Analysis and Parametric Investigation of Different Arrangements of V-Shape Ribs on the Performance of an Optically-Enhanced Parabolic Trough Solar Collector*

In this paper, a V-shape ribbed tube is utilized to improve the thermal performance of a parabolic trough collector (PTC). Six different rib arrangements were employed, and a detailed analysis is presented. Furthermore, the effect of adopting a secondary reflector (SR) on the temperature distribution around both a smooth and a ribbed parabolic trough receiver (PTR) tube is conducted. A computational fluid dynamics model is employed to study the heat transfer and fluid flow characteristics inside the tube. Results show that V-shape ribs are an effective tool to stir up the flow and increase the velocity gradient of the fluid near the inner surface of the tube. Moreover, results from the study show that the secondary reflector contributes to a further decrease in the tube surface temperature and hence improves the overall thermal efficiency of the collector. A parametric study is also carried out to investigate the thermal enhancement of a double-reflector parabolic trough collector when using an in-line mixed V-shape (IMVS) ribbed absorber tube, which shows the best enhancement among the investigated arrangements. Three different heat transfer fluids (HTFs) are investigated, and a wide range of fluid inlet temperatures are studied. Also, various geometric parameters of the V-shape rib are analyzed to determine the optimum design of such a modification to the wall of the absorber tube. The optimized ribbed tube design showed a performance enhancement of about 64%.