Packings effective area calculation

Kiel et al. [36] used one-dimensional two-phase model to calculate gas-solids mass transfer coefficients. Basic assumptions for the model were (i) gas-solid mass transfer is the only resistance for adsorption and (ii) the effective area for mass transfer is equal to the external siuface area of the spheres. Radial effects were neglected due to the good radial distribution properties of the regularly stacked packing. Axial dispersion in the gas phase was also estimated from the experimental results presented by Roes and van Swaaij [29,30]. 

Principles of Rigorous Absorber Design Danckwerts and Alper [Trans. Tn.st. Chem. Eng., 53, 34 (1975)] have shown that when adequate data are available for the Idnetic-reaciion-rate coefficients, the mass-transfer coefficients fcc and /c , the effective interfacial area per unit volume a, the physical solubility or Henry s-law constants, and the effective diffusivities of the various reactants, then the design of a packed tower can be calculated from first principles with considerable precision. 

This has been shown to correlate for a wide variety of tower packings, various operating conditions, and physical properties of the solute and inert gases. The k(j calculated must be used in conjunction with the effective interfacial areas determined by Shulman [65] Figure 9-47, to establish a reliable value for kGa. Figure 9-47 should be used with the abscissa as G/Vp/0.075 for inert gas other than air [67] ... 

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. 

Very few direct measurements of the reaction of surface silanol groups on quartz have been reported. This is apparently caused by the small effects due to the limited surface areas available. Adsorption of sodium ions on quartz was measured by radioactive tracer techniques by Gaudin et al. (293). Saturation was achieved at high pH (>10) and sodium ion concentrations above 0.07 Jlf. The calculated packing density of silanol groups was 4.25/100 A. Goates and Anderson (294) titrated quartz with aqueous sodium hydroxide and alcoholic sodium ethylate. The occurrence of two types of acidic groups was reported. 

In adiabatically operated industrial hydrogenation reactors temperature hot spots have been observed under steady-state conditions. They are attributed to the formation of areas with different fluid residence time due to obstructions in the packed bed. It is shown that in addition to these steady-state effects dynamic instabilities may arise which lead to the temporary formation of excess temperatures well above the steady-state limit if a sudden local reduction of the flow rate occurs. An example of such a runaway in an industrial hydrogenation reactor is presented together with model calculations which reveal details of the onset and course of the reaction runaway. 

In most types of separation equipment such as packed or spray towers, the interfacial area that is effective for mass transfer cannot be accurately determined. For this reason it is customary to report experimentally observed rates of transfer in terms of transfer coefficients based on a unit volume of the apparatus rather than on a unit of interfacial area. Such volumetric coefficients are designated as Kca, kLa, etc., where a represents the interfacial area per unit volume of the apparatus. Experimentally observed variations in the values of these volumetric coefficients with variations in flow rates, type of packing, etc., may be due as much to changes in the effective value of a as to changes in k. Calculation of the overall coefficients from the individual volumetric coefficients is made by means of the equations... 

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