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为研究叶片进口位置对小流量工况下离心泵空化性能的影响,应用数值计算方法模拟了比转数为81的离心泵的三种模型,得到不同进口边位置的离心泵空化特性,并分析了叶轮内部流场与空化性能曲线的影响关系。结果表明,在小流量工况下,低比转速离心泵叶片进口边位置越靠前,抗空化性能较好,但严重空化后扬程衰减更快,流道直接被空泡堵塞,流道和叶片表面气泡分布较均匀,且气泡充斥流道速度较快,气泡体积分数各流道差值越小。相比较而言,叶片进口位置越靠后,气泡在流道内部和叶片背面分布不均匀,易出现噪声和振动,但在断裂空化状态,气泡并未完全堵塞流道,扬程下降速度较慢。整体来看,在小流量工况下,叶片进口边位置越靠前,离心泵的抗空化性能较好,并通过试验研究验证了模拟结果的可靠性。研究成果可为小流量工况下低比转速离心泵抗空化性能的优化提供参考。 相似文献
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以多流程板壳式换热器为研究对象,建立了板程与壳程的物理模型并进行数值模拟,分析了流速、流道数对流量分布特性的影响及流量分布特性对传热效率、压降的影响。通过增大导孔直径和改变入口角度对板程进行了优化,通过设置双入口和增加挡板对壳程进行了优化。研究表明:多流程板壳式换热器的板程与壳程均存在严重的流量分布不均匀现象,且板程要比壳程更为严重,不均匀性会随流速和流道数的增大而增大,并导致板程传热效率下降6%~14%、壳程下降2%~5%,且均造成压降的增大;增大导孔直径和改变入口角度均有利于板程流量的均匀分布,但效果有限,双入口模式可以很好地改善壳程流量分布的不均匀性,而添加挡板虽使不均匀性降低,但是造成了压降的增大。 相似文献
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全钒液流电池因具有优异的安全性和超长的循环寿命,使其在规模储能领域具有广阔的应用前景。但钒电池较高的储能成本限制了它的规模化发展,大幅提高其功率密度进而降低储能成本是实现钒电池商业化的有效途径。流场是影响钒电池功率密度的关键部件之一,匹配的流场能够有效改善钒电池在高倍率放电时的浓差极化,从而实现较高的功率密度。但目前关于不同流场性能优劣的研究结论却存在较大分歧,严重影响了它们的工程化应用。本工作针对钒电池中最为常用的蛇型和插指型流道,通过仿真和实验相结合的方式系统地研究了比流量、流场尺寸对传质及电池性能的影响规律,并揭示了这两种流场在不同工况下得出不同甚至相反结论的根本原因。结果显示,在相同比流量下,电解液在蛇型流道电极内的流速远大于插指型流道,所以在低比流量下蛇型流道的性能明显好于插指型流道;增加比流量或提高流场尺寸均可提升电池的性能,由于插指型流道的临界流量大于蛇型流道,所以插指型流道性能的提升幅度明显大于蛇型流道,进而导致两种流场间的性能差异会随着比流量和流场尺寸的增加逐渐减小甚至出现性能反转。本工作不仅加深了对钒电池流场结构及其传质过程的认识,也为流场的工程化应用提供了依据和方向。 相似文献
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In this study, we present a rigorous mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells gas concentration and current density distribution in mass transfer area and chemical reaction area performed in 3‐D geometry. The model is based on the solution of the conservation equations of mass, momentum, species, and electric current in a fully integrated finite‐volume solver using the CFDRC commercial code. The influences of fuel cell performance with two kinds of flow channel pattern design are studied. The gas concentration of the straight flow pattern appears excessively non‐uniform, resulting in a local concentration polarization. On the other hand, the gas concentration is well distributed for the serpentine flow pattern, creating a better mass transfer phenomena. The performance curves (polarization curves) are also well correlated with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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In proton exchange membrane fuel cells, baffled flow channels enhance the reactant transfer from flow channels to gas diffusion layers. However, the reactant transfer depends on both the diffusive transfer and convective transfer, and how the baffles in flow channels affect them is still unknown. Therefore, in this work, a two‐dimensional, two‐phase, nonisothermal, and steady‐state model of proton exchange membrane fuel cells is developed, and these two transfer processes from flow channels to gas diffusion layers are comparatively studied. Simulation results show that first of all, the reactant transfer from flow channels to gas diffusion layers mainly depends on the diffusive transfer. Therefore, if the desire is to enhance the mass transfer from flow channels to gas diffusion layers, the diffusive mass transfer should be enhanced firstly. Being guided by this goal, a porous‐blocked baffled flow channel is developed. This flow channel design can further enhance the reactant transfer from flow channels to gas diffusion layers, and the cell performance can be improved. Moreover, when the porosities of porous blocks at the front place of flow channels are lower, the cell power is also increased but the pumping power can be reduced a lot. 相似文献
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Jianyu Cao Juan Xu Zhidong Chen Wenchang Wang Qinghong Huang Zhiqing Zou 《国际能源研究杂志》2013,37(4):370-376
A 6‐cell silicon‐based micro direct methanol fuel cell (μDMFC) stack utilized the serial flow path design was developed. The effect of the structure of flow path on the performance of the stack was investigated using polarization characterization and electrochemical impedance analysis. Further, the voltage distribution for individual cells under different current density was discussed. The results indicated that the μDMFC stack with the serial flow path design exhibited better performance than that utilized the parallel flow path due to uniform mass transfer of methanol as a result of the use of the serial flow path. Such a μDMFC stack generates a peak output power of ca. 187 mW, corresponding to an average power density of ca. 21.7 mWcm‐2, and exhibits a steady‐state power output for more than 100 h. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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为进一步提高管壳式换热器壳程换热效率,设计了一种布置于壳程肋片上的仿生鸟喙式涡流发生器。采用ANSYS FLUENT软件结合田口正交试验模拟了矩形通道中鸟喙式涡流发生器的传热特性,分析了纵向高度、斜截角度、迎流攻角、入口距离、流向间距5种结构参数对强化传热和综合热性能的贡献率及最佳结构组合。流动通道为长方体,其长、宽、高分别为1 600,240和40 mm,温度为286.86 K的空气流体从入口以1.491~3.195 m/s的速度流入,通道底部为337.048 K的恒温换热面。结果表明:纵向高度对于强化换热特性的贡献率最高,达到4744%,最强换热效果组合的换热因子较空矩形通道提高了185.71%;迎流攻角对于综合热性能的贡献率最高,达到了总占比的31.35%,利用正交试验分析得到的最强组合较空通道的综合热性能提高了47.82% 相似文献
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Numerical investigation of innovative 3D cathode flow channel in proton exchange membrane fuel cell 下载免费PDF全文
Two kinds of innovative 3‐dimensional (3D) proton exchange membrane fuel cell (PEMFC) cathode flow channel designs were proposed to improve the water removal on the surface of gas diffusion layer and enhance mass transfer between flow channel and gas diffusion layer. A validated 2‐phase volume of fluid model was used to investigate different water removal behaviors in flow channel. The optimal length of water baffle and other parameters of the proposed designs were determined. A validated 3D PEMFC performance model was adopted to assess the new designs. The results suggest that these 2 designs can improve PEMFC performance as to 9% when operating at the high current density because of the significant enhancement of mass transfer induced by air baffles. 相似文献
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Naphthalene sublimation experiments were conducted to study heat (mass) transfer enhancement by blockages with staggered round and square holes for turbulent air flows through a wide rectangular channel. The blockages and the channel had the same cross-section. The results showed that the blockages enhanced the average heat (mass) transfer on the channel walls by 4.7-6.3 times that for fully developed turbulent flow through a smooth channel. The blockages with round holes enhanced more heat (mass) transfer on the channel walls but caused larger pressure drops than the blockages with square holes, which had a 27% larger flow cross-sectional area. 相似文献
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《International Journal of Hydrogen Energy》2022,47(67):28945-28955
A three-dimensional, two-phase, steady-state numerical model of PEMFC with serpentine flow field was set up. The rectangular or triangular blocks were arranged in the cathode channel to improve cell performance. The results showed that the arranged blocks in the channel can effectively enhance the mass transfer of the reactant, thus improve cell performance. The triangular block has better cell performance in comparison with the rectangular block. The block arranged in the rear of the turn has the best cell performance. The reason for the better cell performance of the arranged block is the combination of the under-rib flow and the secondary flow generated by the block. The secondary flow generated by the block is the main reason for the region near the block. Meanwhile, the under-rib flow is the main reason for the region far away from the block. 相似文献
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膜加湿器是保证质子交换膜燃料电池(PEMFC)正常高效运行的重要组成部分.以燃料电池的板式膜加湿器为研究对象,根据热质交换原理对膜加湿器的传热传质过程进行了理论计算,分析了空气质量流量、膜内加湿侧进口温度和膜内加湿侧进口湿度对传热传质过程的影响.在传热方面:当空气质量流量不同时,随着膜内加湿侧进口温度的变化,膜内的热流量变化趋势不一致;当膜内加湿侧进口相对湿度为95%时,随着空气质量流量的变化,膜内热流量变化不大.在传质方面:当加湿侧进口相对湿度不变时,膜中水传输速率随着空气质量流量的增大而减小;当空气质量流量不变时,膜中水传输速率随着加湿侧进口相对湿度的增大而增大. 相似文献