Packing wetted area

Other correlations based partially on theoretical considerations but made to fit existing data also exist (71—75). A number of researchers have also attempted to separate from a by measuring the latter, sometimes in terms of the wetted area (76—78). Finally, a number of correlations for the mass transfer coefficient itself exist. These ate based on a mote fundamental theory of mass transfer in packed columns (79—82). Although certain predictions were verified by experimental evidence, these models often cannot serve as design basis because the equations contain the interfacial area as an independent variable. 

Effective area should not be confused with wetted area. While film flow of liquid across the packing surface is a contributor, effective area includes also contribiidons from rivulets, drippings, and gas bubbles. Because of this complex physical picture, effecdve interfacial area is difficnlt to measure directly. 

It is only recently that a coordinated group of data became available for wetted areas in Raschig ring and Berl saddle packing [65]. 

The fraction wetted area immediately indicates the effectiveness of contact for the liquid system in the packing. This packing area contact efficiency must be considered in some design problems. 

Onda et al. (1968) published useful correlations for the film mass-transfer coefficients kG and ki and the effective wetted area of the packing aw, which can be used to calculate Hg and HL. 

Relative Kga valid for all systems controlled by mass transfer coefficient (Kg) and wetted area (a) per unit volume of column. Some variation should be expected when liquid reaction rate is controlling (not liquid diffusion rate). In these cases liquid hold-up becomes more important. In general a packing having high liquid hold-up which is clearly greater than that in the falling film has poor capacity. 

Wetted surface area—the number of square feet of packing surface area available for vapor-liquid contacting, per cubic foot of tower volume. 

I. Iliuta, F. Larachi, Mechanistic model for structured-packing containing columns Irrigated pressure drop, liquid holdup and packing fractional wetted area, Ind. Eng. Chem. Res. 40 (2000) 5140-5146. 

Surface features. The surfaces of a few structured packings are smooth (e.g., Fig. 8.10a,g). Most structured packings have a roughened or enhanced surface that assists the lateral spread of liquid, promotes film turbulence, and enhances the area available for mass transfer. Laboratory measurements of absorption rates showed that both mass transfer efficiency and wetted area are enhanced by texturing metal surfaces (28). The extent to which mass transfer was improved varied with the type of texturing used. Texturing employed by... 

The flow channel geometry is illustrated in Fig. 8.9, and dimensions S, B, and h (whenever available) are listed in Table 8.1. The effective area of the packing, ae, is the packing surface area that is wet, i.e.,... 

E] Gas absorption and desorption from water and organics plus vaporization of pure liquids for Raschig rings, saddles, spheres, and rods, dp = nominal packing size, ap = dry packing surface area/volume, aw = wetted packing surface area/volume. Equations are dimensionally consistent, so any set of consistent units can be used. G = surface tension, dynes/cm. 

ACft ratio of wetted area to the actual surface area of packing... 

Shulman et al.48 measured wetted area for 1.27-cm and 3.81-cm Raschig rings and 1.27-cm and 2.54-cm Berl saddles packed in a column operating under countercurrent-flow (air-water) conditions. The results were well correlated by the following relations ... 

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