热循环对硅太阳电池伏安特性的影响

试验研究了太阳电池结构的热循环效应.结果表明:经100次热循环作用后太阳电池伏安特性曲线下移,输出功率降低6‰～7‰;各层胶接材料的热物理性能相差较大,热循环过程中热错配应力累积,使太阳电池胶接结构可能出现裂纹或层间剥离现象.     

热循环下太阳电池板单元结构热应力演变规律研究

利用MSC.Marc大型通用软件研究了热循环条件下太阳电池板单元结构热应力分布及演变规律。结果表明:被粘接层正应力极大值位于结构中点,极小值出现在结构两端;胶层剪切应力极大值位于结构两端,极小值出现在中点;聚酰亚胺薄膜层取得太阳电池板单元结构最大正应力,粘接聚酰亚胺薄膜与碳纤维复合材料的硅橡胶层取得结构最大剪切应力;结构在低温保温阶段的最大正应力及最大剪切应力远大于高温保温阶段的最大应力;太阳电池板单元结构的最大应力值随热循环次数的增加而增加。     

热循环作用下太阳电池板单元结构寿命预测

试验测试了热循环过程中太阳电池板单元结构各被粘接层的热应变值,结合有限元MSC.Marc模拟的结果提出了以热应变极大值或残余热应变作为热循环条件下胶接结构的损伤参量,建立了预测太阳电池板寿命的数学模型。     

热循环中太阳电池胶接结构中热错配应力的温度分布和调整

分析了太阳电池中石英玻璃盖片／硅橡胶粘结剂／硅晶片胶接试样在热循环（143－403K）下热错配应力的温度分布，发现其只与初始应力状态有关，与循环次数无关，建立了热错温应力调整的概念，分别经113K和77K低温处理后，胶接试样的热错配应力－温度曲线下移，下移幅度与冷处理最低温度有关，与冷处理次数无关，与未处理相比，冷处理胶接试样经热循环后,粘结强度提高。     

输电线路弯曲导线分层力学特性模型及仿真分析

为准确评估不同弯曲状态下导线分层应力特性,以LGJ500/45型钢芯铝绞线为研究对象,考虑张力作用下各层股线的轴向应变和轴向扭矩,提出输电线路精细化分层张力、分层应力应变的计算方法,通过建立并模拟不同弯曲角度(0°、15°)的三维导线分层有限元实体模型,对比了理论计算结果,验证了仿真模型的准确性,得出不同弯曲状态下运行张力作用时导线各层间的应力分布规律。结果表明,0°导线在承受轴向张力的作用下,两层钢芯线承担主要张力,且各层钢绞线和各层铝绞线均呈由内至外轴向逐渐增大的趋势;15°弯曲导线分别出现弯曲朝向侧圆周方向应力更高、反方向圆周方向应力更低等导线分层力学特性。     

汇聚太阳能流体流速对吸热器温度场和应力场影响

为研究高汇聚太阳能流体流速对管式吸热器的温度场、热应变及热应力场的影响,本文采用蒙特卡洛与有限单元相结合的光热力顺序解耦计算法分析了不同流速下管式吸热器的温度场、热应变及热应力场的分布。计算结果表明管式吸热器的温度场、热应变及等效热应力均随着流体流速的增加而降低。与轴向热应力和径向热应力相比,切向热应力对管式吸热器的等效热应力的贡献比例更大,均匀化温度沿管式吸热器的圆周方向分布是热应力抑制的有效手段之一。     

层间温度对TP91钢焊接残余应力的影响

通过建立线性焊接的广义平面应变单元的二维(2D)横截面模型,在2D横截面残余应力模型中采用大量的简化参数分析和数据,完成了TP91钢焊接残余应力的有限元数值模拟。在热分析单元模型下得到TP91钢管对接焊形式下的温度场分布情况,然后利用热结构耦合的方法得到TP91钢管的瞬态焊接应力场及焊后残余应力,并分析层间温度对TP91钢残余应力的影响。     

大厚度树脂基复合材料的热风箱加热固化研究

为研究某通航飞机典型树脂基复合材料热风箱加热固化过程中的热应力，建立了包括流固耦合、树脂固化放热的多物理场动量、热量输运模型和热应力模型，并通过实验验证了计算模型和方法的正确性。数值计算了不同厚度的层合板热风箱加热固化过程中的热空气流场，温度场以及层合板热应力场，并与热补仪加热固化过程中的对应参数进行对比。数值计算结果表明：热风箱在层合板周围能形成较高且稳定的温度环境，随着厚度的增大，层合板内温度分布更加均匀，层合板内部的热应力降低，且在固化过程中的热应力波动幅度减小。研究结果还表明，热风箱加热固化的板内热应力值在整个固化过程中均明显低于热补仪加热固化的热应力值，在升温阶段低幅达6%，在降温阶段低幅达10%。对于本文所研究的大厚度树脂基复合材料，热风箱加热固化具有较明显的优势。     

中空充钠气门三维测量及温度场应力场有限元分析

根据发动机的实际工况,建立中空充钠排气门在加载条件下的温度热应力和机械应力的计算模型,计算液态钠的对流系数并采用ANSYS有限元分析软件研究了其热应力和机械应力的分布状态,以及排气门偏心异常条件下的气门应力分布,为中空充钠排气门优选材料和结构优化提供了理论依据。     

基于多轴非线性连续损伤模型的汽轮机转子低周疲劳损伤分析

针对当前汽轮机转子低周疲劳损伤分析存在较大误差的问题,引入了非线性连续损伤力学理论,并结合多轴疲劳损伤的临界面原理,建立了多轴非线性连续损伤累积模型.基于该模型,结合某型船用汽轮机转子典型工况下的瞬态温度场和热应力场的弹塑性有限元分析结果,对复杂应力引起的转子低周疲劳损伤进行分析,并与等效应变法的寿命预测模型和线性损伤累积模型进行了比较.结果表明:基于临界面法的非线性连续损伤累积模型,不仅考虑了多轴复杂应力应变的大小、方向和加载的附加强化效应的影响,而且正确地反映了转子低周疲劳损伤的非线性累积过程,其分析结果更接近于工程实际.     

A photovoltaic/thermal system with a combination of a booster diffuse reflector and vacuum tube for generation of electricity and hot water production

Using water as a coolant to reduce the temperature of solar cells is one of the best methods for improving the efficiency of a photovoltaic/thermal system. However the heat absorbed from the solar cell panel is not enough for providing domestic hot water. In this article, a new architecture of photovoltaic/thermal system is proposed and investigated. A silicon monocrystalline photovoltaic module is used with appropriate reflectors in order to increase insolation in conjunction with a closed loop cooling facility to efficiently extract the panel's heat. The absorbed heat from the photovoltaic/thermal panel, is used to preheat the water flow before entering four vacuum tube solar water heaters placed on both sides of the photovoltaic/thermal panel. Performance evaluation of this system in comparison to a similar bare photovoltaic panel, showed a significant increase in the system's electrical and thermal energy output.     

A thermal model for photovoltaic panels under varying atmospheric conditions

The response of the photovoltaic (PV) panel temperature is dynamic with respect to the changes in the incoming solar radiation. During periods of rapidly changing conditions, a steady state model of the operating temperature cannot be justified because the response time of the PV panel temperature becomes significant due to its large thermal mass. Therefore, it is of interest to determine the thermal response time of the PV panel. Previous attempts to determine the thermal response time have used indoor measurements, controlling the wind flow over the surface of the panel with fans or conducting the experiments in darkness to avoid radiative heat loss effects. In real operating conditions, the effective PV panel temperature is subjected to randomly varying ambient temperature and fluctuating wind speeds and directions; parameters that are not replicated in controlled, indoor experiments. A new thermal model is proposed that incorporates atmospheric conditions; effects of PV panel material composition and mounting structure. Experimental results are presented which verify the thermal behaviour of a photovoltaic panel for low to strong winds.     

Residual stress and plastic strain analysis in the brazed joint of bonded compliant seal design in planar solid oxide fuel cell

This paper uses finite element method (FEM) to predict the residual stress and plastic strain in the brazed joint of sealing foil-to-window frame in bonded compliant seal (BCS) design in a planar solid oxide fuel cell (PSOFC). The effects of window frame material type, sealing foil thickness, filler metal thickness and window frame thickness on residual stress and plastic strain are discussed. Large residual stress is generated in the joint, and the stress and strain are concentrated around the fillet. It is proved that the BCS design can mitigate and trap some residual stress by plastic deformation within the sealing foil. The residual stress and the ability of trapping stress of sealing foil are affected by window frame material and structure thickness. Based on the comprehensive considerations of the impact of residual stress and plastic strain, Alloy 625 as a window frame material is found to be better than Haynes 214, Hastelloy X and SUS 316L. The optimum thickness of sealing foil and filler metal BNi2 are found to be 150 μm and 75 μm, respectively. The residual stress and plastic strain are increased with the increase of window frame thickness.     

Fatigue Analysis on Thermal Characteristics for PBGA by Using Finite Element Method

The stress and strain of Plastic Ball Grid Array (PBGA) is investigated for reliability evaluation, failure analysis, or manufacturing. A one-eighth model is built to estimate the thermal stress and strain of PBGA under thermal cycling temperature (0°C–100°C). The different 3D elements such as Visco107 and Solid45 were selected for modeling of material 37Sn63Pb and Print Circuit Board (PCB), silicon die, substrate, and Epoxy Molding Compound (EMC), respectively. The results show that the maximum equivalent stress and equivalent plastic strain occur in the second outer solder joint and close to the position of chip. The key solder joint can be obtained and the key node of solder joint is 41402. The results indicate that the integrating 3D model can provide a more comprehensive profile for the thermal investigation of the PBGA package than from using any 2D model. The investigation provides a basis for improving reliability of PBGA product in engineering design.     

A hybrid amorphous silicon photovoltaic and thermal solar collector

A hybrid amorphous silicon (a-Si) photovoltaic and thermal solar collector was developed and its performance tested. The solar cells, deposited on glass panels and having an average efficiency of 4% and a total area of 0.9 m², were bonded to the fin and tube aluminum heat-exchange plate using simple technology. This hybrid unit performed well as a thermal solar collector, heating water up to 65°C, while the electric characteristics of the photovoltaic modules showed little change. In addition to saving space this integral unit substantially reduces the balance-of-system cost of the photovoltaic generator. The transmission of light through various layers of an a-Si cell was measured and, in order to improve the thermal efficiency, a novel transparent type of a-Si cell was developed and tested in the hybrid unit. The results obtained show that it is possible to construct simple and cheap hybrid systems having good photovoltaic as well as thermal efficiencies.     

Characteristics of Thermal Stress Evolution During the Cooling Stage of Multicrystalline Silicon

Directional solidification is one of the most popular techniques for the massive production of multicrystalline silicon (mc-Si) for solar cell application due to its well-balanced high conversion efficiency and low production cost. The grown crystal suffers from several types of defects that significantly degrade the photovoltaic performance of solar cells, among which dislocation is the most critical caused by thermal stress. To examine the characteristics of thermal stress and associated fields, therefore, it is significant for the understanding and optimization of the cooling process. In the article, an integrated simulation tool has been developed and used to investigate heat transfer, fluid flow, and thermal stress during the cooling process of mc-silicon. The simulation results were further proved by experimental observations. According to the distortion energy theory, the total strain energy consists of the volumetric strain energy and the shear strain energy, and yield occurs when the shear component exceeds that at the yield point, which is the major cause of the dislocation. Therefore, by analyzing von Mises stress aligned in the direction that has to support the maximum shear load, the regions in the ingot with dislocation generation and multiplication can be evaluated. The displacement indicates the motion of the crystal ingot, and reveals the regions of deformation due to the existence of thermal stress from uneven cooling. Based on the complete investigation of the characteristics of thermal stress and associated displacement, the cooling process could be well comprehended and further optimized with the minimization of dislocation density.     

Review of modern methods and technologies for using of solar energy in the operation of anaerobic digestion systems

The article presents various methods and technologies for using of solar energy in anaerobic bioconversion systems. Various methods of convertion of solar radiation are consistently considered – from its direct use to photovoltaic, thermal, photovoltaic thermal and concentrating. Schemes for introducing solar energy converters into anaerobic bioconversion systems, as well as various solar radiation converters for heat and electricity supply of anaerobic bioconversion systems, are proposed. As power generating components in the article also discusses photovoltaic modules with an extended rated power period, photovoltaic thermal roofing panels with a two-component polysiloxane compound, thermal and photovoltaic thermal solar roofing panels, air-cooled photovoltaic thermal siding panel and concentrator solar photovoltaic thermal module with high-voltage matrix photovoltaic converters. The proposed schemes of systems and design of solar modules will ensure a reduction in the use of thermal energy from the produced gas for power supply for the own needs of anaerobic bioconversion systems, which will make them cheaper and more efficient in operation.     

Experimental investigation and CFD analysis of a solar hybrid PV/T system for the sustainable development of the rural northern part of Bangladesh

An attempt has been made to utilise solar energy more efficiently by developing the single pass hybrid photovoltaic thermal system at the climatic condition of Bangladesh. As the electric energy conversion efficiency of the photovoltaic module falls with the surrounding temperature and air or water used as a suitable solution to make it cool. In this study, air was used as the cooling medium for the solar panel and circular copper tube was placed on the glazed collector for water heating to ensure maximum exploitation of solar energy. Moreover, the photovoltaic panel power was used to circulate the air and make the system self-powered. Maximum collector efficiency was 24.64% for water and 11.20% for air is observed at a mass flow rate 0.00158 and 0.00221 kg/s for water and air respectively at a solar radiation of 1050 W/m². In addition, the combined efficiency of the hybrid system was about 39.68%. By adding glycerin with water at a ratio of 50:1 (% of weight) the combined efficiency reached up to 45.76%. The computational fluid dynamics (CFD) simulation and economic analysis of the designed system strongly support the feasibility of the solar hybrid photovoltaic thermal system as the future sustainable energy source.