非均匀热流密度下槽式集热器吸热管热应力分析

为了分析槽式集热器吸热管的热力性能及其对集热系统安全运行的影响,以LS-2型集热器为研究对象,通过有限元数值模拟方法对槽式集热器吸热管进行热-结构耦合分析。结果表明:吸热管管壁最大温度位于出口处下端(抛物面反射镜反射光线照射区域),吸热管管壁最小温度位于入口处上端(太阳辐照直射区域);太阳直射辐照强度(400～900 W/m~2)越大,工质入口温度(50～300℃)越低,入口流速(1.0～3.5 m/s)越慢,对吸热管的热变形量和热应力影响越大。在集热器实际运行中,当太阳直射辐照强度较高时,工质入口温度和入口流速不能选取太低,否则会造成吸热管热应力增加,影响集热器的使用寿命。     

一种槽式太阳能空气集热器热性能的试验研究

为了研究日光温室用槽式太阳能空气集热器的热性能,基于TracePro光学模拟软件设计了一种槽式太阳能空气集热器,对其进行试验研究,分析了不同因素对集热性能的影响规律。实验结果表明,管中空气流速的变化对集热器集热效率和集热量的影响规律是相同的,在不同的流速下,存在最佳空气流速约为4.4 m/s,使得集热器的集热量和集热效率最大,集热量达到373.2 W,集热效率约为25%,此时集热性能最好。对于不同太阳辐照度,正午时刻之前,太阳辐照度越大,集热器的集热效率越大,正午时刻之后,集热器的集热效率基本保持不变,15:40之后集热器集热效率逐渐减小。当太阳辐照度和管中流速相同时,室外温度越高,集热器集热效率越大,集热性能越好。集热管中空气温度沿着集热管出口方向不断增大,太阳辐照度越大,集热管相同位置空气温度越高。该研究结果可为此种槽式太阳能空气集热器在日光温室的应用中提供参考。     

抛物面槽式太阳集热器的性能研究

建立槽式太阳集热器对太阳辐射的吸收模型和换热模型,应用Matlab编制模拟计算程序,并通过现场测试验证所建模型的准确性。在此基础上模拟研究太阳辐射强度、室外气温及风速、导热油流速、导热油进口温度等参数对集热器性能的影响。结果表明:槽式太阳集热器集热效率随导热油流速和太阳辐射强度的增大而增加;随导热油进口温度的升高而降低;受室外气温及室外风速的影响较小。研究结果可为该集热器的优化设计提供参考依据。     

槽式集热场辅助燃煤机组回热系统混合发电热性能分析

以热力学第一、第二定律为基础,对抛物面槽式集热器进行热效率和(火用)效率分析,并以LS-2典型槽式集热器热性能测试结果为依据,分析不同太阳辐照及工作温度条件下对应的（火用）效率;以此结果作为指导,对以等面积槽式太阳能集热场作为辅助热源替代燃煤发电机组不同回热抽汽集成方式的热力性能进行分析比较,得到此类集热场作为辅助热源与燃煤机组回热系统集成的最佳方案.     

积尘对槽式聚光系统镜面反射率及能流分布的影响研究

针对镜面积尘所导致的槽式太阳能集热系统反射率降低和能流损失问题,该文通过搭建槽式太阳能集热器焦面能流密度分布测试装置,试验研究积尘引起的聚光镜反射率下降及能流密度分布规律。结果表明:在可见光测试区域内,随镜面积尘密度增加,镜面相对反射率的变化量不同,太阳长波辐射较短波反射率下降明显;镜面积尘对汇聚太阳光线路径发生改变,对比洁净镜面,自然积尘25 d后,在太阳直射辐照度约50 W/m2时,集热管壁面能流密度峰值下降约15 kW/m2,且集热管圆周角为180°附近处,其汇聚光线路径变化尤为显著;结合实测数据得到积尘周期和积尘密度对相对反射率的函数关系,该方程可用于大气降尘相近地区积尘后槽式聚光镜相对反射率预测,与实测值相比最大偏差在±0.84范围内。为槽式太阳能聚光集热系统实践运行过程中,确定该地区该季节的最佳除尘时间提供试验依据。     

一种基于新结构的线性腔式太阳能集热器研究

提出一种适用于槽式太阳能热发电系统的新型线性腔式集热器。通过Tracepro模拟聚光镜焦距、弧形结构及开口宽度对系统光学性能的影响;采用热网络模型对该集热器的传热性能进行参数化研究,确定优化的集热器结构为优弧型,开口宽度为70 mm,与其匹配的聚光镜焦距为2100 mm。研究结果表明,当太阳直射辐射强度为500 W/m2,集热温度为650 K时,系统光热转换效率达65.3%。与一类传统真空管集热器的对比表明,该新型线性腔式集热器的集热性能优于UVAC Cermet直通式真空管集热器。另外,该线性腔式集热器生产和维护成本明显低于真空管集热器,对于促进槽式太阳能热发电技术具有重要意义。     

槽式太阳集热器传热与流动性能研究

以槽式太阳集热器为研究对象,建立集热器的传热流动数学模型,通过Fluent模拟,研究其传热、流动性能,并对模拟结果进行实验对比验证,对比结果表明二者吻合较好。在此基础上,分析太阳直射辐射(DNI)、集热器入口流体温度及流速对集热器集热效率、流体温升及压损的影响规律,并对流经集热器传热流体的流速进行优化,从而为槽式太阳集热器的优化设计及运行提供参考依据。     

水平布置方式下抛物槽式集热器辐照量分析

采用适用于中等纬度的Hottel晴天太阳辐射模型,对地处北纬41.34°,水平布置方式下的抛物槽式集热器夏季和冬季的辐照量进行了计算。计算结果表明:水平南北布置的抛物槽式集热器在夏季接收的太阳辐射较多,月辐照量可达1 GJ/m2,而冬季接收的太阳辐射较少,月辐照量为0.3~0.45 GJ/m2,且冬至日辐照量仅为夏至日辐照量的1/4左右;水平东西布置的抛物槽式集热器夏季月辐照量在0.75 GJ/m2左右,而冬季月辐照量为0.5 GJ/m2左右,冬至日辐照量可达夏至日辐照量的1/2以上。由此可见,在北纬41.34°地区应用抛物槽式集热器时,如考虑在夏季使用,应采用水平南北布置方式;若考虑在冬季使用,则应采用水平东西布置方式。     

熔盐槽式太阳能热发电站集热系统性能研究

通过SAM软件建立了建设在中国拉萨市、以低熔点熔盐为集热蓄热工质的80 MW熔盐槽式太阳能热发电站模型,结合理论分析,通过参数分析法,以槽式集热系统的集热效率等性能参数为优化目标,对该槽式电站模型的集热系统进行模拟优化分析。主要分析了集热器的开口宽度和集热系统的布置方案对熔盐槽式电站集热系统性能的影响。通过对比分析各组数据,得到适用于熔盐槽式电站的集热器、集热器阵列最佳布置方案(即集热系统单回路中最佳集热器数量和总回路数)、集热系统工质最佳设计出口温度和集热系统最佳分区数之间的匹配关系。     

小型槽式太阳能集热器优化设计与试验研究

按照高性能低成本的原则设计并制作了集热面积为12 m2的商用小型槽式集热器。其主要创新优化之处包括:1通过免背板设计减少了槽式反射镜面结构的重量和用材,提高了镜面曲率精度;2通过推杆联动机构减少了驱动装置;3反射镜面板分离式结构起到了自清洁功能,减轻了清扫的工作强度;4将闭环反馈技术应用到太阳能跟踪控制系统,可实现四季全天候跟踪。现场试验结果表明:在太阳辐射强度为540~660 W/m2时,该集热器可将循环水加热至170℃以上,系统整体集热效率最高可达0.52,但随水温的升高逐渐降低。     

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.     

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。     

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.     

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.