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。     

中高温太阳选择性吸收表面

８０年代以来,太阳选择性吸收表面的研究与应用有了很大发展,选择性吸收表面在太阳房、热水器上已广泛应用。然而,目前太阳能热利用一般局限在低温（＜１００℃),随着能源短缺和环境污染问题的日益加剧,太阳能的应用领域必将向中高温应用发展,而研制开发中高温太阳选择性吸收表面将成为关键。１材料根据太阳选择性吸收原理,选择性吸收材料大致可分为以下几种类型:具有本征特性的选择性吸收材料,多层膜,不均匀粒子膜,表面微孔穴。目前,作为中高温选择性吸收表面研究最多的金属陶瓷薄膜即属于不均匀粒子膜,本文主要对其进行一些介绍。所谓粒子…     

Mo-SiO2太阳选择性吸收涂层的空气高温热稳定性

采用磁控溅射的方法制作Mo-SiO2太阳能选择性吸收涂层,测量了涂层经过空气高温退火前后在0.34～25μm波长范围内反射曲线的变化情况.刚沉积完的涂层,太阳吸收比达到0.95,发射比为0.093.在空气中500、600℃退火1h后,涂层反射曲线基本不变.在空气中700℃退火1h后,涂层光谱选择性恶化,太阳吸收比下降到0.91,发射比上升到0.6.通过扫描电子显微镜观察了单层Mo、单层SiO2以及SiO2覆盖Mo的样片薄膜在空气中不同温度退火前后的形貌变化,发现以上薄膜表面不再平整,甚至出现裂纹和薄膜脱落,成为Mo-SiO2选择性吸收特性恶化的主要原因.     

三种选择性吸收表面

光谱选择性吸收表面能提高光热转换效率,中高温太阳能集热器一般均采用它作为吸收面。近年来北京化工学院物理教研室太阳能科研组研制了几种光谱选择性吸收表面,现简介如下: 氧化铜选择性吸收表面这项     

陶瓷表面太阳选择性吸收涂层的研究

以普通陶瓷毛胚为基底,采用钒钛磁铁矿渣制备黑釉吸收层,并采用红外灯辅助喷雾热解法制备锑掺杂氧化锡薄膜作为红外反射层,构建结构简单的陶瓷表面太阳选择性吸收涂层,并对涂层微结构和性能进行表征,结果表明:掺锑氧化锡薄膜结晶完全,厚度均一;涂层太阳吸收比可达0.93,法向发射比低于0.25;经500 h的老化性试验后,涂层的太阳吸收比和法向发射比变化小于10%。     

Cr-N-O型选择性吸收涂层制备及热稳定性研究

采用反应磁控溅射方法制备SiO_x/Cr-N-O/Al选择性吸收涂层,该涂层太阳吸收比为95.9%、发射比3.8%、吸收发射比25.2。结合光学显微镜微观形貌分析、X射线衍射结构分析(XRD)、X射线光电子能谱成分分析(XPS)探讨涂层在250和400℃大气环境下热稳定性机理:250℃大气热处理后,涂层保持较高光谱选择性,表面形貌与物相结构未出现明显变化,SiO_x层氧化程度增大导致太阳吸收比升高,金属Cr和金属Al相互扩散导致发射比升高;400℃大气热处理后,涂层光谱选择性降低,表面出现微米级孔洞,XRD及XPS结果表明Cr-N-O吸收层被氧化,导致太阳吸收比降低,金属Cr和金属Al相互扩散导致发射比明显升高。     

高温太阳光谱选择性吸收涂层计算机模拟

在近几年国际高温涂层研究的基础上,根据理论研究和实验结果从几方面因素(如材料、膜层结构、陶瓷中金属组分等)分析了其对高温吸收涂层效率的影响.在Mo-Al2O3双吸收层涂层的基础上,利用计算机计算了金属体积分数配比和膜层厚度变化下整个涂层的吸收比和发射比,计算结果表明,膜厚和吸收层中Mo的体积分数对涂层的吸收比和发射比影响效果差异较大,选择合适的控制因子不仅可以提高涂层的吸收比(a=0.92-0.95),而且还能有效控制涂层的发射比(ε≤0.05).     

TiAlON太阳能吸收膜的制备及高温性能衰减分析

采用直流磁控溅射制备AlON/TiAlON(LMVF)/TiAlON(HMVF)/Cu型太阳能光谱选择性吸收薄膜,并对其光学性能及高温下的衰减机理进行研究。吸收膜沉积态的吸收比和发射比分别为0.951和0.045(100℃)。在500℃的大气气氛中热处理200 h后涂层的光学性能出现小幅衰减。主要的衰减机制为薄膜在高温下O、N和Cu发生轻微扩散及氧化。结果表明AlON/TiAlON(LMVF)/TiAlON(HMVF)/Cu型太阳能吸收膜具有良好的光学性能,可适用于CSP中高温发电及民用生活等方面。     

基于Matlab和正交实验法研究W-Al_2O_3系太阳能吸收膜光学性能变化规律

基于Matlab软件编程,以耐高温双干涉型W-Al_2O_3系太阳能吸收膜为例,采用正交实验方法,模拟研究W-Al_2O_3系高温太阳能吸收膜结构变化对其光学性能的影响规律,找出影响涂层光学性能的关键因素,经过膜系结构优化,获得吸收比达0.929、550℃发射比仅为0.075的涂层组合。     

SnO_2/CrON/Cu太阳能选择性吸收涂层循环热冲击性能研究

采用DC磁控溅射法制备SnO_2/CrON/Cu太阳能光谱选择性吸收涂层并进行中低温循环热冲击试验。对所制备涂层循环热冲击试验前后的光学性能和热稳定性进行表征。该涂层沉积态的吸收比为0.927,100℃发射比为0.048,在25℃/300℃的中低温下经264.25 h的循环热冲后涂层表面粗糙度几乎不变,未出现明显的元素扩散。吸收比仅衰减为0.912,发射比仅增加为0.076。表明该涂层适用于中低温光热利用领域。     

反照率参数化改进对裸土地表能量和热过程模拟的影响

在陆面过程模式BATS中引入考虑太阳天顶角变化的裸土反照率参数化以改善沙漠、戈壁地表的辐射和热状况模拟,并与观测资料进行了对比。结果表明,各方案不同程度地改善了BATS反照率模拟过高和缺乏日变化等偏差,其中Wang等改进的BRDF和B方案分别使BATS在戈壁地表由-67.75 W·m-2的负偏差缩减到-0.59和0.22W·m-2,感热通量的负偏差缩小了一半,地表温度较大的负偏差控制在1K之内。研究结果肯定了太阳天顶角对裸土反照率计算的重要作用,认为上述方案适用于裸土地表。     

ENERGY-FLUX VECTOR OF SURFACE THERMOELASTIC WAVES

The energy-flux vector connected with the kinetic and internal energy of surface thermoelastic waves is considered. It is shown that this vector is not parallel to the surface of the half-space, as it is in classical elasticity. Its direction at a given point varies with the distance of this point from the surface. Its magnitude decays to 0 when this distance tends to infinity and decays exponentially to 0 in the direction of movement of the straight tine in which the planes of constant phase of the superposed waves intersect the surface of the half-space. Some numerical results are presented when the half space is made of copper and thermally insulated.     

多晶硅酸腐蚀表面织构的研究

该文采用HF和HNO3为腐蚀液,在不同温度、添加剂和超声振荡3种情况下来进行多晶硅酸腐蚀表面织构实验研究,发现通过超声振荡,在单位面积上腐蚀坑密度较大.在1min、HFHNO3=121的腐蚀条件下,25℃时加Br2添加剂用超声震荡的方式得到较好的腐蚀效果.腐蚀坑的分布比较均匀,单位面积腐蚀坑较多,而且呈收缩型,这将有利于入射光的多次反射,获得较好的表面减反射效果.     

ACCURATE SURFACE TEMPERATURE PREDICTION AT HIGH SPEEDS

Computational tools of turbulent combustion have practical applications for various fields including liquid rocket engines, but some numerical issues are still presented for solving supercritical combustion. In the present study, several of these numerical issues are studied and discussed. Turbulent flow and thermal fields of gaseous hydrogen/cryogenic liquid oxygen flame at supercritical pressure are simulated by a turbulence model. To realize real-fluid combustions, the modified Soave-Redlich-Kwong (SRK) equations of state (EOS) are implemented into the flamelet model with a look-up table as functions of mean and variance of mixture fraction, scalar dissipation rate, enthalpy, and pressure. For supercritical combustion flows, modified forms of the pressure implicit with splitting of operator (PISO) algorithm for solving the pressure-velocity linked equation are introduced. From a comparison of instantaneous temperature distributions for gaseous hydrogen/cryogenic liquid oxygen flame at supercritical pressure, the capability of each method based on the different solution sequence is examined and the effective sequence is explored. The results show that the updated mixture fraction reflected in the pressure correction loop is a critical factor for numerical stability. Also, the relative performance of six convection schemes for supercritical combustion is discussed.     

THERMOELASTIC SURFACE WAVES OF AN ASSIGNED WAVELENGTH

Propagation of surface waves of an assigned wavelength on a theimoelastic half-space is considered. It is shown that there always exists a quasi-elastic and a quasi-thermal surface wave, both of which satisfying the adopted criteria for behavior at infinity. For each of them the wave is interpreted as a superposition of three dispersive inhomogeneous plane waves. The superposed waves have different directions of propagation and different phase velocities. Their directions of propagation are not parallel to the stressfree surface. The plane of constant amplitude that corresponds to each of the superposed waves is parallel to the stressfree surface and moves to it with constant velocity that is different for each of the superposed waves. Some numerical results are presented when the half-space is made of copper and thermally insulated.     

水面光伏局地生态效应观测事实分析

近年来以水上光伏为核心的“渔光一体”试验项目快速推广,但其建设及运行对局地生态环境的影响尚不明确。为研究水面光伏电站局地生态效应,以扬中通威渔光一体电站为例,于2020年8月20日展开水质和微生物调查。采用类别分析法评估和讨论水面光伏对水体温度、pH值、溶解氧、浊度、叶绿素、化学需氧量（COD）、生化需氧量（BOD）及微生物的影响。结果表明：扬中通威渔光一体电站运行期间,水温降低约0.5 ℃,pH值在大部分时段内低于自然站点, 溶解氧出现双峰值,浊度平均值降低11.83 NTU,叶绿素a平均浓度减少10.1 mg/L,作为污染指标的COD、BOD没有异常升高,微生物种群结构及丰度基本不变。水面光伏电站抑制藻类光合作用,对维持夏季水环境稳定、减少水华现象的发生起到积极的作用。该文的研究结果可为构建区域生态环境效应评估体系,提出水上光伏工程影响下的生态修复与保护措施提供科学依据。     

管状表面绝热层设计的热力学优化

基于熵产分析，时管状表面绝热层进行热力学优化。通过优化绝热层温度分布，提高绝热效果，减小不可逆损失，对１０种材料绝热层进行数值计算，并与传统设计进行比较，得到一些具有工程意义的结论。     

NUMERICAL MODELING OF A NUCLEATE BOILING SURFACE

ABSTRACT

A computer program developed to analyze nucleate boiling over a heated surface is described. The model solves the three-dimensional transient conduction equation within the heater. The conduction solution is coupled with closure relationships to mimic the bubble dynamics and the associated heat transfer coefficients. Sample problems are run using a copper surface subject to partial nucleate boiling in saturated water at atmospheric pressure. The results are shown to be in good qualitative agreement with the pertinent experimental observations.     

THIN FILM EVAPORATION ON A CURVED SURFACE

A mathematical model predicting evaporation and fluid flow in evaporating film region formed on a curved surface is developed to determine the interface temperature, heat flux distribution, and film profile in the thin film region. The numerical results show that the temperature of an equilibrium film on the curved surface of solid wire is larger than that on a flat surface and the equilibrium film thickness formed on the curved surface of solid wire is smaller than the one on the flat surface if the bulk fluid curvature of both evaporating film regions is the same. The rate of increase of the magnitude of total heat transport through the evaporating thin film region per unit length begins to decrease with larger superheat temperature due to the effect of a decreasing evaporating film region length. This potentially produces a limit of the maximum amount of heat transport through the micro regions for a given evaporator geometry. The current investigation provides a better understanding of the effects of interfacial forces on evaporation and fluid flow in thin film regions formed on a curved surface.     

NONSTAGGERED BOUNDARY-FITTED COORDINATE METHOD FOR FREE SURFACE FLOWS

A new approach based on the finite-difference technique has been developed to study the steady incompressible Navier-Stokes equations in the laminar region, where the domain is partially bounded by a free surface. The nonstaggered fractional step method is used to solve the flow equations written in terms of primitive variables. The physical domain is transformed to a rectangle by means of a numerical mapping technique. The location of the phase boundary is accomplished by means of two methods depending on the surface tension effect: the normal-stress boundary condition or the kinematic boundary condition. We have tested the accuracy and efficiency of the numerical method by solving four different test problems: lid-driven flow in an inclined cavity, film in the absence of gravity, the "stick-slip" problem, and the Newtonian jet swell problem.