导流孔径变化对磁力驱动离心泵流动性能的影响

为研究导流孔径变化对磁力驱动离心泵内部流场及水力性能的影响规律,分别以6、8、10 mm~3种不同导流孔径的磁力驱动离心泵模型为研究对象,通过定常、非定常以及流热耦合数值计算与外特性试验相结合的研究方法,分析并得到了导流孔径变化对磁力驱动离心泵外特性、内部流场、温度场以及压力脉动特性的影响规律。研究表明:导流孔径的变化对磁力驱动离心泵外特性曲线、内部流场以及压力脉动特性的影响较小,对冷却循环流道内的流场、温度场以及压力脉动特性的影响较大。     

微型高速泵小流量工况空化特性数值分析

通过CFturbo与UG软件建立及优化模型,基于RNG k-ε湍流模型和Rayleigh-Plesset空化模型,利用CFX(计算流体力学)软件对微型高速离心泵进行数值模拟。通过小流量和不同进口总压工况,对叶轮进口段流动特性、叶片表面和叶轮流道的静压分布以及叶轮流道内空泡数分布3个方面进行流场分析。结果表明:流量对叶轮进口段回流影响较大;叶片前缘到后缘的压力逐渐增大,叶轮流道进口到出口的压力也逐渐增加;扬程系数陡降前的振动是叶轮空化不稳定引起的,随着空化系数的降低,空泡体积数逐渐占据整个叶轮流道,空泡分布也由不对称转变为对称结构;为微型高速泵的设计和研究提供了理论基础。     

颗粒直径及浓度对高速离心泵非定常特性的影响

为探究不同颗粒直径、颗粒浓度对高速离心泵非定常特性的影响,以一台比转速为67的高速离心泵作为研究对象,利用ANSYS CFX软件建立的Mixture混合多相流模型进行了数值模拟计算,分析了高速泵的外特性、内部流场以及压力脉动变化规律。计算结果表明:随着颗粒体积分数的增加,效率最优工况点在向小流量处偏移,并且叶轮进口越偏向大流量工况,效率下降得越快,适当增加颗粒直径,对固液两相流的输送有积极作用;在不同颗粒浓度下,叶轮流道内的压力脉动主频均出现在叶频及倍频处,在颗粒体积分数为0.65%、颗粒直径为D=0.15 mm时,随着进口流量的增加,固相体积在叶轮流道处占比逐渐减小,在叶轮进口处颗粒占比逐渐增大;随着颗粒浓度的增大,叶轮流道内及隔舌处的压力均减小,叶轮流道内、隔舌处的压力和叶轮的径向力增减速度快慢的分界点在颗粒直径D=0.1 mm附近。     

固相颗粒对离心泵内部流场影响的数值分析

为研究颗粒的粒径及体积分数变化对离心泵内部流场的影响,采用ANSYS软件对离心泵进行固液两相流数值模拟分析。研究粒径变化对叶轮流道内固相体积分数分布的影响,分析粒径、体积分数变化对全流道压力的影响。结果表明:在设计流量工况下,随着粒径的增大,叶轮流道内固相体积分数整体呈减小趋势,在叶片压力面进口处固相体积分数最大,且固相颗粒逐渐由叶片吸力面偏向压力面;随着粒径、体积分数的增加,扬程降低,进口负压值增大,泵发生气蚀的可能性增加,在出口处压力降低。     

离心泵转速剧烈波动时的瞬时响应特性研究

为研究离心泵转速剧烈波动时的瞬时响应特性,建立了包含一台低比转速离心泵的循环管路系统,基于用户自定义函数、滑移网格方法和RNG k-ε湍流模型对整个系统进行了非定常流动的自耦合数值计算。结果表明:流量响应滞后于转速变化历程,而扬程响应对转速变化的跟随性则较好;叶轮机械内部的动静干涉效应对转速加速阶段的泵出口压力和减速阶段的进口压力影响最为显著,而对流量和叶轮功率影响较小,转速波动过程中的瞬时流场演化完全滞后于准稳态计算结果。本研究为揭示离心泵转速剧烈波动时的瞬时响应特性提供了重要参考。     

长短叶片离心泵内固液两相流场三维数值模拟

为了分析长短叶片离心泵输送固液两相流时叶轮内部流场和流动规律,应用FLUENT软件分别对普通叶片离心泵和长短叶片离心泵内的固液两相流场进行数值模拟,对比分析两者的总压、静压以及固相颗粒浓度的分布规律。结果表明:无论是普通离心泵还是长短叶片离心泵,它们的静压和总压的变化规律相同,均沿着出流方向有增大趋势,在叶轮出口处压力达到最大值;长短叶片离心泵内固相颗粒浓度减小,明显提高了泵的抗磨损性能;与普通离心泵相比,长短叶片离心泵叶轮流道内颗粒的高浓度区域明显变小,运行更加平稳;长短叶片离心泵中颗粒的分布更均匀,流动损失大大减小,流动状态更好。     

分流叶片周向位置设计及其对离心叶轮内部流动的影响

利用计算流体力学软件,对某高压比、高转速、小流量离心式压气机的半开式叶轮内部三维粘性流场进行了数值模拟研究。重点分析了分流叶片周向位置对叶轮内部流动和性能的影响,提出了适合此半开式离心叶轮分流叶片周向位置的设计方案。结果表明：分流叶片不同周向位置对流场影响明显,当分流叶片偏向长叶片吸力面侧时,叶轮流道内低速区增大,流动分布不均匀。研究还发现：固定分流叶片进口而将出口位置向长叶片压力面侧偏置,可以改善叶轮内部流动情况,提高叶轮性能。     

叶片进口边位置对小流量工况下离心泵空化特性的影响

为研究叶片进口位置对小流量工况下离心泵空化性能的影响,应用数值计算方法模拟了比转数为81的离心泵的三种模型,得到不同进口边位置的离心泵空化特性,并分析了叶轮内部流场与空化性能曲线的影响关系。结果表明,在小流量工况下,低比转速离心泵叶片进口边位置越靠前,抗空化性能较好,但严重空化后扬程衰减更快,流道直接被空泡堵塞,流道和叶片表面气泡分布较均匀,且气泡充斥流道速度较快,气泡体积分数各流道差值越小。相比较而言,叶片进口位置越靠后,气泡在流道内部和叶片背面分布不均匀,易出现噪声和振动,但在断裂空化状态,气泡并未完全堵塞流道,扬程下降速度较慢。整体来看,在小流量工况下,叶片进口边位置越靠前,离心泵的抗空化性能较好,并通过试验研究验证了模拟结果的可靠性。研究成果可为小流量工况下低比转速离心泵抗空化性能的优化提供参考。     

叶轮出口宽度对离心泵内部非定常性能的影响

为了研究多工况下不同叶轮出口宽度对离心泵非定常性能的影响,基于RNG k-ε湍流模型对叶轮出口宽度分别为11、12、13、14和15 mm的离心泵模型分别在0.8Q_d、1.0Q_d、1.2Q_d三种流量工况下进行定常和非定常的数值模拟,得到离心泵的外特性曲线、内部流场以及压力脉动特性,并进行对比分析。结果表明:离心泵的扬程随叶轮出口宽度的增加而增加,存在一个最佳的叶轮出口宽度使其效率最佳且最佳效率点向大流量点偏移;随着叶轮出口宽度的增加,叶轮截面的最大压力值呈先增加后减小再增加的趋势,小流量工况下的湍动能较大区域随叶轮出口宽度的增加由叶轮流道出口向叶轮流道中间发展;各监测点的压力脉动均呈周期性变化,压力系数随流量的增大而增大,在设计和大流量工况下,当叶轮出口宽度为13 mm时压力脉动幅值明显小于其他型式的叶轮,因此适当增大叶轮的出口宽度有利于减小离心泵的压力脉动、提高其性能。     

无油润滑高速离心泵的数值模拟与实验研究

为优化高速泵冷却循环回路和提高可靠性,设计了一种采用动压流体润滑轴承的无油高速离心泵,通过工质流体润滑轴承和冷却电机,将增压流道与冷却循环流道结合,结构更加紧凑。为分析高速离心泵的内部流动特性,采用CFD方法对该泵在设计转速下不同流量时泵内部的流动情况进行了数值模拟,并在搭建的测试台上对模型泵的水力性能进行了实验研究。研究表明:高速离心泵设计工况下内部流道中相对速度和总压的分布均匀;模拟计算的泵扬程和效率与实验值接近,模拟值具有较高精度;工况条件对泵的水力性能有较大影响,应避免过小流量运行。     

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.