Use of Grooved Microchannels to Improve the Performance of Membrane‐Less Fuel Cells

D’Alessandro, Joseph; Fodor, Petru S.

doi:10.1002/fuce.201400047

Cited by 12 publications

(9 citation statements)

References 39 publications

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“…For all the simulations described in this work, we used the computational package COMSOL Multiphysics 5.1 (COMSOL Inc., Stockholm, Sweden) and its computational fluid dynamics/chemical engineering module. The accuracy of the numerical work employed for this type of flow has been previously validated against data obtained from other microfluidic devices [ 49 , 50 ]. In particular, when comparing model data with measured data on similar planar curved microchannels, as presented by Jiang et al [ 50 ], we find mixing times to be less than 0.05 s for Dean numbers equal to or above 140, in agreement with the experimental results.…”

Section: Numerical Model and Mixing Assessmentmentioning

confidence: 99%

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

2018

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In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement the existent rotational flows, leading to a more complex fluid motion. The fluid flow characteristics and associated mixing are determined numerically from computational solutions to Navier–Stokes equations and the concentration-diffusion equation. It is found that the performance of the investigated mixers exceeds that of simple serpentine channels with a more consistent behavior at low and high Reynolds numbers. An analysis of the mixing quality using an entropic mixing index indicates that maximum mixing can be achieved at Reynolds numbers as small as 20 in less than four serpentine mixing units.

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Section: Numerical Model and Mixing Assessmentmentioning

confidence: 99%

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

2018

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“…For such passive methods no additional equipment is necessary. This method for reducing the concentration boundary layer in microfluidic fuel cells has been optimized in several studies by investigating different geometrical parameters such as length and orientation of the ridges (Da Mota et al 2012;D'Alessandro and Fodor 2014;Ha and Ahn 2014;Lee and Ahn 2015;Marschewski et al 2015). However, the small herringbone structures in the microchannels increase the complexity of the manufacturing process and increase the possibility for trapping air bubbles, which lowers the overall efficiency (Howell et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Passive control of the concentration boundary layer in microfluidic fuel cells using Dean vortices

Rösing

Schildhauer

König

et al. 2019

Microfluid Nanofluid

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Microfluidic fuel cells are limited by the formation of concentration boundary layers at the electrodes, resulting in low power density and low fuel utilization. This work demonstrates a novel method to enhance the diffusion-limited mass transport by decreasing the size of the concentration boundary layer using Dean vortices. These vortices are induced by a curved microchannel and enhance the mass transport of fresh reactant towards the electrodes. Numerical simulations were performed to show the influence of the Dean vortices on the performance of a microfluidic fuel cell. Furthermore, a curved microfluidic device with segmented electrodes was fabricated, which allows to experimentally investigate the effect of the enhanced diffusion-limited mass transport on the current density of a model redox couple and thus to prove the concept and the numerical results. It is shown that the Dean vortices, evolving in the curved channel, cause a convective transport of fresh solution towards the electrodes yielding a high current density and resulting in an improvement of 30% using a curved microfluidic fuel cell instead of a straight one. On condition that diffusive and convective mass transport are well-balanced, this approach promises not only a higher power density, but also a much higher fuel utilization.

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“…In fact, design S4, with the vacant zone at the centerline, resembles a geometry also studied previously in Ref. [26,28], albeit at a different dimensional range. The electrodes were in total 5.2 mm long and 175 μm wide, thus anode and cathode were separated by 50…”

Section: Introductionmentioning

confidence: 63%

“…Later, the same group studied differently shaped grooved electrode surfaces in order to find an optimum design [27]. Also, Alessandro and Fodor [28] numerically studied membraneless fuel cells and optimized angled grooves for maximum fuel utilization.…”

Section: Introductionmentioning

confidence: 99%

On the mass transfer performance enhancement of membraneless redox flow cells with mixing promoters

Marschewski

Ruch

Ebejer

et al. 2017

International Journal of Heat and Mass Transfer

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Membraneless flow cells for electrochemical energy conversion exploit the laminarity of microscale flows to avoid undesirable mixing of reactants. To increase the performance of microfluidic redox flow cells we employ herringbone-inspired flow promoters, thereby increasing convection of each individual species to the electrodes, while minimizing reactant mixing. Polarization curves from electrochemical discharge measurements with a dilute anthraquinone / iron redox system reveal that the presence of flow promoters substantially boosts device performance. Mass transfer enhancement for devices with flow promoters is demonstrated through both higher limiting currents and increased power density; the former is more than double compared to a plain reference microchannel for Reynolds numbers of Re > 155. The chaotic mixing effect induced by the flow promoters becomes also apparent in the scaling regimes, the limiting currents are proportional to Re 0.58 instead of Re 1/3 (as for purely laminar flow). Further, we quantify the area specific resistance (ASR) of the electrolyte in our membraneless devices finding a reduction of more than one order of magnitude compared to the ASR of conventional membranes employed in redox flow cells. Overcoming mass transfer limitations, this work highlights the necessity of passive mixers in significantly raising the performance of microfluidic flow cells.

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Use of Grooved Microchannels to Improve the Performance of Membrane‐Less Fuel Cells

Cited by 12 publications

References 39 publications

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section

Passive control of the concentration boundary layer in microfluidic fuel cells using Dean vortices

On the mass transfer performance enhancement of membraneless redox flow cells with mixing promoters

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