微孔膜对锌空气电池失水的影响

将不同规格的微孔膜覆盖于锌空气电池气体扩散电极表面,探究微孔膜对锌空气电池失水和性能的影响。实验结果表明:在微孔间距小于临界间距时,覆盖微孔膜可使锌空气电池的失水量减少40%~80%,而不会阻碍氧气的传输。微孔数目越少,电池失水量越少,放电性能也越好。当微孔间距达到临界值时,电池失水量达到最小值。氧气在微孔膜上的通量远高于水蒸汽在微孔膜上的通量。     

锌空气电池电极表面渗液现象的研究

渗液问题是锌空气电池的主要问题之一.本文通过如下实验:聚四氟乙烯膜(PTFE,poly tetra fluoro ethylene)表面特性实验、电池风冷放电、空气电极电压实验和类列斯实验,对可能影响电池渗液的因素进行了研究.这些因素包括:PTFE膜、温度、电压、电荷总量、电解质溶液.实验结果表明:PTFE膜经过KOH溶液浸泡一段时间后,其接触角会显著变小,疏水性变差;温度和电压会对渗液现象产生影响;在各类电解质溶液中,KOH溶液渗液最严重;放电过程中的电荷总量对渗液问题基本没影响.实验结果分析得出,这类电池渗液主要是由于上述因素导致电解液表面张力变化,引起气液界面移动导致的.     

基于平面度的燃料电池电化学性能模拟

 固体氧化物燃料电池的翘曲会影响电极-盖板界面的接触情况,从而影响电化学性能,对相关制造工艺提出了很大的挑战．为了分析燃料电池平面度对放电过程的影响,揭示其潜在的风险,我们建立了两个基于有限元法的仿真模型,对考虑平面度缺陷的燃料电池封装和放电进行分析．在对固体氧化物燃料电池进行平面度测量的基础上,首先建立了具有真实燃料电池翘曲特性的几何模型,分析封装过程中接触压力的分布情况．然后将接触电阻的仿真结果导入到三维多物理场耦合模型中,模拟具有平面度缺陷的燃料电池电化学性能．计算结果展示了燃料电池两侧封装过程中接触压力的分布情况．通过对比有接触电阻和无接触电阻的燃料电池电流密度,分析了电池与盖板的接触对放电过程的影响．结果表明,燃料电池的凹陷面较难达到满意的接触状态,需要比凸起面更大的封装压力．燃料电池表面接触电阻的变化将引起电流传导路径的变化,产生局部高电流或低电流．这项工作强调了在燃料电池中保持均匀分布的接触电阻的重要性,为今后的优化工作奠定了基础．     

储层含水条件下致密砂岩/页岩无机质纳米孔隙气相渗透率模型

页岩及致密砂岩储层富含纳米级孔隙,且储层条件下页岩孔隙(尤其无机质孔隙)及致密砂岩孔隙普遍含水,因此含水条件下纳米孔隙气体的流动能力的评价对这两类气藏的产能分析及生产预测具有重要意义.本文首先基于纳米孔隙内液态水及汽态水热力学平衡理论,量化了储层孔隙含水饱和度分布特征;进一步在纳米孔隙单相气体传质理论的基础上,考虑了孔隙含水饱和度对气体流动的影响;最终建立了含水饱和度与气相渗透率的关系曲线. 基于本文岩心孔隙分布特征,计算结果表明:储层含水饱和度对气体流动能力的影响不容忽视,在储层含水饱和度20%的情况下,气相流动能力与干燥情况相比将降低约10%;在含水饱和度40% 的情况下,气相流动能力将降低约20%.      

直流电晕放电中的离子风增强带电气溶胶沉积

为解决我国水资源短缺问题和开发大气水资源的急迫需求,突破之前单电极电晕放电离子源的离子密度较低、气溶胶荷电困难的难题,开发了一套基于离子风增强带电气溶胶沉积的负直流电晕放电系统.该系统利用多个针电极与接地的网状电极,实现了大面积、阵列式的负直流电晕等离子体,可以对流经其中的气溶胶进行高效的荷电和处理.虽然单电极放电产生的开放空间中的离子密度是双电极放电的20倍,但双电极放电区域的电场约为单电极放电的15倍,放电电流也更大.强电场推动离子流进行定向运动,同时推动中性分子,使该装置可以产生速度高达2 m/s的离子风,而与之相比,单电极电晕放电的离子风速低于检测限.双电极电晕放电产生的离子风带动了云室中空气的流动,可以有效促进气溶胶的荷电、碰并以及在接地网状电极上的沉积,可以快速减少空气中的气溶胶密度,所需的时间仅为单电极放电的1/4.在水雾气溶胶的沉积实验中,其水雾的总沉积量是单电极放电的8.3倍.因此,双电极放电系统是诱导降水或消除致病生物气溶胶的潜在有效方法.     

储氢高压容器钢壁中氢的浓度分布规律研究

储氢高压容器中的氢通过渗透会进入容器钢壁并在钢壁中扩散,最终透过容器外表面进入容器存放环境中.在容器钢壁中的氢会引起材料力学性能变化,从而引起容器承载能力变化.要认识这些变化,首先就要了解氢在钢壁中的渗透、扩散规律和浓度的瞬态分布规律.针对球形高压容器外表面满足一般传质边界条件的情况,建立求解容器壁中氢浓度的解析理论模型,导出了容器壁中瞬态氢浓度和渗透到环境中的氢累积量的理论公式.通过解析计算,给出了器壁中氢浓度和氢在环境中的累积渗透量随时间的变化曲线,分析了相应的变化规律.这些公式和规律性认识为后续的容器壁材料力学性能分析和容器承载能力评估提供了前提.     

GAS-WATER TWO-PHASE DIFFUSION MODEL FOR UNSATURATED LAYERED COVER SYSTEMS

为了研究垃圾填埋场内部生物降解产生的气体(以甲烷为主) 和氧气等在非饱和覆盖层中的运移规律,建立了气体在成层非饱和覆盖层中的一维扩散模型. 该模型考虑了覆盖层含水量瞬态变化和气体扩散的耦合作用. 采用有限元多物理场耦合分析软件COMSOL Multiphysics 4.3进行求解. 其计算结果与前人实验结果能符合得很好. 研究结果表明,对典型垃圾填埋场中厚度为1m的非饱和黏土覆盖层,含水量变化对覆盖层中气体污染物的扩散运移有显著影响. 与含水量稳态变化情况相比,20 d到100 d的运移时间内同一覆盖层深度处耦合含水量作用下,气体相对浓度可以相差接近8倍. 含水量是气体在非饱和覆盖层中不稳定运移的重要影响因素.     

电阻率测试技术在沉积物-盐水-甲烷水合物体系中的应用

利用自制的一维天然气水合物(NGH)开采模拟实验系统,通过对NGH生成过程中电阻率、温度、压力等的变化规律进行分析,验证了在海洋沉积物体系中用电阻率法测试NGH的可行性。实验结果表明,电阻率可以清楚地反映NGH的成核及生长过程。NGH开始成核时消耗了溶液中的水分和甲烷气体,增加了离子之间的连通性,使电阻率降低;晶核开始生长为NGH后,由于生成的NGH类似于绝缘体,并且使得孔隙连通性变差,电阻率逐步升高,NGH大量生成后电阻率保持稳定。然后进行NGH降压分解实验,随着NGH的分解,NGH饱和度下降,电阻率也逐渐下降。     

钛合金表面双层辉光离子无氢渗碳层摩擦磨损性能研究

利用双层辉光放电离子渗碳原理,以格栅状高纯度固体石墨作为源极,钛合金作为阴极,氩气作为工作气体,依靠辉光放电和空心阴极效应在钛合金(Ti6Al4V)材料表面制备了具有特殊物理、化学性能的渗碳层;采用X射线衍射和辉光放电光谱分析了渗碳层的相组成及C元素分布;并考察了渗层的摩擦磨损性能.结果表明:复合渗碳层中形成了高硬相TiC及游离态C减摩相;渗层内C元素的含量呈梯度分布;经复合渗碳处理后材料的表面硬度大幅度提高,由表及里硬度成梯度降低;经渗碳处理后材料的减摩和抗磨性能显著改善,摩擦系数降低50%以上,比磨损率降低3个以上数量级.     

等离子体电解沉积的研究现状

等离子体电解沉积(PED)是一门新兴的材料表面处理技术.本文详细介绍了等离子体电解沉积的机 理及其在材料表面改性、生物材料、电子材料、高性能材料等方面的应用.其基本原理是: 当两极之间的电势差达到一定程度时, 电极与电解液界面处的电势突变产生的高电场强度, 可以击穿界面处的钝化膜、气体等电介质, 使得电极表面局部瞬间高温并发生复杂的物理、 化学反应, 从而在电极表面制备特定性能的陶瓷层或渗透层.在结构材料的应用方面, 可以 利用PED技术在铝合金、钛合金、镁合金等轻金属表面制备陶瓷层、可以对钢铁基体进行快 速碳氮共渗或涂覆金属镀层, 以提高这些材料的抗磨擦、耐腐蚀等性能.选择含有钙、磷元 素的电解液或是在电解液中添加羟基磷灰石粉末进行PED处理, 可以在钛合金表面制备具有 生物活性的陶瓷膜, 从而使植入体与自然骨形成分子水平的化学键合.选择适当的电解液, 可以制备BaTiO等离子体电解沉积;陶瓷层;表面改性;生物 材料;电子薄膜;DLC薄膜;氮化碳Plasma electrolytic deposition,Ceramic layer,Surface modification,Biomaterials,Electrolytic films,DLC films,Nitrogen-containing carbon films国家自然科学基金(50071066)2004年5月25日等离子体电解沉积(PED)是一门新兴的材料表面处理技术.本文详细介绍了等离子体电解沉积的机 理及其在材料表面改性、生物材料、电子材料、高性能材料等方面的应用.其基本原理是: 当两极之间的电势差达到一定程度时, 电极与电解液界面处的电势突变产生的高电场强度, 可以击穿界面处的钝化膜、气体等电介质, 使得电极表面局部瞬间高温并发生复杂的物理、 化学反应, 从而在电极表面制备特定性能的陶瓷层或渗透层.在结构材料的应用方面, 可以 利用PED技术在铝合金、钛合金、镁合金等轻金属表面制备陶瓷层、可以对钢铁基体进行快 速碳氮共渗或涂覆金属镀层, 以提高这些材料的抗磨擦、耐腐蚀等性能.选择含有钙、磷元 素的电解液或是在电解液中添加羟基磷灰石粉末进行PED处理, 可以在钛合金表面制备具有 生物活性的陶瓷膜, 从而使植入体与自然骨形成分子水平的化学键合.选择适当的电解液, 可以制备BaTiO等离子体电解沉积;陶瓷层;表面改性;生物 材料;电子薄膜;DLC薄膜;氮化碳Plasma electrolytic deposition,Ceramic layer,Surface modification,Biomaterials,Electrolytic films,DLC films,Nitrogen-containing carbon films国家自然科学基金(50071066)2004年5月25日等离子体电解沉积(PED)是一门新兴的材料表面处理技术.本文详细介绍了等离子体电解沉积的机 理及其在材料表面改性、生物材料、电子材料、高性能材料等方面的应用.其基本原理是: 当两极之间的电势差达到一定程度时, 电极与电解液界面处的电势突变产生的高电场强度, 可以击穿界面处的钝化膜、气体等电介质, 使得电极表面局部瞬间高温并发生复杂的物理、 化学反应, 从而在电极表面制备特定性能的陶瓷层或渗透层.在结构材料的应用方面, 可以 利用PED技术在铝合金、钛合金、镁合金等轻金属表面制备陶瓷层、可以对钢铁基体进行快 速碳氮共渗或涂覆金属镀层, 以提高这些材料的抗磨擦、耐腐蚀等性能.选择含有钙、磷元 素的电解液或是在电解液中添加羟基磷灰石粉末进行PED处理, 可以在钛合金表面制备具有 生物活性的陶瓷膜, 从而使植入体与自然骨形成分子水平的化学键合.选择适当的电解液, 可以制备BaTiO等离子体电解沉积;陶瓷层;表面改性;生物 材料;电子薄膜;DLC薄膜;氮化碳Plasma electrolytic deposition,Ceramic layer,Surface modification,Biomaterials,Electrolytic films,DLC films,Nitrogen-containing carbon films国家自然科学基金(50071066)2004年5月25日等离子体电解沉积(PED)是一门新兴的材料表面处理技术．本文详细介绍了等离子体电解沉积的机理及其在材料表面改性、生物材料、电子材料、高性能材料等方面的应用．其基本原理是：当两极之间的电势差达到一定程度时，电极与电解液界面处的电势突变产生的高电场强度，可以击穿界面处的钝化膜、气体等电介质，使得电极表面局部瞬间高温并发生复杂的物理、化学反应，从而在电极表面制备特定性能的陶瓷层或渗透层．在结构材料的应用方面，可以利用PED技术在铝合金、钛合金、镁合金等轻金属表面制备陶瓷层、可以对钢铁基体进行快速碳氮共渗或涂覆金属镀层，以提高这些材料的抗磨擦、耐腐蚀等性能．选择含有钙、磷元素的电解液或是在电解液中添加羟基磷灰石粉末进行PED处理，可以在钛合金表面制备具有生物活性的陶瓷膜，从而使植入体与自然骨形成分子水平的化学键合．选择适当的电解液，可以制备BaTiO3、SrTiO3、NaTaO3、SrZrO3等钙钛矿结构电子薄膜．利用有机溶液高电压电解，可以制备类金刚石(DLC)薄膜、氮化碳等高性能的材料．文中对PED涂层的残余应力、涂层与基体的结合力、界面断裂韧性、微观缺陷对宏观性能的影响等力学问题进行了讨论．等离子体电解沉积在轻金属特别是铝合金表面制备陶瓷层已经取得了成功，在钢铁材料的表面处理、DLC薄膜和氮化碳的制备等方面有一些初步进展，在生物活性陶瓷薄膜和电子薄膜方面也有应用前景．     

Dynamics of a “collective” bubble in a magma melt flow behind the decompression wave front

Specific features of the dynamics of the wave field structure and growth of a “collective” bubble behind the decompression wave front in the “Lagrangian” section of the formed cavitation zone are numerically analyzed. Two cases are considered: with no diffusion of the dissolved gas from the melt to cavitation nuclei and with the diffusion flux providing an increase in the gas mass in the bubbles. In the first case, it is shown that an almost smooth decompression wave front approximately 100 m wide is formed, with minor perturbations that appear when the front of saturation of the cavitation zone with nuclei is passed. In the case of the diffusion process, the melt state behind the saturation front is principally different: jumps in mass velocity and viscosity are observed in the vicinity of the free surface, and the pressure in the “collective” cavitation bubble remains unchanged for a sufficiently long time interval, despite the bubble growth and intense diffusion of the gas from the melt. It is assumed that the diffusion process (and, therefore, viscosity) actually become factors determining the dynamics of growth of cavitation bubbles beginning from this time interval. A pressure jump is demonstrated to form near the free surface.     

Measurement of Capillary Pressure–Saturation Relationships Under Defined Compression Levels for Gas Diffusion Media of PEM Fuel Cells

Measurements of capillary pressure–saturation relationships under defined levels of compression for gas diffusion layers (GDL) of polymer electrolyte membrane fuel cells as thin, mixed-wettable porous media have been carried out in a newly constructed device. This article lines out the construction principle of the cell and the preconditioning procedure of the sample to measure the capillary pressure–saturation relationships under well-defined conditions and loads of compression. Three commercial GDLs (Freudenberg H2315T10A, H2315T10AC1, and SGL Carbon BA24) have been examined and a compression-depending hysteresis of the capillary pressure–saturation relationship has been measured and identified.     

Balancing particle properties for practical lithium-ion batteries

As a state-of-the-art secondary battery, lithium-ion batteries (LIBs) have dominated the consumer electronics market since Sony unveiled the commercial secondary battery with LiCoO₂ as the negative electrode material in the early 1990s. The key to the efficient operation of LIBs lies in the effective contact between the Li-ion-rich electrolyte and the active material particles in the electrode. The particle properties of the electrode materials affect the lithium ion diffusion path, diffusion resistance, contact area with the active material, the electrochemical performance and the energy density of batteries. To achieve satisfied comprehensive performance and of LIBs, it is not only necessary to focus on the modification of materials, but also to balance the properties of electrode material particles. Therefore, in this review, we analyze the influence of particle properties on the battery performance from three perspectives: particle size, particle size distribution, and particle shape. A deep understanding of the effect and mechanism of particles on electrodes and batteries will help develop and manufacture practical LIBs.     

Heat Transfer and Gas Flow through Feed Stream within Horizontal Pipe

In the feeding process, the feed stream forms a moving packed bed of particle from the feedstock in the feed channel. When the feeding is at emergency interruption especially in the case of flooding and uncontrollable discharge, the hot gases from reactor would infiltrate into the feed stream. The high heat penetration into feed stream would affect the feeder performance. In this paper, transient thermal response of feed stream within horizontal pipe is described mathematically with a gas flow and heat transfer model. Influences of varied factors on the thermal penetration into feed stream are examined for different conditions. The temperature of the packed-bed particles and the gas velocity distribution curves are obtained for the feeding service at interruption and at normal operating conditions. The numerical results show that the thermal penetration to the packed-bed particles by the seepage flow fluid is high only in the position near the gas entrance. The thermal penetration depth tends to increase with the seepage flow velocity and decrease with feeding rate. There is no appreciable thermal penetration in the feed stream when the feeding service is at normal running. The operating conditions and the porosity of solid bed have importance effects on the gas velocity and temperature field in the thermal penetration zone. A test system is set up to determine the transient thermal response experimentally for the packed bed of particles within a horizontal pipe. The model results are found to compare favorably with the experimental data.     

A new approach to analyze entrance region mass transfer within a falling film

A boundary layer model is developed to analyze diffusion through a laminar falling film for incomplete penetration of the dissolved gas. Regarding the rather intractable nature of the problem, Kantorovich Integral Method is chosen. Accordingly, a mass transfer boundary layer is assumed to keep growing perpendicularly to the falling film until it hits the wall. Such an approach is superior to its preceding artworks based on Higbie’s penetration theory in terms of implementation of more realistic conditions/modeling assumptions. Furthermore, unlike penetration model, this approach gives a criterion whether the diffusion is complete. Comparing the two models, boundary layer model estimates up to 2.3 % larger mass transfer coefficients. Moreover, a sensitivity analysis of liquid velocity distribution upon Sherwood number is conducted. It is found that the local velocity at gas–liquid interface is of highest dominance. Experimental data of SO₂ absorption in water reported in literature is exploited to validate the model. It is shown that boundary layer model better fits the experimental data.     

Gas discharge from a tube into a vacuum with unsteady mass and energy addition

We examine the problem of ideal gas discharge from a cylindrical tube closed at one end into a vacuum, with unsteady mass and energy addition. The gas mass is formed by vaporization of the tube wall material due to the thermal flux from the heated gas. Under the assumption of uniform energy addition throughout the volume varying in accordance with the damped oscillation law, we obtain approximate relations for the mass of the discharging gas and the impulse of the pressure forces on the end wall as a function of time and energy.The resulting impulse values are compared with those determined for unsteady expansion into a vacuum of an ideal gas of given mass when energy is added to it. An increase of the impulse calculated by this technique in comparison with the value calculated using the proposed technique is shown.     

Investigation of time-dependent two-dimensional displacement in a porous medium in the self-similar formulation of the problem

Two-dimensional flow through a porous medium when a gas is injected into a permeable aquifer of infinite extension is investigated. The self-similar asymptotic solutions which describe the early stage of the time-dependent two-dimensional process of gas spreading along the caprock over the aquifer are constructed. The asymptotics are constructed on the assumption of the considerable aquifer thickness when the processes in the neighborhood of the aquifer base have no effect on flow along the caprock. Two-dimensional wave patterns describing the gas saturation distribution are investigated by means of the direct numerical simulation. The dimensions of the gas accumulation region are estimated as functions of the similarity parameters.     

用十字形超细药条离散群同步起爆实现超低比冲量加载

余弦分布载荷的化爆加载技术是高空核爆软X射线辐照下空间结构动态响应考核的主要手段。为适应新型空间飞行器结构考核的复杂构型、高同步性和低比冲量载荷设计要求,提出了一种用十字形超细药条离散群同步起爆实现超低比冲量加载的方法。实验结果验证表明：(1)所制作的十字形超细药条,最小截面尺寸为0.33 mm×0.5 mm,传爆性能稳定,并可通过直径0.5 mm的柔爆索直接起爆;(2)与相同布药密度的条状布药方式相比,布药空间均匀度提高了76.7%;(3)所采用的21点柔爆索同步起爆网络,起爆率达100%,起爆不同步性小于1μs。进一步建立了离散片炸药加载数值计算模型,分析了离散片炸药群同步起爆加载的比冲量空间分布和匀化规律,将匀化过程分为扩散段、叠加段和均匀段3个阶段;对比了方形、十字形、短条形3种形状药片阵列的比冲量演化过程,发现十字形药片所需匀化距离最短、均匀度最高,仅需约0.8倍布药间距即可使比冲量均匀度偏差降至10%以下。     

Numerical and experimental investigation of convective drying in unsaturated porous media with bound water

The heat and mass transfer in an unsaturated wet cylindrical porous bed packed with quartz particles was investigated theoretically for relatively low convective drying rates. Local thermodynamic equilibrium was assumed in the mathematical model describing the multi-phase flow in the unsaturated porous media using the energy and mass conservation equations to describe the heat and mass transfer during the drying. The drying model included convection and capillary transport of the free water, diffusion of bound water, and convection and diffusion of the gas. The numerical results indicated that the drying process could be divided into three periods, the temperature rise period, the constant drying rate period and the decreasing drying rate period. The numerical results agreed well with the experimental data verifying that the mathematical model can evaluate the drying performance of porous media for low drying rates. The effects of drying conditions such as the ambient temperature, the relative humidity, and the velocity of the drying air, on the drying process were evaluated by numerical solution.