抛物槽式太阳能集热器集热性能的实验研究

依托山东省泰安市某抛物槽式太阳能集热供暖系统搭建实验平台,对不同天气类别、法向直接辐照度、导热油入口温度等因素对抛物槽式太阳能集热器集热性能的影响进行了研究。研究结果显示：1)太阳能集热器的瞬时集热效率受天气影响较大,晴天时,太阳能集热器的最大瞬时集热效率可达0.73;风天时,受风速影响,太阳能集热器的最大瞬时集热效率为0.61;雾天时,法向直接辐照度受到空气中颗粒物的削弱,太阳能集热器的最大瞬时集热效率为0.46;而雨天时,太阳能集热器的瞬时集热效率处于0.03～0.08之间。2)在导热油入口温度一定的情况下,随着法向直接辐照度增大,太阳能集热器的瞬时集热效率也随之增大。3)当法向直接辐照度为500和600 W/m²时,太阳能集热器的瞬时集热效率随导热油入口温度的增大呈先增大后减小的趋势;而当法向直接辐照度为700和800 W/m²时,由于较高的法向直接辐照度弥补了太阳能集热器的部分热损,太阳能集热器的瞬时集热效率随导热油入口温度的增大一直呈增大趋势,但增幅较为平缓。以期研究结果可为抛物槽式太阳能集热器在采暖工程的进一步应用提供理论支持。     

水平布置方式下抛物槽式集热器辐照量分析

采用适用于中等纬度的Hottel晴天太阳辐射模型,对地处北纬41.34°,水平布置方式下的抛物槽式集热器夏季和冬季的辐照量进行了计算。计算结果表明:水平南北布置的抛物槽式集热器在夏季接收的太阳辐射较多,月辐照量可达1 GJ/m2,而冬季接收的太阳辐射较少,月辐照量为0.3~0.45 GJ/m2,且冬至日辐照量仅为夏至日辐照量的1/4左右;水平东西布置的抛物槽式集热器夏季月辐照量在0.75 GJ/m2左右,而冬季月辐照量为0.5 GJ/m2左右,冬至日辐照量可达夏至日辐照量的1/2以上。由此可见,在北纬41.34°地区应用抛物槽式集热器时,如考虑在夏季使用,应采用水平南北布置方式;若考虑在冬季使用,则应采用水平东西布置方式。     

槽式太阳能集热器热性能实验测试

针对天津市槽式太阳能集热系统性能测试平台,对不同太阳辐射强度、入口流体温度以及不同工质流量状况下集热效率和集热管压降变化规律进行实验测试,通过测试数据对槽式太阳能集热器热性能进行分析.试验结果表明:在天津地区槽式太阳能集热器集热效率可以达到66.1％;太阳辐射强度的增强,会提高集热效率,并且集热器进出口的压降会随之降低...     

槽式集热器真空集热管传热特性研究

通过分析太阳能槽式集热器真空集热管的热性能,建立了槽式集热器真空集热管稳态传热模型,通过和典型实验数据对比,验证该模型的适用性和准确性。在此基础上,分析在无光照条件下,吸热管内壁温度、环境温度、风速和集热管残存气体种类等因素对集热管热损失的影响。结果表明：吸热管内壁温度的升高会增大玻璃管外壁温度和集热管热损失;环境温度和风速对玻璃管外壁温度有显著影响,但对热损失的影响甚微;吸热管与玻璃管之间以辐射传热为主,对流换热受环形区域残存气体种类和压力的影响。     

抛物面槽式太阳能集热器场热损失分析

在已有的计算集热器场吸收有用能量模型的基础上,加入影响集热器场效率的热学因素,优化了集热器场效率计算模型,并验证了优化模型的精确性。利用优化模型对抛物面槽式太阳能集热器场热损失机理进行了研究。结果表明,集热器集热元件热效率、入射角以及由入射角引起的端部损失是影响集热器场效率的主要因素。在太阳辐射强度一定的情况下,入射角越小、集热器热收集元件的热效率越高时,集热器场效率越高。     

小型槽式太阳能集热器优化设计与试验研究

按照高性能低成本的原则设计并制作了集热面积为12 m2的商用小型槽式集热器。其主要创新优化之处包括:1通过免背板设计减少了槽式反射镜面结构的重量和用材,提高了镜面曲率精度;2通过推杆联动机构减少了驱动装置;3反射镜面板分离式结构起到了自清洁功能,减轻了清扫的工作强度;4将闭环反馈技术应用到太阳能跟踪控制系统,可实现四季全天候跟踪。现场试验结果表明:在太阳辐射强度为540~660 W/m2时,该集热器可将循环水加热至170℃以上,系统整体集热效率最高可达0.52,但随水温的升高逐渐降低。     

大尺寸平板太阳集热器集热效率研究

平板型太阳集热器集热效率除了与内部结构参数、运行参数等因素有关外,还受集热器外形尺寸大小的影响.通过建立相同集热面积条件下单一大尺寸平板集热器、并联常规平板集热器的三维物理模型,分析了2类集热系统集热效率、集热量、热损失随尺寸规模的变化关系.发现相同集热面积条件下,相比并联常规平板集热器形式,大尺寸平板集热器集热效率有...     

槽式太阳能热发电站中槽式集热器桩基础的施工工艺研究

以某槽式太阳能热发电站的集热场施工工程为例,在国内尚无相关成熟施工工艺的现状下,针对槽式集热器桩基础施工工程量大,以及地脚螺栓施工精度高、工期紧的特点,对槽式集热器桩基础及地脚螺栓安装、固定的施工工艺进行了研究。在满足工程实践需求的前提下,从桩基础点位测量、桩基础成孔、钢筋笼的制作与安装、地脚螺栓固定架的设计和制作、地脚螺栓的安装及固定、混凝土浇筑等各方面对槽式集热器桩基础施工工艺流程进行了多次论证和现场实际验证,最终提出了一套独特的槽式太阳能热发电站中槽式集热器桩基础的施工工艺。通过实际工程验证,该槽式集热器桩基础施工工艺有效控制了地脚螺栓的施工质量,从而确保了槽式集热器的安装精度,并在大幅加快现场施工进度的基础上满足了工程的施工要求。该施工工艺可广泛应用于其他大规模槽式太阳能热发电站的槽式集热器桩基础施工中。     

槽式太阳能供热光伏系统集热器集热性能的实验研究

文章基于沧州地区的气候特点,通过实验分析了传热工质进口温度、直射辐射量对槽式太阳能供热光伏系统中集热器集热性能的影响情况。实验结果表明:沧州地区3月份晴朗天气条件下,槽式太阳能供热光伏系统的集热效率为0.35～0.65;当运行温度为20～100℃时,随着传热工质入口温度逐渐升高,槽式太阳能供热光伏系统中集热器的集热效率和火用效率均得到明显提高;直射辐射量的增大,会导致槽式太阳能供热光伏系统中集热器的集热效率和火用效率随之升高。     

槽式太阳能集热器热损失计算模型适用性分析

为精确预测太阳能槽式集热器（parabolic trough collector, PTC）的传热损失,基于美国桑迪亚国家实验室（Sandia National Laboratory, SNL）、西班牙太阳能热发电站（Plataforma Solar de Almería, PSA）以及美国安柏瑞德航空航天大学（Embry-Riddle Aeronautical University, ERAU）的实测数据,对16个既有的PTC热损失模型的准确性和适用性进行了分析。结果表明,WANG等模型与SNL的实测数据吻合度最高;DICKES模型与ERAU的实测数据吻合度最高;PATNODE模型与PSA的实测数据吻合度最高。整体而言,在30 ~ 450℃ PTC载热介质工作温度范围内,PATNODE模型计算精度最高,适用性最好;直射辐射强度、入射角以及载热介质温度对集热器热损失的大小起着决定性的作用。     

抛物槽集热器的能量效率

对以镜面不锈钢板为反光材料的抛物槽集热器的能量效率进行了研究,分析了光学效率、热损失对能量效率的影响,计算出有空气夹层的接收器的总热损系数。试验测得的能量效率为21.1%,光学效率为23.9%,总热损系数为10.45W/(m2.℃)。通过对试验数据的分析得知,光学效率是影响能量效率的主要因素,吸收管的传导热损失较辐射热损失大,若将接收器内的空气夹层抽成真空,会大大地减少热损失。     

Design, manufacture and testing of fiberglass reinforced parabola trough for parabolic trough solar collectors

The design and manufacture of a smooth 90° rim angle fiberglass reinforced parabolic trough for parabolic trough solar collector hot water generation system by hand lay up method is described in this paper. The total thickness of the parabolic trough is 7 mm. The concave surface where the reflector is fixed is manufactured to a high degree of surface finish. The fiberglass reinforced parabolic trough was tested under a load corresponding to the force applied by a blowing wind with 34 m/s. Distortion of the parabola due to wind loading was found to be within acceptable limits. The thermal performance of the newly developed fiberglass reinforced parabolic collector was determined according to ASHRAE Standard 93 [ASHRAE Standard 93, 1986. Method of testing to determine the thermal performance of solar collectors. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, GA]. The standard deviation of the distribution of the parabolic surface errors is estimated as 0.0066 rad from the collector performance test according to ASHRAE Standard 93 (1986), which indicates the high accuracy of the parabolic surface.     

Effect of using nanofluids on efficiency of parabolic trough collectors in solar thermal electric power plants

In this paper, forced convection heat transfer nanofluid flow inside the receiver tube of solar parabolic trough collector is numerically simulated. Computational Fluid Dynamics (CFD) simulations are carried out to study the influence of using nanofluid as heat transfer fluid on thermal efficiency of the solar system. The three-dimensional steady, turbulent flow and heat transfer governing equations are solved using Finite Volume Method (FVM) with the SIMPLEC algorithm. The results show that the numerical simulation are in good agreement with the experimental data. Also, the effect of various nanoparticle volume fraction on thermal and hydrodynamic characteristics of the solar parabolic collector is discussed in details. The results indicate that, using of nanofluid instead of base fluid as a working fluid leads to enhanced heat transfer performance. Furthermore, the results reveal that by increasing of the nanoparticle volume fraction, the average Nusselt number increases.     

Performance enhancement of parabolic trough collectors by solar flux measurement in the focal region

Characterization of the optical performance and detection of optical losses of parabolic trough collectors are very important issues in order to improve the optical efficiency of these systems and to ensure the desired quality in solar power plants. Therefore two methods of measuring the solar flux in the focal region were developed: PARASCAN (PARAbolic Trough Flux SCANner) is a solar flux density measurement instrument which can be moved along the receiver axis. The sensor registers the flux distribution in front and behind the receiver with high resolution. The resulting flux maps allow to calculate the intercept factor and to analyse the optical properties of the collector at the finally interesting location, i.e. around the receiver. The camera-target-method (CTM) uses a diffuse reflecting Lambertian target and a calibrated camera which takes pictures of it. The target is held perpendicular to the focal line surrounding the receiver. With the resulting images of this fast and easy method it is possible to visualize the paths of the reflected rays close to the receiver and to detect local optical errors. Both methods are described in detail. Latest measurement results gained at the Eurotrough-II prototype collector built on the Plataforma Solar de Almería (PSA) in Spain are presented and consequences are discussed.     

Three-dimensional numerical study of heat transfer characteristics in the receiver tube of parabolic trough solar collector

The solar energy flux distribution on the outer wall of the inner absorber tube of a parabolic solar collector receiver is calculated successfully by adopting the Monte Carlo Ray-Trace Method (MCRT Method). It is revealed that the non-uniformity of the solar energy flux distribution is very large. Three-dimensional numerical simulation of coupled heat transfer characteristics in the receiver tube is calculated and analyzed by combining the MCRT Method and the FLUENT software, in which the heat transfer fluid and physical model are Syltherm 800 liquid oil and LS2 parabolic solar collector from the testing experiment of Dudley et al., respectively. Temperature-dependent properties of the oil and thermal radiation between the inner absorber tube and the outer glass cover tube are also taken into account. Comparing with test results from three typical testing conditions, the average difference is within 2%. And then the mechanism of the coupled heat transfer in the receiver tube is further studied.     

Optimization of parabolic trough solar collectors

The results of a detailed optical analysis of parabolic trough solar collectors are summarized by a few universal graphs and curve fits. These graphs enable the designer of parabolic trough collectors to calculate the performance and optimize the design with a simple hand calculator. The method is illustrated by specific examples that are typical of practical applications. The sensitivity of the optimization to changes in collector parameters and operating conditions is evaluated.     

槽式聚光热电联供系统抛物反射面的性能参数分析

分析了跟踪方式和太阳张角对理想槽式抛物面反射镜的影响,给出了几何聚光比、相对口径、能流分布、边界角之间的函数关系式。在理想情况下,边界角δ为44.87°时,槽式聚光器的最大聚光比为212.59,此时相对口径为1.652 m。讨论了北京、上海、昆明等地单轴跟踪在全年不同时刻入射角余弦值的变化规律。采取东-西水平轴跟踪时,入射角余弦值与各地纬度无关;采取南-北水平轴跟踪时,春冬两季每天不同时刻入射角的变化范围较大,夏秋两季的变化范围较小。文章针对不同宽度太阳电池和聚光比对抛物镜面参数进行了设计分析。     

Thermal analysis of solar parabolic trough with porous disc receiver

In this paper, 3-D numerical analysis of the porous disc line receiver for solar parabolic trough collector is presented. The influence of thermic fluid properties, receiver design and solar radiation concentration on overall heat collection is investigated. The analysis is carried out based on renormalization-group (RNG) k–ε turbulent model by using Therminol-VP1 as working fluid. The thermal analysis of the receiver is carried out for various geometrical parameters such as angle (θ), orientation, height of the disc (H) and distance between the discs (w) and for different heat flux conditions. The receiver showed better heat transfer characteristics; the top porous disc configuration having w = d_i, H = 0.5d_i and θ = 30°. The heat transfer characteristic enhances about 64.3% in terms of Nusselt number with a pressure drop of 457 Pa against the tubular receiver. The use of porous medium in tubular solar receiver enhances the system performance significantly.     

Modelling of parabolic trough direct steam generation solar collectors

Solar electric generation systems (SEGS) currently in operation are based on parabolic trough solar collectors using synthetic oil heat transfer fluid in the collector loop to transfer thermal energy to a Rankine cycle turbine via a heat exchanger. To improve performance and reduce costs direct steam generation in the collector has been proposed. In this paper the efficiency of parabolic trough collectors is determined for operation with synthetic oil (current SEGS plants) and water (future proposal) as the working fluids. The thermal performance of a trough collector using Syltherm 800 oil as the working fluid has been measured at Sandia National Laboratory and is used in this study to develop a model of the thermal losses from the collector. The model is based on absorber wall temperature rather than fluid bulk temperature so it can be used to predict the performance of the collector with any working fluid. The effects of absorber emissivity and internal working fluid convection effects are evaluated. An efficiency equation for trough collectors is developed and used in a simulation model to evaluate the performance of direct steam generation collectors for different radiation conditions and different absorber tube sizes. Phase change in the direct steam generation collector is accounted for by separate analysis of the liquid, boiling and dry steam zones.     

Solar multiple optimization for a solar-only thermal power plant, using oil as heat transfer fluid in the parabolic trough collectors

Usual size of parabolic trough solar thermal plants being built at present is approximately 50 MW_e. Most of these plants do not have a thermal storage system for maintaining the power block performance at nominal conditions during long non-insolation periods. Because of that, a proper solar field size, with respect to the electric nominal power, is a fundamental choice. A too large field will be partially useless under high solar irradiance values whereas a small field will mainly make the power block to work at part-load conditions.This paper presents an economic optimization of the solar multiple for a solar-only parabolic trough plant, using neither hybridization nor thermal storage. Five parabolic trough plants have been considered, with the same parameters in the power block but different solar field sizes. Thermal performance for each solar power plant has been featured, both at nominal and part-load conditions. This characterization has been applied to perform a simulation in order to calculate the annual electricity produced by each of these plants. Once annual electric energy generation is known, levelized cost of energy (LCOE) for each plant is calculated, yielding a minimum LCOE value for a certain solar multiple value within the range considered.