摘要
直接式太阳能干燥系统在运行过程中,存在物料表面受热易硬化而阻碍其内部水分蒸发的问题,鉴于此,该文设计一种新型槽式复合抛物面聚光集热太阳能干燥系统,其由槽式复合抛物面聚光集热器、物料托盘、风机、空气管、控制系统等组成。利用光学仿真软件对系统中槽式复合抛物面聚光器进行光线追迹,计算分析不同入射偏角对聚光器光学效率、聚光效率等的影响机理。在此基础上,搭建太阳能槽式复合抛物面聚光集热干燥性能测试系统,在实际天气条件下,对聚光集热单元性能展开测试研究。结果表明,当入射光径向偏角为 10 时,聚光器理论光学效率可达到 70.38%,晴天太阳光正入射运行、空气流速为 6.5 m/s时,接收体出口空气温度最高为 37.2 ℃,比径向入射偏角为 10 时提高了 7.8%;加装玻璃盖板可有效提高聚光器光热转换效率,晴天时其最大转换效率为 55%左右,比无玻璃盖板时最大效率提高了约120%。研究结果可为主动式太阳能聚光集热干燥系统的进一步应用提供了参考。
Drying is an energy intensive process, which reduces the moisture content of the material to a certain preselected level to prevent deterioration. The increasing of agro-food products’ cost and the rapid depletion of fossil fuels accelerated the utilization of solar energy for drying. However, conventional open cycle solar drying system has several disadvantages, including the degradation of product quality caused by sudden rain, wind and dust, loss of the products due to rodents, birds and insects. To overcome these disadvantages and ensure better control of solar drying aspects, the direct solar drying systems have been designed and improved over decades. It has been noted that direct exposure to the sun during sunny day, particularly when the ambient temperature reaches to 30 ℃ or higher, might cause case hardening, which trapping moisture inside the products scattered. Based on the previous researches, this paper therefore designs a novel concentrated solar drying system. In this case, a trough compound parabolic concentrator (CPC) as heater is employed for solar-energy collection for heating of inlet air. Apart from this, the system is also configured with several trays, fan, operation air tube, control device, et al. Compared with the previous solar drying system, it not only improves the thermal efficiency of the system but also reduces the land area of the solar collectors. The system is suitable for use distributed and controllable for drying process. Its operation principle of the system can be shown as follows: Several concentrators installed with glass receiver are connected with air tubes. Then in the receiver, a plate heat transfer fin is spread by a black composite material coating to increase the sun absorptivity. The thickness of the fin is 1.5 mm. The air inside the receiver is heated to a higher temperature by the concentrated light. The heated air flows into the drying unit through the hot air pipe driven by fan. Then the flowing hot air passes through the materials placed on the trays. The materials will be heated and moisture will be removed. As the air driven by the fan flows towards exhaust pipe, the waste heat contained in the air in the exhaust pipe will transfer to the supplementary air in the cold air tube, which improves the system energy efficiency. The working principle of the trough compound parabolic concentrator and structure are introduced. A 3D model of the concentrator is obtained in commercial software SolidWorks, then is exported in IGES digital format so that it could be imported to optical analysis software to analyze ray tracing. The concentrating efficiency and optical efficiency of the concentrator have been calculated and analyzed. Based on the simulated results mentioned above, an experimental system driven by several trough compound parabolic concentrators is constructed to study the drying performance of the system outdoors. The geometric parameters of the concentrator unit are the same as the unit previously discussed. The results indicate when the radial incidence angle is 10°, the optical efficiency can reach to 70.38%. The light window is set in the sides of the concentrator has benefit to enhancement of the optical efficiency when axial incidence angle is not 0°. In sunny day, the maximum air temperature of the outlet can be reached to 37.2 ℃, which is higher than that of the unit when radial incidence angle is 10° by 7.8% when the air flow rate is 6.5m/s. A glass cover is placed on concentrator aperture to minimize convective heat losses from the receiver. The maximum thermal efficiency of the device with glass cover can be about 55%, which is higher than that of the concentrator without glass cover by about 120%. Thus, this study is able to provide theoretical and experimental reference for further application for active solar drying technology.
作者
常泽辉
李建业
李文龙
侯静
郑宏飞
Chang Zehui;Li Jianye;Li Wenlong;Hou Jing;Zheng Hongfei(College of Energy and Power Engineering, Inner Mongolia University of Technology, Hohhot 010051, China;College of Mechanical Electrical Heating and Ventilation Engine, Inner Mongolia Technical College of Construction, Hohhot 010070, China;School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2019年第13期197-203,共7页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金项目（51666013）
内蒙古自治区科技重大专项（2018）
内蒙古自治区高等学校科学研究项目（NJZY17491）
内蒙古自治区高校青年科技英才支持计划
内蒙古自治区研究生科研创新项目（S2018111948Z）
关键词
干燥
太阳能
效率
复合抛物面
性能
drying
solar energy
efficiency
compound parabolic
performance
