Concentration gradients decreasing

As i,d is proportional to f2/3 (drop volume is proportional to t, so its surface area is proportional to i2 3) and is also proportional to t 112 (because of the concentration gradient decreasing with x in addition to D expressed in cm2s so that D112 occurs in the equation), we obtain the relationship i,d = ktlie. 

Concentration of a diffusible substance at times h and t2. Note that the concentration gradient decreases over a period of time. 

The concentration gradient (8c/8x)z=0 at the surface depends on time because as uptake occurs, reevaporation back to the gas phase becomes increasingly important and the magnitude of the concentration gradient decreases. 

In contrast to steady-state conditions, the current decreases with time because the concentration gradient decreases ... 

It is well known that the process of diffusion is controlled by thickness of so-called diffusive layer which locates in the layer of a liquid around a bubble. With bubble compression, this layer grows and the concentration gradient decreases with bubble expansion, thickness of the layer decreases and the gradient increases, hence, a rate of gas flow into the bubble increases. 

Plug-flow reactors have a decreasing concentration gradient from inlet to outlet, which means that toxic compounds in the feed remain undiluted during their passage along the reactor, and this may inhibit or kill many of the microorganisms within the... 

O, a large current is detected, which decays steadily with time. The change in potential from will initiate the very rapid reduction of all the oxidized species at the electrode surface and consequently of all the electroactive species diffrising to the surface. It is effectively an instruction to the electrode to instantaneously change the concentration of O at its surface from the bulk value to zero. The chemical change will lead to concentration gradients, which will decrease with time, ultimately to zero, as the diffrision-layer thickness increases. At time t = 0, on the other hand, dc-Jdx) r. will tend to infinity. The linearity of a plot of i versus r... 

Back-diffusion is the transport of co-ions, and an equivalent number of counterions, under the influence of the concentration gradients developed between enriched and depleted compartments during ED. Such back-diffusion counteracts the electrical transport of ions and hence causes a decrease in process efficiency. Back-diffusion depends on the concentration difference across the membrane and the selectivity of the membrane the greater the concentration difference and the lower the selectivity, the greater the back-diffusion. Designers of ED apparatus, therefore, try to minimize concentration differences across membranes and utilize highly selective membranes. Back-diffusion between sodium chloride solutions of zero and one normal is generally [Pg.173]

Films of a pentaerythritol alkyd, a tung oil phenolic and an epoxypolyamide pigmented with iron oxide in the range 5-7% p.v.c. were exposed to solutions of potassium chloride in the range 0.0001-2.0 m. It was found that in all cases the resistance of the films steadily decreased as the concentration of the electrolyte increased. Since the resistances of the films were at no time independent of the concentration of the electrolyte, it was concluded that the Donnan equilibrium was not operative and that the resistance of the films were controlled by the penetration of electrolyte moving under a concentration gradient. 

In a cathodic process, removal of ions from solutions will result in a decrease in their concentration at the electrode/solution interface compared to that in the bulk solution, and this in turn will cause a concentration gradient and consequent diffusion. Furthermore, the potential gradient... 

When a polymer sheet of thickness L is immersed in the gas at a constant pressure, the surface concentration increases instantaneously, to a steady value which is then spread by diffusion throughout the whole bulk of the polymer sheet to finally give a uniform concentration. During the sorption the concentration gradients in the polymer decrease as the time progresses reducing the sorption... 

When the mass transfer resistance within the particle is significant, a concentration gradient of reactant is established within the particle, with the concentration, and hence the reaction rate, decreasing progressively with distance from the particle surface. The overall reaction rate is therefore less than that given by equation 10.195. 

As shown in Fig. 33, the decreasing mechanism of this fluctuation is summarized as follows At a place on the electrode surface where metal dissolution happens to occur, the surface concentration of the metal ions simultaneously increases. Then the dissolved part continues to grow. Consequently, as the concentration gradient of the diffusion layer takes a negative value, the electrochemical potential component contributed by the concentration gradient increases. Here it should be noted that the electrochemical potential is composed of two components one comes from the concentration gradient and the other from the surface concentration. Then from the reaction equilibrium at the electrode surface, the electrochemical potential must be kept constant, so that the surface concentration component acts to compensate for the increment of the concen-... 

This PDE is subject to the initial condition that a = / at t = 0 and boundary conditions that a = a at a = 0 and a = ai at x = oo. The solution is differentiated to calculate the flux as in Equation (11.35). Unlike that result, however, the flux into the surface varies with the exposure time t, being high at first but gradually declining as the concentration gradient at a = 0 decreases. For short exposure times,... 

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