Land widths

Kowal et al. [235] used this method to compare the liquid water distribution in the fuel cell with CFP and CC as cathode DLs at different operating conditions and with a parallel flow field channel design for both anode and cathode plates. It was observed that the CFP DL experienced more flooding at lower current densities than the CC, and it retained more water near the landing widths than in or under the channels (60 vs. 40%, respectively). In addition to showing better performance and water removal, the CC resulted in more uniform water coverage on the landing widths and in the channels of the FF. 

In another, similar study, Mukundan et al. [260] performed 100 freeze-thaw cycles (from -40 to 80°C) with different types of CFPs and CCs. After 100 cycles, no obvious degradation was observed in the carbon cloth DL in fact, the performance of the fuel cell slightly improved. On the other hand, after 45 cycles, the CFPs showed significant breakage of the carbon fibers at the edges between the flow channels and the landing widths (or ribs). Thus, it was concluded that this breakage could potentially become a serious failure mechanism in PEM fuel cells when the system was started at subzero temperatures. 

Contact angle tests showed that the hydrophobic properties on those areas corresponding to the channels had changed substantially (more hydrophilic) compared to other parts of the DL (e.g., those close to the landing widths). The same effect was visible on the surface of the MPL, indicating that loss of the PTFE particles was experienced on both surfaces of the DL. Similar observations regarding the hydrophilicity of the areas in which the FF channels are present were presented previously by St-Pierre and Jia [263]. 

Reservoir (width X denth) Die land (width X depth) Aspect ratio (width / depth) Contraction ratio Ref... 

Land width (flight width). Of an extruder screw, the distance across the tip of the flight, perpendicular to the flight faces. 

The reaction mixture must enter the mould parallel to the lower mould wall over a land width which corresponds to at least four times the film thickness. It is guided tangentially into the mould cavity that is to say, the flow direction is provided by the film gate. 

Clean the die Smooth and polish the die Increase mold temperature Increase air pressure Increase air blowing rate Increase purge time when changing materials Improve die streamlining Increase due to mandrel clearance Decrease material temperature Increase extrusion speed Decrease extrusion die temperature Increase stock temperature Decrease extrusion speed Increase die temperature Improve die streamlining Adjust material temperature Increase pinch blade land width Decrease rate of mold closing Adjust and center die-parison curls toward thin area... 

Anode side flow field 10 parallel meanders channel width/depth 1 mm/1 mm, land width 1 mm... 

Land Width P Unspecified dimension, determined by design ... 

Increased anode landing widths to reduce gas shorting between channels, maximizing the ability of the gas to clear water from the channels. 

Two-dimensional internal mixers made of brass having three different radii of each chamber were used. The (e), (g), and (h) type rotors made of stainless steel similar to those in Fig. 3 were used. The land width of these rotors was 4 mm. Fill factors of 0.6, 0.7, and 0.8 were used. The fill factor of 0.9 was not used because of the high torque to rotate the rotor. In these experiments, the clearance between the rotor tips and the mixing chamber wall was 1 mm. The speed ratio of the two rotors was 1 1 and the rotor speed was 5rpm. The phase angle between the two rotors were 90°. Whenever fine powders such as carbon black, pigment, and so on, were mixed into rubber in the two-dimensional internal mixer equipped with transparent window, we could not observe the mixing behavior except for the start and the end of the... 

Abquetschflache, Steg (hervorstehende Kante nach Guss) land width (of extruder screw)... 

Weak pinch 1. Adjust material temperature 2. Increase pinch blade land width 3. Decrease rate of mold closing... 

Thus, the higher the tortuosity and the lower the porosity of the porous media, the more the diffusion will be restricted. Therefore, from a gas-phase transport perspective the microporous layer in the fuel cell restricts transport from the DM to and from the catalyst layer. Lands also play an important role in restricting gas-phase transport to the catalyst layer. The proper landing width is a balance beween reactant flow restriction and electrical contact limitation. 

It should be emphasized that the constraints listed are not independent. In many cases, design to satisfy one constraint will impact others. An excellent example is the channel to land width ratio, discussed below. 

L = land width IV=channel width 0 = draft angle d = depth W L... 

Obviously, the channel bulk flow velocity and the average bypass velocity f/ave will be related, but the basic physics can be understood with this simple relationship. If BPR is much greater than unity, significant bypass should occur if BPR is much less than unity, significant bypass can be avoided. Channel pressure, flow viscosity, and temperature should have little or no effect, while the hydraulic diameter, channel length, land width, DM permeability, and liquid saturation are the key controlling physical parameters. 

The problem of unintentional crossover, or the bypass phenomenon, can be reduced in several ways. A few ways we can design a flow channel with reduced crossover to an adjacent channel include increased compression, decreased DM f)orosity, and increased land width. Discuss the trade-offs associated with these approaches. 

In, general, as landing width, Wl, narrows, the fuel cell performance improves, until there is either MEA deflection into the channel or the gas diffusion layer crashes because of excessive force applied. The optimum channel size and spacing is therefore a balance between maximizing the open area for the reactant gas access to the gas diffusion layer and providing sufficient mechanical support to the MEA and sufficient conduction paths for electrical current and heat. 

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