Evaluation of HT-PEM MEAs: Load cycling versus start/stop cycling

With the help of consistent conditions for improved batch production and defined quality standards, the lifetime of fuel cell systems should be improved and cost-intensive losses should be minimized at an early state in the production process. Within this work, we concentrated on two accelerated stress tests: load cycling at high current densities and start/stop cycling to compare high temperature (HT) polymer electrolyte membrane (PEM) membrane electrode assemblies (MEAs) of three suppliers to evaluate performances and degradation rates under such conditions. These MEAs have been investigated in-situ via electrochemical characterization. MEAs of three providers differ significantly in their performance and power output for both operation strategies. It was also shown that load cyclization causes greater stress on the MEA than start/stop cycling. Next to the manufacturer comparison, a batch-to-batch evaluation of one provider has been performed including micro-computed tomography (μ-CT) investigations and the determination of the tortuosity of the cathode side gas diffusion layers.     

老井重复压裂后产能预测新模型及其应用

致密油藏由于其自然禀赋较差,需要对已压裂过的层段进行二次或更多次压裂,才能维持期望的产量。在重复压裂期间,漏失的部分压裂液会通过渗吸作用将储层中的致密油置换出来,从而提高采收率。目前,考虑渗吸作用对产能影响的研究较少。文章将致密油井控制区域划分为三个渗流区域,基于达西定律,以渗流力学理论为基础,考虑启动压力梯度、重力和毛管力的作用影响,建立了考虑渗吸作用的致密油藏老井重复压裂后产能预测新模型;选取某地区致密油储层10口重复压裂井进行单井产能计算,计算结果与实际生产结果较接近、误差较小;渗吸作用对油井产能影响比较大,渗吸占比在2.97%～12.77%之间,平均值为6.87%。本文研究结果为致密油压裂后产能预测和压裂效果评价提供了参考。     

500kV交流输变电工程启动调试中断路器分合分试验的分析

在500kV交流输变电工程的建设完成后,需要对其进行启动调试,同时测试的次数要不少于3次的单分单和冲击合闸试验.但是在进行完这项试验后,为了安全考虑要在空载线路上进行分和分试验.本文主要根据实际经验分析出了在某些情况下,进行分和分试验存在一定的风险性,同时结合理论知识提出降低或去除这种风险的方法.     

Head Start: A Canadian model. A review of Poverty and the child, a Canadian study.

Reviews the book, Poverty and the Child, a Canadian Study by Thomas J. Ryan (1972). The primary purpose of the author of this book appears to be to persuade the Canadian government to establish a Canadian equivalent to the Head Start Project which was launched by the government of the United States in 1964. The principal thesis advanced is that the behavior which leads to poverty is learned during the first years of life and most of the volume is devoted to the presentation of research findings which lend support to this view. Finally, it is argued that effective long range plans for interrupting the poverty cycle must involve the socialization or re-socialization of the children of welfare families. In so far as this book points out the urgent need for innovative effort and research on behalf of not only the disadvantaged but all Canadian children and a national commitment which would make this possible it has been an important contribution. However, it probably will not be viewed as a significant addition to the literature in child study. Some will regard the emphasis placed on the shaping effects of the environment as excessive. Furthermore many will be surprised that so little attention is paid to the current disenchantment with Head Start as it has been implemented in the United States. If Canada is to launch a program of compensatory education it should not repeat the mistakes made south of the border. Perhaps here we might begin with a new perspective namely to identify and build on strengths rather than capitulate to the social pathology model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

冶金机械设备运行系统常见故障分析与排除

当前我国重工业发展迅速,冶金工业的技术实力也随之不断加强,其中冶金机械设备在冶金行业的发展中起到支柱作用,逐步向现代化与大型化方向发展,对于机械设备在运行过程中出现的故障,一直是冶金企业需要迫切解决的问题,为此对机械设备运行系统的常见故障进行分析与排除。利用振动诊断技术,对机械设备液压系统进行排查,保证系统压力的稳定;针对启动电机运转无力的问题,通过对启动机的线路和接线柱进行短接,从而排除故障。     

汽车电控机械式自动变速系统微机控制系统及过程控制算法设计

采用8098单片机为系统的控制中心,完成以下工作：对微机控制系统的硬件电路结构进行了设计和调试；对车辆起步过程中的离合器行程实施多目标综合优化与模糊控制相结合的脉宽调制控制,同时使油门开度的控制及时适应其目标值(即司机意图)和离合器行程控制的变化,较完善地解决了以单片机同时控制两个外设的CPU占用问题；提出换档过程中对油门实施数字PD调节,以减小换档冲击和振荡,实现较平稳换档的方案；编制了基本能够符合车辆复杂的操纵规程,适应千变万化的实时工况的主控程序,达到按照车辆的动态三参数换档规律实现自动换档,和对紧急制动、停车等各种工况的及时、正确处理；针对汽车运行环境恶劣的情况,提出了较为具体的系统抗干扰方案。     

PEM Fuel Cell Stack Cold Start Thermal Model

For passenger fuel cell vehicles (FCVs), customers will expect to start the vehicle and drive almost immediately, implying a very short system warmup to full power. While hybridization strategies may fulfill this expectation, the extent of hybridization will be dictated by the time required for the fuel cell system to reach normal operating temperatures. Quick‐starting fuel cell systems are impeded by two problems: (i) the freezing of residual water or water generated by starting the stack at below freezing temperatures and (ii) temperature‐dependent fuel cell performance, improving as the temperature reaches the normal range. Cold start models exist in the literature; however, there does not appear to be a model that fully captures the thermal characteristics of the stack during sub‐freezing startup conditions. Existing models lack the following features: (i) modeling of stack internal heating methods (other than stack reactions) and their impact on the stack temperature distribution and (ii) modeling of endplate thermal mass effect on end cells and its impact on the stack temperature distribution. Unlike a lumped model, which may use a single temperature as an indicator of the stack's thermal condition, a model considering individual cell layers can reveal the effect of the endplate thermal mass on the end cells, and accommodate the evaluation of internal heating methods that may mitigate this effect. This paper presents and discusses results from simulations performed with a new, layered model.     

大型高压电动机的起动设计

阐述了企业 6kV电网供电时 ,在电网短路容量较小而高压电机容量较大情况下起动方案的选择、起动设计的计算、分析和确定 ,以及在实际开车时起动数据的考核等     

Atlas空压机启动时频繁跳车处理经验总结

介绍一起30000 m3/h空分设备正常开车过程中空压机频繁跳车的故障,阐述了故障处理的思路与解决方案,总结了经验,并对空压机的维护提出了更高的要求。     

软件的一种加密原理及实现方法

介绍采用特殊磁道接缝加密技术制作的母盘作为安装软件的防拷贝磁盘;采用硬盘安装参数经加密、保存、比较、判别确定是否为盗版软件,达到软件的防非法拷贝