| Solar energy is one of the best solutions to resolve the world's energy crisis, because it is not only truly inexhaustible, but also clean. China has achieved great success in low temperature (100℃or less) solar thermal applications (solar water heater), but the research and development on the middle-high temperature solar thermal applications (100～300℃) is still insufficient. The majority of industrial process are in dire need of middle-high temperature heat source. Compared with other solar systems, low cost LFR system which adopt flat mirrors and is easy to manufacture, has obvious advantages. LFR technology has aroused universal concern in many countries of the world.Currently, the Linear Fresnel Reflector collector system faces common shadow and block problems, which will result in low system efficiency. It is necessary to optimize the layout of the fresnel system to eliminate these problems. On the other hand, the solar collector system involves in radiation-conduction-convection heat transfer process. The heat transfer within the receiver under high heat flux must be studied deeply in order to achieve the optimal operating conditions. Research in this area has become one of the forefront topics of middle-high temperature solar energy utilization field.This paper studies a new fresnel reflector system coupled the layout of flat mirror field and the design of CPC. The method to resolve the shadow and block problems is explored. The design principle and optimization method of CPC are presented. The formulas to determine the system's parameters are analyzed such as altitude, layout range of reflector field and spacing of neighboring mirror. The best initial angle of each mirror is calculated. According to the theoretical analysis, a typical 1kW fresnel reflector collector system has been designed. Then, with the use of TracePro optical simulation software, the optical field model was built to study the arrangement of the fresnel system and optical performance.Secondly, based on the first law of thermodynamics, the theoretical research of LFR collector with CPC cavity and single tube receiver is carried out. A steady-state model of the system is created with the use of radiation network method and the principle of thermal resistance. The temperature distribution of reflector has been achieved and the thermal performance of this system has been discussed. Simulation results show that the maximum collectting efficiency can achieve 0.65. The collector temperature increases along the receiver tube length. Heat transfer from glass pane is the major aspect of the total thermal loss. Transmissivity of glass pane, reflectivity of CPC cavity and the emissivity of CPC insulation are key factors influencing the thermal performance. In addition, a thermal performance analysis software about CPC cavity collector has been developed by using MATLAB/GUI, which provides a simple and repeatable analysis tool to study the thermal operation of the LFR collector.Finally, according to the optimization results, the 1kW LFR system has been designed and constructed. Experiments have been carried out to test this system's actual performance. System performance such as heat loss, stagnation parameter, CPC cavity temperature distribution and collector thermal efficiency were tested systematically. Experimental results show that the average collector heat loss coefficient is approximately equal to 0.63 W/(m2℃) under the experimental conditions, the system stagnation temperature can reach 270℃, and the stagnation parameter is about 0.52℃m2/W, the temperatures in the CPC cavity have the same trend, but their distribution is uneven. The collector efficiency fitting curve of this system has been gotη=0.618-0.00125(Tr-Ta) according to experimental date. The experimental results show that this middle-high temperature linear fresnel reflector system has optimum performance. |
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