Performance enhancement of direct absorption parabolic trough collector using eccentric annular absorption tube and transparent insulation aerogel

The exploitation of solar energy plays an important role in addressing both energy shortages and environmental issues. To minimize the temperature gradient and enhance the performance of direct absorption parabolic trough collectors (DAPTCs), a novel eccentric annular tube collector based on optical glass and nanofluid combined absorption is developed in this work. An optical-thermal coupled model is proposed and validated to study the performance of the eccentric annular tube collector. According to the model, a parametric investigation is performed to quantify the energy flux distribution, temperature and flow characteristics, and overall thermal collection performance of the novel system. Effects of offset distance, mass flow rate and inlet temperature on collector performance are investigated in detail. Results show that the eccentric annular tube collector with a 4 mm offset distance is recommended as the suggested design. The exergy efficiency of the proposed design under mass flow rate of 0.30 kg/s and nanofluid inlet temperature of 600 K is 30.61 %. To further minimize heat losses at high operating temperatures, transparent insulation aerogels are applied to the surface of the eccentric annular absorption tube. Compared to the evacuated eccentric annular tube collector, the collector efficiency of the modified collector with aerogel is improved by 9.27 %, and the exergy efficiency can be increased by 5.67 % under concentration ratio of 76 suns and inlet temperature of 650 K.