Coalescence 1356 INDEX

Britten, M. and Giroux, H.J. 1991b. Coalescence index of protein stabilized emulsions. Journal of Food Science 56 792-795. 

As with gas—liquid systems, chemical engineering theorists have almost exclusively concerned themselves with the creation of surface area (drop formation), usually relating surface area creation to the expenditure of power raised to an index of around . These expressions are entirely empirical and of only guidance value in the absence of essential experimentation data. Drop coalescence remains a black art. 

Single Surfactant Systems. Relative intensity results for an equilibrium film of the block copolymer B1 in n-decane sandwiched between two water droplets at 25°C, are shown in Table II. The intensity was independent of the bulk polymer concentration within the accuracy of measurement. Assuming a constant film refractive index this implies that the film thickness is independent of surfactant concentration, and an average value of J was used for the calculation of film thickness. Coalescence occurs below a concentration of 0.1 g dm, presumably because there is insufficient... 

Most practitioners deflne the flow behavior of polymers based on the melt flow index however, this property is not entirely relevant to the rotational molding process because it is essentially a shear-free and pressure-free process. The use of zero-shear viscosity has been proposed as a better way to assess the coalescence behavior of resins. Resins with lower zero-shear viscosity coalesce at a faster rate and can thus be processed using a shorter molding cycle.The coalescence of individual powder particles is initiated as the particles stick and melt onto the mold surface or melt front. As the melt deposition process continues, pockets of air remain trapped between partially fused particles and lead to the formation of bubbles. In the rotational molding process, the coalescence of particles occurs at a temperature range close to the melting point of the material thus, from a processing standpoint, low values of zero-shear viscosity at low temperatures (i.e., close to the temperature at which the particles adhere to the mold surface) are preferable. 

Fig. 3. Stereo drawing of a-carbon atoms of L. easel DHFR enzyme with bound inhibitor (methotrexate right center of view) and cofactor (NADPH left center). Stereo viewers are recommended, but many people can see the 3-D image by placing an index card between the Images and staring, one eye on each Image, until the images coalesce. The bound substrate and cofactor have oxygen atoms shaded and nitrogen atoms blackened, respectively. Every fifth residue is numbered (from Ref. 75 with permission).

In this section we discuss index theory, a method that provides global information about the phase portrait. It enables us to answer such questions as Must a closed trajectory always encircle a fixed point If so, what types of fixed points are permitted What types of fixed points can coalesce in bifurcations The method also yields information about the trajectories near higher-order fixed points. Finally, we can sometimes use index arguments to rule out the possibility of closed orbits in certain parts of the phase plane. 

An essential role of the surfactant is to prevent the newly formed drops from coalescing again. Drops frequently encounter each other during the emulsification process. Recoalescence has been shown to occur in the following type of experiment. Two O-W emulsions are made that have identical properties, except that two oils are used that differ, e.g., in refractive index. These emulsions are then mixed and the mixture is rehomogenized. By comparing the refractive index of the droplets so obtained with that of the original ones, it follows that droplets of mixed oil composition have indeed been formed. 

The magnitude of the derivative is called the strain hardening index. A good correlation is observed between its value (between 0.5 and 2.5 in most doughs) and the strain at rupture. There is also a good correlation between the index and the gas holding capacity of the bread, since early coalescence of the cells leads to loss of gas to the atmosphere. 

In the 1970s, the EPA assumed a leading role in pollution control. With the realization that practically all solvents exhibited some level of photochemical activity, new rules—state and national—were focused on the total solvent content of paints as applied. The index used—VOC (volatile organic compound)—did not differentiate between solvents or coalescents but merely set limits in pounds of emissions per gallon of paint (excluding water) for varying industrial applications. 

Stretch void index (SVI). SVI provides an indication of the number voids in the part. It indicates how well the sintering and coalescence have eliminated small voids, which can be present because of the processing technique orthe properties ofthe resin. Voids directly affect the performance of a tube in the end-use. For example, a void free or low void content part will have a longer flex life and greater flex fatigue resistance than a part containing more voids. 

Fly Ash Particles. When coal particles burn in a combustion system, the ash present in coal coalesces into small micron- and submicron-sized particles and are carried throughout the system [240]. It has been shown that the shape of the fly ash particles in combustion chambers is primarily spherical. This suggests that, if the complex index of refraction of fly ash particles is known, the Lorenz-Mie theory can be used to determine the required radiative properties. 

If the aggregates of rod-shaped bacteria cells are assumed to coalesce into spheres, then the foregoing equations predict the variation of scattering eflBciency with the size-refractive index parameter p. Experimentally,... 

Although the coalescence assumption may lead to small errors in the scattering cross section, it does enable the rapid correlation of turbidity data (n) with electronic particle counter data (n and fi), provided the relative refractive index and size regime are known. Because the electronic particle counter measures the aggregate volume, and therefore determines only an equivalent spherical radius, the data from the electronic particle counter relate only to the coalesced-sphere approach. 

Smith et al. showed (albeit without correction for the gas phase flow pattern) that kio data from various scales (7=0.4 to 1.8 m), geometries (T/D = 2 to 3, ///7 = 1), and agitator types (6,12,18 flat-blade, 6-concave-blade, 6-perforated blade disc turbines) could all be correlated by an equation of the form of equation (15.16), so equation (15.16) may apply to other scales and configurations, though this has yet to be demonstrated experimentally. A more recent review , however, presents different values for the index Y for coalescing and non-coalescing systems. It should be borne in mind that this was based on earlier data without correction for the effect of gas flow pattern. 

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