Design and Development of a Parabolic Trough Solar Air Heater for a Greenhouse Dryer

Design and Development of a Parabolic Trough Solar Air Heater (PTSAH) for a Greenhouse Dryer (GD) was done to improve the dryer’s performance. The materials used for the fabrication of the PTSAH included galvanized sheets covered with aluminium foil, an absorber tube made of GI pipe painted matt black to increase heat absorbance at the focal line, mild steel square tubes, shutter plywood, and an axial fan to push air through the absorber tube. Key geometrical parameters used for the design of the PTSAH were a rim angle of 98 degrees, focal length of 0.2608 m, height of 0.3451 m, length of 2 m, and an aperture width of 1.2 m. The PTSAH’s total aperture surface area was 2.4 m2, while its absorber tube surface area was 0.1587 m2. The PTSAH was experimentally tested to establish its thermal performance. It was found that the ambient air recorded an average value of 31.1˚C and that the air heater could increase the air temperature by 45.6˚C above ambient with a thermal efficiency of 5.3%. It can, therefore, be concluded that the PTSAH can significantly improve the performance of a GD by supplying the GD with air at a higher temperature than ambient.

Experimental Investigation on Turbulent Convection in Solar Air Heater Channel Fitted with Delta Winglet Vortex Generator

The paper presents an experimental study on the heat transfer and flow friction characteristics in a solar air heater channel fitted with delta-winglet type vortex generators （DWs）. The experiments are conducted by varying the airflow rate for Reynolds number in the range of 5000 to 24000 in the test section with a uniform heat-flux applied on the upper channel wall. Firstly, the DW pairs are mounted only at the entrance of the lower wall of the test channel （called DW-E） to create multiple vortex flows at the entry. The effect of two transverse pitches （Re= Pt/H= 1 and 2） at three attack angles （a= 30°, 45° and 60°） of the DW-E with its relative height, b/H= 0.5 （half height of channel） is examined. Secondly, the 30° DWs with three different relative heights （blH = 0.3, 0.4 and 0.5） are placed on the upper wall only （absorber plate, called DW-A） of the test channel. The experimental result reveals that in the first case, the 60° DW-E at Rp = 1 provides the highest heat transfer and friction factor while the 30° DW-E at Rp = 1 performs overall better than the others. In the second case, the 30° DW-A at b/H= 0.5 yields the highest heat transfer and friction factor but the best thermal performance is found at b/H = 0.4.

Using the Taguchi Method and Grey Relational Analysis to Optimize the Performance of a Solar Air Heater

Solar energy is regarded as one of the promising renewable energy sources in the world.The main aim of this study is to use the Taguchi-Grey relational grade analysis to optimize the performance of two Solar Air Heaters(SAHs).A typical Grey–Taguchi method was applied.The Orthogonal Array,Signal-to-Noise ratio,Grey Relational Grade,and Analysis of Variance were employed to investigate the performance characteristics of SAH.Experimental observations were made in agreement with Jordanian climate 32°00′N latitude and 36°00′E longitude with a solar intensity of 500 W\m^(2).The operating factors selected for optimization are the tilt angle(T)with three levels(0°,22°,45°),inlet velocity(V)with two levels(1.2,1.8 m/s),and absorber plate material(M)with two levels(Aluminum,wood).In this study,the Grey–Taguchi approach is validated by performing 12 individual experiments.The results show that the process factors sequence required for a maximum SAH efficiency(SAHµ)is V>T>M.Using this approach,we combined the Orthogonal Array design with Grey Relational Analysis.As a result of that,the level of each operating conditions which optimizes both process responses(Temperature difference,ΔT and Solar air heater efficiency,SAHµ)can be specified with a minimum number of tests compared with classic Grey Relational Analysis.The optimal operating conditions of a SAH for multiple performance characteristics are determined as T2,M2,and V2,respectively,which are in congruence with the experimental results.

Experimental Performance Analysis of a Corrugation Type Solar Air Heater(CTSAH)

This paper explains the experimental performance evaluation of a Corrugated Type Solar Air Heater(CTSAH)for understanding its performance in a humid tropical climatic condition in Puducherry,India.This helps in understanding its effectiveness in using it for drying application of products like seafood,etc.Experiments were conducted at different mass flow rates and their effect on the heat gain,efficiency,friction factor heat transfer,etc.,was analyzed.Experiments were carried out at different mass flow rates,i.e.,M1=0.06 kg/s,M2=0.14 kg/s,M3=0.17 kg/s,M4=0.25 kg/s,M5=0.3 kg/s,and were conducted from 11:00 h to 14:00 h.The air inlet&air temperature is found to be at an average of 40°C whereas the incident solar radiation is at an average of 795 W/m2.Experimental results show that the optimum performance of the CTSAH is in the mass flow rate range of 0.14–0.25(kg/s).Also,the calculated useful heat produced,convective heat transfer coefficients,effective efficiency,optical efficiency provides knowledge on the potential use of the air heater.

Temperature Profiles in the Flow Channel of a Natural Convection Solar Air Heater

An experimental investigation was conducted to measure the temperature variation across the flow channel and to determine the performance of a natural convection solar air heater at various tilt angles from 15, 30 and 45°. The results of the temperature profile across the air gap showed that heat transfer from the absorber plate to the air stream was mainly by convection. At a particular section, mean air temperature could be calculated from the arithmetic mean of the temperature profile across the air gap to within ± 2 ℃. The axial air temperature distribution was non linear and did not increase much beyond 1 m of collector length. It tended to decrease towards the end of the collector. Overall glass, absorber plate and mean air temperatures over the entire length of the solar air heater could be determined by averaging the mean axial temperatures to within ± 2 ℃. The heater performed better as inclination increased.

Application of Response Surface Methodology for Analysing and Optimizing the Finned Solar Air Heater

In this research paper,a solar air heater with triangular fins has been experimentally analysed and optimized.Initially,an experimental set-up of a solar air heater having triangular fins has been developed at the location of 28.10°N,78.23°E.The heat transfer rate through fins and fins efficiency has been determined by the Finite Difference Method model equations.The experimental data and modeled data of response parameters have been optimized in MINITAB-17 software by the Response Surface Methodology tool.For creating the response surface design,three input parameters have been selected namely solar intensity,Reynolds number,and fin base-to-height ratio.The range of solar intensity,Reynolds number,and fin base-to-height ratio is 600 to 1000W/m^(2),4000 to 6000,and 0.4 to 0.8 respectively.The response surface design has been analyzed by calculating the outlet temperature,friction factor,Nusselt number,fin efficiency,thermal performance factor,and exergy efficiency.The optimum settings of input parameters:solar intensity is 1000 W/m^(2);Reynolds number is 4969.7,and the fin base to height ratio is 0.6060,on which these response:namely outlet temperature of 92.531℃,friction factor of 0.2350,Nusselt number of 127.761,thermal efficiency of 50.836%,thermal performance factor of 1.4947,and exergy efficiency of 8.762%.

Numerical analysis of the return flow solar air heater(RF-SAH)with assimilation of V-type artificial roughness

A novel design of Return Flow Solar Air Heater(RFSAH)with different arrangements of baffles especially V-Type Artificial roughness is simulated and numerically analyzed with energy balance equations.To enhance the effectiveness of baffles,numerous studies have been conducted.The performance of the RFSAH is studied in terms of thermal efficiency,thermo-hydraulic efficiency,and optimization of baffle parameters.Maximum Thermal efficiency and thermo-hydraulic efficiency are found in RFSAH with baffle on both sides of the absorber plate and mass flow rate above 0.2kg/s.Sensitivity analysis of the influencing parameters is carried out and reported the best performance of the system on selective geometrical parameters(ψ=0.7,β=20%,e/H=1,p/e=0.8,α=60°).The results obtained from the present model are validated with the published experimental results and have been found in quite reasonable agreement with an average error of 16.45%.Thermal and Thermohydraulic efficiency of RFSAH with a baffle on both sides of the absorber plate is maximum among baffles below,above,and on both sides of the absorber plate.It is observed that the thermal efficiency of RFSAH is greater than SF-SAH.The proposed optimum baffles roughness is suggested to increase the air upholding time period for more efficient output.

Thermodynamic Performance Analysis of a Low-Cost,Recycled and Energy-Efficient Solar Air Heater with Waste Beverage Cans:An Experimental Research

Solar air heaters are at the centre of interest owing to their widespread use for various purposes.In the study,thermal performance analysis of a solar air heater that can be easily produced from daily waste materials is done.The system has a low-cost structure with both waste material use and a simple design.The proposed system is tested under different climatic conditions,and the energetic and the exergetic performance figures are obtained for the first time in literature.It is observed from the experimental tests that the results are stable and coherent as well as in good accordance with the similar attempts in literature with some cost reductions and performance improvements.Thermodynamic performance analyses indicate that the maximum energy efficiency of the system is about 21%,whereas the exergy efficiency is 1.8%.The energetic and exergetic outputs of the system are also determined to be 27 W and 3 W,respectively,which is promising.

射流式太阳能空气集热器性能的数值模拟研究

为了提高太阳能空气集热器的性能,建立了射流太阳能空气集热器的数学模型,并分析了空气射流对太阳能空气集热器性能的影响。结果表明:在太阳能空气集热器内设置折流板形成射流流动,不仅可以增加集热板近壁面处的流动速度,还能减小垂直于空气流动方向的速度梯度。射流流动优化了流道内的速度分布,从而有效提高了空气与集热板的对流传热系数。与普通太阳能空气集热器相比,射流太阳能空气集热器的集热效率明显更高。当入口速度从0.5 m/s增加到3.0 m/s时,两者集热效率的差距从5.01%增加到15.38%。然而,射流太阳能空气集热器的压力损失较大,因此其有效效率随空气流量的增加呈现先增加后减小的趋势。在入口速度为2.5 m/s时,有效效率达到了极值63.75%,比普通太阳能空气集热器提高了11.21%。综上所述,利用折流板形成射流能显著提高太阳能空气集热器的集热效率与有效效率。

寒冷地区空气源热泵辅助太阳能热水器供暖性能

为提高太阳能热水器供暖的稳定性并大幅降低空气源热泵供暖的成本,提出空气源热泵辅助太阳能真空管热水器供暖构想,在甘肃省兰州市七里河区魏岭乡绿化村搭建空气源热泵辅助太阳能热水器供暖试验系统,详细研究了晴天、阴天及多云3种典型工况下系统的集热效率、热泵性能系数、系统太阳能保证率和系统能效比等.研究结果表明,晴天、阴天及多云工况下太阳能集热器有效得热量分别为75.5、4.1和49.2 kW·h,集热效率分别为61.3%、26.6%、55.2%,太阳能热泵平均性能系数(COP)分别为3.6、3.4、3.6,空气源热泵平均COP分别为0、2.9、3.1,系统实际供热量分别为113.4、125.9和124.8 kW·h,系统耗电量分别为33.4、50.5和42.7 kW·h,系统太阳能保证率分别为66.6%、3.3%、39.4%,系统能效比分别为3.4,2.5,2.9.研究证明了太阳能真空管集热器-空气源热泵系统用于寒冷地区供暖的可行性,为寒冷地区供暖提供了一种新途径.

抛物面形凸起结构对太阳能空气集热器传热性能的影响

为改善太阳能空气集热器的综合性能,文章将吸热板表面按照V型方式离散地冲压下凹成抛物面形凸起结构,使用数值分析方法研究了不同雷诺数Re、抛物面形凸起结构的高径比(e/d)、气流攻击角(α)和相对节距(p/e)下,空气通道内的流动与传热特性,在综合传热系数最大时得到了凸起结构的最佳参数组合:e/d=1,α=60°,p/e=16。在所研究的雷诺数范围内,与光滑板结构相比,文章的最优结构将空气的进、出口温差平均提高了5.3℃,集热效率相应也平均提高了15%。采用集热效率和有效效率对此结构集热器性能的评价结果表明:文章所设计的抛物面形凸起结构集热器实现了热能利用效率与流体输运能效的有机统一。

太阳能-空气源双能源复合供暖在严寒地区农村住宅中的应用研究

针对空气源热泵热风机在室外低温环境下供暖性能衰减,导致室内冬季供暖效果变差等问题,为充分发挥资源优势,提出了一种太阳能-空气源双能源复合高效集成装置,实现了太阳能集热器与低温空气源热泵热风机联合供暖。介绍了该集成装置的技术原理和控制策略,通过TRNSYS软件对该集成装置在哈尔滨地区农村住宅的供暖效果进行了研究,并对该集成装置供暖和低温空气源热泵热风机单独供暖的效果进行了对比分析。研究结果表明:太阳能-空气源双能源复合高效集成装置实现了太阳能与空气源两种能源更为合理的供暖时段匹配。在整个供暖季,与低温空气源热泵热风机单独供暖相比,该集成装置的供暖效果更好且能耗更低,其系统总能耗降低了2034.8kWh,制热能效比提升了35.06%。

中低温平板太阳能空气集热器的应用现状

太阳能空气集热器结构简单、成本低廉、操作便捷,逐渐被广泛应用于需要提供中低温热源的工农业生产活动中。通过对相关文献进行总结,对中低温平板太阳能空气集热器的原理做了介绍,并对中低温平板太阳能空气集热器在建筑利用、农产品干燥、热气流发电等领域的应用原理与现状做了总结。分析了该领域现今仍存在的技术障碍,对相关先进技术及其发展方向进行了讨论和展望。

太阳能空气集热器强化传热技术的发展现状

综述了太阳能空气集热器强化传热的研究现状。首先介绍了3种太阳能空气集热器的基本流道结构及其优缺点。之后基于3种基本的流道结构,介绍了4种太阳能空气集热器的主要强化传热类型(折流板型、扰流器型、波纹板型与多孔填充床型),并详细介绍了这4种强化传热类型的发展脉络。最后指出了太阳能空气集热器内强化传热研究的发展趋势。

微热管阵列式太阳能平板空气集热器集热性能

该文在传统平板太阳能空气集热器基础上,结合高效热导元件—微热管阵列(micro-heat pipe arrays,MHPA),提出一种全新的平板式太阳能空气集热器,阐明了该集热器的基本结构和工作原理,深入分析了该新型集热器的传热机理。对集热器的热损失情况进行了理论分析,并对该新型集热器的非稳态集热特性进行了试验研究。通过测试该集热器在不同条件下的集热特性,分析了运行参数及气象参数对其性能的影响规律。结果表明,该集热器在风量为290 m3/h,瞬时集热效率稳定在68%,且具有结构简单,可靠性高,集热效率稳定的特点。

带透明蜂窝的太阳空气加热器的实验研究(Ⅰ)——不同结构空气加热器的性能比较

该文报导了对多种带透明蜂窝的太阳空气加热器的实验研究工作。这些空气加热器的结构特点分别为 :Ⅰ型———透明蜂窝作为空气流道的一部分 ;Ⅱ型———透明蜂窝作为普通盖板使用 ;Ⅲ型———两级结构 ,前级为Ⅰ型 ,后级为Ⅱ型。作为比照 ,也做了普通平板型空气加热器的实验。结果表明 ,Ⅰ型太阳能空气加热器具有良好的热性能 :空气质量流率为 5 5kg/h ,进出口平均温差为 31℃时 ,其日平均热效率达 6 4 %。这种结构简单的新型太阳空气加热器在太阳能干燥及采暖等领域有很大的潜在应用价值。

太阳能空气集热器Ⅱ型的数学模型和数值计算

研究了Ⅱ型太阳能空气集热器的集热传热性能。建立了基于二维假设下的流体流动和热量传递的稳态数学 模型，并用有限差分法进行数值求解，得到稳态下太阳能空气集热器中的气流速度、温度分布图以及集热效率与空气 流量、入口空气温度、太阳能入射强度的关系图。计算结果与实验结果吻合很好。结果表明，集热效率随空气流量的 增大而增大，随入口空气温度的升高而急剧下降，随入射强度的增加，集热效率从零迅速增大到最大值而后逐渐略有 减小。

Ⅰ型太阳能空气集热器传热性能分析

研究了太阳能空气集热器Ⅰ型的传热性能,建立了基于一维假设下的热量传递的数学模型,导出了准静态条件下沿程温度分布、出口温度、全天集热效率的近似解.通过计算,分析了进口温度、工质流速、流道深度对集热器传热性能的影响,计算结果表明全天集热效率随工质流速的增大而增大、随进口温度的升高而急剧下降、随着流道深度的增加。

太阳能空气集热器(Ⅰ型)的数学模型研究

用数学模型化方法研究了太阳能空气集热器的集热传热性能。建立了基于二维假设下的流体流动和热量传递的稳态数学模型，并用有限差分法进行数值求解，计算得到稳态下太阳能空气集热器的速度、温度分布图以及集热效率与空气流量、入口空气温度、入射太阳辐照度和表面盖板透过率的关系。结果表明，对Ｉ型太阳能空气集热器，集热效率随空气流量和表面盖板透过率的增加而增大，随入口空气温度和入射太阳辐照度的增大而减小。计算结果与实验结果吻合很好。

复合抛物面聚光式太阳能空气集蓄热一体化系统性能研究

以平板微热管阵列为核心传热元件结合复合抛物面聚光式集热器和相变蓄热器,提出了一种以空气为传热介质的复合抛物面聚光式太阳能集蓄热一体化系统.该系统采用复合抛物面聚光式真空管集热器为集热部件,58#石蜡为相变储热材料,搭接平板微热管阵列为核心热传输元件,在室外测试了2种不同模式(先蓄后取模式和边蓄边取模式)下系统在不同空气流量下的蓄放热性能.同时根据太阳入射光线方位角的变化,结合聚光器入射半角θ,确定了聚光器吸收太阳总辐射时间范围,建立了复合抛物面聚光式太阳能集热器对太阳能辐射能的吸收计算模型.实验结果表明:先蓄后取模式下,集热器吸收太阳辐照量在15 MJ左右,一体化装置的平均蓄热效率在36%左右,取热空气体积流量的变化对该装置日总效率影响不大,维持在34%左右;边蓄边取模式下,随着空气体积流量增加,空气有效利用量增加,装置日总效率增大,空气流量110 m^(3)/h时,空气有效利用量为7.07 MJ,日总效率为45.6%.