Wetted packing, fraction

Van Houten [33] has shown that the maximum packing fraction obtained from the rheology of concentrated alumina suspensions is predictive for the maximum wet packing fraction that can be obtained in colloidal ceramic processing. 

The checkers obtained roughly 30 g. of crude product in each run. Freshly opened Woelm silica gel (obtained from ICN Pharmaceuticals, 26201 Miles Ave., Cleveland, Ohio 44128) was deactivated as above, and 1800 g. was wet-packed with petroleum ether in a 65-mm. internal diameter column. In the first run the column was eluted as above, but a considerable amount of solvent was required to collect the product. Therefore, in the second run the crude product was applied to the column as a solution in petroleum ether, and 1-1. portions of 20% v/v ether petroleum ether, 30% ether, 40% ether, 50% ether, 60% ether, and 70% ether were run through. None of these six fractions contained a significant weight of material. Elution with 2 1. of 80% v/v ether petroleum ether then provided the bromohydrin acetate. 

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. 

The acid-free sample was quantitatively transferred to the cation-exchange resin (oa. 150 ml) wet-packed as described above. Unreactive materials were eluted under an argon atmosphere with pentane for oa, 48 hours at a rate of 6 to 10 drops per minute. The reactive materials were recovered by eluting the resin with benzene and then with an 8% 2-propylamine in methanol solution (V/V). The two eluents were combined to yield the total base fraction. 

O. Shell side of microporous hollow fiber module for solvent extraction Na, = V[dha-)/L]N%N°s M Nsh- D Nlt = K = overall mass-transfer coefficient (3 = 5.8 for hydrophobic membrane. (3 = 6.1 for hydrophilic membrane. [E] Use with logarithmic mean concentration difference. dh = hydraulic diameter 4 x cross-sectional area of flow wetted perimeter (p = packing fraction of shell side. L = module length. Based on area of contact according to inside or outside diameter of tubes depending on location of interface between aqueous and organic phases. Can also be applied to gas-liquid systems with liquid on shell side. [118]... 

SiLLCA Gel Chromatotraphy. The acid-, base-, and neutral-nitro-gen-free asphaltene (.126 g) was dissolved in n-pentane (10 mL) and placed on a silica gel column (30 g) that had been wet-packed with n-pentane. The column was eluted with n-pentane (500 mL) to remove the saturate hydrocarbons. Aromatic hydrocarbons were eluted from the column using 85% n-pentane-15% benzene (250 mL) and 60% benzene-40% methanol (250 mL). UV analyses of the saturate fraction indicated that trace amounts of aromatic hydrocarbons were present. The amount of saturates in the aromatic fraction, if any, is unknown. 

Estimate the effective fraction wetted packing area by Figure 9-46 or 9-43. As a general rule, try not to accept design if fraction wetted is le.ss than 0.5. If it is less, adjust tower conditions to raise value, bearing in mind that this factor is based on scattered and very incomplete data. 

Other phenomena may also be observed in concentrated dispersions. Thus, as the concentration increases, direct particle—particle contacts increase in importance, and as the limiting packing fraction is approached (j) = 0.625 for the random close-packing of spheres) the suspension ceases to flow and the viscosity becomes infinite. Shortly before this limit is reached the suspension (especially if the particles are monodisperse spheres) often exhibits dilatency. When the particles are nearly close-packed, flow can occur only by the particles rolling past one another (Figure 8.8), and this results in an increase in volume the shear thickening is accompanied by dilatence of the system. If the amount of liquid present is insufficient to fill the extra void volume produced, the surface may become dry. This is the familiar phenomenon observed when one steps on wet sand. 

X cross-sectional area of flow wetted perimeter cp = packing fraction of shell side. 

Hydrolyzed polyacrylamide, 26/74 mole % Wet-packed Sephacryl S 1000 superfine (Pharmacia Fine Chemicals) Column size 2.6 cm diameter 70 cm or 100 cm bed height Aqueous solution with 1 MNaCl Collected fractions and analyzed by FALLS. 39... 

Another important factor is wetting. With small diameter fibers and increased packing fractions, sufficient capillary pressure must be exerted to ensure satisfactory infiltration. The infiltration velocity is given by the Washburn equation ... 

Above a critical packing fraction ( >c, foams and emulsions "jam" into a solid phase that can sustain finite shear stresses under shear strain. We will model the macroscopic mechanical response of foams and emulsions above, but still near, this rigidity transition within the context of Durian s "bubble model" for wet foams [8]. 

Although aH these models provide a description of the rheological behavior of very dry foams, they do not adequately describe the behavior of foams that have more fluid in them. The shear modulus of wet foams must ultimately go to zero as the volume fraction of the bubbles decreases. The foam only attains a solid-like behavior when the bubbles are packed at a sufficiently large volume fraction that they begin to deform. In fact, it is the additional energy of the bubbles caused by their deformation that must lead to the development of a shear modulus. However, exactly how this modulus develops, and its dependence on the volume fraction of gas, is not fuHy understood. 

Column Chromatography. The substances to be purified are usually placed on the top of the column and the solvent is run down the column. Fractions are collected and checked for compounds using TLC (UV and/or other means of visualisation). The adsorbent for chromatography can be packed dry and solvents to be used for chromatography are used to equilibrate the adsorbent by flushing the column several times until equilibration is achieved. Alternatively, the column containing the adsorbent is packed wet (slurry method) and pressure is applied at the top of the column until the column is well packed (i.e. the adsorbent is settled). 

Figure 9-43. Fraction packing wetted. Used by permission of Shul-man, H. L., Uiiich, C. F., Prouix, A. Z., etnd Zimmerman, J. O., A.I.Ch.E. Jour., V. 1, No. 2 (1955) p. 253 ail rights reserved.

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. 

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