Comparative Experimental Study On Performance Of Low Concentration Ratio CPC Collectors

Massive exploitation of fossil fuel makes it gradually depleted, and global environmental issues have become increasingly prominent. So it’s imminent to look for a pollution-free, alternative energy. As a kind of clean energy, solar energy has gradually become an important part of energy utilization. In this paper, it studies the compound parabolic concentrator (CPC) in the low-temperature field of solar thermal utilization. Then the per unit area of solar radiation heat flux has been increased. Low concentration ratio CPC collector can obtain 100～200℃ temperature heat, which can be used to produce heating, industrial heat, medium and low temperature thermal power generation, etc.Concentration ratio is an important parameter of the CPC collector, and different concentration ratio has an important influence on the heat collection performance. At present, there is no detailed study on the heat utilization in the middle-temperature range or in different weather conditions. Therefore, low concentration ratio CPC with three kinds of different concentration ratio of 1.5,2.0 and 3.0 has been used in this paper. The work is mainly in the following aspects:(1) Optics simulation software TracePro is applied to make optical simulation of direct irradiation in three kinds of CPC collectors in the case of different angles of incidence. Then we can make a concrete analysis of the trends of the optical efficiency and the proportion of sunlight reaching receiving body over the angle of incidence.(2) Steady heat transfer model of CPC collectors is established, and it provides a theoretical basis for subsequent experiments. Then we make thermal performance analysis of CPC all-glass vacuum tube by three kinds of heat transfer, namely, conduction, convection and radiation, and build physical models and heat grids of CPC vacuum tube collectors, according to the law of conservation of energy to solve. (3) Collector performance of three kinds of different concentration ratio was tested in different proportions of diffuse irradiation at the certain inlet temperature What’s more, analysis of the CPC collector outlet temperature change and the thermal efficiency of the collector at different sunny weather trended over the proportion of diffuse irradiation.(4) In sunny days, the changes of the thermal efficiency of the CPC collector at different temperatures was tested by changing the CPC collector inlet temperature (60 150℃). Then the linear fitting of the scatter plot was drawn, according to the experimental results. In addition, the heat loss rate of the three kinds of CPC collector was analyzed, and CPC collector thermal efficiency was compared under different temperatures.(5) On a clear night, comparative experimental of the heat loss rate of the collector inlet temperature between 60 ℃ and 130℃ was studied, so that it could eliminate the influence of solar radiation on the heat loss of CPC collectors during the experiment. Last, the trend of the heat loss rate of CPC collectors in the condition of different temperature difference with (Tf-Ta) was researched. It turned out that when the inlet temperature is high enough and CPC concentration ratio is higher, heat loss of the collector would be further reduced. In other words, high concentration ratio CPC collectors are more advantageous in the field of a wide range of intermediate temperature applications.