Particle size the effect

The mass transport influence is easy to diagnose experimentally. One measures the rate at various values of the Thiele modulus the modulus is easily changed by variation of R, the particle size. Cmshing and sieving the particles provide catalyst samples for the experiments. If the rate is independent of the particle size, the effectiveness factor is unity for all of them. If the rate is inversely proportional to particle size, the effectiveness factor is less than unity and

experimental points allow triangulation on the curve of Figure 10 and estimation of Tj and ( ). It is also possible to estimate the effective diffusion coefficient and thereby to estimate Tj and ( ) from a single measurement of the rate (48). 

The comprehensive research program included all facets necessary for the development of these catalysts. Laboratory tests were conducted to determine the necessary catalyst loading, the design operating conditions, the effect of particle size, the effect of various trace constituents on catalyst performance, and finally, resistance of the catalyst to thermal upsets. This paper presents only those findings which have direct sig-... 

The experimental data of Espiard et al. (21,22), based on the AOT/ toluene/water/ammonia system, showed an increase in particle size with increase in R. This observation led the authors to conclude that the droplet size of the microemulsion water pool was a key determinant of particle size. The effect of R on particle size was also investigated for silica nanoparticles synthesized in AOT/ decane/water/ammonia microemulsions (31). No particles were observed below about R = 4. However, as R increased from 5 to 9.5, the particle size also increased, in agreement with the observations of Espiard et al. (21,22). As noted previously (see Figure 2.2.3), in this microemulsion system, free water pools do not become... 

Powders vary dramatically in particle size on the basis of their origin. It is common for catalyst manufacturers to classify powders in order to assure users of consistency from batch to batch since suspension, settling rates, filtration, and performance in slurry-phase reactions are all dependent on particle size. The effect on suspension, settling rates, and filtration is obvious. However, factors that favor these are unfavorable for kinetics. For reactions controlled by transport rates from the bulk fluid to the surface of the catalyst, the overall reaction rate is a strong function of geometric surface area and thus is favored by small particles. Pore diffusion resistance is also minimized by smaller particles since reaction paths to active sites are smaller. The only mode of reaction control not influenced by particle size is for those reactions in which rate is controlled by reaction at active sites. Therefore, a compromise for optimum filtration and maximum reaction rates must be made. 

The details of this work revealed the exact effect of structure on the tinting strength of carbon black in addition to the effect of particle size (Fig. 13). Although the effect of structure is somewhat subtle, it is sufficient to cause a tint test between two blacks of the same particle size to appear quite different. So, in order to relate tint readings to absolute particle size the effect of DBP on the reflectance test result must be taken into account. 

Figure 10.6 shows the relative intensities from three opaque particles, in air, of sizes 10, 60 and 200 pm this illustrates how the scattered flux in the forward direction falls off rapidly with decreasing particle size. The effect is also illustrated in Figure 10.7a together with the resulting diffraction pattern fora monosize distribution (Figure 10.7b). 

In order to derive a simplified burning rate expression for AP particles, it is assumed that the area of fastest regression has an effective region of thickness, q, around each AP particle, independent of particle size. The effective region is also assumed to burn at the same rate as the AP particle in the DB matrix. This effective thickness is found experimentally to be... 

In liquid-solid fluidized beds, the bed-to-wall heat transfer coefficient increases with an increase in liquid flow rate due to the reduction in thermal boundary layer thickness. The heat transfer coefficient was also found to increase with the particle size. The effective thermal conductivity of liquid fluidized bed increases sharply with liquid velocity beyond minimum fluidization, passes through a maximum near a voidage of 0.7, and then gradually decreases. 

The rate of reaction induced by a solid catalyst is generally proportional to its surface area and the concentration of the so-called active centers or catalyst sites. The latter are locations of high chemical activity on the surface. Since the specific surface of particulate solids increases with decreasing particle size, the effectiveness of solid catalysts... 

These figures 5.14a to 5.14c show considerable changess in the dependence on impeller speed and pelletization time (X[, X,) as the percent binder solution is varied between Xj = 0.5. Second-order coefficients were found to be influential so the quadratic model was maintained and not simplified further. In particular, as can be seen in the isoresponse curves, the amount of liquid, and its interaction with the impeller speed had large effects on the particle size. The effect of the pelletization time was less significant. 

Particle Size. The effect of particle size of bituminous coke on the gasification rate was studied. Testing conditions were the same as for previous studies 1740°F., 3 atm. absolute pressure, 1 ft./sec. superficial gas velocity, 2% bituminous coal ash in a melt of 4-in. height and 4% carbon charged initially. The results of the tests on three particles sizes are given in Table IV. 

By changing the particle size, the effectiveness factor, liquid mass transfer coefficient, and wetting efficiency are affected. We choose such particle sizes to have complete wetting and tlius be able to use the simple model. For the specified space velocity, the particle size should be lower tlian about 2.5 mm. On the other hand, particles smaller than 0.5 should be avoided for preventing a high pressure drop appeai ance. Furthermore, the values of Z/t/p for 0.5 plug-flow conditions. 

The ignition point can also be reached by changing other parameters, such as reactant concentration, gas velocity, and particle size. The effect of... 

Reference [85] gives many details of the effect of reaction variables such as the temperature at which the AIBN is added the effects of different levels of AIBN, PVP, and styrene on particle size the effect of adding either toluene or water to the reaction medium the addition of water initially or after nucleation and the effect of the level of divinylbenzene and the method of its addition. 

The chemical nature of the oxide has a strong influence on the importance of Pt particle size. The effect is much clearer on silica than it is on y-alumina or on zirconia [16]. It is also very dependent on the chemical reaction considered. It is true for oxidation of NO into NO2, but much less so for its reduction, where the amount of reducing agent may have a stronger role than the initial dispersion and particle size of Pt [17]. 

Spherical particles have a beneficial effect on modulus. The addition of 40% by weight of untreated calcium carbonate to PP homopolymer film increases the flexural modulus by around 30 to 40%, depending on the grade of filler used and its particle size. The effect on the impact strength depends on the polymer used. 

Many factors affect the sulfur capture the most important are Ca/S ratio, recycle ratio, temperature, sorbent type and sorbent particle size. The effects of these parameters will be discussed later in the paper. 

The amount of polymer bonded in the interphase depends on the thickness of the interlayer and on the surface area, where the filler and the polymer are in contact with each other. The size of the interface is more or less proportional to the specific surface area of the filler, which, on the other hand, is inversely proportional to particle size. The effect of immobilized polymer chains depends on the extent of deformation, the modulus shows only a very weak dependence on the specific surface area of the filler (see Fig. 3). 

With medium or large particle size, the effect of structure is not important. 

The drug percolation threshold or including the drug content and the initial pores for these matrices, ranged between 30-36% (w/w). With respect to the excipient percolation threshold, p, differences were found between EC (critical point aroimd 30% w/w) and HCO matrices (6% w/w). The very low percolation threshold of the lipidic matrix-forming excipient was attributed to the different particle sizes of matrixforming excipient and active substance, being the HCO particle size much smaller than the caffeine particle size. The effect of the particle size of a substance in its percolation threshold will be discussed later. 

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