铸造多晶硅中铜沉淀的电子束诱生电流

利用电子束诱生电流(EBIC)研究了不同热处理条件下太阳电池用铸造多晶硅材料中的铜的沉淀特性，并与铜在普通直拉硅单晶中的沉淀行为进行了比较。EBIC观察发现，在铸造多晶硅中，热处理的冷却速率和结晶学缺陷(如晶界和位错)共同影响着铜在多晶硅中的扩散和沉淀性质。样品在快速冷却时，在晶界以及晶粒内形成了很高密度且分布较均匀的细小铜沉淀；而在慢速冷却时，则是形成密度较低，较大尺寸的铜沉淀。EBIC的衬度计算显示，慢速冷却下形成的铜沉淀具有更强的复合特性，且铜沉淀在晶界上的分布具有选择性。最后，讨论了铜沉淀在铸造多晶硅中的形成机理。     

铸造多晶硅铝吸杂的EBIC研究

该文利用电子束诱生电流(EBIC)对太阳电池用铸造多晶硅材料铝扩散吸杂进行了研究.通过对铸造多晶硅中晶界、位错等缺陷不同温度EBIC图像的分析,确定了复合类型,分析了铝扩散的作用.此外,还发现奇怪的位错明衬度缺陷,分析了其产生原因.     

外延晶体硅薄膜电池的EBIC与SR-LBIC特性分析

电子束诱导电流(EBICElectron Beam Induced Current)是研究晶体缺陷(如晶界、位错、沉淀等)复合特性的一种有力工具.该文对以颗粒硅带为衬底的晶体硅薄膜电池表面及电池截面的晶体缺陷、特别是对晶界的复合行为进行了研究.电池表面EBIC照片表明复合中心位于晶界处,在小颗粒集中区域复合越强.截面的EBIC结果表明在颗粒晶界处分别有着强弱复合,与晶界处强的复合行为相比,颗粒内部没有或仅有比较弱的复合行为发生.靠近电池表面处的颗粒晶界和颗粒内部复合行为由于H钝化得到减弱,少数载流子扩散长度随深度的增加而降低.光谱决定的光束诱导电流(SR-LBIC)表明扩散长度在整个电池表面是不均匀的,最大扩散长度与外延层厚度相当.     

用CVD和高温退火技术制备大晶粒多晶硅薄膜

多晶硅薄膜是许多小单晶的集合体,存在大量的晶界。这些晶界把小的单晶体相互分隔,构成了材料的内表面,具有很高的态密度,对光生载流子起着复合中心的作用。晶界密度(或品界复合截面)越高,光生载流子的复合效应越强,这对于半导体器件的制作是十分有害的。 为了降低晶界效应,T.L.Chu等曾利用单向再结晶技术,用经过化学提纯的冶金硅粉     

多晶硅锭高氧浓度与少子寿命的研究

在多晶硅定向凝固高少子、低氧区域通入含氧气体,研究氧浓度对多晶硅锭少子寿命的影响程度。研究结果表明,当间隙氧浓度低于4.5×10~(17)cm~(-3)时,对于铸造多晶硅少子寿命的影响非常小;当间隙氧浓度为4.5×10~(17)~7.0×10~(17)cm~(-3)时,降低平均少子寿命0.50μs;当间隙氧浓度高于7.0×10~(17)cm~(-3)时,硅锭少子寿命受到极大影响,平均少子寿命降低到1.50μs,形成红区。因此,只有当铸造多晶硅尾部间隙氧浓度达到7.0×10~(17)cm~(-3)时,才可能形成尾部红区。     

多晶硅薄膜太阳电池厚度和晶粒尺寸对其性能的影响

利用PC1D计算了结构为n^ /p小和n^ /p—p^ 多晶硅薄膜太阳电他的品粒尺寸和薄膜厚度对其Voc，Jsc和η的影响。计算结果表明：对无陷光结构的多晶硅薄膜太阳电池，要获得10％的效率，薄膜厚度至少应大于22μm；晶粒尺寸大于薄膜厚度的4倍时，晶界复合对载流子寿命的影响可以忽略；同时表明：太阳电他的背表面场(BSF)对提高多晶硅薄膜太阳电他的性能具有很大的作用。     

退火对冶金法太阳能级多晶硅中缺陷影响的研究

研究了不同条件下退火对冶金法太阳能级多晶硅锭不同部位的位错、晶界及择优生长取向的影响。利用金相显微镜,电子背散射衍射和X射线衍射仪分别对退火前后多晶硅锭的位错、晶界和择优生长取向的变化规律进行表征,结果表明:退火前后多晶硅中的位错密度大小始终是中部<底部<顶部。1100℃下随着保温时间的延长,多晶硅中的位错密度逐渐减小,到5.0h后达到回复的极限程度;小角度晶界比例不断减小,直至消失;大角度晶界中R型晶界比例先增加后减小,CSL晶界比例缓慢增加,孪晶晶界Σ3比例呈稳定地增加,到退火5.0h后,其比例约占30%;主峰〈111〉织构峰强一直增加,〈311〉织构峰强则是逐渐减小至零,而〈511〉、〈531〉、〈620〉织构强度则是先减小、后增大、最后再减小,退火保温5.0h后择优生长取向达到高度一致。另外,还得到了不同温度下的极限回复程度。     

变温磷吸杂对多晶硅性能的影响

用微波光电导衰减仪(μ-PCD)研究了不同温度和时间的恒温和变温磷吸杂处理对铸造多晶硅片电学性能的影响。实验发现:变温吸杂明显优于恒温吸杂,特别是对原生高质量多晶硅;其优化的变温磷吸杂工艺为1000℃/0.5h 700℃/1.5h;而在高温恒温吸杂中,多晶硅少子寿命值反而显著下降。实验现象表明:磷吸杂效果主要是与过渡族金属的溶解、扩散和分凝有关。     

太阳能硅片电火花电解复合切割制绒机理研究

提出了一种基于复合工作液的以电火花电解复合加工技术对太阳能硅片进行切割及制绒一体化的新方法.试验表明高速走丝电火花线切割(WEDM-HS)对太阳能硅片切割具有效率高、厚度薄、切缝窄、表面可直接形成绒面结构,表面无明显微裂纹且切割表面不存在电极丝金属残余;在硅表面放电凹坑内由于高温电解复合作用会形成密集、壁面光滑且高深径比的微孔洞结构;绒面结构不受硅材料特别是多晶硅各向同性的影响,且获得的表面反射率略低于目前制绒方法的表面等特性.     

跟踪式CPC热管真空管集热器聚光及集热特性

将曲柄连杆单轴跟踪技术与CPC(复合抛物面聚光器)热管真空管太阳集热器集成,研制一套聚光比为2.3的跟踪式CPC集热器。基于Trace Pro光学软件模拟其跟踪模式下的聚光行为,并对不同跟踪模式下的集热特性进行实验研究。模拟得到横向投影角θt是影响CPC集热器光学性能的主要因素,θt为-23.5°~23.5°时,入射角修正因子(IAM)达到0.95~1.14;跟踪可有效缩小θt,将光学效率提高30%以上;采用三点式间歇跟踪即可获得高于60%的光学效率。实测集热效率分布和光学效率模拟值趋势一致,系统跟踪时高效集热时间为固定式的2.7倍,平均集热效率达到固定式的2.1倍。集热效率归一化线性良好,效率截距为52%,和光学效率模拟值偏差小于12%,佐证了模拟分析结果。     

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。