开路电压与太阳电池少子寿命关系的推导及其应用的研究

从理论上详细推导了晶体硅太阳电池在脉冲光照下,开路电压Voc(t)与少数载流子寿命的关系,同时研究了N-P结势垒电容放电时对Voc(t)的影响;从实验上验证了开路电压随时间的衰减关系,并运用该关系测量了硅太阳电池少数载流子寿命,测量结果较为准确.     

激光掺杂形成硼背场PERL硅太阳电池的研究

研究两种激光器(绿光纳秒调Q激光器和准连续紫外高频锁模激光器)对PERL太阳电池的背面掺硼的效果。通过分析扫描电子显微镜(SEM)、电化学ECV曲线和少子寿命的数据,确定合适的激光器及激光参数。继而研究烧结温度对太阳电池性能的影响。综合分析电池的反射率、内量子效率、电性能参数及烧结后铝硅接触的SEM剖面图,得到最优烧结温度。研究发现用准连续紫外高频锁模激光器(7 W,250 mm/s)进行激光掺硼、以630℃烧结,所得电池效率最高可达19.90%。     

多晶硅太阳电池少子寿命的数值模拟

主要引入载流子的有效迁移率和有效扩散长度两个物理量,对多晶硅的少子寿命进行数值模拟.在此基础上建立了多晶硅太阳电池的一维物理模型,采用数值模拟方法对其在AM1.5太阳光入射下的电池输出特性Lsc、Voc、FF和η进行模拟计算,着重分析了晶粒尺寸和基区少子寿命对多晶硅太阳电池性能的影响.模拟结果表明,晶粒尺寸和少子寿命是影响多晶硅太阳电池性能的两个关键因素.当少子寿命较低时,晶粒尺寸对电池效率的影响不大,此时电池效率的提高受限于少子寿命;当少子寿命增大时,电池效率随晶粒尺寸的增大显著提高.同时,从模拟结果可得到电池效率与少子寿命和晶粒尺寸之间的定量关系.     

利用光谱响应研究太阳电池基区少数载流子扩散长度

针对已有的晶体硅太阳电池基区少数载流子的扩散长度测量模型和测试方法中存在的不足,建立利用光谱响应研究硅太阳电池基区少数载流子的扩散长度的模型,该模型考虑了n+pp+型晶体硅太阳电池背面高低结势垒的影响,对基区少数载流子扩散长度的测量模型进行修正。根据硅太阳电池在900~950 nm的长波光谱响应测试结果,并利用该修正模型得到少数载流子在基区的扩散长度。所得结果与PC1 D模拟结果进行比较,两者相近。     

利用电致发光技术快速测定晶硅太阳电池少子寿命

结合理论分析,讨论太阳电池电致发光的影响因素,提出利用电致发光技术来测定晶硅太阳电池的少子寿命。在完成测试定标后,对比目前普遍使用的微波光电导衰退法,对电致发光法测定单晶和多晶硅少子寿命进行实验验证。结果表明,电致发光测试方法能快速、稳定、准确地测定晶硅太阳电池的少子寿命。     

少子寿命值对太阳电池生产的监控作用

研究了太阳电池工艺过程中少子寿命值的变化,揭示了少子寿命值在太阳电池生产过程中的应用.通过比较工艺前后少子寿命值的变化,可以优化生产工艺,提高电池转换效率,改善电池的性能.经过工艺优化后,多晶硅太阳电池(非绒面)的平均转换效率达到14.75%.     

利用太阳电池I-V特性测量其基区少数载流子寿命

提出了一种新的测量成品太阳电池基区少子寿命的方法,这种方法在电池制备完成后进行测量。此方法还可对印刷电极后烧结这步工艺流程进行少子寿命的监控,以提供改进电极制作工艺信息。     

直拉硅片中间隙氧和硼对太阳电池光衰减影响的研究

为研究间隙氧和硼对于硅片少子寿命和光衰减的影响，实验中采用不同氧碳含量、不同掺杂浓度的p型(100)的直拉硅(Cz-Si)片制作太阳电池，设计了不同温度、气氛的热处理工艺。发现：太阳能级直拉单晶硅片中间隙氧含量和硼的掺杂浓度的不同对于硅片少子寿命的影响有一定的规律；硅片少子寿命值在650℃热处理时有轻微下降，而在后续650℃和950℃的热处理中有着显著的提高。当电阻率一定时，低氧的样片有利于少子寿命的提高；而在氧含量相同的情况下，掺杂硼的浓度越低，对于少子寿命的提高越有利。     

氮化硅薄膜对晶体硅材料和电池的钝化效果研究

利用等离子体增强化学气相沉积技术,在P型直拉单晶硅硅片和铸造多晶硅片以及太阳电池的表面上 沉积了非晶氮化硅(a-SiNx:H)薄膜,并研究了氮化硅薄膜对材料少子寿命和太阳电池性能的影响。研究发现: 氮化硅薄膜显著地提高了晶体硅材料中少子寿命,同时多晶硅太阳电池的开路电压有少量提高,短路电流普遍 提高了1mA/cm2,电池效率提高了2％。实验结果表明:氮化硅薄膜不仅具有表面钝化作用,也有良好的体钝化 作用。     

多晶硅太阳电池低温变温扩散工艺的优化

采用少子寿命测试仪对扩散前后的硅片少子寿命进行了分析,当扩散后的方块电阻控制在55～65Ω时,低温变温扩散工艺处理的硅片少子寿命最高达到12.18μs,低温恒温扩散工艺处理的硅片少子寿命为10.67μs,高温恒温扩散工艺处理的硅片少子寿命为8.20μs。低温变温扩散工艺处理的太阳电池分别比传统的低温恒温扩散工艺处理和高温恒温扩散工艺处理的太阳电池转换效率提高0.79%和0.42%。     

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.     

Contents in Volume 23,2014

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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.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.