Dispersion causes

A low dispersion is desirable in optical glasses used for lenses in cameras, telescopes, etc, because dispersion causes chromatic aberration, a condition which reduces the sharpness of an image. However, it is possible to correct for chromatic aberration by using a combination of glasses having different Abbu numbers (9). 

Dispersion caused by the resistance to mass transfer in the stationary phase is exactly analogous to that in the mobile phase. Solute molecules close to the surface will leave the stationary phase and enter the mobile phase before those that have diffused further into the stationary phase and have a longer distance to diffuse back to the surface. Thus, as those molecules that were close to the surface will be swept along in the moving phase, they will be dispersed from those molecules still diffusing to the surface. The dispersion resulting from the resistance to mass transfer in the stationary phase is depicted in Figure 8. 

It is seen that the normal union can cause significant dispersion and, by drilling out the union, the dispersion is greatly reduced. It must be assumed that the dispersion caused by the modern reduced volume union would fall somewhere between these two extremes. The same authors also measured the dispersion arising from stainless steel frits and their results are shown in Table 4. 

The main hurdle for the use of starch as a reinforcing phase is its hydrophillicity leading to incompatibility with polymer matrix and poor dispersion causing phase separation. Two strategies have been adopted to improve the performance of polysaccharides. 

Pharyngeal aspiration 30 d Higher SWNT dispersion causes higher toxic outcomes [76]... 

Cyanamide and its aromatic derivative, such as 4,4 -methylene bis(phenyl cyanamide), were reported to cure an epoxy resin at elevated temperatures.(4) It is also well known that the dimer of cyanamide (dicyandiamide) is the most important epoxy curing agent in one-package epoxy compounding.(5) Unfortunately, this dimer precipitates from the dispersion causing uneven mixing upon standing. 

As we found in Example 3.1, the dark current of this photocathode when operating at room temperature is I, T = 300 K) 2 x 10 a. The minimum current that can be measured is equal to the current dispersion caused by shot noise over the dark current, so that... 

Figure 24.7 Two extreme input scenarios for chemical being spilled into a river, (a) Constant input rate J (mass per unit time) during time At leading to a rectangular concentration profile, Cin = J IQ. The dashed line shows how dispersion acts on the edges and leaves the concentration in the middle of the cloud unchanged. (b) Gaussian input scenario. The time integral between t = -2G and t = 2c0 comprises 95% of the total input 3H (see Box 18.2). Dispersion causes the variance to increase according to Eq. 24-60. The maximum concentration is given by Eq. 24-62.

Figure 25.1 Heterogeneity is one of the main properties of porous media it not only characterizes the scales shown in the figure, but also occurs on larger scales up to the size of the whole porous system. Three important mechanisms of transport and mixing in porous media are (a) interpore dispersion caused by mixing of pore channels (b) intrapore dispersion caused by nonuniform velocity distribution and mixing in individual channels (c) dispersion and retardation of solute transport caused by molecular diffusion between open and dead-end pores as well as between the water and the...

Loss of volatile solvent from a dispersion, causing the dispersed phase concentration to increase. 

Figure 4.8 Electromigration dispersion caused by mismatched analyte and electrolyte mobilites.

This result was first derived by Aris (1956) using the method of moments. While the resulting model now includes both the effects (axial molecular diffusion and dispersion caused by transerverse velocity gradients and molecular diffusion) it has the same deficiency as the Taylor model, i.e. converting a hyperbolic model into a parabolic equation. 

For capillary numbers greater than the critical value, snap-off occurred even in homogenous bead packs (40). The resulting dispersions caused much greater resistance to flow than the resistance produced by leave-behind lamellae (which do not disperse the nonwetting phase). 

Even when the laboratory test reactor is intended to be representative in a reaction kinetic sense only (thus waiving the demand for correspondence in terms of pressure drop and hold-ups), the process performance data can be affected by differences in mass transfer and dispersion caused by scale reduction. When interphase mass transfer and chemical kinetics are both important for the overall conversions, the above test reactor, which is a relatively large pilot plant reactor, cannot be further reduced in size unless one accepts deviations in test results. 

Causes for deviations from ideal plug flow are molecular diffusion in the gas and dispersion caused by flow in the interstitial channels of the bed, and uneveness of flow over the cross section of the bed. 

To illustrate how dispersion affects the concentration profile in a tubular reactor we consider the injection of a perfect tracer pulse. Figure 14-3 shows how dispersion causes the pulse to broaden as it moves down the reactor and becomes less concentrated. 

Thus, dispersion of Me/C catalysts prepared by impregnation is in many respects dependent on the probability of side processes such as the metal compounds adsorption, even though their intensity is low that makes the proportion of the adsorbed species negligible among the supported precursors. In the general case, the detrimental effect on the metal dispersion caused by deficit of the sites for crystallization of the metal precursors can be compensated by means of repeated impregnation with low-concentrated salt solutions. An example is the preparation of Pt/C from Pt(NH3)2(N02)2 [185]. 

Accordingly, term A is independent of the flow velocity and characterizes the peak dispersion caused by the Eddy diffusion. This effect considers the different pathways for solute molecules in the column packing. The longitudinal diffusion is described by the term Blv. The term C v comprises the lateral diffusion and the resistance to mass-transfer between mobile and stationary phases. These effects depend linearly on the flow velocity. 

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