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排序方式: 共有1731条查询结果,搜索用时 15 毫秒
1.
《International Journal of Hydrogen Energy》2022,47(20):11007-11027
Cathode channel of a PEM fuel cell is the critical domain for the transport of water and heat. In this study, a mathematical model of water and heat transport in the cathode channel is established by considering two-phase flow of water and air as well as the phase change between water and vapor. The transport process of the species of air is governed by the convection-diffusion equation. The VOSET (coupled volume-of-fluid and level set method) method is used to track the interface between air and water, and the phase equilibrium method of water and vapor is employed to calculate the mass transfer rate on the two-phase interface. The present model is validated against the results in the literature, then applied to investigate the characteristics of two-phase flow and heat transfer in the cathode channel. The results indicate that in the inlet section, water droplets experience three evolution stages: the growing stage, the coalescence stage and the generation stage of dispersed water drops. However, in the middle and outlet sections of the channel, there are only two stages: the growth of water droplets, and the formation of a water film. The mass transfer rate of phase change in the inlet section of the channel varies over time, exhibiting an initial increase, a decrease followed, and a stabilization finally, with the maximum and stable values of 1.78 × 10?4 kg/s and 1.52 × 10?4 kg/s for Part 1, respectively. In the middle and outlet sections, the mass transfer rate increase firstly and then keeps stable gradually. Furthermore, regarding the distribution of the temperature and vapor mass fraction in the channel, near the upper surface of the channel, the temperature and vapor mass fraction first change slightly (x < 0.03 m) and then rapidly decrease with fluctuations (x > 0.03 m). In the middle of the channel, the temperature and vapor mass fraction slowly decrease with fluctuation. 相似文献
2.
Chenxu Liu Shuguang Zhang Ruonan Ji Peng Wang Jin Zhang Yu Tian Yonggang Meng Yedong He 《Ceramics International》2019,45(4):4747-4755
Semiconductor particles doped Al2O3 coatings were prepared by cathode plasma electrolytic deposition in Al(NO3)3 electrolyte dispersed with SiC micro- and nano-particles (average particle sizes of 0.5–1.7?µm and 40?nm respectively). The effects of the concentrations and particle sizes of the SiC on the microstructures and tribological performances of the composite coatings were studied. In comparison with the case of dispersing with SiC microparticles, the dispersion of SiC nanoparticles in the coatings was more uniform. When the concentration of SiC nanoparticles was 5?g/L, the surface roughness of the composite coating was reduced by 63%, compared with that of the unmodified coating. Friction results demonstrated that the addition of 5?g/L SiC nanoparticles reduced the friction coefficient from 0.60 to 0.38 and decreased the wear volume under dry friction. The current density and bath voltage were measured to analyze the effects of SiC particles on the deposition process. The results showed that the SiC particles could alter the electrical behavior of the coatings during the deposition process, weaken the bombardment of the plasma, and improve the structures of the coatings. 相似文献
3.
《International Journal of Hydrogen Energy》2021,46(62):31778-31787
NdSrCo2O5+δ (NSCO) is a perovskite with an electrical conductivity of 1551.3 S cm−1 at 500 °C and 921.7 S cm−1 at 800 °C and has a metal-like temperature dependence. This perovskite is used as the cathode material for Ce0.8Gd0.2O2-δ (GDC)-supported microtubular solid oxide fuel cells (MT-SOFCs). The MT-SOFCs fabricated in this study consist of a bilayer anode, comprising a NiO–GDC composite layer and a NiO layer, and a NSCO–GDC composite cathode. Three cell designs with different outer tube diameters, GDC thicknesses, and NSCO/GDC ratios are designed. The MT-SOFC with an outer tube diameter of 1.86 mm, an electrolyte thickness of 180 μm, and a 5NSCO–5GDC composite cathode presents the best performance. The flexural strength of the aforementioned cell is 177 MPa, which is sufficient to confer mechanical integrity to the cell. Moreover, the ohmic and polarization resistance values of the cell are 0.22 and 0.09 Ω cm2 at 700 °C, respectively, and 0.15 and 0.03 Ω cm2 at 800 °C, respectively. These results indicate that the NSCO-GDC composite exhibits high electrochemical activity. The maximum power densities of the cell at 700 and 800 °C are 0.46 and 0.67 W cm−2, respectively, exceeding those of existing electrolyte-supported MT-SOFCs with similar electrolyte thicknesses. 相似文献
4.
腐蚀阴极尖端的新方法 总被引:1,自引:0,他引:1
给出一种腐蚀阴极尖端的新方法,使得对阴极常用金属材料(W,Mo,Ir,Ta等)制作的阴极尖端的腐蚀效果明显,针尖对称性和重复性都很好,成品率和质量都有所提高. 相似文献
5.
The effects of NOx on the performance of proton exchange membrane (PEM) fuel cell were investigated through the introduction of a mixture containing NO and NO2, in a ratio of 9:1, into the cathode stream of a single PEM fuel cell. The NOx concentrations used in the experiments were 1480 ppm, 140 ppm and 10 ppm, which cover a range of three orders. The experimental results obtained from the tests of durability, polarization, reversibility and electrochemical impedance spectroscopy (EIS) showed a detrimental effect of NOx on the cell performance. The electrochemical measurements results suggested that the impacts of NOx are mainly resulted from the superposition of the oxygen reduction reaction (ORR), NO and HNO2 oxidation reactions, and the increased cathodic impedance. Complete recovery of the cell performance was reached after operating the cell with clean air and then purging with N2 for hours. 相似文献
6.
本文通过有关理论依据和试验数据,着重阐述了在显像(示)管测试中,阴极像中心黑洞状缺陷产生的原因以及消除这种缺陷的处理方法。通过这种处理方法处理过的显像(示)管,其整体质量水平(尤其是真空度)将会得到明显的提高。 相似文献
7.
Lithium-ion batteries are becoming more and more important not only for portable electronic devices, but also in prevision of high power electric vehicles. In such an optic, deep studies regarding all the components of a secondary battery are in development. In this study, high voltage cathode materials have been selected. Crystals with spinel structure have a 3D vacancy pathway suitable for Li-ions transport. The material under study was LiNi0.5Mn1.5O4 doped with magnesium replacing the nickel. Various samples were synthesized via three different routes: a solid-state method, a modified sol–gel method and a xerogel method. The structure and morphology of the powders were analyzed with HRTEM and XRD. Electrochemical tests were also performed. A wide range of particle sizes (from micro to nanosize) was the result of the different synthesis routes. Unfortunately pure materials were not always obtained. The electrochemical tests showed improvement of the material's cyclability, by reducing the particle size. The electrochemical tests further confirmed the existence of a Li1+dMn2−dO4 impurity. The results are quite promising, however, further improvement of the purity of the electrode composition are needed. 相似文献
8.
9.
铁电材料用于阴极发射的研究 总被引:1,自引:0,他引:1
铁电材料作为一种新型的阴极材料,具有真空要求低、制作简单、功函数低、响应速度快等特点。本文讨论了铁电阴极发射的机理,回顾了主要铁电阴极材料的发射实验,包括低电压铁电发射实验,最后对铁电阴极材料的应用做了讨论和展望。 相似文献
10.
Computational modeling of cathodic limitations on localized corrosion of wetted SS 316L at room temperature 总被引:1,自引:0,他引:1
The ability of a SS 316L surface wetted with a thin electrolyte layer to serve as an effective cathode for an active localized corrosion site was studied computationally. The dependence of the total net cathodic current, Inet, supplied at the repassivation potential Erp (of the anodic crevice) on relevant physical parameters including water layer thickness (WL), chloride concentration ([Cl−]) and length of cathode (Lc) were investigated using a three-level, full factorial design. The effects of kinetic parameters including the exchange current density (io,c) and Tafel slope (βc) of oxygen reduction, the anodic passive current density (ip) (on the cathodic surface), and Erp were studied as well using three-level full factorial designs of [Cl−] and Lc with a fixed WL of 25 μm. The study found that all the three parameters WL, [Cl−] and Lc as well as the interactions of Lc × WL and Lc × [Cl−] had significant impact on Inet. A five-factor regression equation was obtained which fits the computation results reasonably well, but demonstrated that interactions are more complicated than can be explained with a simple linear model. Significant effects on Inet were found upon varying either io,c, βc, or Erp, whereas ip in the studied range was found to have little impact. It was observed that Inet asymptotically approached maximum values (Imax) when Lc increased to critical minimum values. Imax can be used to determine the stability of coupled localized corrosion and the critical Lc provides important information for experimental design and corrosion protection. 相似文献