Dry packing

Pig. 22. Schematic representation of typical pressure drop as a function of superficial gas velocity, expressed in terms of G = /9q tiQ, in packed columns. O, Dry packing , low Hquid flow rate I, higher Hquid flow rate. The points do not correspond to actual experimental data, but represent examples. 

Fig. 22. Performance cut diameter predictions for typical dry packed bed particle collectors as a function of bed height or depth, packing diameter and packing porosity (void area) S. Bed irrigation increases collection efficiency or decreases cut diameter (271). SoHd lines, = 25 mm dashed lines,...

The term Fp is a dimensionless dry packing factor, specific for a given packing type and size. Values of Fp are given in Table 14-7. For operating pressures above atmospheric, and for certain packing sizes, Lj and Gj a.re calculated differently ... 

Name Material Nominal size Wall thickness, mm Bed weight, kg/m Area, mVm % voids Packing factor Fp, m Dry packing factor Fpd, m Vendor... 

These data are t aluable for determining the total weight of liquid held in the packing, and also the void fraction, in an operating column, e is the void fraction of the dry packing minus the total hold-up, hj. 

Void fraction of packing under operating conditions = void fraction of dry packing minus the total hold-up (not the free volume of dry-packing)... 

The procedure chosen for column packing depends chiefly on the mechanical strength of the packing and its particle size. Particles of diameter > 20 jum can usually be dry-packed, whereas for particles with diameters <20 /xm slurry... 

It is important to wet-pack the column with the eluting solvent. Dry packing results in strong retention of the sample and poor separation, possibly because the small amount of ether in the eluting... 

The packing material, used for the LEG work was Controlled-Pore Glass (CPG) from Electronucleonics, Fairfield, N.J. with various pore diameters similar to those used by others (6,2 ) (500-10,000 A). Each k.6 mm I.D. x 100 cm column was dry packed with the CPG of a specific pore size by tapping and vibration until a terminal, bed volume was reached. Stainless steel 20-ym frits were used on each end of the column along with the appropriate low-dead volume end-fittings. 

The columns used were dry packed using a packing apparatus (purchased from Mandle Scientific). The packing employed was CPG of pore sizes 1000, 2000 and 3000 X and 200-UoO mesh size. The colimins were calibrated using Dow and Polysciences monodispersed polystyrene latices. 

Dry column chromatography 494 Dry packing, columns (LC) 349 Dry test meter 843 Dual oven (GC) 62 Durapak phases (GC) 125 Dwell time, gradient elution, (LC) 489, 563... 

Supports are usually coated with the liquid phase using one r several evaporation methods. In outline, the liquid phase in a itable solvent is mixed with the support, the solvent is and the dried packing is then added to the , empty column... 

Rigid particles with diameters greater than 20 micrometers can be dry-packed efficiently with relatively simple apparatus using the tap-fill method [149]. The empty column. is held... 

A new generalised correlation for pressure drop in packed columns, similar to Figure 11.44, has been published by Leva (1992), (1995). The new correlations gives a better prediction for systems where the density of the irrigating fluid is appreciably greater than that of water. It can also be used to predict the pressure drop over dry packing. 

Analytical hplc these days is nearly always done with microparticulate column packings, which are small porous particles, usually spherical or irregular silica, with nominal diameters of 3,5 or 10 fxm. They combine the best features of the other two types, having high efficiency as well as a large surface area. In bulk, the appearance of a microparticulate silica resembles that of a fine talcum powder. With microparticulates, dry packing methods result in column beds that are unstable under pressure, so they are packed into columns using a slurry of the material in a suitable solvent and under considerable pressure. 

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