Influence of bio-inspired flow channel designs on the performance of a PEM fuel cell

Performance of the proton exchange membrane fuel cell(PEMFC) is appreciably affected by the channel geometry. The branching structure of a plant leaf and human lung is an efficient network to distribute the nutrients in the respective systems. The same nutrient transport system can be mimicked in the flow channel design of a PEMFC, to aid even reactant distribution and better water management. In this work, the effect of bio-inspired flow field designs such as lung and leaf channel design bipolar plates, on the performance of a PEMFC was examined experimentally at various operating conditions. A PEMFC of 49 cm~2 area, with a Nafion 212 membrane with a 40% catalyst loading of 0.4 mg·cm-2 on the anode side and also 0.6 mg·cm~(-2) on the cathode side is assembled by incorporating the bio-inspired channel bipolar plate, and was tested on a programmable fuel-cell test station.The impact of the working parameters like reactants' relative humidity(RH), back pressure and fuel cell temperature on the performance of the fuel cell was examined; the operating pressure remains constant at 0.1 MPa. It was observed that the best performance was attained at a back pressure of 0.3 MPa, 75 °C operating temperature and 100% RH. The three flow channels were also compared at different operating pressures ranging from 0.1 MPa to 0.3 MPa, and the other parameters such as operating temperature, RH and back pressure were set as 75 °C,100% and 0.3 MPa. The experimental outcomes of the PEMFC with bio-inspired channels were compared with the experimental results of a conventional triple serpentine flow field. It was observed that among the different flow channel designs considered, the leaf channel design gives the best output in terms of power density. Further,the experimental results of the leaf channel design were compared with those of the interdigitated leaf channel design. The PEMFC with the interdigitated leaf channel design was found to generate 6.72% more power density than the non-interdigitated leaf channel design. The fuel cell with interdigitated leaf channel design generated5.58% more net power density than the fuel cell with non-interdigitated leaf channel design after considering the parasitic losses.     

使用加热空气的预混天然气催化燃烧的实验研究

In this paper the premixed catalytic combustion emissions such as CO, unburned hydrocarbon （UHC）, NOx and the temperature distribution in the catalytic monolith with ultra low concentration of Pd were studied. Three types of monoliths were used for experiments and the temperature of preheated air was respectively 50℃, 100℃ and 200℃. The results showed that preheated air made radial temperature in the catalytic monolith uniform which helped to avoid local hot spots so as to decrease NOx emission. The experiment also proved that the shorter monolith showed much better catalytic combustion performance than longer one and the temperature at the exit of the shorter monolith was relatively lower. On the contrary, the temperature was higher in the longer monolith and the lethal NOx emission was slightly increased.     

毛竹的主要化学成分分析及热解

In recent years, great attention has been paid to the exploitation and use of biomass energy.Using bamboo as the raw material to produce energy and other chemicals is significantly important. A primary study was made on the pubescens, one kind of bamboo distributed broadly in China with fast growth rate. The contents of cellulose, hemi-cellulose, and lignin in different parts of pubescens with different growth ages, as major components of the cell wall, were determined. The analysis procedures were as follows, firstly the substances other than the above mentioned three were removed chemically,then the hydrolyzed cellulose liquid was oxidized with excess oxidants, and at last titrated. Pubescens powder was packed into the quartz tube reactor, then was heated from room temperature to 300, 350,400, 450, 500, 550℃ and 600℃ respectively in flowing N2. Pyrolysis was held at the final temperature for 10 h. The liquid products were analyzed with GC/MS. The main products in the liquid obtained were.acetic acid, 2,6-dimethoxy phenol, 2,3-dihydrobenzofuran, etc. The pyrolysis temperature exerted great effect on the composition of the liquid products. The distribution of the products could be regulated by controlling pyrolysis temperature.     

Experimental determination of gas holdup and volumetric mass transfer coefficient in a jet bubbling reactor

The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor(JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, p H and superficial gas velocity. The reactor diameter and height were 11 and 30 cm,respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40℃, and two p H values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s~(-1) range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution(BSD) in different superficial gas velocities. The results indicated that at the same temperature but different p H, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the p H value of 6 was higher than that at the p H = 3. At a constant p H but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40℃ were higher than that of the same at 20℃. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient(kla) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs.     

升温升压过程对聚丙烯在超临界水中降解的影响

The effect of increasing course of temperature and pressure on polypropylene （PP） degradation in supercritical water was investigated for developing a process of recycling waste plastic. A group of experiments was carded out in a reaction system at a pressure of 26MPa, temperature of 380℃ or 400℃ for 30min, 70min, and 120min by Course One （the increasing course of temperature and pressure is via gaseous regions to supercritical regions）, and the other group was carried out at corresponding holding conditions by Course Two （the increasing course of temperature and pressure is via liquid regions to supercritical regions）. The time of the increasing courses was about 30min. Products were analyzed by Ostward-type viscometer, gaseous chromatography, and mass spectrometers （GC/MS）. Characterization results suggested that different increasing courses of temperature and pressure would give rise to different results, although they were treated under the similar holding conditions. It was also found that Course Two was more effective on PP degradation in supercritical water.     

金属卟啉催化的甲苯氧化及工艺优化

Catalytic activities of a series of metalloporphyrin complexes in selective aerobic oxidation of toluene were investigated.The effects of different central metal ions in metalloporphyrins[T（p-Cl）PPMCl（M=Fe,Co,Mn,Cu）] on the reaction course had been examined and it was found that T（p-Cl）PPCu presented the highest catalytic activity in the reaction.The reaction conditions of toluene oxidation were optimized by using orthogonal experiment design.Five relevant factors were investigated：temperature,air pressure,catalyst loading,air flow rate and reaction time.The effects of the five factors on both toluene conversion and total yield of benzaldehyde and benzyl alcohol were discussed.The research results showed that the reaction temperature was the most significant factor influencing toluene oxidation.On the basis of the margin analysis,the optimum conditions for the toluene conversion and the total yield of benzaldehyde and benzyl alcohol respectively were achieved,under which the toluene conversion was up to 14.67%and the total yield of benzaldehyde and benzyl alcohol reached 5.89%.     

电极极性影响EHD强化沸腾传热的机理

The effects of electrode polarities on EHD enhancement boiling heat transfer were investigated theoretically and experimentally based on the analysis of electric field distribution affected by superheat boundary layer and charge injection. The results showed that electric field distribution was changed by the charge induced by temperature gradients in the superheat boundary layer, but the change was independent of electrode polarities. However, when electric charge injection occurred, the electrode applied positive high voltage might generate different characteristics of charge injection from that generated by applied negative high voltage. If the electric field on the surface of heat transfer increased due to charge injection, the augmentation effects would increase. The experiments demonstrated that positive high voltage gave larger enhancement factors than negative high voltage. The experimental phenomena could be interpreted well on the basis of charge injection characteristics.     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

酯化反应蒸馏过程的模型化及模拟研究

In this paper,a generalized model of the reactive distillation processes was developed via rate-based approach. The homotopy-continuation method was employed to solve the complicated nonlinear model equations efficiently. The simulation on the reactive distillation processes was carried out with the profiles of stage temperature,composition and flow rate for both vapor and liquid phases obtained. Based on careful analysis of the simulation results, the pitfalls in experimental design were detected. Finally, a software package for the simulation of reactive distillation processes was developed.     

空气与水逆流直接接触热质交换模型计算及与实验比较

According to general equations deducted from a model of heat and mass transfer of air and water in direct contact counter flow reported in the author‘s previous work, the outlet parameters of air and water counter flow through a paper wet pad were calculated by using the MATLAB-software. Comparing the calculation results with experiment data of prior researchers, the deviation of calculated outlet air wet bulb temperature from experimental outlet air wet bulb temperature was less than 10%, the deviation of calculated outlet water temperature from experimental outlet water temperature was less thang 9%, and the deviation of calculated outlet air dry bulb temperature from experimental outlet air dry bulb temperature was less than 10% when NTUh was more than 0. 6. The deviation of calculated outlet air dry bulb temperature from experimental outlet air dry bulb temperature was more than 10% when NTUh was less than 0. 6. The model calculations were in good agreement with experiments and the general equations could be used to design evaporation cooling equipment, such as wet pad and so on.     

移动硬盘盒精密热流道注塑模具设计

热流道注塑模具在模具行业中的应用越来越广泛,采用热流道系统不仅可以保证塑件质量、提高材料的利用率,还能显著提高塑件的生产效率。通过对移动硬盘塑料件的结构及成型工艺特点进行分析,设计了移动硬盘塑料件热流道注射模具,重点对热流道模具热平衡计算和热流道浇注系统进行了分析计算,模具采用单点热流道、一模两件潜伏式浇口、外滑块抽芯机构及斜推杆抽芯成型倒扣设计。实践证明,该移动硬盘塑料件模具设计结构合理,在提高塑料件成型质量的同时,提高了材料的利用率及生产效率,为同类结构特点的热流道注塑模设计提供了参考。     

多点热流道模具流道板的结构设计

本文对热流道组件的关键部件流道板的结构特点、设计要点作了较详细的讨论,并结合一模四腔热流道模具的实验研究予以具体说明。     

浇口偏置笔记本电脑外壳注塑模设计

通过对笔记本电脑外壳塑料件的结构及成型工艺特点进行分析,设计了浇口偏置热流道注塑模。模具采用单点偏心热流道设计、偏置扇形浇口侧进料设计及斜推杆侧向抽芯成型倒扣设计,有效地解决了塑料件成型可能引起的质量问题。实践证明,该模具设计结构合理、紧凑,动作可靠,在提高塑料件成型质量的同时进一步降低了制造成本,为同类结构特点的注塑模设计提供了参考。     

基于Pro/E旋转桶热流道注塑模设计

热流道模具非常适合成型薄壁大型塑件,针对洗衣机旋转桶塑件,利用CAE软件进行充型模拟,确定最佳进胶点数量与位置,按照理论模型进行流道尺寸计算。基于Pro/E的模具设计模块,进行三维热流道浇注系统设计,进行动、定模模仁的拼接、镶件设计,利用EMX提供的标准件完成模具全三维装配设计。通过参数化建模技术,实现产品设计、模具设计和模具制造3个环节的并行开发。模具投产后,塑件尺寸、形位符合要求.     

面像识别机外壳热流道注塑模具设计

分析了面像识别机外壳的成型工艺,介绍了一种成型该制品的热流道注塑模具的设计方法。首先利用Moldflow软件对制品进行了模流分析,确定了浇口的数量和位置,进而设计了最佳的浇注系统;并通过冷热流道的模流分析对比确定了热流道的结构,设计了热流道系统的结构和尺寸。此外,在模流分析的基础上,根据制品的精度要求及模具结构要求,设计了动模倒装结构和定距分型机构,实现了制品的反向推出;最后生成了整个模具的总装配图。     

透明壳盖件热流道注塑模的设计

介绍了大批量、高精度要求的透明壳盖产品的热流道注塑模设计,详述了该热流道注塑模具的设计思路、总体结构和工作原理。根据产品结构,在模具上设计了X型4点进料的热流道系统、精度定位机构、推管推杆脱模机构及循环冷却系统。模具结构精密紧凑,能有效地节约原料,提高产品质量,易于自动化生产。     

水表PMMA字轮盒热流道注塑模具设计

通过对水表PMMA字轮盒的结构和成型工艺分析，设计了其热流道注塑模具的总体结构。并详细介绍了热流道系统的结构和先复位机构。采用该模具成功实现了以热流道形式对字轮盒进行大批量自动化生产。     

水表PMMA字轮盒热流道注塑模具设计

通过对水表PMMA字轮盒的结构和成型工艺分析,设计了其热流道注塑模具的总体结构,并详细介绍了热流道系统的结构和先复位机构。采用该模具成功实现了以热流道形式对字轮盒进行大批量自动化生产。     

某汽车行李箱尾门槛板成型CAE优化分析

汽车行李箱尾门槛板内饰件因其注塑量大,流道流程长,因而采用热流道模成型较为适宜。模具设计中,浇口位置和冷却方式的选择对产品的成型质量起到关键作用。利用MoldFlow软件对浇注系统、冷却系统及成形工艺的设定进行了两种方案的有限元模拟分析。通过CAE模流分析,对塑件在模具中的浇口位置和冷却方案进行了优化,改善了模具成型中如翘曲变形、熔接痕等潜在的缺陷,获得了合理的热流道注射模设计结构,提高了塑件成型质量,有效地缩短了汽车行李箱尾门槛板内饰件注塑模具的研制周期。     

游戏机手柄热流道立式注塑4层叠层注塑模设计

设计了一种4层叠层模用于实现游戏机手柄的高效率注塑生产,解决了塑件成型时在保证塑件成型精度的基础上,单次注塑量产数量4倍倍增难题。4层叠层模的结构由4层结构相同的单层模具通过一定的空间组序排列组装后,应用立式注塑机来进行注射成型。单层模结构设计采用两板式2次开模热流道浇注两板模形式,第一次开模用于热流道嘴与塑件的冷流道部分分离,第二次开模用于塑件从型腔镶件中脱模脱出。为解决单层模做4层叠层组合后,顶出板无动力顶出的问题,在单层模的模架模板侧边对称设置了拉杆,将单层模在开模动力转化为单层模中顶出板的顶出拉力,巧妙地解决了单层模做4层叠层安装后各单层模的顶出元件顶出板无推动力的问题。模具结构布局及机构的驱动设置设计合理,有较好的工程设计参考意义。