Ratio surface/volume

For the analysis of primary particles it is possible to calculate the spherical diameter for a particle from Rg described above as P = (5/3) Pg or 2.6 Rg. It is also possible to calculate diameter for a particle through the volume/surface ratio, which is called the Sauter mean... 

In a study of the porosity of alumina-pillared montmorillonites (Al-PILCs), Zhu et al. (1995) have obtained values of the mean slit-width of 0.8-0.9 nm from the volume/surface ratio. In this case, the nitrogen adsorption values were in agreement with the corresponding dm values of c. 0.8 nm. However, effective micropore volumes obtained from the nitrogen isotherms and from water sorption data were significantly different and it was suggested that the density of the sorbed water was lower than that of liquid water. 

As already indicated, by applying the Kelvin equation (assuming hemispherical meniscus formation) and correcting for the adsorbed layer thickness, we are able to calculate the ranges of apparent pore width recorded in Table 12.5. The values of mean pore diameter, w, are obtained from the volume/surface ratio, i.e. by applying the principle of hydraulic radius (see Chapter 7) and assuming the pores to be non-intersecting cylindrical capillaries and that the BET area is confined to the pore walls. 

The volume/surface ratio should be as high as possible to minimize wall effects at container surface... 

Representativeness of samples must be assured (Quevauviller 1995), and suitable sample containers must be used and carefully pre-deaned. The volume/surface ratio should be high in order to reduce adsorption or other effects of the container walls. If species oxidation is expected to occur, sampling should be performed in an inert gas atmosphere. Steel needles are not suitable for blood sampling (especially those with narrow ID) due to contaminating breakage of erythrocytes. Urine samples should be taken from a mid-stream urine flow. 

To conclude, geometric disorientation is the most preferrable form of the FIA channel, since it combines ease of production with excellent radial mixing, while offering a low flow resistance and smooth passage so that unwanted microbubbles or solid particles are not entrapped. Also the volume/surface ratio of these reactors is larger than in packed reactors, which is an important feature for most FIA applications, where interaction between the solutes and the channel surface is not desired. 

To conclude, packed reactors are the most effective means of promoting radial mass transfer in a flowing stream. They have, however, much lower volume/surface ratio than tubular and 3-D reactors, which is a disadvantage if interactions between solutes and surfaces are undesirable. The smaller the dp is, the larger N, surface area, and pressure drop will be. In general, short reactors (L up to 25 cm) are practical beyond that length, the use of packed reactors becomes progressively more difficult. 

For first-order reactions and moderate values of less than the value of i] for a slab with the same volume/surface ratio. As shown in Table 4.2, the maximum difference is about 14%. This small difference means that solutions for complex kinetic models that were obtained for the flat-slab case can be used to get approximate effectiveness factors for spherical catalysts. 

Figure 3.10(a) shows a typical structure of immiscible constituents on the fracture surface of a PP/PET blend [40]. Droplets of PET are embedded in a PP matrix. Since the surface energy of the interface is unfavourably high, the PET assumes the highest possible volume/surface ratio. The lack of PP residues on the surface of the PET particles indicates low adhesion between the two phases. As a consequence, although the individual constituents are ductile, their weak interface promotes debonding and low ductility. 

Heats of sublimation are usually difficult to measure for high-melting compounds because of their low vapor pressures. One can calculate heats of sublimation with rather good accuracy for aromatic hydrocarbons in general, but fullerene has a volume/surface ratio that is markedly different from that found with essentially all other aromatic hydrocarbons (except other fuUerenes), so that the refiabihty of this calculation is less certain here than usual. 

The crevice gap h (Fig. 2) controls the volume/surface ratio of the crevice the smaller this ratio, the faster the environment changes due to surfece reactions. However, the crevice gap must be wide enough for the environment to enter but it becomes inefficient if it is too wide. Figure 4 [1] shows the extent of crevice corrosion of unalloyed steel in nitric acid as a function of the gap. For stainless steels in chloride environments, short incubation times are obtained for crevice gaps of the order of a micrometer or less [2,3] and the incubation time increases rapidly with the crevice width. As a consequence, surface roughness is of major importance, and, for example, crevice corrosion can be avoided by polishing the surfaces in contact with seals to a smooth finish. 

The autoclaves, internally clad with tantalum, had a capacity of 1.5 L. The volume of test solution was 1.3 L, leading to a volume/surface sample ratio ranging from 5.9 to 7.2 mL/cm. Taking into consideration the autoclave surface as well, the ratio became 1.7 to 1.8mL/cm, which is similar to the volume/ surface ratio for 73 mm (2 7/8 inch) tubing. Special care was taken to avoid galvanic contact between the samples and the tantalum autoclave surface, by hanging the specimen in suitable glass devices. 

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