大型太阳能烟囱发电站热力分析与计算

利用热力学方法建立太阳能烟囱发电系统中集热棚、烟囱及风力透平的热气流能量转换过程的理论模型及求解方法.鉴于太阳能烟囱发电站的大尺寸特征,采用一维假设建立热气流传热模型,使用龙格-库塔方法对非线性能量方程进行数值求解.对集热棚直径3 600 m,烟囱高950 m,设计功率100 MW的大型太阳能烟囱发电站进行分析与计算,给出了该电站的风力透平轴功率随质量流量和太阳辐射强度变化的规律,为风力透平机组提供热力气动设计参数,为大规模开发利用太阳能提供借鉴.     

太阳能烟囱发电系统非稳态传热问题及性能分析

建立了包含蓄热层的太阳能烟囱发电系统非稳态传热数学模型,研究了集热系统特性和蓄热层的增温效应,结果表明:蓄热层表面温度、气流温度、集热棚板温度相互影响,随时间有较大波动;气流温升主要发生在气流入口至集热棚半径1/3处,蓄热层表面温度沿径向逐渐升高,在集热棚出口段有明显下降;集热棚板、蓄热层底部及四周是系统热量损失的主要地方;系统运行非稳定期,在没有太阳辐射时,深层蓄热层不参与向气流放热过程,而是继续从浅层蓄热层吸热,浅层蓄热层贮存的热量并不全向气流传递。系统运行平稳期,蓄热层底层的温度趋于定值;理论发电功率的变化趋势与气流温度随时间变化趋势一致。     

荒漠中的发电站——太阳能烟囱发电站

一前言 太阳能烟囱发电技术是通过集热棚吸取太阳热能使棚内空气温度升高,根据烟囱的原理,在烟囱内将形成强大的气流,利用这股气流形成的风力驱动风机,带动发电机发电。太阳能烟囱发电系统主要由透光的采光大棚、烟囱及风力涡轮机构成,如图1所示。     

太阳能烟囱制冷系统的研究

通过分析制冷系统和太阳能烟囱热气流发电系统的技术和特点,提出了太阳能烟囱制冷系统.将太阳能烟囱系统与制冷系统相结合进行制冷,可实现制冷不用电.该系统由烟囱、集热棚、蓄热层、涡轮机、开启式制冷压缩机、冷凝器和变速器等组成.介绍了太阳能烟囱制冷系统的结构特点、工作原理以及系统相关参数的计算方法.分析结果表明,太阳能烟囱制冷系统结构简单,运行维护方便,制冷不用电,无污染,具有良好的环境效应,可根据环境温度改变压缩机运行转速调节供冷负荷,能有效解决热带及沙漠地区的供冷及供电问题.     

太阳能热气流发电系统的传热与流动数值分析

建立了集热棚、烟囱以及多孔蓄热层的太阳能热气流发电系统传热与流动数学模型,分析了太阳辐射对蓄热介质的蓄热特性的影响.计算结果表明,在太阳辐射为200～800W/M2的范围内,随着太阳辐射的增强,蓄热介质的蓄热比例先减小后增大;烟囱底部的最小相对压力显著减小,流动速度增大;系统内空气的温升增大,蓄热介质表面的温度也显著升高.     

风力增压联合海水淡化太阳能烟囱电站初探

建立风力增压联合海水淡化太阳能烟囱电站(WSSCPPCSD)的数学模型,以西班牙太阳能烟囱电站原型为基础进行数值模拟,并用对比的方法分别对太阳能烟囱电站(SCPP)、联合海水淡化太阳能烟囱电站(SCPPCSD)及WSSCPPCSD却有所降低,通过风力增压系统在烟囱出口提供64.5 Pa的负压,可使SCPPCSD量提高8.22 kg/h,太阳能综合利用率提高到13.2%。风力增压系统不仅能显著增加发电量,而且可提高淡水产出。     

基于集热影响系数d的太阳能烟囱集热效率分析

针对呼和浩特地区太阳辐照资源,以太阳能烟囱为研究对象,在呼和浩特地区应用太阳能烟囱进行可行性分析。太阳能烟囱在定集热棚半径定壁温条件下,对不同集热棚倾角进行数值模拟计算,引入集热影响系数d,对集热棚内流场努赛尔数(Nu)进行分析,比较不同倾角下温度场、压力场、速度场、集热效率。研究表明,集热棚集热影响系数d存在最大值,在不同集热棚倾角下,集热棚内温度场、压力场、速度场变化较大,集热效率存在最大值。认为在定集热棚半径条件下,集热棚倾角选取10°作为呼和浩特地区太阳能烟囱集热棚倾角更经济适合。修正了以往国内外太阳能烟囱集热棚倾角的选取方法。     

太阳能热气流发电流道优化分析

以西班牙太阳能热气流电站为原型进行数值模拟,得出了太阳能烟囱内的速度场、压力场和温度场分布;研究了集热棚坡度、分流板高度和弧度等因素对系统发电性能及涡轮机位置的影响。研究结果表明:集热棚坡度增加时,烟囱的抽吸作用增强,空气流速增加,有利于提高太阳能热气流发电的输出功率;当集热棚坡度约为0.5°时,其作用最为明显,对于提高系统发电性能最为有利;增加分流板有利于气流发电站的优化,当分流板高度略微高于集热棚高度时,优化效果较好;分流板弧度越小,越有利于系统的优化;集热棚坡度对涡轮机位置有影响,改变分流板的几何因素对涡轮机位置没有影响。     

不同蓄热方式下太阳能烟囱的温升性能

针对太阳能烟囱的不同应用背景,设计不同蓄热方式的实验系统,考察太阳能烟囱内部的温度分布及温升性能.实验结果表明,密闭水体的蓄热方式的温升最大,由于水分蒸发消耗了部分太阳热量,开放水体系统的温升效果最差,多孔材料的加人使集热后的空气温度进一步降低;非蒸发体系中的空气温度沿着主体流动方向存在最大值,蒸发体系中的空气温度分布总体呈上升趋势,但具体变化会因水分蒸发的强弱而不同.温度分布的结果表明为了避免出现集热棚下的热量散失段,需要对太阳能烟囱的结构参数进行优化设计.     

太阳能烟囱发电系统的性能研究

采用通用商业CFD软件ANSYS Fluent 13.0对太阳能烟囱发电系统进行数值模拟,获得太阳能烟囱发电系统的空气流速分布。结果表明:在其他条件不变的情况下,集热棚周边高度对系统的发电功率几乎没有影响;太阳能烟囱发电系统的烟囱直径存在最佳值,使太阳能烟囱发电系统的输出功率最大;集热棚斜度也存在最佳值,使系统输出发电功率最大。     

Analysis of chimney height for solar chimney power plant

Current in solar chimney power plant that drives turbine generators to generate electricity is driven by buoyancy resulting from higher temperature than the surroundings at different heights. In this paper, the maximum chimney height for convection avoiding negative buoyancy at the latter chimney and the optimal chimney height for maximum power output are presented and analyzed using a theoretical model validated with the measurements of the only one prototype in Manzanares. The results based on the Manzanares prototype show that as standard lapse rate of atmospheric temperature is used, the maximum power output of 102.2 kW is obtained for the optimal chimney height of 615 m, which is lower than the maximum chimney height with a power output of 92.3 kW. Sensitivity analyses are also performed to examine the influence of various lapse rates of atmospheric temperatures and collector radii on maximum height of chimney. The results show that maximum height gradually increases with the lapse rate increasing and go to infinity at a value of around 0.0098 K m^?1, and that the maximum height for convection and optimal height for maximum power output increase with larger collector radius.     

Analysis of solar chimney power plant utilizing chimney discrete model

The paper presents a mathematical thermal model for steady state airflow inside a solar chimney power plant using modified Bernoulli equation with buoyancy effect and ideal gas equation. The study evaluates the use of constant density assumption across the solar chimney and compares it with more realistic chimney mathematical discrete model that allows density variation across the chimney. The result shows that using a constant density assumption through the solar chimney can simplify the analytical model however it over predicts the power generation. The results show that the chimney height, the collector radius, the solar irradiance, and the turbine head are essential parameters for the design of solar chimneys. The maximum power generation depends on the turbine head and the relation is not monotonic.     

Constructal solar chimney configuration

In this study, we describe the constructal-theory search for the geometry of a solar chimney. The objective is to increase the power production over the area occupied by the plant. The ratio height/radius, maximum mass flow rate and maximum power under the constraints of a fixed area and volume are determined. We find that the power generated per unit of land area is proportional to the length scale of the power plant. The analysis is validated by a detailed mathematical model. Pressure losses are reported in terms of the dimensionless length scale of the system, and are illustrated graphically. They indicate that the pressure drop at the collector inlet and at the transition section between the collector and chimney are negligible, and the friction loss in the collector can be neglected when the svelteness (Sv) of the entire flow architecture is greater than approximately 6.     

Solar chimney turbine characteristics

A typical layout of a solar chimney power plant has a single axial turbine with radial inflow through inlet guide vanes at the base of the chimney. Turbine efficiency depends on the turbine blade row and turbine diffuser loss coefficients. The paper presents analytical equations in terms of turbine flow and load coefficient and degree of reaction, to express the influence of each coefficient on turbine efficiency. It finds analytical solutions for optimum degree of reaction, maximum turbine efficiency for required power and maximum efficiency for constrained turbine size. Characteristics measured on a 720 mm diameter turbine model confirm the validity of the analytical model. Application to a proposed large solar chimney plant indicates that a peak turbine total-to-total efficiency of around 90% is attainable, but not necessarily over the full range of plant operating points.     

Solar chimney and building ventilation

This study is concerned with the design of a solar chimney to induce ventilation in a building. CFD modelling techniques were used to assess the impacts of inclination angle, double glazing and low-emissivity finishes on the induced ventilation rate. It was found that for a south-facing chimney, an inclination angle of 67.5° from the horizontal was optimum for the location chosen, giving 11% greater efficiency than the vertical chimney, and that a 10% higher efficiency was obtained by using a low-emissivity wall surface.     

Performance of a solar chimney

A mathematical model of a solar chimney was proposed in order to predict its performance under varying ambient and geometrical features. Steady state heat transfer equations were set up using a thermal resistance network and solved using matrix inversion. Existing correlations of heat transfer coefficients were utilised. Property values for the air flow in the duct were based on mean bulk or film temperatures. The performance of the chimney was evaluated by predicting the temperatures of the glass glazing and the heat-absorbing wall and also the temperature and velocity of the induced air flow in the chimney. The effects of air gap and solar radiation intensity on the performance of different chimneys were investigated. In order to verify the theoretical model, experiments were conducted on a 2 m high×0.45 m wide physical model with air gaps of 0.1, 0.2 and 0.3 m. Experiments were carried out outdoors on the roof and the experimental model exposed to both direct and diffuse solar radiation. Air velocities between 0.25 m s⁻¹ and 0.39  m s⁻¹ for radiation intensity up to 650 W m⁻² were obtained. No reverse air flow circulation was observed even at the large gap of 0.3 m.     

Dynamic similarity in solar chimney modeling

Dimensionless variables are proposed to guide the experimental study of flow in a small-scale solar chimney: a solar power plant for generating electricity. Water and air are the two working fluids chosen for the modeling study. Computational fluid dynamics (CFD) methodology is employed to obtain results that are used to prove the similarity of the proposed dimensionless variables. The study shows that air is more suitable than water to be the working fluid in a small-scale solar chimney model. Analyses of the results from CFD show that the models are dynamically similar to the prototype as suggested by the proposed dimensionless variables.     

Experimental investigation on solar-flue gas chimney

Flue gases exhausted from thermal power plants contain more than 50% of the fuel thermal energy. In the present work, experimental investigation was carried out to study the utilization of thermal energy in flue gases to enhance the performance of modified solar chimney consisting of Savonius wind rotor. A modified solar chimney model was designed and fabricated to carry out experimental measurement. The model consists of thermal energy conversion unit; Savonius wind rotor and a chimney. The thermal energy in the flue gas transfers to the air particles in the air channel across the absorber plate and results in upward air stream due to the buoyancy effect. With an 9 absorber area of 2.36 re＇and flue gas mass flow rate of0.18 kg/s, air velocity＇ of 4.1 m/s was achieved at the top of the thermal unit. Increasing the mass flow rate of the flue gas to 0.24 kg/s enhances the air velocity to be 4.6 m/s. The results have demonstrated the possibility＇ of utilizing the thermal energy in the waste flue gas to enhance the performance of a solar chimney and facilitate the continuous operation during the absence of the sun.     

关于太阳能建筑气流电站的设想

一前言 最早的"烟囱"形太阳能气流电站是由上百吨钢板建造的,其缺陷是大烟囱耗费材料多,在室外日晒雨淋薄钢板容易生锈,使用寿命短.为解决大烟囱经久耐用的问题,则需要投入更多的材料和人力,耗费巨大,成为气流电站推广使用的拦路虎.     

Effect of chimney shadow on the performance of wind supercharged solar chimney power plants: A numerical case study for the Spanish prototype

Three-dimensional numerical simulations for a solar chimney power plant (SCPP) and wind supercharged solar chimney power plant (WSSCPP) based on the Spanish prototype using the solar ray-tracing algorithm were performed to study the shadow effect of the chimney. The area of the shadow region increases with an increase in the incident angle of the solar rays. A parametric study was performed by varying the incident angle from 0° to 30°. The temperature and velocity distributions at different incident angles were analyzed. In addition, we investigated the chimney shadow effect in several comprehensive SCPP systems. The findings show that the turbine shaft powers of the SCPP and WSSCPP were reduced by 22.4% and 13.7%, respectively, when the incident angle increased from 0° to 30°. In conclusion, it is important to consider the chimney shadow effect when estimating the performance in the design and cost analysis of SCPP systems.