On Fresnel Reflector Solar Collectors With Cavit Recevier

Two types of concentration solar collectors based on Fresnel reflectortechniques were proposed，line-focus and point-focus Fresnel reflectorsolar collectors coupled with cavity receiver. Both theoretical andexperimental analyses were performed with respect to the optical andthermal performance of proposed solar collectors. The main work of thispaper is summarized below.1. The second law thermodynamic investigation on solar thermalconversion process of solar collectors with cavity receiver was conducted.Stagnation temperature and optimal operating temperature of solarcollectors with minimum entropy generation were obtained to furtheroptimize the design and operation conditions of Fresnel reflector solarcollectors with cavity receiver.2. A linear Fresnel reflector solar collector with total mirror area of14.4m~2was designed. Theoretical study on the optical performanceindicates the optical efficiency of the proposed linear Fresnel reflectorsolar collector can reach up to77.5%with normalized incident solar beam. Furthermore, the thermal performance was predicted by employing CFDmethod. The radiative heat loss from cavity receiver was found to be thedominant model of the total heat loss. As the operating temperatureincreases from90°C to250°C, the total heat loss increases from54W/m to246.7W/m and heat loss coefficient increases from11.4W/m~2K to21.0W/m~2K.3. The experimental setup of linear Fresnel reflector solar collectorwas built to study its thermal performance. The stagnation parameter forthe solar collector turns out to be0.364m~2K/W with stagnation temperatureof260°C. The thermal efficiency is45%at90°C with heat loss of65W/m.When operating temperature rise up to150°C, the thermal efficiencydecreases to36.6%with heat loss of110W/m.4. A novel solar beam-down tower based on Fresnel reflectortechnique was proposed and a prototype including three heliostats withtotal mirror area of24m~2was designed. The optical performance of theprototype was studied. It is found the optical efficiency can reach up to65%without considering the effect of incidence angle. The heat loss waspredicted by using CFD method. As operating temperature increases from100°C to250°C, the total heat loss increases from524.7W to1927.8W andthe heat loss coefficient increases from38.8W/m~2K to51.6W/m~2K 5. Experimental study was conducted to investigate the thermalperformance of the solar beam down prototype. Experimental results showthat the thermal efficiency is54%at80°C and decreases to51.6%at110°C. The heat loss coefficient increases from34.89W/m2K to38.6W/m2K with the temperature increases from80°C to110°C.