Packings wetted surface area

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

Structured packing has about 50 percent more open area than Raschig rings and two or three times their wetted surface area. Hence, structured packing has largely replaced packing in the form of rings, in many packed towers. 

Since liquid does not completely wet the packing and since film thickness varies with radial position, classical film-flow theory does not explain liquid flow behavior, nor does it predict liquid holdup (30). Electrical resistance measurements have been used for liquid holdup, assuming liquid flows as rivulets in the radial direction with little or no axial and transverse movement. These data can then be empirically fit to film-flow, pore-flow, or droplet-flow models (14,19). The real flow behavior is likely a complex combination of these different flow models, that is, a function of the packing used, the operating parameters, and fluid properties. Incorporating calculations for wetted surface area with the film-flow model allows prediction of liquid holdup within 20% of experimental values (18). 

Wetted surface area of the packing per unit volume, ft /ft3, given by Eq, (9,16)... 

C. Absorption and and distillation, counter-current, gas and liquid individual coefficients and wetted surface area, Onda et al. correlation for random packings... 

Mears,53 Paraskos et al.,66 Montagna and Shah,38 and Montagna et al.59 have recently shown that ineffective catalyst wetting can cause the reactor performance to be dependent on the liquid velocity. The y used a correlation of Puranik and Vogelpohl69 for the effectively wetted surface area of the packing to explain the effects ofliquid hourly space velocity and the length of the catalyst bed on the performance of bench-scale HDS reactors. 

Fig. 14. Wetted surface area of packing as a function of superficial liquid velocity (L20) (I) plastic (2) ceramic (3) plastic coated with a hydrophilic layer (corresponding to solid symbols).

The function of the packing material in an air stripper is to provide a large wetted surface area for mass transfer of contaminants to the gas phase, or ambient air. Several shapes and sizes are available, such as rings, saddles, and spheres. The packing material is commonly manufactured from polypropylene, PVC, or ceramic. 

Onda, K., H. Takenuchi and Y. Kogama. Effect of Packing Materials on the Wetted Surface Area. Kagaku Kogaku 31 (1967) 126. 

Wetted surface area In a packed bed, the area of the packing exposed to the internal reflux. A measure of the packing s vapor-liquid contacting efficiency. 

Not all fee wetted surface area is effective for the mass transfer processes. It is well known that a part of fee wetted area is not movable first of all because of capillary forces at fee places of touching of nei bour packing elements. After saturation fee immovable area does not take part any more in fee mass transfer process and should not be taken into account in calculation of fee apparatuses. 

Onda et d. [141] calculate the liquid-side mass transfer coefficient fixnn its volumetric value and the wetted surface area of the packing, determined by their own equation (93). 

It must be mention here dial theoretically from the channel model, first present by Zhavoronkov et al. [33], follows that the pow in equation (225) is 3 inst of 5. The difference between the two powers is connected with the fret that according to the theoretical model, the film thickness in the packing is constaid over the whole wetted surface area. 

Packed Towers (also known as wet-scrubbers) A packed tower is a vessel that is filled with some suitable packing material. The liquid is introduced at the top of the tower and flows down through the packing to the bottom, and in so doing, exposes a large surface area to contact with the gas. The gas may be introduced at either end of the tower since the gas and liquid flows may be either co-current or counter-current. The counter-current operation is most commonly used. 

Lobo et al. [47] proposed the packing factor, F, and experimentally determined that it better represented the data than the calculated a/e term. Values calculated using surface area per cubic foot and percent free gas space from manufacturer s tables can be as much as 40% off. The ralues are dependent upon the method of packing the tower, i.e., dry dumped, wet dumped, or wet dumped and shaken. The latter condition may approximate the situation after a tower has been running a while and the packing settled. 

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