Abstract
A numerical study is conducted to compare the current most popular flow field configurations, porous, biporous, porous with baffles, Toyota 3D fine-mesh, and traditional rectangular flow field. Operation at high current densities is considered to elucidate the effect of the flow field designs on the overall heat transfer and liquid water removal. A comprehensive 3D, multiphase, nonisothermal computational fluid dynamics model is developed based on up-to-date heat and mass transfer sub-models, incorporating the complete formulation of the Forchheimer inertial effect and the permeability ratio of the biporous layers. The porous and baffled flow field improves the cell performance by minimizing mass transport losses, enhancing the water removal from the diffusion layers. The baffled flow field is chosen for optimization owing to the simple design and low manufacturing cost. A total of 49 configurations were mutually compared in the design of experiments to show the quantitative effect of each parameter on the performance of the baffled flow field. The results elucidate the significant influence of small geometry modifications on the overall heat and mass transfer. The results of different cases have shown that water saturation can be decreased by up to 33.59% and maximal temperature by 7.91 °C when compared to the reference case which is already characterized by very high performance. The most influencing geometry parameters of the baffles on the cell performance are revealed. The best case of the 49 studied cases is further optimized by introducing a linear scaling factor. Additional geometry modifications demonstrate that the gain in performance can be increased, but at a cost of higher pressure drop and increased design complexity. The conclusions of this work aids in the development of compact and high-performance proton exchange membrane fuel cell stacks.
Highlights
This design enhanced the interfacial flux between the gas diffusion layers (GDLs) and flow field channels, improved the oxygen transport towards the catalyst layers (CLs), and removed liquid water from the porous electrode more efficiently, significantly increasing the limiting current density compared with other less-complex flow fields, e.g., serpentines [12]
It is easy to investigate the effect of the flow field design when the electrochemical parameters are kept constant in all studied cases
As one of the novelties, the inertial term of the Forchheimer effect is introduced in the 3D multiphase nonisothermal computational fluid dynamic model, which is very important, as demonstrated in this work, for improved water removal at high current densities
Summary
The currently popular mitigation strategies can be roughly categorized into: (i) slightly increasing the flow field complexity by adding baffles or obstacles inside the channels; and (ii) introducing secondary porous layers or microstructures for water removal from the GDLs and the CLs during operation It is still not clear which approach results in higher performance due to the absence of direct comparison to date and the two research directions seem to diverge. One of the most complex flow field designs, named 3D fine-mesh flow field, was applied on the 1st generation Toyota MiraiTM (2014–2019), where repeating 3D micro-lattices were employed as baffles, as described by Konno et al [11] This design enhanced the interfacial flux between the GDL and flow field channels, improved the oxygen transport towards the CLs, and removed liquid water from the porous electrode more efficiently, significantly increasing the limiting current density compared with other less-complex flow fields, e.g., serpentines [12]. Every mentioned deficiency has been resolved in the numerical model shown in this work, using equations from works [25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42], to avoid overcrowding the manuscript with equations, please refer to the numerical model in the
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