Ribs, separators

Reactant supply and water removal is optimized by so called interdigitated flow fields where gas flow is forced across the ribs separating the flow field channels through the macroporous part of the gas diffusion electrodes at the expense of high pressure drop between reactant inlet and outlet. 

The isothermal boundary in this case was made by soldering a thick copper cross to the wall of the silver block and to the tops of the ribs separating the sample and reference platforms. In this way, an isothermal boundary separated each of the platforms into identical compartments which were in poor thermal communication with each other. 

The choice for severe applications below 250 hp is the totally enclosed fan-cooled (TEFC) motor (see Figure 7-1). TEFC motors separate the internal and external ventilating air. Breathing is the only way external air ever gets inside. At some size above 250 HP, manufacturers presently switch from a rib-cooled to an exchanger-cooled motor for totally... 

Plate valves are typically used for high speed separable compressors. Plate valves are similar to ring valves with the rings connected by ribs. Instead of individual elements opening and closing, all valve ports o[)en and close at the same time. 

Figure 14. Polyethylene separator cross-ribs in the margin area...

Figure 16. Polyethylene separator intermediate vertical ribs...

The development of the starter battery in Japan has taken an independent course (see Sec. 9.2.1.2), visibly expressed by the separator s thick glass mat and its lack of spacing ribs (cf. Fig. 19). The cellulosic backweb impregnated with phenolic resin, generally in use until around 1980 and largely identical to the separator of the same type already mentioned has been completely replaced by thin ( 0.3 mm) fleece materials made of organic fibers. 

Flexible polyethylene separators have facilitated a novel cell construction the separator material, supplied in roll form, is wound so that it meanders around electrodes of alternating polarity (Fig. 23), requiring ribs in the cross-machine direction such profiles are available commercially [60],... 

A mixture of powdered poly(vinyl chloride), cyclohexanone as solvent, silica, and water is extruded and rolled in a calender into a profiled separator material. The solvent is extracted by hot water, which is evaporated in an oven, and a semiflexible, microporous sheet of very high porosity ( 70 percent) is formed [19]. Further developments up to the 75 percent porosity have been reported [85,86], but these materials suffer increasingly from brittleness. The high porosity results in excellent values for acid displacement and electrical resistance. For profiles, the usual vertical or diagonal ribs on the positive side, and as an option low ribs on the negative side, are available [86],... 

The prime requirements for the separators in alkaline storage batteries are on the one hand to maintain durably the distance between the electrodes, and on the other to permit the ionic current flow in as unhindered a manner as possible. Since the electrolyte participates only indirectly in the electrochemical reactions, and serves mainly as ion-transport medium, no excess of electrolyte is required, i.e., the electrodes can be spaced closely together in order not to suffer unnecessary power loss through additional electrolyte resistance. The separator is generally flat, without ribs. It has to be sufficiently absorbent and it also has to retain the electrolyte by capillary forces. The porosity should be at a maximum to keep the electrical resistance low (see Sec. 9.1.2.3) the pore size is governed by the risk of electronic shorts. For systems where the electrode substance... 

The filtrate runs down the ribbed surface of the plates and is then discharged through a cock into an open launder so that the filtrate from each plate may be inspected and any plate can be isolated if it is not giving a clear filtrate. In some cases the filtrate is removed through a closed channel although it is not then possible to observe the discharge from each plate separately. 

Other important parts of the cell are 1) the structure for distributing the reactant gases across the electrode surface and which serves as mechanical support, shown as ribs in Figure 1-4, 2) electrolyte reservoirs for liquid electrolyte cells to replenish electrolyte lost over life, and 3) current collectors (not shown) that provide a path for the current between the electrodes and the separator of flat plate cells. Other arrangements of gas flow and current flow are used in fuel cell stack designs, and are mentioned in Sections 3 through 8 for the various type cells. 

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