抛物槽式集热器热效率研究

介绍槽式集热器的结构及其工作过程,对集热器进行热性能分析,研究已有集热器热力学模型,并对其进行优化,利用该模型计算各个部位的热损失大小以及集热器热效率,分析得出影响集热器热效率的主要因素,定量分析这些因素对集热器效率的影响趋势,并解释其原因。     

不同月份及不同安装角度时平板太阳能集热器接收的太阳辐照量分析

通过理论计算模型推算出在山东省济南市不同月份及不同安装角度时平板太阳能集热器接收的太阳辐照量理论数据,并与实际测量数据进行对比.结果表明:理论数据与实测数据存在高度的一致性;与安装角度为75°时相比,安装角度为90°时平板太阳能集热器接收的太阳辐照量有所下降;通过对全年不同安装角度下平板太阳能集热器接收的太阳辐照量实测...     

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。     

槽式太阳能聚焦集热器太阳跟踪方式的优化研究

通过数值模拟的方法为槽式太阳能聚焦集热器选取一种最佳的太阳跟踪方式,具体研究内容包括:地表日太阳直射辐射量的计算、不同太阳跟踪方式时槽式太阳能聚焦集热器的抛物面反射镜年接收太阳直射辐射总量的对比,以及南北倾斜式跟踪方式最佳倾角的研究.研究发现,在上海地区,槽式太阳能聚焦集热器的抛物面反射镜接收的太阳直射辐射量从高到低排...     

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...     

槽式太阳能集热器运行特性分析

分析与研究了槽式太阳能聚光集热器运行特性,建立了槽式太阳能聚光集热器运行特性参数的数学模型,应用该模型以我国西部太阳能热发电的典型地区为计算地点,对槽式太阳能聚光集热器的太阳入射角余弦、入射角修正系数、遮挡系数、端部损失及镜场运行效率等运行特性参数进行了计算。结果表明：槽式太阳能集热器正午时刻入射角余弦达到最小值,余弦效应最为明显;遮挡损失和端部损失对槽式集热器的运行影响总体不大,在日出、日落时刻会发生遮挡效应,最大端部损失发生在正午时刻;槽式太阳能聚光集热器镜场效率正午时刻之前单调下降,正午时刻后,随高度角的下降而单调增加,在正午时刻达到最小值,夏至日镜场效率峰值约为0.74,冬至日的峰值约为0.47,差值约为0.27。     

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。     

槽式抛物面太阳能聚焦集热器的理论研究

建立了槽式抛物面太阳能聚焦集热器(PTC)的一维、非稳态传热模型,给出了沿轴线的光强分布公式,对PTC的热性能进行了数值模拟,并与实验结果进行了比较,模拟结果与实验结果的误差在4.6%以内,两者吻合较好,验证了模型的合理性.对采用不同形式集热器的太阳能双效吸收式制冷系统的性能进行了分析对比,结果显示,采用PTC的太阳能吸收式制冷系统具有最佳的系统性能.     

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。     

槽式太阳能集热器立柱安装精度的研究

结合实际槽式太阳能集热器立柱安装工程,通过对工程中出现的安装误差问题进行分析,明确集热器立柱安装精度的控制要点,编制正确的安装工艺路线,实现立柱的高精度安装,从而保证槽式太阳能集热器的安装精度,为槽式太阳能集热器的高效运行奠定坚实基础。     

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.     

Alternative designs of parabolic trough solar collectors

Parabolic trough collector (PTC) is the most established solar concentrating technology worldwide. The conventional parabolic trough collectors are used in various applications of medium and high-temperature levels. However, there are numerous studies which investigate alternative designs. The reasons for examining different PTC configurations regard the thermal efficiency increase, the reduction of the manufacturing cost and the development of more compact designs. The objective of this review paper is to summarize the existing alternative designs of PTC and to suggest the future trends in this area. Optical and thermal modifications are examined, as well as the use of concentrating thermal photovoltaic collectors. The optical modifications include designs with secondary concentrators, stationary concentrators and strategies for achieving uniform heat flux. The thermal modifications regard the use of nanofluids, turbulators and the use of thermally modified receivers with insulation, double-coating and radiation shields. The concentrating thermal photovoltaics are systems with flat or triangular receivers which can operate in low or in medium temperature levels with the proper alternative designs. It has been found that there are many promising choices for designing PTC with higher thermal performance and lower cost. The conclusions of this work can be used as guidelines for future trends in linear parabolic concentrating technologies.     

Heat losses from parabolic trough solar collectors

Parabolic trough solar collector usually consists of a parabolic solar energy concentrator, which reflects solar energy into an absorber. The absorber is a tube, painted with solar radiation absorbing material, located at the focal length of the concentrator, usually covered with a totally or partially vacuumed glass tube to minimize the heat losses. Typically, the concentration ratio ranges from 30 to 80, depending on the radius of the parabolic solar energy concentrator. The working fluid can reach a temperature up to 400°C, depending on the concentration ratio, solar intensity, working fluid flow rate and other parameters. Hence, such collectors are an ideal device for power generation and/or water desalination applications. However, as the length of the collector increases and/or the fluid flow rate decreases, the rate of heat losses increases. The length of the collector may reach a point that heat gain becomes equal to the heat losses; therefore, additional length will be passive. The current work introduces an analysis for the mentioned collector for single and double glass tubes. The main objectives of this work are to understand the thermal performance of the collector and identify the heat losses from the collector. The working fluid, tube and glass temperature's variation along the collector is calculated, and variations of the heat losses along the heated tube are estimated. It should be mentioned that the working fluid may experience a phase change as it flows through the tube. Hence, the heat transfer correlation for each phase is different and depends on the void fraction and flow characteristics. However, as a first approximation, the effect of phase change is neglected. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

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.     

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.     

Thermal enhancement of solar parabolic trough collectors by using nanofluids and converging-diverging absorber tube

Parabolic trough collectors are the most mature technology for utilizing the solar energy in high temperature applications. The objective of this study is the thermal efficiency enhancement of the commercial parabolic collector IST-PTC by increasing the convective heat transfer coefficient between the working fluid and the absorber. There are two main factors which influence on this parameter, the working fluid type and the absorber geometry. For this reason three working fluids are investigated, thermal oil, thermal oil with nanoparticles and pressurized water. Moreover, a dimpled absorber tube with sine geometry is tested because this shape increases the heat transfer surface and increases the turbulence in the flow. The final results show that these two techniques improve the heat transfer coefficient and the thermal efficiency of the collector. More specifically, the use of nanofluids increases the collector efficiency by 4.25% while the geometry improvement increases the efficiency by 4.55%. Furthermore, collector parameters such as the heat loss coefficient, the exergetic efficiency, the pressure losses and the absorber temperature are presented for all the examined cases. The model is designed with Solidworks and is simulated by its flow simulation studio.     

Energy performance enhancement of solar thermal power plants by solar parabolic trough collectors and evacuated tube collectors-based preheating units

Solar steam power plant is the dominant technology in the category of solar thermal power systems. In steam power cycles, there is usually a couple of steam lines, extracted from medium-pressure and low-pressure turbines, to preheat the working fluid before the boiler. This although leads to an increase in the energy efficiency of the cycle, reduces the contribution of the turbine proportionally. Therefore, finding an alternative method of preheating the working fluid would be effective in further enhancement of the efficiency of the system. In this study, the feasibility of using solar collectors for the preheating process in a solar steam power plant is investigated. For this, parabolic trough solar collectors and evacuated tube solar collectors based on a wide range of different scenarios and configurations are employed. The plant is designed, sized and thermodynamically analyzed for a case study in Saudi Arabia where there is a large solar irradiation potential over the year. The results of the simulations show that, among all the considered scenarios, a power cycle aided by a set of parabolic trough collectors as the preheating unit is the best choice technically. This configuration leads to about 23% increased power generation rate and 6.5% efficiency enhancement compared to the conventional design of the plant.     

The integration of parabolic trough solar collectors and evacuated tube collectors to geothermal resource for electricity and hydrogen production

In this study, electricity and hydrogen production of an integrated system with energy and exergy analyses are investigated. The system also produces clean water for the water electrolysis system. The proposed system comprises evacuated tube solar collectors (ETSCs), parabolic trough solar collectors (PTSCs), flash turbine, organic Rankine cycles (ORC), a reverse osmosis unit (RO), a water electrolysis unit (PEM), a greenhouse and a medium temperature level geothermal resource. The surface area of each collector is 500 m². The thermodynamics analysis of the integrated system is carried out under daily solar radiation for a day in August. The fluid temperature of the medium temperature level geothermal resource is upgraded by ETSCs and PTSCs to operate the flash turbine and the ORCs. The temperature of the geothermal fluid is upgraded from 130 °C to 323.6 °C by the ETSCs and PTSCs. As a result, it is found that the integrated system generates 162 kg clean water, 1215.63 g hydrogen, and total electrical energy of 2111.04 MJ. The maximum energy and exergy efficiencies of the overall system are found as 10.43% and 9.35%, respectively.