Serpentine flow field

Hydrogen gas from serpentine flow field finds a pathway to catalyst layer... 

M. V. Williams, H. R. Kunz, and J. M. Fenton. Influence of convection through gas-diffusion layers on limiting current in PEM FCs using a serpentine flow field. Journal of the Electrochemical Society 151 (2004) A1617-A1627. 

D. P. Wilkinson and O. Vanderleeden. Serpentine flow field design. In Handbook of fuel cells—Fundamentals, technology and applications, ed. W. Vielstich, H. A. Gasteiger, and A. Lamm, 316-324. New York John Wiley Sons (2003). 

Figure 11. Current and water activity distributions in a low humidity 50 cm fuel cell with serpentine flow field at 0.6 V or average current density of 0.71 A/cm. The membrane is 18/rmthick (EW < 1000). The anode/cathode feed conditions are pressure = 3/3 atm, relative humidity = 75%/dry, stoichiometry = 1.2/2, and cell temperature = 80 °C.

Cathode Stainless Steel Serpentine Flow-Field Current Collector... 

Another method to determine current distribution in a PEM fuel cell was presented by Sun et al.169 in which they designed a current distribution measurement gasket that can be placed anywhere in the fuel cell (usually at the back of the cathode side) and can measure the local current density at various point along the active area of the cell. The advantage of this approach is that it can be used without having to modify any component of the cell. The same technique was also used by Zhang et al.170 to compare the performance of interdigitated and serpentine flow fields. 

Figure 7. Comparison of PDS-CF polarization curves from three MEAs, each evaluated first in the standard quad-serpentine flow field, and...

While the model presented applies to a wide range of PEM fuel cell operational regimes there are some caveats to its application. We assume the flux of gas and heat out of the catalyst layer scale with the current density. This would not be the case, for example, with a dry anode feed and a wet cathode feed, which would generate water transport independent of the current level. We assume there is no lateral pressure gradient imposed in the x direction across the GDL such as would arise in interdigitated or serpentine flow fields we consider straight flow fields. 

W-k. Lee, S. Shimpalee and J.W. Van Zee, Verif5nng Predictions of Water and Current Distributions in a Serpentine Flow-Field PEMFC, J. Electrochem. Soc., 150, A341-A348 (2003). 

Dutta et al. [54] used the unified approach to study mass transport between the channels of a PEM fuel cell with a serpentine flow field. Their model is three-dimensional and allows for multi-species transport. They studied the effect of flow channel width in the serpentine flow field on velocity distribution, gas mixture distribution and reactant consumption. Serpentine flow fields allow for a greater area for diffusion of the supply gases. Their results showed that for low humidity conditions, water transport is dominated by electro-osmotic effects, i.e., water flows from anode to cathode at the side of the cell closer to the gas channel inlet. At the outlet side of the cell, water transport is dominated by back diffusion, and it flows in the opposite direction. Thus the serpentine flow field allows for circulation of the water within the cell. 

The channels of most plate heat exchanger/reactors are switched in parallel, which reduces the pressure drop compared to alternative flow patterns such as serpentine flow fields. However, flow equipartition is crucial for parallel flow arrangements. It is achieved by perforated plates [89] when a whole stack of plates is fed in parallel from the plate front. Such pinhole plates create additional pressure drop. In case the feed gas is distributed to each plate first and then by a dedicated inlet section to each channel of the plate, a sophisticated geometry of this inlet section [90] helps to achieve flow equipartition. An alternative is the variation of the channel width over the reactor length axis [91]. 

Ubong et al. also presented a three-dimensional model of a channel pair [32]. The isothermal model incorporated a Butler-Vohner-type equation for electrochemistry and was solved with the finite element method. Simulations were vahdated against a single cell with triple serpentine flow field, which was operated in the temperature range 120-180 °C. The results showed that there is no drastic decrease in cell voltage at high current density due to mass transport hmitation. This is explained by the absence of accumulation of liquid water. It was also concluded that reaction gases need not be humidified. 

Siegel et al. recently presented a CFD cell model with a six-channel serpentine flow field [34]. The model is isothermal and steady state. The description of the catalyst layer follows an agglomerate approach, which takes diffusivity and solubility of gases in phosphoric acid into account. The submodel for the temperature dependence of the conductivity of the phosphoric acid is critically discussed. In the range 150-160 °C, good agreement with experimental results was obtained. 

Figure 30.14 Typical flow fields of PEFCs. (a) Parallel flow field (b) serpentine flow field (c) pin flow field and (d) in-terdigitated flow field.

Kim, C.J. (2009) Numerical study to examine the performance of multi-pass serpentine flow-fields for cooling plates in polymer electrolyte membrane fuel cells. /. Power Sources, 194 (2), 697-703. 

Fig. 17.3 Nyquist plot for HT-PEMFC operating with MEAs fiom different suppliers at 0.2 A/cm. H2/Air (AHj/ Air = 1.2/2). T = 160 "C, p = 1 atm, fivefold serpentine flow fields, contact pressure = 0.75 MPa...

In Fig. 17.12, an example of a three-dimensional tomographic image volume is presented. This is a model of a Celtec P2100 MEA, which has been analyzed post-mortem by p-CT investigations. It shows the GDL material that has been significantly deformed by the compression forces of the serpentine flow field, the imprint of the flow flelds (channel and land area) is clearly visible, also showing the irreversible effect of compression on the GDL under the land area. 

Fig. 17. 13 MEA thickness changes as function of contact pressure for MEAs of different suppliers and measured with grid and fivefold serpentine flow fields.

Fig. 17.17 Selected points of polarization curves as function of contact pressure for MEAs from different suppliers and measured with different flow field types, (a) Celtec -P2100 MEA with grid flow fields, (b) Celtec -P2100 MEA with fivefold serpentine flow fields and (c) Dapozol -G55 MEA with grid flow fields (ini/ Air = 1.2/2 ). (d) EuMA-Tech MEA with fivefold...

---