SUMMARYIn this study, we present a rigorous mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells gas concentration and current density distribution in mass transfer area and chemical reaction area performed in 3-D geometry. The model is based on the solution of the conservation equations of mass, momentum, species, and electric current in a fully integrated finite-volume solver using the CFDRC commercial code. The influences of fuel cell performance with two kinds of flow channel pattern design are studied. The gas concentration of the straight flow pattern appears excessively nonuniform, resulting in a local concentration polarization. On the other hand, the gas concentration is well distributed for the serpentine flow pattern, creating a better mass transfer phenomena. The performance curves (polarization curves) are also well correlated with experimental data.
A full scope three-dimensional model is proposed in this paper to investigate the local flowfields and electrochemical parameters within a proton exchange membrane fuel cell. Based on the computational fluid dynamics, this model can simulate the multi-dimensional hydraulic transport phenomena, electrochemical reactions, and current transfer, etc. The localized distribution characteristics of flowfields and electrochemical parameters can be obtained. The predicted relationships between cell voltage and current density (i.e. performance curve) correspond well to the experimental data. The positive effects of both the temperature and pressure on the cell performance are precisely captured. In addition, the present model can also reasonably simulate the concentration polarization effect that decreases the cell performance, as the cell is operated at the higher current density.Keywords: proton exchange membrane fuel cell, computational fluid dynamics, three-dimensional model
INTRODUCTION
The proton exchange membrane water electrolyzer (PEMWE) requires a high operating voltage for hydrogen production to accelerate the decomposition of hydrogen molecules so that the PEMWE ages or fails. According to the prior findings of this R&D team, temperature and voltage can influence the performance or aging of PEMWE. As the PEMWE ages inside, the nonuniform flow distribution results in large temperature differences, current density drops, and runner plate corrosion. The mechanical stress and thermal stress resulting from pressure distribution nonuniformity will induce the local aging or failure of PEMWE. The authors of this study used gold etchant for etching, and acetone was used for the lift-off part. The wet etching method has the risk of over-etching, and the cost of the etching solution is also higher than that of acetone. Therefore, the authors of this experiment adopted a lift-off process. Using the flexible seven-in-one (voltage, current, temperature, humidity, flow, pressure, oxygen) microsensor developed by our team, after optimized design, fabrication, and reliability testing, it was embedded in PEMWE for 200 h. The results of our accelerated aging test prove that these physical factors affect the aging of PEMWE.
A direct-forcing immersed boundary method with large-eddy simulation was used to simulate the phenomenon of the vortex-induced vibration (VIV) of multiple cylinders in a flow field. The present study analyzed the influence of an upstream stationary cylinder on the vibration behavior of two side-by-side cylinders downstream in a staggered position. The latter two side-by-side cylinders were allowed to vibrate in the cross-flow direction. By using different center-to-center distances between cylinders, damping ratios, mass ratios, Reynolds numbers, and diameters of the upstream stationary cylinder, the VIV response and energy conversion efficiency of the vibrating cylinders were studied. The results showed that the amplitude and efficiency of the vibrating cylinders are significantly enhanced at reduced velocity UR*≥6.0 when compared with a single vibrating cylinder. The maximum values of amplitude and efficiency can be shifted and enhanced, respectively, by adjusting the mass ratio and damping ratio. Reducing the diameter of the stationary upstream cylinder can effectively improve efficiency, especially in the lock-in region.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.