空气作工质的真空集热管内流动与换热分析

Flow and Heat Transfer Analysis in the Solar Vacuum Collector Using Air as Working Fluid

针对热水作工质时真空集热管内普遍存在的冻结、腐蚀等问题,本文采用空气作工质,推导了空气作工质时真空集热管的集热效率、热损系数和集热管出口温度的方程,分析了影响空气作工质时各项参数对集热器热性能的影响。通过改变集热管进口空气流量来获得尽可能高出口温度的热空气,从而降低热损系数,提高集热效率。此外,由于热空气可以直接送入干燥室干燥物料,不需要二次转换,节能效果好。由理论分析和试验结果可以预见,利用空气作工质的真空传热管具有潜在的应用价值和前景。

Concerned with problems of widespread freezing, corrosion and so on while water is used as working fluid in the vacuum tube collector of solar energy utilization, in this paper, air is adopted to be working fluid in the collector. Air collector efficiency, heat loss coefficient and outlet temperature equations are derived. Parameters that influence on collector thermal performance also have been analysed. Through experiments of changing the inlet air flow rate, we can adjust the hot air outlet temperature as high as possible, which helps to reduce the heat loss and improve the collector efficiency. Besides, the hot air can be directly used for drying, which means that good energy saving effect would be achieved because of simplifying heat transfer process. By theoretical analysis and experimental demonstrations, it can be predicted that using air as heat trans- ferring medium in the collector tube has potential academic value and broad application prospects.