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991.
在膜蒸馏的不同构型中,直接采用环境空气作为冷却媒介的空气冷却式构型很大程度上简化了系统配置。在强化传热的条件下,其跨膜通量与水冷构型接近。对空气冷却式膜蒸馏构型的传热过程进行理论分析,并通过量化分析各参数对膜蒸馏传热性能的影响,构建综合的传热模型。引入关联热阻系数这一概念,用以量化空气冷却的参数对膜蒸馏过程总传热系数的抑制作用。通过模拟计算研究了冷凝板导热系数、空气流速、冷凝板肋化系数、料液温度等参数对膜蒸馏传热性能的影响,并分析和量化多参数对关联热阻系数的综合影响。结果表明冷凝板导热系数、空气流速、冷凝板肋化系数是影响关联热阻系数的重要因素,各参数对膜蒸馏传热性能的综合影响得以量化。以上研究为后续传质模型的研究提供了指导。 相似文献
992.
Jianfeng HuaJianqiu Li Minggao Ouyang Languang LuLiangfei Xu 《International Journal of Hydrogen Energy》2011,36(16):9896-9905
Although electric-powered vehicles have developed rapidly in recent years, with significant progress in the lithium power battery industry, the Fuel Cell Electric Vehicle (FCEV) is still a competitive choice for a clean transportation solution, because of its extended driving range, zero emissions, and fast fuel recharging capability. In particular the fuel cell hybrid bus used for city traffic is the FCEV type most likely to be commercialized. Demonstration programs for a fuel cell bus fleet have been operated for a few years in China. It is necessary to develop comprehensive diagnostic tools to increase the reliability of these systems, because fuel cell city buses serve large numbers of passengers using public transportation. This paper presents a diagnostic analysis and implementation study based on the Principal Component Analysis (PCA) method for the fuel cell system. This diagnostic system was successfully implemented for detecting a fuel cell stack sensor network failure in the fuel cell bus fleet at the Shanghai Expo in 2010. 相似文献
993.
A free vibration analysis of a polymer electrolyte membrane fuel cell (PEMFC) is performed by modelling the PEMFC as a 20 cm × 20 cm composite plate structure. The membrane, gas diffusion electrodes, and bi-polar plates are modelled as composite material plies. Energy equations are derived based on Mindlin's plate theory, and natural frequencies and mode shapes of the PEMFC are calculated using finite element modelling. A parametric study is conducted to investigate how the natural frequency varies as a function of thickness, Young's modulus, and density for each component layer. It is observed that increasing the thickness of the bi-polar plates has the most significant effect on the lowest natural frequency, with a 25% increase in thickness resulting in a 17% increase in the natural frequency. The mode shapes of the PEMFC provide insight into the maximum displacement exhibited as well as the stresses experienced by the single cell under vibration conditions that should be considered for transportation and stationary applications. This work provides insight into how the natural frequencies of the PEMFC should be tuned to avoid high amplitude oscillations by modifying the material and geometric properties of individual components. 相似文献
994.
Nano-sized platinum and ruthenium dispersed on the surface LiCoO2 as catalysts for borohydride hydrolysis are prepared by microwave-assisted polyol process. The catalysts are characterized by transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Very uniform Pt and Ru nanoparticles with sizes of <10 nm are dispersed on the surface of LiCoO2. XRD patterns show that the Pt/LiCoO2 and Ru/LiCoO2 catalysts only display the characteristic diffraction peaks of a LiCoO2 crystal structure. Results obtained from XPS analysis reveal that the Pt/LiCoO2 and Ru/LiCoO2 catalysts contain mostly Pt(0) and Ru(0), with traces of Pt(IV) and Ru(IV), respectively. The hydrogen generation rates using low noble metal loading catalysts, 1 wt.% Pt/LiCoO2 and 1 wt.% Ru/LiCoO2, are very high. The hydrogen generation rate using Ru/LiCoO2 as a catalyst is slightly higher compared with that of Pt/LiCoO2. 相似文献
995.
Cheng Bi Huamin Zhang Yu Zhang Xiaobing Zhu Yuanwei Ma Hua Dai Shaohua Xiao 《Journal of power sources》2008
A self-humidifying composite membrane based on Nafion® hybrid with SiO2 supported sulfated zirconia particles (SiO2–SZ) was fabricated and investigated for fuel cell applications. The bi-functional SiO2–SZ particles, possessing hygroscopic property and high proton conductivity, were homemade and as the additive incorporated into our composite membrane. X-ray diffraction (XRD) and Fourier infrared spectrum (FT-IR) techniques were employed to characterize the structure of SiO2–SZ particles. Scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS) measurements were conducted to study the morphology of composite membrane. To verify the advantages of Nafion®/SiO2–SZ composite membrane, the IEC value, water uptake, proton conductivity, single cell performance and areal resistance were compared with Nafion®/SiO2 membrane and recast Nafion® membrane. The single cell employing our Nafion®/SiO2–SZ membrane exhibited the highest peak power density of 0.98 W cm−2 under dry operation condition in comparison with 0.74 W cm−2 of Nafion®/SiO2 membrane and 0.64 W cm−2 of recast Nafion® membrane, respectively. The improved performance was attributed to the introduction of SiO2–SZ particles, whose high proton conductivity and good water adsorbing/retaining function under dry operation condition, could facilitate proton transfer and water balance in the membrane. 相似文献
996.
997.
A self-humidifying membrane based on sulfonated poly(ether ether ketone) (SPEEK) hybrid with sulfated zirconia (SO42−/ZrO2, SZ) supported platinum catalyst (Pt-SZ catalyst) was synthesized for fuel cell applications. The SZ, a solid state superacid with hygroscopic properties and proton-conductive properties, was employed to synthesize the Pt-SZ catalyst. The self-humidifying membrane (SPEEK/Pt-SZ) was characterized by TEM, FT-IR, TGA and SEM coupled with EDX. The SPEEK/Pt-SZ membrane exhibited higher water uptake and proton conductivity than the plain SPEEK membrane. Consequently, the SPEEK/Pt-SZ self-humidifying membrane under dry operation showed a higher open circuit voltage (OCV) of 1.015 V and a maximum power density of 0.95 W cm−2, relative to 0.96 V and 0.54 W cm−2 for the plain SPEEK membrane. The incorporation of the catalytic, hygroscopic and proton-conductive Pt-SZ catalyst in the SPEEK matrix facilitated water balance and proton conduction, accordingly improved the single cell performance under dry operation. In addition, the enhanced OCV and the decreased area ohmic resistance confirmed the effect of Pt-SZ catalyst in the self-humidifying membrane on suppressing reactant crossover and the membrane self-humidification. 相似文献
998.
Jeff T. Gostick Marios A. IoannidisMichael W. Fowler Mark D. Pritzker 《Journal of power sources》2007
A pore network model of the gas diffusion layer (GDL) in a polymer electrolyte membrane fuel cell is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions. Geometric parameters of the pore network model are calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials and the model is subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, the relative permeability of water and gas and the effective gas diffusivity are computed as functions of water saturation using resistor-network theory. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. Alternative relationships are suggested that better match the pore network model results. The pore network model is also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but it may become a significant source of concentration polarization as the GDL becomes increasingly saturated with water. 相似文献
999.
Novel composite electrolyte membranes consisting of [EMIm](FH)nF (EMIm = 1-ethyl-3-methylimidazolium, n = 1.3 and 2.3) ionic liquids and fluorinated polymers were synthesized and their physical and electrochemical properties were measured under unhumidified conditions for their application to the intermediate temperature fuel cells. The ionic conductivities of composite membrane, P(VdF-co-HFP)/s-DFBP-HFDP/[EMIm](FH)2.3F (1/0.3/1.75 in weight ratio), were 11.3 and 34.7 mS cm−1 at 25 and 130 °C, respectively. The open circuit voltage (OCV) observed for the single cell using [EMIm](FH)2.3F composite electrolyte was ∼1.0 V at 130 °C for over 5 h. The maximum power density of 20.2 mW cm−2 was observed under the current of 60.1 mA cm−2 at 120 °C. From the high thermal stability and high ionic conductivity, the fluorohydrogenate ionic liquid composite membranes are regarded as promising candidates for the electrolytes of the unhumidified intermediate temperature fuel cells. 相似文献
1000.
Lixin YouHongtan Liu 《International Journal of Heat and Mass Transfer》2002,45(11):2277-2287
A unified two-phase flow mixture model has been developed to describe the flow and transport in the cathode for PEM fuel cells. The boundary condition at the gas diffuser/catalyst layer interface couples the flow, transport, electrical potential and current density in the anode, cathode catalyst layer and membrane. Fuel cell performance predicted by this model is compared with experimental results and reasonable agreements are achieved. Typical two-phase flow distributions in the cathode gas diffuser and gas channel are presented. The main parameters influencing water transport across the membrane are also discussed. By studying the influences of water and thermal management on two-phase flow, it is found that two-phase flow characteristics in the cathode depend on the current density, operating temperature, and cathode and anode humidification temperatures. 相似文献