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

Effects of Anode Flow Field Design on CO2 Bubble Behavior in μDMFC

Clogging of anode flow channels by CO2 bubbles is a vital problem for further performance improvements of the micro direct methanol fuel cell (μDMFC). In this paper, a new type anode structure using the concept of the non-equipotent serpentine flow field (NESFF) to solve this problem was designed, fabricated and tested. Experiments comparing the μDMFC with and without this type of anode flow field were implemented using a home-made test loop. Results show that the mean-value, amplitude and frequency of the inlet-to-outlet pressure drops in the NESFF is far lower than that in the traditional flow fields at high μDMFC output current. Furthermore, the sequential images of the CO2 bubbles as well as the μDMFC performance with different anode flow field pattern were also investigated, and the conclusions are in accordance with those derived from the pressure drop experiments. Results of this study indicate that the non-equipotent design of the μDMFC anode flow field can effectively mitigate the CO2 clogging in the flow channels, and hence lead to a significant promotion of the μDMFC performance

Water droplet accumulation and motion in PEM (Proton Exchange Membrane) fuel cell mini-channels

Effective water management is one of the key strategies for improving low temperature Proton Exchange Membrane (PEM) fuel cell performance and durability. Phenomena such as membrane dehydration, catalyst layer flooding, mass transport and fluid flow regimes can be affected by the interaction, distribution and movement of water in flow plate channels. In this paper a literature review is completed in relation to PEM fuel cell water flooding. It is clear that droplet formation, movement and interaction with the Gas Diffusion Layer (GDL) have been studied extensively. However slug formation and droplet accumulation in the flow channels has not been analysed in detail. In this study, a Computational Fluid Dynamic (CFD) model and Volume of Fluid (VOF) method is used to simulate water droplet movement and slug formation in PEM fuel cell mini-channels. In addition, water slug visualisation is recorded in ex situ PEM fuel cell mini-channels. Observation and simulation results are discussed with relation to slug formation and the implications to PEM fuel cell performance

Characterising PEM fuel cell performance using a current distribution measurement in comparison with a CFD model

The characterisation of a proton exchange membrane (PEM) fuel cell with a straight channel flow field design is performed. Spatially resolved current distribution measurements, at different air flow rates, are compared to numerical simulation results. The numerical model is validated by agreement of the measured and simulated current distribution. The test cell is segmented. It is operated at steady state conditions and the gas flow rates and cell temperature are controlled. The numerical simulation is realised with a PEM fuel cell model based on FLUENT(exp TM) computational fluid dynamics (CFD) software. It accounts for mass transport in the gaseous phase, heat transfer, electrical potential field and the electrochemical reaction. It provides three-dimensional distributions of, e.g., current densities, reactant concentrations and temperature

Investigation of fractal flow-fields in portable proton exchange membrane and direct methanol fuel cells

The flow-field design can have great influence on the operating performance of both proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs). Inhomogeneous transport of reactants to and products from the active area of these low-temperature fuel cells result in loss of power. Newly designed fractal structures are tested as flow-fields in PEMFCs and DMFCs for portable applications. To achieve a uniform fluid distribution and simultaneously minimize energy demand for mass transport (pressure loss), a computer algorithm is developed to provide a given area with a multiple ramified fluid network. By virtue of the self-similarity, the structures of such a network are called fractals. These are investigated and compared with common serpentine and parallel flow-fields. For both PEMFCs and DMFCs fractal flow-fields show similar performance to parallel designs. The most stable and highest power output is reached with the serpentine flow-field