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  • 1.
    Birgersson, Erik
    KTH, Superseded Departments, Mechanics.
    Mathematical Modeling of Transport Phenomena in Polymer Electrolyte and Direct Methanol Fuel Cells2004Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with modeling of two types of fuel cells:the polymer electrolyte fuel cell (PEFC) and the directmethanol fuel cell (DMFC), for which we address four majorissues: a) mass transport limitations; b) water management(PEFC); c) gas management (DMFC); d) thermal management.

    Four models have been derived and studied for the PEFC,focusing on the cathode. The first exploits the slenderness ofthe cathode for a two-dimensional geometry, leading to areduced model, where several nondimensional parameters capturethe behavior of the cathode. The model was extended to threedimensions, where four di.erent flow distributors were studiedfor the cathode. A quantitative comparison shows that theinterdigitated channels can sustain the highest currentdensities. These two models, comprising isothermal gasphaseflow, limit the studies to (a). Returning to a two-dimensionalgeometry of the PEFC, the liquid phase was introduced via aseparate flow model approach for the cathode. In addition toconservation of mass, momentum and species, the model wasextended to consider simultaneous charge and heat transfer forthe whole cell. Di.erent thermal, flow fields, and hydrodynamicconditions were studied, addressing (a), (b) and (d). A scaleanalysis allowed for predictions of the cell performance priorto any computations. Good agreement between experiments with asegmented cell and the model was obtained.

    A liquid-phase model, comprising conservation of mass,momentum and species, was derived and analyzed for the anode ofthe DMFC. The impact of hydrodynamic, electrochemical andgeometrical features on the fuel cell performance were studied,mainly focusing on (a). The slenderness of the anode allows theuse of a narrow-gap approximation, leading to a reduced model,with benefits such as reduced computational cost andunderstanding of the physical trends prior to any numericalcomputations. Adding the gas-phase via a multiphase mixtureapproach, the gas management (c) could also be studied.Experiments with a cell, equipped with a transparent end plate,allowed for visualization of the flow in the anode, as well asvalidation of the two-phase model. Good agreement betweenexperiments and the model was achieved.

    Keywords:Fuel cell; DMFC; PEFC; one-phase; two-phase;model; visual cell; segmented cell; scale analysis; asymptoticanalysis.

  • 2.
    Birgersson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    Noponen, M.
    Vynnycky, Michael
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    Analysis of a two-phase non-isothermal model for a PEFC2005In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 5, p. A1021-A1034Article in journal (Refereed)
    Abstract [en]

    A non-isothermal, two-phase model for a polymer electrolyte fuel cell (PEFC) is presented, analyzed, and solved numerically under three different thermal, and two hydrodynamic, modeling assumptions; the consequences of these are then discussed in terms of thermal and water management and cell performance. The study is motivated by recent experimental results that suggest the presence of previously unreported, and thus unmodeled, thermal contact resistances between the components of PEFCs and the discrepancy in the value for the capillary pressure that is used by different authors when modeling the two-phase flow in PEFCs. For the three different thermal assumptions (assuming effective heat conductivities, isothermal flow, and interfacial and bulk conductivites), liquid saturations of around 10% are obtained at the cathode active layer for 1000 mA cm(-2) and a cell voltage of 0.6 V. When lowering the capillary pressure (hydrodynamic assumption), liquid saturations of almost 30% and locally up to 100% are observed at the active layer of the cathode. At this current density and voltage, temperature differences across the cell of around 9 degrees C are predicted. In addition, the effect of varying clamping pressure within the framework of the model is touched upon. The benefits of the scaling analysis conducted here, to predict correctly, prior to numerical computations, important characteristic cell performance quantities such as current density and temperature drop are also highlighted.

  • 3.
    Birgersson, Erik
    et al.
    KTH, Superseded Departments, Mechanics.
    Nordlund, Joakim
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Vynnycky, Michael
    KTH, Superseded Departments, Mechanics.
    Picard, Cyril
    KTH, Superseded Departments, Mechanics.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Reduced two-phase model for analysis of the anode of a DMFC2004In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 151, no 12, p. A2157-A2172Article in journal (Refereed)
    Abstract [en]

    An isothermal two-phase ternary mixture model that takes into account conservation of momentum, mass, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The slenderness of the anode allows a considerable reduction of the mathematical formulation, without sacrificing the essential physics. The reduced model is then verified and validated against data obtained from an experimental DMFC outfitted with a transparent end plate. Good agreement is achieved. The effect of mass-transfer resistances in the flow field and porous backing are highlighted. The presence of a gas phase is shown to improve the mass transfer of methanol at higher temperatures (>30 degreesC). It is also found that at a temperature of around 30 degreesC, a one-phase model predicts the same current density distribution as a more sophisticated two-phase model. Analysis of the results from the two-phase model, in combination with the experiments, results in a suggestion for an optimal flow field for the liquid-fed DMFC.

  • 4.
    Birgersson, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    Vynnycky, Michael
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory.
    A quantitative study of the effect of flow-distributor geometry in the cathode of a PEM fuel cell2006In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 153, no 1, p. 76-88Article in journal (Refereed)
    Abstract [en]

    An isothermal three-dimensional model describing mass, momentum and species transfer in the cathode of a proton exchange membrane fuel cell has been used to study four different flow-distributors: interdigitated, coflow and counterflow channels, and a foam. A quantitative comparison of the results shows; that the interdigitated channels can sustain the highest current densities, followed in descending order by the foam, the counterflow and the coflow channels. The foam yields the most uniform current density distribution at higher currents, but care should be taken as to its permeability to avoid unreasonably high-pressure drops.

  • 5.
    Luna, Fabio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Birgersson, Erik E.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Martinez, Joaquin
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Transport Phenomena.
    Diffusion equation applied to isothermal drying of a multicomponent liquid film2005In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 23, no 11-sep, p. 1953-1975Article in journal (Refereed)
    Abstract [en]

    Liquid-side-controlled drying by convection of a multicomponent liquid film is studied. Interactive diffusion in liquid phase is considered the main mechanism for mass transfer. Assuming an isothermal drying process and a constant matrix of multicomponent diffusion coefficients, an analytical solution of the diffusion equation is developed. The equations are decoupled by a similarity transformation and solved by the method of variable separation. The solution is applied to the drying of ternary mixtures, one of them containing a component of negligible volatility. The variation of diffusion coefficients along the process trajectory was taken into account by a piecewise application of the solution in time intervals with averaged coefficients from previous time steps. Despite the simplifications made, the analytical solution gives a god insight into the selectivity of the drying process and is computationally fast. The limitations of the analytical solution and the prospect of applying the solution to the description of a nonisothermal process are discussed. It would introduce an important computational economy since the rigorous treatment of multicomponent drying leads to partial differential equations with variable coefficients, which can only be solved by time-consuming iterative procedures.

  • 6. Noponen, Matti
    et al.
    Birgersson, Erik
    KTH, Superseded Departments, Mechanics.
    Ihonen, Jari
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Vynnycky, Michael
    KTH, Superseded Departments, Mechanics.
    Lundblad, Anders
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    A two-phase non-isothermal PEFC model: Theory and validation2004In: Fuel Cells, ISSN 1615-6846, E-ISSN 1615-6854, Vol. 4, no 4, p. 365-377Article in journal (Refereed)
    Abstract [en]

    A two-dimensional, non-isothermal, two-phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the stream-wise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6°C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm-2.

  • 7.
    Nordlund, Joakim
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Picard, C
    Birgersson, Erik
    KTH, Superseded Departments, Mechanics.
    Vynnycky, Michael
    KTH, Superseded Departments, Mechanics.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The design and usage of a visual direct methanol fuel cell2004In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 34, no 8, p. 763-770Article in journal (Refereed)
    Abstract [en]

    In order to better understand the influence of gas evolution on the performance of the direct methanol fuel cell ( DMFC) anode, a visual DMFC, comprising of a transparent anode and a cathode endplate with an integrated heat exchanger, and a picture analysis methodology were developed. The result was an inexpensive, but very powerful, tool for analyzing the role of two-phase flow. An important finding is that gas bubbles do not appear uniformly throughout the fluid flow matrix, but rather only at a few active sites. Another important finding is that the gas saturation ( volume fraction of gas/volume fraction of liquid) increases along the streamwise direction.

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