Nonuniform conditions

If most of the light is absorbed in passing through the reaction chamber, laha will vary through the cell, nonuniform conditions will prevail, and simple analysis of the over-all kinetics will be impossible. 

It should be recognized that the boundary conditions of the problem will establish the value of the hydrodynamic velocity, u. In the case of most turbulent flows the indirect influence of molecular diffusion on the hydro-dynamic velocity can be neglected. It should be emphasized that the hydrodynamic velocity is the time-average point velocity in Reynolds sense (R2). Under unsteady, nonuniform conditions of flow between parallel plates the material balance may be expressed for turbulent flow in the following form ... 

With galvanostatic instead of potentiostatic control, the potential would vary along a CER, which could compound the problem of selectivity variation caused by concentration changes. In both potentiostatic and galvanostatic operation, the nonuniform conditions may promote side reactions, including local electrode deactivation processes. 

Phase Separation under Nonuniform Conditions in Polymeric Systems 1101... 

The feed system is the name given to the flow melt passage in the mold, between the nozzle of the injection molding machine and the mold cavities. This apparently utilitarian feature has a considerable effect on both the quality and economy of the molding process. The feed system must conduct the plastics melt to the cavity at the right temperature, must not impose an excessive pressure drop or shear input, and should not result in nonuniform conditions at the cavities of multi-... 

The previous equation would result in a sharp drop of cell potential as the limiting current is approached (as shown in Pigure 3-6). However, because of nonuniform conditions over the porous electrode area, the limiting current is almost never experienced in practical fuel cells. In order to experience a sharp drop of cell potential when the limiting current density is... 

Micropore Diffusion. In very small pores in which the pore diameter is not much greater than the molecular diameter the diffusing molecule never escapes from the force field of the pore wall. Under these conditions steric effects and the effects of nonuniformity in the potential field become dominant and the Knudsen mechanism no longer appHes. Diffusion occurs by an activated process involving jumps from site to site, just as in surface diffusion, and the diffusivity becomes strongly dependent on both temperature and concentration. 

The nonuniformity of drop dispersions can often be important in extraction. This nonuniformity can lead to axial variation of holdup in a column even though the flow rates and other conditions are held constant. For example, there is a tendency for the smallest drops to remain in a column longer than the larger ones, and thereby to accumulate and lead to a locali2ed increase in holdup. This phenomenon has been studied in reciprocating-plate columns (74). In the process of drop breakup, extremely small secondary drops are often formed (64). These drops, which may be only a few micrometers in diameter, can become entrained in the continuous phase when leaving the contactor. Entrainment can occur weU below the flooding point. 

Indicators can determine if uniform steam penetration has been achieved during a Bowie Dick-type test. Produced in the form of sheets (23 X 30 cm), chemical indicators are capable of uniform color change over their entire surface when exposed to pure saturated steam under test conditions. Nonuniform color development is an indication of failure of the test. U.S. and international stands for the performance and accuracy of chemical indicators have been pubHshed (13,14). 

The distribution of current (local rate of reaction) on an electrode surface is important in many appHcations. When surface overpotentials can also be neglected, the resulting current distribution is called primary. Primary current distributions depend on geometry only and are often highly nonuniform. If electrode kinetics is also considered, Laplace s equation stiU appHes but is subject to different boundary conditions. The resulting current distribution is called a secondary current distribution. Here, for linear kinetics the current distribution is characterized by the Wagner number, Wa, a dimensionless ratio of kinetic to ohmic resistance. 

Nonuniform Feedstock should be blended before milling feedstock causes, feej t-ock before commencing milling opera- variation in oper- moisture content) ating conditions resulting in overheating. CCPS G-1 CCPS G-23 CCPS G-29... 

Heterogeneity, nonuniformity and anisotropy are defined as follows. On a macroscopic basis, they imply averaging over elemental volumes of radius e about a point in the media, where e is sufficiently large that Darcy s law can be applied for appropriate Reynolds numbers. In other words, volumes are large relative to that of a single pore. Further, e is the minimum radius that satisfies such a condition. If e is too large, certain nonidealities may be obscured by burying their effects far within the elemental volume. 

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