全玻璃真空太阳能热管半球发射比测量及仪器

全玻璃真空太阳集热管内选择性吸收涂层的 发射比是个非常重要的光-热性能参数,GB/ T17049-2005规定太阳选择性吸收涂层的半球发射 比εh≤0．080(80℃±5℃)。这里讨论发射比的测量 方法及准确度。早期的办法是在生产集热管吸收     

Al-AlN太阳能选择性吸收涂层的中频溅射工艺研究

探讨了AlN膜和渐变Al-AlN选择性吸收涂层的中频溅射技术,结果表明:增大铝靶电流或减小氩气流量有助于改善AlN反应溅射的工艺稳定性;随着氮气流量的增加,AlN膜的N/Al原子比增大,减小氩气流量或增大铝靶电流对制备满足理想化学计量比的AlN膜有利;AlN膜的致密性随氮气流量和铝靶电流的增大而改善,但氩气流量对AlN致密性没有明显影响;制备的渐变Al-AlN选择性吸收涂层可见光反射率低于6％.光谱选择性较好.     

溅射光谱选择性吸收表面的进一步改善

采用直流圆柱形磁控反应溅射研制了α-C:H(丁烷),Al-O、Si-O与Al-C-F等薄膜。在波长为0.5微米时,这些薄膜的折射率n分别为1.85、1.70、1.50与1.40,消光系数k都很低。Al-C-F薄膜是比较理想的减反射膜,不仅折射率低,而且沉积速率高,约为SiO_x的四倍,AlO_x的十五倍。 Al-O膜(60nm)、Si-O膜(70nm)或Al-C-F膜(70nm)溅射沉积在以铜为基底的渐变不锈钢-碳涂层上,构成新的选择性吸收涂层,其太阳吸收率α_s(AM2)均达0.96(真空500℃烘烤1小时),室温发射率ε分别约为0.04、0.04与0.05,α_s/ε约19—24。 研制了具有Al-C-F/α-C:H/SS-C/Cu吸收涂层的全玻璃真空集热管。在100℃时这种吸收涂层的发射率约为0.055。     

不锈钢衬底表面形貌对AlN/AlN-Cr/Cu太阳能选择性吸收涂层光热性能的影响

在数值仿真计算和实验两方面研究不锈钢衬底表面形貌对AlN/AlN-Cr/Cu太阳能选择性吸收涂层光热性能的影响。在数值仿真计算中,建立一维三角形光栅结构模型对衬底表面形貌进行简化,采用严格耦合波分析(RCWA)的方法,仿真计算并分析光栅深度T_z和周期T_x对涂层的太阳吸收比α和400℃热发射比ε的影响。实验上,制备具有不同深度和间隔起伏表面的不锈钢衬底,采用磁控溅射的方法在其上沉积相同结构参数的AlN/AlN-Cr/Cu太阳能选择性吸收涂层,测定涂层性能参数,并分析不锈钢衬底形貌对其的影响。数值计算和实验结果表明:对于一个在已优化涂层组分和厚度的AlN/AlN-CdCu太阳能选择性吸收涂层,不锈钢衬底表面起伏对涂层高温光热转换将产生不利的影响。随着不锈钢衬底表面平均起伏深度的增加,涂层的太阳吸收比α基本保持不变,而400℃时的热发射比ε则明显逐渐增大。为保证涂层有效的光热转化效率,建议不锈钢衬底表面起伏的深宽比T_z/T_x≤1/20,深度T_z≤0.2μm。     

溅射太阳能选择性吸收涂层

溅射太阳能选择性吸收涂层,应用于太阳能集热器。它是采用单个圆柱(或平板)铝阴极,于氩气中溅射铝膜为底层,先后于氩-氮(或氩-一氧化碳)混合气体与纯氮(纯一氧化碳)中反应溅射成份渐变的铝-氮(或铝-碳-氧)复合吸收材料。涂层的太阳吸收率α     

全玻璃真空太阳集热管半球发射比测量及仪器

全玻璃真空太阳集热管内选择性吸收涂层的发射比是个非常重要的光-热性能参数,GB/T17049-2005规定太阳选择性吸收涂层的半球发射比εh≤0.080(80℃±5℃).这里讨论发射比的测量方法及准确度.早期的办法是在生产集热管吸收涂层时,在镀膜机内挂上40×40mm的玻璃片,以此来代替该管的吸收涂层,通常测量其法向发射比.虽然该办法不理想,但也有益于生产中的检验.目前,有些厂家仍然使用此方法.     

先进太阳选择性吸收涂层的发展

槽式抛物面太阳场运行温度的提高,由400℃至＞450℃,能增加总太阳发电效率和减小槽式抛物面发电厂的发电成本.当前的太阳选择性涂层不具备在较高工作温度所需的稳定性和工作性能.本文目的是开发更有效的太阳选择性涂层,在高于450℃时有高的太阳吸收比(α＞0.96)和低的热发射比(在450℃时,ε＜0.07),他们在高于450℃是热稳定的,在空气中是理想的,且具有改善了耐久性和生产制造性,因此减少了成本,利用计算机辅助光学设计软件,使多层太阳选择涂层具有超过目标的光学性能(吸收比为0.959,450℃时发射比为0.070)和比一般商业涂层有更低的热损失,那些具有高热稳定性的材料用计算机模型化了,这些超过设定的目标1％的发射比约等于1.2％吸收比.关键问题是沉积涂层的方法,为了沉积这单独的一层层薄膜,为了模型化的选择性多层结构的原型,使用由离子束辅助(IBAD)和电子束(电子束)共同沉积,这是由于它的灵活性和低的材料成本,实验工作聚焦在模型化的高温太阳选择性涂层;沉积一个个单层和模型化的涂层;测量光、热、形貌和成分等性质,并利用数据使模型化和沉积特性的有效性;涂层再优化;测量涂层工作性能和耐久性,将描述开发一个耐久的和先进的选择性涂层的过程.     

真空沉积双层黑铬选择性涂层

本文介绍了用于全玻璃真空管太阳能集热器的真空沉积双层黑铬选择性涂层的工艺和性能。其α_s为89％—91％,ε_n为5％—7％(80℃)。该涂层经300℃—400℃、1小时的烘烤后,α_s和ε_n基本没有变化。 应用激光干涉法,在λ=6328(?)波长下对每层黑铬涂层的光学常数进行了初步测定,并用测定的数据计算了该波长下双层涂层的反射率,其结果与分光光度计测定的反射率基本相符。结果表明,第二层黑铬具有减反射作用,因而使真空沉积的双层黑铬选择性涂层具有较高的吸收率,并仍保持其低的红外发射率。 还应用了电子显微镜、电子衍射与x光衍射等对黑铬选择性涂层进行了表面形貌观察与物相分析。 对所试制的真空沉积双层黑铬真空集热样管的试验表明,涂双层黑铬的真空集热管的集热性能优于单层黑铬的集热管。     

Al-C-F/渐变SS-C/Al选择性吸收表面

建立了铝与不锈钢两个平面磁控靶溅射系统。反应溅射沉积了一组SS-C复合材料、α-C:H与Al-C-F均匀薄膜。运用椭偏仪-分光光度计法确定了上述薄膜在太阳光谱范围(0.35—2.5μm)内的光学常数谱值(?)(λ)=n(λ)-ik(λ)。 对多层膜系的模型用计算机进行优化设计与计算。实验表明,溅射沉积Al-C-F/变渐SS-C/Al选择性吸收表面,其反射率谱值与计算出的最佳谱值基本一致,太阳吸收率α≈0.96,法向发射率ε_n≈0.06(80℃)。经真空中450℃烘烤1小时,该表面的光学性能基本没有变化。这种优质表面用于玻璃真空集热管有良好的前景。     

光谱选择性吸收涂层中的衬底金属

采用平面磁控溅射技术在玻璃上制备的金属铝膜,随氩气压强的升高及膜层的加厚而铝膜表面变得粗糙、反射率下降。以渐变不锈钢-碳为吸收层,分别以铝膜、不锈钢膜及玻璃为衬底构成的选择性吸收涂层,太阳吸收率可达95％(AM2),热发射率则分别为0.05、0.18及0.63。光谱选择性吸收涂层的热发射率主要取决于衬底材料的红外反射率。     

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%.     

Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

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.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

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.     

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。