Experimental study on heat transfer performance of high temperature heat pipe with large length-diameter ratio for heat utilization of concentrated solar energy

Abstract

• A conceptual model of dish concentrated solar receiver based on finned high temperature heat pipe (HTHP) is designed. • A batch of HTHPs with large length to diameter ratio and excellent performance were prepared. • The frozen start-up, steady heat transfer and consecutive operation performance of the HTHP with large length to diameter ratio are studied theoretically and experimentally. • A finned HTHP with excellent performance is prepared, and its enhanced heat transfer capacity was verified by experiment. Solar receiver, as the core device of the dish concentrated solar thermal power generation system, is becoming a research focus and has attracted much attention. High temperature heat pipe, which works by following the principle of vapor–liquid circulation, has the ability to flatten the temperature of the hot spot, and maintain excellent heat transfer performance with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density; Through the structural design, the compressed air flows outside of the high temperature heat pipe, and thus, compared with flowing in the pipe, the heat transfer coefficient is increased and the flow resistance is reduced. In view of the above advantages, we designed a dish concentrated solar receiver with finned high temperature heat pipe as the core heat transfer device, prepared a high temperature heat pipe with a large length-diameter ratio, and conducted a quantitative performance study comprehensively and systematically. The present study verified the safety and stability of the high temperature heat pipe with the illumination of concentrated facula with inhomogeneous ultra-high energy flux density, theoretically analyzed the process of frozen start-up and heat transfer limits of high temperature heat pipe, explored the reasonable frozen start-up mode, carried out the parameter optimization and consecutive long-time operation stability test, and quantitatively verified the enhanced heat transfer capacity of finned high temperature heat pipe through the experiment. The results show that the HTHP prepared by the same process can operate safely and stably with the illumination of concentrated facula at the average energy flux density of 2.3 × 10 6 W/m 2 , and maintain a high temperature above 700 ℃ as well as excellent temperature uniformity, which fully verifies the feasibility and superiority of HTHP as the core heat transfer device of the dish concentrated solar receiver. In addition, these results can provide quantitative experimental data and theoretical reference for the design and development of the dish concentrated solar receiver.