轴流转桨式水轮机抬机现象处理

针对满天星水电站轴流转桨式水轮机组抬机现象,从理论上分析了抬机原因,并结合试验和现场处理经验提出了消除抬机现象的防范措施,对确保电站安全运行有指导意义,可供同类工程借鉴.     

轴流式水轮机反向水推力系数Kp的求取及抬机力计算

众所周知,轴流、斜流、贯流式水轮机在甩负荷过程中,往往出现抬机现象,使机组某些零件损坏,被迫停机检修,严重地影响了机组正常运行.造成机组抬机的原因,一是由于导水机构快速关闭,尾水管出现断流引起的反水锤;另一种是水轮机进入水泵工况运行的水泵升力;再则就是反水锤与水泵升力联合作用造成抬机.安装高程为负值的轴流式水轮机,产生抬机现象往往是由于反转水泵工况引起,而反向水推力系数K_p需试验确定,这就给抬机力的计算带来了很大的困难,所以本文着重探讨反向水推力系数K_p的求取,并讨论几个影响水推力的主要参数.     

八盘峡电站水轮发电机组抬机问题的分析和处理

文中叙述了水轮机组抬机的原因分析、防止措施、处理可能性的分析及处理效果等。     

薄叶气封流场结构与密封、扭矩特性的数值研究

采用CFX商业软件,数值模拟了薄叶气封内的三维流动,分析了薄叶气封的流场结构和密封特性以及扭矩随转速和抬起量的变化。结果表明,由于薄叶间距很狭窄,壁面对气体的黏性阻抗大于气流的膨胀加速,气体同时降低速度与密度,泄漏流量明显减小。此外,转子转数与薄叶抬起量的变化几乎不影响泄漏量。在转子转数一定时,薄叶上抬量愈小,转子承受的摩擦扭矩愈大。而当薄叶上抬量一定,转子转数增加,摩擦扭矩增大。     

轴承动态标高变化引起的转子油膜失稳的试验研究

设计出了适合于现场测试的汽轮机组轴承标高动态测量装置。利用该装置对国产某300MW汽轮机轴承的动态标高进行了测量。测量结果表明，该型汽轮机组在开机至带满负荷的过程中，2号轴承的标高持续上抬，最大上抬量达400μm，而3号轴承的标高有所下降，从而导致2号轴承的动态载荷过大，1号轴承的载荷减轻，进而使得1号轴承的油膜失稳，2号轴承的润滑状态恶化。     

一起东风4B型机车柴油机"飞车"原因浅析

1 事故概况 1998年12月8日,我段东风4B3372号机车担当沪杭线货物牵引任务,当列车运行至七宝站时,柴油机突然停机,此时柴油机转速为920r/min.副司机进动力室检查,发现极限调速器动作,抬复原手柄后起机,提转速到860r/min,柴油机极限调速器又动作,复原后再起机.由于一时紧张,连续两次起机均未成功.司机用筷子顶死DLS强迫起机,当转速上升至800r/min时,极限调速器再次动作,司机也未仔细检查,抬复原手柄继续起机.起机后柴油机转速直升至1400r/min,发生"飞车",造成机破.     

成品铝活塞清洗设备

改成品铝活塞现行人工手抬式水基热溶液浸洗，为链条传送式高压煤油喷洗、压缩空气吹干、光电计数式装置机械清洗，是一项用人少、效率高、成本低的较为先进的清洗技术。     

1E75F风冷汽油机通过鉴定

BJ15型手抬机动消防泵是1976年公安部七局向四川消防机械厂下达的一项科研任务。该产品同它的动力——IE75F二冲程风冷汽油机于1982年10月通过部级鉴定,现已投入小批生产。IE75F主要性能参数是:     

9E HRSG高压汽包上抬关联部件应力分析及监测

某热电厂早期进口的9E HRSG高压汽包上抬过程中,汽包或与汽包相连的部件可能产生过大的变形和应力。为评估抬升过程的安全性,采用有限元软件对汽包及关联部件进行应力应变分析,并对抬升过程进行动态监测。结果表明此次抬升对汽包、相关管道和锅炉今后的运行无影响。     

浅谈极软岩综放面两巷超前支护方式

简要介绍了铁法煤业集团有限公司小康煤矿在极软岩、易自燃的厚煤层中,针对综放工作面两巷超前软岩支护难题,采用了架设梯形木棚、锚杆、锚索、单体液压支柱、铰接梁、π钢抬棚、喷白泥浆等多种形式复合支护,取得较好的支护效果,确保了矿井安全高效集约化生产的需要.     

Development of methods for evaluating hydrogen compatibility and suitability

The embrittlement of metals exposed to hydrogen environments is well documented. With the deployment of hydrogen fuel cell vehicles in the consumer sector, there is a need to improve the engineering basis for the selection of materials of construction for equipment that stores and distributes high-pressure gaseous hydrogen. This brief overview summarizes publicly available guidance for evaluating materials compatibility with high-pressure gaseous hydrogen. Additionally, a new standard for measuring engineering data in gaseous hydrogen and evaluating materials suitability for service in gaseous hydrogen is introduced: the CHMC1 standard provides a general framework for qualifying materials for hydrogen service. The CHCM1 standard is unique in its broad scope and performance-based strategy for quantitatively assessing materials in their service environment and for the intended structural requirements.     

A panel cointegration analysis of the demand for oil in the Middle East

This article applies recently developed panel unit root and panel cointegration techniques to estimate the long-run income and price elasticities for oil in the Middle East. The results for the panel indicate that demand for oil is highly price inelastic and slightly income elastic in the Middle East. There is considerable variation in the results for the income variable across countries, with the coefficient on the income variable statistically insignificant for several countries. The coefficient on the price variable is statistically significant in all cases with the expected sign and the price elasticity is uniformly low. While the results for the income variable differ across countries, the results for the panel as a whole suggest that the demand for oil in the Middle East is being driven largely by strong economic growth, while consumers are largely insensitive to price changes.     

A mixture fraction framework for the theory and modeling of droplets and sprays

A mixture fraction is carefully defined for evaporation and combustion of droplets and sprays. The definition is valid at points in either the liquid or gas phases and care is taken to distinguish between definitions based on conserved scalars appropriate for heat transfer and those for mass transfer. Results are presented for Spalding B numbers and values of the mixture fraction at the droplet surface for the fast chemistry case and for the case where the droplet cannot sustain an envelope flame. The classical theory for an isolated droplet with spherical symmetry yields simple formulae when expressed in mixture fraction terms. New results are then readily obtained for several quantities of interest in spray modeling. The formulation provides a seamless unification of droplet evaporation processes with gas-phase mixing and reaction. Mixing in a turbulent spray jet is identified as a model problem that clarifies the role of large scale structures in the overall mixing process. Important constraints on the parameter space for sprays are shown to be greatly clarified when expressed in the mixture fraction framework. It is shown how the classical approach for segregated flow with Eulerian/Lagrangian modeling of dispersion and transfer processes in turbulent sprays can be upgraded to include fluctuations in the temperature and composition surrounding the droplets on top of those coming from the turbulent velocity fluctuations. Such preliminary calculations that assume a simple chemically reacting system can readily be upgraded using flamelet functions derived from counterflow experiments or computations: these can then form the starting point for full chemistry calculations using such approaches as conditional moment closure.     

Considerations for the selection of an applicable energy efficiency test procedure for electric motors in Malaysia: Lessons for other developing countries

Electric motors are a major energy-consuming appliance in the industrial sector. According to a survey, electric motors account for more than 70% of the total growth from 1991 to 2004 in electricity consumption in this sector in Malaysia. To reduce electricity consumption, Malaysia should consider resetting the minimum energy efficiency standards for electric motors sometime in the coming year. The first step towards adopting energy efficiency standards is the creation of a procedure for testing and rating equipment. An energy test procedure is the technical foundation for all energy efficiency standards, energy labels and other related programs. The test conditions in the test procedure must represent the conditions of the country. This paper presents the process for the selection of an energy test procedure for electric motors in Malaysia based on the country's conditions and requirements. The adoption of test procedures for electric motors internationally by several countries is also discussed in this paper. Even though the paper only discusses the test procedure for electric motors in Malaysia, the methods can be directly applied in other countries without major modifications.     

Derivation of the conditional moment closure equations for spray combustion

In this work we derive the fundamental equations for conditional moment closure (CMC) modelling of individual phases set in a two-phase flow. The derivation is based on the instantaneous transport equations for the single phase that involve a level set/indicator function technique for accounting for interfaces. Special emphasis is put on spray combustion with the CMC equations formulated for the gas phase. The CMC equations are to be viewed as an adjunct to existing methods for the modelling of the dynamics of sprays: they provide a refinement of the modelling of chemical reactions in the gas phase. The resulting CMC equations differ significantly from those already in use in the literature. They contain, of course, unclosed terms that need to be modelled. Investigation of the unclosed terms associated with evaporation at the droplet surface is well beyond the capabilities of laboratory measurement or direct numerical simulation. It is proposed that modelling of these terms be based on the well-established ‘laws’ of similarity between heat and mass transfer: an example is detailed for one example of the general modelling of the spray dynamics. Other unclosed terms are important throughout the gas phase. Models used for these terms in single-phase flows are reviewed and it is proposed that any modifications needed for these models be investigated by DNS of suitable model problems having good resolution of the flow and mixing in the inter-droplet space. It is proposed that a spray analogue of the scalar mixing layer that has been widely studied in single-phase flows be used as the model problem for such DNS studies and also for LES and RANS modelling.     

A compact,closed‐form solution for the optimum,ideal wind turbine

The classical momentum solution for the optimum induced‐flow distribution of a wind turbine in the presence of wake swirl can be found in many textbooks. This standard derivation consists of two momentum balances (one for axial momentum and one for angular momentum), which are combined into a formula for power coefficient in terms of induction factors. Numerical procedures then give the proper induction factors for the optimum inflow distribution at any radial station; and this, in turn, gives the best possible power coefficient for an ideal wind turbine. The present development offers a more straightforward derivation of the optimum turbine. The final formulas give the identical conditions for the ideal wind turbine as do the classical solutions—but with several important differences in the derivation and in the form of the results. First, only one momentum balance is required (the other being redundant). Second, the solution is provided in a compact, closed form for both the induction factors and the minimum power—rather than in terms of a numerical process. Third, the solution eliminates the singularities that are present in current published solutions. Fourth, this new approach also makes possible a closed‐form solution for the optimum chord distribution in the presence of wake rotation. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance analysis of the SOFC–MGT hybrid system with gasified biomass fuel

Analysis of electricity generation efficiency of the biomass SOFC–MGT hybrid system has been made for several cases of different composition of fuel relevant to typical air-, oxygen- and steam-blown biomass gasification processes. Reference case for comparison is the one where pure methane is used as fuel. In the analysis, multi-stage model for internal reforming SOFC module developed previously has been used with some modification. It is found that efficiency achieved for all the three cases of different types for biomass fuel is reasonably high and so that the biomass SOFC–MGT hybrid system is promising. However, in all the three cases, efficiency is lower than the counterpart of pure methane case, both in the SOFC module and in the hybrid system. Among the biomass fuel cases, efficiency is found to be highest with steam-blown biomass fuel both for the SOFC module and for the hybrid system. The lowest efficiency is found in the case of air-blown fuel. In addition, effects of higher steam content in the biomass fuel and variety in composition of biomass fuel for each gasifying agent are also studied.     

关于电厂凝汽器胶球清洗装置技术改造的探讨

针对火力发电厂所用凝汽器胶球清洗装置系统使用多年来所存在的问题,提出切实可行的技术改造方案。尤其对系统中的二次滤网、收球网和系统管路的安装这几个关键部套进行了深刻的剖析,结合多年来对此类设备进行过技术改造之后所取得的实践经验,综合提出本改造方案与同行和专家商确。