Packings underwetting

The above rules of thumb apply to organic and hydrocarbon systems, whose surface tensions are relatively low (a < 25 mN/m). For higher surface tensions, the liquid does not adhere well to the packing surfaces (underwetting), causing higher HETPs. In a water-rich system (a = 70 mN/m or so) HETPs obtained from Eqs. (14-156), (14-158), and (14-159) need to be doubled. For intermediate surface tension systems (some amines and glycols, whose surface tension at column conditions is 40 to 50 mN/m), HETPs obtained from Eqs. (14-156), (14-158), and (14-159) need to be multiplied by 1.5. 

Underwetting may be alleviated by changing the material and surface roughness of the packing. 

Underwetting is a packing surface phenomenon, which breaks up liquid film. The tendency of the liquid film to break (the degree of wet-... 

Some tests by Koshy and Rukovena (110,111) with aqueous, high-relative-volatility systems (a >2) gave much lower random packing efficiencies at high and low L/V than close to total reflux. They interpreted the results as an LfV ratio effect however, underwetting (below) can also explain these data. 

Underwetting (Sec. 8.2.16). With aqueous-organic systems, HETP tends to increase at the aquedus end of the column, both with random and structured packings. 

Summary. In the preloading regime, packing size, type, and distribution affect HETP. With aqueous-organic systems, HETP may be sensitive to underwetting and composition. HETP of structured packings may also be affected by pressure (at high pressure), and vapor and liquid loads. 

Ponchon-Savarit diagram. 26 Ponter underwetting theory, 516, 517 Porter rivulet model. 542 Porter and Jenkins packing HETP, 532-534 regime transition. 332 Poynting factor. 7 Prado and Fair tray efficiancy, 375 PRO/II. 169, 170,180... 

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