MgO混凝土自生体积变形与压蒸膨胀变形的相关性

为促进外掺MgO混凝土的推广应用,对MgO混凝土的自生体积变形与压蒸膨胀变形的变化趋势及其相关性进行了试验研究,发现外掺MgO的一、二级配混凝土自生体积和砂浆压蒸膨胀变形均随着MgO掺量的增大而增大,但超过安定掺量后砂浆的压蒸膨胀变形急剧增大,而混凝土自生体积变形无明显急剧增大的现象,与砂浆试件的压蒸膨胀变形无密切相关性。研究结果表明,以水泥砂浆试件的压蒸膨胀率不超过0.5%来确定混凝土中的MgO安定掺量,虽然安全,但偏于保守。     

复掺磷渣粉与石灰石粉完全替代粉煤灰对外掺MgO碾压混凝土性能的影响

针对部分水利水电工程很难采购到粉煤灰或粉煤灰落地价格过高的问题,以复掺磷渣粉与石灰石粉完全取代粉煤灰配制的外掺氧化镁(Mg O)碾压混凝土为例,采用力学试验、变形观测、压汞测试、扫描电镜观察等手段,研究复掺磷渣粉与石灰石粉对外掺Mg O碾压混凝土的力学性能、自生体积变形性能、微观性能的影响。结果表明,与单纯使用粉煤灰作为掺合料配制的外掺Mg O碾压混凝土相比,采用复掺磷渣粉与石灰石粉完全替代粉煤灰配制的外掺Mg O碾压混凝土的工作性、抗渗性和抗冻性无明显变化,对自生体积膨胀变形影响不大,但无害孔减少,平均孔径和孔隙率总体增大;随着石灰石粉掺量增大或磷渣粉掺量减少,外掺Mg O碾压混凝土的抗压强度、劈拉强度、极限拉伸值下降;在石灰石粉掺量超过20%后,龄期90d的外掺Mg O碾压混凝土的抗压强度低于常用的坝体混凝土抗压强度的最低值15MPa。     

MgO掺量对混凝土不同浇注温度下拱坝应力的影响

为了研究不同浇筑温度下MgO掺量对混凝土拱坝应力的影响,采用有限元数值模拟对某外掺MgO混凝土拱坝施工期温度场、应力场进行仿真分析,对比不同掺量不同浇筑温度下特征点的温度、应力和掺MgO引起的自生体积变形过程。结果表明,不同浇筑温度下,MgO对应力场有效补偿量相差不大,对于低温季节浇筑的混凝土,适当增加MgO的掺量可有效补偿坝体应力;对于高温季节,温降产生的拉应力很大,最好配合分缝措施或避开高温季节浇筑。     

水泥净浆、水泥砂浆的压蒸膨胀率及孔隙结构与MgO掺量的关系研究

为合理确定混凝土中的MgO外掺量,通过室内试验测定了不同MgO外掺量的硬化水泥净浆、水泥砂浆的压蒸膨胀率,并对压蒸后的试样进行压汞试验、扫描电镜分析、背散射电子分析和X射线能谱分析。结果表明,MgO的掺量明显影响试样的密实度和孔隙结构。当MgO外掺量大于一定数值后,水泥浆、水泥砂浆的压蒸膨胀率发生显著增长,孔隙率明显增大,孔隙结构逐渐劣化。同时,水泥砂浆容许的MgO掺量多于水泥净浆,即利用水泥砂浆压蒸试件测得的MgO极限掺量比水泥净浆多。     

水灰比对外掺氧化镁混凝土自生体积变形的影响

为研究外掺氧化镁混凝土性质,试验研究了水灰比对外掺氧化镁混凝土自生体积变形的影响.结果表明,水灰比对外掺氧化镁混凝土的自生体积变形有重要影响,混凝土的自生体积变形随着水灰比的增大而增大.同时,再次验证了外掺氧化镁混凝土的延迟微膨胀特性.     

MgO微膨胀混凝土筑坝技术述评

外掺MgO微膨胀混凝土坝体防裂技术可有效补偿坝体在降温期的拉应力。从MgO应力补偿的基本原理出发,介绍了MgO混凝土材料性能、膨胀模型、施工方法及安全监测等方面的研究现状,分析了MgO微膨胀混凝土筑坝技术在推广应用中存在的突出问题,从MgO混凝土高掺量的体积安定性、考虑多因素的精确膨胀模型、外掺MgO与其他温控措施的配套使用等方面探讨了亟待攻克的技术难点和发展方向。     

高寒地区高拱坝外掺MgO混凝土的温度应力补偿效果研究

鉴于外掺MgO微膨胀混凝土筑坝技术对提高高寒地区混凝土坝的施工速度和经济效益的意义,对高寒地区高拱坝外掺MgO混凝土的温度应力进行了仿真计算,分析了不同MgO掺量对温度应力补偿效果的影响及坝体不同部位掺MgO的膨胀补偿效果。结果表明,在大坝内部,掺MgO对混凝土能起到较好的温度应力补偿作用,且在一定范围内MgO掺量越大,应力补偿作用越明显;对大坝表面混凝土,掺MgO可能使混凝土表面拉应力增大,可通过加强表面保温来有效控制表面拉应力,且宜采用长期保温的温控措施。     

掺石粉与掺粉煤灰的碾压混凝土坝温控措施对比分析

针对石粉替代或部分替代粉煤灰作为碾压混凝土的掺合料后,其热力学性能指标均发生变化的问题,以中国西部地区某在建水电工程溢流坝段碾压混凝土为例,基于温度场和应力场的三维有限元分析技术,通过控制浇筑温度、混凝土外表面保温、通水冷却等技术措施,分别对掺石粉与未掺石粉碾压混凝土施工期与运行期的温度及应力进行分析,得出了掺石粉与未掺石粉碾压混凝土温度及应力的变化特性。结果表明,掺石粉碾压混凝土对整个施工期的坝体温控防裂有利,且可有效减小温控难度。     

外掺MgO混凝土快速筑拱坝技术应用综述

全面统计分析了全坝采用外掺MgO混凝土不分横缝(或设少量诱导缝)快速施工技术建成的混凝土拱坝的基本情况,并介绍了各拱坝的工程特征、施工实际情况、浇筑特点、工程规模与质量、长期观测的混凝土自生体积变形、应用效果、经济效益等,可供类似工程借鉴和参考.     

基于单因素试验的三级配RCC施工配合比研究

根据坝体碾压混凝土性能指标和施工要求,利用单因素试验研究了坝体不同标号三级配混凝土的 粗细骨料组合、粉煤灰掺量、水胶比和砂率,并采用绝对体积法给出了施工配合比。试验结果表明,当 采用玄武岩与灰岩为粗细骨料组合、大石∶中石∶小石为35∶35∶30、砂率为32%、用水量为88 kg/m3、 粉煤灰掺量为50%时,能满足C25、C20和C15坝体碾压混凝土各项性能指标和施工要求。     

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。     

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.     

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.