The Effects of the Geometry of a Current Collector with an Equal Open Ratio on Output Power of a Direct Methanol Fuel Cell

The open ratio of a current collector has a great impact on direct methanol fuel cell(DMFC)performance.Although a number of studies have investigated the influence of the open ratio of DMFC current collectors,far too little attention has been given to how geometry(including the shape and feature size of the flow field)affects a current collector with an equal open ratio.In this paper,perforated and parallel current collectors with an equal open ratio of 50%and different feature sizes are designed,and the corresponding experimental results are shown to explain the geometry effects on the output power of the DMFC.The results indicate that the optimal feature sizes are between 2 and 2.5 mm for both perforated and parallel flow field in the current collectors with an equal open ratio of 50%.This means that for passive methanol fuel cells,to achieve the highest output power,the optimal feature size of the flow field in both anode and cathode current collectors is between 2 and 2.5 mm under the operating mode of this experiment.The effects of rib and channel position are also investigated,and the results indicate that the optimum pattern depends on the feature sizes of the flow field.

Open Space Ratio的译名、概念辨析与适用价值

Open Space Ratio(OSR)是《1961纽约市区划决议案》中居住环境控制的核心概念与重要指标,自1990年代始国内的许多学者引进这个概念,并倡导作为规划控制指标,因此也催生了中文术语"空地率"。本文系统梳理国内有关"OSR"和"空地率"研究的30余年学术文献,基于《1961纽约市区划决议案》的法律文本,对OSR的译名及其概念作出全面的阐释,澄清了OSR指标的意义、应用目的及其范围,辨析了OSR与中文术语"空地率"本质性的概念差异,建议将OSR指标引入控制性详细规划的居住环境控制,调整和完善我国控制性详细规划的指标控制体系。

Effect of Structural Parameters on the Performance of NS High-efficiency Composite TraysⅠ.The Effect of Aperture and Opening Ratio on NS High-efficiency Composite Trays

In this paper,the structure and characteristics of the NS high-efficiency composite trays based on the doublelayer aperture jet sieve plate and compositely structured packing were investigated.The effect of aperture and opening ratio of plate on the fluid dynamics of the NS high-efficiency composite trays,such as the dry tray pressure drop,the wet tray pressure drop,the entrainment,the froth height,the leakage and mass transfer characteristics,were investigated.As a result, the low pressure drop,the high efficiency and the high capacity are the main advantages of the NS high-efficiency composite trays compared to other types of trays.According to this study,small aperture is useful for reducing the pressure drop and entrainment with a high mass transfer efficiency;while large aperture can achieve high capacity and efficiency in a broader operating range at the same pressure drop and entrainment.

火灾后正六边形孔蜂窝组合梁受力性能研究

火灾后蜂窝组合梁受力性能研究可为建筑结构受火后的加固修复提供重要依据。文章通过两个火灾后正六边形孔蜂窝组合梁的静力加载试验,分析了不同开孔率的正六边形孔蜂窝组合梁的破坏形态和承载性能。结果表明:火灾后正六边形孔蜂窝组合梁在正弯矩作用下会发生弯曲破坏,临近梁端的第3个孔压缩变形较为严重且两侧钢梁腹板局部屈曲,两加载点之间板顶混凝土破坏严重,钢梁上部板面出现纵向贯通裂缝;开孔率是影响火灾后正六边形孔蜂窝组合梁极限承载力的重要因素,相较于开孔率为70%的蜂窝组合梁,开孔率为60%的蜂窝组合梁的极限承载力和延性分别提高了20%和35%;所提出的正六边形孔蜂窝组合梁受火后剩余承载力计算方法具有较好的精度。

正方形泄放口尺寸对高压氢气泄漏激波传播与自燃特性的影响研究

实验研究了高压氢气从不同尺寸泄放口释放到管道中的激波传播特性和自燃发生规律,采用了三种尺寸的正方形泄放口,面积分别为113 mm^(2)(开口率λ=4/5),75 mm^(2)(λ=2/3),49 mm^(2)(λ=1/2)。结果表明,开口率的减小会削弱管道内激波的强度和传播速度,并抑制激波在向下游传播过程中的发展。同时发现,随着开口率的减小,氢气自燃所需的最小泄放压力增大。进一步,当开口率减小时,氢气自燃的整体火焰强度减弱,火焰传播速度减小。特别是在开口率较小的条件下(λ=1/2),当泄放压力增大时,管道内最大火焰强度未有明显增长,表明开口率减小对整体火焰强度有一定的抑制作用。

几何参数对轮缘推进器水动力性能影响的研究

轮缘推进器是近年来发展起来的一种无轴组合式特种推进器。与传统推进器相比,轮缘推进器在水动力设计和性能分析方面存在诸多挑战,水动力性能的研究对轮缘推力器的设计和应用具有重要意义。为了研究几何参数对轮缘推力器水动力性能的影响,本文以7叶轮缘驱动推力器为基本模型,基于面元法原理,利用编译的面元法代码对轮缘推力器在开阔水域的工作状态进行了数值模拟。通过求解每个面元的速度场,计算了水动力性能和叶片表面压力分布。此外,本文选择了几个典型的几何特征,如螺距比和叶片数,通过进行变参数分析,比较了不同几何参数下轮缘推力器的敞水性能。结果表明:本文的相关研究对轮缘推力器的设计和开发具有参考价值。

坚守底线,强化选择——开敞空间率在国土空间详细规划中的适用性研究

国土空间规划体系的改革要求详细规划发挥法定规划和政策工具的双重作用。城乡规划体系下的传统控制性详细规划虽对我国城市建设发展贡献巨大,但其静态蓝图式的管控方式显然难以适应国土空间详细规划的新要求。因此,通过对传统控制性详细规划核心指标“失衡”之源的分析,指出详细规划阶段缺乏一个可以直接平衡公平与效率的统领性指标。开敞空间率因具有统筹协调多个开发控制指标的联动作用,能够在坚守公共利益底线的基础上强化市场自主选择的可能性,故能促进构建编管一体的详细规划规则体系。基于此,结合国土空间详细规划的发展需求,探讨开敞空间率在国土空间详细规划中的适用性,提出构建以开敞空间率为核心、基础指标和特色指标相结合、刚性底线和弹性管控相结合的规则化开发控制指标体系。

基于DHMM-ESUM的露天矿运输系统车铲比优化研究

在露天矿生产中,如何利用现有的资源条件对电铲与卡车进行合理配比,充分发挥设备的效率,是提高矿山企业生产效益的关键。以安家岭露天矿生产系统收集的数据为基础,首先运用排队理论构建以电铲为采掘中心,卡车为运输工具的闭合排队网络模型,将运输系统分为4个排队子系统,分析各项服务时间的概率分布;基于离散隐马尔可夫模型(discrete hidden Markov model,DHMM)与拓展求和(extended summation,ESUM)算法分析系统作业性能,获取电铲设备的运行状态和班次生产能力。然后,应用蒙特卡洛法建立随机动态规划模型,以产量期望值最大化为目标对露天矿的车铲比进行优化。最后,对生产系统进行仿真建模分析,结果验证了基于DHMM-ESUM对车铲比进行优化的有效性和准确性。

不同剪跨比下低矮开洞剪力墙抗震性能试验

核电厂房的剪力墙具有剪跨比低和配筋率高的特点,为满足人员通行以及设备管道的布置,需要在剪力墙中开设洞口,然而,关于低矮开洞剪力墙抗震性能的研究比较有限。为此,设计3个1∶2.7的大比例尺低矮钢筋混凝土剪力墙试件,通过拟静力试验研究剪跨比对此类剪力墙抗震性能的影响。研究内容包括试件的破坏模式、滞回曲线、延性系数、刚度退化、耗能能力和变形能力等方面的分析和讨论。结果表明:低矮开洞剪力墙的破坏主要是由墙肢的斜向主裂缝宽度明显增大引起,导致承载力快速下降;剪跨比的减少使得低矮剪力墙的承载力、刚度和单圈耗能效果增加,但变形能力和极限位移显著降低,从而导致累计耗能较小;剪跨比较小的试件容易在洞口上方产生塑性铰,随后连梁的转动会导致洞口附近的混凝土压碎,且剪切效应较显著。此外,小洞口的存在会产生严重的不对称性,影响其抗震性能。

Influence of cutterhead opening ratio on soil arching effect and face stability during tunnelling through non-uniform soils

Tunnelling has increasingly become an essential tool in the exploration of underground space.A typical construction problem is the face instability during tunnelling,posing a great threat to associated infrastructures.Tunnel face instability often occurs with the soil arching collapse.This study investigates the combined effect of cutterhead opening ratio and soil non-uniformity on soil arching effect and face stability,via conducting random finite-element analysis coupled with Monte–Carlo simulations.The results underscore that the face stability is strongly associated with the evolution of stress arch.The obtained stability factors in the uniform soils can serve as a reference for the design of support pressure in practical tunnelling engineering.In addition,non-uniform soils exhibit a lower stability factor than uniform soils,which implies that the latter likely yields an underestimated probability of face failure.The tunnel face is found to have a probability of failure more than 50%if the spatial non-uniformity of soil is ignored.In the end,a practical framework is established to determine factor of safety(FOS)corresponding to different levels of probability of face failure considering various opening ratios in non-uniform soils.The required FOS is 1.70 to limit the probability of face instability no more than 0.1%.Our findings can facilitate the prediction of probability of instability in the conventionally deterministic design of face pressure.

基于高空模拟试车台大口径套筒式柱塞阀流动特性分析

为了准确描述大口径套筒式柱塞阀内速度、压力和流阻系数的变化规律,通过Fluent软件模拟开度、压比对套筒式柱塞阀流动特性的影响。结果表明:阀内速度和压力都沿着阀芯轴线对称分布,当开度增加时,轴向射流汇集区速度增大,出口速度随之增大,速度均匀性降低,节流窗口处气流压力减小,轴向压力趋于均匀,流阻系数随开度增加先迅速减小后趋于稳定;当压比增大时,进口速度先保持不变而后不断减小,存在临界压比,速度和压力逐渐趋于均匀,压比越大流阻系数下降越显著。

基于NSGA-Ⅱ的固体火箭发动机壳体不同开口比封头补强优化

封头补强工艺作为壳体封头承载能力提升的典型手段,其补强工艺参数对不同开口比壳体补强后应力水平、壳体质量的影响规律不明晰。为此,构建了?300 mm壳体分析模型,并结合径向基函数(RBF)神经网络分析方法拟合优化变量与优化目标间的映射关联,开展了补强角度、补强层数、补强区域对应力响应水平的影响规律研究。最后,基于非支配排序遗传算法(NSGA-Ⅱ)获得了最优开口比以及使壳体特性系数达到最大的最优补强参数。结果表明,优化后壳体的特性系数比未补强壳体提高16.28%,比未优化的编织布补强壳体提高6.53%。研究成果可以为不同开口比壳体补强工艺参数的选定提供理论依据。

因设备机型造成的胎面脱层问题研究

上、下挤出机,机型差异较大,厚规格胎面在复合挤出过程中,经常会出现脱层问题。通过挤出机螺杆优化、口型开板比例调整,口型维修,工艺参数固化,挤出机温控以及预热等措施的执行,厚规格胎面脱层问题得到了有效的解决。

不同开度可调涡轮导叶前缘气膜冷却效果研究

针对变循环发动机的可调低压涡轮导叶开展了不同开度下的前缘气膜冷却效果研究。采用数值仿真的方法,研究了5种典型导叶开度下的导叶表面压力系数分布规律,探究了开度与冷气吹风比对叶片前缘气膜出流特性和覆盖特性的影响规律。结果表明:导叶开度的减小导致前缘的气动驻点位置向压力面方向移动,造成前缘冷气射流更多地流向吸力面侧,使吸力面气膜冷却效率提高;此外,导叶开度的减小导致吸力面与压力面的冷气贴壁效果都有提高,但两者的具体机理不同。导叶开度的变化对前缘气膜孔最佳吹风比影响较小,不同开度下的最佳吹风比都在1.0附近。由于导叶开度为0°时滞止线位于气膜孔排4之上,堵塞效应显著,与开度为5°、−5°条件相比,面平均气膜冷却效率降低了13.6%。

多因素耦合的光伏水泵提水系统配置优化方法

为探究提水效率影响因素及系统配置对光伏水泵提水系统性能影响,该研究利用光伏水泵循环提水系统,探究不同辐照强度、阀门开度、提水高度下光伏组件利用效率、水泵运行效率、管路效率变化规律,并构建系统流量计算模型,根据该模型计算各个区间的提水量占比及不同提水高度下提水系统的参数,根据该系统整体效率和太阳能利用率确定最优提水高度;在此基础上,通过增加光伏组件面积及蓄水池数量降低提水系统提水成本及提高太阳能利用率,并确定提水成本最低时光伏组件面积和蓄水池数量。研究结果表明:确定光伏组件利用效率随辐照强度变化关系及水泵高效率运行区间,并确定光伏水泵最优提水高度为20 m,太阳能利用率为64.05%,整体利用效率为4.521%,提水成本为0.151元/m^(3);在最优提水高度的基础上,讨论了增加光伏板面积及蓄水池数量对太阳能利用率与提水成本的影响,当提水成本最低时,光伏板面积为3.71 m2,成本为0.143元/m^(3),太阳能利用率为90.83%;蓄水池数量为4个,成本为0.145元/m^(3),太阳能利用率为94.62%,表明增加光伏板面积和蓄水池数量有效降低提水成本和提高太阳能利用率,为光伏水泵提水系统配置的优化提供新思路。

蒸汽安全阀仿真分析与结构优化

采用ANSYS CFX流场仿真技术对优化后的锅炉管道用蒸汽安全阀流场排量和升力系数进行研究。结果表明:结构优化后的蒸汽安全阀开高设计合理,具有较好的排放性能,临界压力比在0.400~0.497之间,流阻损失小。阀瓣结构优化后,升力曲线得到改善,能够迅速达到设计开高要求,及时排放压力,减少颤振等问题的发生。

低温环境下柴油机冷起动性能试验研究

为改善柴油机冷起动性能,对某排量为2.5 L、采用进气加热器预热的柴油机开展环境温度为-30℃极寒条件下的冷起动试验,研究压缩比、节气门开度、预热方式、控制策略等对柴油机冷起动性能的影响。试验结果表明:压缩比为17.0,采用进气加热器时,柴油机加热时间较长,功率消耗大,无法正常起动;增大压缩比和节气门开度,能够提高压缩终了时缸内混合气的压力和温度,改善低温时柴油机的冷起动性能,但效果不佳;采用预热塞预热,柴油机起动迅速,起动时间为3.95 s,可有效提高柴油机冷起动性能;预热塞和燃油油束的相对距离通常设置为0.4~2.0 mm。

经济合理剥采比的计算方法和应用

以工程设计实例为依据,论述了露天开采经济合理剥采比的计算方法和适用条件。分析和探讨了支建煤矿经济合理剥采比计算方法,原矿盈利比较法、原矿成本比较法计算出来的经济合理剥采比分别为20.3m^(3)/m^(3)、26.9m^(3)/m^(3),取整后以20m^(3)/m^(3)作为矿床经济合理剥采比指标。

Wind-induced internal pressure fluctuations of structure with single windward opening

A frequency domain method for estimating wind-induced fluctuating internal pressure of structure with single windward opening is presented in this paper and wind tunnel tests were carried out to verify the theory. The nonlinear differential equation of internal pressure dynamics and iteration algorithm were applied to calculate fluctuating internal pressure and time domain analysis was used to verify the accuracy of the proposed method. A simplified estimation method is also provided and its scope of application is clarified. The mechanism of internal pressure fluctuation is obtained by using the proposed method in the frequency domain and a new equivalent opening ratio is defined to evaluate internal pressure fluctuation. A series of low-rise building models with various openings and internal volumes were designed for wind tunnel tests with results agreeing well with analytical results. It is shown that the proposed frequency domain method based on Gaussian distribution of internal pressure fluctuations can be applied to predict the RMS internal pressure coefficient with adequate accuracy for any opening dimensions, while the simplified method can only be used for structure with single dominant opening. Helmholtz resonance is likely to occur when the equivalent opening ratio is adequately high, and controlling individual opening dimension is an effective strategy for avoiding Helmholtz resonance in engineering.

Hydrodynamic Characteristics of Square Heaving Plates with Opening Under Forced Oscillation

The existence of the heaving plates can improve the heaving motion performance of an offshore structure significantly by providing both extra added mass and damping.In the current research,numerical investigation is carried out on the hydrodynamic characteristics of both isolated square heaving plate and double square heaving plates with opening by an immersed boundary-lattice Boltzmann method.The effects on hydrodynamic performance of plates due to Keulegan-Carpenter(KC)number,frequency number,opening ratio,opening distribution and spacing of plates are examined.It is found that the heaving plates with optimized opening ratio can provide additional damping compared with the plates without opening.Better hydrodynamic characteristics of double plates can be obtained with the increase of plate spacing.