An effective mesh strategy for CFD modelling of polymer electrolyte membrane fuel cells

Computational fluid dynamics (CFD) is a major tool in PEM fuel cell research. Typical three-dimensional PEM fuel cell models involve more than 106 mesh elements. This makes the computation very intense and necessitates a methodology to mesh the computational domain that can keep the number of elements to a minimum while maintaining good accuracy. In this study, the effect of computational mesh in each direction on the accuracy of the solution is investigated in a systematic way. It is found that the mesh in different directions has a different degree of influence on the solution suggesting that the mesh in one direction can be coarser than the other. The proposed mesh strategy is capable of greatly reducing the number of mesh elements, hence computation time, while preserving the characteristics of important flow-field variables. Moreover, it is applicable to a wide range of cell sizes and flow-field configurations and should be used as a guideline for mesh generation

Numerical study on the formability of metallic bipolar plates for Proton Exchange Membrane (PEM) fuel cells

Thin stamped bipolar plates (BPPs) are viewed as promising alternatives to traditional graphite BPPs in proton exchange membrane fuel cells. Metallic BPPs provide good thermal/electrical conductivity and exhibit high mechanical strength, to support the loads within the stack. However, BPPs manufactured by stamping processes are prone to defects. In this study, the effect of the tool’s geometry on the thin sheet formability is investigated through finite element simulation. Despite the broad variety of flow field designs, most of BPPs comprise two representative zones. Hence, in order to reduce the computational cost, the finite element analysis is restricted to these two zones, where the deformation induced by the stamping tools is investigated. The channel/rib width, the punch/die fillet radii, and the channel depth are the parameters studied. The analysis is conducted for a stainless steel SS304 with a thickness of 0.15 mm. The results show that the maximum value of thinning occurs always in the U-bend channel section, specifically in the fillet radius of the die closest to the axis of revolution.This research was funded by the Portuguese Foundation for Science and Technology (FCT) under projects PTDC/EMS-TEC/0702/2014 (POCI-01-0145-FEDER-016779) and PTDC/EMS-TEC/6400/2014 (POCI-01-0145-FEDER-016876) by UE/FEDER through the program COMPETE 2020. The support under the project MATIS (CENTRO-01-0145-FEDER-000014) is also acknowledged

Visualisation of water droplets during the operation of PEM fuel cells

A transparent proton exchange membrane fuel cell (PEMFC) has been designed to enable visualisation of water droplets during its operation. Images of the formation of droplets on the surface of the gas diffusion layer (GDL) on its cathode side, which result in water accumulation and blockage to the airflow channels, were recorded using a CCD camera. Measurement of the cell current and droplet characterisation have been carried out simultaneously and the effect of the airflow and external resistive load has been quantified. The droplet images show that water accumulation occurs first in the middle channels of a serpentine reactant-flow fuel cell design and that no droplets are formed at the bends of the flow channels. Water blockage to the airflow path was caused by the overlapping of two land-touching droplets developing on each side of the channel. Flooding was found to be more susceptible to the airflow than the other test operating conditions

Gasification of Pelletized Corn Residues with Oxygen Enriched Air and Steam

This work studied generation of producer gas using oxygen-enriched air and steam mixture as gasifying medium. Corn residues consisting of cobs and stover were used as biomass feedstock. Both corn residues were pelletized and gasified separately with normal air, oxygen enriched air and steam mixture in a fixed bed reactor. Effects of oxygen concentration in enriched air (21-50%), equivalence ratio (0.15-0.35), and steam to biomass ratio (0-0.8) on the yield of product gas, the combustible gas composition such as H2, CO, and CH4, the lower heating value (LHV), and the gasification efficiency were investigated. It was found that the decrease in nitrogen dilution in oxygen enriched air increased proportion of combustible gas components, improved the LHV of producer gas, but gasification efficiency was not affected. The increase in equivalence ratio favoured high product gas yield but decreased combustible gas components and LHV. It was also observed that introduction of steam enhanced H2 production but excessive steam degraded fuel gas quality and decreased gasification efficiency. The highest gasification efficiency of each oxygen concentration was at equivalence ratio of 0.3 and steam to biomass ratio of 0.58 for cob, and 0.22 and 0.68 for stover, respectively

Performance Characteristics of a PEM Fuel Cell with Parallel Flow Channels at Different Cathode Relative Humidity Levels

In fuel cells flow configuration and operating conditions such as cell temperature, humidity at each electrode and stoichiometric number are very crucial for improving performance. Too many flow channels could enhance the performance but result in high parasite loss. Therefore a trade-off between pressure drop and efficiency of a fuel cell should be considered for optimum design. This work focused on numerical simulation of the effects of operating conditions, especially cathode humidity, with simple micro parallel flow channels. It is known that the humidity at the cathode flow channel becomes very important for enhancing the ion conductivity of polymer membrane because fully humidified condition was normally set at anode. To investigate the effect of humidity on the performance of a fuel cell, in this study humidification was set to 100% at the anode flow channel and was changed by 0–100% at the cathode flow channel. Results showed that the maximum power density could be obtained under 60% humidified condition at the cathode where oxygen concentration was moderately high while maintaining high ion conductivity at a membrane

A Novel Method for In-Situ Monitoring of Local Voltage, Temperature and Humidity Distributions in Fuel Cells Using Flexible Multi-Functional Micro Sensors

In this investigation, micro voltage, temperature and humidity sensors were fabricated and integrated for the first time on a stainless steel foil using micro-electro-mechanical systems (MEMS). These flexible multi-functional micro sensors have the advantages of high temperature resistance, flexibility, smallness, high sensitivity and precision of location. They were embedded in a proton exchange membrane fuel cell (PEMFC) and used to simultaneously measure variations in the inner voltage, temperature and humidity. The accuracy and reproducibility of the calibrated results obtained using the proposed micro sensors is excellent. The experimental results indicate that, at high current density and 100%RH or 75%RH, the relative humidity midstream and downstream saturates due to severe flooding. The performance of the PEM fuel cell can be stabilized using home-made flexible multi-functional micro sensors by the in-situ monitoring of local voltage, temperature and humidity distributions within it

A Novel Vortex-Induced Vibration Based Piezoelectric Powered Generator for Maritime Propulsion Systems

Vortex Induced Vibrations (VIVs), a phenomenon where the fluid flow causes oscillations against an object called a bluff body by vortex shedding, have been studied as a source of renewable energy. However, few studies have focused on the use of VIVs for maritime propulsion. In this investigation, a novel VIV based piezoelectric generator and rechargeable battery were created for use as a maritime propulsion system. The purpose of this research was to see if piezoelectricity is a feasible source of power for a maritime propulsion system. It was hypothesized that if different velocities are applied to a piezoelectric generator, then 3.4 m/s would produce the most power to operate a model ship. In order to determine the feasibility of the generator, testing was conducted in stages, where each stage saw different modifications to the generator. Each generator design was then exposed to eight different velocities. Afterwards, the data was analyzed through the use of line graphs, box plots, and ANOVAs. It was determined that although the hypothesis was partially supported in some cases, it was ultimately not supported due to the behavior of the most powerful configuration. Furthermore, the ANOVA tests determined that significant differences existed between frequencies as a result of velocity and spring constant, while the number of piezoelectric transducers and velocity affected the voltage (p\u3c⍺). No combination achieved enough output to sufficiently operate a model ship. However, the effectiveness of the generator can be improved by implementing an efficient circuit and modification of the transducers

The Impact of Damper Properties on the Amplitude and Frequency of Bluff Body Behaviors Under Vortex-Induced Vibration for Maritime Engines

Vortex Induced Vibrations (VIV) are a phenomenon where the fluid flow causes oscillations against an object called a bluff body by vortex shedding. This phenomenon has recently been studied as a source of renewable energy. The purpose of this study was to test the feasibility of a direct VIV powered maritime propulsion system. It was hypothesized that testing conditions would allow for operation of the proposed mechanical propulsion system and that the combination of the largest bluff body with the lowest damping would achieve the highest amplitude in its vibration. A structure was created to support the bluff body and damper. The bluff bodies consisted of four designs and were suspended by eight types of dampers. The combinations were then exposed to fluid flow at eight different velocities. Results were analyzed by investigating the relationship of velocity against amplitude and frequency. Regressions were also done for statistical analysis. The 2.75 cm bluff body with the 4.35 cm damper achieved the highest amplitude at 1.6 m/s. However, the regressions determined that the data was not statistically significant, and the independent variables did not correlate with the dependent variables (p\u3e�), although these tests did not account for the lock-in region of VIV. In addition, results show that all combinations did not achieve the ability to make a direct drive engine feasible. However, the results demonstrate that it is possible to create a VIV power generator for the propulsion system

A novel vortex-induced vibration based piezoelectric powered generator for maritime propulsion systems

Vortex Induced Vibrations (VIVs), a phenomenon where the fluid flow causes oscillations against an object called a bluff body by vortex shedding, have been studied as a source of renewable energy. However, few studies have focused on the use of VIVs for maritime propulsion. In this investigation, a novel VIV based piezoelectric generator and rechargeable battery were created for use as a maritime propulsion system. The purpose of this research was to see if piezoelectricity is a feasible source of power for a maritime propulsion system. It was hypothesized that if different velocities are applied to a piezoelectric generator, then 3.4 m/s would produce the most power to operate a model ship. In order to determine the feasibility of the generator, testing was conducted in stages, where each stage saw different modifications to the generator. Each generator design was then exposed to eight different velocities. Afterwards, the data was analyzed through the use of line graphs, box plots, and ANOVAs. It was determined that although the hypothesis was partially supported in some cases, it was ultimately not supported due to the behavior of the most powerful configuration. Furthermore, the ANOVA tests determined that significant differences existed between frequencies as a result of velocity and spring constant, while the number of piezoelectric transducers and velocity affected the voltage (p&lt;⍺). No combination achieved enough output to sufficiently operate a model ship. However, the effectiveness of the generator can be improved by implementing an efficient circuit and modification of the transducers.</jats:p