Water transport plate

PVDF/graphite composites can lend themselves as the best materials for both molded and coated plates. A key component of a fuel cell stack is the bipolar plate. Also referred to as a water transport plate or a separator... 

Typically a plate should be made as impermeable as possible to prevent crossover of fluids. However, UTC Power creatively uses porous water transportable plate achieving superior performance, especially in the high current density region, due to its unique ability to manage liquid water. The plate has hydrophilic pores with a diameter of ca. 1 pm and its bulk porosity is... 

Weber, A.Z., and Darling, R.M. (2007) Understanding porous water-transport plates in polymer-electrolyte fuel cells, J. Power Sources, 168, 191-199. 

The research group led by Dr. Djilali at the University of Victoria has developed an ex situ experimental technique using fluorescent microscopy to study the liquid water transport mechanisms inside diffusion layers and on their surfaces [239-243]. The diffusion layer is usually placed between two plates (the top plate may or may not have a channel) the liquid water, which is pumped through a syringe pump, flows from the bottom plate through the DL. Fluorescein dye is added to the water for detection with the microscope. 

As shown in Figure 16b, the 2-D rib models deal with how the existence of a solid rib affects fuel-cell performance. They do not examine the along-the-channel effects discussed above. Instead, the relevant dimensions deal with the physical reality that the gas channeFdiffusion media interfaces are not continuous. Instead, the ribs of the flow-channel plates break them. These 2-D models focus on the cathode side of the fuel-cell sandwich because oxygen and water transport there have a much more significant impact on performance. This is in contrast to the along-the-channel models that show that the underhumidification of and water transport to the anode are more important than those for the cathode. 

FIGURE 12.11 Comparison of liquid water transport for two 50-cm single-cell PEM fuel cells using commercial graphite composite bipolar plates (a) surface modified and (b) as received (0.1 A/cm, 1.5/2.0 Hj-air stoichiometry, 100% RH). 

A countercurrent plate-and-frame dialyzer is to be sized to process 1.0 m3/h of an aqueous solution containing 25 wt% H2S04 and smaller amounts of copper and nickel sulfates. A wash water rate of 1000 kg/h is to be used, and it is desired to recover 60% of the acid at 298 K. From laboratory experiments with an acid-resistant vinyl membrane, a permeance of 0.03 cm/min for the acid and a water-transport number of +0.8 were reported. Transmembrane transport of copper and nickel sulfates is negligible. For these operating conditions, it has been estimated that the combined external mass-transfer coefficients will be 0.02 cm/min. Estimate the membrane area required. 

Excess oxidant, fuel, and product water are leaving the anode and cathode flow plates respectively through the media distribution structures. Normally most water is removed via the cathode, however, the detailed distribution of water removal rate between anode and cathode side is depending on the operatirMi conditions where a cathode pressure higher than the anode pressure and the use of thin electrolyte membranes are favoring water transport to the anode side. 

Lebedeva, T. L. Kuptsov, S. A. Feldstein, M. M. Plate, N. A., Molecular Arrangement of Water Associated with Poly (N-vinyl pyrrolidone) in the First Hydrate Shell. In Water Transport in Synthetic Polymers, lordanskii, A. L. Startsev, O. V. Zaikov, G. E., Eds. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences Moscow, 2003 pp 69-93. 

According to experiments performed under appropriate conditions, about 1% of the fission product iodine present in the flashed primary coolant volume is transported with the steam phase, about half of it in form of aerosols (Aim and Dreyer, 1980). This figure agrees well with that reported by Morell et al. (1985) and Hellmann et al. (1991), obtained in flashing experiments from small-diameter pipes (see Section 6.2.2.). In the experiments of Aim and Dreyer (1980), which were carried out in an uncoated steel vessel, only particulate iodide and elemental h were detected in the atmosphere of the vessel. The rate of plate-out of iodine from the atmosphere was found to depend on the specific geometric conditions of the experimental setup. In a comparatively small vessel, deposition halftimes of 8.5 hours for h and of 0.9 hours for aerosol iodide were measured within the first two hours after blowdown these values increased to 9.9 and 5.7 hours, respectively, during the following 22 hours. From other experiments markedly different values have been reported (e. g. CSE tests, see Section 7.3.S.3.8.). The reasons for these differences are not only due to the dimensions and true surface areas present in the respective experimental facility, but also to various other parameters, such as initial concentrations, turbulences in the atmosphere, rate of water droplet plate-out and of steam condensation. 

St-Pierre (2009) provides a comprehensive tabulation of the hterature on contaminant performance losses and mechanisms. The water management of the MEA can be affected by the presence of contaminants the membrane water content and water transport is reduced by the presence of contaminant cations degradation products from plate and seal materials can adsorb onto stack materials and affect water management by increasing hydrophilicity of electrode materials and contaminant materials may block the MEA pore stracture, resulting in reduced gas diffusion in the electrode and gas diffusion layers. 

Transparent fuel cells [77-84] are widely used to characterize the water removal process on the flow field of a PEM fuel cell. As they allow optical access to the flow field, one can observe the formation of water droplets and the water removal process in the flow channels. A transparent cell usually includes a transparent plastic end plate, a copper plate to serve as the current collector, and a flow field plate on the anode side, cathode side, or both, as shown in Fig. 3.22. For the test setup, a high-speed camera is required to record the status of liquid water in the flow channels. Thus, water flooding at different stages or under various conditions can be recorded, as shown in Fig. 3.23 [81 ]. In this way, the visualization of water transport and removal in a transparent cell can be used to optimize the operating conditions, the structural designs of the flow field and gas diffusion layer, and the screening of materials for the gas diffusion layer. 

Sugar-beet cossettes are successfully extracted while being transported upward in a vertical tower by an arrangement of inclined plates or wings attached to an axial shaft. The action is assisted by staggered guide plates on the tower wall. The shell is filled with water that passes downward as the beets travel upward. This configuration is employed in the BMA diffusion tower (Wakeman, loc. cit.). 

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