Thermal performance analysis of eccentric double-selective-coated parabolic trough receivers with flat upper surface

Abstract

The Parabolic trough collector (PTC) system combined with molten salt energy storage system has gathered increasing attention owing to its advantages of high operating temperature and stable power output. However, the substantial heat loss experienced by parabolic through receivers (PTR) under high temperatures imposes limitations on the thermal efficiency and power generation potential of the PTC system. In this study, a novel eccentric double-selective-coated parabolic trough receiver is proposed. The upper surface of the receiver is flattened to further reduce radiation heat loss. Various distances from collector focus are explored to determine the most suitable opening angle of secondary selective coating, ensuring the highest thermal efficiency. The results show that, although the eccentricity causes partial optical loss, the reduced upper surface area and the resultant larger secondary coating opening angle contribute to a significant reduction in heat loss and an improved thermal efficiency of the novel receiver. The thermal efficiency of the new absorber can be improved by up to 20.59 % (under direct normal irradiance of 600W/m2 and a receiver surface temperature of 600 °C). Furthermore, the higher the emissivity and the lower the absorptivity of the solar selective coating, the better the performance of the novel absorber tube.