Channel Plate Collectors

As already mentioned, boundary conditions for the dependent variables of the transport equations at the interfaces between different layers of the same domain are not required. At the gas channel entries, conditions of the first kind have to be prescribed for the gas mixture velocities, pressures, temperatures, and component concentrations. At the interfaces between the gas channels and the plate collectors, boundary conditions of the first kind have to be prescribed for the gas mixture velocity components (no slip condition) and for the temperature if the temperature of the cooling (heating) agent is known, or boundary conditions of the second kind are prescribed if the wall is adiabatic. 

Unlike the array collector, with a microchannel plate all ions of only one m/z value are detected simultaneously, and instrument resolution does not depend on the number of elements in the micro-channel array or on the separation of one element from another. For a microchannel plate, resolution of m/z values in an ion beam depends on their being separated in time by the analyzer so that their times of arrival at the plate differ. 

An optimum relationship between the DL and the flow field channels is a key factor in the overall improvement of fhe fuel cell s performance at both high and low current densities. Currently, flow field designs are typically serpentine, interdigitated, or parallel [207,264]. The FF plate performs several functions If is a current collector, provides mechanical support for the electrodes, provides access channels for the reactants to their respective electrode surfaces and for the removal of producf water, and it prevents mixing of oxidant, fuel, and coolant fluids. 

Localized AC impedance and current distributions were measured by Brett et al." on a single linear channel with the segmented cathode current collector plate. Figure 26 shows their measured current density and membrane resistance distributions along the... 

The final element on the outer side of the unit cell (Figs. 1 and 2) is the current collector plate, which typically contains the machined gas flow field. These two functions of current collector and gas flow field may be fulfilled, in principle, by two separate components but, in most of the cells and and stacks tested so far, the flow field is machined in the current collector plate using a range of geometries, e.g., a single serpentine channel, parallel channel flow and series-parallel combinations. The specific flow-field geometry may be critical in fulfilling the requirements of effective water supply and effective liquid water removal from the cathode. 

Cell frames contain a system of gas channels integrated in the bipolar plate, the so-called flow field for the distribution of fuel and air evenly over the entire active electrode area of the anode and the cathode the dimensions of channels and ribs are usually in the millimetre range. The cell frames act as well as current collectors, and thus a good electrical conductivity is required, fn addition, the ceU frames can contain cooling channels, either for air cooling or for liquid cooling. Various cooling concepts have already been realised. 

Liquid distributors are often used to correct liquid flow to a more uniform pattern and/or to add more liquid to the reactor. Liquid distributors are also often used to redistribute the liquid phase as well, but a simpler option, shown in Figure 9.9, would be a perforated plate with directional facing. Liquid collectors are used to channel the liquid into the liquid oudet in order to prevent converted/used liquid to stay in the column bottom. The hardest portion of designing a collector is to not interfere with gas distribution, and the available designs are quite wide and diverse. TBRs, on the other hand, tend to use liquid collectors, which are only used for collecting and extracting liquid. 

The final component of a fuel cell to be discussed in this chapter is the current collector plates (CCP) or more commonly called the bipolar plates (BP) or flow field plate (FFP). As observed in Fig. 7.1 the fuel cell stack is composed by a number of BP, each of which will separate a pair of MEA and with two end plates completing the stack. At either side of the BP, an arrange of channels provide the flow paths for the fuel and oxygen. One of those faces is in contact with the anode of one MEA and the other face with the cathode of the other MEA, hence, the name bipolar plate. The end plates have channels only on one face, and the stack is typically completed by two metal plates with a series of bolts that holds the stack... 

Reaetants enter the cell through gas channels, which are embedded in the current collectors (bipolar plate). The gas diffusion layers (GDL) are used to uniformly distribute the reactants across the surface of the catalyst layers (CL), as well as to provide an electrical connection between the catalyst layers and the current collectors. 

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