Aeration factor

The aeration factor P has been determined for bubble-cap and sieve plates, and a representative correlation of its values is shown in Fig. 14-32. Values of P in the figure may be calculated from... 

FIG. 14-32 Aeration factor for pressure drop calculation, sieve plates. [Bolles and Fair, Encyclopedia of Chemical Processing and Design, vols. 16, 86. J. M. McKetta (ed.), Marcel Dekker, New Yoik, J9S2.]... 

Figure 8-126. Aeration factor, sieve trays. Used by permission. Smith, B. D. Design of Equilibrium Stage Processes, Chapter 15, by J. R. Fair, McGraw-Hili Book Co. (1963), all rights reserved.

Va = vapor velocity based on active area, ft/sec P = aeration factor, dimensionless. Figure 8-126... 

Vh = vapor velocity through valve holes, ft/sec P = tray aeration factor, dimensionless AP = tray pressure drop, in. liquid pvm = valve metal density, tj = tray deck thickness, in. 

Aeration factor (usually = 1.0) or Friction factor for firoth cross flow. Equation 8-255 Friction factor for liquid gradient, cross-flow for sieve trays... 

Aeration factor, f, dimensionless k = Slope of equilibrium line/slope of operating line A = Liquid gradient (corrected) for tray or tray section, in. 

Unfortunately, we do not have clear liquid, either in the downcomer, on the tray itself, or overflowing the weir. We actually have a froth or foam called aerated liquid. While the effect of this aeration on the specific gravity of the liquid is largely unknown and is a function of many complex factors (surface tension, dirt, tray design, etc.), an aeration factor of 50 percent is often used for many hydrocarbon services. 

WH = weir height, in AF = aeration factor GPM = gallons (U.S.) per minute... 

The aeration factor AF is the relative density of the foam, to the density of the clear liquid. It is a combination of complex factors, but is typically 0.5. 

Before a total sieve tray pressure drop can be summed, the froth pressure in inches of clear liquid over the active area must be calculated. This froth height actually reduces the HHDS value by a factor called the aeration beta correction. This has been done by Smith, who plotted the aeration factor beta vs. FGA (see Eq. (3.120) for FGA). Equation (3.121) is a curve-fit of Smith s beta curve plot [16]. Generally a beta factor of 0.7 to 0.8 is calculated using Eq. (3.121). 

Downcomer backup flooding occurs when the backup of aerated liquid in the downcomer exceeds the available tray spacing. Downcomer backup can be calculated by adding the clear liquid height on the tray, the liquid backup caused by the tray pressure drop, and the liquid backup caused by the friction loss at the downcomer outlet. The downcomer backup is then divided by an aeration factor to give the aerated liquid backup. 

The downcomer aeration factor < tdc is defined by Eq. (6.18). It describes the fractional volumetric liquid holdup in the downcomer. 

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. 

Popular aeration factor prediction criteria are rules of thumb based on the foaming tendency of the system (Table 6.4). The three criteria listed are supplementary, with one criterion adding examples not listed by the others. The author recommends applying the criteria accordingly. For instance, an aeration factor of 0.4 is appropriate to either mineral oil absorbers or for systems whose vapor density exceeds 3 lb. ft3. The criterion of Fair et al. (18) is perhaps a little conservative compared to the others. 

The relationship in Eq. (6.47a) is more popular and will be adopted here. The tray aeration factor, p, is obtained from Fig. 6.22a for sieve trays (18,31) and Fig. 6.226 for valve trays (5,80). For sieve and valve... 

Figure 6.22 (Continued) Tray aeration factor prediction for pressure drop calculations. (t>) A modified version of the correlation in a, suitable for valve trays. (Part b from George F. Klein. Chemical Engineering, May 3, p. 81, 1982, reprinted courtesy of Chemical Engineering)...

Tray aeration factor in pressure drop equation, Eq. (6.47a). 

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