FIG. 14-29 Effect of liquid rate and fractional hole area on flood capacity. FRI sieve tray test data, cyclohexane/n-heptane, 165 kPa (24 psia), DT = 1.2 m (4 ft), S = 610 mm (24 in), hw = 51 mm (2 in), dH = 12.7 mm (0.5 in), straight downcomers, Ad/At = 0.13. (From T. Yanaggi and M. Sakata, Ind. Eng. Chem. Proc. Des. Dev. 21, 712; copyright © 1982, American Chemical Society, reprinted by permission.)
York, 1992). Figure 14-29 demonstrates the effect of liquid rate and fractional hole area on CSB. As liquid load increases, CSB first increases, then peaks, and finally declines. Some interpret the peak as the transition from the froth to spray regime [Porter and Jenkins, I. Chem. E. Symp. Ser. 56, Summary Paper, London (1979)]. CSB increases slightly with fractional hole area at lower liquid rates, but there is little effect of fractional hole area on CSB at high liquid rates. CSB,slightly increases as hole diameter is reduced.
For sieve trays, the entrainment flood point can be predicted by using the method by Kister and Haas [Chem. Eng. Progr., 86(9), 63 (1990)]. The method is said to reproduce a large database of measured flood points to within ± 15 percent. CSBflood is based on the net area. The equation is
CSB,flood = 0.0277(dhc/p1)0125(pG/pi)01(TS/hct)05 (14-81)
where dh = hole diameter, mm
C = surface tension, mN/m (dyn/cm) pG, Pl = vapor and liquid densities, kg/m3 TS = tray spacing, mm hct = clear liquid height at the froth-to-spray transition, mm;
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