环境气压对掺气设施空腔长度的影响分析

低气压环境下泄水建筑物空化空蚀风险增大,环境气压对掺气减蚀效果的影响程度是高海拔地区高坝水力设计时需重点关注的问题。采用CFD数值仿真方法,建立跌坎和挑坎两种不同体型的掺气设施模型,分析不同环境气压下的掺气设施的空腔长度,研究环境气压对高速水流掺气效果的影响。结果表明,环境气压越低,高速水流掺气空腔长度越小,掺气效果越弱,高海拔地区高速水流防蚀设计应合理考虑环境气压的影响程度。     

龙开口水电站冲沙底孔泄槽段掺气设施试验研究

以龙开口水电站冲沙底孔泄槽段为例,针对常规掺气设施不能确保掺气效果问题,基于原设计方案提出了2个优化方案,并通过水工模型进行了试验和比较分析,确定了较合理的掺气设施。结果表明,有压出口底部采用突跌掺气并加设挑坎,泄槽段采用坎槽结合式的掺气形式,掺气减蚀效果较好。     

某水电站溢流坝陡槽高速泄流掺气减蚀试验研究

为有效解决陡槽高速泄流情况下的空化空蚀问题,借鉴二滩水电站#1泄洪洞掺气坎的修复经验,通过国内某溢流坝陡槽段大比尺模型试验,研究了底掺气设施有无加设侧掺气坎的掺气空腔长度、掺气浓度、通气量等参数与流速的关系。结果表明,泄水陡槽加设适宜的侧掺气坎后,未影响底空腔的长度,有助于形成稳定完整的底空腔和侧空腔,且使水体掺气浓度及通气量显著增加,不仅避免了陡槽侧墙空蚀的发生,还可加强过流底板的保护作用。     

一种新型掺气设施的模型试验研究

高速明渠流建筑物中常通过设置掺气坎来避免可能发生的空化空蚀破坏,但当明渠的坡度较缓时,掺气空腔容易回水,从而影响掺气效果,对此提出在小底坡明渠有压进口处设置一个楔形体,将水流分成上、下两股进入明渠。通过模型试验研究这种新型掺气设施的空腔形态、掺气特性。试验结果表明,当有压出口处的水流速度达到2.7m/s时,在两股水流之间就能形成一个稳定的掺气空腔,此时对应的水流弗劳德数约为2.0,空腔内并无回水,掺气效果良好;随着出口流速的增加,掺气空腔不断加长,掺气量也不断增加。试验得到了不同流量下掺气空腔形态的变化规律及沿程断面掺气浓度分布规律,并拟合了计算楔形掺气设施空腔长度的经验公式。研究成果可为优化掺气设施设计和工程应用提供参考。     

基于VOF模型溢洪道掺气槽位置数值模拟

为解决高水头溢洪道空蚀破坏问题，设计了3种方案，分别在桩号0+130.73、0+161.78、0+186.39处加设掺气槽，其对应的弗劳德数Fr分别为6.65、7.91、8.53,并采用RNGκ-ε紊流模型和物理模型试验的方法，分析易发生空蚀破坏断面的掺气浓度及沿程水流空化数指标。结果表明，在桩号0+186.39处加设掺气槽，在易发生空蚀破坏截面临底掺气浓度大于15%,沿程水流空化数均大于0.3,效果优于其他2种方案，可有效解决溢洪道空蚀破坏问题。     

格栅式底流消能掺气特性研究

对于底流消能，格栅的布置能够缩短消力池长度，使其更容易适应地形条件的变化。为此，通过FLOW-3D中的掺气模型对圆孔Γ形格栅式消力池内水气两相流进行数值模拟。结果表明，纵向临底掺气浓度沿程递减(由31.3%减小到8.0%),在格栅位置出现明显下降，栅前(^#6断面)临底空穴数最小为5.6,格栅附近空穴数均在9.0左右，栅后空穴数远大于9.0;栅前沿轴线方向近底气泡尺寸沿程增大(由0.9 mm增大到8.1 mm),栅后近底板气泡尺寸则沿程减小(由1.6 mm减小到接近0 mm);流速较大区域较小直径的气泡在掺气减蚀中起主要作用，对混凝土固体边界的保护作用明显，包括格栅在内的消力池结构不易发生空蚀破坏。     

陡坡溢洪道掺气坎空腔长度及掺气坎角度试验

以苏家河口水电工程为例,针对其陡坡溢洪道掺气坎对流量大小适应性较差的问题进行了试验,对#2掺气坎3种体型(1∶4、1∶10、1∶15)进行了挑角的优化设计。结果表明,在陡坡溢洪道设置掺气坎时应保证挑角和坎高与单宽流量相互匹配,即挑角在3°～5°之间的空腔长度能满足各种工况,否则可能出现掺气坎适应性很差的问题,不利于工程泄洪时的正常和安全运行;空腔长度与挑角在小流量情况下呈指数关系,在大流量情况下呈对数关系,这为实际工程设计提供了依据。     

台阶式溢洪道掺气坎水流空腔长度和通气量的试验研究

通过试验研究了台阶式溢洪道初始掺气点的位置、在首部台阶上游加掺气挑坎情况下挑坎后的水流流态、空腔长度、通气量。得出了初始掺气点、空腔长度和通气量的确定方法,供工程参考。     

底流消能工水流结构与掺气浓度分布试验研究

底流消能工中水流紊动剧烈、大量掺气,面临着空化空蚀问题.为研究底流消能工气体迁移扩散运动与水流结构相互作用机理,采用水力学试验开展研究,对底流消能工进行水流结构划分,通过调整流量与尾坎高度,改变入射Fr数及跃后水深与跃前水深比,分别测出消力池内掺气浓度值,并分析数据研究水流结构区气体的运动机理,得到消能工内掺气浓度分布...     

斜鼻坎挑流消能在黑石罗水库的应用

针对黑石罗水库现状连续式鼻坎消能效果较差,可能威胁河床及岸坡稳定的现状,通过水工模型试验,将挑流消能连续式鼻坎优化为斜鼻坎,即将鼻坎挑射角度由定值调整为渐次增大,同时偏转大角度挑射一侧反弧段边墙至泄槽轴线位置,去除小角度挑射一侧边墙及部分反弧段底板,迫使出坎水舌在平面上转向的同时沿竖向大幅拉开,在保证出射水流平顺归入河床的同时,增大挑射水流和空气的接触面积,最大限度消除水体能量,从而降低水股对落点的冲刷,达到保护河岸及相邻建筑物安全的目的。试验结果表明,斜鼻坎可以很好地适应狭窄地形条件,有效降低挑射水流对鼻坎下游的冲刷。研究成果为类似工程提供了参考。     

Ash-forming elements in four Scandinavian wood species. Part 1: Summer harvest

Woody biomass in Finland and Sweden comprises mainly four wood species: spruce, pine, birch and aspen. To study the ash, which may cause problems for the combustion device, one tree of each species were cut down and prepared for comparisons with fuel samples. Well-defined samples of wood, bark and foliage were analyzed on 11 ash-forming elements: Si, Al, Fe, Ca, Mg, Mn, Na, K, P, S and Cl. The ash content in the wood tissues (0.2–0.7%) was low compared to the ash content in the bark tissues (1.9–6.4%) and the foliage (2.4–7.7%). The woods’ content of ash-forming elements was consequently low; the highest contents were of Ca (410–1340 ppm) and K (200–1310), followed by Mg (70–290), Mn (15–240) and P (0–350). Present in the wood was also Si (50–190), S (50–200) and Cl (30–110). The bark tissues showed much higher element contents; Ca (4800–19,100 ppm) and K (1600–6400) were the dominating elements, followed by Mg (210–2400), P (210–1200), Mn (110–1100) and S (310–750), but the Cl contents (40–330) were only moderately higher in the bark than in the wood. The young foliage (shoots and deciduous leaves) had the highest K (7100–25,000 ppm), P (1600–5300) and S (1100–2600) contents of all tissues, while the shoots of spruce had the highest Cl contents (820–1360) and its needles the highest Si content (5000–11,300). This paper presented a new approach in fuel characterization: the method excludes the presence of impurities, and focus on different categories of plant tissues. This made it possible to discuss the contents of ash element in a wide spectrum of fuel-types, which are of large importance for the energy production in Finland and Sweden.     

NEXT GENERATION ENGINEERED MATERIALS FOR ULTRA SUPERCRITICAL STEAM TURBINES

正1 ABSTRACT To reduce the effect of global warming on our climate,the levels of CO2emissions should be reduced.One way to do this is to increase the efficiency of electricity production from fossil fuels.This will in turn reduce the amount of CO2emissions for a given power output.Using US practice for efficiency calculations,then a move from a typical US plant running at 37%efficiency to a 760℃/38.5 MPa(1 400/5 580 psi)plant running at 48%efficiency would reduce CO2emissions by 170kg/MW.hr or 25%.     

Contents in Volume 23,2014

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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.     

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.     

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。     

Assessment methods of material ageing using Sdobyrev''s creep rupture model

The physical aspects of the activation energy, in higher and high temperatures, of the metal creep process were examined. The research results of creep-rupture in a uniaxial stress state and the criterion of creep-rupture in biaxial stress states, at two temperatures, are then presented. For these studies creep-rupture, taking case iron as an example the energy and pseudoenergy activation was determined. For complex stress states the criterion of creep-rupture was taken to be Sdobyrev's, i.e. σ_red = σ₁ β + (1 − β)σ_i, where: σ₁-maximal principal stress, σ_i-stress intensity, β-material constant (at variable temperature β = β(T)). The methods of assessment of the material ageing grade are given in percentages of ageing of new material in the following mechanical properties: 1) creep strength in uniaxial stress state, 2) activation energy in uniaxial stress state, 3) criterion creep strength in complex stress states, 4) activation pseudoenergy in complex stress states. The methods 1) and 3) are the relatively simplest because they result from experimental investigations only at nominal temperature of the structure work, however, for methods 2) and 4) it is necessary to perform the experimental investigations at least at two temperatures.     

Production of hydrogen from sewage biosolids in a continuously fed bioreactor: Effect of hydraulic retention time and sparging

Hydrogen was produced from primary sewage biosolids via mesophilic anaerobic fermentation in a continuously fed bioreactor. Prior to fermentation the sewage biosolids were heated to 70 °C for 1 h to inactivate methanogens and during fermentation a cellulose degrading enzyme was added to improve substrate availability. Hydraulic retention times (HRT) of 18, 24, 36 and 48 h were evaluated for the duration of hydrogen production. Without sparging a hydraulic retention time of 24 h resulted in the longest period of hydrogen production (3 days), during which a hydrogen yield of 21.9 L H₂ kg⁻¹ VS added to the bioreactor was achieved. Methods of preventing the decline of hydrogen production during continuous fermentation were evaluated. Of the techniques evaluated using nitrogen gas to sparge the bioreactor contents proved to be more effective than flushing just the headspace of the bioreactor. Sparging at 0.06 L L min⁻¹ successfully prevented a decline in hydrogen production and resulted in a yield of 27.0  L H₂ kg⁻¹ VS added, over a period of greater than 12 days or 12 HRT. The use of sparging also delayed the build up of acetic acid in the bioreactor, suggesting that it serves to inhibit homoacetogenesis and thus maintain hydrogen production.     

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.