Separation effects

As ions and neutrals evaporate from a heated filament surface, the amount of sample decreases and the surface densities (C, Cq) must decrease. Therefore, Equation 7.1 covers two effects. The first was discussed above and concerns the changing value for the ratio n+/n° as the temperature of the filament is varied, and the other concerns the change in the total number of ions desorbing as the sample is used up. The two separate effects are shown in Figure 7.8a,b. Combining the two effects (Figure 7.8c) reveals that if the temperature is increased to maintain the flow of ions, which drops naturally as the sample is used up (time), then eventually the flow of ions and neutrals becomes zero whatever the temperature of the filament because the sample has disappeared from the filament surface. 

In pressure diffusion, a pressure gradient is estabUshed by gravity or in a centrifugal field. The lighter components tend to concentrate in the low pressure (center) portion of the fluid. Countercurrent flow and cascading extend the separation effect. 

Thus, the separative capacity of a stage is directiy proportional to the stage upflow as well as to the square of the separation effected. 

A second type of apparatus based on the pressure diffusion effect is the separation nozzle. Pressure gradients in a curved expanding jet produce an isotopic separation similar to that in a centrifuge. The separation effect obtained with a single jet is relatively small, and separation nozzle stages, similar to gaseous diffusion stages, must be used in a cascade to realize most of the desired separations. 

In azole chemistry the total effect of the several heteroatoms in one ring approximates the superposition of their separate effects. It is found that pyrazole, imidazole and isoxazole undergo nitration and sulfonation about as readily as nitrobenzene thiazole and isothiazole react less readily ica. equal to m-dinitrobenzene), and oxadiazoles, thiadiazoles, triazoles, etc. with great difficulty. In each case, halogenation is easier than the corresponding nitration or sulfonation. Strong electron-donor substituents help the reaction. 

The pressure drop through the filter is a function of two separate effects. The clean filter has some initial pressure drop. This is a function of filter material, depth of the filter, the superficial gas velocity, which is the gas velocity perpendicular to the filter face, and the viscosity of the gas. Added to the clean filter resistance is the resistance that occurs when the adhering particles form a cake on the filter surface. This cake increases in thickness as approximately a linear function of time, and the pressure difference necessary to cause the same gas flow also becomes a linear function with time. Usually, the pressure available at the filter is limited so that as the cake builds up the flow decreases. Filter cleaning can be based, therefore, on (1) increased pressure drop across the filter, (2) decreased volume of gas flow, or (3) time elapsed since the last cleaning. 

Filtration Basic. .. separation layer. The longer the filtration takes, the higher the separation effect, since after the initial phase the actual cake filtration will start. The. .. http //www.filterpressen.de/html e/filtration/basic.htm [More Results From www.filterpressen.de]... 

The liquid bulk flow limits the upward flow of small particles from the internal side and has a significant influence on the separating effect. Hydroclones are applied successfully for classification, clarification and thickening of suspensions containing particles from 5 to 150 tm in size. 

Isokinetic Sampling I he sample gas partial volume flow must be extracted isokinetically to avoid aerodynamic separation effects and to ensure correct particle size distribution. Isokinetics means that the velocity and direction of the sample gas partial flow at the sample nozzle are the same as at the main gas stream. ... 

The separating effect, G, or power of centrifuge is the ratio of acceleration obtained in the machine terrestrial gravity, as illustrated in Figure 4.18. Noting that... 

The principle of the solid bowl centrifuge is illustrated in Figure 4.19. It is essentially a device for enhancing the rate of sedimentation. The application of high G, however, creates stress in the machine and is equivalent to the application of pressure (cf. pressure filtration). There is therefore a balance to be struck between separating effect and stress. 

Thus for the same separation effect in plant and laboratory G = Go Therefore... 

Nevertheless, the interpretation of the calibration curve in the form of a selectivity curve is an excellent tool for the comparison of the separation effectivity for columns of different origin. 

In SEC, universal calibration is often utilized to characterize a molecular weight distribution. For a universal calibration curve, one must determine the product of log(intrinsic viscosity molecular weight), or log([7j] M). The universal calibration method originally described by Benoit et al. (9) employs the hydro-dynamic radius or volume, the product of [tj] M as the separation parameter. The calibration curves for a variety of polymers will converge toward a single curve when plotted as log([7j] M) versus elution volume (VJ, rather than plotted the conventional way as log(M) versus V, (5). Universal calibration behavior is highly dependent on the absence of any secondary separation effects. Most failures of universal calibration are normally due to the absence of a pure size exclusion mechanism. 

It is claimed that a measures electrophilic assistance by the solvent, b measures nucleophilic assistance, and that at least three, and sometimes four, parameters are required to perform a dissection into these separate effects. These workers also decomposed Y into ir and a contributions, and N into tt and p contributions. Abraham et al. have compared the performance of Eqs. (8-79) and (8-80) and find that they are about equally successful in correlating data. 

For systems with one sidestream drawoff, either above or below the feed, Tsuo et al. [102] propose a method for recognizing that the minimum reflux ratio is greater for a column with sidestream drawoff. At the sidestream the operating line has an inflection. For multifeed distillation systems, the minimum reflux is determined by factoring together the separate effect of each feed [103]. 

Figure 12-137 illustrates the separate effect of a partially closed outlet damper or vane on a pressure-volume curve. 

Laboratory tests, although often necessarily conducted under conditions that are not met in service, nevertheless have a number of advantages over the other types of tests. Because conditions can be controlled at will it is possible to identify the separate effects of a number of factors on the corrosion behaviour. These factors include the type and condition of the metal surface, the environmental composition, temperature and pressure, movement of the specimen relative to the environment, time of exposure and so on. Laboratory tests, at least in principle, also enable comparisons to be made under identical conditions of the relative corrosion behaviour of... 

For less polar monomers, the most extensively studied homopolymerizations are vinyl esters (e.g. VAc), acrylate and methacrylate esters and S. Most of these studies have focused wholly on the polymerization kinetics and only a few have examined the mierostructures of the polymers formed. Most of the early rate data in this area should be treated with caution because of the difficulties associated in separating effects of solvent on p, k and initiation rate and efficiency. 

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