Hydrodynamic current distribution

One of these is the "shape change" phenomenon, in which the location of the electrodeposit is not the same as that of the discharge (deplating) process. Thus, upon cycling, the electrode metal is preferentially transferred to new locations. For the most part, this is a problem of current distribution and hydrodynamics rather than being a materials issue, therefore it will not be discussed further here. 

P. K. Shukla and M. E. Orazem, "Hydrodynamics and Mass-Transfer-Limited Current Distribution for a Submerged Stationary Hemispherical Electrode under Jet Impingement," Electrochimica Acta, 49 (2004) 2901-2908. 

Subsequent work by Kruglikov and coworkers [217, 316] explored the action of levelers under well defined hydrodynamic conditions. The analogy between the diffusive flux distribution and the primary current distribution (i.e. Laplace equation) was used for calculating the leveling power. The expression for the attenuation of the amplitude of a sinusoidal profile was shown to be ... 

A characteristic of the primary distribution, in general, is that it is less uniform than the secondary distribution for a given electrode geometry and the electrochemical cell device. There is only one exception that arises from the concentric cylindrical electrode system depicted in Figure 13.2a, where both the primary and the secondary current distributions are uniform in the case of the forced convective hydrodynamics (rotating electrodes). 

On ship hulls protected by impressed current, flush-mounted anodes are used in order to avoid additional hydrodynamic resistance. Around the anode, the nearest steel surface is covered with a dielectric shield or coating with the aim of obtaining a better current distribution. 

Current distribution through the electrode which controls the current efficiency Is also dependent on the mass-transfer characteristics of the system and on the control of potential over the working electrode surface. Thus In bulk, porous or three-dimensional electrodes It Is usually mass-transfer characteristics which control most situations. The Nernst diffusion model (Fig. 1) gives a simplified picture of the electrode-solution Interface conditions. This simplified picture, however, does not account for real operating conditions since the stationary diffusion layer thickness Is strongly dependent on the solution flow characterIcs. Most modern hydrodynamic treatments take these factors Into account. 

Shukla PK, Orazem ME (2004) Hydrodynamics and mass-transfer-limited current distribution for a submerged stationary hemispherical electrode under jet impingement. Electrochim Acta 49 2901-2908... 

The hydrodynamics, electrode movement and complex current distribution of fluidized-bed electrodes must all be considered. In particular inactive zones must not appear as and will be reduced. 

Reaction engineering parameters. The achievement of a correct rate and selectivity of production requires control and uniformity of the potential and current distribution. In turn, very high rates will usually involve a uniformly high mass transport over the electrode, achieved by provision of the required hydrodynamics. The electroactive area per unit reactor volume may need to be high if the available current density is low and a compact design is required. Adequate heat transfer must be available between the reactor and its environment. 

The constancy of the diffusion layer over the entire surface and thus the uniform current-density distribution are important features of rotating-disk electrodes. Electrodes of this kind are called electrodes with uniformly accessible surface. It is seen from the quantitative solution of the hydrodynamic problem (Levich, 1944) that for RDE to a first approximation... 

Thus far, these models cannot really be used, because no theory is able to yield the reaction rate in terms of physically measurable quantities. Because of this, the reaction term currently accounts for all interactions and effects that are not explicitly known. These more recent theories should therefore be viewed as an attempt to give understand the phenomena rather than predict or simulate it. However, it is evident from these studies that more physical information is needed before these models can realistically simulate the complete range of complicated behavior exhibited by real deposition systems. For instance, not only the average value of the zeta-potential of the interacting surfaces will have to be measured but also the distribution of the zeta-potential around the mean value. Particles approaching the collector surface or already on it, also interact specifically or hydrodynamically with the particles flowing in their vicinity [100, 101], In this case a many-body problem arises, whose numerical... 

Aquatic animals use their chemical senses in all aspects of their lives, from reproductive behavior to feeding, habitat selection, and predator avoidance. The hydrodynamic properties determine the possibilities and limits of chemical communication in water. As a medium, water is as dynamic as air, so that convection and advection are far more important for odor transport than is diffusion. Distribution by currents is even more important in water because compounds of similar molecular weight diffuse four orders of magnitude more slowly than in air (Gleeson, 1978). Diffusion of odorants may be important only in the submillimeter range, while turbulence is typical for water masses above the centimeter range. 

Fig. 1. Influence of evaporation on hydrodynamics (upper half) and salt distribution in the strip (no current applied) (lower half). A flow of buffer originates in each buffer compartment (B1 and Bn) with a velocity Vx and V2. The resultant Vf has a velocity Vf = 0 in the center of the strip (C). There is a corresponding increase in the quantity of salt. Quantity of Na (Q) plotted against distance d increases above the original quantity (A) toward the center of the strip (C). The different curves 1, 2, and 3 give the results after 1, 2, and 3 hours evaporation (A8).

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