积尘对槽式聚光系统镜面反射率及能流分布的影响研究

INFLUENCE OF DUST ACCUMULATION ON MIRROR REFLECTIVITY AND ENERGY FLUX DISTRIBUTION OF TROUGH CONCENTRAING SYSTEM

针对镜面积尘所导致的槽式太阳能集热系统反射率降低和能流损失问题,该文通过搭建槽式太阳能集热器焦面能流密度分布测试装置,试验研究积尘引起的聚光镜反射率下降及能流密度分布规律。结果表明:在可见光测试区域内,随镜面积尘密度增加,镜面相对反射率的变化量不同,太阳长波辐射较短波反射率下降明显;镜面积尘对汇聚太阳光线路径发生改变,对比洁净镜面,自然积尘25 d后,在太阳直射辐照度约50 W/m2时,集热管壁面能流密度峰值下降约15 kW/m2,且集热管圆周角为180°附近处,其汇聚光线路径变化尤为显著;结合实测数据得到积尘周期和积尘密度对相对反射率的函数关系,该方程可用于大气降尘相近地区积尘后槽式聚光镜相对反射率预测,与实测值相比最大偏差在±0.84范围内。为槽式太阳能聚光集热系统实践运行过程中,确定该地区该季节的最佳除尘时间提供试验依据。

A test device for measuring the energy density of the focal plane of the trough solar collector was established and the reflectivity and energy flux distribution were also studied in this paper in order to solve the reflectivity reduction and energy flux loss of the system caused by dust accumulation of the mirror. The results show that the reflectivity is changed in different mode, in which the reflectivity of the long wave decreases more than that of the shorter wave in the visible light range with dust accumulation on the mirror. The sun light reflection path is also changed due to dust accumulation of the mirror. When the sun direct irradiance increases about 50 W/m2,the peak of the energy flux in the wall surface of the receiving pipe is reduced about 15 kW/m2 under the condition of dust accumulation 25 days compared with that of the clean condition. In addition,the convergence light path is changed obviously around 180° of the circumferential angle of the receiving tube. The functional relationship between the relative reflectivity and the dust accumulation period and density was obtained according to the data measured, which can also be used to predict the relative reflectivity of the trough concentrator in adjacent areas. The error range between the predicted and measured value is around ±0.84. This work provides an experimental basis for determining the optimal dust removal time.