Anode Flow Channel Research Articles

A two-dimensional, two-phase mass transport model for liquid-feed DMFCs

A two-dimensional, isothermal two-phase mass transport model for a liquid-feed direct methanol fuel cell (DMFC) is presented in this paper. The two-phase mass transport in the anode and cathode porous regions is formulated based on the classical multiphase flow in porous media without invoking the assumption of constant gas pressure in the unsaturated porous medium flow theory. The two-phase flow behavior in the anode flow channel is modeled by utilizing the drift-flux model, while in the cathode flow channel the homogeneous mist-flow model is used. In addition, a micro-agglomerate model is developed for the cathode catalyst layer. The model also accounts for the effects of both methanol and water crossover through the membrane. The comprehensive model formed by integrating those in the different regions is solved numerically using a home-written computer code and validated against the experimental data in the literature. The model is then used to investigate the effects of various operating and structural parameters, such as methanol concentration, anode flow rate, porosities of both anode and cathode electrodes, the rate of methanol crossover, and the agglomerate size, on cell performance.

Water flooding and pressure drop characteristics in flow channels of proton exchange membrane fuel cells

Water flooding of the flow channels is one of the critical issues to the design and operation of proton exchange membrane fuel cells (PEMFCs). The liquid water and total pressure drop characteristics both in the anode and cathode parallel flow channels of an operating PEMFC were experimentally studied. The gas/liquid two-phase flow both in the anode and cathode flow channels was observed, and the total pressure drop between the inlet and outlet of the flow field was measured. The effects of cell temperature, current density and operating time on the total pressure drop were investigated. The results indicated that the total pressure drop in the flow channels mainly depends on the resistance of the liquid water in the flow channels to the gas flow, and the different flow patterns distinguish the total pressure drops in the flow field. Clogging by water columns result in a higher pressure drop in the flow channels. The total pressure drop measurement can be considered as an in situ diagnoses method to characterize the degree of the flow channels flooding. The liquid water in the cathode flow channels was much more than that in the anode flow channels. The pressure drop in the cathode flow channels was higher than that in the anode flow channels. During the fuel cell operation, the cell performance decreased gradually and the pressure drop both in the anode and the cathode flow channels increased. The rate of flooding at the cathode side reached 49.56% under experimental conditions after 78 min of operation. However, it was zero at the anode side.

1212 エタノール直接発電型固体高分子燃料電池のアノード側流路形状の検討 : 遺伝的アルゴリズムを用いた流動数値解析による流路形状最適化(GS-6 燃料電池)

1212 エタノール直接発電型固体高分子燃料電池のアノード側流路形状の検討 : 遺伝的アルゴリズムを用いた流動数値解析による流路形状最適化(GS-6 燃料電池)

Investigation of the Shape of the Anode Flow Channel in a Direct Ethanol Polymer Electrolyte Fuel Cell (Optimization of the Sharp Turn Corner Shape by Numerical Flow Analysis with a Genetic Algorithm)

Polymer electrolyte fuel cells, which have been developed for mobile equipment, are mainly direct methanol fuel cells (DMFC). From the standpoint of safety to a human body, it is desirable to use ethanol as fuel. In order to improve the performance of direct ethanol fuel cells (DEFC), it is necessary to investigate the fuel flow pattern in the anode flow channel with many sharp turn corners in the fuel cell, and to improve the channel shape. So, in this study, the velocity distribution of the water flow in a micro-channel was numerically analyzed using the authors' GTT code and the calculated results were verified by the velocity measurement with a line LDV system. For reducing the pressure loss in consideration of the suppression of flow stagnation in the channel, it was attempted to optimize the sharp turn corner shape by three-dimensional numerical flow analysis with a genetic algorithm (GA) and a shape with less pressure loss was found.

Three-dimensional transport model of PEM fuel cell with straight flow channels

In this work, an isothermal, steady-state, three-dimensional (3D) multicomponent transport model is developed for proton exchange membrane (PEM) fuel cell with straight gas channels. The model computational domain, includes anode flow channel, membrane electrode assembly (MEA) and cathode flow channel. The catalyst layer within the domain has physical volume without simplification. A comprehensive set of 3D continuity equation, momentum equations and species conservation equations are formulated to describe the flow and species transport of the gas mixture in the coupled gas channels and the electrodes. The electrochemical reaction rate is modified by an agglomerate model to account for the effect of diffusion resistance through catalyst particle. The activation overpotential is predicted locally in the catalyst layer by separately solving electric potential equations of membrane phase and solid phase. The model is validated by comparison of the model prediction with experimental data of Ticianelli et al. The results indicate the detailed distribution characteristics of oxygen concentration, local current density and cathode activation overpotential at different current densities. The distribution patterns are relatively uniform at low average current density and are severely non-uniform at higher current density due to the mass transfer limitation. The local effectiveness factor in the catalyst layer can be obtained with this model, so the mass transport limitation is displayed from another point of view.

Study of water distribution and transport in a polymer electrolyte fuel cell using neutron imaging

A procedure to utilize neutron imaging for the visualization of two-phase flow within an operating polymer electrolyte fuel cell has been developed at the Penn State Breazeale Nuclear Reactor. Neutron images allow us to visualize the liquid water inside the flow channel (∼0.5 mm deep) and gas diffusion media (∼200 μm thick) in real operating conditions. The current temporal and spatial resolution for radioscopy is approximately 30 frames/s and 129 μm/pixel in a 50 cm 2 image area. Continuous digital radioscopy can be recorded for 45 min. The determination of water volume within the cell has been enabled by referencing a calibration look-up table that correlates neutron attenuation to an equivalent liquid water thickness. It was found that liquid water tends to accumulate at specific locations within the fuel cell, depending on operating conditions. Anode flow channel blockage was observed to occur at low power, while higher power conditions resulted in more dispersed distribution of liquid droplets. Under high-power conditions, liquid water tended to accumulate along or under the channel walls at 180° turns, and radioscopy revealed that individual liquid droplet velocities were several orders of magnitude less than that of the reactant flow, indicating a slug-flow regime up to at least 1 A/cm 2.

Real-time water distribution in a polymer electrolyte fuel cell

Knowledge of the species distribution within a polymer electrolyte fuel cell (PEFC) is critical to fully characterize the local performance and accurately quantify the various modes of water transport. This paper describes the results of a newly developed real-time technique for in situ measurement of water vapor, nitrogen and oxygen distributions within the reactant flow channels of an operating PEFC using an Agilent real-time gas analyzer (RTGA). The RTGA was interfaced directly to the fuel cell at various locations along the single path serpentine anode and cathode flow channels of a specially designed fuel cell. Species distribution data are combined with measured high frequency resistance and current distribution. The periodic presence of liquid water droplets in the cathode at high current density and at locations near the cathode exit is also observed.

A model for the liquid feed direct methanol fuel cell

Mass transport is a factor which limits the performance of solid polymer electrolyte fuel cells operating at relatively high current densities. The direct methanol solid polymer electrolyte fuel cell, unlike the hydrogen cell, suffers from mass transport limitations predominantly at the anode. In the liquid feed cell the mass transport limitations arise from diffusion of methanol in the carbon cloth covering the active electrocatalyst layer and from hydrodynamic limitations in the anode flow channel. A model of the methanol mass transport processes is presented which is used to predict the effective methanol concentration at the catalyst surface and thereby the anode polarisation. This model, together with an empirical model of the open circuit voltage and the cathode overpotential model, is used to predict the overall cell voltage, current density response of the fuel cell.