半透明玻璃管束吸热芯聚集太阳光传输特性分析

为研究石英玻璃管束吸热芯对聚集太阳光的传输穿透性能,建立石英玻璃管束吸热芯多表面界面反射、折射和介质吸收光路传播模型。采用动态包覆面蒙特卡洛射线踪迹法(MCRTM)加速算法,模拟分析聚集太阳光束在石英玻璃管束吸热芯的传输过程,考虑玻璃光束倾斜角度、结构参数和聚集太阳光集中度等因素对聚集太阳光辐射传输性质的影响。结果表明石英玻璃管束吸热芯(长度5 cm,壁厚0.4 mm)对聚集太阳光的吸收比低于5%,是一种较为理想的低吸收换热芯材料,此结论为半透明玻璃管束吸热芯的创新发展提供了参考依据。     

一种多孔介质太阳能吸热器传热研究

为了研究塔式太阳能多孔介质吸热器的传热传质特性,建立吸热器稳态传热模型,选择适合多孔介质太阳能吸热器的体积对流换热系数模型,采用数值方法求解,并分别分析孔隙密度、孔隙率和入口空气速度对温度场的影响。文中技术可以为同类型太阳能吸热器的设计和改造提供参考。     

浅谈太阳集热器吸热涂层

浅谈太阳集热器吸热涂层木子太阳集热板芯是组成平板式太阳热水器的核心部件，附着在集热板芯上的太阳吸热涂层的优劣又直接影响着太阳热水器的性能。太阳吸热涂层总体上可分为非选择性涂层与选择性涂层两大类。区分它们吸热性能的重要指标是其吸收比α与发射比ε的比值α...     

多孔介质太阳能吸热器性能分析

采用4种多孔骨架中辐射传输模型,包括:忽略多孔骨架内部辐射模型(模型A)、Rosseland模型(模型B)、均匀内热源模型(模型C)与吸热器中辐射传输满足Beer定律的模型(模型D),推导得到了局部非热平衡条件下4种模型所对应的吸热器中多孔骨架温度、空气温度和吸热器热效率的解析解,分析了多孔骨架孔隙率、导热系数和孔隙直径对吸热器性能的影响。结果表明,对模型A和模型B,吸热器中最高温度位于吸热器进口处;对模型C,吸热器中最高温度位于吸热器出口处;而在模型D中,吸热器中吸热器内部或吸热器的出口处温度最高。吸热器效率取决于多孔骨架导热系数、孔隙率和孔隙直径等参数,当吸热器中内热源均匀分布时,吸热器效率是最高的。     

多孔介质-双层玻璃幕墙传热与流动特性

基于多孔介质具有吸收和贮存太阳能的特点,在双层玻璃幕墙通道内设置了多孔介质层,利用多孔介质充分收集与贮存太阳能用于建筑供暖,并采用数值模拟法研究了幕墙的传热与流动特性.结果表明,玻璃幕墙能充分利用太阳能加热新风供暖,集热效率高又节能,有推广价值.     

聚光太阳能热发电中吸热器吸收涂层的选择

对各类聚光比的聚光太阳能热发电中的吸热器吸收涂层进行了研究,同时对耐高温太阳吸收涂层进行了高温热处理和辐射性能测试.研究表明,菲涅耳线式和抛物面槽式聚光吸热器由于聚光比较小,吸热体表面温度较低,主要采用选择性涂层以提高吸热表面温度和吸热效率;而塔式和抛物面碟式聚光吸热器由于聚光比大,吸热体表面温度较高,高温时的吸收涂层在红外波段的吸收率下降,因此主要采用高吸收率的耐高温涂料为太阳吸收涂层.     

多孔介质特性参数对燃烧温度及压力影响的数值模拟研究

考查了两段式多孔介质内预混气燃烧的温度与压力分布情况。建立了甲烷／空气预混气体在多孔介质内燃烧的二维数学模型,运用FLUENT软件求解瞬态控制方程的方法计算出燃烧稳定后多孔介质内的温度、与压力分布,并考查了不同当量比、多孔介质辐射衰减系数和导热系数对温度和压力分布的影响。结果表明,甲烷／空气预混气体在多孔介质中燃烧,当量比越大温度峰值越高,压力梯度越大;小孔介质辐射衰减系数的改变对温度分布和压力分布没有明显的影响,而大孔介质辐射衰减系数对温度分布和压力分布有较大的影响;增加多孔介质的导热系数,会使固相与气相温度均有所升高,燃烧区域压力降低。     

多孔介质蒸发制冷板应用于建筑墙体的性能分析

把含湿多孔介质置于建筑墙体结构中,在室外环境的作用下,多孔介质外表面和内部的水分蒸发吸热,为房间提供部分冷量。文章表述将含湿多孔介质置于建筑北墙中,在建立多孔介质热湿平衡的基础上,采用描述非饱和多孔介质热质迁移的数学模型,分析了室外环境参数及多孔床层结构对床层内温度分布、蒸发量场及水蒸气迁移的影响,为多孔介质应用于建筑结构的推广和应用提供理论指导。     

LNG低温闪蒸气动态吸脱附特性的格子玻尔兹曼模拟

为研究LNG闪蒸气在低温储存环境下的吸/脱附特性及热效应,基于格子玻尔兹曼方法建立了多孔介质内闪蒸气流动传热传质的数值模型,并考虑闪蒸气在多孔介质表面的吸附作用和内部微晶孔扩散作用及传热效应,分析不同孔隙率多孔介质材料的闪蒸气低温吸附热力学特性。结果表明：闪蒸气的吸附作用使多孔介质温度明显升高,吸附速率与孔隙率呈负相关,吸附量和温度变化受孔隙率影响较小;环境热量驱动下闪蒸气从多孔介质中脱附,通过脱附吸热抵消了约45%的外部漏热侵入,且随着孔隙率增大闪蒸气脱附吸热效应增强。     

多孔介质燃烧器的辐射输出效率和污染物

使用双温度体积平均模型、详细化学反应机理GRI3．0,对甲烷,空气预混气在多孔介质燃烧器内的预混火焰进行模拟．分析不同当量比和质量流量下的预热效率、辐射输出效率以及污染物排放情况,并对辐射输出效率随多孔介质热物性参数的变化进行敏感性分析．结果表明,增大相间对流换热系数或减小当量比、质量流量及固相消光系数都可以提高辐射输出效率,减小当量比或质量流量可以减少污染物排放．在所有的影响因素中,当量比的影响最大,发展超贫燃燃烧技术是获得高效低污染多孔介质燃烧器的关键．     

Thermal performance of linear Fresnel reflecting solar concentrator with trapezoidal cavity absorbers

Thermal performance of the four identical trapezoidal cavity absorbers for linear Fresnel reflecting solar device were studied and compared. The absorbers were designed for operating in conjunction with a prototype Fresnel solar reflector. Rectangular and round pipe sections were used as absorber by placing in the trapezoidal cavity. The absorber pipes were coated with ordinary dull black board paint and black nickel selective surface. The bottom of the cavity was provided with plane glass to allow the solar radiation to be reflected from the Fresnel reflector. The other three sides of the cavity absorber were insulated to reduce heat loss. Thermal performance of the Fresnel reflecting concentrator with each trapezoidal cavity absorber was studied experimentally at different concentration ratio of the reflector. The study revealed that the thermal efficiency was influenced by the concentration ratio and selective surface coating on the absorber. The thermal efficiency decreased with the increase in the concentration ratio of the Fresnel reflecting collector. The selective surface coated absorber had a significant advantage in terms of superior thermal performance as compared to ordinary black painted absorber. The round pipe (multi-tube) receiver had higher surface area to absorb solar energy as compared to rectangular pipe receiver. Thermal efficiency of the solar device with round pipe absorber was found higher (up to 8%) as compared to rectangular pipe absorber.     

多孔介质太阳能集热组合墙的耦合传热与流动分析

针对接触型和分隔型多孔介质太阳能集热组合墙系统,分析了太阳辐射及环境温度变化时,组合墙内传热与流动变化.多孔介质太阳能集热组合墙中,多孔介质起半透明隔热体和蓄热体的作用.多孔介质集热层的孔隙率、粒径、材料热导率和多孔介质集热层在组合墙中的位置对系统的采暖效果影响较大.     

太阳能集热组合墙系统的耦合传热与流动分析

针对太阳能集热组合墙系统，分析了太阳辐射及环境温度变化时，组合墙内传热与流动变化。太阳能集热组合墙系统中，多孔介质起半透明隔热体和蓄热体的作用。多孔介质的空隙率、粒径大小对系统的采暖效果影响较大。     

Development of a solar receiver for a high-efficiency thermionic/thermoelectric conversion system

Solar energy is one of the most promising energy resources on Earth and in space, because it is clean and inexhaustible. Therefore, we have been developing a solar-powered high-efficiency thermionic/thermoelectric conversion system which combines a thermionic converter (TIC) with a thermoelectric converter (TEC) to use thermal energy efficiently and to achieve high efficiency conversion. The TIC emitter must uniformly heat up to 1800 K. The TIC emitter can be heated using thermal radiation from a solar receiver maintained at a high temperature by concentrated solar irradiation. A cylindrical cavity-type solar receiver constructed from graphite was designed and heated in a vacuum by using the solar concentrator at Tohoku University. The maximum temperature of the solar receiver enclosed by a molybdenum cup reached 1965 K, which was sufficiently high to heat a TIC emitter using thermal radiation from the receiver.     

Compact Linear Fresnel Reflector solar thermal powerplants

This paper evaluates Compact Linear Fresnel Reflector (CLFR) concepts suitable for large scale solar thermal electricity generation plants. In the CLFR, it is assumed that there will be many parallel linear receivers elevated on tower structures that are close enough for individual mirror rows to have the option of directing reflected solar radiation to two alternative linear receivers on separate towers. This additional variable in reflector orientation provides the means for much more densely packed arrays. Patterns of alternating mirror inclination can be set up such that shading and blocking are almost eliminated while ground coverage is maximised. Preferred designs would also use secondary optics which will reduce tower height requirements. The avoidance of large mirror row spacings and receiver heights is an important cost issue in determining the cost of ground preparation, array substructure cost, tower structure cost, steam line thermal losses, and steam line cost. The improved ability to use the Fresnel approach delivers the traditional benefits of such a system, namely small reflector size, low structural cost, fixed receiver position without moving joints, and non-cylindrical receiver geometry. The modelled array also uses low emittance all-glass evacuated Dewar tubes as the receiver elements. Alternative versions of the basic CLFR concept that are evaluated include absorber orientation, absorber structure, the use of secondary reflectors adjacent to the absorbers, reflector field configurations, mirror packing densities, and receiver heights. A necessary requirement in this activity was the development of specific raytrace and thermal models to simulate the new concepts.     

Thermal Analysis of a Volumetric Solar Receiver

The volumetric receiver has received wide attention due to its high thermal efficiency. This paper studied a new type of a solid-liquid composite volumetric receiver. The heat transfer in a solid-liquid composite volumetric solar receiver was analyzed using a one-dimensional unsteady simulation model of the solid-liquid receiver. The model included absorption of the incident solar radiation by the glass window, the silicon carbide porous ceramic heat absorber panel and the water. The results were verified against experimental data for a volumetric receiver and the error did not exceed 10%. It can be used to predict the heat transfer in solid-liquid composite volumetric receivers.     

Exergy Analysis of Photo-Thermal Interaction Process between Solar Radiation Energy and Solar Receiver

A unified theory of non-equilibrium radiation thermodynamics is always in search as it is meaningful for solar energy utilization. An exergy analysis of photo-thermal interaction process between the solar radiation energy and solar receiver is conducted in this paper. The non-equilibrium radiation thermodynamic system is described. The thermodynamic process of photo-thermal interaction between the solar radiation and solar receiver is introduced. Energy, exergy and entropy equations for the photo-thermal process are provided. Formulas for calculating the optimum receiving temperatures of the solar receiver under both non-concentration and solar concentration conditions are presented. A simple solar receiver is chosen as the calculation example to launch the exergy analysis under non-concentration condition. Furthermore, the effect analysis of solar concentration on the thermodynamic performance of the solar receiver for solar thermal utilization is carried out. The analysis results demonstrate that both the output exergy flux and efficiency of the solar receiver can be improved by increasing the solar concentration ratio during the solar thermal utilization process. The formulas and results provided in this paper may be used as a theoretical reference for the further studies of non-equilibrium radiation thermodynamic theory and solar thermal utilization.     

Computations of the optical properties of metal/insulator-composites for solar selective absorbers

Solar selective absorbers are very useful for photo thermal energy conversion. The absorbers normally consist of thin films (mostly composite), sandwiched between the antireflection layer and (base layer on) a metallic substrate, selectively absorbing in the solar spectrum and reflecting in the thermal spectrum. The optical performance of the absorbers depends on the thin film design, thickness, surface roughness and optical constants of the constituents. The reflectivity of the underlying metal and porosity of the antireflection coating plays important roles in the selectivity behavior of the coatings. Computer simulations, applying effective medium theories, have been used to investigate the simplest possible design for composite solar selective coatings. A very high solar absorption is achieved when the coating has a non-uniform composition in the sense that the refractive index is highest closest to the metal substrate and then gradually decreases towards the air interface. The destructive interference created in the visible spectrum has increased the solar absorption to 98%. This paper also addresses the optical performance of several metals/dielectric composites like Sm, Ru, Tm, Ti, Re, W, V, Tb, Er in alumina or quartz on the basis of their refractive indices. The antireflection coating porosity and surface roughness has been analyzed to achieve maximum solar absorption without increasing the thermal emittance. Antireflection layer porosity is a function of dielectric refractive index and has nominal effect on the performance of the coating. While, up to the roughness of 1×10⁻⁷ m RMS, the solar absorption increases and for higher roughness, the thermal emittance increases only.     

Efficiency of combined solar photothermal plants

The efficiency of a combined solar photothermal plant for electric and thermal energy generation has been evaluated with account for the daily variation of solar radiation and atmospheric temperature. It is shown that in the summer with the heat removal temperature 40°C it is possible to utilize additionally up to 50% of the solar radiation energy even in the absence of thermal insulation of receiver bottom.     

High temperature solar gas heating comparison between packed and fluidized bed receivers—I

Present investigation has been concerned with high temperature gas heating through porous media (SiC and ZrO₂ particles) in both a fluidized bed receiver and a packed bed receiver. As a rule, gases being transparent to solar radiation, the porous media act as (i) an absorber (ii) a gas-solid heat exchanger. The main thermal features of the systems have been measured using the 6.5 kW solar furnace of the “Laboratoire d'Energétique Solaire” in Odeillo, France. Theoretical approach, temperature profile, gas outlet temperature as a function of mean flux density, and thermal efficiency of the receiver have been reported. Great improvements of the thermal efficiency may be expected from the newly designed receivers.