Concentric cylindrical cell

Surface wave formation and stationary vortex formation are particularly effective demonstrations of convection enhancement via magnetic fields. A theoretical prediction for aqueous electrolytes was corroborated by experimental evidence produced in a concentric cylindrical cell using copper electrodes and aqueous cupric sulfate electrolytes. Similar observations were reported by Gak and co-workers. Self-sustained oscillations induced by nonhomogeneous periodic and aperiodic magnetic fields have been demonstrated in photographs showing contiguous six- and seven-vortex cluster domains in the experimental apparatus. 

Fig.4.1. Dependence of the concentration of free CH3 radicals in a quartz cylindrical cell on the distance between the film sensor and the point where the radicals are produced, for different temperatures of the vessel walls 25 C (/), 140 C (2), 24rC O), 269 C (4), and 300 C (5).

One characteristic of shear banded flow is the presence of fluctuations in the flow field. Such fluctuations also occur in some glassy colloidal materials at colloid volume fractions close to the glass transition. One such system is the soft gel formed by crowded monodisperse multiarm (122) star 1,4-polybutadienes in decane. Using NMR velocimetry Holmes et al. [23] found evidence for fluctuations in the flow behavior across the gap of a wide gap concentric cylindrical Couette device, in association with a degree of apparent slip at the inner wall. The timescale of these fluctuations appeared to be rapid (with respect to the measurement time per shear rate in the flow curve), in the order of tens to hundreds of milliseconds. As a result, the velocity distributions, measured at different points across the cell, exhibited bimodal behavior, as apparent in Figure 2.8.13. These workers interpreted their data... 

Hence c(g/ml) is the concentration of colloidal suspension G90 is the reading on the LS photometer at 6 = 90°, 2 is the path length, which equals the cell diameter when using a cylindrical cell t is the turbidity obtained from measurements of optical density. Table 4 gives the results of calibrating a Sofica instrument with colloidal... 

Here distilled water instead of argon is pumped into the test cell at the crevice between the sample and the sample mounting. With a few exceptions, the Avesta cell is like the usual electrochemical cell for corrosion measurements (Figs. 14 and 15). The Avesta cell is made up of two concentric cylindrical glass pieces with a top and bottom made of polyvinylidene fluoride pieces. 

Rotating platinum screens have been used for electrogravimetric analyses. Commercial instruments employ two concentric cylindrical platinum screen electrodes with one or both electrodes rotating to increase convection. The cell itself is usually a beaker with a sample volume of about 150 mL. Typically, no cell top is used, and when running multiple analyses, there should be adequate ventilation to prevent accumulation of hydrogen. A simple operational amplifier circuit can be constructed for the instrument. The commercial instruments available are expensive given the simplicity of this type of experiment. 

Fig. 8 Osmotic coefficient as a function of counterion concentration cc for the poly(p-phenylene) systems described in the text. The solid line is the PB prediction of the cylindrical cell-model, the dashed curve is the prediction from the correlation corrected PB theory from Ref. [58]. The full dots are experiments with iodine counterions and the empty dots are results of MD simulations described in ref. [29,59]. The Manning limiting value of l/2 is also indicated...

As determined from HPLC, the purity of the peptide was greater than 90%. Steady-state fluorescence spectra of this peptide were collected from 310-480 nm with an excitation wavelength of 264 nm. A 1 cm pathlength cuvette was used with concentrations of 8.6 pM. The emission quantum yields were determined relative to N-acetyl-L-tryptophanamide at pH = 6.9 (f = 0.13) (17). Steady-state circular dichroism spectra were obtained using a 0.5 mm pathlength cylindrical cell and concentrations of 0.26 mM. The mean molar ellipticity [0] (deg cm dmol" ) was calibrated with (+)-10-camphorsulfonic acid. Concentrations of the solutions were determined by measuring the absorbance of 4-methylaminobenzoic acid. 

Before presenting numerical results, it is worth summarizing the main characteristics of the experimental results for the osmotic pressure of polyelectrolyte solutions [9, 17, 18, 57, 107], The measured osmotic coefficients most often exhibit strong negative deviations from ideality. The measured values are a) lower than it was predicted by the cylindrical cell model theory, b) rather (but not completely) insensitive to the nature of the counterions, and c) also insensitive to the polyelectrolyte concentration in a dilute regime and/or for... 

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). 

In order to determine experimentally the diffusion coefficient on the basis of Fick s first law, one has to study steady-state diffusion. To do this, one has to maintain constant concentrations, c, and c2, at both sides of a cylindrical cell with cross-sectional area S and length /, and to measure the flux, i.e. the amount of substance, Am/At, carried through such a cell per unit time. Since the concentration gradient in such an experiment is constant along the entire cell length, /, and is given by... 

Figure 16.20. (a) Copper concentration at cell outlet, and voltage versus time (b) current versus time and (c) flow rate versus time, for a pulsed experiment in fine sand. Cylindrical ceU is 11cm in diameter, and soil length is 20 cm (Reeve, 2007). 

The second example is the spatially and temporally resolved observation of the explosion of an O2/O3 mixture in a cylindrical cell, initiated by a TEA CO2 laser [1388]. The progress of the reaction is monitored through the decrease of the O3 concentration, which is detected by a time-resolved measurement of the UV absorption in the Hartley continuum of O3. If the UV probe beam is split into several spatially separated beams with separate detectors (Fig. 10.8), the spatial progression of the explosion front in time can be monitored. 

This chapter presents the simulation of a button cell data reported by Liu et al. [38]. The model parameters derived here are further used in the performance analysis presented in the later chapters. A schematic representation of button cell is given in Fig. 6.1. The configuration is basically a concentric cylindrical assembly intercepted by the membrane electrode assembly (MEA). The fuel and air inlet are through the inner cylindrical pipe, which reaches above the anode and cathode. The product gas outlet is through the concentric space between the inner and outer cylinder. 

Another complication that may interfere with estimating the ohmic drops is the cell geometry. The electrodes do not always extend from one side of the cell wall to the other, and they may have differing geometries and sizes. Under these conditions, Eq. (165) is not directly applicable. Thus, when two concentric cylindrical electrodes are used, the electric resistance in a narrow gap, dR, between the cylinders is ... 

Fig. 14 The osmotic coefficient calculated at different counterion concentrations using various models. The results for a finite rod calculated using the spherical cell model (empty circles), cylindrical cell with adjustable getnnetry (empty square, and bulk system (empty triangles) are found to be in very good agreemoit. The dotted line is a numerical fit to the bulk data drawn to guide the eye. The solid line is the prediction of the PB theory and the dashed line fits the results obtained from MMMID [135] simulations for an infinitely long rod (filled circles). Experimentally measured osmotic coefficient for iodide (open diamonds) and chloride (filled diamonds) counterions [131] are also showir Figure adapted liom [133]...

Optimization of the electrochemical cell s geometry is the primary factor that determines the uniformity of current distribution. The two major geometrical arrangements are parallel-plate electrodes and concentric cylinders. PaiaUel-plate geometry is common in large-scale production of base metals when the metal concentration in the electrolyte is high. Cylindrical cells are used in the treatment of less concentrated solutions, in the recovery of noble metals, and also in the production of base metals. The current distribution between two parallel electrodes is only uniform when a nonconducting containment of the same cross section surrounds the interelectrode space. 

F ure 12.49 Elecirocheniical cell consisting of two concentric cylindrical electrodes. 

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