太阳能Braysson热机性能优化及参数设计

建立太阳能Braysson热机系统的一般模型,探讨集热器的辐射热损、太阳辐照强度、工质变比热容、有限速率热传导、工质与热源间的传热系数比等对系统性能的影响,应用数值计算和图解方法,对热机系统的功率、效率、集热器的最佳工作温度等性能参量进行分析和优化,同时也详细讨论了一些重要性能界限,所得结论不仅能导出相关论文的主要结果,且可为太阳能热机的性能参数设计提供参考。     

太阳能建筑外墙传热系数朝向差异设计研究

结合太阳能建筑室外热作用朝向差异显著的特点,对不同朝向外墙单位面积日平均失热量进行分析,提出"传热系数朝向差异"的太阳能建筑墙体热工设计方法。借助建筑分析模型,确立墙体节材量随基础传热系数和室内计算温度的变化关系;对比分析拉萨、银川及西安3个地区太阳能建筑的墙体节材性特点及传热系数朝向差异设计下的墙体内壁面温度动态变化规律。结果表明:采用墙体传热系数朝向差异化设计可减少墙材用量,且太阳辐射强度越高的地区节材性越明显,该方法不会对室内热环境产生不利影响。     

二次换热平板型太阳能热水器的热性能研究

对夹层换热器的传热效率和总传热系数以及带夹层换热器平板型太阳能热水器的热性能进行测试与分析,对比分析三种热水器的平均日效率和平均热损系数。测试结果表明,夹层换热器的换热效率都在85%以上,一天中的平均总传热系数(UA)hx为88.16 W/K;带夹层换热器的平板太阳能热水器的平均日效率为49.8%,低于普通平板太阳能热水器的平均日效率(53.4%),但要高于全玻璃真空管太阳能热水器的平均日效率(48.7%)。     

The enhancement on heat capacity of nitrate salt heat storage materials by doping SiO2 nanoparticles

多元混合硝酸盐作为高温传热流体在聚光式太阳能热发电系统中具有良好的应用前景。本工作利用水溶液法,在具有较低熔点的NaNO₃-KNO₃-LiNO₃三元共混合硝酸盐中掺入SiO2纳米颗粒,有效地提高了混合硝酸盐储热材料的比热容,其中掺入较低质量分数（0.0625%）的纳米颗粒比掺入较高质量分数（1%、0.25%）的纳米颗粒能获得更高的比热容。利用聚乙烯吡咯烷酮（Polyvinylpyrrolidone,PVP）作为分散剂,增强了SiO2纳米颗粒在硝酸盐中的分散性,有效地缓解了制备过程中纳米流体中纳米颗粒的团聚。同时,本工作还研究了纳米颗粒的团聚对其增强比热容效果的影响,并通过使用分散剂,进一步提高了硝酸盐储热材料的比热容。最终结合上述关系,引入界面热阻和半固体层模型,讨论了掺入纳米颗粒增强硝酸盐储热材料比热容的机理。     

NaNO_3-KNO_3-NaNO_2三元混合相变熔盐结构与物性的分子动力学模拟CSCD

相变熔盐目前是太阳能热发电的重要传蓄热介质,其结构和性质之间的定量关系是相变熔盐研究的热点。本文采用分子动力学方法,利用Buckingham势函数,对NaNO_3-KNO_3-NaNO_2三元混合熔盐的结构和性质进行了研究。计算了混合熔盐在不同温度下的径向分布函数、配位数、角分布函数等结构信息,以及密度、剪切黏度、热导率、比热容等性质。结果表明,计算得到的各项性质与文献值吻合较好,验证了势函数和计算方法的可靠性,为计算机模拟指导熔盐配方、熔盐构效关系定量研究奠定了基础。     

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.     

新建建筑围护结构的传热系数变化研究

对严寒地区新建建筑围护结构的干燥过程进行了模拟,建立了不同干燥时期的热质耦合传递质能平衡方程,确立了围护结构各层多孔介质材料导热系数随含湿量和结冰量的变化关系,对围护结构传热系数的变化情况进行了模拟,分析了新建建筑传热系数随着围护结构不断干燥的逐年变化规律。模拟结果表明:在严寒地区,新建建筑围护结构冬季的传热系数由于内部含湿量结冰要高于夏季围护结构传热系数,但围护结构冬季传热系数逐年下降,尤其前三年下降较明显。     

两侧对流条件下平面冻结凝固相变换热分析

通过无因次分析的方法,在相界面两侧均是对流条件下,得到了平面冰层厚度和速度的时变规律、生长条件、极限厚度、温度场分布特点等重要结论,提出了凝固换热全传热系数和衰减特征时间的概念,并给出了理论公式用于换热量计算.结果表明,凝固换热是一个非稳态过程,初始阶段凝固潜热释放强化了换热,衰减特征时间之后,冰层热阻开始恶化换热效果,并最终无限趋近于一稳定状态.     

可再生能源文献信息

GW０２０５０１四托盘太阳能农作物干燥系统的传热和传质系数．AnwarSI，等．IntJAmbientEenrgy，２００１，２２（１）：４８～５６（英文）通过热力分析考虑了基本能量平衡方程，确定了影响水分去除的各传热和传质系数。用第四阶Runge－Kutta法求解了４个耦合的微分方程，得到了不同温度的传热系数和水分去除型式。发现①在传质过程中，即水分去除过程中，蒸发传热系数起着重要作用；②装在不同托盘中的农作物温度和工作传热系数受太阳能集热器长度和干燥室空气质量流率的影响。GW０２０５０２新型光致电发光器件．HauchA，等．Ele…     

循环床非流化下料管内竖管传热的试验研究

对循环流化床下料管内竖管的局部和整体传热进行了试验研究。结果表明：颗粒之间的导热热阻是影响该类传热的主要原因，还讨论了其它影响传热的因素如物料比热容、颗粒尺寸，空隙率等。其平均传热系数在１４０￣２００Ｗ／ｍ＾２．Ｋ之间，该结果为循环床下料管内布置受热面提供了可靠依据。     

Numerical Simulation of the Performance of a Capillary Thermal Driven Ejector Refrigerator

A capillary driven ejector refrigerator is a new refrigeration system that can use solar energy and other low-grade heat sources. In this paper, the performance of the refrigeration system is simulated numerically by use of an iteration algorithm and block exchanging technology for all unit models. The flow and heat transfer characteristics in a solar collector, generator, ejector, condenser, and evaporator are analyzed and calculated. The results show that when the generating temperature is higher than 75–80°C and the environmental temperature is lower than 35°C, the system can work normally; the coefficient of performance of this refrigeration system is in the range of 0.05–0.15 by use of water as a refrigerant. The cooling capacity and COP increase with an increasing generative temperature and decreasing condensing pressure.     

基于太阳辐射值的喷射制冷系统动态性能分析

为了了解气象参数对喷射制冷系统性能的影响,选取HCFC-134a作为制冷剂,基于EES软件建立了太阳能喷射制冷系统动态性能仿真程序,模拟研究了太阳辐射值对系统性能的影响。研究表明:一定运行工况下,随着太阳辐射量的增加,系统COP呈现先升高后下降的趋势;发生热量和发生温度均呈现递增趋势;制冷量则呈现先增加,当太阳辐射到达一定值时,系统的制冷量则基本不变的趋势。系统在相同蒸发温度和冷凝温度下运行时,存在一个最佳发生热量工作区,在该最佳发生热量区,系统COP最大,出冷量也最多。     

Heat Transfer Performance of an Edge-Shaped Finned Tube

The third-generation heat transfer technologies, such as three-dimensional fin and dimple, are still important means of improving energy efficiency and will continue to be challenging issues. This paper presents condensation heat transfer performance of an edge-shaped finned tube fabricated by a ploughing–extruding process. The edge-shaped finned tube integrates more than one heat transfer enhancement technology and can enhance the heat transfer capacity greatly. It is seen that the overall heat transfer coefficient and heat flux increase with inlet velocity of cold water increasing, and decrease with inlet temperature of cold water increasing, whereas the shell-side heat transfer coefficient decreases with inlet velocity of cold water increasing and increases with inlet temperature of cold water increasing. At the same inlet velocity, the shell-side heat transfer coefficient for the edge-shaped finned tube is improved by 5–7 times compared to that of a smooth tube. At the same temperature difference between wall and vapor, the shell-side heat transfer coefficient is also higher than what had been reported in the literature. The shell-side heat transfer coefficient of the edge-shaped finned tube decreases with the increase of fabrication parameter feed at the same inlet velocity or inlet temperature of cold water.     

中倍聚光太阳电池液浸散热特性的模拟实验

提出了一种将太阳电池液浸到冷却介质中,电池与介质间进行直接接触式换热的冷却方式.设计了小型实验装置,选用二甲基硅油为冷却介质,采用长弧氙灯模拟聚光条件,选择模拟材料制作太阳电池模拟片,进行了模拟实验研究.结果表明:采用液浸冷却方式,能够从模拟片表面带走72.2kW/m~2的热负荷,同时将模拟片的温度冷却到70℃以下;模拟片与介质间的单相对流传热系数能够达到约750W/(m~2·℃);介质温度的改变对模拟片与介质间的对流换热温差和对流传热系数影响较小.     

高温熔盐吸热器的传热研究和系统设计

本文对非均匀辐射热流密度太阳能熔盐吸热器传热过程进行了模拟研究,得到了熔盐吸热器内部的温度、传热性能等特征参数。结果表明在轴向和径向上熔盐流体温度和管壁的温度都非常不均匀,同时其综合传热性能要高于按照Sieder-Tate公式的计算值。并对10 MW塔式太阳能热发电的熔盐吸热器进行了设计和分析。     

Diurnal response of solar air heaters

A time-dependent heat transfer model has been developed to predict the diurnal performance of a conventional solar air heater which consists of a flat passage between two metallic plates through which the heating fluid (air) is made to pass. The effect of various parameters such as the heat capacities of the glass cover, the absorbing plate and the air streams, as well as the heat transfer coefficient from the absorbing plate to the air stream, have been investigated. It is found that the heat capacities of the glass cover and the absorber do not alter the performance characteristics of the solar air heater while the heat capacity of the air stream significantly influences both the rise in temperature of the fluid and the shift in phase. However, the effective heat transfer coefficient from the absorbing plate to the air stream significantly affects the diurnal response of a solar air heater.     

Preliminary investigation of a transcritical CO2 heat pump driven by a solar‐powered CO2 Rankine cycle

In this paper, a transcritical carbon dioxide heat pump system driven by solar‐owered CO₂ Rankine cycle is proposed for simultaneous heating and cooling applications. Based on the first and second laws of thermodynamics, a theoretical analysis on the performance characteristic is carried out for this solar‐powered heat pump cycle using CO₂ as working fluid. Further, the effects of the governing parameters on the performance such as coefficient of performance (COP) and the system exergy destruction rate are investigated numerically. With the simulation results, it is found that, the cooling COP for the transcritical CO₂ heat pump syatem is somewhat above 0.3 and the heating COP is above 0.9. It is also concluded that, the performance of the combined transcritical CO₂ heat pump system can be significantly improved based on the optimized governing parameters, such as solar radiation, solar collector efficient area, the heat transfer area and the inlet water temperature of heat exchange components, and the CO₂ flow rate of two sub‐cycles. Where, the cooling capacity, heating capacity, and exergy destruction rate are found to increase with solar radiation, but the COPs of combined system are decreased with it. Furthermore, in terms of improvement in COPs and reduction in system exergy destruction at the same time, it is more effective to employ a large heat transfer area of heat exchange components in the combined heat pump system. Copyright © 2012 John Wiley & Sons, Ltd.     

基于相变微胶囊悬浮液的太阳能光伏热系统的研究进展

在太阳能光伏热系统中,光伏电池温度过高会导致太阳能发电效率下降。相变微胶囊悬浮液(MEPCMS)是一种潜热型功能性流体,将其作为冷却介质用于太阳能光伏热系统可以有效降低光伏电池温度,提高系统的能量利用率。针对相变微胶囊易泄露、导热性差等问题提出了改性方法,使其具有光热转换功能并提升了综合性能。基于性能评价指标分析了太阳能光伏热系统性能的影响因素。结果发现,流速、浓度和太阳辐照量是影响MEPCMS在太阳能光伏热系统中换热性能的关键因素。适当增加MEPCMS浓度和流速能提高工质的换热性能,在降低光伏板温度的同时增加太阳辐照量和系统热电产量,但需结合太阳辐照量大小合理匹配工质的浓度和流速。未来研究方向可集中在提升MEPCMS在太阳能光伏热系统中的换热性能、探究运行参数和太阳辐照量之间的匹配关系、优化集热器结构、利用其蓄热性解决太阳能间歇性等方面。     

An experimental heat transfer study for periodically varying-curvature curved-pipe

Experiments were conducted for water flowing through a varying-curvature curved-pipe inside a larger diameter straight pipe to form a double-pipe heat exchanger with water as the working medium. The heat transfer coefficients were obtained using the Wilson plot method. The effects of the Dean, Prandtl, Reynolds number and the curvature ratio on the average heat transfer coefficients and the friction factors are presented. A higher Dean number results in a higher heat transfer rate. It is found that the heat transfer rate may be increased by up to 100%, as compared with a straight pipe, while the friction coefficient increased by less than 40%. Therefore, it is promising to use S-shaped pipes instead of straight pipes for the performance enhancement for a heat exchanger such as a solar collector.     

用于太阳热发电的铅-铋合金传热特性分析

介绍了液态铅-铋(LBE)合金的热物理及传热特性,提出了将铅-铋共晶合金用于太阳热发电高温传热工质的构想.并建立了流体传热特性计算模型,对液态铅-铋合金与传统太阳热发电传热工质-熔盐的传热特性进行了对比模拟计算.结果表明:在热力循环中,采用液态LBE合金作为传热工质与熔盐相比,不但具有更高的热效率和热经济性,而且还可大大节省投资成本,因此其作为高温传热工质在太阳能热发电领域具有广阔的应用前景.