Effects of ribs on thermal performance of curved absorber tube used in cylindrical solar collectors

Improving the thermal performance of the absorbers is an effective technique to increase solar energy conversion to thermal energy. In common cylindrical solar collectors (CSCs), solar radiations hit one side of the curved absorber tube (CAT), leading to a non-uniform temperature distribution and sometimes thermal stress. To overcome these challenges, the use of rectangular ribs on the internal sides of the CAT is suggested in this study. The main objective is to investigate the advantages of ribs on each side of the CAT. Therefore, a 3D numerical study is carried out based on the real conditions, and the results are validated against previous empirical data. Then, the effects of ribs height are analyzed at different mass flow rates. The results reveal that embossing the ribs on the upper side is more effective than other cases. This results in the best thermal performance in which the heat absorption enhances averagely about 47.7%, compared to the smooth CAT. Accordingly, the penalty in the pumping power is about 88.9%. Moreover, it is found that the overall performance of the CAT can be improved up to 120% compared with the original shape by embossing the ribs on the upper side. (C) 2020 Elsevier Ltd. All rights reserved.