Bipolar systems

The application of external electrical fields can enhance filtration efficiency beyond a simple system. Bipolar electrostatic charge between the fabric and the particles can induce migration to the filter surface and particle agglomeration in the aerosol. 

The so called E-SPART system can determine number (mass) of particles in real time up to 100 s1. With this system, bipolar charge-to-mass ratios of 0 to 20 pC/g for 0.4 to 20 pm toner particles have been measured using a combination of acoustic excitation to determine aerodynamic particle diameter and electric field migration velocity to determine particle charge (Mazumder et. al., 1991). 

The technological development of electrolyzers started with a mono polar cell consisting of a cathode part and an anode part separated by a diaphragm, hi multi-cell systems, bipolar plates are used carrying the cathode material for one cell and on its backside the anode material for the neighbor cell. The functions of the bipolar plate are the continuous supply of the membrane electrode with H2 on one side and with O2 or air on the other side and the regulation of the water balance by providing moisture for the membrane on the H2 side and remove the product water on the O2 side. 

The diffusion model [5, 6] has been developed for mass transfer study within the system bipolar plate - gas diffusion layer (with micro-porous sublayer) - electrocatalytic layer . It was shown that the current density distribution is a complex function and depends mainly on the electrochemical parameters of the MEA (electrocatalytic layer activity) and... 

In a two-electrode system (bipolar or monopolar), the forward and reciprocal current densities are identical, so therefore ... 

A subsidiary of lEC and Toshiba Corp. called ONSI Corp. was formed for the commercial development, production, and marketing of packaged PAEC power plants of up to 1-MW capacities. ONSI is commercially manufacturing 200-kW PAEC systems for use in a PC25 power plant. The power plants are manufactured in a highly automated faciHty, using robotic techniques to assemble the repeating electrode, bipolar separator, etc, units into the fuel cell stack. 

The reaction mixture is filtered. The soHds containing K MnO are leached, filtered, and the filtrate composition adjusted for electrolysis. The soHds are gangue. The Cams Chemical Co. electrolyzes a solution containing 120—150 g/L KOH and 50—60 g/L K MnO. The cells are bipolar (68). The anode side is monel and the cathode mild steel. The cathode consists of small protmsions from the bipolar unit. The base of the cathode is coated with a corrosion-resistant plastic such that the ratio of active cathode area to anode area is about 1 to 140. Cells operate at 1.2—1.4 kA. Anode and cathode current densities are about 85—100 A/m and 13—15 kA/m, respectively. The small cathode areas and large anode areas are used to minimize the reduction of permanganate at the cathode (69). Potassium permanganate is continuously crystallized from cell Hquors. The caustic mother Hquors are evaporated and returned to the cell feed preparation system. 

Figure 15-2a shows the stray current interference by a bipolar high-voltage dc power line [7]. When the system breaks down, large voltage cones occur in the soil at the grounding installation. A few kilometers away, the current density in the soil is relatively low. 

The principal circuit diagram for a bipolar system is shown in Fig. 15-2a and the current distribution in the case of breakdown of a monopolar system in Fig. 15-2b. I and II are the respective ac systems. 

Fig. 15-2 Stray current interference from high-voltage dc transmission installations (a) bipolar system, (b) monopolar system.

The diodes widiiii the power supply typieally dissipate a large amount of power. These are the input reetifiers and the output reetifiers. In a bipolar eentered switehiiig power supply, the output reetifiers dissipate as mueh power as the bipolar power switehes, so their eontribution to the heat within the system is signiheant. The physieal situation is shown in Figure A-5. 

Ion chromatography (see Section 7.4). Conductivity cells can be coupled to ion chromatographic systems to provide a sensitive method for measuring ionic concentrations in the eluate. To achieve this end, special micro-conductivity cells have been developed of a flow-through pattern and placed in a thermostatted enclosure a typical cell may contain a volume of about 1.5 /iL and have a cell constant of approximately 15 cm-1. It is claimed15 that sensitivity is improved by use of a bipolar square-wave pulsed current which reduces polarisation and capacitance effects, and the changes in conductivity caused by the heating effect of the current (see Refs 16, 17). 

Small-format lead-acid batteries with immobilized electrolyte are still used in some applications such as hand lanterns. Low-cost six or twelve-volt batteries (e.g. 6 Ah size) are used in child-driven toy cars and other sizes in emergency-light or alarm systems, kept on trickle-charge. Efforts are being made to produce bipolar systems which give 30 percent improvements. 

Despite the fact that the zinc/ ferricyanide system employs an alkaline electrolyte, the electrode reactions are quite similar to those in zinc/halogen batteries and battery constructions are usually bipolar too. 

Figure 7. Current-potential curve of a bipolar membrane of hydrous ironflll) oxide in chloride solution. FeCl3(aq)/Fe(HI)(oxideyNaCl(aq)-Na2Mo04(aq).l The system is kept at room temperature. C, cation A, anion. (Reproduced bom M. Sakashita and N. Sato, Corrosion 35,351,1979, Fig. 4 with permission from NACE International.)...

A significant step for the commercialization of bipolar electrochemical promotion units has been made recently by Christensen, Larsen and coworkers at Dinex Filter Technology A/S in Denmark.18 20 The goal is the development of an efficient catalyst system for the aftertreatment of Diesel exhausts. This is one of the most challenging problems of current catalytic research. 

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