蜂窝密封泄漏流动特性影响因素的数值研究

采用RNGk-ε两方程紊流模型和Simple算法,利用Fluent软件对蜂窝密封内的三维流动情况进行了数值模拟,从压比、蜂窝芯格尺寸、蜂窝深度、蜂窝壁厚等因素分析蜂窝密封的泄漏流动特性.结果表明:蜂窝密封特殊的六边形蜂窝结构可以将泄漏流分割成许多小涡流,气体在蜂窝腔中呈逆时针螺旋式三维紊流运动;随着压比的增大,蜂窝密封泄漏量增加,压比越大,泄漏量增加的趋势减缓;蜂窝芯格尺寸小,泄漏流被分割成小涡流的个数多,密封间隙摩阻效应大,泄漏量减少;蜂窝深度增大,泄漏量减少,蜂窝深度大于4 mm时,泄漏量减少的趋势减缓;随着蜂窝壁厚的增加,泄漏量略有减少.     

孔型密封泄漏特性影响因素研究

采用计算流体力学方法研究孔型密封的泄漏特性,特别是孔形和面积比对泄漏特性的影响。结果表明:随转速增加泄漏量减小,随压比增加泄漏量增大并趋稳,最大压比的泄漏量为0.118 kg/s;相同面积比与孔数下,圆孔密封性能最好,蜂窝孔(六边形)次之,矩形孔最差;且传统蜂窝密封性能优于六棱台形式的蜂窝密封,泄漏量减小10.61%;随孔深增加泄漏量减小并趋稳,最大孔深的泄漏量为0.114 kg/s;面积比增加有利于提高密封性能;改变蜂窝孔对边距比减小壁厚对密封性能更有利。     

蜂窝汽封流场及泄漏特性的数值模拟研究

建立了蜂窝汽封三维流场数值模型,系统地分析了蜂窝孔径尺寸、蜂窝高度、入口压力等结构与运行参数对汽封流场及泄漏特性的影响.计算结果与分析表明,在运行参数不变的情况下,降低蜂窝孔径大小或增加蜂窝高度都有利于降低汽封泄漏量,提高密封效果.而在结构参数不变的情况下,汽封泄漏量随入口压力增大而增加,而随旋转速度增大出现减小的趋势.     

不同背压下蜂窝密封泄漏性能实验研究

蜂窝密封是减小透平机械工质泄漏的重要部件,本文设计并搭建了蜂窝密封泄漏实验装置,采用实验与理论相结合的方法,研究了背压阀门开度λ、转速及进口压力对蜂窝密封泄漏量的影响。结果表明：实验结果与理论计算吻合较好,相对误差在6%以内;在同一背压阀门开度下,密封泄漏量随着进口压力增大而增加,随着转速升高密封泄漏量几乎保持恒定;在进口压力和转速不变情况下,密封泄漏量随着背压阀门开度的增大而增加,当背压阀门开度λ=1时泄漏量达到峰值;与背压阀门开度λ=1相比较,当背压阀门开度λ=0时密封泄漏量最高可降低约15.9%。     

汽轮机轴端汽封改造技术分析

汽轮机轴端密封技术均为梳齿式结构,且后轴封处轴颈为光轴,汽封漏汽量大.蜂窝式汽封能有效抑制汽流在密封腔中周向流动,在高压差、小间隙密封时,仍能保证机组的稳定运转,从而降低泄漏损失,提高了机组效率.     

透平机械密封技术研究进展

对现代透平机械的密封技术研究进行了综述,重点介绍了透平机械中广泛应用的迷宫密封、蜂窝密封和刷式密封技术的密封原理、结构形式和国内外研究现状.对透平机械密封技术的泄漏流动、传热特性以及动力学特性的研究方法和研究结论进行了讨论,介绍了西安交通大学叶轮机械研究所TurboAero研究小组在透平机械密封技术方面的具体研究工作.展望了透平机械密封间隙泄漏流动传热以及汽流激振的研究和发展方向,为提高我国透平机械密封技术的整体设计水平和运行经济性提供有益的技术参考.     

汽轮机斜孔腔蜂窝密封泄漏性能优化数值研究

蜂窝密封是目前汽轮机中最先进的密封方式,能够有效减少密封间隙同时显著提高转子的动力特性,蜂窝密封的结构创新和孔腔形状的几何优化是降低运行中泄漏率的有效途径。本文通过引入轴向倾斜角参数,提出了一种中心轴线与转轴轴线成一定角度的倾斜孔型蜂窝密封,利用Fluent软件模拟了不同孔腔几何形状的蜂窝密封的三维流场和压力分布,研究了几何参数对倾斜孔型蜂窝密封泄漏率的影响。结果表明：迎风倾斜孔型蜂窝密封与直孔型和斜齿迷宫密封相比,泄漏率有望显著降低,并探讨了轴向倾角对倾斜孔型蜂窝密封泄漏量的影响机理。     

后夹板结构对刷式密封泄漏特性和温度分布的影响

采用数值方法求解基于Non-Darcian多孔介质模型的雷诺平均Navier-Stokes(RANS)方程和能量方程,研究了5种后夹板结构对刷式密封泄漏特性和温度分布的影响.结果表明:数值预测得到的刷式密封泄漏量与实验值吻合良好,验证了数值方法的有效性;在后夹板上设置开槽对泄漏量的减小没有益处,其中与下游腔室相连的开槽会导致泄漏量大幅增大;5种后夹板结构刷式密封的最高温度均发生在刷丝与转子的接触面上,后夹板开槽结构对刷丝束尖端温度的降低并未起到作用.     

基于热力学效应的迷宫密封封严机理数值研究

热力学效应的研究是揭示迷宫密封封严机理的关键。建立了三维迷宫密封热力学求解模型,推导了考虑热力学效应的密封泄漏量公式,研究了压比、偏心率、密封间隙对迷宫密封熵增与泄漏量的影响规律,从热力学效应角度分析了迷宫密封的流场特性与泄漏特性。研究结果表明:所建立的密封泄漏量公式能够反映热力学效应与泄漏量之间的关系;熵增反映了迷宫密封气体动能转换成热能的程度,热力学效应越充分,熵增的幅度就越小,密封性能越好。压比、偏心率和密封间隙是通过影响气体热力学效应来影响密封泄漏量的;泄漏量随压比和密封间隙的增大而增大,二者近似呈线性关系。随着偏心率的增大,密封封严性能降低,相比于转子同心工况,偏心率为0.9时泄漏量增大了6%。转子高速旋转下与气体摩擦产热所产生的功率耗散会引起气体温度升高。通过研究迷宫密封流场特性和能量耗散,从热力学效应角度进一步揭示了迷宫密封的封严机理。     

考虑摩擦热效应的刷式密封性能仿真研究

建立包含转子的刷式密封三维理想切片模型,通过商用ANSYS系列软件计算了不同工况条件下刷式密封与转子的温度场分布情况,在热分析基础上进行了刷式密封热-结构耦合分析.结果 表明:随着上下游压差增大,刷式密封泄漏量逐渐增大,刷式密封泄漏量随着转子转速的增加呈微弱的下降趋势;在工作开始阶段的温升过程中,刷式密封的最高温度随着...     

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.