| 全玻璃真空管太阳能集热器对流换热试验与模拟 |
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| 引用本文： | 张涛,韩吉田,田瑞,于泽庭.全玻璃真空管太阳能集热器对流换热试验与模拟[J].农业工程学报,2016,32(5):206-212. |
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| 作者姓名： | 张涛 韩吉田 田瑞 于泽庭 |
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| 作者单位： | 1. 山东大学能源与动力工程学院,济南,250061;2. 内蒙古工业大学能源与动力工程学院,呼和浩特,010051 |
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| 基金项目： | 国家自然科学基金项目（51376110）；教育部博士点基金项目（2013013110006）；国家基金重大国际（地区）合作研究项目（61320106011） |
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| 摘 要： | 以可再生能源总能系统为研究背景,通过搭建太阳能辅助燃料电池试验平台,逐步完成不同涂层材料、内置导流板太阳能集热器自然对流试验研究;在试验验证基础上,分别建立太阳能集热器自然对流和强迫对流三维数学模型,应用场协同和火积理论分析流动和传热数据。自然对流研究表明,吸收率在0.95~1.0、发射率在0.06~0.16时,随吸收率升高,发射率降低,热效率升高1.71%,火积增量逐渐增大;加装导流板后,真空管内部混流消失,底部流动得到强化,实验热效率提高2.17%;确定全玻璃真空管热水器导流板合理板厚为2 mm,合理板长为距离真空管底部60~100 mm,合理位置为中心线以上16~20 mm;强迫对流研究表明,横双排集热器雷诺和努赛尔数、火积增量均高于竖单排集热器,火积耗散低于竖单排集热器。确定太阳能辅助燃料电池集热场在中低温条件下,自然对流采用内置导流板集热器,强迫对流采用横双排集热器。
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| 关 键 词： | 太阳能 热水器 传热 太阳能辅助燃料电池 全玻璃真空管太阳能集热器 场协同 火积耗散 |
| 收稿时间： | 2015/6/19 0:00:00 |
| 修稿时间： | 2015/11/5 0:00:00 |
Experiment and simulation for convective heat transfer in all-glass evacuated tube solar collectors |
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| Zhang Tao,Han Jitian,Tian Rui and Yu Zeting.Experiment and simulation for convective heat transfer in all-glass evacuated tube solar collectors[J].Transactions of the Chinese Society of Agricultural Engineering,2016,32(5):206-212. |
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| Authors: | Zhang Tao Han Jitian Tian Rui and Yu Zeting |
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| Abstract: | Abstract: The experimental study of natural convection for solar collectors with different coating materials and being equipped with guide plate is carried out step by step through the experimental platform of solar-assisted fuel cells under the research background of renewable total energy systems, which mainly include solar energy comprehensive utilization, solid oxide fuel cells, gas turbine and Kalina refrigeration cycle. The three-dimensional mathematical model on natural convection and forced convection of solar collectors is established to study the flow and heat transfer data with the field synergy and entransy principle on the basis of experimental verification. The natural convection results show that the thermal efficiency and the entransy increment rise gradually with the absorption rate increasing from 0.95 to 1.0 and the emission rate decreasing from 0.06 to 0.16, and the thermal efficiency of experiment for high absorption is 1.17% higher than that of low absorption. The thermal efficiency of experiment for solar collectors increases by 2.17% after equipped with guide plate, because the mixed flow in the vacuumvacuum tube disappears and the guide plate strengthens the flow at the bottom of the vacuum tube. The reasonable plate thickness of guide plate for all-glass vacuum tube water heaters is 2 mm, the reasonable plate length of guide plate is 60-100 mm distance from the bottom of the vacuum tube, and the reasonable position of guide plate is 16-20 mm above the axial line of the vacuum tube. The forced convection results show that the Reynolds number and the Nusselt number decrease gradually after the fluent flow into manifold but the Reynolds number and the Nusselt number increase gradually at the exit of manifold. Although the fluent is extremely volatile along the vacuum tube, the Reynolds number and the Nusselt number of horizontal double collectors are higher than that of vertical single collector. The angle between speed vector and temperature gradient vector is 0° with downward fluid and 180° with upward flow, because the collector overall temperature is gradually reduced from vacuum tube bottom to manifold. It makes more fluid absorb the bottom heat, because the internal flow of vacuum tube is smooth and the mixed flow in vacuum tube disappears. Manifold velocity gradually decreases because there is backflow interiorly, but temperature increases because fluid absorbs solar radiation, and the field synergy in collector outlet is higher than others because temperature field is consistent with velocity field according to numerical simulation. Although the entransy increments of vertical single collector and horizontal double collectors are negative values in initial period, they gradually rise with the heat time increasing. There are 2 parts for entransy dissipation in the vacuum tube. The entransy dissipation of horizontal double collectors (from 0.2 to 1.8 m) is less than that of vertical single collector along the vacuum tube axis because the definite condition is to give heat flux boundary. The entransy dissipation of horizontal double collectors (from 0 to 0.2 m) is less than that of vertical single collector along the vacuum tube axis because the definite condition is constant temperature when hot water in vacuum tube flows into water tank and heat transfer occurs between hot and cold water. Enhancement of heat transfer effect of horizontal double collectors is better than that of vertical single collector, because its entransy increment is higher than that of vertical single collector and its entransy dissipation is better than that of vertical single collector. It is determined that the solar collectors with guide plate can be adopted in natural convection and the horizontal double collectors can be employed in forced convection in the thermal field of solar-assisted fuel cells with low and medium temperature. |
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| Keywords: | solar energy water heaters heat transfer the solar-assisted fuel cells all-glass evacuated tube solar collectors field synergy principle entransy dissipation |
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