三维肋管肋结构参数对流动传热特性的影响

为了探究三维肋管肋结构参数对管外流动和传热特性的影响,采用控制变量法通过实验研究了热空气横掠三维肋管时,管外努塞尔数Nu与欧拉数Eu随肋结构参数的变化规律。与相同实验工况下的光管对比,分析了不同肋高、肋宽以及轴向间距对三维肋管综合传热性能的影响。结果表明：在一定流速范围内,Nu随着肋高和肋宽的增加而增加,随着轴向间距的增加而减小;相同换热条件下,三维肋管综合性能评价指标（Performance Evaluation Criterion,PEC）优于光管;且换热管的PEC随着肋高和肋宽的增加而增加,随着轴向间距的增加反而减小。     

三维内肋螺旋管内强化换热实验

采用实验方法测试了三维内肋螺旋管内的流动传热性能。实验用的螺旋管曲率δ=0．0663,测试段长1．15m,试验工质为水。对螺旋光管和两种不同结构尺寸的三维内肋管进行了测试,测量的雷诺数范围约为Re=1000～8500。结果表明,三维内肋对螺旋管内的对流换热仍然有较大的强化效果,同时流阻也有一定程度的增加。与未加肋的螺旋光管相比,在测试的流动范围内,两种三维内肋管的平均换热强化比达1．71和2．03．热力性能系数为1．2～1．66。     

水平三维肋管外含不凝性气体的水蒸汽凝结换热的实验研究

对水平光管和三维肋管管外具有不同空气含量的水蒸汽凝结换热性能进行了实验研究。获得了不凝性气体含量和壁面过冷度对光管和三维肋管凝结换热性能的影响规律。实验结果表明：在相同的工况条件下，水平三维肋管的凝结换热系数是光管的1．7～2．9倍；不凝性气体含量越高，凝结换热系数越低；壁面过冷度越大，凝结换热系数越大。最后，获得了水平三维肋管管外凝结换热实验关系式。图8表1参9     

三维内微肋水热管强化传热实验

首次报道了三维内微肋两相闭式热虹吸管的传热性能，在实验范围内，与光管相比，竖直放置时，平均沸腾换热系统可以提高50%-238%，平均凝结换热系数可以提高100%-222%，小倾角下，平均沸腾换热系数可以提高51%-171%，平均凝结换热系统可以提高42%-17%，三维内微肋结构能够大大强化热管的沸腾换热与凝结换热，有效地减小热管的内热阻。     

油浸式自冷变压器用三维肋管散热器换热特性研究

为研究三维肋管散热器的自然对流换热特性,分析不同温升下三维肋管散热器的强化换热性能,搭建了模拟油浸式自冷变压器工作过程的实验平台,在不同功率下分别测试了片间距为45 mm的片式散热器、排间距为45和55 mm的三维肋管散热器的进口温升,拟合得到散热器的温升-功率曲线,计算出3个散热器在相同温升下的散热量.研究表明:相比...     

紧凑型强化传热管管束受限空间内沸腾强化换热特性

采用满液式蒸发换热器，利用强化传热管管束受限空间内早期沸腾强化机理，将中小热负荷条件下的自然对流换热转化为核沸腾换热。其换热性能大大优于降膜式蒸发换热器。对紧凑型滚压表面传热管管束在受限空间内沸腾强化换热进行实验研究，确认了满液式蒸发换热器使用紧凑型滚压强化管束具有良好的换热性能，在小管间距时有显著的沸腾换热复合强化效应。     

有内热源的肋片散热数值分析

利用流体区域与固体区域温度场耦合的方法求解含内热源肋片的稳态自然对流换热问题,讨论了肋片材料、肋片间距和内热源强度对整个散热的影响。得出各种情况下流场和温度场的变化和不同情况下散热效果的标志性参数——最高温度的变化规律如下：内热源越强,最高温度越高;肋片间距增加,最高温度降低;提出了具体的计算式;导热系数大于10W／（m·K）的金属材料,肋片最高温度不受材料热物理性质的影响。     

几何结构对后台阶三维缝隙换热影响的研究

针对涡轮叶片尾缘冷却结构特点,建立了后台阶三维缝隙结构气膜冷却特性试验台;测量了缝隙中心和肋中心下游气膜换热系数的局部分布;研究了不同几何结构参数对换热系数的影响规律,其中缝宽/肋宽比b1/b2的变化参数是0.67、1.0及1.5,缝高/唇厚比H/d的变化参数是0.5、1.0及2.0。试验结果表明:缝后中心线与肋后中心线的换热系数随轴向距离的增加其总的趋势都是减小;换热系数随着缝高/唇厚比的减小,曲线变得比较平缓;换热系数在不同的缝宽/肋宽比时,曲线基本整体地上下移动,但吹风比不同Bc不同时,曲线移动幅度区别较大。     

管内插入网状肋强化换热的数值研究

采用三维数值模拟方法研究了网状肋用于圆形通道的流动换热特征,分析了雷诺数Re、肋的形状、肋的网格间距、肋的直径以及流体与固体的导热系数比kf/ks对通道平均阻力系数和换热性能的影响,并引入换热性能评价指标PEC对2种网状肋进行了比较.结果表明:管内插入网状肋对流动阻力系数和换热性能有很大影响;方形肋的换热效果比圆形肋好,但其阻力较大;随着Re的减小,2种肋的降温效果均增强;肋的网格间距越小,则换热效果越好但阻力越大;随着肋直径的增大和流体与固体导热系数比kf/ks的减小,换热效果增强.     

垂直布置B30波槽管管外膜状凝结的实验研究

在略高于大气压的凝结条件下,对垂直布置渡槽管管外膜状凝结换热进行了实验研究。实验结果表明：垂直布置时波槽管具有一定的强化传热效果,在实验范围内,最佳波槽管的总传热系数约比光管提高27％-43％,而阻力系数约为光管的2．94-3．48倍,垂直布置的强化传热效果不如水平布置的好。通过对实验数据的回归分析,得到了垂直管管内对流换热、管外凝结换热及阻力系数的实验关联式。     

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.