Optimization strategies and verifications of negative thermal-flux region occurring in parabolic trough solar receiver

Prospects for parabolic trough collector are growing as the market increasingly values concentrated solar-thermal utilization. Parabolic trough solar receivers, the key components of parabolic trough collector system, seriously suffer degradation of photothermal conversion performance at high operating temperature due to considerable emissive heat loss, which exerts significantly negative influence on the overall performance and development of parabolic trough collector and subsequent thermal utilization systems. This study examines the spectral emissive heat loss and circumferential heat transfer characteristics around the parabolic trough solar receiver. In this framework, a new concept is proposed, i.e. the negative thermal-flux region in which negative net heat gain occurs, accordingly enlightening and giving birth to new optimization strategies for reducing emissive heat loss of the parabolic trough receiver. A novel parabolic trough receiver with an inner radiation shield in the negative thermal-flux region is designed, manufactured and comprehensively tested. The results show a validity of the existence of the negative thermal-flux region and great potential of new optimization methods to achieve breakthrough enhancement of heat-collecting performance in parabolic trough collector system. Compared with the prototype solar receiver, the heat loss of proposed solar receiver is effectively reduced by 28.1% at absorber temperature of 600 °C, the heat-collecting and exergetic efficiencies are significantly enhanced by 12.9 and 17.6% at the solar irradiance of 600 W/m² and inlet temperature of 550 °C.