An Evaluation to the Performance of Evacuated Tube Solar Heaters for Arid and Hot Areas

Solar energy applications could be the best alternative to the conventional fuels for the purposes of domestic,water and space heating and some industries in the sunny,arid,and hot areas.In the present study,the performance of an evacuated tube solar heater for water heating for months of February and March was experimentally investigated.This was performed in a hot and arid area(Nasiriya City,South of Iraq).A solar heater with ten evacuated tube solar collectors with a capacity of 100 liter was used in the experiments.Each evacuated tube had a length of 1.8m with an outside diameter of 8 cm.It was observed that for the two selected months,water temperature of the solar heater reached a maximum more than 70°C during sunny days with no heat extraction from the tank of the solar heater.Moreover,heat was extracted from the solar collector with four different flowrates 0.5,0.75,1,and 1.25 l/min,respectively.The results showed that temperature of the solar heater behaved differently from the static situation.When the heat extraction begun,there was a gradual and noticeable decrease in the water temperature of the heater.The observed decrease was slight with the lowest flowrate(0.25 l/m)and becomes sharp with the highest flowrate(1.25 l/min).However,water temperature of the solar heater remained higher than 40°C for the investigated flowrates except the case of 1.25 l/min.The results showed that evacuated tube solar heater can work efficiently in arid and hot areas in winter and spring seasons when the conditions of solar radiation are suitable.

Enhanced efficiency in Concentrated Parabolic Solar Collector(CPSC) with a porous absorber tube filled with metal nanoparticle suspension

In this study, effects of different nanoparticles and porosity of absorber tube on the performance of a Concentrating Parabolic Solar Collector(CPSC) were investigated. A section of porous-filled absorber tube was modeled as a semi-circular cavity under the solar radiation which is filled by nanofluids and the governing equations were solved by FlexPDE numerical software. The effect of four physical parameters, nanoparticles type, nanoparticles volume fraction(φ), Darcy number(Da) and Rayleigh number(Ra), on the Nusselt number(Nu) was discussed. It turns out that Cu nanoparticle is the most suitable one for such solar collectors, compared to the commonly used Fe_3O_4, Al_2O_3, TiO_2.With the increased addition of Cu nanoparticles all the parameters φ, Da and Ra shows a significant increase against the Nu, indicates the enhanced heat transfer in such cases. As a result, low concentration of Cu nanoparticle suspension combined with porous matrix was supposed to be beneficial for the performance enhancement of concentrating parabolic solar collector.

Manufacturing and Thermal Performance Test of (Compound) Solar Collector in Damascus City

Solar water collectors that uses for domestic and industrial applications within temperature up to, are classified under two main types: Flat Plate collector (FP), and Evacuated Tube collector (ET). Thermal performance test results showed that each type have different thermal features. Comparison between (FP & ET) collectors showed that they could take advantages of different thermal features of two types when they work in the same climatic conditions and overlap of these thermal features when they work in different operational conditions. They can take advantage of these features through (compound) solar collector. Compound solar water Collector (CO) composed of a part of flat plate collector shape (FP), and a part of evacuated tube collector shape (ET). Booth have equal reference area, and connected together to be as one Solar collector (CO). Water entered first flat part (FP), then evacuated tube part (ET) then to tank or end-use. In this paper, present design and manufacturing as well the thermal performance test of (compound) solar collector, according to Standard Specification of tests, was EN12975:2001. Mechanical test for (CO) collector conducted successfully according to durability, reliability, and safety requirements. In addition, thermal performance was tested in steady state at the climatic conditions of Damascus city, and concluded the thermal performance of (FP & ET) that constitute (CO) collector. The results showed enhancement of thermal performance.

Performance and Optimization of a Small Hybrid Solar-Thermal Collector

A hybrid solar collector was designed to investigate the effects of combining two different solar collector techniques on the overall collector’s effectiveness. While most solar collectors focus only on one solar collection method, the small hybrid system uses a flat plate collector in conjunction with five evacuated tubes to absorb the most energy possible from both direct and diffuse solar radiation. Data was collected over four months while the system operated at different flow rates and with various levels of available insolation from the sun to evaluate the performance of the solar collector. To understand the relative contribution of the flat plate collector and the evacuated tubes, temperature differences across each part of the system were measured. The results indicate the average first law efficiency of the hybrid system is 43.3%, significantly higher than the performance of the flat plate alone. An exergy analysis was performed for this system to assess the performance of the flat plate system by itself. Results of the second law analysis were comparable to the exergetic efficiencies of other experimental collectors, around 4%. Though the efficiencies were in the expected range, they reveal that further improvements to the system are possible.

Performance of Water in Glass Evacuated Tube Solar Water Heater under Kenya Climatic Condition

Solar water heaters which provide a cost-effective and environmental friendly approach to hot water generation are in widespread application. Evacuated tube solar water heaters perform better than flat plate solar water heaters as a result of their greater surface area exposed for sunlight absorption. Water-in-glass evacuated tube solar water heaters are widely used as compared to heat-pipe solar water heaters due to their short payback periods. In this study, the performance of water-in-glass evacuated tube solar water heater is investigated through experiments under the climatic conditions in Kenya. The results revealed a daily efficiency range of 0.58 - 0.65 and a daily final outlet temperature greater than 55°C given an initial temperature of 25°C.

Developments of solar collectors in China

China has abundant solar energy resource. Solar thermal collectors, particularly all-glass evacuated tubular collectors, have been studied and developed for 30 years, and solar thermal industry has developed rapidly for 15 years. There are various solar thermal systems, with an operation area of around 108 million m2 in 2007. These systems mainly provide domestic hot water, but some other applications are under extensive study and development as well.

全玻璃真空太阳集热管关键技术参数研究进展

全玻璃真空太阳集热管是太阳能热利用系统的重要组成部分,其性能参数的优劣直接影响到太阳能热利用系统的热性能、耐久可靠性和节能效果。文章从真空管基本结构和工作原理的介绍出发,对影响真空管性能的光学性能、热性能等关键技术参数及玻璃管材料、真空性能等其他技术要求的研究进展做了详细分析,并在长期从事科研和检测工作的基础上,给出了提升真空管的产品性能可从玻璃管生产优化、新涂层开发、真空性能加强、技术创新、先进设备开发、标准修订等方面的建议。

级联型潜热储存耦合热泵系统性能研究

为提高太阳能利用率和热泵热力学性能,将真空管集热器、热泵和填充床等结合,提出一种级联型潜热储存耦合热泵系统用于建筑供热。针对太阳能集热及室外温度等条件,将太阳能蓄热和室外空气作为热泵的热源进行系统集成设计。在FLUENT和EES中分别建立填充床和热泵的热力学模型,并分析填充床的换热流体流量、放热温度和用户回水温度对系统热力性能的影响。结果表明,填充床流体流量从0.05 kg/s增至0.07 kg/s时,热泵系统整体平均性能指数下降0.16;填充床作为热源的放热温度升高20℃时,填充床供热增加74269 kJ,有效放热率下降21.9%;当用户回水温度升高10℃时,热泵系统整体平均性能指数下降0.19,有效放热率下降16.2%。

太阳能真空集热管热损分析与试验研究

基于热平衡法提出了一种动态热平衡热损计算方法,并进行了验证,同时分析了环境温度、进口温度、流量对真空集热管热损的影响。结果表明,热损随着环境温度的降低、进口熔盐温度的升高和熔盐质量流量的降低而增大;当辐照强度在700 W/m2以上时,真空集热管获得的热量大于热损并能稳定工作,说明槽式光热电站在东南沿海等太阳能资源相对不足的地区有一定的适用性。

新型槽式太阳能真空吸热管设计方法及其光学性能研究

针对传统槽式太阳能集热系统工质运行温度受限,以及真空吸热管表面能流密度分布不均而引起的热应力过大等问题,文章在不改变聚光器结构的条件下,提出了一种新型的槽式太阳能真空吸热管的设计方法,通过减小金属内管直径、下移金属内管位置以及在金属内管上方加装双曲线型二次聚光器来提高太阳能聚光比,改善了金属吸热管表面能流密度分布。利用仿真计算方法研究了新型槽式太阳能真空吸热管的光学性能,结果表明:和传统槽式太阳能真空吸热管相比,该新型结构在仅损失1.88%光学效率的情况下将聚光比从62 kW/m^(2)提升至71 kW/m^(2);能流密度分布均匀度改善了55.05%,提升了聚光-吸热系统的整体性能。

内插式真空管集热器集热性能提升技术研究综述

真空管太阳能集热器是太阳能热利用的重要途径。内插式真空管集热器是一种结构优化后的真空管集热器,为提升其集热性能,介绍了内插式真空管集热器的工作原理,对其传热机理进行了分析,归纳了当前对内插式真空管集热器的集热性能的研究现状,并在此基础上通过建立集热效率关于环境参数及流量的关联式、改进内插管主管和支管管径尺寸、综合优化集热器布置方式及管间距并设置反射板的方式等方法分析了存在的问题,为低成本、高效率的内插式真空管集热器的研究发展提供了参考依据。

Study of the Solar Energy Drying Device and Its Application in Traditional Chinese Medicine in Drying

Background: We referred to nearly 40 years of development and application progress of solar dryer in China literature, especially its application in the field of Chinese herbal medicine drying. Objective: We explored the development direction of China’s development and application of solar dryers, especially focusing on its development and application in traditional Chinese medicine drying. Method: Five types of solar dryers including the greenhouse type solar dryer, the collector type solar dryer, the collector-greenhouse type hybrid solar dryer, the integrated solar dryer and the focusing type solar dryer accounted for the development and application of solar dryers up to 95% in China. The first three types of solar dryers are low temperature dryer (less than or equal to 70°C), while the latter two kinds of solar dryers are high temperature dryer (more than 70°C). In this paper, we respectively introduced and compared the structure, working principle, applications, advantages and disadvantages, and the research status of these five dryer. Results: The integrated solar dryer and the focusing type solar dryer belong to the high temperature dryer types are the future direction of development. Among them, the integrated solar dryer is relatively simple structure and has more promotion prospects. These two kinds of key drying device used in the dryer is the development direction of high efficient vacuum tube. On the other hand, because of their low cost, simple structure and the dry material requirements etc., the three types of low temperature dryers at low temperature for drying materials are also indispensable in the practical application. In contrast, the collector-greenhouse type hybrid solar dryer has more advantages, is the development direction of low temperature drying category. Conclusion: The collector tube which is the key element of the dryer was the core technology of solar dryer. Our country develops more successful of the all-glass vacuum solar thermal collectors and heat pipe-glass vacuum tube. Efficient vacuum tube collector technology is the future developed direction and is equally important to improve the quality of traditional Chinese medicine and dried.

Modelling, Transient Simulation and Economic Analysis of Solar Thermal Based Air Conditioning System in Gujarat

Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO2 emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO2 per million ft2 in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.

内置转子太阳能集热管流动与传热特性的数值模拟研究

通过数值模拟方法模拟了非均匀加热工况下内置两叶片转子和低流阻转子的太阳能集热管的流动与强化传热特性,得到了集热管内的温度分布、湍动能分布、努塞尔数以及阻力系数等参数,并通过综合性能评价因子(PEC)对内置转子集热管的综合强化传热性能进行了衡量。结果表明:内置转子后,管内流体的温度分布更加均匀,并且升温速率明显提升,若控制出口温度一致,则内置两叶片转子集热管的长度相较于光管可减少46.15%;内置两叶片转子和低流阻转子集热管内的努赛尔数和阻力系数相较于光管均有明显提升,其中内置两叶片转子集热管提升幅度较大,努赛尔数和阻力系数相较于光管分别提升94%~190%和308%~449%;通过PEC对两种集热管的综合强化传热性能进行衡量,两种集热管的PEC值均大于1,内置两叶片转子集热管具有最大值1.82。

紧凑型热管真空管集热器集热特性分析

为充分利用闲置建筑屋顶,为建筑和工业过程提供中温热能,设计了一种紧凑型热管真空管集热器(HPETC)。以南京地区为例,通过构建集热器传热热阻理论模型,并使用方差分析法,分析其集热特性。结果表明:集热器在523.15 K工作状态下具有24.56%的热效率;4种因素对热效率的影响程度从小到大分别为直射辐射、选择性吸收涂层(SAC)发射率、真空管内压力、进口温度;当真空管内压力小于0.01 Pa时,降低SAC发射率对热效率提升具有显著作用。

新型高效聚光集热管的技术研究与应用效能分析

针对普通的全玻璃真空太阳能集热管外置复合抛物面聚光集热板存在增大风阻且易在下雪时积雪的情况,研制了一种在外管内壁镀制反射镜面的新型高效聚光集热管,对该集热管的技术创新性进行了介绍,对其能效指标及优势进行了分析,并对其应用前景进行了阐述。性能测试结果显示:该集热管采用的太阳能选择性吸收涂层的太阳吸收比大于等于0.96(AM1.5)、半球发射比小于等于0.05(测试温度为80±5℃),达到了国际先进水平。通过对比普通全玻璃真空太阳能集热管和新型高效聚光集热管的应用效果发现:新型高效聚光集热管的热损仅为普通全玻璃真空太阳能集热管的50%;在同等条件下,新型高效聚光集热管的集热效率比普通全玻璃真空太阳能集热管的约高0.02,能够获得更高的热水温度,实现了中温段太阳能产品的开发及推广应用。

太阳能生物质互补清洁供热系统集成研究

基于我国生物质利用和太阳能集热技术的实际情况及能量综合梯级利用思路,研究性提出一种新颖的太阳能生物质互补清洁供热系统。新系统将太阳能集成到生物质锅炉中,利用菲涅尔集热装置直接加热补给水产生工业蒸汽和真空管集热装置预热补给水,并兼顾生物质锅炉热力除氧热源,多余热量进入蓄热罐进行存储。新系统通过调节生物质锅炉颗粒燃料量,适应对外供热负荷变动和太阳能波动所带来的输入热量变化导致蒸汽量变化的工况。以河北沧州地区某供热量20 t/h的太阳能生物质互补供热系统为例,性能估算分析表明,太阳能输入能量份额为20.31%,太阳能年度等效利用小时数为74 d(1779 h),真空管集热系统的加热能力是补给水预热负荷的4.47倍。研究表明,合理的热力系统集成方式是提高太阳能热利用系统性能和降低工业蒸汽成本的关键所在。研究成果将为开创我国太阳能生物质互补供热新局面提供新思路。

真空管直膨式太阳能热泵系统性能分析

该文将真空管集热器与直膨式太阳能热泵结合,提出一种真空管直膨式太阳能热泵系统。实验研究典型工况下太阳辐照度、循环水温度对系统性能的影响,并探讨压缩机变频条件下系统的动态性能。结果表明,提高太阳辐照度、降低循环水温度有利于提高系统性能,在太阳辐照度为850 W/m^(2),循环水温度为55℃时系统取得最大COP,为5.36。压缩机频率为42 Hz的系统COP为4.08,较45、47、50 Hz分别提高1.23%、8.5%、13.6%。