Thermodynamic Analysis and Optimization of Flat Plate Solar Collector Using TiO_(2)/Water Nanofluid

To research solar energy's efficiency and environmental benefits,the thermal efficiency,exergy,and entropy of solar collectors were calculated.The experiment involved two glass-topped collectors,fluid transfer tubes,and aluminum heat-absorbing plates.Glass wool insulation minimized heat loss.A 0.5% TiO_(2)/Water nanofluid was created using a mechanical and ultrasonic stirrer.Results showed that solar radiation increased thermal efficiency until midday,reaching 48.48% for water and 51.23% for the nanofluid.With increasing mass flow rates from 0.0045 kg/s to 0.02 kg/s,thermal efficiency improved from 16.26% to 47.37% for water and from 20.65% to 48.76% for the nanofluid.Filtered water provided 380 W and 395 W of energy in March and April,while the nanofluid increased it to 395 W and 415 W during these months.Mass flow generated energy,and the Reynolds number raised entropy.The noon exergy efficiency for nanofluids was 50%-55%,compared to 30% for water.At noon,the broken exergy measured 877.53 W for the nanofluid and 880.12 W for water.In Kirkuk,Iraq,the 0.5% TiO_(2)/Water nanofluid outperformed water in solar collectors.

Studies on solar flat plate collector evaporation systems for tannery effluent(soak liquor)

Heat and mass transfer analysis of an incompressible, laminar boundary layer over solar flat plate collector evapora- tion systems for tannery effluent (soak liquor) is investigated. The governing equations are solved for various liquid to air velocity ratios. Profiles of velocity, temperature and concentration as well as their gradients are presented. The heat transfer and mass transfer coefficients thus obtained are used to evaluate mass of water evaporated for an inclined fibre-reinforced plastic (FRP) solar flat plate collector (FPC) with and without cover. Comparison of these results with the experimental performance shows encouraging trend of good agreement between them.

Solar Thermal Systems Performances versus Flat Plate Solar Collectors Connected in Series

This paper shows the modeling of a solar collective heating system in order to predict the system performances. Two systems are proposed: 1) the first, Solar Direct Hot Water, which is composed of flat plate collectors and thermal storage tank, 2) the second, a Solar Indirect Hot Water in which we added an external heat exchanger of constant effectiveness to the first system. The mass flow rate by a collector is fixed to 0.04 Kg·s–1 and the total number of collectors is adjusted to 60. For the first system, the maximum average water temperature within the tank in a typical day in summer and annual performances are calculated by varying the number of collectors connected in series. For the second, this paper shows the detailed analysis of water temperature within the storage and annual performances by varying the mass flow rate on the cold side of the heat exchanger and the number of collectors in series on the hot side. It is shown that the stratification within the storage is strongly influenced by mass flow rate and the connections between collectors. It is also demonstrated that the number of collectors that can be connected in series is limited. The optimization of the mass flow rate on cold side of the heat exchanger is seen to be an important factor for the energy saving.

Thermal Loss Analysis of a Flat Plate Solar Collector Using Numerical Simulation

In this paper,we studied theoretically and numerically heated losses of a flat solar collector to model the solar water heating system for the Kazakhstan climate condition.For different climatic zones with a growing cost for energy or lack of central heating systems,promising is to find ways to improve the energy efficiency of the solar system.The mathematical model(based on ordinary differential equation)simulated the solar system work process under different conditions.To bridge the modeling and real values results,we studied the important physical parameters such as loss coefficient,Nu,Ra,and Pr values.They impacted the efficiency of flat solar collectors and heat losses of the system.The developed mathematical models,the design and composition of the software and hardware complex,and automated control and monitoring systems allow solar hot water heating systems to increase the energy efficiency of life support systems and heat supply of buildings by reducing energy consumption for heat supply.The simulation result showed that during the daytime,the temperature of water in the collector is 70°C;the storage of heated water since heated water is cooled at night.We defined that a work period of the system can be extended with high efficiency(April-October)for Almaty region.

Numerical Investigation and Optimization of a Flat Plate Solar Collector Operating with Cu/CuO/Al_(2)O_(3)–Water Nanofluids

Nanofluids are a potential alternative to significantly improving the performance of heat transfer applications. In this work, a numerical analysis to examine the eff ect of dispersing copper(Cu), copper oxide(CuO), and aluminum(Al2O3) nanoparticles in pure water on the performance of a flat plate solar collector(FPSC) and a numerical model was proposed. The influence of the nanofluid type on the thermal efficiency was critically investigated and discussed. The eff ect of the mass flow rate on the performance was also analyzed and discussed. Based on correlations of the thermophysical properties of nanofluids, a sensitivity analysis was used to analyze the impact of the nanoparticles on the base fluid. The results indicate that the performance of the FPSC with Cu/water nanofluid was better than that of FPSCs using CuO/water or Al2O3/water nanofluids. When the mass flow rate of the nanofluids was 8.0 L/min, the efficiency of the FPSC was much greater than those at the flow rates of 5.0 L/min and 2.0 L/min. Mean enhancements in thermal efficiency of 4.44%, 4.27%, and 4.21% were observed when 2.0 L/min was applied using Cu/water, Cu O/water, and Al2O3/water nanofluids, respectively. Improvements in thermal efficiency of 2.76%, 2.53%, and 2.47% occurred when 8.0 L/min was applied.

拉萨地区平板太阳能集热系统变流量运行策略及效益分析

针对室外环境参数波动变化以及蓄热系统温度波动特性,提出一种太阳能集热系统变流量运行调控策略,建立最优流量优化模型,回归得到不同工况下最优流量值多项式函数,并与定流量运行策略下的系统运行性能进行对比分析。结果表明:与定流量运行方式相比,采用变流量调控策略时,集热系统净收益显著提升。对于拉萨地区100 m^(2)串并联形式平板太阳能集热系统,采用变流量运行策略时,虽然运行泵耗增加,但集热量增益更大,相比单位集热面积流量为0.02 m^(3)/(h·m^(2))时,集热系统净收益增加了468.7 MJ,提高了6.75%。

高寒地区平板热管式太阳能集热系统热性能研究

基于呼和浩特地区高寒气候条件,搭建两组完全一致的平板热管式太阳能集热系统,通过实验对比分析太阳辐射强度、传热工质流量、集热板表面积尘等因素对集热器瞬时集热效率以及系统热性能的影响。结果表明,在同等外界条件下,集热器的集热效率随着工质流量的增加而增大,集热效率与太阳辐射强度变化趋势相近,随积尘密度的增加,集热板表面积尘导致系统的得热量减少,集热性能下降。

电控离子交换复合膜电极的界面结合行为与提锂性能

【目的】电控离子交换(ESIX)作为一种新型的离子选择性分离和回收的技术,可以用于从盐湖中提取锂资源。其中,集流体与电活性复合膜之间的界面结合行为对复合膜的电控提锂性能具有重要的影响。【方法】以LiMn2O_(4)为电活性锂离子交换材料,并分别以钛板和石墨板为集流体制备了钛基和碳基复合膜电极。通过附着力测试探讨了集流体与复合膜的界面结合行为,并采用循环伏安、交流阻抗、恒流充放电测试分析了不同复合膜电极的电化学性能。【结果】结果表明:石墨板与复合膜之间的粘附强度(1.33N/cm)约为钛板(0.71N/cm)的2倍,且碳基复合膜电极表现出更优异的电化学性能。在10次连续的ESIX过程中,碳基复合膜电极具有更好的提锂性能。这是由于石墨板与复合膜之间具有更充分的粘结性,使两者之间显现出更杰出的界面导电性,从而增强了复合膜电极的电活性和循环稳定性。此外,钛板在多次氧化还原后表面生成的氧化膜会产生较大界面电阻,从而降低了钛板的导电性。

平板集热器冬季高流速运行数值模拟研究

针对平板集热器(FPSC)冬季热水收集温度不足等问题提出高流速运行方案,以期提高系统的集热性能以及全年利用率.通过CFD技术数值模拟FPSC系统在不同流速工况下(0.02~0.15 kg/s)各组件温度的变化情况,计算系统的集热效率,结合温度云图对比高流速运行的优势.结果显示,高流速运行能够减少集热损失,具有更佳的集热性能.

锂离子电池复合铜箔集流体及其制备方法

集流体作为锂离子电池汇集电流和支撑活性物质的重要结构,在高性能锂离子电池开发中占据着举足轻重的地位。相比于传统铜箔,复合铜箔是一种新型的轻质负极集流体,其独特的“Cu-聚合物-Cu”三明治结构可以显著降低集流体重量,增加电池的质量能量密度。同时,绝缘且柔韧的聚合物中间层可以阻断电子的横向传输,缓解充电过程负极嵌锂引起的膨胀应力,从而提高电池的安全性能和循环性能。介绍了复合铜箔中间层类型,评述了复合铜箔作为负极集流体的优势,总结了磁控溅射、真空蒸镀、化学镀、水电镀等典型复合铜箔制备方法,展望了复合集流体的应用前景,提出了未来需要重点关注和有待加强的研究方向和内容。

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.

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.

湿式除尘器双Y型滤尘板除尘效果实验研究

为研究非平行平板结构滤尘板在矿用湿式除尘器中的除尘效果,设计了一种双Y型新式滤尘板。搭建湿式除尘实验平台,通过选定滤网目数、滤尘板与细水雾喷嘴间距作为影响因素,开展滤尘板除尘效果实验,分析研究两因素对新型滤尘板除尘效果的影响。结果表明:一定工况下,滤网目数的增加能显著提升双Y型滤尘板除尘效率,在60目时除尘效率达到最高值,净化阻力与滤网目数呈正相关;一定工况下,双Y型滤尘板除尘效率随滤尘板与喷嘴间距的增加先增后减,当滤尘板与喷嘴距离为45 cm时除尘效率达到最高值,净化阻力随距离的增加先增后减,但距离的改变对新型滤尘板净化阻力的影响较小,实验结果为湿式除尘器结构参数的优化提供了理论依据和指导。

并联气体开关导通分散性对平行板汇流装置放电电流的影响

为研究平行板汇流脉冲功率装置中并联开关导通分散性对装置放电电流的影响,依据实验结果,建立气体开关导通分散性模型和不同参数模块的电路仿真模型,分析放电电流随开关导通分散性大小和回路参数变化的规律。研究结果表明:开关导通分散性会引起回路出现过电流,降低回路电感和回路电容,增加负载电感和并联路数将导致过电流极值的进一步增加;过电压是开关延时数微秒依旧能够导通的必要条件,仅一台开关延迟导通时存在过电流幅值的最大值,模块1在70 kV工作电压时回路的最大过电流峰值607 kA,过电流倍数1.33;模块2在35 kV工作电压时回路的最大过电流峰值590 kA,过电流倍数15.6。随着延时导通开关数量和开关导通分散性的增加,负载电流峰值降低,电流上升时间增加,而各回路之间的电荷重新分布使负载电流受影响小于回路电流。负载电流的可用性和装置的安全运行允许负载电流峰值的波动≤5%,需要模块1分散性≤587.5ns,模块2分散性≤35.25μs,对应的过电流最大值分别为504 kA和135 kA。

SCC型湿式除尘器除尘区域流场分析及结构优化

对SCC型湿式除尘器除尘区域流场流动进行分析,基于FLUENT软件采用气-固两相流和气-液-固三相流进行数值模拟研究,对不同时刻金属颗粒和液滴颗粒分布图、金属颗粒物轨迹、速度矢量进行对比,发现加入液滴颗粒后,除尘效率明显上升。通过正交试验研究了导流板长度、导流板倾角、导流板间距对被壁面及导流板捕集金属颗粒所占总数比例的影响,结果显示:各因素对被壁面及导流板捕集金属颗粒所占总数比例的影响主次顺序为导流板长度、导流板倾角、导流板间距,其最佳参数组合是A2B2C2,即导流板长度L=650 mm、导流板倾角θ=22.5°、导流板间距H=450 mm。显著性分析结果表明:导流板长度L对综合除尘效率有一定影响,导流板倾角θ和导流板间距H对综合除尘效率无明显影响。

基于Comsol和BBD的折流板太阳能空气集热器结构优化

太阳能空气集热器是太阳能干燥系统的重要部件,集热器结构设计对集热性能具有重要影响。设计一款基础折流板集热器,通过太阳能模拟器测试集热器在一定边界和材料参数条件下的出口温度。基于Solidworks和Comsol构建集热器三维实体模型,采用reliable-k-ε湍流模型数值研究集热器的集热性能。结果表明,出口温度试验值和模拟值相对误差小于0.70%,数值模拟有效,可靠性高。基于BBD(Box-Behnken Design)试验和响应面法,研究折流板不同倾斜角度组合对集热性能的影响,分析试验结果得到最佳参数组合:折流板1倾斜角度为-10°,折流板2倾斜角度为10°,折流板3倾斜角度为-10°,折流板4倾斜角度为10°,并以此优化集热器折流板布置,得到一款倾斜折流板集热器。与基础折流板集热器相比,倾斜折流板集热器出口温度升高1.63 K,集热效率提升4.01%,入口、出口压力损失降低44.80%。基于流体旁通效应,对折流板进行开孔,进一步优化吸热板的积热和流场分布,得到一款开孔型倾斜折流板集热器。与基础折流板集热器相比,开孔型倾斜折流板集热器出口温度升高2.03 K,集热效率提升4.99%,入口、出口压力损失降低43.13%。对开孔型倾斜折流板集热器入口风速条件进行单因素试验,得到较优的入口风速条件,即0.5~1.0 m/s,可以满足农产品太阳能干燥需求。

多孔介质辅助平板式太阳能集热器热性能强化的数值仿真研究

多孔介质材料具有良好的传热和蓄热性能。设计了新型多孔介质辅助平板式太阳能集热器的二维数值仿真模型,对其内部热性能进行了数值模拟,研究多孔介质块的形状(矩形、梯形、三角形结构)、布置数量和渗透率(达西数Da=10^(-5)~10^(-2))等因素对平板式太阳能集热器热性能强化的影响;然后考虑到插入多孔介质伴随的压降和摩擦阻力损失,提出了评价集热器传热性能与阻力损失的性能评估标准。研究结果表明:在平板式太阳能集热器换热通道插入4种不同形状的多孔介质块,矩形多孔介质块背部附近区域更易产生涡区,集热器内传热性能最强,但通道内流动阻力系数大,从而导致阻力损失大。当多孔介质区域总长度一定时,随着多孔介质块布置数量的增加,涡区数量相应增加,集热器内传热性能加强,且通道内流动阻力损失呈现先增加后降低的规律。多孔介质块渗透率对集热器传热性能的影响显著,当Da=10^(-2)时,集热器传热性能最强。集热器内多孔介质块布置任意数量、高渗透率(Da=10^(-2))条件下,矩形多孔介质块的性能评估标准最佳;在多孔介质块布置数量(N=6)较多、低渗透率(Da=10^(-5)、Da=10^(-4))条件下,三角形多孔介质块的性能评估标准最佳。

Application of entransy theory in the heat transfer optimization of flat-plate solar collectors

The flat-plate solar collector is an important component in solar-thermal systems,and its heat transfer optimization is of great significance in terms of the efficiency of energy utilization.However,most existing flat-plate collectors adopt metallic absorber plates with uniform thickness,which often works against energy conservation.In this paper,to achieve the optimal heat transfer performance,we optimized the thickness distribution of the absorber with the constraint of fixed total material volume employing entransy theory.We first established the correspondence between the collector efficiency and the loss of entransy,and then proposed the constrained extreme-value problem and deduced the optimization criterion,namely a uniform temperature gradient,employing a variational method.Finally,on the basis of the optimization criterion,we carried out numerical simulations,with the results showing remarkable optimization effects.When irradiation,the ambient temperature and the wind speed are 800 W/m2,300 K and 3 m/s,respectively,the collector efficiency is enhanced by 8.8% through optimization,which is equivalent to a copper saving of 30%.We also applied the thickness distribution optimized for wind speed of 3 m/s in heat transfer analysis with different wind speed conditions,and the collector efficiency was remarkably better than that for an absorber with uniform thickness.

Fabricating ultralight and ultrathin copper current collectors for high-energy batteries

Improving cell-level gravimetric and volumetric energy density is essential to achieve high-performance batteries in the rapidly evolving field of energy storage technology,which requires consideration of all cell components.Traditional current collectors(CCs)made of metal foil,especially the copper(Cu)current collector of the anode,possess high mass and cost yet do not contribute to capacity.Reducing the weight of Cu CC with minimum thickness and desirable mechanical strength is critical in enhancing energy density but is technically challenging.Herein,we demonstrate a fast and scalable chemical coating method based on electroless plating for fabricating ultralight CC(∼1.72mg cm^(−2))with a thin Cu layer(500nm)on an ultrathin polyethylene(PE)polymer scaffold(5μm).The ultralight and ultrathin CC possesses high metal purity,high mechanical strength,high thermal stability,and outstanding electrochemical performances in lithium-ion and lithium-metal battery systems.Our ultralight CC only exhibits∼30% of the weight of 6μm Cu foil,leading to a 5−10% improvement in cell-level gravimetric energy density without sacrificing volumetric energy density.Moreover,the simplicity and scalability of the chemical coating method make it a promising solution for the mass production of ultra-thin and lightweight current collectors.