Analyzing thermal properties of solar evacuated tube arrays coupled with mini-compound parabolic concentrator

Effective utilization of solar energy resource enables to improve the thermal performance of solar evacuated tube. In present work, the back side of solar vacuum tube was coupled with mini-compound parabolic concentrator (mini-CPC). The thermal characteristics of the presented mini-CPC solar vacuum tube were analyzed theoretically and experimentally. A mathematical model of heat transfer for the mini-CPC vacuum tube was established according to the energy conservation, and solved by iterative calculation based on home-built C programming language. The obtained numerical solutions fit in well with the experimental results. Furthermore, analysis indicates the vacuum interlayer plays a crucial role in hindering heat transfer. The thermal-convection resistance (R-co-air,R-conv) dominates the heat loss from cover tube to ambient rather than thermal-radiation resistance (R-co-sky,R-rad). The measured final temperature increment of working water for the mini-CPC and ordinary evacuated tube can reach 63.4 K and 49.8 K, respectively. An experimental result also reveals that the thermal efficiency of the mini-CPC vacuum tube is increased by 24.3%-29.2% compared with that of vacuum tube without mini-CPC, considering various weather conditions. Consequently, the designed mini-CPC evacuated tube shows a preferable performance, which may provide a certain reference in technology for engineering applications. (c) 2020 Elsevier Ltd. All rights reserved.