Efficiency enhancement of the parabolic trough solar collector using the rotating absorber tube and nanoparticles

Enhancing the thermal performance of parabolic trough collectors (PTC) is of major interest to maximize solar energy absorption. In common PTCs, solar irradiation is focused on the lower part of the absorber tube which causes high temperatures, thermal stress, and tube deformation. To overcome these problems, it is suggested to rotate the absorber tube with a specified frequency to reduce the high surface temperature and increase the solar energy absorption. In addition, a nanofluid (Al2O3-Therminol) is utilized as the heat-carrying fluid. Effects of various parameters, including the rotational speed, absorber tube material, flow rate, and nanoparticles concentration on the collector efficiency were studied. An approximate 2D-transient model of PTC is proposed and a steady-laminar numerical simulation is conducted for the 3D cases. Results indicate that the aluminum is the best choice among the other materials used for the absorber tube, providing about 16 K higher output temperature which is nearly 5% higher than that of the steel. Also, a more uniform surface temperature distribution and a higher collector thermal efficiency could be met. Accordingly, an average increase of 15% in the thermal efficiency of the collector and a maximum decrease of 64 K in the absorber tube temperature are reachable. (C) 2019 Elsevier Ltd. All rights reserved.