太阳能烟囱发电系统的CFD模拟研究

太阳能烟囱发电技术是一项综合应用温室效应技术、烟囱技术及风力涡轮发电技术于一体的太阳能发电新技术,是实现大规模开发和利用太阳能的一种新途径.采用计算流体动力学(CFD)方法对太阳能烟囱发电系统的速度场、压力场和温度场进行了数值模拟.结果表明:在其它条件不变的情况下,集热棚周边高度对系统的发电功率没有影响;太阳能烟囱直径存在一最佳值,使发电系统输出的发电功率最大.     

腔式太阳能高温空气吸热器传热过程数值模拟

介绍了一种应用于塔式太阳能热发电站的腔式高温空气吸热器,建立了吸热器内部空气流动及传热过程模拟数学模型,并通过数值方法,模拟了吸热器内部的空气流场和温度场。结果得知:空气进入吸热器后,沿内壁面轴向高速流动,随着深度的增加,速度越来越小,到达底部时速度最小;在压差的作用下,进入吸热器内部的空气会不断流向和冲刷针肋及壁面,而主流方向的流量不断减少;空气通过冲刷高温针肋及壁面不断吸收热量,温度不断升高;由于吸热器底部空气速度较小,对流换热系数较小和热流密度较大,因此该处温度较高,是整个吸热器的最脆弱部位;在高辐照强度情况下,虽然加大空气流量可降低吸热器壁面的温度,但由于其对流换热系数与空气流速不成正比例,壁面温度一般还会有所升高。     

High efficient configuration design and simulation of platelet heat exchanger in solar thermal thruster

Solar thermal propulsion system includes solar thermal propulsion and nuclear thermal propulsion, and it is a sig- nificant issue to improve the heat transfer efficiency of the solar thermal thruster. This paper proposes a platelet configuration to be used in the heat exchanger core, which is the most important component of solar thermal sys- tem. The platelet passage can enhance the heat transfer between the propellant and the hot core heated by the concentrated sunlight. Based on fluid-solid coupled heat transfer, the paper utilized the platelet heat transfer characteristic to simulate the heat transfer and flow field of the platelet passage. A coupled system includes the coupled flow and heat transfer between the fluid region and solid region. The simulation result shows that the propellant can be heated to the design temperature of 2300K in platelet passage of the thermal propulsion system, and the fluid-solid coupled method can solve the heat transfer in the platelet structure more precisely.     

多效蒸馏/闪蒸太阳能海水淡化系统数值模拟

根据顺流五效蒸馏/闪蒸太阳能海水淡化装置,参照广东地区春分日和冬至日太阳能辐射量情况,通过数值模拟对这套太阳能海水淡化系统运行参数进行分析,得出一年内不同季节系统最佳运行参数;同时得到了春秋季和冬季不同运行条件下相邻两效间的最大压力差,为系统全年能否正常工作的判定提供依据,从而为太阳能海水淡化系统运行奠定理论基础。     

Computer simulation calculations for estimation of the energy conservation in solar heated buildings

The paper describes the development of a simple and handy microcomputer theoretical simulation model, suitable for investigation of the performance of a low cost solar heating system which is believed to be suitable for use under the local meteorological conditions. Hour by hour simulations have shown that substantial solar fractions can be achieved even in existing buildings, and the introduction of easily accessible daily mean meteorological data allows the investigation of the thermal performance and energy conservation in buildings for any location in Greece.     

平板式太阳能空气集热器流道改进的试验研究和数值模拟

对传统平板式太阳能空气集热器的流道进行了改进,把对角型进出口流道改为多进出口式流道。对改进的集热器的性能进行了试验测试。新的进出口流道消除了吸热板和空气换热不均的现象,出口温度提升明显。在相同条件下,集热器的瞬时效率增加约20%。用CFD方法对集热器内部的流场结构和传热进行的数值模拟对比表明,传统集热器内部存在流动死区,中心截面温度分布不均匀,吸热板上有局部的高温区域,改进后的集热器流场和温度场分布得较均匀。     

多孔太阳墙结构热特性及应用分析

结合多孔太阳墙建筑,运用数值模拟方法分析了不同太阳墙结构对室内送风参数的影响,比较了太阳能房间与普通房间在工作区范围内的热舒适性,并对太阳能房间的窗墙面积比进行了优化改进。研究表明:对太阳墙的设计优化,增大了太阳墙面积,提高了室内热舒适性;改进后房间窗墙比为0.303,窗地比为0.2,符合节能建筑要求。     

Comparative study of different solar cooling systems for buildings in subtropical city

In recent years, more and more attention has been paid on the application potential of solar cooling for buildings. Due to the fact that the efficiency of solar collectors is generally low at the time being, the effectiveness of solar cooling would be closely related to the availability of solar irradiation, climatic conditions and geographical location of a place. In this paper, five types of solar cooling systems were involved in a comparative study for subtropical city, which is commonly featured with long hot and humid summer. The solar cooling systems included the solar electric compression refrigeration, solar mechanical compression refrigeration, solar absorption refrigeration, solar adsorption refrigeration and solar solid desiccant cooling. Component-based simulation models of these systems were developed, and their performances were evaluated throughout a year. The key performance indicators are solar fraction, coefficient of performance, solar thermal gain, and primary energy consumption. In addition, different installation strategies and types of solar collectors were compared for each kind of solar cooling system. Through this comparative study, it was found that solar electric compression refrigeration and solar absorption refrigeration had the highest energy saving potential in the subtropical Hong Kong. The former is to make use of the solar electric gain, while the latter is to adopt the solar thermal gain. These two solar cooling systems would have even better performances through the continual advancement of the solar collectors. It will provide a promising application potential of solar cooling for buildings in the subtropical region.     

Comfort criteria for passively cooled buildings a pascool task

The application of passive cooling techniques to buildings in warm climates creates the need for appropriate comfort criteria. Conventional comfort criteria, usually based upon laboratory experiments, seem to be unnecessarily severe. The paper describes preliminary findings of the PASCOOL Thermal Comfort task which, responding to renewed interest in behavioural aspets of thermal comfort, sets out to establish appropriate limits by field studies and theoretical considerations.     

Techno-economic performance analysis of solar cooling systems

Vapour absorption cooling systems, powered by solar thermal energy, are now commercially manufactured in sizes ranging from 1.5 to over 20 RT (one refrigeration ton = 3.51 kW of cooling). The needed thermal energy at appropriate temperature potential can either be provided by solar thermal collectors or else from a solar pond. The paper gives the assessment criteria and results for technical and economic evaluation of the performance of absorption chiller using a solar pond. These results, based on Kuwait's environmental data and costs, have been compared with three alternate cooling systems, namely:

• 1 Solar thermal collector absorption cooling system.
• 2 Solar photovoltaic cooling system.
• 3 Standard vapour compression cooling system.

The criteria, used for performance evaluation of the solar cooling systems on a technical basis, consists of assessing the extent to which such systems can make a positive contribution in a conserving fossil fuel. This is done by first estimating the total electrical energy needed by the standard system (defined in para. 3 above) to produce one unit of cooling output. Solar cooling systems are then analysed and compared with a standard system to establish their electrical energy saving or generation capability, after accounting for the parasitic electrical energy used in pump/fan motors and equivalent energy needed for the production of soft water (used-up in the cooling tower) from seawater desalination. The economic analysis considers the cost and life of subsystems and that of the electrical and water desalination plants to arrive at the unit cooling cost. The unit cooling is defined as the ratio of amortized capital investments plus operation and maintenance costs over the year and the total yearly cooling production by the system. The results show that the solar pond absorption cooling system is the closest competitor to the conventional cooling system.     

太阳能热气流电站中涡轮机流动特性分析

对太阳能热气流电站中的涡轮机进行了设计和数值模拟.建立了涡轮机区域流体流动的物理数学模型,并对其进行数值模拟;研究了涡轮机的转速与压降对涡轮机的流量、输出功率和能量转换效率的影响.通过与相近实验模型的试验结果对比,证明了设计方案和数值模拟方法是有效的.     

Mathematical Simulation of Evaporating Brine by Solar Radiation for the Production of Salt

A computer simulation model of salt pan is presented. The transient behavior and the effects of various parameters of the salt pans, such as the depth of the brine layer, the absorptance of the soil surface, the thermal properties of the soil beneath the brine layer and the depth of the underground water table, on the evaporation process of salt pans are discussed. The effects of extra insulation layer and the intensity of solar radiation are also examined.     

太阳能辅助热泵干燥粮食的数值模拟研究

粮食的干燥过程实质上是多孔介质热湿耦合传递的过程。基于多孔介质热质传递理论,通过数值模拟的方法,针对利用太阳能辅助热泵干燥粮食时热风随时间变化的情况,采用综合温度和空气绝对湿度作为瞬态边界条件来对干燥过程中粮食内部温度和水分的变化进行模拟研究。模拟结果显示小麦水分在干燥150h后达到安全水分13.6%(干基),而实验结果显示小麦水分在干燥135h后达到安全水分13.6%(干基),二者对比相差不大,并且模拟温度与试验温度吻合较好。     

太阳能空调综合系统在住宅小区应用的可行性探讨

经济性是制约太阳能空调普及推广应用的难题。文中介绍了一种太阳能空调和热水站综合系统方案,即在居民住宅楼的屋顶布置太阳能集热器阵,结合地源水低温热源系统,建设全年供应全体住户生活热水的太阳能热水站,以及夏季和冬季供应顶一、二层住户空调冷、热水的综合系统．提出了一种双效与单效耦合的板壳式溴化锂吸收式制冷机循环方案,白天日照时段采用双效循环运行并进行蓄热,而在其余时段切换为单效循环利用蓄热运行。该方案不仅效率高、而且其单位体积蓄能罐的蓄能密度极大,可实现无需用辅助能源而完全靠太阳能进行昼夜空调。由于综合利用系统中集热器的投资费用被所有热水用户分摊,空调用户的投资可很快从节省的电费中得到回收。     

CFD方法与间接蒸发冷却换热器的三维数值模拟

采用计算流体力学(CFD)和数值传热学方法,对间接蒸发冷却器内流体流动与热质交换过程进行简化和假设,建立了换热器内三维层流流动与传热的数学物理模型。采用交错网格离散化非线性控制方程组,编制了三维simple算法程序。对间接蒸发冷却器内的流场、温度场及浓度场进行数值模拟研究,得到换热器内的流体流动状态和热流分布,并分析了通道宽度变化对换热器内流体流动与换热的影响。     

夏季降温的太阳房实验分析

对建造在南宁市西郊的一座被动式太阳房在夏季运行时的实验数据进行了分析，其屋顶集热表面在夏季夜间能产生一定的致冷效果。所制取的冷空气不但在夜间可以对该太阳房起到降温的作用，并且可以储藏起来以供白天降温使用。     

阿拉善牧区附加阳光间式太阳房模拟研究

用DeST-h软件建立附加阳光间被动式太阳房模型、模拟并得出该太阳房住宅一个采暖期室内逐时温度;整理、计算、对比太阳房与对比房室内平均温度,认为附加阳光间被动式太阳房在阿拉善牧区的应用是可行的。     

A theoretical simulation of light scattering of nanocrystalline films in photoelectrochemical solar cells

A Monte Carlo simulation method of light scattering in nanocrystalline films based on solutions of Maxwell's equations is proposed. A nanocrystalline film is assumed to be superposition of randomly distributed nanoparticles and deviation of the nanocrystalline film from the randomness. Since a scattering field of the randomly and densely distributed nanoparticles can be neglected, a scattering field of the nanocrystalline film results in a sum of scattering fields of the deviant parts in the nanocrystalline film. In the method, configurations of the deviant parts are simulated with a random function of a computer language. A simulation converges in small number of the configuration patterns. The simulation theoretically demonstrates that almost all of the incident light to the nanocrystalline films in the photoelectrochemical solar cells penetrate without scattering.     

Questionable effects of antireflective coatings on inefficiently cooled solar cells

A model for temperature effects in p–n junction solar cells is introduced. The temperature of solar cells and the losses in the solar cell junction region caused by elevated temperatures are discussed. The model developed is examined for low-cost silicon solar cells. Plots of output power and efficiency as functions of the time throughout the day are presented. In order to improve the shape of the output power and efficiency curves throughout the day the coherence between technical parameters of the solar cells and the climate in the operation region is observed and examined. It is shown how the drop in output power around noon can be avoided by fitting technical parameters of the solar cells to the climate.     

Optimal use of solar collectors for residential buildings

Solar radiation is an abundant free resource which may be used in the form of solar heated water. This is achieved in solar collectors which, unfortunately, are expensive devices and, further, the warm water must be stored in accumulators—items which also cost money. This paper shows how we have optimized the situation for a block‐of‐flats in Sweden. In order to find this point we have used the minimum life‐cycle cost (LCC) concept as a criterion. The best solution is therefore found when that cost finds its lowest value. It is also examined under which conditions solar collectors are part of the optimal solution and further it is calculated what happens if this optimal point is abandoned, i.e. how much will the LCC increase if other than optimal solutions are chosen. LCC optimization for multi‐family buildings almost always results in a heating system with low operating costs such as district heating or dual‐fuel systems where a heat pump takes care of the base load and an oil boiler the peak. The installation cost must, however, be kept to a reasonable level. Expensive solar panel systems are therefore normally avoided if the lowest LCC shall be reached, at least for Swedish conditions. This is so even if the solar system has a very low operating cost. For buildings where the only alternative energy source is electricity, solar collectors seem to be on the rim of profitability, i.e. for an energy price of about 0.6 SEK kWh^?1. Copyright © 2001 John Wiley & Sons, Ltd.