三角形微槽中的气体滑移流动特性

针对三角形微槽利用正交函数法求解了带一阶滑移边界条件的N-S方程，对不可压燃气体在等腰三角形和等边三角形微槽道内的充分发展层流滑移流动特性进行了理论分析，获得了三角形微槽内的速度分布和阻力特性的分析解，计算结果表明，正交函数法适用于三角形微槽内滑移流动特性的分析计算，在滑移流区，三角形微槽边界上出现滑移流动，且随着Knudsen数（气体分子的平均自由程与流道特征尺寸之比）的增大，壁面上的滑移速度越大，流动阻力随之减小，但三角形微槽的三个角区边界上的滑移速度增加较小，三角形微槽的高宽比对无量纲阻力常数随Kn的变化关系影响很小。     

微通道内气体-近壁颗粒流动传热数值模拟研究

数值模拟了微通道受限空间内气体-近璧颗粒流动与传热过程,所建模型考虑微尺度气体的可压缩与交物性特征,且在通道和颗粒壁面采用速度滑移和温度跳跃边界条件以考虑滑移区气体动量/能量非连续效应.在此基础上,计算分析了克努森数(Kn)和颗粒偏移比对颗粒表面拖曳力系数(CD)以及传热努塞尔数(Nu)的影响规律.研究结果表明:受气体...     

喷管内水蒸气凝结相变的数值模拟研究

引入水蒸气真实气体物性,考虑相变、速度滑移等影响因素,建立了超音速水蒸气非平衡凝结流动数值模型,通过与实验数据对比,验证了模型的正确性。随后对喷管内水蒸气超音速流动进行了数值模拟研究,清晰的捕捉到了"X型"凝结激波,并对其形态形成原因进行了分析。通过与理想蒸汽模拟对比,结果表明:水蒸气的非平衡凝结会形成凝结激波现象,导致流场中压力和温度突然升高,速度骤然降低;随后对非平衡凝结现象发生后,液滴半径、液滴数和湿度的增长趋势进行了计算分析。发现在喉部下游0.1 m处,液滴数由0突跃至1014数量级,表明水蒸气发生非平衡凝结,极短时间内产生了大量凝结核,液滴半径和湿度也在短时间内迅速增加。     

毛细芯蒸汽槽道孔径对环路热管（LHP）传热性能影响研究

设计并通过3D打印制备了3种毛细芯结构：无嵌入式槽道（蒸汽槽道）毛细芯、嵌入式槽道毛细芯（同孔径槽和异孔径组合槽）。通过实验研究了毛细芯蒸汽槽道对环路热管（Loop Heat Pipe,LHP）传热性能的影响。实验结果表明：在低热负荷启动时,3种毛细芯均能成功启动且蒸发器出口（te-out）及冷凝器进口（tc-in）由于气液两相流的存在出现周期性温度振荡;嵌入式槽道毛细芯启动响应快（76 s）、温度振荡（tc-in）幅度小（±1.0 ℃）,同孔径槽毛细芯稳定温度低（36.8 ℃）,异孔径组合槽毛细芯由于大孔径（500 μm）不利于低热负荷下的蒸发,启动稳定温度高（38.7 ℃）;在变热负荷运行过程中,嵌入式槽道毛细芯有效蒸汽排出面积更大、蒸汽干度更高,在中、高热负荷,温度振荡（tc-in）得到明显改善;异孔径组合槽设计更有利于内部产生蒸汽高效排出,在高热负荷工况下,异孔径组合槽毛细芯壁面温度为85.0 ℃,比无嵌入式槽道毛细芯低了8.0 ℃。     

垂直矩形窄通道启动过程壁温变化特性研究

以去离子水为介质,对竖直矩形窄通道在启动过程中壁面温度的变化规律进行了研究。将一次启动与二次启动时壁面温度的变化特性进行了对比,并改变入口温度,研究了入口温度对启动壁面温度的影响。结果表明：一次启动时壁面温度经过三个阶段,即急剧上升阶段、缓慢升高阶段、缓慢上升至最高壁面温度后又缓慢降至稳态饱和沸腾阶段;二次启动时产生的沸腾滞后现象较一次启动时明显;提高入口温度可增加饱和沸腾段,减少壁面温度的波动,在一定程度上可避免壁面温度过冲对换热器的损坏。     

基于唯象分析方法的壁面润湿模型

着眼于接触角的滞后现象,采用唯象分析方法建立了滞后张力模型.对固-液-气三相接触线附近区域的流动进行了分析,研究发现,壁面无滑移条件是应力奇点产生的直接原因;根据前驱膜和夹带膜理论,提出了消除应力奇点的方法.在上述研究基础上,提出了基于唯象分析方法的壁面润湿模型.研究结果表明,壁面润湿模型的计算结果与已有的实验结果具有较好的一致性,能够反映接触角的滞后性及壁面性质对润湿过程的影响.应用建立的壁面润湿模型对壁面润湿过程的影响因素进行了分析,得出了液体黏度、气液表面张力和固壁接触线特征参数对壁面润湿的影响规律.     

高浓度水煤浆的流变特性与壁面滑移效应试验研究

在水煤浆综合输送试验装置上,采用直径分别为25 mm、32 mm、40mm和50 mm的圆管,对质量分数为65.3%、67.1%和68.2%的高浓度水煤浆进行了流动特性和滑移特性试验研究.从合理假设的滑移速度模型和流动结构出发,得出滑移速度和真实流变特性的确定方法,获得了不同浓度和管径下试验水煤浆的滑移速度及真实流变特性.结果表明:所采用的滑移速度模型能很好地描述所试验水煤浆的宏观滑移流动规律;煤浆浓度较高时,呈现显著的非牛顿流体特性,壁面滑移效应显著;壁面滑移效应与煤浆的真实流变特性关系密切,两者共同支配管内流动,对流动特性影响显著.     

三角形粗糙元的微通道内流动换热的模拟分析

应用蒙特卡洛直接模拟(direct simulation Mont Carlo,DSMC)方法数值分析具有三角粗糙元表面平行平板微通道内气体二维流动与换热.模拟表明:微通道内粗糙元对流动与换热有明显的扰动;粗糙微通道内的壁面速度滑移小于光滑微通道,并随粗糙元变大,速度出现更为严重的跳跃,甚至出现漩涡,增加了通道内的压力损失;随粗糙元变大,气体在壁面处滞留时间变长,增加了单位质量气体与壁面之间的换热.     

滑移流区纤维束蓄热体换热性能数值研究

随着蓄热体基础部件的尺寸细小化,玄武岩蓄热体的纤维直径微小,顺排排列后,内部形成微细流道。为探究微尺度下产生的尺度效应对玄武岩纤维束内部流道流动和传热的数值模拟的影响,建立了蓄热体的二维层流模型。通过Ansys 17.0 fluent中的UDF函数添加了滑移边界条件,以添加滑移边界条件前后的壁面努塞尔数(Nu)减小百分比为评价指标,对比分析二维纤维束微流道的数值模拟中,滑移边界条件对不同工况下流固换热的影响程度。模拟结果表明：随着温度和间距的增大,添加滑移边界条件后的Nu下降程度会增大;随着纤维排数和入口速度的增加,Nu下降程度会减小;纤维束直径d为20μm,排数小于5排,中心间距超过3 d时,添加了滑移边界条件的Nu的降幅达到了1%以上,在数值模拟中不可忽略滑移流区的影响。     

大型低温多效蒸发器管束区域内三维流动特性研究

基于大型低温多效海水淡化蒸发器典型的正三角形管束排列结构,使用多孔介质模型对大型多管束降膜蒸发器进行了三维数值模拟研究.结果 表明:管束区域蒸汽出现了分层流动,管束顶部区域和底部区域蒸汽速度很小,压力较高;除雾器布置会对管束区域二次蒸汽的流动产生影响,靠近除雾器管束区域的蒸汽速度明显较大,且沿着管长方向蒸汽速度逐渐增大,在末端处达到最大速度;蒸汽速度沿着管排方向先增大后减小,沿着管列方向先减小后增大;二次蒸汽沿着轴向通道流动时,蒸汽速度逐渐增大,到达轴向通道出口时蒸汽速度达到最大,当蒸汽流出轴向通道后速度逐渐减小,并在蒸发器出口上部和下部形成大漩涡;蒸发器内蒸汽的阻力损失主要发生在速度梯度变化较大的轴向通道,而在管束区域内的阻力损失较小.     

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%.     

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.     

Contents in Volume 23,2014

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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.     

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.