串联环翼式桥墩间冲刷防护影响研究

环翼式桥墩纵向串联布置时,为深入研究桥墩局部冲刷防护问题,从减小冲坑大小和近底垂向流速的方向出发,通过制作桥墩模型,设计正交试验,研究单向水流条件下桥墩间距、下游侧桥墩防冲板的安装高程及数量对两个纵向串联桥墩中下游侧桥墩的冲刷深度的影响,并对所测结果进行极差分析和SPSS方差分析。结果表明,下游侧桥墩防冲板安装高程的显著性比两桥墩间中心间距大小和下游侧桥墩防冲板安装数量的显著性要高,且下游侧桥墩防冲板的安装数量对桥墩冲刷的影响最小,影响效果从大到小依次为下游侧桥墩防冲板的安装高程、桥墩间距、下游侧桥墩防冲板的安装数量。     

某小型风机提高风能利用率的研究

为了提高Savonius小型垂直式风力机的风能利用率,采用CFD方法研究了在来风方向增加导流板对该垂直式风力机风能利用率的影响。研究中建立了数值计算模型并使用Fluent软件进行仿真分析,比较了有无导流板、不同导流板长度、不同安装角度和不同安装位置情况下叶片周围的流场分布以及叶片对转轴产生的静态力矩。仿真结果表明,增加导流板能够显著提高该型风机叶片对转轴的静态力矩;同时,导流板长度和安装角度对此是重要的影响因素;而在一定范围内,不同导流板位置对静态力矩所带来的影响可以忽略。合理安装导流板可以使得该型风机的叶片静态力矩提高20%~40%,进而提高Savonius型风机的风能利用率。     

DAS汽封泄漏特性及影响因素研究

DAS(DEC Advanced Seal)汽封是透平机械中抑制流体泄漏的关键部件。以某机组隔板汽封为对象建立DAS汽封计算流体力学(Computational Fluid Dynamics, CFD)模型,研究不同运行工况(压比、转速)和结构参数(DAS齿厚、DAS齿数以及安装位置)对汽封泄漏量的影响。结果表明：DAS汽封泄漏量随压比升高而变大,并呈现较好的线性相关性;随转速升高而下降;随DAS齿厚增加呈先增后减趋势,当DAS齿厚(1.17 mm)为低齿齿厚(0.13 mm)9倍时,泄漏量达到最大。随DAS齿数增加,DAS齿的安装位置对泄漏量影响逐渐减小,1个DAS齿最佳安装位置在靠近入口段,泄漏量较原始模型降低4.65%;2个DAS齿最佳安装位置分别在靠近进口段和出口段,较原始模型泄漏量降低7.81%;3个DAS齿较原始模型泄漏量最高降低为11.01%。     

桐子林水电站导流明渠消能抗冲试验及明渠方案优化

针对桐子林水电站明渠功能及特点,明确了明渠消能防冲的原则,通过模型试验给出了宽、窄明渠方案有无消能设施情况下的18种子方案,下游处的消能防冲水力学指标及有关参数,对比分析了各子方案明渠出口、下游河道及下游围堰堰面的冲刷情况,指出窄明渠方案中15种子方案消能防冲效果均较差,宽明渠方案中3种子方案消能防冲效果均较好,且以明渠出口处设置反坡并在出口末端设置柔性混凝土板、在其后设置长度20 m左右的相互串联的钢筋石笼（子方案18）效果最好,为优化后的最佳推荐方案。     

单个透水丁坝对溢洪道泄槽弯道水流流态影响试验研究

为了研究单个透水丁坝对溢洪道泄槽弯道水流流态的影响,采用PVC板制作试验模型,进行了溢洪道泄槽弯道凹岸3个位置(1/4、1/2、3/4弯道处)、3个角度(45°、60°、75°)布置单个透水丁坝的水力学试验。利用试验结果,分析了溢洪道泄槽弯道水面均匀度、弯道横断面最大水面横比降、壅水曲线等弯道水流特征。结果表明,与无透水丁坝相比,弯道内布置单个透水丁坝后的弯道水面均匀度均有增加;单个透水丁坝布置角度为60°或75°时,弯道横断面最大水面横比降减小。在布置角度相同、布置位置不同的条件下,单个透水丁坝在弯道1/4处引起的壅水曲线的长度最短;在弯道1/4处,当单个透水丁坝布置角度为60°或75°时,弯道内的壅水曲线长度最短;在弯道1/2或3/4处,当单个透水丁坝布置角度为75°时,弯道内的壅水曲线长度最短。     

不同型式导流板对贴附通风性能的影响

为了探讨在相同条件下房间采用贴附送风加导流板通风方式时,导流板参数变化对室内工作区气流组织的影响,构建具有平面热源的房间,进行数值模拟研究。利用Fluent软件在非等温条件下探究导流板的角度、长度、安装高度对贴附射流气流组织的影响,分析不同形式的导流板对人员工作区流场均匀性、稳定性方面的差异及人员热舒适性的影响。结果显示:导流板与墙壁角度为100°时,气流在房间大部分区域形成场间循环,改变导流板角度不能明显改善头脚温差。长度更长的导流板带走房间余热的能力更强,与导流板长度10 cm、5 cm的房间相比,导流板长度为15 cm的房间工作区平均温度分别低0.4℃、1.2℃。导流板安装位置超过一定高度后,对室内气流组织的影响降低。研究结果为贴附送风加导流板通风方式提供参考。     

不同冲角端壁翼刀控制压气机叶栅二次流的实验研究

对不同冲角下端壁翼刀安装在不同周向位置的压气机叶栅进行的实验研究,结果表明,叶栅总损失随翼刀位置的变化趋势是远离吸力面时损失降低,靠近吸力面时损失升高,冲角变化时叶栅总损失降低的最佳翼刀位置发生变化;在距离吸力面位置70%相对节距处安装翼刀后叶栅总损失在一定的冲角范围内(-9°~+6°)仍然比常规叶栅低。在负冲角下,安装翼刀对流道内流动的影响有随冲角的增大而减小的趋势;在正冲角下,安装翼刀对流道内的影响有随冲角增大而加强的趋势。     

太阳能热水器传热传质和强化传热研究

在低温太阳能光热光伏联合应用试验台的基础上,结合GB/T 17049—2005,利用Gambit、Ansys Fluent和Tecplot软件,对全玻璃真空管太阳能热水器进行传热传质和强化传热分析。结果表明:所建立的二维数值计算模型,能准确反映同一条件下,全玻璃真空管太阳能热水器的变化趋势;在数值模拟基础上,确定了单面受热时的最佳安装角度为51°,加装反光板类似双面受热的最佳安装角度为38°;在粗略估算和细化分析的基础上,确定了不同真空管结构的最佳导流板长度及安装位置;通过实验和数值模拟,确定了58mm×1 800mm为优化的全玻璃真空管结构。     

超大型湿冷塔进风流场及导流装置数模研究及应用

基于Fluent软件,采用标准k-ε湍流模型进行应力封闭,对某工程塔内传热传质过程进行三维数值计算。计算分析了塔内外空气的速度场、温度场,建立了相关方程及气水两相间传热传质理论模型。结合工程实际情况,对冷却塔进风流场进行深入分析:1)导风板的存在降低了塔侧空气绕流流速,增大了冷却塔进风口流场的对称性,使塔内空气动力场的均匀程度增加;导风板安装高度和长度对冷却塔进风流场产生较大影响,以高11 m、长8 m导风板对# 1、# 2冷却塔性能的改善作用最大;2)导风板安装角度和块数对冷却塔进风流场产生一定影响,在导风板安装角度由0°至20°变化、在导风板安装块数由60块至90块变化时,两塔冷却性能变化影响较小。     

基于能量法的动水压力与冲刷作用下桥墩结构体系屈曲分析

为研究冲刷与动水压力耦合作用下桥墩结构体系屈曲荷载及影响因素,采用能量法推导冲刷作用下桥墩结构体系的屈曲荷载计算公式,与等效单柱模型及有限元法进行对比验证,并利用能量法公式分析了墩长、桩根数、土质类型、桩长等因素的影响。结果表明,冲刷深度为0～15 m范围内,以有限元计算结果为基准,能量法的平均误差为9.97%,等效单柱法的平均误差为34.67%,能量法公式与有限元基本吻合;减少墩长、增加桩根数、选用正方形桩等可增加桥墩结构体系的屈曲承载能力;考虑4种河床土质时,桥墩结构体系的最佳桩长范围为22～26 m。研究结果可供河流冲刷下桥墩结构体系稳定性的工程应用参考。     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Aerodynamic performance effects of leading-edge geometry in gas-turbine blades

The purpose of this paper is to illustrate the advantages of the direct surface-curvature distribution blade-design method, originally proposed by Korakianitis, for the leading-edge design of turbine blades, and by extension for other types of airfoil shapes. The leading edge shape is critical in the blade design process, and it is quite difficult to completely control with inverse, semi-inverse or other direct-design methods. The blade-design method is briefly reviewed, and then the effort is concentrated on smoothly blending the leading edge shape (circle or ellipse, etc.) with the main part of the blade surface, in a manner that avoids leading-edge flow-disturbance and flow-separation regions. Specifically in the leading edge region we return to the second-order (parabolic) construction line coupled with a revised smoothing equation between the leading-edge shape and the main part of the blade. The Hodson–Dominy blade has been used as an example to show the ability of this blade-design method to remove leading-edge separation bubbles in gas turbine blades and other airfoil shapes that have very sharp changes in curvature near the leading edge. An additional gas turbine blade example has been used to illustrate the ability of this method to design leading edge shapes that avoid leading-edge separation bubbles at off-design conditions. This gas turbine blade example has inlet flow angle 0°, outlet flow angle −64.3°, and tangential lift coefficient 1.045, in a region of parameters where the leading edge shape is critical for the overall blade performance. Computed results at incidences of −10°,   −5°,   +5°,   +10° are used to illustrate the complete removal of leading edge flow-disturbance regions, thus minimizing the possibility of leading-edge separation bubbles, while concurrently minimizing the stagnation pressure drop from inlet to outlet. These results using two difficult example cases of leading edge geometries illustrate the superiority and utility of this blade-design method when compared with other direct or inverse blade-design methods.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Hydrogen production by steam-gasification of carbonaceous materials using concentrated solar energy – V. Reactor modeling,optimization, and scale-up

A chemical reactor for the steam-gasification of carbonaceous particles (e.g. coal, coke) is considered for using concentrated solar radiation as the energy source of high-temperature process heat. A two-phase reactor model that couples radiative, convective, and conductive heat transfer to the chemical kinetics is applied to optimize the reactor geometrical configuration and operational parameters (feedstock's initial particle size, feeding rates, and solar power input) for maximum reaction extent and solar-to-chemical energy conversion efficiency of a 5 kW prototype reactor and its scale-up to 300 kW. For the 300 kW reactor, complete reaction extent is predicted for an initial feedstock particle size up to 35 μm at residence times of less than 10 s and peak temperatures of 1818 K, yielding high-quality syngas with a calorific content that has been solar-upgraded by 19% over that of the petcoke gasified.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法,这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

汽轮机数字电液调节系统挂闸异常的技术完善

分析了200MW汽轮机数字电液调节系统在运行中存在的挂闸异常问题,采取了相应的技术处理措施,且运行实践效果良好。     

新型高压共轨ECU升压模块的数字化开发与优化

为了提高喷油器电磁阀的响应速率,提出了一种基于CPLD(复杂可编程逻辑器件)应用于高压共轨ECU的数字升压模块。鉴于该升压电路结构参数多,其升压电压的恢复响应要求高等特征,基于Pspice建立了升压电路的仿真模型,研究了不同电路参数下升压模块的输出特性,全面优化了该升压模块的性能。结果显示,该升压模块的最大转换效率可以达90%以上。在柴油发动机上对ECU的试验表明,升压电压最大波动不超过10%,其恢复时间仅为1.3ms,功率管最大温升仅为41℃,满足整机运行范围内ECU的需求。     

Trace metal chemistry and silicification of microorganisms in geothermal sinter, Taupo Volcanic Zone, New Zealand

As part of a pilot study investigating the role of microorganisms in the immobilisation of As, Sb, B, Tl and Hg, the inorganic geochemistry of seven different active sinter deposits and their contact fluids were characterised. A comprehensive series of sequential extractions for a suite of trace elements was carried out on siliceous sinter and a mixed silica-carbonate sinter. The extractions showed whether metals were loosely exchangeable or bound to carbonate, oxide, organic or crystalline fractions. Hyperthermophilic microbial communities associated with sinters deposited from high temperature (92–94°C) fluids at a variety of geothermal sources were investigated using SEM. The rapidity and style of silicification of the hyperthermophiles can be correlated with the dissolved silica content of the fluid. Although high concentrations of Hg and Tl were found associated with the organic fraction of the sinters, there was no evidence to suggest that any of the heavy metals were associated preferentially with the hyperthermophiles at the high temperature (92–94°C) ends of the terrestrial thermal spring ecosystems studied.