8.9 L柴油机用高压油管的设计与研究

为了验证直列泵8．9L柴油机用高压油管的设计,采用模拟计算和发动机整机试验相结合的方法进行了研究开发。首先使用Pro／E完成高压油管结构设计、3D模型和整机布置,然后运用ANSYS对高压油管进行FEA模态分析,最后进行了发动机性能试验、油管应力测试和发动机耐久性试验。同时还建立了高压油管设计的标准化工作流程。结果表明:高压油管设计满足发动机欧-Ⅱ排放、整机性能、可靠性及整机布置等所有要求。     

Reliability assessment of underground pipelines under the combined effect of active corrosion and residual stress

Lifetime management of underground pipelines is mandatory for safe hydrocarbon transmission and distribution systems. Reliability analysis is recognized as a powerful decision-making tool for risk-based design and maintenance. Both the residual stresses generated during the manufacturing process and in-service corrosion reduce the ability to resist internal and external loading. In this study, the residual stress distribution in large diameter pipes has been characterized experimentally in order to be coupled with the corrosion model. During the pipe lifetime, residual stress relaxation occurs due to the loss of pipe thickness as material layers are consumed by corrosion. The reliability-based assessment of residual stress effects is applied to underground pipelines under a roadway, with and without active corrosion. It has been found that the residual stress greatly increases the failure probability, especially in the early stage of the pipe lifetime.     

Pressure Drop Control Using Multiple Orifice System in Compressible Pipe Flows

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钢套筒混凝土压力管道内水压承载性能有限元分析

为了研究新型结构钢套筒混凝土压力管道(SSCP)的内水压承载性能,建立SSCP非线性有限元模型,通过施加管道自重、管道内水重和逐级增大的均匀内水压力模拟SSCP从生产到运行各个阶段的受力状况,得到各工况下SSCP的应力变化特点和塑性开展规律。结果表明,SSCP在内水压力较小、未达到开裂压力Pb的工况下处于完全弹性状态,各构件应力均能满足正常工作要求,安全度较高。随着内水压力的增加,达到Pb后,管底混凝土管芯内表面最先出现塑性并不断沿轴向和管腰方向扩展。在施加内水压力过程中,内层钢筒承担的拉应力大于外层钢筒。     

Transient flow field and performance analysis of a claw pump for FCVs

The claw-type hydrogen pump has been applied in fuel cell vehicles (FCVs) because of its compact structure, high reliability, and oil-free quality. In this study, a three-dimensional transient computational fluid dynamics (CFD) modelling of a claw-type hydrogen pump used in FCVs was established. Hexahedral structured grids were generated and updated at an increment of 3° in rotating angle to ensure the mesh quality of the whole solving process. The leakage of radial clearance (RC) and axial clearance (AC) was considered. The presented modelling and simulation methods were validated by operating a claw pump at different pressure ratios. The pressure and velocity vector fields in both AC and middle plane, along with the mechanism of the fluid field distribution were analyzed in detail. The in-depth relationship amongst the fluctuation of discharge pressure, outlet mass flow rate and discharge area during the whole working process was revealed. P-θ and V-θ diagram of the whole operating cycle were analyzed. The influence of AC and RCs respectively on the volumetric efficiency of a claw pump was compared and evaluated. It is concluded that back flow in suction pipe happened near 360° as part of the discharge chamber was cut off from the exhaust port and high pressure gas from carryover flowed back into the inlet pipe. The pressure increase during the displacement process, theoretically zero, is actually significant and even comparable to the pressure increase during the compression and discharge process. In addition, volumetric efficiency is most sensitive to axial clearance, followed by radial clearance between rotor and casing, while radial clearance between the rotors has the least influence.     

Quantifiable destructive and non-destructive methods for lifetime assessments of Eskom''s high temperature plant

Over long exposure periods high temperature and high pressure components suffer degradation of their properties and this accumulated damage subsequently leads to cracking and failure. State-of-the-art quantifiable destructive and non-destructive methods for lifetime assessment of reliability and maintainability of Eskom's plant are used. Geometry, strain rate, mode of load, materials, fabrication technique and history are all important factors affecting the component life and material microstructure. Novel cost-effective techniques have been developed by Eskom for the assessment of the effective temperature of components operating in the creep regime. Accumulated creep strain is measured directly on the component during a certain service interval. This information is then used to calculate the remanent life of a component. A library of more than 30 000 metallographic replicas representative of approximately 6000 components exists and these ‘fingerprints’ are of great value in the overall life predictions.     

Mass transfer characteristics of the hydrophilic membrane with the isolation of heat transfer effect by isothermal bath

The efficiency and lifetime of a proton exchange membrane fuel cell (PEMFC) system is critically affected by the humidity of incoming gas which should be maintained properly for normal operating conditions. But the experimental characteristics of the humidifier are rarely reported. Water transport through the hydrophilic membrane is a coupled phenomenon of heat and mass transport. In this study, a laboratory scale test bench is designed to investigate the characteristics of water transport through the hydrophilic membrane. The mass transfer capability of the hydrophilic membrane is evaluated over various flow rates, temperature, pressure, and flow arrangements. In the experiment, the test bench is submerged in a constant temperature bath in order to isolate the effect of temperature variation between dry air and humid air. The results show the water transport of the hydrophilic membrane is significantly affected by operating temperature and operating pressure. Additionally, the flow arrangement demonstrates a minor effect but it should be considered along with the heat transfer effect.     

Investigation on the calculation model of burst pressure for tube and casing under practical service environment

The burst strength of tube and casing is important to the storage and development of hydrogen gas and natural gas. Studies on the current classic models to calculate burst pressure of tube and casing show that they are not suitable to predict the burst pressure of tube and casing under modern manufacturing technology level due to without considering the effects of radius-thickness ratio and practical service environment (capped-end condition and capped-open conditions). Hence, for the thin-wall (20＜D/t＜40) tube and casing, based on the deformation instability and finite strain theory, this paper has established the equations to calculate burst pressure of thin-wall pipe under capped-end condition and capped-open conditions by adopting the power-law constitutive relation. For the thick-wall (5 ≤ D/t ≤ 20) tube and casing, based on the failure criterion of through-wall yield, the unified algorithms of burst pressure for thick-wall pipe under capped-end condition and capped-open condition have been derived by adopting unified strength theory. The burst pressure model which can calculate the burst pressure of thick-wall pipe under modern manufacturing technology level, has been presented combining with weighting twin shear stress yield criterion. Numerical and experimental comparisons show that the calculated results of this equation are closest to the test data, and its accuracy and reliability are obviously superior to other models, and the service environment of tube and casing has a great impact on the burst pressure.     

System reliability of corroding pipelines

A methodology is presented in this paper to evaluate the time-dependent system reliability of a pipeline segment that contains multiple active corrosion defects and is subjected to stochastic internal pressure loading. The pipeline segment is modeled as a series system with three distinctive failure modes due to corrosion, namely small leak, large leak and rupture. The internal pressure is characterized as a simple discrete stochastic process that consists of a sequence of independent and identically distributed random variables each acting over a period of one year. The magnitude of a given sequence follows the annual maximum pressure distribution. The methodology is illustrated through a hypothetical example. Furthermore, the impact of the spatial variability of the pressure loading and pipe resistances associated with different defects on the system reliability is investigated. The analysis results suggest that the spatial variability of pipe properties has a negligible impact on the system reliability. On the other hand, the spatial variability of the internal pressure, initial defect sizes and defect growth rates can have a significant impact on the system reliability.     

泵站压力管道振动特性分析及减振优化设计

为探究泵站压力管道的不同布置形式对管道振动的影响,选取宁夏盐环定泵站工程二泵站#1压力管道为研究对象,建立基于流固耦合的泵站压力管道水流ALGOR数值模型,并采用DASP振动测试系统获取振动信号对模拟结果进行验证,分析压力管道水流流态对管道振动的激励特征并提出优化设计方案。结果表明,压力管道进水管处、支管总管相接处及总出水管处均有强烈的振动,但进水管的振动较出水总管振动更为强烈;减振优化设计方案中,调整支管距离对降低水流对管道振动的激励效果微弱,增大管径及改变总管走向对其效果较好,其中总管走向在2°～5°之间较佳,不仅能降低管道振动,而且能减少泵站能耗损失。研究结果可为高扬程泵站压力管道的优化设计提供理论依据。     

Power switch failures tolerance and remedial strategies of a 4-leg floating interleaved DC/DC boost converter for photovoltaic/fuel cell applications

In recent years, many researchers have proposed new DC/DC converters in order to meet the fuel cell requirements. The reliability of these DC/DC converters is crucial in order to guarantee the availability of fuel cell systems. In these converters, power switches ranked the most fragile components. In order to enhance the reliability of DC/DC converters, fuel cell systems have to include fault-tolerant topologies. Usually, dynamic redundancy is employed to make a fault-tolerant converter. Despite this kind of converter allows ensuring a continuity of service in case of faults, the use of dynamic redundancy gets back to increase the complexity of the converter. In order to cope with reliability expectations in DC/DC converters, floating interleaved boost converters seem to be the best solution. Indeed, they have much to offer for fuel cells and DC renewable energy sources (i.e. photovoltaic system), including reduced input current ripple and reliability in case of faults. Despite the offered benefits of this topology, operating degraded modes lead up to undesirable effects such as electrical overstress on components and input current ripple increasing. The aim of this paper is to carry out a thorough analysis of these undesirable effects and to propose remedial strategies to minimize them.     

Introduction of SCRI model for creep rupture life assessment

A “service condition-creep rupture property” interference model (SCRI model for short) based on Z parameter method is proposed to predict the reliability of creep rupture life for high temperature components. The dispersibility of creep rupture property and the fluctuation of service conditions such as servicing temperature and stress are considered in this model. The scattering of creep rupture data is generally supported by normal distribution. Monte-Carlo method is applied to evaluate the reliability at a certain operating condition by simulating the fluctuation of service temperature and stress. HK40 steel has been used as an example to demonstrate the influence of creep rupture property dispersibility and operating condition fluctuation on the result of reliability evaluation.     

Development and CFD analysis for determining the optimal operating conditions of 250 kg/day hydrogen generation for an on-site hydrogen refueling station (HRS) using steam methane reforming

The objective of this study to develop and undertake a comprehensive CFD analysis of an effective state-of-the-art 250 kg/day hydrogen generation unit for an on-site hydrogen refueling station (HRS), an essential part of the infrastructure required for fuel cell vehicles and various aspects of hydrogen mobility. This design consists of twelve reforming tubes and one newly designed metal fiber burner to ensure superior emission standards and performance. Experimental and computational modeling steps are conducted to investigate the effects of various operating conditions, the excess air ratio (EAR) at the burner, the gas hourly space velocity (GHSV), the process gas inlet temperature, and the operating pressure on the hydrogen production rate and thermal efficiency. The results indicate that the performance of the steam methane reforming reactor increased significantly by improving the combustion characteristics and preventing local peak temperatures along the reforming tube. It is shown that EAR should be chosen appropriately to maximize the hydrogen production rate and lifetime operation of the reformer tube. It is found that high inlet process gas temperatures and low operating pressure are beneficial, but these parameters have to be chosen carefully to ensure proper efficiency. Also, a high GHSV shortens the residence time and provides unfavorable heat transfer in the bed, leading to decreased conversion efficiency. Thus, a moderate GHSV should be used. It is shown that heat transfer is an essential factor for obtaining increased hydrogen production. This study addresses the pressing need for the HRS to adopt such a compact system, whose processes can ensure greater hydrogen production rates as well as better durability, reliability, and convenience.     

Bubble nucleation in advanced ODS ferritic steels for fusion applications

Abstract

Oxide dispersion strengthened (ODS) ferritic steels have been suggested as an advanced ferritic steel for service as the structure of a fusion power plant operating at high temperatures (up to 800°C) as well as low swelling fast reactor fuel cladding. Powder metallurgical methods are used to fabricate such steels, which contain a fine dispersoid of nanometric scale strengthening particles. In this paper, the author investigates the possibility that the ODS particles not only strengthen the steel, but also act as centres for the nucleation of bubbles containing transmutation helium atoms, generated over the 5–10 year lifetime in the replaceable first wall blanket by 14 MeV fusion neutrons. Calculations suggest that the lifetime swelling of such materials will be of the order of 2% in a fusion power plant, and the helium atoms are prevented from reaching grain boundaries where embrittlement might otherwise occur.     

注汽锅炉高温高压炉管破裂诊断分析

油田注汽锅炉的炉管是高温高压设备，由于长期在恶劣工况下运行．容易发生材质老化和损伤积累，突发性事故也会频频发生，给企业职工的生命安全和国家财产带来严重威胁，因此时主蒸汽炉管进行诊断分析与寿命预测尤为迫切和重要。本文结合工程实例，对主蒸汽炉管的失效模式、影响运行寿命的主要因素以及寿命预测的方法进行了较为系统的分析，为油田注汽锅炉主蒸汽炉管的寿命管理提供了理论依据和分析方法，以达到预防和降低事故、减少损失的目的。     

水电站输水系统明钢管可靠度评估

目前水电站明钢管可靠度评估主要结合跨中管壁部位进行计算,但并未充分反映其他部位对结构可靠性的影响。为此需考虑钢材强度参数、静水压力、水锤和焊缝系数的随机特性,建立水电站明钢管跨中管壁、支承环近旁管壁边缘、加劲环及其近旁管壁、支承环及其近旁管壁4个基本部位的强度安全功能函数,给出了基于JC法的管道结构可靠度评估方法。按当前设计方法确定的明钢管结构,加劲环及其近旁管壁和支承环及其近旁管壁的可靠指标低于目标可靠指标,不能充分保障结构强度安全,存在局部失效的风险。     

Finite-Volume Method for Creep Analysis of Thin RF MEMS Devices Using the Theory of Plates

Creep is a critical physical mechanism responsible for the failure of radio-frequency (RF) capacitive micro-electro-mechanical systems (MEMS) switches, especially those operating at high RF power. Accurate modeling of creep in RF MEMS metallic membranes is necessary to estimate device lifetime and to improve their reliability. Moreover, the devices are frequently very thin, with aspect ratios as high as 1:500, and conventional three-dimensional structural modeling is onerous and unnecessary. In this article we extend a cell-centered finite-volume approach, previously developed to model thin membranes using Mindlin-Reissner plate theory, to study creep in RF MEMS devices. Results show that the present methodology can accurately predict the long-term creep behavior in thin RF MEMS devices in a computationally efficient manner.     

Committee Report-recommended Practice on Specific Aspects of Cable Installation in Power-Generating Stations

In the late 1940's high voltage pipe-type feeders were first installed in the United States. Since that time, over 2360 circuit miles of underground high voltage pipe-type cables have been installed throughout the country. Con Edison has approximately 652 circuit miles of high pressure pipe-type cable on its system, operating at 69, 138 or 345 kV. The typical pipe-type cable system is comprised of a steel pipe, containing 3 cables, with splices located at intervals of approximately 2000 feet. The pipe is filled with dielectric fluid which is maintained at a nominal operating pressure of 200 psig. Pressurization on the feeder is maintained automatically by pumping plants. For the 345 kV system, these plants sometimes include cooling capability. As the pipe type cable system grows older, leaks of dielectric fluid develop. The major causes of leaks are corrosion, contractor damages, effects of stray currents and localized pipe wear due to vibration. Quick detection and location of dielectric fluid leaks, particularly without the need to deenergize the feeder, is of prime importance to the utility industry. Raychem Corporation has been involved with the development of sensor cables for the detection and location of fluid leaks such as water and gasoline. This technology has been enhanced to address the problem of pipe type cable dielectric fluid leaks and a new system has been developed. The new system uses a sensor cable which is buried in the trench with the pipe type cable.     

半开式自调节重力热管应用研究

本文提出了一种新型半开式自调节重力热管,解决了开式重力热管存在的密封液倒灌和液位失温问题。可广泛应用于电站锅炉排烟及高温工业废气的余热回收,具有较高的可靠性和显著的节能效果。     

Energy and thermal performance of heat pipe/cooling coil systems in hot‐humid climates

The objective of this study is to evaluate the magnitude of reduction in cooling and reheat energy when a heat pipe system is incorporated with the cooling coil of an air‐conditioning system. The heat pipe/cooling coil (HP/CC) system performance is determined by several parameters that are related to both the air‐conditioner cooling coil and the heat pipe physical characteristics as well as the condition of the air entering and leaving the system. In order to appreciate the impact of these parameters and their relative influence on energy consumption and the required indoor air conditions, a simple mathematical model incorporating the parameters of HP/CC is formulated. The model describes the overall system performance at varying entering and leaving air conditions. The model is then applied to a case study as an example of an application to investigate these relationships for a better understanding of the system behaviour and the influencing design parameters. It is evident that due to the coupling nature of the heat pipe and the cooling coil actions, a unique system performance will be obtained for each combination of heat pipe effectiveness and cooling coil by‐pass factor. A proper selection of both the heat pipe and the cooling coil characteristics is found to be necessary for a satisfactory performance under the given operating conditions. Copyright © 2000 John Wiley & Sons, Ltd.