Flow field design

From Lu and Reddy [44], with permission of International Journal of Hydrogen Energy. 

Another approach is to integrate capillaries into the separator plate of the flow field [47-49]. The capillaries end within the channel and suck water droplets to the other side of the separator plate, where they evaporate. Using a porous material, which is laid over the separator plate, the distribution of the water droplets over the outer surface of the separator plate and the evaporation are enhanced. If done so, a gas-impermeable membrane should be integrated in order to prevent the loss of hydrogen on the anode side. 

---

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. 

Kramer et al. [272] used this same technique to compare two different flow field designs— inferdigifafed and serpentine— and their interactions with the cathode diffusion layer. If was shown thaf the bottom of the interdigitated channels got plugged with liquid water that was not removed properly. On the other hand, the serpentine FF could transport the water inside the channels more effectively, but inside the cathode DL accumulation of wafer was still evident. 

In addition to the three basic FF designs mentioned, various new FF channel concepts (e.g., biomimetic or fractal flow fields, improved mass transfer channels with variable channel cross section, etc.) have been proposed recently [275]. In all cases, the DL requirements and design will depend on the type of FF design. Therefore, it is critical to understand the relationship between any flow field design and the corresponding DL. 

T. V. Nguyen and W. Fie. Interdigitated flow field design. In Handbook of fuel cells—Fundamentals, technology and applications, ed. W. Vielstich, H. A. Gasteiger, and A. Lamm, 325-336. New York John Wiley Sons (2003). 

A. Turhan, K. Heller, J. S. Brenizer, and M. M. Mench. Passive control of liquid water storage and distribution in a PEFC through flow field design. Journal of Power Sources 180 (2008) 773-7 3. 

M. V. Williams, E. Begg, A. A. Peracchio, H. R. Kunz, and J. M. Fenton. Gonvection considerations in PEMFC flow field design. 203rd Electrochemical Society Meeting, Paris (Abstract 1246) (2003). 

K. Yoshizawa, K. Ikezoe, Y. Tasaki, et al. Analysis of gas diffusion layer and flow-field design in a PEMFC using neutron radiography. Journal of the Electrochemical Society 155 (2008) B223-B227. 

X. Li and I. Sabir. Review of bipolar plates in PEM fuel cells Flow-field designs. International Journal of Hydrogen Energy 30 (2005) 359-371. 

One of the benefits of a 3-D model is the ability to examine the effect of flow-field design. For example, Kumar et showed that having hemispherical... 

From the foregoing discussion, it is clear that, in a DMFC, the air cathode has to be operated under rather challenging conditions, that is, with a low air feed rate at nearly full water saturation. This type of operating conditions can easUy lead to cathode flooding and thus poor and unstable air cathode performance. To secure better air cathode performance, we have made great efforts to improve the ell cathode structure and cathode flow field design to facilitate uniform air distribution and easy water removal. The performance of our 30-cell DMFC stacks operated with dry air feed at low stoichiometry is reported in the following section. 

The use of LIF in fuel cells is less extensive than PIV, but has produced valuable results. Bazylak et al.101 used ex-situ testing to quantify the effects that cell compression have on GDL hydropho-bicity by damaging the GDL and PTFE layer. Lozano et al.102,103 and Barreras et al.5 conducted a series of LIF experiments on mock fuel cells with various flow field designs (diagonal, serpentine, and... 

Performance of a stack of cells is limited by performance of the weakest cell in stack. It is therefore important to achieve high uniformity in performance of the individual cells in the stack, through stack design, mass production techniques, quality control, and automated stack assembly process. Optimum flow field design may be obtained by careful Computational Fluid Mechanic techniques and experimental validation including flow visualization techniques. 

In a multichannel flow-field design the channels with normal and lowered pressure may alternate and one may expect that the latter will effectively remove excessive water from the cathode compartment. Such a flow field may have advantages over the interdigitated flow field since gas flow in the water-draining (Red) channels is externally driven and can be varied to reach optimal conditions. 

Arico, A.S. Creti, P. Baglio, V. Modica, E. Antonucci, V. Influence of flow field design on the performance of a direct methanol fuel cell. J. Power Sources 2000, 91 (2), 202-209. 

Zhou, T. and Liu, H.T., Heat Transfer Enhancement in Fuel Cells with Interdigitated Flow Field Design, Int. J. Computer Applications in Technology, in publication, 2002. 

Optimize the fuel cell flow field design for optimized water management and air bleed utilization with the catalyst and EB components. 

Developed a unique flow field design via modeling and basic principles of gas transport that optimizes the uniformity of hydrogen and air mass flow velocities for the matched EB media and increases high current density performance over conventional designs. 

Flow field design and relative orientation of media and coolant flow (e.g. co-flow, counter-flow, cross-flow) have dramatic influence on power, stability, and endurance of the PEFC. 

Fig. 1.11 Typical flow field designs (a) direct supply, (b) pillars, (c) parallel, (d) serpentine, (e) parallel/serpentine, (f) spiral, (g) interdigitated, (h) spiral/interdigitated (Reproduced from Ref. [57] with permission)...

---