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Fangming Jiang - One of the best experts on this subject based on the ideXlab platform.
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effects of reactants coolant non uniform inflow on the cold Start performance of pemfc stack
International Journal of Hydrogen Energy, 2020Co-Authors: Ahmed Mohmed Dafalla, Fangming JiangAbstract:Abstract The failure at equally distributing reactants among different channels within the stack leads to uneven reaction and gas concentration distribution in the catalyst layers, which consequently impacts the performance and durability of proton exchange membrane fuel cell stacks (PEMFCs). A three-dimensional, transient, non-isothermal cold Start Model for PEMFCs with parallel flow-field configuration and coolant circulation is developed in this work to investigate the effects of non-uniform distribution of reactants/coolant inflow rates on the cold Start process. The results show that the effect of non-uniform inflow on ice formation amount is obvious and that on the distribution uniformity of current density is apparent over the cold Start survival time. Additionally, the simulation predictions show that the non-uniform initial membrane water content distribution due to the purge procedure can significantly increase the rate of ice growth and deteriorate the uniformity of current density distribution in the membrane. It is found that high stoichiometry operating condition is favorable to cold Startup, but may result in drying in the membrane at regions close to the channel inlet side. As non-uniform inflow rates issue is inevitable in actual PEMFC stack operation conditions, our results demonstrate that the initial membrane water content and cathode stoichiometry ratio need to be identified to moderate the effects of reactants/coolant inflow maldistribution and to maintain a stable cold Start performance for the PEMFC stack.
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Effect of Cathode Pore Volume on PEM Fuel Cell Cold Start Species conservation * Electrochemical Society Active Member. z
2020Co-Authors: Ashis Nandy, Fangming Jiang, Chao-yang Wang, Ken S ChenAbstract:Start-up of a proton exchange membrane ͑PEM͒ fuel cell from subzero temperatures, commonly referred to as cold Start, remains a major challenge for automotive applications. In this work, we theoretically and experimentally study the effect of catalyst layer ͑CL͒ pore volume ͑or, more directly, CL thickness͒ on the cold-Start performance of a PEM fuel cell for both isothermal and nonisothermal operations. Special attention is directed to determining the limits of a cold-Start performance with an ultrathin CL ͑1 m͒. The cold-Start product water or the operational time approaches a minimum nonzero asymptote as the CL is gradually made infinitesimally thin. For a PEM fuel cell with standard cell thermal mass, e.g., 0.4 J/cm 2 K, and with moderately low initial membrane water content ͑ 0 = 7͒, successful Start-up from −20°C at 100 mA/cm 2 can be achieved for CL thicknesses of 10 m and above, whereas a CL thickness of 20 m is required for successful self-Start-up from −30°C. However, successful Start-up can be achieved even with a 1 m thick CL, given certain adjustments to cell design and material properties. In particular, we study the effects of cell thermal mass and membrane water diffusivity and present a design map for self-Start-up of a 1 m CL PEM fuel cell from various subfreezing temperatures. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3355867͔ All rights reserved. Cold-Start capability remains one of the greatest challenges for automotive application and commercialization of polymer electrolyte fuel cells ͑PEFCs͒. Many recent experimental and theoretical studies have been carried out to elucidate the fundamental mechanisms of cold Start of a PEFC. 3-9 More recently, based on the dependence of cold-Start characteristics on cell temperature obtained from isothermal studies, many nonisothermal cold-Start simulations have been performed, involving realistic automotive conditions and stack thermal environments. Ice formation in the CCL during cold Start depends on complex water flow behavior inside the cell. 3-9 As shown schematically in Although many studies have been performed to characterize and predict cold-Start behavior under a range of operating conditions and membrane electrode properties, 20 all were focused on a standard CL with a thickness of ϳ10 m, and no attention has been paid to the cold-Start performance of a PEFC with a much thinner CL. As fuel cell technology moves toward a thinner CL to reduce Pt loading ͑such as 3M nanostructured thin-film CL with a thickness of 0.4 m͒ and to remove carbon from the electrode for corrosion avoidance, understanding the cold-Start consequences of these thin CLs is very important to downselect new technologies for nextgeneration fuel cell vehicles. In this paper, we explore the effect of CL thickness on PEFC cold Start, both theoretically and experimentally. More importantly, this work aims to shed light on the desirable material and operating parameters for achieving self-Start-up of a PEFC with a thin CL under automotive conditions. The present paper is organized as follows. First, a brief description of the nonisothermal cold-Start Model built upon the work of Mao et al. Theoretical Analysis This section briefly describes the theoretical analysis of cold Start based on a one-dimensional ͑1D͒, nonisothermal, multiphase Model previously developed and used by Mao et al
Ahmed Mohmed Dafalla - One of the best experts on this subject based on the ideXlab platform.
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effects of reactants coolant non uniform inflow on the cold Start performance of pemfc stack
International Journal of Hydrogen Energy, 2020Co-Authors: Ahmed Mohmed Dafalla, Fangming JiangAbstract:Abstract The failure at equally distributing reactants among different channels within the stack leads to uneven reaction and gas concentration distribution in the catalyst layers, which consequently impacts the performance and durability of proton exchange membrane fuel cell stacks (PEMFCs). A three-dimensional, transient, non-isothermal cold Start Model for PEMFCs with parallel flow-field configuration and coolant circulation is developed in this work to investigate the effects of non-uniform distribution of reactants/coolant inflow rates on the cold Start process. The results show that the effect of non-uniform inflow on ice formation amount is obvious and that on the distribution uniformity of current density is apparent over the cold Start survival time. Additionally, the simulation predictions show that the non-uniform initial membrane water content distribution due to the purge procedure can significantly increase the rate of ice growth and deteriorate the uniformity of current density distribution in the membrane. It is found that high stoichiometry operating condition is favorable to cold Startup, but may result in drying in the membrane at regions close to the channel inlet side. As non-uniform inflow rates issue is inevitable in actual PEMFC stack operation conditions, our results demonstrate that the initial membrane water content and cathode stoichiometry ratio need to be identified to moderate the effects of reactants/coolant inflow maldistribution and to maintain a stable cold Start performance for the PEMFC stack.
M Samland - One of the best experts on this subject based on the ideXlab platform.
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spectral and atmospheric characterization of 51 eridani b using vlt sphere
Astronomy and Astrophysics, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, A Cheetham, D MesaAbstract:Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (~0.5′′, ~13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual-band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y - to H -band range and providing additional photometry in the K12-bands (2.11, 2.25 μ m). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT-NACO ( L ′) Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J -band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter f sed . We find that the atmosphere is highly super-solar ([Fe/H] = 1.0 ± 0.1 dex), and the low \hbox{${f_{\rm sed} = 1.26^{+0.36}_{-0.29}}$} value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The Model radius and surface gravity estimates suggest higher planetary masses of \hbox{${M_\mathrm{gravity} = 9.1^{+4.9}_{-3.3} \, {M}_\mathrm{J}}$}. The evolutionary Model only provides a lower mass limit of > 2 M J (for pure hot-Start). The cold-Start Model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown-dwarf companions more massive than 20 M J beyond separations of ~2.5 au and giant planets more massive than 2 M J beyond 9 au.
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spectral and atmospheric characterization of 51 eridani b using vlt sphere
arXiv: Earth and Planetary Astrophysics, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, A Cheetham, D Mesa, R Gratton, B Biller, Z WahhajAbstract:51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, recently discovered by direct imaging. Being only 0.5" away from its host star it is well suited for spectroscopic analysis using integral field spectrographs. We aim to refine the atmospheric properties of this and to further constrain the architecture of the system by searching for additional companions. Using the SPHERE instrument at the VLT we extend the spectral coverage of the planet to the complete Y- to H-band range and provide photometry in the K12-bands (2.11, 2.25 micron). The object is compared to other cool and peculiar dwarfs. Furthermore, the posterior probability distributions of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. For probing the innermost region for additional companions, archival VLT-NACO (L') SAM data is used. We present the first spectrophotometric measurements in the Y- and K-bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity and cloud sedimentation parameter f_sed. We find that the atmosphere is highly super-solar (Fe/H~1.0) with an extended, thick cloud cover of small particles. The Model radius and surface gravity suggest planetary masses of about 9 M_jup. The evolutionary Model only provides a lower mass limit of >2 M_jup (for pure hot-Start). The cold-Start Model cannot explain the planet's luminosity. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at Solar System scales and exclude brown-dwarf companions more massive than 20 M_jup beyond separations of ~2.5 au and giant planets more massive than 2 M_jup beyond 9 au.
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Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
Astronomy and Astrophysics - A&A, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, D Mesa, R Gratton, A.c. Cheetham, B.a. Biller, Z WahhajAbstract:Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0‐type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (similar to 0.5 `', similar to 13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual‐band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y‐to H‐band range and providing additional photometry in the K12‐bands (2.11, 2.25 mu m). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT‐NACO (L') Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J‐band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter f(sed). We find that the atmosphere is highly super‐solar ([Fe/H] = 1.0 +/‐ 0.1 dex), and the low f(sed) = 1.26(‐0.29)(+0.36) value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The Model radius and surface gravity estimates suggest higher planetary masses of M‐gravity = 9.1(‐3.3)(+4.9) M‐J. The evolutionary Model only provides a lower mass limit of > 2 M‐J (for pure hot‐Start). The cold‐Start Model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown‐dwarf companions more massive than 20 M‐J beyond separations of similar to 2.5 au and giant planets more massive than 2 M‐J beyond 9 au.
Kui Jiao - One of the best experts on this subject based on the ideXlab platform.
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Two-dimensional simulation of cold Start processes for proton exchange membrane fuel cell with different hydrogen flow arrangements
2020Co-Authors: Xu Xie, Owe Wang, Zirong Yang, Ji Xua, Zhi Liu, Kui JiaoAbstract:© 2020 Hydrogen Energy Publications LLC Proton exchange membrane (PEM) fuel cells with an off-gas recirculation anode (ORA) or dead-ended anode (DEA) are widely adopted in engineering. However, those two hydrogen flow arrangements may cause anodic water and nitrogen accumulation in comparison with the flow-through anode (FTA) mode, which causes significant performance degradation. In this paper, a two-dimensional cold-Start Model is developed with detailed consideration of water phase changes and the nitrogen crossover phenomenon. A simplified electrochemical module is built to calculate the current density distribution in the Model. The simulation results are consistent with the experimental data at both subzero temperatures and normal operating temperatures. The effects of hydrogen flow arrangements, flow configurations, and Startup strategies are investigated during Startup process from subzero to normal operating temperatures. Much less ice is generated in counter-flow cases than in co-flow cases during constant current operation. A relatively lower Startup voltage can effectively shorten the cold-Start process and enhance the cold-Start capacity for the PEM fuel cell. The ORA mode has the best hydrogen flow arrangement due to its general abilities, including higher hydrogen utilization efficiency, higher anodic nitrogen tolerance, better output performance and better Startup capability
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elucidating the constant power current and voltage cold Start modes of proton exchange membrane fuel cell
International Journal of Heat and Mass Transfer, 2014Co-Authors: Yueqi Luo, Kui Jiao, Bin JiaAbstract:Abstract Constant power cold Start mode of proton exchange membrane (PEM) fuel cell is essential in practical applications, however, unlike the constant current and voltage cold Start modes, the constant power mode was largely ignored in previous fundamental Modeling and experimental studies. In this study, a PEM fuel cell stack cold Start Model for analyzing the constant power cold Start process is developed, and the fundamental differences among the various Start-up modes are elucidated. In the constant power cold Start mode, the Start-up process may fail before the ice fully covers the cathode catalyst layers (CLs), because the stack may not be able to supply the required power output, which is different from the constant current and voltage Start-up modes. The initial water content and Start-up temperature could limit the power output significantly. The constant power can be controlled at higher current (CPHC) or lower current (CPLC). In the CPHC mode, the current density decreases and the stack voltage increases during the cold Start process, while it is reversed in the CPLC mode. Generally, the CPLC mode produces less heat during cold Start process than the other Start-up modes, because the current density is often kept at low level.
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Modeling of assisted cold Start processes with anode catalytic hydrogen oxygen reaction in proton exchange membrane fuel cell
International Journal of Hydrogen Energy, 2013Co-Authors: Qian Guo, Yueqi Luo, Kui JiaoAbstract:Abstract Catalytic hydrogen–oxygen reaction is a potentially effective way to help Start up proton exchange membrane fuel cells (PEMFCs) from sub-zero temperatures. In this study, the anode hydrogen–oxygen catalytic reaction is implemented in a three-dimensional multiphase cold Start Model. It is found that successful cold Start from −20 °C can be achieved with the assist of the catalytic reaction in galvanostatic mode. With anode catalytic reaction, the Start-up current density must be moderate, because a high current density lowers the assisted heating effect, and a low current density slows down the Start-up process. The temperature difference between the anode and cathode catalyst layers (CLs) is negligible, which indicates that the heating location in the electrodes for the catalytic reaction makes no significant difference. The humidification of anode due to the catalytic reaction also reduces the ohmic resistance of the membrane, leading to enhanced performance during the Start-up processes.
D Mesa - One of the best experts on this subject based on the ideXlab platform.
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spectral and atmospheric characterization of 51 eridani b using vlt sphere
Astronomy and Astrophysics, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, A Cheetham, D MesaAbstract:Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (~0.5′′, ~13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual-band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y - to H -band range and providing additional photometry in the K12-bands (2.11, 2.25 μ m). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT-NACO ( L ′) Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J -band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter f sed . We find that the atmosphere is highly super-solar ([Fe/H] = 1.0 ± 0.1 dex), and the low \hbox{${f_{\rm sed} = 1.26^{+0.36}_{-0.29}}$} value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The Model radius and surface gravity estimates suggest higher planetary masses of \hbox{${M_\mathrm{gravity} = 9.1^{+4.9}_{-3.3} \, {M}_\mathrm{J}}$}. The evolutionary Model only provides a lower mass limit of > 2 M J (for pure hot-Start). The cold-Start Model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown-dwarf companions more massive than 20 M J beyond separations of ~2.5 au and giant planets more massive than 2 M J beyond 9 au.
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spectral and atmospheric characterization of 51 eridani b using vlt sphere
arXiv: Earth and Planetary Astrophysics, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, A Cheetham, D Mesa, R Gratton, B Biller, Z WahhajAbstract:51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0-type star, recently discovered by direct imaging. Being only 0.5" away from its host star it is well suited for spectroscopic analysis using integral field spectrographs. We aim to refine the atmospheric properties of this and to further constrain the architecture of the system by searching for additional companions. Using the SPHERE instrument at the VLT we extend the spectral coverage of the planet to the complete Y- to H-band range and provide photometry in the K12-bands (2.11, 2.25 micron). The object is compared to other cool and peculiar dwarfs. Furthermore, the posterior probability distributions of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. For probing the innermost region for additional companions, archival VLT-NACO (L') SAM data is used. We present the first spectrophotometric measurements in the Y- and K-bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity and cloud sedimentation parameter f_sed. We find that the atmosphere is highly super-solar (Fe/H~1.0) with an extended, thick cloud cover of small particles. The Model radius and surface gravity suggest planetary masses of about 9 M_jup. The evolutionary Model only provides a lower mass limit of >2 M_jup (for pure hot-Start). The cold-Start Model cannot explain the planet's luminosity. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at Solar System scales and exclude brown-dwarf companions more massive than 20 M_jup beyond separations of ~2.5 au and giant planets more massive than 2 M_jup beyond 9 au.
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Spectral and atmospheric characterization of 51 Eridani b using VLT/SPHERE
Astronomy and Astrophysics - A&A, 2017Co-Authors: M Samland, Paul Molliere, M Bonnefoy, A L Maire, F Cantalloube, D Mesa, R Gratton, A.c. Cheetham, B.a. Biller, Z WahhajAbstract:Context. 51 Eridani b is an exoplanet around a young (20 Myr) nearby (29.4 pc) F0‐type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (similar to 0.5 `', similar to 13 au) and is well suited for spectroscopic analysis using integral field spectrographs. Aims. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. Methods. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual‐band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y‐to H‐band range and providing additional photometry in the K12‐bands (2.11, 2.25 mu m). The object is compared to other known cool and peculiar dwarfs. The posterior probability distributions for parameters of cloudy and clear atmospheric Models are explored using MCMC. We verified our methods by determining atmospheric parameters for the two benchmark brown dwarfs Gl 570D and HD 3651B. We used archival VLT‐NACO (L') Sparse Aperture Masking data to probe the innermost region for additional companions. Results. We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J‐band flux to values 40% fainter than previous measurements. Cloudy Models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter f(sed). We find that the atmosphere is highly super‐solar ([Fe/H] = 1.0 +/‐ 0.1 dex), and the low f(sed) = 1.26(‐0.29)(+0.36) value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The Model radius and surface gravity estimates suggest higher planetary masses of M‐gravity = 9.1(‐3.3)(+4.9) M‐J. The evolutionary Model only provides a lower mass limit of > 2 M‐J (for pure hot‐Start). The cold‐Start Model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown‐dwarf companions more massive than 20 M‐J beyond separations of similar to 2.5 au and giant planets more massive than 2 M‐J beyond 9 au.
