竖直排列硅纳米孔阵列强化光学吸收的机理

光伏发电是太阳能利用的重要途径之一。提高单晶硅的光学吸收特性可以提高光伏利用效率,降低制造成本。采用时域有限差分法计算了具有竖直排列纳米孔阵列结构的单晶硅薄膜的光学特性,发现纳米孔阵列强化光学吸收的机理包括等效折射率减小、纳米尺度效应和电磁波谐振效应。计算结果表明,合理设计纳米孔阵列的排列周期和孔径可以大幅增强单晶硅薄膜的光学吸收,使纳米孔阵列单晶硅薄膜光伏器件的理论效率比相同厚度单晶硅片光伏器件高85.5%,并预期可以使100μm量级厚度的纳米孔结构单晶硅薄膜具有和102μm量级厚度的单晶硅片相当的光伏特性。     

含吸收散射粒子半透明介质层的容积吸收特性分析

将Ｍｉｅ散射理论与蒙特卡罗法相结合分析了含吸收散射粒子半透明介质层的容积吸收特性。考虑了半透明入射表面的折射与反射,不透明壁面的漫反射,半透明介质的吸收以及粒子系的吸收和独立多次非规则各向异性散射。直接由粒子复折射率,粒径及入射辐射波长等基本参数,根据Ｍｉｅ散射理论确定粒子系的吸收,散射因子以及非规则的各向异性散射分布。计算分析了介质层光学厚度、粒子复折射率、尺度参数、粒子系特征参数以及锥形入射时     

冷辐射板吸收太阳辐射的特性研究

为计算辐射空调系统中冷辐射板吸收太阳辐射能的大小及比例,在分析室内太阳光线传播的基础上,提出采用一种线性方程的方法.结果表明,以本文房间为例,冷辐射板吸收的太阳辐射能的大小以及比例在夏至日表现为正午最小,冷辐射板所吸收的太阳辐射能理论上最大能达到32 W/m2,吸收系数在0.13～0.28之间变化.冷辐射板所吸收的太阳...     

基于石墨烯电极的聚合物太阳能电池光学减反层的研究

石墨烯薄膜具有低阻且在可见光谱区具有高透过率,可应用于聚合物太阳能电池透明电极。本文基于时域有限差分分析方法（FDTD）,研究了石墨烯太阳能电池的反射损耗及光吸收特性,并通过在玻璃基板与石墨烯间添加氧化镍层（NiO）进行光学减反射。理论分析表明：优化的NiO /石墨烯透明电极结构,能够成为氧化铟锡（ITO）的良好替代电极。     

竖直板上液膜吸收特性的数值分析

用混合法建立了液膜在竖直板上的气液两相流CDF模型,在分析国内外有关传热传质的文献基础上,简要介绍了竖直板上降膜吸收的理论,介绍了竖直板上液膜的研究结果并对后续研究进行了展望。     

氨水富液再生及再生液吸收特性的试验研究

在常压、60～90℃下通过试验系统对氨水吸收CO2后的富液的再生特性以及再生液的吸收能力进行了研究,得到了影响氨水富液再生的因素及再生液的吸收性能.结果表明:提高再生温度可以增大CO2的再生速率和再生程度;氨水富液负荷对再生有很大影响,负荷低于0.4 molCO2/mol NH3时,再生率维持在较低水平,随后再生率随负荷上升而线性增加;负荷为0.6 molCO2/mol NH3时,氨水富液已基本丧失脱碳能力,再生后其吸收性能得到一定恢复;在再生液中添加少量的新鲜氨水,有助于恢复再生液对CO2的吸收能力;综合考虑富液再生与再生液吸收两方面,推荐氨水循环脱碳时负荷变化范围为富液0.6 mol CO2/mol NH3,贫液0.4 mol CO2/mol NH3.     

弯扭耦合的旋转机械轴系弯振特性的研究

随着旋转机械在役运行时间的增加,转子部分多数会有质量偏心现象出现。这使得转子轴系的扭转振动与弯曲振动的耦合作用明显增强。在已有耦合振动方程基础上,采用有限差分、Newmark积分法求得动力响应,以300 MW汽轮发电机组为研究对象,将其模化为多支承分布质量模型,采用FFT、STFT和wavelet多种方法分析它在简谐衰减、非同期并列两种典型工况激励下以及不同偏心函数、弯扭下的弯振特性。分析结果为研究旋转机械复杂转子系统耦合振动中弯振特性的定量、定性分析提供了依据。图24参7     

臭氧氧化结合化学吸收同时脱硫脱硝的研究——石灰石浆液吸收特性理论分析

为开发臭氧氧化结合化学吸收同时脱除多种污染物技术,对石灰石吸收脱除臭氧氧化产物(SOx和NOx)的吸收反应机理进行了研究,应用气液固平衡理论对SOx和NOx在石灰石浆液中的吸收特性进行了分析,结果表明烟气中CO2对SOx和NOx吸收的影响可以忽略,并得到浆液在吸收容量所能承受的最大气液比M.当[CaCO3]=0.05 mol/l,临界点M=600～700;当LCaCO3]=0.1 mol/l,临界点M=1200～1300;当[CaCO3]=0.15 mol/l,临界点M=1900～2000.     

微尺度乙醇扩散火焰特性的实验研究与数值解析

以大空间中圆形陶瓷微管形成的液体乙醇扩散火焰为研究对象.用实验和数值解析的方法研究了微尺度液体乙醇扩散火焰的火焰结构和温度分布.实验证明,在喷管尺寸相同条件下液体乙醇流量增大,火焰温度随之升高,火焰体积增大.通过数值解析观察了火焰和微管内温度场分布以及微管内热质传递现象.数值解析结果与实验一致.     

庚烷池火辐射及其对相邻油池的引燃特性

油库罐区时常发生由着火油罐的强烈热辐射而引燃相邻油罐的火灾事故,扩大燃烧范围。因此,需要对储油罐火焰辐射及其对相邻油池的引燃特性进行研究。本文采用内径分别为74 mm、114 mm、150 mm和200 mm的4种圆形石英玻璃油盘,开展不同油盘间距条件下的庚烷池火和点火实验。结果表明,根据圆柱体模型计算得到的辐射热流预测值与实验值吻合较好.当油盘尺寸一定时,随着油盘间距增大,待引燃油盘点接收的辐射热流逐渐减小;而当油盘间距相同时,油盘直径越大,待引燃油盘中心点接收的辐射热流越大。点火过程按照时间顺序划分为3个阶段:加热升温阶段、蒸气积聚阶段和点火阶段。随着油盘尺寸变大,庚烷的临界辐射热流随之变大且作为低闪点燃料,庚烷的临界辐射热流比高闪点燃料小得多.     

Flame structure and NOx emission characteristics in a single hydrogen combustor

In this study, the effects of fuel-induced swirl number on the flame structure and NOx emissions are observed. A tube-type nozzle with four fuel injection holes is used. The fuel injection holes are located away from the centerline of the nozzle to induce a low swirl effect in the flow. First, the flame structure changes with the fuel-induced swirl number, separating into four small flames in the high-swirl region; the flames are classified into three types. Subsequently, NOx emissions decrease with an increase in the fuel-induced swirl number. However, this shows a stepwise discontinuous change rather than a gradual change. The NOx emission is linearly proportional to the residence time of the combustion gas, which is calculated using the flame volume and flame structure. In conclusion, the change in the flame structure by the fuel-induced swirl is a decisive factor in the reduction of the NOx.     

Three-dimensional numerical simulation of free convection and entropy generation in a cubic cavity containing a heat source

The present article provides a three-dimensional numerical investigation of thermal convection and entropy generation. The lattice Boltzmann method, coupled with the finite difference approach, is applied to perform numerical simulations. The validation of these numerical approaches for thermal convection simulation and entropy calculation is performed by comparing our numerical results with those in the published literature for the case of benchmark problems. The physical geometry studied in this paper concerns a hot obstacle having the shape of a plus sign (+) placed in the center of a cubic enclosure. This cube is filled with air of a Prandtl number of 0.71 and characterized by two cold vertical walls. The heat exchange between the fluid and the hot body is studied as a function of the Rayleigh number (${10}^3\le \mathit{Ra}\le {10}^7$). The performed simulations show that the heat transfer rate can be increased by about 429% by switching from $\mathit{Ra}={10}^3$ to ${10}^7$. The entropy generation due to fluid friction, heat transfer, and total entropy are also calculated and discussed. For an irreversibility coefficient $\mathit{\phi }={10}^{-4}$, the analysis of the results showed that for low values of the Rayleigh number ($\mathit{Ra}={10}^3$), the entropy production due to temperature gradients predominates over that produced by viscous effects. In the cases of $\mathit{Ra}={10}^4$ and ${10}^5$, entropy generation is due to both fluid friction and heat transfer. However, when the Rayleigh number becomes large ($\mathit{Ra}{\ge 10}^6$), entropy generation due to viscosity predominates over entropy production related to heat exchange. These results have important implications for the optimization and design of heat transfer systems in various industrial applications.     

CKD5型机车底架结构设计及有限元分析

CKD5型机车是大连机车车辆有限公司为刚果设计、生产的电传动内燃机车,其车体为外廊式底架承载单司机室结构,底架主要承担机车上部设备载荷及机车牵引和制动所产生的牵引力和制动力。介绍了底架钢结构及主要参数和底架有限元分析以及在设计中采取的相关措施。     

不同入射角风波流海上漂浮式风力机频域与时域动态特性

采用边界元并结合多体动力学方法分析了张力腿平台(TLP)漂浮式风力机结构,研究了平台结构在不同方向上的频域与时域运动响应变化,并比较了漂浮式平台在海洋环境条件下风波流联合作用时和波浪载荷独立作用时的运动响应,得到了平台结构在时域中的动力响应.研究结果表明:漂浮式平台在频域变化范围内,运动响应主要集中在低频部分,绕射力对漂浮式海上风力机TLP的作用力不能忽略;风波流联合作用时的运动响应标准差大于波浪载荷独立作用时的运动响应标准差,且平台偏离平衡位置的程度更加剧烈;平均运动响应及标准差在入射角分别为0°、22.5°和45°时相差微小.研究结果对海上张力腿平台结构设计与优化具有很高的参考价值.     

Thermal performance of straight porous fin with variable thermal conductivity under magnetic field and radiation effects

The present numerical study reports the thermal performance of the straight porous fin with temperature-dependent thermal conductivity, radiation, and magnetic field effects. The heat transfer model comprising the Darcy's law for simulating flow with solid-fluid interactions in porous medium, Rosseland approximation for heat transfer through radiation, Maxwell equations for magnetic field effect and linearly varying temperature dependent thermal conductivity, results into highly nonlinear ordinary differential equation. The governing equation is solved using a finite difference scheme with suitable boundary conditions. The obtained solutions are physically interpreted by considering the impact of different nondimensional parameters on thermal performance, efficiency, and effectiveness of the system through plotted graphs. A detailed result with regard to the Nusselt number at the fin base is calculated. The results obtained are observed to be in excellent agreement with previous studies. From the study, it is observed that there is a significant effect on the thermal performance of the fin in the presence of porous constraints; also, results reveal that the nonlinear thermal conductivity parameter strengthens the thermal performance, efficiency, and effectiveness of the fin. Furthermore, the results of the study reveal that the rate of heat transfer of the fin increases with the increase in the magnetic parameter and radiation parameter.     

基于有限时间热力学的相变蓄放冷特性分析与研究

相变蓄冷技术可以有效解决能源转换与存储问题。但相变材料具有导热性能差,传热不均匀等问题。引入有限时间热力学概念,建立更为实际的蓄冷系统数学模型,对相变蓄冷系统进行热力学优化。通过解析计算,得出蓄冷系统高低温热源与蓄放冷时间的关系式。对比理想状态下与添加不可逆热损耗时蓄冷系统的功率与效率,为相变蓄冷技术的应用提供了理论基础与指导。     

Three‐dimensional visualization of an electrically conducting and viscous dissipative fluid flow over a moving permeable vertical cylinder

This study numerically scrutinizes the boundary layer flow of an electrically conducting and viscous dissipative fluid past an impulsively started permeable vertical cylinder together with thermal radiation. The solutions of the governing problem are accomplished using the Crank‐Nicholson scheme. The impressions of pertinent parameters on the flow patterns of the fluid particles as well as on the velocity, temperature, and distributed regions are captured and visualized three‐dimensionally.     

Design and analysis of electrothermal metasurfaces

Electrothermal metasurfaces have garnered considerable attention owing to their ability to dynamically control thermal infrared radiation. Although previous studies were mainly focused on metasurfaces with infinite unit cells, in practice, the finite-size effect can be a critical design factor for developing thermal metasurfaces with fast response and broad temperature uniformity. Here, we study the thermal metasurfaces consisting of gold nanorods with a finite array size, which can achieve a resonance close to that of the infinite case with only several periods. More importantly, such a small footprint due to the finite array size yields response time down to a nanosecond level. Furthermore, the number of the unit cells in the direction perpendicular to the axis of nanorods is found to be insensitive to the resonance and response time; thus, providing a tunable aspect ratio that can boost the temperature uniformity in the sub-Kelvin level.