Packings effective surface area

Packing Nominal size, in. Approximate average weight per ft3 of tower volume, lb Approximate average total surface area of packing, ft /ft3 of tower volume Percent tree-gas space = t x 100 Packing factor, ap/e3, effective surface area/(void fraction)1, ft3 per ft3 of tower volume (dry-packed values for use with Fig. 16-20)... 

Note that all these data concern experiments in the absence of reaction and in conditions where it can be assumed that all surfaces of the packing are wetted (dissolution of solid particles). However, when a reaction is occurring, mass transfer may be constrained to a region close to the pore openings on the outer surface of the particles and hence the effective surface area for mass transfer could be considerably less than the external surface of the catalyst, leading to lower values k a. More studies are needed on porous catalysts at conditions where external transport is important. 

THE PACKED BED SURFACE AREA, ft 2/ft 3 BED EFFECTIVE PARTICLE DIAMETER, ft. ... 

In process engineering the ratio of the effective surface area of the packing to the given total surface area is called the degree of wetting... 

Numerous relations have been worked out for the determination of the degree of wetting of packing units but they differ very strongly [9]. Questions of the effective surface area of packings and practical possibilities of determining it independent of the kind of process have been thoroughly discussed by Kolev [9a]. He considered, above aU, the influence of viscosity. 

Before the method of Danckwerts for determination of the effective surface area of the packings, the gas-side controlled mass transfer coefficieDt was measured using sublimation of naphthalene from packings covered with this material. The quantity of the sublimated naphthalene can be determined measuring the weight of the elements before and after the experiments [80] and measuring the concentration of the naphthalene [26, 81] by a... 

The effective surface area a is the suffice area of the packing per 1 m of its volume, effective for the mass transfer processes. Because it is related wife fee wetted area of fee packing eh, both values are usually considered together. Their dimension is mVm or m ... 

Method for determination of the effective surface area from data obtained in a packed bed column ami a laboratory column with spheres... 

The above discussed methods allow determination of the effective surface area of the packings for irrigation with water or solution of similar properties. To study the effect of the liquid phase properties, the following mefood is proposed [83]. 

Similarly to the liquid holdup, the effective surface area has also its d effect In this case it is tl surface of the drops and jets over and under the packing. Calculating the value of Og using for example Eq. (69), we take into account also the end effect Practic l, at a given value of fee packing height Hi fee real end effect can be obtained 1 fee equation ... 

The increasing of the wettability of the packing material leads to an increase of the effective surface area. 

Parallel to the measurements of the effective surface area, the pressure drop of the packing is also investi ted by using a differential manometer, with accuracy 0.1 Pa. The column diameter was 470 mm. The height of the packing in all experiments was 2400 mm. A special liquid phase distributor was used... 

For the second two packings they are 206.3 and 177 m /m respectively. In the first case the effective surface area of RSR is about 8 % higher for dl liquid superficial velocities. In the second, at low liquid superficial velocities, it is about 11% higher, and at high values of Z up to 11% lower. Because the comparable packings have not exactly the same values of die specific surface it is difficult to tell which packing form is more proper to obtam higher effect sur ce. 

A comparison of all investigated metal packings with aU plastic ones shows, as expected, that at the same specific surftce and Iquid siqierficial velocity, the metal packing has gneater effective surface area and lovi r pressure drop. 

There are many investiptions and different equations for calculating the effective surface area of random packings given in the literature [87-95]. The first of them are proposed by Semmelbauer [93], They are as follows ... 

Accepting that the effective surface area is equal to the wetted aita of the packing, Onda et al. [129], using own data and data of other investigators, obtain the equations ... 

Fig. S9. Influence of superficial liquid velocity on the ratio of the effective surface area to tfae total sur ce area of the P27-60 packing at different values of the liquid phase viscosity.

It can be seen, that packing No 1 is practically completely wetted at liquid superficial velocity about 7.10 m /(m s). At this liquid velocity the ratio of effective to total surfece of packing No 2 is about 0.78. At =10 m /(m s) it is about 0.8 and is not increasmg with fiirtiier incrc ing of L The ct that the effective area of this packing cannot reach the specific area is explained [64] with the small packing hydraulic diameter at which the influence of the thickness of the liquid film on the hydraulic diameter, respectively on the effective surface area, is not to be eliminated. That is, at =10 mV(m s) this packing is also completely wetted. 

Some eiqperimental data [187,195,196] fc the effective surface area of the Holpack packings, given in Table 35, are repr imiled in Fig. 100. The data are obtained using the method of Danckwerts for absorption of CO2 in NaOH solution. For comparison some data for Intalox saddles and Pall rings are also presented. 

In Fig. 101 foe same data for foe effective surface area divided foe specific surface area of foe packing are presented. 

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