predict the flood point because it does not include the effects of gas velocity on liquici holdup. The model of Stichlmair et al. [Gas... 

These relationships are not restricted to any type of contactor they can be used to predict either the flooding velocity at a given holdup. 

Pressure drop through gauze and sheet metal structured packings [115] applies for the region below the loading point and cannot predict the flood point because liquid holdup vs. gas velocity is not included. The latest version of the equation is in Reference 108 ... 

At low liquid rates, the onset of instability occurs at a constant value of the total superficial velocity, and is predictable from holdup and flooding data for wetted wall columns. As liquid flow rates increase, Nicklin and Davidson predict that unstable flow begins at lower values of the gas flow rate. For high liquid flow rates, however, the slug length becomes important, and the unstable flow will begin at higher values of gas flow rate. Therefore, a definite liquid flow rate exists at which an unstable flow pattern appears with a minimum gas flow rate. 

Downcomer aeration factor prediction. The fractional liquid holdup varies from about 0.3 in the froth zone to close to unity in the clear liquid zone (Fig. 6.12a). The height of each zone is a complex function of system properties, operating conditions, and downcomer geometry. This makes it practically impossible to theoretically predict the average downcomer aeration factor <(>. . Correlations in the literature (e.g., 46) are based on limited data obtained in atmospheric pressure simulator work with small downcomers. It is therefore difficult to recommend them for commercial-size applications. Zuiderweg (17) presented a plot of downcomer aeration factors derived theoretically from commercial-scale high-pressure flood data. However, the plot is based on a handful of data and is therefore difficult to recommend for general aeration factor prediction. 

Mackowiak (73a, 736) derived a new flood correlation. Like the Billet and Schultes correlation, it is based on the drop entrainment modal and takes liquid holdup into account. Unlike Billet and Schultes, Mackowiak uses a different set of premises and expressions. Ma6ko-wiak s correlation applies for both random and structured packings, has a good theoretical basis and was shown (73a, 786) to predict a large number of flood data to within 8 percent. On the debit side, the correlation is complex and requires the availability of four constants for each packing. Matkowiak also states (73a) that for high liquid rates, Mersmann s film model is more suitable than his drop model. 

Garwin and Smith (G13) undertook an extensive study of a spray column with benzene dispersed in water, and determined overall heat-transfer coefficients as a function of holdup and phase velocity. Drop size was found to be independent of the water flow rate, and predictable by means of Hayworth and Treybal s equation (H12). However, this may not be true near the flooding point, where relatively few runs were made. The volumetric heat-transfer coefficient increased moderately with increasing water flow rate (except at the high benzene flow rates, where the observed increase was very high) and with benzene flow ratio and holdup. Statistical treatment of their results (T2) yields... 

Billet and Schultes [314] developed a plqrsical model for prediction of liquid holdup in two-phase countercurrent columns. The model is valid firr random and structured packinp and requires an experimental constant depending on the packing tyj and dimensions. Fru calculation of the tot liquid holdup at the flooding point Htp, the same authors [316] offered the equation ... 

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